JP4464173B2 - Electrode material for lithium secondary battery, electrode structure having the electrode material, and secondary battery having the electrode structure - Google Patents

Description

  The present invention relates to an electrode material for a lithium secondary battery composed of particles containing silicon as a main component, an electrode structure having the electrode material, and a secondary battery having the electrode structure.

  Recently, since the amount of CO2 gas contained in the atmosphere is increasing, the possibility of global warming due to the greenhouse effect has been pointed out. Thermal power plants convert thermal energy obtained by burning fossil fuels into electrical energy, but because of the large amount of CO2 gas emitted by combustion, it is difficult to construct new thermal power plants. Yes. Therefore, as an effective use of power generated by generators such as thermal power plants, surplus power nighttime power is stored in secondary batteries installed in ordinary households and used in the daytime when power consumption is high So-called load leveling has been proposed to level the load.

  In addition, the development of secondary batteries with high energy density is expected for electric vehicle applications that are characterized by not discharging substances related to air pollution including COx, NOx, hydrocarbons, and the like. Furthermore, for power supply applications of portable devices such as book-type personal computers, video cameras, digital cameras, mobile phones, and PDAs (Personal Digital Assistants), it is an urgent task to develop a small, lightweight, and high-performance secondary battery.

  As such a small, lightweight, high-performance secondary battery, a lithium intercalation compound that deintercalates lithium ions from the interlayer is used as a positive electrode material, and lithium ions are formed from carbon atoms. The development of so-called “lithium ion batteries” of rocking chair type using a carbon material typified by graphite, which can be intercalated between the layers of a six-membered ring network plane, as a negative electrode material has been put into practical use and is generally used. ing.

  However, in this “lithium ion battery”, a negative electrode composed of a carbon material can theoretically intercalate only a maximum of 1/6 lithium atoms per carbon atom. A secondary battery having a high energy density comparable to that of the primary battery cannot be realized.

  If a negative electrode made of carbon in a “lithium ion battery” is intercalated with a lithium amount greater than the theoretical amount during charging, or if charging is performed under conditions of high current density, lithium metal is dendrited on the surface of the carbon negative electrode. There is a possibility that it will grow into a (dendritic) shape and eventually lead to an internal short circuit between the negative electrode and the positive electrode through repeated charge / discharge cycles. A “lithium ion battery” exceeding the theoretical capacity of a graphite negative electrode will provide a sufficient cycle life. It is not done.

  On the other hand, a high-capacity lithium secondary battery using metallic lithium as a negative electrode has attracted attention as a secondary battery exhibiting a high energy density, but has not yet been put into practical use.

  This is because the cycle life of charge / discharge is extremely short. The main reasons for the extremely short charge / discharge cycle life are that metal lithium reacts with impurities such as moisture in the electrolyte and an organic solvent to form an insulating film, or the surface of the metal lithium foil is not flat and the electric field is concentrated. It is thought that there is a place, and this causes lithium metal to grow in a dendrite shape due to repeated charging and discharging, causing an internal short circuit between the negative electrode and the positive electrode, leading to a life.

  A method of using a lithium alloy composed of lithium and aluminum for the negative electrode in order to suppress the progress of the reaction between metal lithium and water or an organic solvent in the electrolyte, which is a problem of the secondary battery using the metal lithium negative electrode. Has been proposed.

  However, in this case, since the lithium alloy is hard, it cannot be spirally wound, so that a spiral cylindrical battery cannot be produced, the cycle life is not sufficiently extended, and energy comparable to a battery using metallic lithium as a negative electrode. The present situation is that a wide range of practical use has not been achieved because the density cannot be sufficiently obtained.

  By the way, in order to solve the above problems, as a secondary battery using a negative electrode for a lithium secondary battery made of silicon or a tin element, U.S. Pat. No. 6,051,340, U.S. Pat. No. 5,795,679, U.S. Pat. No. 283627, Japanese Patent Laid-Open No. 2000-311681, and WO 00/17948 have been proposed.

  Here, in US Pat. No. 6,051,340, an electrode layer formed of a metal that is alloyed with lithium of silicon or tin and a metal that is not alloyed with lithium of nickel or copper on a current collector of a metal material that is not alloyed with lithium. A lithium secondary battery using the formed negative electrode is proposed.

In US Pat. No. 5,795,679, a lithium secondary battery using a negative electrode formed from an alloy powder of an element such as nickel and copper and an element such as tin is used. In US Pat. No. 6,432,585, the electrode material layer has an average particle size of 0.5. A lithium secondary battery using a negative electrode having particles of ˜60 μm of silicon or tin of 35 wt% or more, a porosity of 0.10 to 0.86, and a density of 1.00 to 6.56 g / cm ³ Has proposed.

  JP-A-11-283627 discloses a lithium secondary battery using a negative electrode having silicon or tin having an amorphous phase, and JP-A 2000-311681 discloses amorphous tin having a non-stoichiometric composition. -A lithium secondary battery using a negative electrode made of transition metal alloy particles, and Japanese Patent Application WO 00/17948 proposed a lithium secondary battery using a negative electrode made of non-stoichiometric amorphous silicon-transition metal alloy particles. ing.

  However, in the lithium secondary battery according to each of the above proposals, the efficiency of the amount of electricity associated with the release of lithium with respect to the amount of electricity associated with the first insertion of lithium has not been obtained to the same level as the graphite negative electrode, and further improvement in efficiency Was expected. Further, since the electrode of the proposed lithium secondary battery has a higher resistance than the graphite electrode, it has been desired to reduce the resistance.

  Japanese Patent Laid-Open No. 2000-215887 improves conductivity by forming a carbon layer on the surface of a metal or semimetal, particularly silicon particles, capable of forming a lithium alloy by a thermal chemical vapor deposition method such as benzene. Thus, a lithium secondary battery has been proposed that suppresses volume expansion during alloying with lithium, prevents electrode destruction, and has a high capacity and high charge / discharge efficiency.

However, in such a lithium secondary battery, the theoretical storage capacity calculated from Li _4.4 Si as a compound of silicon and lithium is 4200 mAh / g, whereas the amount of electricity exceeding 1000 mAh / g. Electrode performance that enables lithium insertion / extraction has not been achieved, and development of a negative electrode having a high capacity and a long life is desired.

  Accordingly, the present invention has been made in view of the above circumstances, and has an electrode material for a high capacity lithium secondary battery with low resistance and high charge / discharge efficiency, an electrode structure having the electrode material, and the above-mentioned An object of the present invention is to provide a secondary battery having an electrode structure.

The present invention relates to an electrode material for a lithium secondary battery comprising particles of a solid state alloy containing silicon as a main component, wherein the solid state alloy has a silicon content of 50 wt% or more and 95 wt% or less. A , consisting of one or more alloys selected from Si- A-E, wherein A is the first element and one or more elements selected from the group consisting of tin, silver, zinc and titanium And the atomic ratio of the element A in the Si-A is lower than the atomic ratio of silicon, and in the Si-AE, one or more selected from the group consisting of tin and zinc is A as the first element. a element, E is copper in the second element, aluminum, vanadium, yttrium, zirconium, merely one or more elements selected from the group consisting of boron, the element a in the Si-a-E Element E Child ratio lower than the atomic ratio of silicon, the atomic ratio of the previous SL first element A is rather high than the atomic ratio of the second element E, wherein the alloy consists of elements selected from the said A E A pure metal or a solid solution is contained, and the particle structure of the alloy is a microcrystal or non-crystal of a pure metal or a solid solution composed of an element selected from A and E in microcrystalline silicon or amorphized silicon. It is a particle in which crystal quality is dispersed, and is characterized in that it contains a eutectic composed of two or more elements selected from silicon, A and E.

  According to the present invention, the silicon and the elements other than silicon constituting the silicon alloy become a homogeneous solution in a molten state, the crystallization of silicon intermetallic compound is small, and by selecting an elemental composition that includes a eutectic, Microstructured silicon alloy particles in which microcrystals or amorphous elements of elements other than silicon are dispersed in microcrystalline silicon or amorphized silicon can be produced.

  Then, by forming an electrode structure with a low-resistance, high charge / discharge efficiency, high-capacity lithium secondary battery electrode material formed by doping boron or the like into such a microstructured silicon alloy fine powder The electrode structure can store and release a large amount of lithium repeatedly with high efficiency. Furthermore, by using this electrode structure as a negative electrode to form a lithium secondary battery, a high capacity and high energy density secondary battery can be obtained. Can be produced.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 6.

  The present inventors investigated the relationship between the silicon dopant, the amount of insertion and desorption electricity of lithium, and the potential of insertion and desorption in the following experiment.

  That is, p-type silicon powder doped with boron, n-type silicon powder doped with phosphorus or antimony, graphite powder as a conductive auxiliary material, and a binder are mixed on a copper foil. 1M (LiPF6 salt is added to an organic solvent obtained by mixing metal lithium as a counter electrode and ethylene carbonate and diethyl carbonate as an electrolyte solution in a volume ratio of 3: 7 to a fabricated electrode (silicon electrode). The amount of electricity accompanying lithium insertion / extraction electrochemically with respect to the silicon electrode (lithium insertion / extraction amount) was measured using the dissolved electrolyte solution (mol / liter).

  As a result, both the highly doped n-type silicon and p-type silicon have a large amount of insertion and desorption electricity of lithium and a desorption efficiency with respect to insertion, and a small potential change with respect to lithium into which lithium is inserted and desorbed. The potential curve was flatter. It was also found that the electric capacity and potential can be controlled to some extent by selecting the kind of dopant and the doping amount. Since highly doped silicon has a low resistance, it has a high electron conductivity. When an electrode is formed from this silicon, it is considered that the electrical resistance of the electrode itself is low and the electrochemical reaction proceeds smoothly.

  In addition, when electrochemical lithium insertion / extraction was repeated, the boron element-doped silicon particles showed less decrease in lithium insertion / extraction, and lithium could be stably taken in and out.

The reason for this is that
(I) Since p-type dopant atoms such as boron atoms replaced with silicon atoms are ionized negatively, insertion of lithium atoms that are easy to positively ionize by releasing electrons is not prevented.
(Ii) When silicon is doped with a p-type dopant, the specific resistance of silicon decreases and the resistance of the electrode decreases.
Is mentioned.

  Here, FIG. 2 schematically shows the reaction of electrochemically inserting lithium into a silicon crystal, and FIG. 2A shows the case of intrinsic semiconductor silicon that does not contain impurity atoms. It is. (Actually contains some impurity elements.)

  FIG. 2B shows a case of p-type silicon doped with boron as an impurity atom. In this case, an attractive force acts between a lithium atom that is easily ionized positively and a boron atom that is ionized negatively. Therefore, it is assumed that the insertion of lithium ions is easy.

  FIG. 2C shows the case of n-type silicon doped with phosphorus as an impurity atom. In this case, a repulsive force acts between a positively ionized lithium atom and a positively ionized phosphorus atom. Therefore, it is assumed that the insertion of lithium ions is not easy.

  In addition, the above results may be that when p-type silicon, particularly boron-doped silicon, is used as the negative electrode material of the lithium secondary battery, the resistance of the negative electrode is naturally reduced and the insertion reaction of lithium ions may be easy. .

Here, the doping amount of the p-type dopant and the n-type dopant is preferably in a range in which the resistance of the electrode used in the lithium secondary battery is lowered and the storage capacity is increased, and the range is 1 × 10 in terms of atomic ratio with respect to silicon. The range of ^{−8 to} 2 × 10 ⁻¹ is preferable, and the range of 1 × 10 ⁻⁵ to 1 × 10 ⁻¹ is more preferable. Doping the p-type dopant and the n-type dopant at the same time is also preferable in terms of reducing the resistance.

  In addition, aluminum and gallium are also effective as the p-type dopant, but boron having a small ion radius is more preferable. Boron doping, particularly addition of boron exceeding the solid solution limit, has the effect of facilitating the amorphization. For this reason, when particles or an alloy mainly composed of boron-added silicon is used as a negative electrode material for a lithium secondary battery, an electrode having a long repeated life can be manufactured.

  Furthermore, the present inventors investigated the amount of electricity and the efficiency during the repeated electrochemical lithium insertion / extraction of the electrode using silicon alloy particles as the electrode material, and the expansion coefficient of the electrode. As a result, the element distribution in the alloy particles is less biased, and the smaller the silicon crystal particles, the higher the amount of lithium insertion / desorption electricity, and the more stable lithium insertion / desorption can be performed. It was found that an electrode having a low expansion coefficient can be produced.

In addition, as one aspect of the present invention, which is preferable in order to make the unevenness of the element distribution in the silicon alloy particles less uniform and to make the silicon crystal grains smaller,
(1) Silicon constituting the silicon alloy and elements other than silicon form a uniform solution in a molten state.
(2) The silicon alloy includes a eutectic,
(Note that this eutectic includes a eutectic of silicon and a first element A described later, a eutectic of silicon and a second element E described later, and a eutectic of the first element A and the second element E. Crystal, including combinations of these)
(3) There are few crystallization of the intermetallic compound formed between the silicon and the elements other than silicon constituting the silicon alloy.
It has also been found that it is effective to produce a silicon alloy having such an elemental composition.

  Here, since the composition near the eutectic point is easily amorphized, it is preferable in the present invention to adopt the composition near the eutectic point.

  Further, when an intermetallic compound is formed between silicon and an element other than silicon, the original performance of storing lithium contained in silicon is degraded. Accordingly, the alloy particles constituting the electrode material of the present invention preferably contain a pure metal or a solid solution. This is because pure metals and solid solutions are considered to be superior to intermetallic compounds in terms of lithium insertion / extraction. Of course, the existence of silicon intermetallic compounds in the alloy is not denied, but the ratio of silicon intermetallic compounds is preferably 0 or less. In the preferred alloy particles used in the present invention, a pure metal and a solid solution may coexist, or one or both of a pure metal and a solid solution and an intermetallic compound may coexist.

  The silicon content in the silicon alloy is preferably 50% by weight or more and 95% by weight or less, and more preferably 53% by weight or more in order to exhibit the performance of a high storage capacity as a negative electrode material of a lithium secondary battery. More preferably, it is 90% by weight or less.

  Further, in addition to the alloy composition of the above composition, silicon alloy particles having an average particle diameter of preferably 0.02 μm to 5 μm, more preferably 0.05 μm to 3 μm, and most preferably 0.1 μm to 1 μm are formed into fine particles. Alternatively, it has been found that pulverization and further amorphization of the silicon alloy are effective for obtaining the desired performance.

  Here, “amorphization” refers to a crystal structure having an amorphous phase, and in the observation of a crystal lattice image by a high-resolution transmission electron microscope, The place where a pattern is not observed is recognized. The crystallite size of the silicon alloy particles in the amorphization as observed from a transmission electron microscope is preferably in the range of 10 nm to 100 nm, and more preferably in the range of 5 nm to 50 nm.

  By micronizing or micronizing and / or amorphizing a silicon alloy having the above composition, the microstructure of the silicon alloy is microcrystalline or amorphous in elements other than silicon in microcrystalline silicon or amorphous silicon. A structure with dispersed quality can be obtained. Here, “fine powder” is an aggregate of “fine particles”. Silicon can extract and extract a lot of lithium electrochemically, but by making the silicon crystallite smaller, the lithium insertion and desorption reaction can be made uniform, and the volume expansion and contraction due to repeated insertion and desorption are uniform. As a result, the repetition life is also prolonged.

  FIG. 1 schematically shows a cross-sectional structure of particles of the silicon alloy of the present invention that has been micronized and amorphized. In (a) and (b) of FIG. 101 is a group of microcrystallized or amorphized silicon crystals, 102 is a group of microcrystallized or amorphized crystals of the first element A (other than silicon) contained in the silicon alloy, 103 is silicon A group of microcrystallized or amorphized crystals of the second element E (other than silicon) contained in the alloy.

  That is, the silicon alloy particle 100 in FIG. 1A is an alloy particle composed of at least a silicon element and a first element A, and the silicon alloy particle 100 in FIG. Alloy particles composed of one element A and second element E.

  Then, by forming the silicon alloy having the element composition according to the above-described (1), it is possible to solidify from the molten liquid mixed uniformly. However, when the difference between the melting point of the first element next to silicon as the main component of the silicon alloy and the melting point of silicon is large, for example, when the first element is tin, even if the molten liquid is quenched, Tin with a low melting point segregates at the grain boundaries of silicon.

  Therefore, a uniform alloy composition cannot be obtained with an alloy of silicon and tin. In order to solve this problem, an alloy obtained by rapidly cooling a liquid in which an alloy composition is melted is first pulverized into fine powder, and then the alloy composition is obtained by a mechanical alloying method using a pulverizer such as a ball mill. (Uniform dispersion of composition elements in the alloy) and amorphization are simultaneously performed. Thereby, the alloy particles 100 more uniformly dispersed as shown in FIG. 1A or FIG. 1B can be produced without uneven distribution of elements other than silicon and silicon elements.

  Therefore, when the silicon alloy particle 100 according to the preferred embodiment of the present invention is used as a negative electrode material for a lithium secondary battery, the lithium can be more uniformly inserted during charging, and the expansion during the lithium insertion can also occur uniformly. Expansion is also reduced. For this reason, it becomes possible to produce a lithium secondary battery with a high storage capacity, improved charge / discharge efficiency, and a long charge / discharge cycle life.

  The crystal microstructure of the silicon alloy particles 100 of the present invention can be observed with a transmission electron microscope and limited field electron diffraction. The degree of microcrystallization or amorphization can be evaluated by measuring the half width of the X-ray diffraction peak. Here, if the ratio of the amorphous phase is increased due to amorphization, the peak of the sharp X-ray diffraction chart which is crystalline becomes wider and more broad.

  For this reason, the half width of the diffraction intensity with respect to 2θ of the main peak of the X-ray diffraction chart is preferably 0.1 ° or more, and more preferably 0.2 ° or more. The crystallite size calculated from the half-value width of the X-ray diffraction peak is preferably 60 nm or less, and more preferably 30 nm or less.

  In order to reduce the crystallite size of silicon or silicon alloy, it is effective to add a boron element exceeding the solid solution limit or to add yttrium and zirconium elements. The amount of boron element added is preferably in the range of 0.1 to 5% by weight. The addition of yttrium and zirconium elements is preferably in the range of 0.1 to 1% by weight.

  By the way, it is thought that the insertion / release reaction of lithium occurs from the grain boundary of the crystal. However, since there are many grain boundaries by microcrystallizing or amorphizing the silicon or silicon alloy crystal, the lithium insertion / desorption is performed. The separation reaction is performed uniformly, which increases the storage capacity and the charge / discharge efficiency.

  Further, microcrystallization or amorphization of the crystal loses the long-range order of the crystal structure, so that the degree of freedom is increased and the change of the crystal structure when lithium is inserted is reduced. As a result, expansion during insertion of lithium is reduced. In addition, repetition of lithium insertion / extraction further promotes silicon amorphization.

  Thereby, when the silicon alloy particles of the present invention are employed as a negative electrode material for a lithium secondary battery, a secondary battery with high charge / discharge efficiency, high capacity, and long charge / discharge cycle life can be obtained. Note that the reason why the lifetime is extended is that there is little change in the crystal structure of silicon due to the insertion and release of lithium.

When the silicon alloy is composed of the first element A having a lower atomic ratio than silicon and silicon but having the second highest atomic ratio after silicon (see FIG. 1A), wherein (1), (2), in view of (3), tin, silver, zinc, one or more elements selected from titanium down or Ranaru group is preferred. Moreover, the possible first element is electrochemically intercalating and deintercalating lithium, tin, zinc, if an element of silver or we selected, further has the same effect as the silicon crystal grains, a lithium secondary A high performance material can be obtained as a negative electrode material for a secondary battery .

  In the case of an alloy of silicon and tin, indium, gallium, zinc, and silver, each is uniform in a molten solution state and does not melt at all in a solid state. In the case of an alloy of silicon and silver, there is a eutectic crystallization of Si and Ag. In the case of an alloy of silicon and aluminum, it is uniform in a molten solution state, and a partial solid solution is formed, and eutectic crystallization of Si and Si—Al solid solution occurs.

  In the case of an alloy of silicon and titanium, it is preferable that silicon is 67 atomic% or more, and it is uniform in a molten state in this range. Furthermore, it is more preferable that silicon has a composition of 85 atomic% or more. In this case, the formation of TiSi2 intermetallic compound is small, and eutectic crystallization of Si and TiSi2 occurs. Therefore, the composition of silicon and titanium in an alloy formed of silicon and titanium preferably has a composition in the vicinity of 85:15. However, a higher silicon ratio is preferable from the viewpoint of improving the power storage performance.

  In the case of an alloy of silicon and copper, in the case of the present invention in which silicon is 50 atomic% or more, it is uniform in a molten solution state, the formation of an intermetallic compound of Cu3Si is small, and the eutectic of Si and Cu3Si There is crystallization.

  The eutectic is effective in that the crystal grains in the alloy can be reduced. The composition near the eutectic point is also easily amorphized.

Further, the silicon alloy is composed of at least a first element A having a lower atomic ratio than silicon and silicon but having a higher atomic ratio after silicon, and a second element E having a higher atomic ratio after the first element. (See FIG. 1B), the first element A is one or more elements selected from the group consisting of tin, silver, zinc, and titanium, and the second element E is copper. , a aluminum, vanadium, yttrium, zirconium, merely one or more elements selected from the group consisting of boron, the first element a and second element E are different elements (a ≠ E), it Is more preferable.

  Here, the effect of the second element E is that the eutectic with the first element A is crystallized, the crystal grains of the first element A are reduced, or the eutectic with silicon is crystallized to form a silicon crystal. The point is to make the grains smaller. Furthermore, the second element E is easier to form an oxide than silicon, and is effective in suppressing the generation of silicon oxide. If a large amount of silicon oxide is present in the silicon or silicon alloy, lithium oxide is formed by electrochemical lithium insertion reaction, and the efficiency of desorption (release) with respect to the amount of lithium insertion decreases. It becomes a factor.

  Preferable more specific examples of the silicon alloy (Si-AE alloy) composed of three or more elements include Si-Sn-Ti alloy, Si-Sn-Al alloy, Si-Sn-Zn alloy, Si-Sn. -Ag alloy, Si-Sn-B alloy, Si-Sn-Sb-B alloy, Si-Sn-Cu-B alloy, Si-Sn-Cu-Sb-B alloy, Si-Al-Cu alloy, Si-Al -Ti alloy, Si-Al-Zn alloy, Si-Al-Ag alloy, Si-Zn-Ti alloy, Si-Zn-Sn alloy, Si-Zn-Al alloy, Si-Zn-Ag alloy, Si-Zn- Cu alloy, Si—Sn—Al—Ti alloy, Si—Sn—Zn—Ti alloy, Si—Sn—Ag—Ti alloy, and the like can be given.

  Here, the Sn—Zn-based alloy has a eutectic point near the atomic ratio Sn: Zn = 85: 15, and the Sn—Ag-based alloy has a eutectic point near the atomic ratio Sn: Ag = 95: 5. Sn—Al alloys have eutectic points near the atomic ratio Sn: Al = 97: 3, and Al—Cu alloys have eutectic points near the atomic ratio Al: Cu = 82: 18. Furthermore, an Al—Zn alloy has a eutectic point in the vicinity of an atomic ratio of Al: Zn = 89: 11.

  By crystallizing the eutectic crystal, the crystal grains of Sn, Zn, Al, and Ag are reduced. In the silicon alloy, it is preferable to select a composition in which an element other than silicon is eutectic while maintaining a silicon ratio capable of maintaining a capacity as a negative electrode material for a lithium secondary battery. In the case where tin, aluminum, zinc, silver, which can insert and desorb lithium electrochemically, is contained in the silicon alloy composed of three or more elements, so that these crystals are microcrystalline or amorphous. It is preferable to select a composition near the eutectic point.

Of course the above silicon alloy, lowering the electrical resistance, in order to increase the capacity, boron, aluminum, gallium, antimony, one or more dopants selected from the group consisting of phosphorus, 1 × in atomic ratio to silicon It is preferable to be doped with 10 ^-8 ~2 × 10- ¹ range, and more preferably is doped in the range of ^{1 × 10 -5 ~1 × 10 -1} . Especially as a dopant, boron with a small ionic radius of a p-type dopant is more preferable.

  When aluminum or titanium, vanadium, yttrium, or zirconium is adopted as one of the constituent elements of the above-described silicon alloy of the present invention, another effect is that oxygen and silicon react and oxidize during the silicon alloy preparation process or pulverization process. The formation of silicon can be suppressed. This is because aluminum atoms or titanium, vanadium, yttrium, and zirconium atoms form more stable bonds with oxygen atoms than silicon atoms. If silicon oxide is formed, the efficiency of electrochemical lithium insertion / extraction from the silicon alloy decreases. This is presumably because lithium reacts with silicon oxide to form inactive lithium oxide.

  The average particle diameter of the primary particles of the silicon or silicon alloy of the present invention is 0.02 to 5 so that the lithium insertion and desorption reaction can be uniformly and rapidly performed as a negative electrode material of a lithium secondary battery. It is preferably in the range of 0.0 μm, more preferably in the range of 0.05 to 3.0 μm, and most preferably in the range of 0.1 to 1.0 μm.

  If the average particle size is too small, handling becomes difficult, the contact area between particles when an electrode is formed increases, and the contact resistance increases. Aggregating the primary particles to enlarge the particles facilitates handling and leads to a reduction in electrical resistance.

  Further, by compounding a material selected from carbon material, magnesium metal, carbon material and magnesium metal into the silicon particles having silicon as a main component or silicon alloy particles having silicon as a main component, When used as a negative electrode material for a lithium secondary battery, it is possible to enhance performances related to the charge / discharge efficiency, battery voltage, discharge current characteristics, charge / discharge repetition characteristics, and the like.

  The compounding of the carbon material can reduce fatigue due to volume expansion and contraction at the time of repeated insertion and release (release) of electrochemical lithium, and can extend the life. The amount of addition to the alloy containing silicon as a main component is preferably 1 to 10% by weight, more preferably 2 to 5% by weight, with no significant decrease in the amount of lithium insertion / desorption (release).

  The composite of magnesium metal has the effect of increasing the battery voltage when a lithium secondary battery is formed. However, when the ratio of the magnesium metal to be combined is increased, the voltage of the manufactured battery is increased, but since the ratio of silicon is decreased, the electric capacity that can be stored is decreased.

  In addition, the outermost surface of the finely divided silicon powder or silicon alloy powder is preferably covered with a thin oxide layer of about 2 to 10 nm in order to suppress a rapid reaction with oxygen. The thickness of the oxide film can be measured by analyzing the oxygen element in the depth direction with a surface analysis device such as scanning micro-Auger analysis.

  In the present specification, “average particle size” means an average primary particle size (average particle size in a non-aggregated state).

  By the way, microcrystallization or amorphization of the silicon or silicon alloy particles of the present invention can be evaluated by electron diffraction, neutron diffraction, high-resolution electron microscope observation, etc. in addition to the X-ray diffraction analysis. .

  In electron beam diffraction, a halo-like diffraction pattern is obtained when amorphization progresses. In high-resolution electron microscope observation, a striped lattice image indicating the presence of fine regular regions is observed (a microcrystalline structure dotted with striped patterns), or a labyrinth pattern in which no striped lattice image is observed. A structure with advanced amorphization is observed.

  In addition, from the radial distribution function of the central atom from the radial atom distribution function obtained from the X-ray absorption fine structure (XAFS) analysis of the X-ray absorption fine structure (XAFS) analysis of the X-ray absorption fine structure (XAFS) analysis Information about distance can be obtained. As a result, it is observed that the long-range order of the interatomic distance is lost if the amorphization is progressing.

  In the present invention, the size of the crystallites of the particles can be determined from the half width of the peak of the X-ray diffraction curve using CuKα as the radiation source and the diffraction angle, using the following Scherrer equation.

Lc = 0.94λ / (βcos θ) (Scherrer equation)
Lc: crystallite size λ: wavelength of X-ray beam β: half width of peak (radian)
θ: Bragg angle of diffraction line

  The crystallite size obtained by the above formula becomes smaller as the amorphization progresses.

  The crystallite size calculated from the above formula of the electrode material of the present invention is preferably 60 nm or less, and more preferably 30 nm or less.

  When the amorphous material is used as a negative electrode material for a lithium secondary battery, it is possible to suppress changes in expansion and contraction due to repeated insertion / extraction (release) of lithium due to charge / discharge, and the repetition life is long.

  Next, a method for producing silicon particles and silicon alloy particles will be described.

  The silicon particles mainly composed of silicon of the present invention are prepared by mixing a predetermined amount of raw silicon and a doping element material, melting and cooling to form a silicon ingot, and then through a multi-stage pulverization process. It can be obtained as a fine powder having an average particle diameter of 1.0 μm. In addition, as a pulverizer used in the fine pulverization step of the above pulverization step, a ball mill such as a planetary mill, a vibration ball mill, a conical mill, or a tube mill, or a media mill such as an attritor type, a sand grinder type, an animer mill type, or a tower mill type should be used. Can do. The material of the ball as the grinding media is preferably zirconia, stainless steel, or steel. As the dopant, boron, antimony, and phosphorus are preferable, and boron is more preferable.

  The silicon alloy particles of the present invention are prepared by mixing a predetermined amount of a first element metal material, a second element metal material, and a doping element material, if necessary, into raw material silicon to form a molten metal. Then, the silicon alloy particles having a powder shape are produced. As a spraying method, a gas atomizing method in which spraying is performed with a high-pressure inert gas, a water atomizing method in which spraying is performed with high-pressure water, or the like can be used.

The molten metal is preferably cooled rapidly. This is because the molten metal is in a homogeneously melted state, and by rapidly cooling the molten metal, the composition in the silicon alloy composed of elements having different melting points becomes more uniform. The cooling rate is preferably in the range of 10 ³ to 10 ⁸ K / s.

  Next, after forming an ingot of a silicon alloy, it is preferably 0.02 to 5.0 μm, more preferably 0.05 to 3.0 μm, still more preferably 0.1 to 1.0 μm, through a multi-stage pulverization process. It can be obtained as a fine powder having an average particle size of. Furthermore, it can be made amorphous by a treatment with a ball mill or the like. As the amorphizing pulverizer, a vibration mill, a planetary mill, a high-speed rotating mill, or the like is preferable.

  As a more preferable method, a raw material is mixed and melted to form a molten metal, and then sprayed with an inert gas to form a powder (so-called gas atomization method). After forming the particle powder by the atomization method (spraying method) such as the method of spraying with high pressure water (so-called water atomizing method) or the method of pouring the atomized metal into the water stream rotating at high speed, it is further pulverized The silicon powder or silicon alloy powder having an average particle diameter of preferably 0.02 to 5.0 μm, more preferably 0.05 to 3.0 μm, and still more preferably 0.1 to 1.0 μm. The method of obtaining is mentioned.

  In addition, by applying ultrasonic waves during the injection of the molten metal, the elemental composition inside the alloy particles obtained by the injection can be made more uniform. Moreover, amorphization is facilitated by increasing the cooling rate in the atomization method. Furthermore, the powder obtained by the above atomization method is treated with an amorphizing pulverizer such as a ball mill to uniformize the distribution of constituent elements in the alloy and promote the amorphousization of the alloy. be able to.

  Also, after mixing and melting the raw materials to form a molten metal, the powder or ribbon obtained at a high cooling rate of the gun method, single roll method, or twin roll method is further pulverized, Silicon powder or silicon alloy powder having an average particle size of preferably 0.02 to 5.0 μm, more preferably 0.05 to 3.0 μm, and even more preferably 0.1 to 1.0 μm. Obtainable. Of course, the obtained powder can be further amorphized by treatment with a ball mill or the like.

  In the ball mill treatment, it is preferable to add an antioxidant such as graphite, alcohol, fatty acid or the like to the powder of silicon or silicon alloy from the viewpoint of suppressing the reaction with fine powder oxygen after the treatment. Since graphite is hard and poor in malleability and ductility, it is difficult to solidify and has an effect of preventing the material from adhering to the grinding container. Further, since it is chemically stable and difficult to oxidize and difficult to alloy, oxidation can be suppressed by covering the surface of the finely pulverized negative electrode material particles.

  When a carbon material or magnesium metal is compounded with silicon or silicon alloy particles, it is preferable to perform a pulverizing process such as a ball mill under a mild mixing condition rather than an amorphizing condition.

  In addition, a material that is a raw material of the silicon powder or silicon alloy powder of the present invention is supplied into a plasma gas obtained by applying a high frequency to an inert gas and evaporated to obtain an amorphous particle size of 10 to 100 nm. A fine powder can be obtained. By applying a magnetic field at the time of high frequency application, plasma can be stabilized and fine powder can be obtained more efficiently.

  The fine powder of silicon or silicon alloy is easily oxidized in the air, and the dissolution reaction easily proceeds in an alkaline aqueous solution. Therefore, it is preferable to cover the surface of the fine powder with an oxide film or a carbon film. By performing the pulverization step in a liquid such as alcohol, a thin oxide film can be formed on the surface of the fine powder.

  In addition, before the fine powder is taken out by fine pulverization, a fine oxide film is formed on the surface by performing a treatment that is exposed to an inert gas atmosphere such as nitrogen gas or argon gas containing a low concentration of oxygen gas. Powders can also be obtained.

  Here, the oxygen concentration in the nitrogen gas or the inert gas is preferably in the range of 0.01 to 5.0% by volume, and more preferably in the range of 0.05 to 2.0% by volume. The weight% of oxygen element in the fine powder having a thin oxide film formed on the surface is preferably in the range of 0.1 to 15% by weight, more preferably in the range of 0.2 to 10% by weight, and 0.2 to 5% by weight. % Is most preferred.

  When the oxygen element amount and the oxide amount contained in the silicon powder or silicon alloy powder of the present invention are large, a high discharge amount and high charge / discharge efficiency cannot be expected when used as an electrode material for a lithium secondary battery. This is because lithium and an oxide react with each other during the lithium insertion reaction to change into an inactive substance such as lithium oxide and cannot be electrochemically released.

  In addition, if there is not enough oxygen content to cover the surface of the silicon powder or silicon alloy powder of the present invention and become an anti-oxidation film, that is, if there is no oxide content, it will be easily oxidized in the air and will be charged and discharged in the battery Inactive reactants will be formed.

  The above-mentioned carbon film for preventing oxidation can be formed by mixing fine powder carbon such as graphite powder and acetylene black at the time of pulverization or amorphization of silicon or silicon alloy.

  The silicon fine particles or silicon alloy fine particles of the present invention can also be formed by a method such as sputtering, electron beam vapor deposition, or cluster ion beam vapor deposition.

  Moreover, when using silicon as a raw material of this invention, you may contain impurities, such as Ca, Al, and Fe. In order to provide an inexpensive negative electrode material for a lithium secondary battery, the purity is preferably 99.99% or less, more preferably 99.9% or less, and still more preferably 99.6% or less.

  FIG. 3 shows a schematic cross-sectional structure of the electrode structure of the present invention. 3A, reference numeral 302 denotes an electrode structure, and the electrode structure 302 includes an electrode material layer 301 and a current collector 300. The electrode material layer 301 includes the electrode structure 301 shown in FIG. It consists of particles (silicon Si or silicon alloy powder) 303 containing silicon as a main component as shown in FIG. 1, a conductive auxiliary material 304, and a binder 305. In FIG. 3, the electrode material layer 301 is provided only on one surface of the current collector 300. However, depending on the battery configuration, the electrode material layer may be formed on both surfaces of the current collector 300. Good.

  Here, the content of the conductive auxiliary material 304 is preferably 5% by weight to 40% by weight, and more preferably 10% by weight to 30% by weight. The content of the binder 305 is preferably 2% by weight or more and 20% by weight or less, and more preferably 5% by weight or more and 15% by weight or less. The content of particles (powder) 303 containing silicon as a main component contained in the electrode material layer 301 is preferably in the range of 40 wt% to 93 wt%.

  The conductive auxiliary material 304 includes amorphous carbon such as acetylene black and ketjen black, carbon material having a graphite structure such as graphite, carbon fiber, and carbon nanotube, nickel, copper, silver, titanium, platinum, aluminum, cobalt Iron, chromium and the like can be used, and graphite is particularly preferable. As the shape of the conductive auxiliary material, a shape selected from a spherical shape, a flake shape, a filament shape, a fiber shape, a spike shape, a needle shape, and the like can be preferably used. Furthermore, by adopting two or more different types of powders, the packing density at the time of forming the electrode material layer can be increased and the impedance of the electrode structure 302 can be reduced.

  As the material of the binder 305, polyvinyl alcohol, water-soluble ethylene-vinyl alcohol copolymer, polyvinyl butyral, polyethylene glycol, carboxymethyl cellulose sodium, hydroxyethyl cellulose, and other water-soluble polymers, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene are used. Examples thereof include fluorine resins such as polymers, polyolefins such as polyethylene and polypropylene, styrene-butadiene rubber, polyimide, polyamic acid (polyimide precursor), and polyamideimide. As a material used for the binder, a material having a tensile strength of 100 to 400 MPa and an elongation of 40 to 100% is preferable, and polyimide, polyamic acid (polyimide precursor), and polyamideimide are more preferable materials.

  When forming an electrode, a polymer material such as polyacrylonitrile or polymethylmethacrylate that absorbs the electrolyte and gels can be added to the binder to form a composite. In view of reducing the electrical resistance of the electrode, it is preferable.

  In addition, the current collector 300 serves to efficiently supply the current consumed by the electrode reaction at the time of charging or to collect the current generated at the time of discharging. When applied to the negative electrode of a battery, the material forming the current collector 300 is preferably a material having high electrical conductivity and inert to battery reaction. Preferable materials include those made of one or more metal materials selected from copper, nickel, iron, stainless steel, titanium, and platinum. As a more preferable material, copper which is inexpensive and has low electric resistance is used.

  The shape of the current collector is plate-like, but the “plate-like” is not specified in terms of the practical range, and is called a “foil” having a thickness of about 100 μm or less. It includes forms. Further, a plate-like member such as a mesh shape, a sponge shape, or a fiber shape, a punching metal, an expanded metal, or the like may be employed.

  Next, a manufacturing procedure of the electrode structure 302 will be described.

  First, the conductive auxiliary material powder and the binder 305 are mixed with the silicon or silicon alloy powder, which is a particle mainly composed of silicon of the present invention, and the solvent of the binder 305 is appropriately added and kneaded. Prepare a slurry. Next, the prepared slurry is applied to the current collector 300 and dried to form the electrode material layer 301. Then, the electrode material layer 301 is pressed, and the thickness and density of the electrode material layer 301 are adjusted to form the electrode structure 302. To do.

  In addition, as said coating method, a coater coating method and a screen printing method are applicable, for example. Further, the main material, the conductive auxiliary material 304 and the binder 305 can be added to the current collector without adding a solvent, or only the negative electrode material and the conductive auxiliary material 304 can be added without mixing the binder 305. The electrode material layer 301 can be formed by pressure forming.

Here, if the density of the electrode material layer 301 is too large, expansion when lithium is inserted increases and peeling from the current collector 300 occurs. If the density is too small, the resistance of the electrode increases, so that the charge / discharge efficiency decreases and the voltage drop during battery discharge increases. Therefore, the density of the electrode material layer 301 of the present invention is more it is preferably in the range of 0.8 to 2.0 g / cm ^3, in the range of 0.9~1.5g / cm ³ preferable.

  Note that the electrode structure 302 formed of only the silicon particles or the silicon alloy particles of the present invention without using the conductive auxiliary material 304 and the binder 305 can be formed by a method such as sputtering, electron beam evaporation, or cluster ion beam evaporation. Thus, the electrode material layer 301 can be directly formed on the current collector 300.

  However, if the thickness of the electrode material layer 301 is increased, peeling tends to occur at the interface with the current collector 300, and thus the above evaporation method is not suitable for forming the thick electrode structure 302. In order to prevent the peeling at the interface, the current collector 300 is provided with a metal layer, oxide layer, or nitride layer having a thickness of 1 to 10 nm to form irregularities on the current collector 300 so that the interface adheres. It is preferable to improve the property. As a more specific oxide layer or nitride layer, a silicon or metal oxide layer or nitride layer is preferably used.

  By the way, the secondary battery according to the present invention includes a negative electrode, an electrolyte, and a positive electrode using the electrode structure having the above-described features, and utilizes a lithium oxidation reaction and a lithium ion reduction reaction.

  FIG. 4 is a diagram showing the basic configuration of the lithium secondary battery of the present invention. In FIG. 4, 401 is a negative electrode using the electrode structure of the present invention, 402 is an ion conductor, and 403 is a positive electrode. 404 are negative terminals, 405 is a positive terminal, and 406 is a battery case (housing).

  Here, in the secondary battery, an ionic conductor 402 is laminated between the negative electrode 401 and the positive electrode 403 to form an electrode group, and in a dry air or dry inert gas atmosphere in which the dew point is sufficiently controlled, After this electrode group is inserted into the battery case, the electrodes 401 and 403 are connected to the electrode terminals 404 and 405, and the battery case is sealed.

  In addition, when using what held electrolyte solution to the microporous plastic film as the ion conductor 402, the microporous plastic film is sandwiched between the negative electrode 401 and the positive electrode 403 as a short-circuit preventing separator. After forming the electrode group, it is inserted into the battery case, the electrodes 401 and 403 are connected to the electrode terminals 404 and 405, and the battery is assembled by injecting an electrolyte before sealing the battery case.

  The lithium secondary battery using the electrode structure made of the electrode material of the present invention for the negative electrode has high charge / discharge efficiency, capacity and energy density due to the beneficial effect of the negative electrode.

  Here, the positive electrode 403 serving as a counter electrode of a lithium secondary battery using the above-described electrode structure of the present invention as a negative electrode is at least a lithium ion source and is made of a positive electrode material serving as a lithium ion host material, preferably lithium. It consists of a layer formed from a positive electrode material that serves as an ion host material and a current collector. Further, the layer formed from the positive electrode material is preferably made of a positive electrode material which becomes a lithium ion host material and a binder, and in some cases, a material obtained by adding a conductive auxiliary material thereto.

  As a positive electrode material which is a lithium ion source and used as a host material for the lithium secondary battery of the present invention, lithium-transition metal (composite) oxide, lithium-transition metal (composite) sulfide, lithium-transition metal (composite) More preferred are nitrides and lithium-transition metal (composite) phosphorous oxides. Examples of the transition metal element of the transition metal oxide, transition metal sulfide, transition metal nitride, and transition metal phosphate compound are metal elements having a d-shell or f-shell, such as Sc, Y, lanthanoid, and actinoid. , Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pb, Pt, Cu, Ag, Au are used. In particular, Co, Ni, Mn, Fe, Cr, and Ti are preferably used. Lithium-transition metal (composite) oxide, lithium-transition metal (composite) sulfide, lithium-transition metal (composite) nitride, lithium-transition metal (composite) phosphorus oxide, particularly lithium-transition metal The (composite) oxide contains 0.001 to 0.01 yttrium Y element or Y and zirconium Zr element with respect to lithium Li1.0, thereby making the crystal grains finer and more. Li can be released and inserted repeatedly and stably.

  When the shape of the positive electrode active material is a powder, a positive electrode is produced by using a binder, or sintering or vapor-depositing to form a positive electrode active material layer on the current collector. Further, when the positive electrode active material powder has low conductivity, it is necessary to appropriately mix a conductive auxiliary material as in the formation of the active material layer of the electrode structure. As the conductive auxiliary material and the binder, those used for the electrode structure 302 of the present invention described above can be similarly used.

  Here, the current collector material used for the positive electrode is preferably aluminum, titanium, nickel, or platinum, which is a material having high electrical conductivity and inert to battery reaction. Specifically, nickel, stainless steel, Titanium and aluminum are preferable, and aluminum is more preferable because it is inexpensive and has high electrical conductivity. The shape of the current collector is plate-like, but the “plate-like” is not specified in terms of the practical range, and is called a “foil” having a thickness of about 100 μm or less. It includes forms. Further, a plate-like member such as a mesh shape, a sponge shape, or a fiber shape, a punching metal, an expanded metal, or the like may be employed.

In addition, the ion conductor 402 of the lithium secondary battery of the present invention includes a separator holding an electrolytic solution (an electrolyte solution prepared by dissolving an electrolyte in a solvent), a solid electrolyte, and a polymer gel or the like. Lithium ion conductors such as solidified electrolytes, composites of polymer gels and solid electrolytes can be used. Here, the conductivity of the ionic conductor 402 is preferably 1 × 10 ⁻³ S / cm or more, more preferably 5 × 10 ⁻³ S / cm or more as a value at 25 ° C.

Examples of the electrolyte include lithium ions (Li ⁺ ) and Lewis acid ions (BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BPh ₄ ⁻ (Ph: phenyl group). LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiBPh ₄ , LiSbF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) 3 salts such as _C and mixed salts thereof, and the like. It is desirable that the salt be sufficiently dehydrated and deoxygenated by heating under reduced pressure.

  Further, examples of the electrolyte solvent include acetonitrile, benzonitrile, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethylformamide, tetrahydrofuran, nitrobenzene, dichloroethane, diethoxyethane, 1,2-dimethoxyethane, Chlorobenzene, γ-butyrolactone, dioxolane, sulfolane, nitromethane, dimethyl sulfide, dimethylsulfoxide, methyl formate, 3-methyl-2-oxazolidinone, 2-methyltetrahydrofuran, 3-propyl sydnone, sulfur dioxide, phosphoryl chloride, thionyl chloride, Sulfuryl chloride or a mixture thereof can be used. As the solvent for the electrolyte, a combination of ethylene carbonate, γ-butyrolactone, and diethyl carbonate is more preferable because a decomposition reaction hardly occurs even at a higher charging voltage.

  The above solvent is dehydrated with, for example, activated alumina, molecular sieve, phosphorus pentoxide, calcium chloride or the like, or depending on the solvent, it is distilled in the presence of an alkali metal in an inert gas to remove impurities and dehydrate. It is good.

  In order to prevent leakage of the electrolytic solution, it is preferable to use a solid electrolyte or a solidified electrolyte. Examples of the solid electrolyte include glass such as an oxide composed of lithium element, silicon element, oxygen element, phosphorus element, or sulfur element, and a polymer complex of an organic polymer having an ether structure. As the solidified electrolyte, a solution obtained by gelling the electrolytic solution with a gelling agent and solidifying it is preferable.

  As the gelling agent, it is desirable to use a porous material having a large liquid absorption amount, such as a polymer that swells by absorbing the solvent of the electrolytic solution, or silica gel. Examples of the polymer include polyethylene oxide, polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, and vinylidene fluoride-hexafluoropropylene copolymer. Further, the polymer preferably has a crosslinked structure.

  In addition, since the ion conductor 402 which comprises the separator which plays the role which prevents the short circuit of the negative electrode 401 and the positive electrode 403 in a secondary battery may have a role which hold | maintains electrolyte solution, it has a pore which can move lithium ion. It is necessary to have a large number and to be insoluble and stable in the electrolytic solution.

  Therefore, as the ion conductor 402 (separator), for example, glass, polyolefin such as polypropylene or polyethylene, a micropore structure such as a fluororesin, or a non-woven material is preferably used. Moreover, the metal oxide film which has a micropore, or the resin film which compounded the metal oxide can also be used.

  Next, the shape and structure of the secondary battery will be described.

  Specific examples of the secondary battery of the present invention include a flat shape, a cylindrical shape, a rectangular parallelepiped shape, and a sheet shape. Examples of the battery structure include a single layer type, a multilayer type, and a spiral type. Among them, the spiral cylindrical battery has a feature that the electrode area can be increased by winding a separator between the negative electrode and the positive electrode, and a large current can be passed during charging and discharging. Moreover, a rectangular parallelepiped type or sheet type battery has a feature that a storage space of a device configured by storing a plurality of batteries can be used effectively.

  Next, the battery shape and structure will be described in more detail with reference to FIGS. FIG. 5 is a cross-sectional view of a single-layer flat (coin-type) battery, and FIG. 6 is a cross-sectional view of a spiral cylindrical battery. The lithium secondary battery having these shapes basically has the same configuration as that shown in FIG. 4 and includes a negative electrode, a positive electrode, an ion conductor, a battery housing, and an output terminal.

  5 and 6, 501 and 603 are negative electrodes, 503 and 606 are positive electrodes, 504 and 608 are negative electrode caps or negative electrode cans as negative electrode terminals, 505 and 609 are positive electrode cans or positive electrode caps as positive electrode terminals, 502 and 607. Is an ion conductor, 506 and 610 are gaskets, 601 is a negative electrode current collector, 604 is a positive electrode current collector, 611 is an insulating plate, 612 is a negative electrode lead, 613 is a positive electrode lead, and 614 is a safety valve.

  Here, in the flat type (coin type) secondary battery shown in FIG. 5, the positive electrode 503 including the positive electrode material layer and the negative electrode 501 including the negative electrode material layer are formed by, for example, a separator that holds at least an electrolyte solution. The laminated body is laminated via a conductor 502, and this laminated body is accommodated from the positive electrode side in a positive electrode can 505 as a positive electrode terminal, and the negative electrode side is covered with a negative electrode cap 504 as a negative electrode terminal. And the gasket 506 is arrange | positioned in the other part in a positive electrode can.

  In the spiral cylindrical secondary battery shown in FIG. 6, a positive electrode 606 having a positive electrode (material) layer 605 formed on the positive electrode current collector 604 and a negative electrode (material) formed on the negative electrode current collector 601. ) The negative electrode 603 having the layer 602 is opposed to, for example, an ionic conductor 607 formed of a separator holding at least an electrolytic solution, and forms a multilayer structure having a cylindrical structure wound in multiple layers.

  The laminate having the cylindrical structure is accommodated in a negative electrode can 608 serving as a negative electrode terminal. Further, a positive electrode cap 609 as a positive electrode terminal is provided on the opening side of the negative electrode can 608, and a gasket 610 is disposed in another part of the negative electrode can. The electrode stack having a cylindrical structure is separated from the positive electrode cap side by an insulating plate 611.

  The positive electrode 606 is connected to the positive electrode cap 609 via the positive electrode lead 613. The negative electrode 603 is connected to the negative electrode can 608 via the negative electrode lead 612. A safety valve 614 for adjusting the internal pressure inside the battery is provided on the positive electrode cap side. As described above, the layer made of the above-described negative electrode material fine powder of the present invention is used for the active material layer of the negative electrode 601 and the active material layer 602 of the negative electrode 603.

Next, an example of a method for assembling the battery shown in FIGS. 5 and 6 will be described.
(1) Ion conductors 502 and 607 serving as separators are sandwiched between the negative electrodes 501 and 603 and the formed positive electrodes 503 and 606, and incorporated into the positive electrode can 505 or the negative electrode can 608.
(2) After injecting the electrolytic solution, the negative electrode cap 504 or the positive electrode cap 609 and the gaskets 506 and 610 are assembled.
(3) The above (2) is caulked.

  Thereby, the battery is completed. It is desirable that the above-described lithium battery material preparation and battery assembly be performed in dry air from which moisture has been sufficiently removed or in a dry inert gas.

  Next, members constituting such a secondary battery will be described.

  As materials for the gaskets 506 and 610, for example, fluororesin, polyolefin resin, polyamide resin, polysulfone resin, and various rubbers can be used. In addition to the “caulking” using a gasket as shown in FIGS. 5 and 6, glass sealing tube, adhesive, welding, soldering, or the like is used as a battery sealing method. Further, as the material of the insulating plate 611 in FIG. 6, various organic resin materials and ceramics are used.

  As an outer can of a battery, it is comprised from the positive electrode can or negative electrode can 505,608 of a battery, and the negative electrode cap or positive electrode cap 504,609. Stainless steel is suitably used as the material for the outer can. As other materials for the outer can, an aluminum alloy, a titanium clad stainless material, a copper clad stainless material, a nickel-plated steel plate and the like are often used.

  Since the positive electrode can 505 in FIG. 5 and the negative electrode can 608 in FIG. 6 also serve as a battery housing (case) and a terminal, the above stainless steel is preferable. However, when the positive electrode can 505 or the negative electrode can 608 does not serve as a battery housing and a terminal, in addition to stainless steel, a metal such as zinc, a plastic such as polypropylene, or a composite material of metal or glass fiber and plastic is used. Can do.

  As a safety valve 614 provided in the lithium secondary battery as a safety measure when the internal pressure of the battery increases, for example, rubber, a spring, a metal ball, a rupture foil, or the like can be used.

Hereinafter, the present invention will be described in more detail with reference to Examples and Reference Examples .

(Preparation of electrode material)
First, examples for preparing the negative electrode material will be described.

Example 1
Granular silicon (purity 99.6%) and massive titanium were mixed at an atomic ratio of 85:15 (weight ratio 76.8: 23.2), and an Si-Ti alloy was prepared with an arc melting apparatus under vacuum. Next, the Si—Ti alloy previously obtained by arc melting was melted with a single roll method apparatus, and the molten metal was blown with argon gas onto a rotating copper roll and quenched to prepare a Si—Ti alloy. Next, the Si—Ti alloy was pulverized for 2 hours using a silicon nitride ball in an argon gas atmosphere by a planetary ball mill apparatus to obtain a fine powder electrode material.

(Example 2)
Granular silicon (purity 99.6%), massive titanium and massive boron are mixed at an atomic ratio of 85: 15: 0.85 (weight ratio 76.8: 23.2: 0.3), and an arc melting apparatus under vacuum A boron-doped Si-Ti alloy was prepared. Next, the boron-doped Si—Ti alloy previously obtained by arc melting is melted with a single roll method apparatus, the molten metal is blown with argon gas onto a rotating copper roll, and rapidly cooled to obtain a boron-doped Si—Ti alloy. Produced. Next, the boron-doped Si—Ti alloy was pulverized for 2 hours using a ball made of silicon nitride in an argon gas atmosphere by a planetary ball mill apparatus to obtain a fine powder electrode material.

(Example 3)
Granular silicon (purity 99.6%) and massive titanium were mixed at an atomic ratio of 85:15 (weight ratio 76.8: 23.2), and an Si-Ti alloy was prepared with an arc melting apparatus under vacuum. Next, the granular tin is added to the Si—Ti alloy obtained by the arc melting previously in an atomic ratio of Si: Sn: Ti = 76.2: 10.3: 13.5 (weight ratio 53.3: 30.5: 16.05) was added by a single roll method apparatus, and the molten metal was blown with argon gas onto a rotating copper roll and quenched to prepare a Si—Sn—Ti alloy. Next, the Si—Sn—Ti alloy was pulverized for 2 hours using a silicon nitride ball in an argon gas atmosphere in a planetary ball mill apparatus to obtain a fine powder electrode material.

Example 4
In the Example 3, granular tin was added to the Si—Ti alloy obtained by arc melting with an atomic ratio of Si: Sn: Ti = 76.4: 20.0: 3.6 (weight ratio 60: 35: 5). What was added was dissolved in a single roll method apparatus, and the molten metal was blown with argon gas onto a rotating copper roll and quenched to prepare a Si—Sn—Ti alloy. Other than that was carried out similarly to Example 3, and obtained the electrode material of the fine powder of Si-Sn-Ti alloy.

(Example 5)
Silicon, tin, and aluminum are mixed in an atomic ratio of 74.0: 19.4: 6.6 (weight ratio of 60: 35: 5), dissolved in a single roll method apparatus, and the molten metal is rotated with argon gas. It sprayed on the roll made from copper, and quenched, and obtained the Si-Sn-Al alloy powder. Next, the obtained Si—Sn—Al alloy powder was further pulverized for 2 hours using a ball of silicon nitride in an argon gas atmosphere in a planetary ball mill apparatus to obtain a fine powder electrode material.

(Example 6)
Silicon, zinc, and aluminum are mixed in an atomic ratio of 69.0: 27.6: 0.4 (weight ratio of 50.5: 47.1: 2.4) and melted in an argon gas atmosphere to melt the molten argon. Si—Zn—Al alloy powder was obtained by a gas atomization method injecting with gas. Next, the obtained Si—Zn—Al alloy powder was pulverized in isopropyl alcohol in a media mill apparatus using zirconia beads, and an electrode of an Si—Zn—Al alloy fine powder having an average particle size of 0.3 μm. Obtained material. Further, the obtained Si—Zn—Al alloy fine powder was pulverized for 2 hours using a ball made of silicon nitride in an argon gas atmosphere in a planetary ball mill apparatus to obtain a fine powder electrode material.

( Reference Example 1 )
Silicon, aluminum, and copper are mixed in an atomic ratio of 73.5: 21.9: 4.6 (weight ratio of 70:20:10), dissolved in a single roll method apparatus, and the molten metal is rotated with argon gas. A Si-Al-Cu alloy powder was obtained by spraying on a copper roll and quenching. Next, the obtained Si-Al-Cu alloy powder was further pulverized for 2 hours using a ball made of silicon nitride in an argon gas atmosphere in a planetary ball mill apparatus to obtain an electrode material of Si-Al-Cu alloy fine powder. It was.

(Example 7 )
In the gas atomization method of Example 6, silicon, tin, aluminum, and titanium were 84.1: 11.5: 0.4: 4.0 in atomic ratio (59.8: 35.0 in weight ratio). 0.2: 5.0) Si-Sn-Al-Ti alloy powder was obtained in the same manner as in Example 6 except that Si-Sn-Al-Ti alloy powder was obtained.

(Example 8 )
Silicon, tin, and zinc are mixed at an atomic ratio of 81.0: 16.2: 2.8 (51.9: 43.9: 4.2 by weight) and melted in an argon gas atmosphere to form a molten metal. After that, Si—Sn—Zn alloy powder was obtained by a water atomization method in which the molten metal was injected with high-pressure water. Next, the obtained Si—Sn—Zn alloy powder was pulverized in isopropyl alcohol with a media mill apparatus using zirconia balls to obtain Si—Sn—Zn alloy fine powder having an average particle size of 0.3 μm. Next, the obtained Si—Sn—Zn alloy fine powder was further pulverized for 2 hours in a planetary ball mill apparatus using silicon nitride balls in an argon gas atmosphere to obtain a fine powder electrode material.

( Reference Example 2 )
Si-Sn-Ag alloy powder in which silicon, tin, and silver are 81.8: 17.1: 1.1 (63: 35: 2 by weight) in the single roll method apparatus of Example 5 The electrode material of the Si—Sn—Ag alloy fine powder was obtained by the same operation as in Example 5 except that

( Reference Example 3 )
In the water atomization method of Example 8 , silicon, tin, zinc, and titanium were 82.7: 11.3: 2.0: 4.0 in atomic ratio (58.0: 33.9 in weight ratio). 3.3: 4.8) An electrode material of Si-Sn-Zn-Ti alloy fine powder was obtained in the same manner as in Example 5 except that the Si-Sn-Zn-Ti alloy powder was obtained.

(Example 9 )
In the same manner as in Example 5, silicon, tin, and boron were mixed at a weight ratio of 62: 36: 2, dissolved in a single roll method apparatus, and the molten metal was blown with argon gas onto a rotating copper roll and quenched. Si-Sn-B alloy powder was obtained. Subsequently, the obtained Si—Sn—B alloy powder was further pulverized for 2 hours using a ball made of silicon nitride in an argon gas atmosphere in a planetary ball mill apparatus to obtain a fine powder electrode material.

(Example 10 )
Example 9 in analogy to the silicon, tin, antimony in a weight ratio of 58: 34: 8 were mixed, except for obtaining a Si-Sn-Sb alloy powder by a single roll method apparatus, as in Example 9 By operation, an electrode material of Si—Sn—Sb alloy fine powder was obtained.

(Example 11 )
In the same manner as in Example 9 , except that silicon, tin, antimony, and boron were mixed at a weight ratio of 60: 35: 4: 1 to obtain Si—Sn—Sb—B alloy powder by a single roll method apparatus. In the same manner as in Example 9 , an electrode material of Si-Sn-Sb-B alloy fine powder was obtained.

(Example 12 )
In the same manner as in Example 9 , except that silicon, tin, copper, and boron were mixed at a weight ratio of 59: 34: 5: 2, and a Si-Sn-Cu-B alloy powder was obtained using a single roll method apparatus. In the same manner as in Example 9 , an electrode material of Si—Sn—Cu—B alloy fine powder was obtained.

(Example 13 )
In the same manner as in Example 9 , except that silicon, tin, aluminum, and boron were mixed at a weight ratio of 59: 34: 5: 2 to obtain Si—Sn—Al—B alloy powder by a single roll method apparatus. In the same manner as in Example 9 , an electrode material of Si-Sn-Al-B alloy fine powder was obtained.

(Example 14 )
In the same manner as in Example 9 , except that silicon, tin, aluminum, and antimony were mixed at a weight ratio of 56: 33: 4: 7, and a Si-Sn-Al-Sb alloy powder was obtained using a single roll method apparatus. In the same manner as in Example 9 , an electrode material of Si-Sn-Al-Sb alloy fine powder was obtained.

(Example 15 )
In the same manner as in Example 9 , silicon, tin, aluminum, antimony, and boron were mixed at a weight ratio of 58: 34: 5: 2: 1, and the Si—Sn—Al—Sb—B alloy was mixed using a single roll method apparatus. An electrode material of Si—Sn—Al—Sb—B alloy fine powder was obtained in the same manner as in Example 9 except that the powder was obtained.

(Reference Example 4 )
Silicon powder having an average particle size of 10 μm and a purity of 99.6% by weight was pulverized in isopropyl alcohol by a media mill apparatus using zirconia balls to obtain a silicon fine powder having an average particle size of 0.3 μm. Subsequently, a silicon nitride ball was used in a planetary ball mill apparatus in an argon gas atmosphere and pulverized for 2 hours to obtain a silicon fine powder electrode material.

(Reference Example 5 )
Granular silicon (purity 99.6% by weight) and massive titanium were mixed at an atomic ratio of 65:35 (weight ratio 52:48), and first, a Si—Ti alloy was prepared in an arc melting apparatus under vacuum. Next, the Si—Ti alloy previously obtained by arc melting was melted with a single roll method apparatus, and the molten metal was blown with argon gas onto a rotating copper roll and quenched to prepare a Si—Ti alloy. Subsequently, the obtained Si—Ti alloy was pulverized for 2 hours using a silicon nitride ball in an argon gas atmosphere by a planetary ball mill apparatus to obtain a fine powder electrode material.

Note that the composition of silicon and titanium is a composition that partially melts in a molten liquid state, that is, a composition in which liquids having different concentrations exist, and TiSi ₂ is easily crystallized in a solid state.

(Reference Example 6 )
Granular silicon (purity 99.6% by weight) and granular nickel are mixed at an atomic ratio Si: Ni = 65.9: 34.1 (weight ratio 48:52), and the Si—Ni alloy is mixed in an arc melting apparatus under vacuum. Prepared. Next, the Si—Ni alloy previously obtained by arc melting was melted with a single roll method apparatus, and the molten metal was blown with argon gas onto a rotating copper roll and quenched to prepare a Si—Ni alloy. Subsequently, the obtained Si—Ni alloy was pulverized for 2 hours using a ball made of silicon nitride in an argon gas atmosphere in a planetary ball mill apparatus to obtain a fine powder electrode material.

Silicon and nickel are known to form various intermetallic compounds (NiSi ₂ , NiSi, Ni ₂ Si ₃ , Ni ₂ Si, etc.). With the above silicon and nickel composition, Si ₂ Ni is formed. Easy composition.

Next, the results of analyzing the electrode materials obtained in Examples 1 to 15 and Reference Examples 1 to 6 will be described.

  The analysis of the electrode material of the above-mentioned silicon alloy is considered to influence the performance of the negative electrode of the lithium secondary battery. The analysis was made from the viewpoint of the element distribution in the alloy.

  The crystal structure of the silicon alloy of the present invention suitable for the negative electrode material of the lithium secondary battery is that there are few silicon intermetallic compounds that are considered to have low lithium storage performance, the crystal of each element forming the alloy is a microcrystal, or Examples thereof include a crystal structure that has been amorphized and a distribution of elements in the alloy that is less unevenly distributed and more uniformly distributed.

  As an analysis method, X-ray diffraction analysis, observation with a transmission electron microscope, energy dispersive X-ray spectroscopy (commonly known as EDXS) analysis, electron diffraction analysis, and the like were used.

  Here, the formation of the intermetallic compound can be confirmed from a pattern of X-ray diffraction or electron beam diffraction. In addition, when the crystal is microcrystalline or amorphized, the half-value width of the X-ray diffraction peak becomes broad, the crystallite size calculated from the Scherrer equation becomes small, and the electron beam diffraction From a ring pattern to a halo pattern, a high-resolution observation using a transmission electron microscope reveals a fine stripe or maze pattern on the crystal lattice.

  Furthermore, when the distribution of the elements in the alloy is less unevenly distributed and more uniformly distributed, it is observed as an image with less unevenness of density in the alloy particles by transmission electron microscope observation (particularly dark field image), In elemental mapping by EDXS analysis combined with a transmission electron microscope, the distribution of elemental distribution in the particles is observed to be small.

First, in the analysis and evaluation of the crystal structures of the electrode materials obtained in Examples 1 to 15 and Reference Examples 1 to 3 , the half-value width of the X-ray diffraction peak is broad, and a fine stripe pattern is observed with a transmission electron microscope. Or a maze-like pattern was observed. From this, it was found that any of the examples was a material having a structure that has been microcrystalline or amorphized. In addition, when the Scherrer crystallite size was calculated | required from the measurement result of X-ray diffraction, all were the range of 7-40 nm.

In the EDXS analysis relating to the element distribution of the electrode materials obtained in Examples 1 to 15 and Reference Examples 1 to 3 , there is little deviation of the elements in the alloy particles, and the pattern shown in FIG. 1 (a) or (b). As shown in the figure, it was found that the distribution was almost uniform. Example 1 Detection of the intermetallic compound of silicon at 15 and Reference Examples 1 to 3, by area electron diffraction in the X-ray diffraction and transmission electron microscope, of Example 1～4,7, 12, reference A very small amount was observed in the alloys containing titanium or copper of Examples 1 and 3 .

On the other hand, in the analytical evaluation of the crystal structure of the electrode material obtained in Reference Examples 5 and 6 , the half-value width of the X-ray diffraction peak is narrower than those in the previous Examples 1 to 15 and Reference Examples 1 to 3 , A large striped pattern of regular regions was observed with a transmission electron microscope. From the X-ray diffraction peak pattern and the limited-field electron diffraction pattern, TiSi ₂ intermetallic compound was confirmed in Reference Example 5 , and NiSi ₂ intermetallic compound was confirmed in Reference Example 6 .

In addition, in the transmission electron microscope observations (especially dark field images) of Reference Examples 5 and 6 , images with large unevenness in density were observed in the alloy particles, and from the element mapping by EDXS analysis combined with the transmission electron microscope, the particles Inside, the uneven distribution of the titanium or nickel elements was confirmed.

  Next, an electrode structure was prepared using fine powders of various silicon or silicon alloys obtained by the above-described procedure as follows, and the lithium insertion / desorption performance of this electrode structure was evaluated.

First, 66.5% by weight of various silicon or silicon alloy fine powders obtained by the above-described procedure and a flat graphite powder (specifically, an approximately 5 μm diameter and about 1 μm thick as a conductive auxiliary material). 10.0% by weight of disc-shaped graphite powder), 6.0% by weight of graphite powder (substantially spherical with an average particle size of 0.5 to 1.0 μm), acetylene black (substantially spherical) The average particle size is 4 × 10 ⁻² μm) 4.0% by weight, and 10.5% by weight of polyvinyl alcohol as a binder (binder) and 3.0% by weight of sodium carboxymethylcellulose are mixed, Water was added and kneaded to prepare a slurry.

  Next, the slurry thus prepared was coated on a 15 μm thick electrolytic copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness was adjusted with a roll press, and the thickness was 25 μm. An electrode structure having an active material layer was prepared. Then, the electrode structure was cut into a size of 2.5 cm × 2.5 cm, and a copper tab was welded to obtain a silicon electrode.

[Evaluation procedure for lithium storage and release]
Next, a lithium electrode having a thickness of 100 μm was pressure-bonded to the copper foil to produce a lithium electrode. Next, 1M (mol / liter) of LiPF ₆ salt was dissolved in an organic solvent obtained by mixing ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7 to prepare an electrolytic solution.

  Then, this electrolytic solution is impregnated into a porous polyethylene film having a thickness of 25 μm, the above-described silicon electrode is disposed on one surface of the film, and the above-described lithium electrode is disposed on the other surface. The polyethylene film was sandwiched between the two. Next, in order to obtain flatness, it was sandwiched between glass plates from both sides, and further covered with an aluminum laminate film to produce an evaluation cell.

  The aluminum laminate film was a three-layer film in which the outermost layer was a nylon film, the middle layer was an aluminum foil with a thickness of 20 μm, and the inner layer was a polyethylene film. The lead terminal portion of each electrode was fused and sealed without being laminated.

  Then, in order to evaluate the function of the electrode structure as a negative electrode, a lithium insertion / desorption cycle test (charge / discharge cycle test) was performed.

That is, the lithium electrode is an anode, the silicon electrode is a cathode, and the above-described evaluation cell is connected to a charge / discharge device. First, a current density of 0.112 mA / cm ² (70 mA per 1 g of active material layer of the silicon electrode, that is, 70 mA). The electrode for evaluation was discharged at a weight of g / electrode layer, and lithium was inserted into the silicon electrode layer. Next, the evaluation cell is charged at a current density of 0.32 mA / cm ² (200 mA / electrode layer weight g), lithium is desorbed from the silicon layer, and the weight of the silicon electrode layer or lithium per silicon powder or silicon alloy powder. The amount of electricity accompanying insertion / extraction was evaluated in the voltage range of 0-1.2V.

  The results of evaluating the performance of lithium insertion / extraction of the electrode structure were as follows.

First, as a result of evaluating the ratio (efficiency) of the amount of electricity associated with the release of lithium to the amount of electricity associated with the first and 10th insertions of lithium, the efficiency of the first time was about 85% in Reference Examples 5 and 6 . In the electrodes made from the electrode materials of Examples 1 to 9 and Reference Examples 1 to 3 of the present invention, the efficiency of the first time was about 90% or more. The efficiency of the 10th time was 99.5% or more.

Lithium emission quantity of electricity definitive the electrode prepared by the electrode material of Reference Example 5 and Reference Example 6, the 10th dropped to below 87% of the first round. However, the amount of electricity released from lithium in the electrode made of the electrode material of the present example was maintained almost 100% of the first time even at the tenth time.

In the electrode using the silicon powder of Reference Example 4 , the lithium insertion efficiency of the first time and the tenth time was 89% and 98%, respectively. It decreased to 70% of the first time.

The amount of electricity accompanying the first lithium release was as follows. In the electrodes prepared from the electrode materials of the silicon alloy fine powders of Examples 1 to 15 and Reference Examples 1 to 3 , all showed an electric quantity of 1400 to 1800 mAh / g per electrode layer weight (excluding the current collector weight). It was. The electrode produced from the silicon fine powder of Reference Example 4 exhibited a lithium discharge electricity amount of 2000 mAh / g per electrode layer weight. The electrodes produced from the silicon alloy fine powders of Reference Example 5 and Reference Example 6 showed only lithium discharge electricity amount of 400 mAh / g or less.

  It was found that the silicon alloy electrode produced in this example has a long cycle life, and can store and discharge approximately 4 to 6 times the amount of electricity (the amount of electricity per electrode layer weight) of an electrode produced from graphite. .

In addition, regarding Examples 4, 5, 9 to 15 and Reference Examples 1 and 2 , a peak related to silicon at a diffraction angle of 2Θ = 28.4 ° by X-ray diffraction analysis before and after ball milling of the produced alloy powder. Desorption (release) efficiency and Li release for the first insertion when the electrochemical Li insertion and desorption reaction of the electrode made using the alloy fine powder after ball milling is performed. The amount of electricity involved is summarized in Table 1.

  From the results of Table 1 above, it was found that the desorption (release) efficiency with respect to the first insertion of lithium was very high, and the amount of electricity accompanying Li release per electrode layer weight was also extremely high. Amorphization can be promoted by ball milling, but most of the alloys to which boron is added at a high concentration have a wide half-value width of the peak related to silicon in the X-ray diffraction chart even before ball milling, and are amorphous. It was confirmed that crystallization is easy to promote. From empirical data, it is known that a lithium secondary battery using a negative electrode material that is promoted to be amorphous has a long charge / discharge life.

  Next, the resistance of the electrode layer was evaluated.

Each of the electrode materials of Examples 1 to 15 and Reference Examples 1 to 3 was used, and a slurry was prepared in the same procedure as the production of the electrode structure. After applying the slurry on the polyester sheet and drying, a roll press machine To prepare a sample of the electrode layer. When the sheet resistance of the electrode layer prepared by the above method was measured by a four-end needle measurement method, in each case, the electrode layer formed from the electrode material doped with boron was a sheet rather than the one not doped with boron. The resistance value was low.

Next, a secondary battery was fabricated as Example 16 of the present invention.

(Example 16 )
In this example, an electrode structure in which electrode layers were provided on both sides of a current collector using the negative electrode material of the present invention was prepared, and the cross-sectional structure shown in FIG. No. 18650 size (diameter 18 mmφ × height 65 mm) lithium secondary battery was fabricated.

(1) Production of Negative Electrode 603 Using silicon alloy fine powder as the electrode material of Examples 1 to 15 and Reference Examples 1 to 3 , respectively, 69% by weight of silicon alloy fine powder and flat graphite as a conductive auxiliary material 10% by weight of a powder (specifically, a substantially disc-shaped graphite powder having a diameter of about 5 μm and a thickness of about 1 μm), and a graphite powder (substantially spherical with an average particle size of 0.5 to 1.0 μm ) 6% by weight, 4% by weight of acetylene black (substantially spherical, its average particle size is 4 × 10 ⁻² μm), and polyamic acid having a solid content of 14% as a binder (binder) ( A N-methyl-2-pyrrolidone solution of polyimide precursor) was mixed in an amount of 11% by weight in terms of solid content, and N-methyl-2-pyrrolidone was added and kneaded to prepare a slurry. Next, the slurry thus prepared is applied to both sides of a 15 μm thick electrolytic copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness is adjusted with a roll press, and the thickness is 25 μm. An electrode structure having an active material layer was prepared. The electrode structure obtained in the previous procedure was cut into a predetermined size, and a nickel ribbon lead was connected to the electrode by spot welding to obtain a negative electrode 603.

(2) Fabrication of positive electrode 606
(a) Lithium citrate and cobalt nitrate are mixed at a molar ratio of 1: 3, and an aqueous solution in which citric acid is added and dissolved in ion-exchanged water is sprayed into an air stream at 200 ° C. A precursor of cobalt oxide was prepared.
(b) The lithium-cobalt oxide precursor obtained in (a) above was further heat-treated at 850 ° C. in an oxygen stream.
(c) After mixing 92% by weight of the lithium-cobalt oxide prepared in (b) with 3% by weight of graphite powder and 5% by weight of poly (vinylidene fluoride), N-methyl-2-pyrrolidone is added to form a slurry. Was made.
(d) The slurry obtained in (c) above was applied to and dried on both sides of a 20 micron thick aluminum foil current collector 604, and then the thickness of the positive electrode active material layer on one side was adjusted to 90 microns with a roll press. did. Further, aluminum leads were connected with an ultrasonic welder and dried under reduced pressure at 150 ° C. to produce a positive electrode 606.

(3) Electrolyte preparation procedure
(a) A solvent was prepared by mixing ethylene carbonate and diethyl carbonate from which water had been sufficiently removed at a volume ratio of 3: 7.
(b) A solution obtained by dissolving 1 M (mol / liter) of lithium hexafluorophosphate (LiPF ₆ ) in the solvent obtained in the above (a) was used as an electrolytic solution.

(4) Separator 607
A polyethylene microporous film having a thickness of 25 microns was used as a separator.

(5) Assembling of the battery The assembling was performed in a dry atmosphere in which moisture having a dew point of −50 ° C. or less was controlled.
(a) The separator 607 was sandwiched between the negative electrode 603 and the positive electrode 606, wound in a spiral shape so as to have a separator / positive electrode / separator / negative electrode / separator configuration, and inserted into a negative electrode can 608 made of stainless steel.
(b) Next, the negative electrode lead 612 was connected to the bottom of the negative electrode can 608 by spot welding. A constriction was formed on the upper part of the negative electrode can with a necking device, and a positive electrode lead 613 was welded to a positive electrode cap 609 with a gasket 610 made of polypropylene by a spot welder.
(c) Next, after injecting the electrolytic solution, the positive electrode cap was put on, the positive electrode cap and the negative electrode can were caulked with a caulking machine, and the battery was fabricated.

  This battery was a positive electrode capacity-regulated battery in which the capacity of the negative electrode was larger than that of the positive electrode.

(6) Evaluation About each battery, charging / discharging was performed and the discharge capacity was measured.

As a result, the discharge capacity of the lithium secondary battery using the electrode structures formed from the electrode materials of Examples 1 to 15 and Reference Examples 1 to 3 as the negative electrode exceeded 2800 mAh, and the average operating voltage was It was 3.3V.

(Example 17 )
In this example, an electrode structure in which electrode layers were provided on both sides of a current collector using the negative electrode material of the present invention was prepared, and the cross-sectional structure shown in FIG. No. 18650 size (diameter 18 mmφ × height 65 mm) lithium secondary battery was fabricated.

(1) Production of negative electrode 603 A mixture of silicon, tin, and boron in a weight ratio of 74.5: 25.0: 0.5 was melted under an argon gas atmosphere to form a molten metal, and then the water stream was rotated at high speed. A Si—Sn—B alloy powder was obtained by pouring a metal atomized with argon gas. Next, the obtained Si—Sn—B alloy powder was pulverized in isopropyl alcohol with a media mill apparatus using zirconia balls to obtain Si—Sn—B alloy fine powder having an average particle size of 0.3 μm. Next, the obtained Si-Sn-B alloy fine powder was further pulverized for 2 hours using an stainless steel ball in an argon gas atmosphere with an attritor, and further the weight of the Si-Sn-B alloy fine powder was adjusted to 100 parts. On the other hand, 2 parts of graphite powder, 1 part of carbon fiber and 1 part of multi-walled carbon nanotube were added and pulverized to obtain an electrode material of silicon alloy fine powder in which a carbon material was compounded.

  Next, 69% by weight of a silicon alloy fine powder obtained by compounding the obtained carbon material, and a flat graphite powder (specifically, a substantially disc-like shape having a diameter of about 5 μm and a thickness of about 1 μm) as a conductive auxiliary material. 10% by weight of graphite powder, 10% by weight of graphite powder (substantially spherical and its average particle size is 0.5 to 1.0 μm), and N of polyamic acid (polyimide precursor) having a solid content of 14%. -Methyl-2-pyrrolidone solution was mixed with 11% by weight in terms of solid content, and N-methyl-2-pyrrolidone was added and kneaded to prepare a slurry. Next, the slurry thus prepared was applied to both sides of a 10 μm-thick electrolytic copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness was adjusted with a roll press, and the thickness was 25 μm. An electrode structure having an active material layer was prepared. The electrode structure obtained in the previous procedure was cut into a predetermined size, a nickel ribbon lead was connected to the electrode by spot welding, and dried under reduced pressure at 200 ° C. to obtain a negative electrode 603.

(2) Fabrication of positive electrode 606
(a) Lithium citrate and cobalt nitrate are mixed at a molar ratio of 1: 3, and an aqueous solution in which citric acid is added and dissolved in ion-exchanged water is sprayed into an air stream at 200 ° C. A precursor of cobalt oxide was prepared.
(b) The lithium-cobalt oxide precursor obtained in (a) above was further heat-treated at 850 ° C. in an oxygen stream.
(c) 3% by weight of graphite powder and 1% by weight of carbon fiber were mixed with 93% by weight of the lithium-cobalt oxide prepared in (b) above, and 3% by weight of the solid component of polyamic acid (polyimide precursor) Then, an N-methyl-2-pyrrolidone solution of polyamic acid was added so as to prepare a slurry.
(d) The slurry obtained in (c) above was applied and dried on both sides of a 17 micron thick aluminum foil current collector 604, and then the thickness of the positive electrode active material layer on one side was adjusted to 90 microns with a roll press. did. Furthermore, an aluminum lead was connected with an ultrasonic welder and dried under reduced pressure at 200 ° C. to produce a positive electrode 606.

A battery was fabricated in the same manner as in Example 16 except that the above negative electrode and positive electrode were fabricated and a micropore polyethylene film having a thickness of 17 μm was used as the separator.

  As a result of conducting a charge / discharge test with constant current-constant voltage charging (maximum voltage 4.2V), the discharge capacity exceeded 3400 mAh, and the average operating voltage was 3.3V. Moreover, from the result of the repeated charge / discharge test of the obtained battery, the battery using the negative electrode material combined with the carbon material had a charge / discharge of 1.5 times or more compared to the battery not combined with the carbon material. It was found that a repeated life can be obtained.

(Example 18 )
(1) A lithium secondary battery having a cross-sectional structure of 18650 (diameter: 18 mmφ × height: 65 mm) having the cross-sectional structure shown in FIG. 6 was produced in the same manner as in Example 17 except that the negative electrode was produced.
(1) Production of negative electrode 603 After mixing silicon, tin, and boron in a weight ratio of 74.5: 25.0: 0.5 and melting in an argon gas atmosphere to form a molten metal, the molten metal is sprayed with high-pressure water. Si-Sn-B alloy powder was obtained by the water atomization method. Next, the obtained Si—Sn—B alloy powder was pulverized in isopropyl alcohol with a media mill apparatus using zirconia balls to obtain Si—Sn—B alloy fine powder having an average particle size of 0.3 μm.

  Next, the obtained Si—SnSi—Sn—B alloy fine powder was further pulverized for 2 hours in an argon gas atmosphere using a stainless steel ball in an attritor, and further, the Si—Sn—B alloy fine powder weight 100 3 parts of graphite powder, 2 parts of carbon fiber, and 30 parts of metal magnesium powder were added and pulverized to obtain an electrode material of silicon alloy fine powder in which a carbon material and magnesium metal were combined. As a result of X-ray diffraction analysis, metal magnesium peaks were observed in the obtained alloy fine particles.

  Next, 69% by weight of a silicon alloy fine powder obtained by compounding the obtained carbon material, and a flat graphite powder (specifically, a substantially disc-like shape having a diameter of about 5 μm and a thickness of about 1 μm) as a conductive auxiliary material. 10% by weight of graphite powder, 10% by weight of graphite powder (substantially spherical and its average particle size is 0.5 to 1.0 μm), and N of polyamic acid (polyimide precursor) having a solid content of 14%. -Methyl-2-pyrrolidone solution was mixed with 11% by weight in terms of solid content, and N-methyl-2-pyrrolidone was added and kneaded to prepare a slurry.

  Next, the slurry thus prepared was applied to both sides of a 10 μm-thick electrolytic copper foil (electrochemically produced copper foil) with a coater, dried, and the thickness was adjusted with a roll press, and the thickness was 25 μm. An electrode structure having an active material layer was prepared. The electrode structure obtained in the previous procedure was cut into a predetermined size, a nickel ribbon lead was connected to the electrode by spot welding, and dried under reduced pressure at 200 ° C. to obtain a negative electrode 603.

In other cases, the battery produced in the same manner as in Example 17 was subjected to a charge / discharge test with constant current-constant voltage charge (maximum voltage 4.2 V). As a result, the discharge capacity exceeded 3000 mAh, and the average operating voltage was It was 3.5V.

(Example 19 )
Except for the use of the electrolyte solution (2) below a positive electrode prepared with the following (3) of the, in the same manner as in Example 17, lithium 18650 size having the sectional structure shown in FIG. 6 (diameter 18Mmfai × height 65 mm) A secondary battery was produced.

(2) Fabrication of positive electrode 606
(a) lithium citrate and 1 cobalt nitrate were mixed in a molar ratio of 3 for Li element of lithium citrate, 0.1 mol ratio of preparative yttrium nitrate _{Y (NO 3) 3 · 6H} 2 O and , Zirconium oxyacetate ZrO (CH ₃ COO) _{2 in a} molar ratio of 0.4 with respect to Li element and citric acid were added, and an aqueous solution dissolved in ion-exchanged water was sprayed into an air stream at 200 ° C., A fine powder lithium-cobalt oxide precursor was prepared.
(b) The precursor of lithium-cobalt oxide containing yttrium element and zirconium element obtained in (a) above was further heat-treated at 850 ° C. in an oxygen stream.
(c) After mixing 92% by weight of the lithium-cobalt oxide containing yttrium and zirconium elements prepared in (b) above with 3% by weight of graphite powder and 5% by weight of polyvinylidene fluoride powder, N-methyl-2 -Pyrrolidone was added to make a slurry.
(d) The slurry obtained in (c) above was applied to and dried on both sides of a 20 micron thick aluminum foil current collector 604, and then the thickness of the positive electrode active material layer on one side was adjusted to 90 microns with a roll press. did. Further, aluminum leads were connected with an ultrasonic welder and dried under reduced pressure at 150 ° C. to produce a positive electrode 606.

(3) Electrolyte preparation procedure
(a) A solvent in which ethylene carbonate, γ-butyrolactone, and diethyl carbonate from which water had been sufficiently removed was mixed at a volume ratio of 1.5: 1.5: 7 was prepared.
(b) A solution obtained by dissolving 1.5 M (mol / liter) of lithium tetrafluoroborate (LiBF ₄ ) in the solvent obtained in (a) above was used as an electrolytic solution.

Except for the above operations, a battery produced in the same manner as in Example 17 was subjected to a charge / discharge test with constant current-constant voltage charge (maximum voltage 4.4 V). As a result, the discharge capacity was over 3700 mAh, and the average operation was performed. The voltage was 3.3V.

The schematic cross section of the silicon alloy particle of this invention. The figure for demonstrating reaction which lithium ion inserts into intrinsic silicon, p-type silicon, and n-type silicon. The conceptual diagram which shows typically the cross section of one embodiment of the electrode structure which consists of negative electrode material fine powder of the lithium secondary battery of this invention. The conceptual diagram which shows typically the cross section of one embodiment of the secondary battery (lithium secondary battery) of this invention. Sectional drawing of a single layer type flat type (coin type) battery. Sectional drawing of a spiral type cylindrical battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Silicon alloy particle 101 Silicon microcrystal group 102 First element microcrystal group 103 Second element microcrystal group 301 Electrode material layer 302 Electrode structure 303 Negative electrode material fine powder 304 Conductive auxiliary agent 305 Binder 401, 501, 603 Negative electrode 403, 503, 606 Positive electrode 402, 502, 607 Ion conductor 404 Negative electrode terminal 405 Positive terminal 406 Battery case (battery housing)
506 Negative electrode cap 505 Positive electrode can 506, 610 Gasket 601 Negative electrode current collector 602 Negative electrode active material layer 604 Positive electrode current collector 605 Positive electrode active material layer 608 Negative electrode can (negative electrode terminal)
611 Insulating plate 612 Negative electrode lead 613 Positive electrode lead 614 Safety valve

Claims (13)

In an electrode material for a lithium secondary battery comprising particles of a solid state alloy containing silicon as a main component,
The solid-state alloy is composed of one or more alloys selected from Si-A and Si -AE having a silicon content of 50 wt% to 95 wt%,
In the Si-A, A is a first element and one or more elements selected from the group consisting of tin, silver, zinc, and titanium, and the atomic ratio of the element A in the Si-A is silicon atoms. Lower than the ratio,
In the Si-A-E, A is one or more elements selected from the group consisting of tin and zinc as the first element, and E is the second element as copper, aluminum, vanadium, yttrium, zirconium, a least one element selected from the group consisting of boron, the atomic ratio of the Si-a-E in the element a and the element E is lower than the atomic ratio of silicon, prior Symbol atoms of the first element a ratio rather high than the atomic ratio of the second element E,
The alloy contains a pure metal or a solid solution composed of an element selected from the A and the E,
The alloy particles have a structure in which microcrystals or amorphouss of pure metal or solid solution composed of an element selected from A and E are dispersed in microcrystalline silicon or amorphized silicon. An electrode material for a lithium secondary battery comprising a eutectic composed of two or more elements selected from silicon, A and E. 2. The electrode material for a lithium secondary battery according to claim 1, wherein the composition of the alloy is an elemental composition that completely melts in a molten liquid state of the alloy. The eutectic is
(A) a eutectic of silicon and the first element A,
(B) a eutectic of silicon and the second element E,
(C) a eutectic with the first element A and second element E (d) pre-Symbol (a), (b), claims, characterized in that either a combination of eutectic (c) Item 2. The electrode material for a lithium secondary battery according to Item 1. The silicon of the alloy is doped with an element as one or more dopants selected from the group consisting of boron, aluminum, gallium, antimony, and phosphorus in an atomic ratio of 1 × 10 ⁻⁸ to 2 × 10 ^−1. The electrode material for a lithium secondary battery according to claim 1, wherein: 5. The electrode material for a lithium secondary battery according to claim 4, wherein the ratio of the dopant to silicon is in the range of 1 × 10 ⁻⁵ to 1 × 10 ^{−1 in} atomic ratio. The electrode material for a lithium secondary battery according to claim 4 or 5 , wherein the dopant is boron.   2. The electrode material for a lithium secondary battery according to claim 1, wherein an average particle diameter of the alloy particles containing silicon as a main component is 0.02 μm to 5 μm.   2. The electrode material for a lithium secondary battery according to claim 1, wherein the shape of the alloy particles containing silicon as a main component is a fine powder.   2. The lithium secondary battery according to claim 1, wherein a material selected from the group consisting of carbon material, metallic magnesium, and carbon material and metallic magnesium is combined with the alloy particles mainly composed of silicon. Electrode material. And the electrode material according to any one of claims 1 to 9, conductive auxiliary material, a binder, the electrode structure characterized by being composed of a current collector. The electrode structure according to claim 10 , wherein the conductive auxiliary material is a carbon material. Claim 10 or the negative electrode using the electrode structure according to 11, the electrolyte and comprises a positive electrode, a secondary battery, characterized by using the reduction reaction of the oxidation reaction and a lithium ion of lithium. The secondary battery according to claim 12, wherein the positive electrode material constituting the positive electrode is a lithium-transition metal composite oxide containing at least an element composed of yttrium, yttrium and zirconium.

Images