JP2002237294A - Negative electrode for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a nonaqueous electrolyte secondary battery suppressing cycle degradation with high capacity using silicon as a main active material, and moreover mechanically flexible to allow the manufacture of batteries in various forms. SOLUTION: In this negative electrode for the nonaqueous electrolyte secondary battery, a current collector is jointed to a silicon film layer comprising a silicon film or the like that may contain a dopant such as phosphorus, directly or through a conductor layer such as a silicon alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the negative electrode.

[0002]

2. Description of the Related Art A lithium ion battery, which is a non-aqueous electrolyte secondary battery, has a positive electrode composed of a positive electrode active material capable of absorbing and releasing lithium ions and a current collector, and a negative electrode active material capable of absorbing and releasing lithium ions. It comprises a negative electrode composed of a substance and a current collector, a non-aqueous electrolyte obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent, a separator, a battery container, and the like. Such non-aqueous electrolyte secondary batteries have a higher energy density than secondary batteries using aqueous electrolytes such as nickel-metal hydride batteries, so they are mainly used as power sources for portable electronic devices such as notebook computers and mobile phones. Demand is growing. In recent years, the power consumption of these portable electronic devices has increased due to their multifunctionality and high performance, and accordingly, increasing the capacity of nonaqueous electrolyte secondary batteries has become an important issue.

In a non-aqueous electrolyte secondary battery, during discharge, lithium ions are desorbed from the negative electrode active material and occluded in the positive electrode active material via the non-aqueous electrolyte. At this time, electrons corresponding to all charges of lithium ions desorbed from the negative electrode active material are taken out as a current to an external circuit to drive an electronic device. Therefore,
In order to increase the capacity of the nonaqueous electrolyte secondary battery, it is essentially important for the negative electrode active material to increase the amount of lithium ions that can be inserted and released reversibly. Hereinafter, in order to represent the amount of occlusion and release of lithium ions in the negative electrode active material, the discharge capacity of a non-aqueous electrolyte secondary battery manufactured using lithium metal as a counter electrode with respect to the negative electrode active material is used. Expressed as capacity.

[0004] As a negative electrode active material of a non-aqueous electrolyte secondary battery that is put into practical use today, a carbon-based material (hereinafter, also simply referred to as carbons) such as graphite, hard carbon or soft carbon is used. Carbon has good cycle characteristics with a small decrease in capacity even after repeated charge and discharge, and also has a danger of short-circuiting and ignition due to dendrite generation, which is a particular problem with negative electrode active materials such as lithium metal and lithium alloy. Since it is not present, it is an excellent negative electrode active material. However, the capacity of carbons used today has almost reached the theoretical capacity (372 mAh / g for graphite), and it has been difficult to achieve even higher capacities in carbons. Therefore, in order to increase the capacity of the nonaqueous electrolyte secondary battery, a negative electrode active material having a higher capacity than carbons is required.

It is known that Si or an alloy containing Si (hereinafter, also simply referred to as silicon, etc.) has a higher capacity than carbons as a negative electrode active material of a nonaqueous electrolyte secondary battery. Yes. O. Besenh
Ard et al. Electrochem. Soc.
113, 457 (1986)｝. In the case of graphite among carbons, one lithium ion per 6 carbon atoms is used.
In the case of Si, one atom of Si atoms is absorbed and released.
4.4 lithium ions can be stored and released per unit
Individual. As a result, the capacity per unit weight of Si was 4200 mAh / g, and the capacity of the aforementioned graphite was 372 mh / g.
It has a significantly higher capacity than Ah / g.

[0006] As described above, silicon and the like are materials having a significantly higher capacity than carbons, but when these materials are occluded with lithium ions, the volume expansion of Si at most 4.1 times occurs. The negative electrode active material is mechanically broken by the volume expansion. Due to the destruction of this negative electrode active material,
Since the electron conduction path indispensable for the charge / discharge reaction is destroyed, the amount of the negative electrode active material that can participate in the charge / discharge decreases with the repetition of the charge / discharge. When Si is used as a negative electrode active material of a non-aqueous electrolyte secondary battery, this cycle deterioration is particularly remarkable, and the capacity almost disappears after repeated charge and discharge several times, and as a secondary battery, In many cases, the function cannot be performed.

In order to solve the cycle deterioration of silicon and the like, a silicon / carbon composite in which nanometer-sized silicon is dispersed in a carbonaceous matrix has been proposed {A. M. Wilson et al. Electroc
hem. Soc. 142, 326 (1995). This silicon / carbon composite is a powder produced by simultaneous CVD of silicon and carbon and contains silicon at a maximum of 48 wt%. As described above, by diluting silicon with carbon, the volume expansion of the composite is reduced, and the charge and discharge 3
No noticeable cycle deterioration is observed up to 0 cycles. However, as a result of dilution with carbon, the capacity per unit weight of the composite decreases, and only about 400 mAh / g is obtained in charge and discharge at a practical current density. Therefore, even if this silicon / carbon composite is used, the effect of improving the capacity of the non-aqueous electrolyte secondary battery is hardly obtained.

As another method for solving the cycle deterioration of silicon or the like, a method has been proposed in which silicon is combined with carbon into a composite sintered body (Japanese Patent No. 2948205).
issue). This silicon / carbon composite sintered body is obtained by applying a powder obtained by heat-treating a mixture of silicon powder and pitch-granulated graphite to a copper foil as a current collector using polyvinylidene fluoride as a binder, and further heat-treating the same. It is formed. In the silicon / carbon composite sintered body, when the final voltage of lithium ion occlusion is 25 mV (control electrode: lithium metal), the volume expansion of the silicon / carbon composite sintered body is about 1.4.
As a result, cycle deterioration can be suppressed. In addition, the capacity per unit weight of the silicon / carbon composite sintered body is 600 mAh / g, which is higher than the capacity of carbons, and can improve the capacity of the nonaqueous electrolyte secondary battery.

As described above, the silicon / carbon composite sintered body is an excellent negative electrode active material having both high capacity and good cycle characteristics. However, since the silicon / carbon composite sintered body has no flexibility and is brittle, it is not possible to further perform processing such as winding or folding on the negative electrode plate.
Normally, an electrode plate of a non-aqueous electrolyte secondary battery is formed by applying an active material to a current collector, and a positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween. . In non-aqueous electrolyte secondary batteries, the diffusion of lithium ions limits the reaction and limits battery characteristics, so it is necessary to increase the electrode area and compensate for this by densely winding the positive and negative electrode plates. It is an essential requirement for manufacturing. or,
In order to improve the capacity of the battery by filling the battery container having a limited capacity with as much active material as possible, it is essential to densely wind the electrode plates. Due to such circumstances,
In the case of a silicon / carbon composite sintered body that cannot be wound, it can be said that it is practically difficult to produce an actual lithium ion battery, for example, a mainstream cylindrical battery for a notebook computer, using this as a negative electrode.

As another method for solving the cycle deterioration of silicon or the like, carbon-coated silicon powder has been proposed (Japanese Patent Laid-Open No. 2000-21587). This carbon-coated silicon powder is obtained by coating a silicon powder having an average particle diameter of 8 μm with 50 wt% or less of carbon by an external thermal CVD method, and has a cutoff voltage of 50 to 80 mV of lithium ion occlusion.
(Contrast electrode: metallic lithium)
Cycle deterioration can be suppressed even at a capacity of 0 to 1500 mAh / g and charge / discharge of about 100 cycles.

However, the carbon-coated silicon powder is
When this is applied on a current collector such as a copper foil to produce a negative electrode, the filling amount per unit volume cannot be increased. Therefore, although the capacity per unit weight of the carbon-coated silicon powder is high, there is a problem that the capacity as a negative electrode plate manufactured using the same is not necessarily improved.
In general, it is said that the preferable particle size of the negative electrode active material is about 2 to 5 μm in consideration of increasing the packing density on the current collector. However, silicon has a high hardness, and when it is finely divided, there is a danger of dust explosion.
It is difficult to industrially produce fine silicon powder having the above-mentioned particle size, and as a result, it is industrially difficult to produce powder having an appropriate particle size to increase the packing density even in carbon-coated silicon powder. Has become difficult.

[0012]

As described above, it is known that silicon and the like are theoretically high-capacity negative electrode active materials. However, as a negative electrode for a nonaqueous electrolyte secondary battery using silicon or the like, silicon is highly used. A negative electrode in which cycle deterioration is suppressed by capacity has not been conventionally known, and such a negative electrode is required to increase the capacity of a nonaqueous electrolyte secondary battery.

[0013]

The present inventors have studied various forms of silicon on an electrode plate in order to solve the above-mentioned problems, and as a result, have found that silicon powder or silicon powder composited with carbon or the like as in the prior art. Instead of coating on the current collector, by forming a film made of silicon directly on the current collector, it has been found that it has excellent characteristics as a negative electrode of a non-aqueous electrolyte secondary battery and to complete the present invention. Reached.

That is, the present invention is a negative electrode for a non-aqueous electrolyte secondary battery, wherein a current collector is bonded to a silicon-based film layer directly or via a conductor layer.

Among the non-aqueous electrolyte secondary batteries of the present invention, those in which a carbon film is laminated on the surface on the side opposite to the side where the above-mentioned silicon-based film current collector is bonded are further cycled. It has the characteristic that the characteristics are good.

Further, the second invention of the present invention is characterized in that it includes a step of forming a silicon-based film layer which may contain a dopant on a film-like current collector by a CVD method. This is a method for producing a negative electrode for a non-aqueous electrolyte secondary battery.

In the manufacturing method of the present invention, when an inductively coupled plasma CVD method is used for forming a silicon-based film layer, a silicon-based film layer having good cycle characteristics can be formed in a large area at a high speed. The negative electrode for a non-aqueous electrolyte secondary battery of the present invention can be efficiently produced. Also, CVD
By subjecting the film-shaped current collector to plasma treatment prior to the formation of the silicon-based film layer by the method, a negative electrode for a non-aqueous electrolyte secondary battery having better cycle characteristics can be manufactured.

Further, a third aspect of the present invention is a non-aqueous electrolyte secondary battery comprising the negative electrode of the present invention.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The negative electrode for a non-aqueous electrolyte secondary battery according to the present invention is characterized in that a current collector is joined to a silicon-based film layer. The silicon-based film layer constituting the negative electrode of the present invention should be formed of a film containing at least 80 atomic%, more preferably at least 90 atomic%, of Si of the 14th group of the periodic table and the third period. Often, in addition to a film made of Si alone, a film made of an alloy of Si and another metal element, or a film made of Si
It may be a film made of a solid solution in which a dopant and other elements are dissolved. Further, the crystallinity, the crystal orientation, the structure of the microstructure, and the like of the substance constituting the silicon-based film layer are not particularly limited.

S which may be contained in the silicon-based film layer
Elements other than i are not particularly limited, and any kind of element can be contained.

However, when the silicon film contains a dopant, the electrical conductivity of the silicon film layer is improved,
Since good charge / discharge is performed even at a high charge / discharge rate, the silicon-based film layer is preferably made of a silicon film that may contain a dopant. As such a dopant, an element belonging to Group 13 of the periodic table such as boron, aluminum, gallium, or indium that imparts p-type semiconductivity to a silicon film, and an n-type semiconductivity is imparted to a silicon film. Periodic table 1 of phosphorus, arsenic, antimony, etc.
Group 5 elements can be mentioned. It is particularly preferable that the silicon film has an n-type semiconductivity since electron conductivity becomes high and a high capacity may be maintained even when charging and discharging are performed at a high current density.

Generally, the electronic conductivity of silicon containing a dopant increases in proportion to the content of the dopant.
On the other hand, in the negative electrode of the present invention, the higher the electron conductivity, the more the charge and discharge at a high current density tends to be possible.
The content of the dopant can be appropriately selected according to desired battery characteristics. However, if the added amount of the dopant exceeds the solid solubility limit of silicon to the silicon, the excess dopant has no effect of improving electron conduction. Therefore, the preferable addition amount of the dopant is equal to or less than the solid solution of the dopant in silicon. For example, when the dopant is phosphorus, the addition amount is preferably about 2.6 at% or less, and when the dopant is arsenic, the addition amount is preferably about 3.6 at% or less.

The thickness of the silicon-based film layer is not particularly limited, and may be determined depending on the capacity of the intended nonaqueous electrolyte secondary battery, the density of the silicon film, and the capacity per unit weight. It is preferable that the thickness is approximately 0.5 to 100 μm. If the thickness of the silicon film layer is too thin, the capacity per unit area of the silicon-based film layer decreases, so that the capacity per unit area of the negative electrode also decreases, and a high capacity nonaqueous electrolyte secondary battery may not be obtained. Yes. If the silicon-based film layer is too thick, cycle deterioration may occur. From such a viewpoint, the thickness of the silicon-based film layer is 1 to
Particularly preferably, it is 50 μm.

Although the size and shape of the silicon-based film layer are not particularly limited, the silicon-based film layer may be formed of a powdery non-aqueous electrolyte secondary battery in a conventional negative electrode for a non-aqueous electrolyte secondary battery. Since this is equivalent to a “mixture layer formed by applying a paste composed of a negative electrode active material, a conductivity-imparting material, a binder and a solvent”, it is naturally determined according to the shape of the intended battery. For example, in the case of a 18650 type cylindrical battery, the silicon film layer has a width of about 60 mm and a length of about 1000 mm.
In the form of a ribbon.

The above-mentioned silicon-based film layer is joined to the current collector directly or via the conductor layer to form the negative electrode for a non-aqueous electrolyte secondary battery of the present invention.

The current collector can be used without any particular limitation from known negative electrode current collectors such as copper foil, nickel foil, stainless steel foil and titanium foil. The shape and size of the current collector are not different from those of the current collector of the conventional negative electrode. Furthermore, for the purpose of increasing the surface area of the current collector, it is possible to form irregularities or pores on the surface of these metal foils, or to perform surface processing called expanded metal, and to improve the current collector in the conventional negative electrode. The same is true.

When bonding the silicon-based film layer to the current collector,
When a conductor layer having electron conductivity is interposed between the silicon-based film layer and the current collector, cycle deterioration may be particularly suppressed. The conductor to be interposed is not particularly limited, but a compound of silicon and a collector metal, a solid solution of silicon and a collector metal, or the like can be used. For example, Cu ₃ Si is used as a conductor to be interposed when the current collector is a copper foil.
(Η phase, η ′ phase, η ″ phase in Si—Cu binary system),
Cu ₁₅ Si ₄ (same ε phase), Cu _0.83 Si _0.17 (same δ)
Phase), Cu ₅ Si (gamma phase), β phase or Cu ₇ Si
(Same κ phase), Cu in which Si is dissolved, or Si in which Cu is dissolved.
When the current collector is a nickel foil, the conductor to be interposed is Ni ₃ Si (β in Ni-Si binary system).
₁ phase, β ₂ phase, β ₃ phase), Ni ₃₁ Si ₁₂ (gamma phase), Ni ₂
Si (same δ phase), Ni ₃ Si ₂ (same ε phase), NiSi, β
-NiSi _2, α-NiSi ₂ compounds such as, and Si and the like Si solute was Ni or Ni is solid-solved. When the current collector is a titanium foil, the conductor to be interposed is Ti ₃ Si, Ti ₅ Si ₃ , T
_{i 5 Si 4, Ti 6 Si} 5, TiSi, compounds such as TiSi _2, and Si and the like Si solid solution was Ti or Ti is solid-solved. Further, as a conductor to be interposed when the current collector is a stainless steel foil, Fe ₂ S
i (β phase in binary system of Fe—Si), η phase, FeS
i (same ε phase), FeSi ₂ (same ζ phase), etc., Fe in which Si is dissolved or Si in which Fe is dissolved, or Cr ₃ Si, α-Cr ₅ Si ₃ , CrSi, Cr
Si ₂ , Cr in which Si is dissolved, or Si in which Cr is dissolved, or Ni ₃ Si (β ₁ phase, β ₂ phase, β ₃ phase in a Ni—Si binary system), Ni ₃₁ Si ₁₂ (same as above) γ
Phase), Ni ₂ Si (same δ phase), Ni ₃ Si ₂ (same ε phase),
Compounds such as NiSi, β-NiSi ₂ , α-NiSi ₂ ,
And Ni in which Si is dissolved or Si in which Ni is dissolved
And the like.

When the above-described conductor layer is interposed between the silicon-based film and the current collector, the conductor layer does not necessarily need to be provided so as to cover the entire surface of the silicon-based film. It may be a form that is scattered in a specific way. In addition, the method of interposing is not particularly limited. For example, a method in which a conductor layer and a silicon film are sequentially stacked on a current collector, or a method in which a silicon film layer is formed on a current collector,
By performing a heat treatment or the like, a method of reacting the silicon and the current collector in a portion where they are in contact with each other to form a conductor at the interface can be preferably employed. In a method for forming a silicon-based film layer using a CVD method described later, a conductor interposed at the same time as the formation of the silicon film layer is formed by appropriately adjusting the manufacturing conditions such as the temperature of the current collector. You can also.

The thickness of the conductor layer when the conductor is interposed is not particularly limited. However, when the conductor to be interposed is electrochemically inert, the thickness of the conductor layer is extremely large. If the thickness is large, the capacity of the negative electrode may decrease. Therefore, for such a reason, the thickness of the conductor is preferably 50% or less of the thickness of the silicon-based film layer. For example, when a part of the silicon-based film layer is converted into a conductor layer by heat treatment or the like, the thickness of each layer is analyzed by analyzing the spatial composition distribution of the cross section of the negative electrode by energy dispersive X-ray spectroscopy or the like. Can be obtained by: When the conductor layer is formed by such a method, if the relationship between the processing conditions and the thickness of the formed conductor layer is checked in advance, the thickness can be controlled by the processing conditions. Can be.

When a current collector is bonded to the silicon-based film layer directly or via a conductor layer, the form of the bond, for example, whether or not a chemical bond is formed is not particularly limited. Since the negative electrode bonded to the current collector may be subjected to steps such as winding and punching when forming the battery, the negative electrode must have a bonding strength at which each layer is not peeled off at least in the operation in such a step. Is desirable.

In the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the surface of the silicon-based film on the side opposite to the side where the current collector is bonded (hereinafter, also simply referred to as the surface of the silicon film layer). When a carbon film is laminated, particularly good cycle characteristics may be exhibited.

At this time, the crystallinity of the carbon film laminated on the surface of the silicon-based film layer is not particularly limited, and may be either crystalline or amorphous. Such a method of laminating a carbon film can be adopted from a widely known method. For example, a carbon film may be laminated on the surface of the silicon-based film layer by applying a slurry of carbon powder on the surface of the silicon film layer to remove the dispersion medium and then performing a heat treatment as necessary. it can. Alternatively, the surface of the silicon film layer can be formed by coating the surface of the silicon film layer with a carbon precursor such as various resins, tar or pitch, and then performing a heat treatment. Further, a carbon film can be laminated on the surface of the silicon film layer by a CVD method using a volatile hydrocarbon or the like as a carbon source.

The thickness of the carbon film is not particularly limited since the effect of improving the cycle characteristics due to the presence of the carbon film in the form of a silicon-based film is not so affected by the thickness of the carbon film. However, since the capacity of carbon is generally smaller than the capacity of silicon, if the carbon film is too thick, the capacity per unit volume of the negative electrode may decrease, and if the thickness of the carbon film is extremely thin, In some cases, the coating of the silicon film layer becomes substantially incomplete, and it may be difficult to obtain the effect of improving the cycle characteristics. Therefore, from such a viewpoint, the carbon film thickness is desirably 1 nm to 1 μm.

The method for producing the negative electrode for a non-aqueous electrolyte secondary battery of the present invention is not particularly limited. For example, (1) After applying a slurry made of silicon powder to a current collector to remove a dispersion medium, A method for producing a negative electrode for a non-aqueous electrolyte secondary battery of the present invention by heat-treating this to form a silicon film layer, (2) a method of cutting a thin piece from a silicon ingot and joining it to a current collector, (3 ) A method using a PVD method such as a vacuum evaporation method, a sputtering method or an ion plating method, (4)
Method of electrochemically depositing silicon on current collector {R. D. Rauh et al., DOE / ET / 23046-
-T2 (1981) or M.P. Piwowar et al.,
International Conference O
n Environmental Degradation
n Of Engineering Materials
Proceedings 53-58, (1999)｝, (5) A method of forming a silicon-based thin film on a current collector by a chemical vapor deposition method (CVD method) can be suitably adopted.

Among these methods, it is relatively easy to form a silicon-based film layer continuously and at an arbitrary thickness and composition (dopant concentration), and it is possible to manufacture the silicon-based film layer at a relatively low cost. C on the current collector foil of (5) above
It is particularly preferable to adopt a method of forming a silicon film layer by the VD method (the manufacturing method of the present invention).

In the manufacturing method of the present invention, the CVD method
A silicon-based film layer is formed on a film-shaped current collector using an apparatus, and a known CVD apparatus can be used without any particular limitation.

That is, a reaction chamber capable of maintaining the inside thereof airtight, a material gas supply means for supplying a material gas as a raw material of the silicon-based film layer of the present invention into the reaction chamber, and an inside of the reaction chamber. In the above, a CVD apparatus having excitation means for depositing a silicon film layer from a material gas and holding means for holding a current collector on which a silicon-based film layer is formed can be used.

The method of forming a silicon film layer using such a CVD apparatus is not particularly limited. For example, it can be performed by the same method as when a silicon thin film is formed on a substrate in the production of a solar cell or the like. . That is, as a material gas used for forming a silicon-based film, a compound containing gasifiable silicon can be used without limitation. Specific examples of such a compound include silane compounds such as monosilane, disilane, trisilane, monochlorosilane, dichlorosilane, trichlorosilane, tetrachlorosilane, difluorosilane, and tetrafluorosilane. Alternatively, they can be used in combination. Further, it can be used after being diluted with a non-precipitating gas such as hydrogen, helium, argon, neon, and krypton. When a dopant is contained in the silicon-based film layer, a dopant gas such as phosphine or arsine containing an element of Group 15 of the periodic table such as phosphorus or arsenic is added to the above material gas in accordance with a desired dopant concentration. You may be accompanied.

Excitation means for depositing a silicon-based film layer from a material gas can be used without any particular limitation from a known method. If the CVD method which can be used for the production of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention is categorized by means of excitation, for example, a thermal CVD method in which a material gas is heated to a high temperature to deposit a silicon film layer, An inductively-coupled or capacitively-coupled plasma CVD method in which a material gas is applied with electromagnetic waves such as microwaves or high-frequency waves to convert the material gas into plasma and deposit a silicon film layer, or an ECR plasma CVD method in which a static magnetic field is applied together with the electromagnetic waves Can be mentioned.

As described above, in the production method of the present invention,
Although various excitation methods can be adopted, when a high temperature is required to deposit the silicon film layer, a chemical reaction between the silicon-based film layer and the current collector proceeds, and it is difficult to control this. There may be. From such a viewpoint, when the negative electrode of the present invention is manufactured by the CVD method, it is preferable to excite the material gas by plasma. Among them, it is particularly preferable to excite a material gas as inductively coupled plasma because a silicon film layer can be formed over a large area with a simple device. When performing the inductively coupled plasma CVD (ICP-CVD) method, Japanese Journal of Applied Physics, Vol. 36, Jpn. J. Appl. Phys. Vol. 36 (1997), pp. 3714-372.
0 and 38, Jpn. J. Appl. Phys. Vol. 38 (199
9), pp. 3655-3659}, an ICP-CVD apparatus in which a high-frequency coil (also referred to as an RF antenna) is disposed inside a reaction chamber can be suitably used.

When depositing a silicon film layer by the CVD method, a film-like current collector is previously formed with hydrogen, helium, argon,
When surface treatment is performed by plasma of a non-precipitating gas such as neon or krypton, cycle deterioration may be suppressed in the obtained negative electrode, which is suitable for producing the non-aqueous electrolyte secondary battery negative electrode of the present invention. It is.

The holding means for holding the current collector on which the silicon film layer is formed in the reaction chamber is not particularly limited. However, when the current collector is wound in a roll shape in the form of a film, If a mechanism capable of supplying and collecting the current collector in a roll-to-roll manner is provided, the negative electrode of the present invention can be manufactured continuously.

In the method for manufacturing a negative electrode according to the present invention, the conditions for forming the silicon-based film layer on the current collector are not particularly limited, and may be appropriately determined according to the apparatus to be used. Is 1 to 1000 mTorr, especially 3
~ 300 mTorr, current collector temperature is 100 ~ 600
C., particularly preferably 150 to 450C. When a material gas is excited by inductively coupled plasma, the applied high frequency power is 20 W to 3 kW, particularly 100 W to
Preferably, it is 2 kW. The thickness of the silicon film layer is
By examining the relationship between the reaction time and the film thickness under predetermined conditions in advance, the control can be performed by the reaction time.

The thus produced negative electrode for a non-aqueous electrolyte secondary battery of the present invention has a high capacity and good cycle characteristics. In addition, it has flexibility enough to withstand processing such as winding.

Further, in the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the conventional negative electrode of carbons, that is, the negative electrode applied to a current collector foil as a paste containing carbon powder as a negative electrode active material together with a binder is applied. In comparison, since there is no inclusion other than the active material and the packing density of the active material is high, the capacity per thickness of the active material layer is high. That is, in the case of a negative electrode composed of a conventional active material powder coating, when a coating thickness of about 100 μm is required,
In the negative electrode of the present invention, although depending on the charge / discharge conditions, approximately the same capacity can be obtained when the thickness of the silicon film layer is about 10 μm. Therefore, by using the negative electrode of the present invention, it is possible to fill a large amount of the active material into a battery can of a certain volume, as compared with the conventional negative electrode. It can be seen that the negative electrode for a secondary battery is particularly excellent in producing a high capacity nonaqueous electrolyte secondary battery.

Conventionally, when a negative electrode is manufactured using a powdered negative electrode active material made of carbons, a solvent is added to a mixture of the negative electrode active material and a binder to form a paste. After coating and drying on the top, it had to be pressed further to form a coating film, and it was necessary to go through a number of steps to produce a negative electrode. On the other hand, the negative electrode of the present invention can directly produce the negative electrode from the current collector and the raw material of the active material by using the CVD method, so that the production process can be simplified and the yield can be improved accordingly. is there.

The production of a nonaqueous electrolyte secondary battery using the negative electrode of the present invention does not require the production of a negative electrode from a powdered negative electrode active material through a number of steps. It can be said that it is an advantage in the manufacturing method when manufacturing batteries using
Except for, there is no particular difference from the conventional method. For example,
It can be manufactured by the following method.

That is, first, a known powdery positive electrode active material, a binder such as polytetrafluoroethylene or polyvinylidene fluoride, and a solvent such as N-methylpyrrolidone are kneaded using a kneader or the like to prepare a paste. . As the positive electrode active material, widely known materials can be used. For example, chalcogen compounds such as sulfides such as TiS ₂ , MoS ₂ and FeS ₂ , selenides such as NbSe ₃ and the like, or Cr ₂ O ₅ and Cr ₃ O _{8, V 3 O 8, V} 2 O 5, V
Oxides of transition metals such as ₆ O ₁₃ , LiMn ₂ O ₄ , LiM
Composite oxides of lithium and transition metals such as nO ₂ , LiV ₃ O ₅ , LiNiO ₂ , and LiCoO ₂ , or conjugated polymers such as polyaniline, polyacetylene, polyparaphenylin, polyphenylenevinylene, polypyrrole, and polythiophene, and disulfide bonds A material capable of inserting and extracting lithium such as a crosslinked polymer having

Next, the paste is applied to a current collector,
After drying and removing the solvent, the coating film is subjected to pressure treatment to obtain a positive electrode. The positive electrode, the negative electrode of the present invention, the non-aqueous electrolyte, and, if necessary, the separator are inserted into a desired battery container, and the non-aqueous electrolyte is injected, and then sealed.

As the non-aqueous electrolyte, the separator, and the like, materials used in conventional non-aqueous electrolyte secondary batteries are used without any problem.

For example, propylene is used as the non-aqueous electrolyte.
Carbonate, ethylene carbonate, 1,2-dimethoate
Xiethane, 1,2-diethoxyethane, γ-butyrol
Coutone, tetrahydrofuran, 1,3-dioxolane,
4-methyl-1,3-dioxolan, diethyl ether
, Sulfolane, methyl sulfolane, acetonitrile,
Propionitrile, etc. alone or in combination of two or more
LiClO in non-aqueous solvent _Four, LiPF₆, LiAsF₆,
LiBF_Four, LiB (C₆H_Five)_Four, LiCl, LiBr,
CH_ThreeSO_ThreeLi, CF_ThreeSO_ThreeLithium salt such as Li
Non-aqueous electrolyte with dissolved supporting salt
Can also be used. In addition, such a solution is
Gel electrolyte impregnated with
Polymer electrolyte with the above-mentioned supporting salt added to oxide etc.
Can also be used as a non-aqueous electrolyte.

As the separator, a separator having a low resistance to the movement of ions and an excellent solution holding property may be used. For example, a polymer pore filter made of polypropylene, polyethylene, polyester, polyflon, or the like, a glass fiber filter, a nonwoven fabric, or a nonwoven fabric made of glass fibers and these polymers can be used. Further, when the temperature inside the battery becomes high, a material that melts to close the pores and prevent short circuit between the positive electrode and the negative electrode is preferable.

[0053]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 A silicon film was formed on a copper foil having a thickness of 25 μm using an ICP-CVD (inductively coupled CVD) apparatus having a structure basically the same as that described in the above-mentioned document. Pure gas of 100% monosilane and hydrogen as a diluent gas were used as material gases and supplied into the reaction chamber at 30 cc / min and 90 cc / min. When the pressure in the reaction chamber is 10
0mTorr, a high frequency coil about 5cm away from the copper foil and a 600W from a 13.56MHz high frequency power supply
A high frequency was supplied at the output. By heating the copper foil to 190 ° C. and performing a plasma CVD process for a processing time of 30 minutes,
The negative electrode for a non-aqueous electrolyte secondary battery of the present invention was obtained.

When the cross section of the obtained negative electrode was observed using a scanning electron microscope (hereinafter also referred to as SEM), the thickness of the silicon film layer was about 10 μm. When this negative electrode was analyzed by powder X-ray, the silicon film layer
i, and no other compounds or solid solutions were detected.

A lithium ion battery was prepared using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. The production of the lithium ion battery and the evaluation of the initial charge / discharge capacity and the cycle characteristics were performed as follows.

Preparation of Lithium Ion Battery: The negative electrode for a non-aqueous electrolyte secondary battery of the present invention was punched into a circular shape having a diameter of 15.958 mm, and this was used as a negative electrode. The non-aqueous electrolyte is LiP
Using a solution of F ₆ (concentration of 1 mol / liter) in a mixed solvent of equal volumes of ethylene carbonate and diethyl carbonate, a lithium coin was used as a counter electrode via a separator to produce a 2016 coin cell battery.

Measurement of charge / discharge capacity: The charge / discharge cycle test of the lithium battery was performed using a charge / discharge device (manufactured by Hokuto Denko), and the discharge time t (unit: time) was measured to determine the charge of the negative electrode active material. The discharge capacity was measured. In the charge / discharge cycle test, the current density was set to 0.3 mA / cm ² , and charge / discharge was performed at a voltage of 25 mV to 1.4 V with respect to the counter electrode.
The charge / discharge capacity was calculated by normalizing the weight increase due to the formation of the film layer.

Table 1 shows the results of the charge / discharge test of this negative electrode.

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[Table 1]

Example 2 A negative electrode for a non-aqueous electrolyte secondary battery of the present invention was prepared in the same manner as in Example 1 except that the copper foil was heated to 360 ° C.

When the obtained negative electrode was analyzed by powder X-ray, the silicon film layer was composed of Si and Cu ₁₅ Si ₄ . As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was about 10 μm. Similarly, the thickness of Cu ₁₅ Si ₄ obtained by SEM observation of the cross section of the negative electrode and energy dispersive X-ray spectroscopy (hereinafter also referred to as EDS) using an electron beam of the SEM as an excitation source was about 0.1 μm. .

A lithium ion battery was prepared using the negative electrode of this non-aqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 3 The same procedure as in Example 2 was carried out except that phosphine diluted to 1000 ppm with hydrogen was added to the material gas and the diluent gas at a supply rate of 5 cc / min as the material gas for the dopant. A negative electrode for a water electrolyte secondary battery was produced.

The obtained negative electrode was analyzed by powder X-ray.
At this time, the silicon film layer is made of Si and Cu₁₅Si_FourConsists of
Was. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was
Was about 10 μm. SEM observation of cross section of negative electrode and
Cu determined by EDS ₁₅Si_FourThickness is about 0.1
μm. The average concentration of the dopant is
On Si measured by on-detection mass spectrometer
It was about 1.0 atomic%.

A lithium ion battery was fabricated using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 4 The same procedure as in Example 2 was carried out except that phosphine diluted to 1000 ppm with hydrogen was supplied as a dopant material gas at a supply rate of 13 cc / min. A negative electrode for a water electrolyte secondary battery was produced.

The obtained negative electrode was analyzed by powder X-ray.
At this time, the silicon film layer is made of Si and Cu₁₅Si_FourConsists of
Was. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was
Was about 10 μm. SEM observation of cross section of negative electrode and
Cu determined by EDS ₁₅Si_FourThickness is about 0.1
μm. The average concentration of the dopant is
On Si measured by on-detection mass spectrometer
It was about 2.5 atomic%.

A lithium ion battery was fabricated using the negative electrode of the non-aqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 5 A negative electrode for a non-aqueous electrolyte secondary battery of the present invention was produced in the same manner as in Example 4 except that the treatment time was changed to 6 minutes.

When the obtained negative electrode was analyzed by powder X-ray, the silicon film layer was composed of Si and Cu ₁₅ Si ₄ . As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was about 2 μm. SEM observation of cross section of negative electrode and E
The thickness of Cu ₁₅ Si ₄ determined by DS is about 0.1 μm.
m. The average concentration of the dopant was about 2.5 atom% with respect to Si as measured by a secondary ion detection mass spectrometer.

A lithium ion battery was fabricated using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 6 Example 4 except that the CVD process was performed for a processing time of 90 minutes.
In the same manner as in the above, a negative electrode for a nonaqueous electrolyte secondary battery of the present invention was produced.

The obtained negative electrode was analyzed by powder X-ray.
At this time, the silicon film layer is made of Si and Cu₁₅Si_FourConsists of
Was. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was
Was about 30 μm. SEM observation of cross section of negative electrode and
Cu determined by EDS ₁₅Si_FourThickness is about 0.1
μm. The average concentration of the dopant is
On Si measured by on-detection mass spectrometer
It was about 2.5 atomic%.

A lithium ion battery was fabricated using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 7 A negative electrode for a non-aqueous electrolyte secondary battery of the present invention was produced in the same manner as in Example 4 except that a Ni foil was used instead of a copper foil.

The obtained negative electrode was analyzed by powder X-ray.
At this time, the silicon film layer is made of Si and Ni₃₁Si₁₂Consists of
Was. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was
Was about 10 μm. SEM observation of cross section of negative electrode and
Ni determined by EDS ₃₁Si₁₂Is about 0.3
μm. The average concentration of the dopant is
On Si measured by on-detection mass spectrometer
It was about 2.5 atomic%.

A lithium ion battery was fabricated using the negative electrode of this non-aqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 8 A negative electrode for a non-aqueous electrolyte secondary battery of the present invention was produced in the same manner as in Example 4 except that a Ti foil was used instead of a copper foil.

When the obtained negative electrode was analyzed by powder X-ray, the silicon film layer was composed of Si and Ti ₃ Si. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was about 10 μm. The thickness of Ti ₃ Si obtained by SEM observation of the cross section of the negative electrode and EDS was about 0.2 μm.
m. The average concentration of the dopant was about 2.5 atom% with respect to Si as measured by a secondary ion detection mass spectrometer.

A lithium ion battery was prepared using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 9 A negative electrode for a non-aqueous electrolyte secondary battery of the present invention was prepared in the same manner as in Example 4 except that a stainless steel foil (SUS304) was used instead of the copper foil.

When the obtained negative electrode was analyzed by powder X-ray, the silicon film layer was composed of Si and the α ₁ phase in a binary system of Fe—Si. As a result of SEM observation of the cross section of the negative electrode,
The thickness of the silicon film layer was about 10 μm. The thickness of the α ₁ phase determined by SEM observation of the cross section of the negative electrode and EDS was about 0.1 μm. The average concentration of the dopant was about 2.5 atom% with respect to Si as measured by a secondary ion detection mass spectrometer.

A lithium ion battery was fabricated using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 10 Using an ICP-CVD apparatus, methane gas was supplied at 2 cc / min to a reaction chamber maintained at 100 mTorr.
By holding at 360 ° C. for 1 minute at a high frequency output of 600 W, a carbon film layer was formed on the surface of the silicon film layer produced in the same manner as in Example 4 to produce a negative electrode for a non-aqueous electrolyte secondary battery of the present invention. did.

The obtained negative electrode was analyzed by powder X-ray.
At this time, the silicon film layer is made of Si and Cu₁₅Si_FourConsists of
Was. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was
Was about 10 μm. SEM observation of the negative electrode cross section or
Cu determined by EDS ₁₅Si_FourAnd carbon film layer
Both thicknesses were about 0.1 μm. Also, silicon film
The average concentration of dopant in the layer is determined by the secondary ion detector
Approximately 2.5 sources for Si
% Of children.

A lithium ion battery was fabricated using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 11 Prior to the formation of the silicon film layer, the hydrogen supply rate was 20 cc /
A negative electrode for a non-aqueous electrolyte secondary battery of the present invention was produced in the same manner as in Example 4, except that the copper foil was subjected to hydrogen plasma etching at a high-frequency output of 1 kW.

The obtained negative electrode was analyzed by powder X-ray.
At this time, the silicon film layer is made of Si and Cu₁₅Si_FourConsists of
Was. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was
Was about 10 μm. SEM observation of cross section of negative electrode and
Cu determined by EDS ₁₅Si_FourThickness is about 0.1
μm. The average concentration of the dopant is
On Si measured by on-detection mass spectrometer
It was about 2.5 atomic%.

A lithium ion battery was fabricated using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 12 A negative electrode for a non-aqueous electrolyte secondary battery of the present invention was produced in the same manner as in Example 4 except that arsine was used instead of phosphine.

The obtained negative electrode was analyzed by powder X-ray.
At this time, the silicon film layer is made of Si and Cu₁₅Si_FourConsists of
Was. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was
Was about 10 μm. SEM observation of cross section of negative electrode and
Cu determined by EDS ₁₅Si_FourThickness is about 0.1
μm. The average concentration of the dopant is
On Si measured by on-detection mass spectrometer
It was about 2.3 atomic%.

A lithium ion battery was prepared using the negative electrode of this non-aqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Example 13 A non-aqueous electrolyte secondary battery of the present invention was prepared in the same manner as in Example 4 except that no high frequency was applied in the CVD process, the heating temperature of the copper foil was 450 ° C., and the processing time was 120 minutes. A negative electrode was prepared.

When the obtained negative electrode was analyzed by powder X-ray, the silicon film layer was composed of Si, Cu ₁₅ Si ₄ and Cu ₃ S
It consisted of i. As a result of SEM observation of the cross section of the negative electrode, the thickness of the silicon film layer was about 10 μm. SE of negative electrode section
The thickness of Cu ₁₅ Si ₄ and Cu ₃ Si determined by M observation and EDS was about 2 μm. The average concentration of the dopant was about 2.5 atomic% with respect to Si as measured by a secondary ion detection mass spectrometer.

A lithium ion battery was fabricated using the negative electrode of the nonaqueous electrolyte secondary battery, and the charge / discharge capacity and cycle characteristics of the negative electrode were evaluated. Table 1 shows the results.

Comparative Example 1 2.5 parts by weight of polyvinylidene fluoride as a binder, 44 parts by weight of acetylene black as a conductivity-imparting material were added to silicon powder obtained by pulverizing an Si single crystal containing no dopant in a mortar, Further, N-methyl-2-pyrrolidone was added as a solvent and kneaded to prepare a paste. This paste is uniformly applied on a copper foil to a thickness of 300 μm, and
After drying at 00 ° C. for 24 hours, it was rolled to obtain a negative electrode.

Table 1 shows the results of the charge / discharge test of this negative electrode.

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By using the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte secondary battery having high capacity and good cycle characteristics can be manufactured.

Claims (6)

[Claims] 1. A negative electrode for a non-aqueous electrolyte secondary battery, wherein a current collector is joined to a silicon-based film layer directly or via a conductor layer. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a carbon film is laminated on a surface of the silicon-based film opposite to the surface to which the current collector is bonded. For negative electrode. 3. The non-aqueous electrolysis according to claim 1, further comprising a step of forming a silicon-based film layer which may contain a dopant on the film-like current collector by a CVD method. A method for producing a negative electrode for a liquid secondary battery. 4. The manufacturing method according to claim 3, wherein the silicon-based film layer which may contain a dopant is formed by an inductively coupled plasma CVD method. 5. The manufacturing method according to claim 3, wherein the film-like current collector is subjected to a plasma treatment, and then a silicon-based film layer which may contain a dopant is formed by a CVD method. Method. 6. A non-aqueous electrolyte secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.