JP6572551B2 - Negative electrode active material for lithium ion secondary battery and method for producing the same - Google Patents

Description

  The present invention relates to a negative electrode active material for a lithium ion secondary battery and a method for producing the same.

  As mobile devices such as smartphones and tablet terminals have higher performance and vehicles equipped with lithium ion secondary batteries such as EVs and PHEVs have been demanded to increase the capacity of lithium ion secondary batteries. At present, graphite is mainly used as the negative electrode material of lithium ion secondary batteries. However, for further increase in capacity, the theoretical capacity is high, and elements such as silicon and tin that can absorb and release lithium ions are used. Development of negative electrode materials using metals or alloys with other elements has been activated.

  On the other hand, it is known that an active material made of a metal material capable of inserting and extracting lithium ions significantly expands when alloyed with lithium by charging. Therefore, the active material is cracked and refined, and the structure of the negative electrode using these is also broken and the conductivity is cut. Therefore, the negative electrode using these metal materials has a problem that the capacity is remarkably lowered with the passage of cycles.

In response to this problem, a technique has been proposed in which these metal materials are made into fine particles and combined with carbonaceous material or graphite. Such composite particles have significantly higher cycle characteristics than the use of these materials alone as a negative electrode material, because these metal materials are alloyed with lithium and conductivity is ensured by carbonaceous materials and graphite even when they are miniaturized. It is known to improve. For example, in Patent Document 1, the active material of the negative electrode includes fine particles having a carbonaceous material layer formed on the surface, and the fine particles are composed of at least one element selected from Mg, Al, Si, Ca, Sn, and Pb. In addition, it is disclosed that the average particle diameter is 1 to 500 nm, and the atomic ratio of the fine particles in the active material is 15% or more. Patent Document 2 discloses metal-carbon composite particles in which metal particles are embedded in a plurality of phases of carbon, and the carbon contains graphite and amorphous carbon. The metal particles include Mg, Al, It is described that any one of Si, Zn, Ge, Bi, In, Pd, and Pt is used, and the average particle diameter is preferably 0.1 to 20 μm. Patent Document 3 discloses a so-called core shell in which the negative electrode active material includes graphite core particles, a carbon coating (shell) that covers the graphite core particles, and metal particles that are dispersed and positioned inside the carbon coating. The graphite core particles have an average particle size of 1 to 20 μm, the coating thickness of the carbon coating is 1 to 4 μm, and the metals alloyed with lithium include Cr, Sn, Si, Al, Mn, Ni , Zn, Co, In, Cd, Bi, Pb, and V, and at least one substance selected from the group consisting of V and an average particle size of 0.01 to 1.0 μm is preferable. Furthermore, Patent Document 4 discloses a mixing step in which expanded graphite or flake graphite having a specific surface area of 30 m ² / g or more and a battery active material that can be combined with lithium ions are mixed to obtain a mixture, and the mixture is spheroidized. And a spheronization step for producing a substantially spherical composite active material for a lithium secondary battery containing a battery active material that can be combined with graphite and lithium ions. The battery active material that can be combined with lithium ions contains at least one element selected from Si, Sn, Al, Sb, and In, and the average particle size is preferably 1 μm or less. .

  In the method using the finely divided metal material, the more the metal material is made finer, the less the expansion per particle due to the insertion of lithium at the time of charging, the less likely it is to break, and the cycle life is improved. However, the surface of the metal fine powder has a natural oxide film, which suppresses ignition of the metal in the atmosphere as a passive state. The thickness of the natural oxide film is almost constant as long as the oxidation treatment conditions are constant regardless of the particle size of the fine powder. Therefore, the smaller the particle size, the higher the weight ratio of the natural oxide film in the particles. The first charge to the metal fine powder as the active material starts with the reaction of lithium with the natural oxide film, but the lithiated oxide film does not subsequently remove and insert lithium, resulting in irreversible capacity and initial charge / discharge. Efficiency is reduced. Accordingly, there is a problem that the initial charge / discharge efficiency is reduced when the particle size of the metal fine powder is reduced. For example, in Patent Document 5, the relationship between the average particle diameter of silicon and the content of oxygen element when silicon particles are pulverized is investigated, and when the average particle becomes smaller than 2 μm, the oxygen element content rapidly increases. It has been shown that efficiency decreases.

  Another reason that the capacity of the negative electrode using a metal material is significantly reduced over the course of the cycle is that lithium, occluded Si, Sn, etc. are highly active, so that the electrolyte is decomposed and lithium is inactivated. is there. Therefore, combining the method using the finely divided metal material and the method of compounding with a carbonaceous material, graphite or the like, suppressing the pulverization due to cracking of the metal particles, securing the conductive path, The generation of cracked gas and the generation of an inactive lithium compound film cause irreversible expansion that does not return completely during discharge, which spurs cycle deterioration.

Therefore, it is disclosed that a film made of an oxide of Si, Ti, Al, and Zr is formed on the surface of the negative electrode active material by a sol-gel method (see, for example, Patent Document 6). Further, a negative electrode material having a reaction part containing at least one of Si and Sn and a coating part made of a metal oxide such as TiO ₂ or ZrO ₂ provided on a part of the surface, and a coating part for the reaction part It has also been proposed that an excellent charge / discharge efficiency can be obtained with a high capacity by setting the ratio to 0.01 mass% or more and 10 mass% or less (see, for example, Patent Document 7). Further, a composite composed of ultrafine Si phase particles and oxides surrounding the Si phase particles, and a negative electrode material exhibiting excellent charge / discharge cycle characteristics have been proposed (for example, patents). Reference 8). However, even in these methods, when a long cycle was carried out, the irreversible expansion was not sufficiently suppressed.

Japanese Patent Laid-Open No. 10-3920 JP 2000-272911 A JP 2010-129545 A Japanese Patent No. 5227483 JP 2004-185810 A JP 2004-335334 A JP 2007-141666 A Special table 2007-500421 gazette

  The present invention is a negative electrode active material for a lithium ion secondary battery comprising Si or a Si alloy (hereinafter collectively referred to as “Si compound”) and a carbonaceous material or a carbonaceous material and graphite, A negative electrode active material that provides a lithium ion secondary battery that has high charge / discharge efficiency in the initial stage and cycle, large discharge capacity, long cycle life, and low irreversible expansion caused by the cycle even if fine particles are used, and a method for producing the same It is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that in a negative electrode active material for a lithium ion secondary battery comprising a Si compound and a carbonaceous material or a carbonaceous material and graphite, the carbonaceous material Is compounded with a complex oxide of lithium and at least one element selected from the group of transition metals, Group 13 or Group 15 elements (hereinafter referred to as “lithium compound”), Even when fine particles are used, it is possible to obtain a negative electrode active material that provides a lithium ion secondary battery with high charge and discharge efficiency in the initial stage and cycle, large discharge capacity, long cycle life, and low irreversible expansion caused by the cycle. The headline and the present invention were completed.

That is, the present invention includes: a Si compound, the negative active material for a lithium ion secondary battery comprising a graphite carbonaceous material or carbonaceous material, the average particle diameter D ₅₀ of the Si compound is 0.01 to 5 [mu] m, A negative electrode active material for a lithium ion secondary battery, wherein the carbonaceous material is complexed with a lithium compound.

  Hereinafter, the negative electrode active material for a lithium ion secondary battery of the present invention will be described in detail.

  In the present invention, Si is a general grade metal silicon having a purity of about 98%, a chemical grade metal silicon having a purity of 2 to 4N, a chlorinated and purified by distillation using 4N, a single crystal growth method High-purity single crystal silicon that has undergone a deposition step by the above, or those doped with elements of Group 13 or 15 of the periodic table to be p-type or n-type, and polishing or cutting of wafers generated in the semiconductor manufacturing process There is no particular limitation as long as the purity is higher than that of general-purpose grade metal silicon, such as scraps and waste wafers that have become defective in the process.

  The Si alloy referred to in the present invention is an alloy containing Si as a main component. In the Si alloy, the element contained other than Si is preferably one or more elements of Groups 2 to 15 of the periodic table, and the selection and / or addition amount of the element having a melting point of the phase contained in the alloy of 900 ° C. or more. Is preferred.

In the negative electrode active material for a lithium ion secondary battery of the present invention, the average particle diameter _{D 50} of the Si compound is 0.01 to 5 [mu] m, more preferably in the range of 0.05 to 0.5 [mu] m. If it is smaller than 0.01 μm, the capacity and initial efficiency due to surface oxidation are drastically reduced, and if it is larger than 5 μm, cracks are severely caused by expansion due to lithium insertion, resulting in severe cycle deterioration. D ₅₀ is a volume average particle diameter measured by a laser particle size distribution meter.

  The content of the Si compound is preferably 10 to 80% by weight, and more preferably 15 to 50% by weight. When the content of the Si compound is less than 10% by weight, a sufficiently large capacity cannot be obtained as compared with the conventional graphite, and when it exceeds 80% by weight, the cycle deterioration becomes severe.

  The carbonaceous material referred to in the present invention is an amorphous or microcrystalline carbon material, and easily graphitized carbon (soft carbon) that is graphitized by a heat treatment exceeding 2000 ° C. and non-graphitizable carbon (hard carbon) that is difficult to graphitize. )

  In the negative electrode active material for a lithium ion secondary battery of the present invention, the carbonaceous material content is preferably 5 to 90% by weight, and more preferably 8 to 40% by weight. When the content of carbonaceous material is less than 5% by weight, the carbonaceous material cannot cover the Si compound, the conductive path becomes insufficient, and the capacity deterioration easily occurs. When the content is larger than 90% by weight, the capacity is sufficient. It is not obtained.

The graphite referred to in the present invention is a crystal whose graphene layer is parallel to the c-axis, natural graphite obtained by refining ore, artificial graphite obtained by graphitizing the pitch of oil or coal, etc. There are oval or spherical, cylindrical or fiber shapes. In addition, these graphites are subjected to acid treatment, oxidation treatment, and then expanded by heat treatment. Part of the graphite layer is exfoliated to form an accordion, or a pulverized product of expanded graphite, or an ultrasonic wave, etc. Exfoliated graphene or the like can also be used. The particle size of the graphite contained in the negative electrode active material of the present invention is not particularly limited smaller than the size of the anode active material particles, the thickness of the graphite particles is less than 1/5 of the average particle diameter D ₅₀ of the active material Is preferred. Addition of graphite increases the conductivity and strength of the active material particles, and improves charge / discharge rate characteristics and cycle characteristics. The (002) plane spacing d002 measured by X-ray diffraction of graphite particles is preferably 0.338 nm or less, which means highly graphitized graphite. When d002 exceeds this value, the effect of improving conductivity by graphite becomes small.

  In the negative electrode active material for a lithium ion secondary battery of the present invention, when a carbonaceous material and graphite are contained, the respective contents are preferably 5 to 40% by weight and 20 to 80% by weight, and 8 to 30% by weight. A proportion of 40 to 70% by weight is more preferred. When the content of the carbonaceous material is less than 5% by weight, the carbonaceous material cannot cover the Si compound and graphite, adhesion between the Si compound and graphite becomes insufficient, and formation of active material particles tends to be difficult. Moreover, when larger than 40 weight%, the effect of the graphite whose electroconductivity is higher than a carbonaceous material is not fully drawn out. On the other hand, when the graphite content is less than 20% by weight, the effect of graphite having a conductivity higher than that of carbonaceous material is not sufficient, and when it is more than 80% by weight, a sufficiently large capacity cannot be obtained as compared with conventional graphite. .

The lithium compound referred to in the present invention is a lithium salt of an oxoacid of at least one element selected from the group of transition metals and group 13 or group 15 elements. For example, in the case of transition metals, lithium cobaltate ( LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), various lithium manganates (LiMn ₂ O ₄ , LiMnO ₂ , Li ₂ MnO _3, etc.), lithium ferrate (LiFeO ₂ ), lithium iron phosphate (LiFePO ₄ ), various Lithium titanate (Li ₂ Ti ₂ O ₄ , Li ₄ Ti ₅ O ₁₂ , Li ₆ Ti ₅ O ₁₂ etc.), various lithium niobates (LiNbO ₃ , Li ₂ Nb ₂ O ₅ etc.), lithium tungstate (LiWO ₂ ), lithium molybdate (LiMoO ₂₎ and the like, in the case of periodic table group 13 aluminate Lithium (LiAlO _2), lithium metaborate (LiBO _2), and lithium tetraborate _{(Li 2} B 4 _{O 7),} and the like, if the periodic table group 15, lithium triphosphate _(Li 3 _PO 4), lithium pyrophosphate (Li ₄ P ₂ O ₇ ) and the like. The lithium compound referred to in the present invention may be a solid solution or a mixture thereof, or a non-stoichiometric compound having a non-stoichiometric composition, or may not exhibit a clear crystal phase.

  By compounding the carbonaceous material and the lithium compound, the carbonaceous material conducts electrons, the lithium compound conducts lithium ions, and lowers the resistance associated with charge and discharge. In addition, it is considered that at least one element selected from the group of transition metals and Group 13 or Group 15 elements is slightly doped into the Si compound by the heat treatment when manufacturing the negative electrode active material, thereby increasing the electrical conductivity. It is done. More preferable elements from the viewpoint of electrical conductivity include boron in the periodic table group 13 and phosphorus in the periodic table group 15. The complex oxide of lithium containing these elements has a melting point of 800 to 1000 ° C., and solid phase or liquid phase firing proceeds during firing as described later, and it is integrated with the carbonaceous material to closely surround Si or the Si alloy. Cheap.

  The lithium compound referred to in the present invention is formed by bonding fine grains, and the grain size is preferably 0.2 μm or less from the viewpoint of the particle strength of the completed negative electrode active material.

  In the negative electrode active material for a lithium ion secondary battery of the present invention, the content of the lithium compound is 0.5 to 80% by weight, more preferably 0.5 to 65% by weight. When the amount is less than 0.5% by weight, the effect of increasing the initial charge / discharge efficiency and the discharge capacity is small. When the amount is more than 80% by weight, the conductivity is lowered and a sufficient capacity cannot be obtained.

In the negative electrode active material for a lithium ion secondary battery of the present invention, a metal element having a valence different from that of at least one element selected from the group of transition metal, group 13 or group 15 element contained in the lithium compound, More preferably, the lithium compound is further contained. For example, LiMn ₂ having trivalent and tetravalent Mn added by adding metal elements such as 1 to 3 valent Na, Cu, Mg, Al, Ni to Li ₄ Ti ₅ O ₁₂ having tetravalent Ti. A metal element such as Na, Cu or Mg having a valence of 1 to 2 is added to O ₄ , Li _{1 + x} Al _x Ge _2−x (PO ₄ ) ₃ (0 ≦ x ≦ 1), Li _{5 + x} La ₃ Zr _x A _{2-xO 12} (A is one or more elements selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, and Ge, 1.4 ≦ x ≦ 2) , Li _3x La _{2 / 3-x} AO ₃ (A is Ti or Zr, 0.2 ≦ x ≦ 0.05), and the like.

  In the negative electrode active material for a lithium ion secondary battery of the present invention, the lithium compound may further contain a conductive additive. Examples of the conductive assistant include carbon black, acetylene black, and CNT. The particle size is 1 μm or less, and the addition amount is 30% by weight or less based on the weight of the lithium compound. Moreover, it is preferable that the surface treatment which can ensure dispersibility with respect to the solvent to be used is made at the time of addition.

Negative active material for a lithium ion secondary battery of the present invention is a composite particle having an average particle diameter D ₅₀ which shape is rounded 1 to 40 [mu] m, preferably 2 to 30 m. When D ₅₀ is less than 1 μm, it becomes bulky and it becomes difficult to produce a high-density electrode, and when it exceeds 40 μm, the unevenness of the applied electrode becomes intense and it becomes difficult to produce a uniform electrode. Moreover, it is preferable that the average particle diameter of the Si compound is 1/5 or less of the average particle diameter of the negative electrode active material, and the carbonaceous material complexed with the lithium compound covers at least the active material surface.

From the viewpoint of cycle characteristics, the more preferable range of the average particle diameter D ₅₀ of the negative electrode active material is 2 to 20 μm, and the 10% particle diameter D ₁₀ is 1 μm or more and the number of flaky particles having a thickness of less than 1 μm is small. Is preferred.

  Composite particles with rounded shapes are those in which the corners of particles produced by pulverization, etc. are rounded, spherical or spheroid shapes, discs or oval shapes with thickness and rounded corners, or those Is a deformed one with rounded corners. When the shape is rounded, the bulk density of the composite particles is increased, and the packing density when the negative electrode is formed is increased. In addition, the carbonaceous material that is complexed with the lithium compound covers at least the active material surface, so that the lithium ion that is solvated in the electrolytic solution during charging and discharging is complexed with the lithium compound. Since only lithium ions react with the Si compound and / or graphite away from the solvent on the surface, the decomposition product of the solvent becomes difficult to be generated, and the charge / discharge efficiency is increased.

  In the negative electrode active material for a lithium ion secondary battery of the present invention, the Si compound is sandwiched between thin graphite layers having a thickness of 0.2 μm or less together with a carbonaceous material combined with the lithium compound, The structure is laminated and / or network-like, the thin graphite layer is curved near the surface of the active material particles to cover the active material particles, and the surface of the outermost layer is combined with the lithium compound. The carbonaceous material is preferably covered.

  In the present invention, the graphite thin layer refers to expanded graphite or expanded graphite in which the above-mentioned graphite is subjected to acid treatment and oxidation treatment and then expanded by heat treatment, and a part of the graphite layer is peeled off to form an accordion shape. , Pulverized material, graphene delaminated by ultrasonic waves, or the like, or graphite made of a graphene layer (thickness 0.0003 μm) to several hundred layers (thickness 0.2 μm) produced by receiving a compressive force. It is a thin layer. The thinner the graphite thin layer, the thinner the Si compound sandwiched between the graphite thin layers and the carbonaceous material layer that is complexed with the lithium compound, and the better the transmission of electrons to the Si compound. When the thickness exceeds 0.2 μm, the electron transfer effect of the graphite thin layer is reduced. When the graphite thin layer is linear when viewed in cross section, its length is preferably at least half the size of the negative electrode active material particles for electron transfer, and more preferably about the same as the size of the negative electrode active material particles. When the graphite thin layer is network-like, it is preferable for electron transfer that the graphite thin layer network is connected to more than half of the size of the negative electrode active material particles, and it may be about the same size as the negative electrode active material particles. Further preferred.

  In the present invention, the graphite thin layer is preferably curved near the surface of the active material particles to cover the active material particles. With such a shape, there is a risk that the electrolyte enters from the end face of the graphite thin layer, the Si compound or the end face of the graphite thin layer is in direct contact with the electrolyte, and a reactant is formed during charge and discharge, resulting in reduced efficiency. Reduce.

  In the negative electrode active material for a lithium ion secondary battery of the present invention, the content of the Si compound is 10 to 80% by weight, the content of the carbonaceous material is 5 to 90% by weight, and the content of the lithium compound is 0.00. It is preferably 5 to 80% by weight.

  In the negative electrode active material for a lithium ion secondary battery of the present invention, the content of the Si compound is 10 to 60% by weight, the content of the carbonaceous material is 5 to 40% by weight, and the content of the graphite is 20%. It is preferable that the content of the lithium compound is 0.5 to 65% by weight.

In the negative electrode active material for a lithium ion secondary battery of the present invention, the specific surface area is more preferably 0.5 to ²⁰ m ² / g.

In the negative electrode active material for a lithium ion secondary battery of the present invention, the composite of the carbonaceous material and the lithium compound is highly baked simultaneously with carbonization of the carbon precursor described later, and thus forms a dense structure. Therefore, there are few pores leading to the inside of the negative electrode active material particles, and the lithium ions solvated in the electrolytic solution during the charge / discharge process are difficult to directly contact the Si compound and / or graphite, and the specific surface area is 0. By being 5-20 m < ² > / g, since reaction with Si compound or graphite, and electrolyte solution is suppressed and reaction with the carbonaceous material and electrolyte solution on the surface is also kept small, the efficiency of charging / discharging increases. Combined with the improvement in particle strength by densification of the negative electrode active material, cracks due to the expansion of the Si compound are suppressed, and irreversible expansion is reduced.

As a second form of the negative electrode active material for a lithium ion secondary battery of the present invention, the surface of the round Si carbon composite particle comprising Si or Si alloy, carbonaceous material and graphite is used as the transition metal. A negative electrode active material for a lithium ion secondary battery, which is coated with a coating layer of a lithium compound which is a composite oxide of at least one element selected from the group of Group 13 or Group 15 elements and lithium. The average particle diameter of the Si or Si alloy is 0.01 to 5 μm, and the average particle diameter D ₅₀ of the negative electrode active material is 1 to 40 μm. There is a negative electrode active material for a lithium ion secondary battery.

When the average particle diameter D ₅₀ of the negative electrode active material described above is less than 1 [mu] m, it becomes difficult to produce a high density of the electrode becomes bulky, when more than 40 [mu] m, uniform electrode becomes intense unevenness of coated electrodes Becomes difficult to produce. From the viewpoint of cycle characteristics, a more preferable range of the average particle diameter D ₅₀ is 2 to 20 μm, more preferably 3 to 15 μm, a 10% particle diameter D ₁₀ is 1 μm or more, and a flaky particle having a thickness of less than 1 μm. It is preferable that there is little.

  The lithium compound referred to in the present invention is formed by bonding fine grains, and the grain size is preferably 0.2 μm or less from the viewpoint of the particle strength of the completed negative electrode active material.

  In the second embodiment of the negative electrode active material for a lithium ion secondary battery according to the present invention, the Si carbon composite particles include the Si or Si alloy and a graphite thin layer having a thickness of 0.2 μm or less together with the carbonaceous material. The structure is sandwiched and spreads in a layered and / or network form, and the graphite thin layer is curved near the surface of the active material particles to cover the active material particles. Lithium ion secondary battery characterized in that it is coated with a coating layer of a lithium compound that is a composite oxide of lithium and at least one element selected from the group of transition metals, group 13 or group 15 elements Negative electrode active material.

  In the second embodiment of the negative electrode active material for a lithium ion secondary battery of the present invention, the Si compound content is 10 to 60% by weight, the carbonaceous material content is 5 to 40% by weight, and the graphite content is The amount is preferably 20 to 80% by weight, and the lithium compound content is preferably 0.5 to 65% by weight. The content of the lithium compound is more than 9% by weight and more preferably 33% by weight or less, and more preferably 10% by weight or more and 25% by weight or less.

In the second embodiment of the negative electrode active material for a lithium ion secondary battery of the present invention, at least one element selected from the group of transition metals, group 13 or group 15 elements contained in the coating layer of the lithium compound More preferably, a metal element having a valence different from that of the lithium compound is further included in the lithium compound coating layer. For example, LiMn ₂ having trivalent and tetravalent Mn added by adding metal elements such as 1 to 3 valent Na, Cu, Mg, Al, Ni to Li ₄ Ti ₅ O ₁₂ having tetravalent Ti. A metal element such as Na, Cu or Mg having a valence of 1 to 2 is added to O ₄ , Li _{1 + x} Al _x Ge _2−x (PO ₄ ) ₃ (0 ≦ x ≦ 1), Li _{5 + x} La ₃ Zr _x A _{2-xO 12} (A is one or more elements selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, and Ge, 1.4 ≦ x ≦ 2) , Li _3x La _{2 / 3-x} AO ₃ (A is Ti or Zr, 0.2 ≦ x ≦ 0.05), and the like.

  In the second embodiment of the negative electrode active material for a lithium ion secondary battery of the present invention, it is more preferable that the lithium compound coating layer further contains a carbonaceous material or a conductive additive.

  Next, the manufacturing method of the negative electrode active material for lithium ion secondary batteries of this invention is demonstrated.

  The method for producing a negative electrode active material for a lithium ion secondary battery according to the present invention includes a step of mixing a Si compound, a carbon precursor, a lithium compound, and, if necessary, a graphite, a step of granulating and densifying, and a pulverization And forming the composite particles, and firing the composite particles in an inert atmosphere.

Raw material Si compound is an average particle diameter _{D 50} using the powder of 0.01 to 5 [mu] m. In order to obtain a Si compound having a predetermined particle diameter, the above-described Si compound raw material (ingot, wafer, powder, etc.) is pulverized by a pulverizer, and in some cases, a classifier is used. In the case of a lump such as an ingot or a wafer, it can be first pulverized using a coarse pulverizer such as a jaw crusher. After that, for example, a ball or bead is used to move the grinding medium, and the impact force, frictional force, or compression force of the kinetic energy is used to grind the material to be crushed, the media agitation mill, or the compression force of the roller. Rotation of a roller mill that pulverizes, a jet mill that collides crushed objects with the lining material or collides with each other at high speed, and pulverizes by the impact force of the impact, and a rotor with a fixed hammer, blade, pin, etc. It can be finely pulverized by using a hammer mill, pin mill, disk mill that pulverizes the material to be crushed using the impact force of the colloid, a colloid mill that uses shear force, or a high-pressure wet-on-front collision disperser "Ultimizer". . The pulverization can be used for both wet and dry processes. For further fine pulverization, very fine particles can be obtained, for example, by using a wet bead mill and gradually reducing the diameter of the beads. In order to adjust the particle size distribution after pulverization, dry classification, wet classification, or sieving classification can be used. In the dry classification, the process of dispersion, separation (separation of fine particles and coarse particles), collection (separation of solid and gas), and discharge are performed sequentially or simultaneously, mainly using air flow. Pre-classification (adjustment of moisture, dispersibility, humidity, etc.) before classification, or the moisture in the airflow used so that the classification efficiency is not lowered due to the influence of shape, air flow disturbance, velocity distribution, static electricity, etc. It is done by adjusting the oxygen concentration. In a dry type in which a classifier is integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained.

  As another method for obtaining a Si compound having a predetermined particle size, a method in which the Si compound is heated and evaporated by plasma or laser and solidified in an inert gas, or a CVD or plasma CVD using a gas raw material is used. These methods are suitable for obtaining ultrafine particles of 0.1 μm or less.

  The carbon precursor as a raw material is not particularly limited as long as it is a polymer mainly composed of carbon and becomes a carbonaceous material by heat treatment in an inert gas atmosphere, but is not limited to petroleum pitch, coal pitch, synthetic pitch, Tar, cellulose, sucrose, polyvinyl chloride, polyvinyl alcohol, phenol resin, furan resin, furfuryl alcohol, polystyrene, epoxy resin, polyacrylonitrile, melamine resin, acrylic resin, polyamideimide resin, polyamide resin, polyimide resin, etc. it can.

  The lithium compound as a raw material is a composite oxide powder of lithium and at least one element selected from the group of transition metals, Group 13 or Group 15 elements, and Si in the same manner as the Si compound described above. It is preferable to use a material pulverized to an average particle size comparable to that of the compound. As a method of compounding the lithium compound with the negative electrode active material, a compound of at least one element selected from the group of transition metals, group 13 or group 15 elements, and lithium alkoxide or fatty acid salt is used. There is also a method, but by using a powder obtained by pulverizing a composite oxide in advance, gas is generated in the firing step, decomposition of a group 13 or group 15 element compound and lithium alkoxide or fatty acid salt, Since there is no composition shift due to evaporation of the product or the like, dense negative electrode active material particles can be obtained. As a pulverization method, it is preferable to make it as small as possible using a wet bead mill.

  As the raw material graphite, natural graphite, artificial graphite obtained by graphitizing the pitch of petroleum or coal, and the like can be used, and scaly, oval or spherical, cylindrical or fiber-like are used. In addition, these graphites are subjected to acid treatment, oxidation treatment, and then expanded by heat treatment. Part of the graphite layer is peeled off to form an accordion-like form, or a pulverized product of expanded graphite, or an ultrasonic wave between layers. Exfoliated graphene or the like can also be used. The raw material graphite is preliminarily adjusted to a size that can be used in the mixing process, and the particle size before mixing is 1 to 100 μm for natural graphite or artificial graphite, or 5 μm to 5 mm for expanded graphite or expanded graphite pulverized product, graphene Degree.

  These Si compounds, carbon precursors, lithium compounds, and optionally mixed with graphite, when the carbon precursor is softened or liquefied by heating, the Si compound, carbon precursor, It can be carried out by kneading a lithium compound and, if necessary, graphite. In addition, when the carbon precursor is dissolved in a solvent, Si compound, carbon precursor, lithium compound and, if necessary, graphite are added to the solvent, and the Si compound is dissolved in the solution in which the carbon precursor is dissolved. The carbon precursor, the lithium compound, and, if necessary, graphite are dispersed and mixed, and then the solvent is removed. The solvent to be used can be used without particular limitation as long as it can dissolve the carbon precursor. For example, when pitch or tar is used as the carbon precursor, quinoline, pyridine, toluene, benzene, tetrahydrofuran, creosote oil or the like can be used. When polyvinyl chloride is used, tetrahydrofuran, cyclohexanone, nitrobenzene or the like can be used. When phenol resin or furan resin is used, ethanol, methanol or the like can be used.

  As a mixing method, when the carbon precursor is heat-softened, a kneader (kneader) can be used. In the case of using a solvent, in addition to the above-described kneader, a Nauter mixer, a Roedige mixer, a Henschel mixer, a high speed mixer, a homomixer, or the like can be used. Further, the jacket is heated with these apparatuses, and then the solvent is removed with a vibration dryer, a paddle dryer or the like.

  With these devices, the carbon precursor is solidified, or stirring in the process of solvent removal is continued for a certain amount of time, so that the Si compound, carbon precursor, lithium compound, and, if necessary, a mixture with graphite are granulated. Consolidated. Further, the carbon precursor is solidified or the mixture after removing the solvent is compressed by a compressor such as a roller compactor and coarsely pulverized by a crusher, whereby granulation and consolidation can be achieved. The size of the granulated / consolidated product is preferably 0.1 to 5 mm in view of ease of handling in the subsequent pulverization step.

  The granulated / consolidated material is pulverized by ball mill, medium agitation mill, roller mill for pulverizing using the compressive force of the roller, or lining material to be crushed at high speed. A jet mill that collides with each other or collides with each other and crushes by the impact force of the impact, a hammer mill that crushes the material to be crushed using the impact force of the rotation of a rotor with a fixed hammer, blade, pin, etc. A dry pulverization method such as a pin mill or a disk mill is preferred. In order to adjust the particle size distribution after pulverization, dry classification such as air classification and sieving is used. In the type in which the pulverizer and the classifier are integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained.

  The composite particles obtained by pulverization are fired in an argon gas or nitrogen gas stream or in an inert atmosphere such as a vacuum. The firing temperature is preferably 300 to 1000 ° C, more preferably 500 to 1000 ° C, and particularly preferably 600 to 900 ° C. When the firing temperature is less than 300 ° C., the irreversible capacity of the amorphous carbon derived from the carbon precursor is large, and the cycle characteristics are poor, so that the battery characteristics tend to deteriorate. On the other hand, when the firing temperature exceeds 1000 ° C., the reaction between the Si compound and the lithium compound occurs, the possibility that the lithium compound is decomposed becomes strong, and the discharge capacity tends to decrease.

  The method for producing a negative electrode active material for a lithium ion secondary battery of the present invention includes a step of mixing and dispersing an Si compound, a carbon precursor, a lithium compound, and, if necessary, graphite in a solvent in which the carbon precursor is dissolved, It is preferable to include a step of granulating and densifying, a step of forming composite particles having a round shape by pulverization and spheronization, and a step of firing the composite particles in an inert atmosphere.

  As a method of pulverizing the granulated / consolidated product and subjecting it to spheronization, it is pulverized by the above-mentioned pulverization method to adjust the particle size, and then passed through a dedicated spheronization device, and the above-mentioned jet mill or rotor rotation. There is a method of spheroidizing by repeating the method of pulverizing the material to be crushed by using the impact force of or by extending the processing time. Dedicated spheroidizing devices include Hosokawa Micron's Faculty (registered trademark), Nobilta (registered trademark), Mechano-Fusion (registered trademark), Nippon Coke Industrial Co., Ltd. COMPOSI, Nara Machinery Co., Ltd. hybridization system, Earth Technica Examples include kryptron orb and kryptron eddy.

  In the method for producing a negative electrode active material for a lithium ion secondary battery of the present invention, the Si compound, carbon precursor, lithium compound, expanded graphite or flaky graphite is mixed and dispersed in a solvent in which the carbon precursor is dissolved. And a step of granulating and densifying, a step of forming a composite particle having a round shape by pulverization and spheronization, and a step of firing the composite particle in an inert atmosphere. .

  Expanded graphite and flaky graphite are made from acid-treated graphite obtained by acid-treating and oxidizing natural graphite and artificial graphite. Expanded graphite is an acid-treated graphite that is expanded by heat treatment, and part of the graphite layer is peeled off to form an accordion. In addition, exfoliated graphite is pulverized, or graphene delaminated with ultrasonic waves or the like is flaky graphite. In expanded graphite, it can be expanded greatly by sufficiently performing acid treatment and increasing the temperature gradient of heat treatment, and the thickness of the graphite thin layer of the negative electrode active material obtained by sufficiently mixing and dispersing can be increased. Since it can be made thin, good electrical conductivity and cycle characteristics can be obtained.

  As a manufacturing method of the second embodiment of the negative electrode active material for a lithium ion secondary battery of the present invention, first, in the method for manufacturing a negative electrode active material for a secondary battery described above, a step of mixing and dispersing without adding a lithium compound Si carbon through a step of granulating and densifying, a step of forming a composite particle having a round shape by pulverization and spheronization, and a step of firing the composite particle in an inert atmosphere Composite particles are produced.

  Next, a lithium compound is prepared to coat the lithium compound. The lithium compound as a raw material is a composite oxide powder of lithium and at least one element selected from the group of transition metals, Group 13 or Group 15 elements, and Si in the same manner as the Si compound described above. It is preferable to use a material pulverized to an average particle size comparable to that of the compound. Further, at least one element selected from the group of transition metals, Group 13 or Group 15 elements, and lithium alkoxides, fatty acid salts, and inorganic salts can also be used.

  The prepared lithium compound raw material is dispersed in an appropriate solvent such as ethanol, mixed and stirred with Si carbon composite particles, and the solvent is removed with a dryer to produce Si carbon composite particles coated with the lithium compound raw material. Furthermore, it can bake and can carry out to coating with a lithium compound. If the atmosphere at the time of baking is less than 300 ° C., the atmosphere may be in the air. The lithium compound raw material is coated with a tumbling fluidized coating device, etc., by flowing Si carbon composite particles in a fluidized bed, spraying the lithium compound raw material dispersed in a solvent, and simultaneously drying and further heating to coat the lithium compound. You may go up.

  The negative electrode active material for a lithium ion secondary battery of the present invention thus obtained can be used as a negative electrode material for a lithium secondary battery.

  The negative electrode active material of the present invention is, for example, kneaded with an organic binder, a conductive additive and a solvent, and formed into a sheet shape, a pellet shape or the like, or applied to a current collector, and the current collector A negative electrode for a lithium secondary battery is formed by integrating with the body.

  As the organic binder, for example, polyethylene, polypropylene, ethylene propylene polymer, butadiene rubber, styrene butadiene rubber, butyl rubber, and a polymer compound having a large ion conductivity can be used. Polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide and the like can be used as the polymer compound having a high ionic conductivity. The content of the organic binder is preferably 3 to 20% by weight based on the whole negative electrode material. In addition to the organic binder, carboxymethyl cellulose, polysodium acrylate, other acrylic polymers, or fatty acid esters may be added as a viscosity modifier.

  The type of the conductive agent is not particularly limited, and may be any electron-conductive material that does not cause decomposition or alteration in the configured battery. Specifically, Al, Ti, Fe, Ni, Cu, Zn, Ag, Metal powder and metal fiber such as Sn, Si, or graphite such as natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, various resin fired bodies, etc. Etc. can be used. The addition amount of the conductive agent is 0 to 20% by weight, more preferably 1 to 10% by weight, based on the whole negative electrode material. When the amount of the conductive agent is small, the conductivity of the negative electrode material may be poor and the initial resistance tends to be high. On the other hand, an increase in the amount of conductive agent may lead to a decrease in battery capacity.

  There is no restriction | limiting in particular as said solvent, N-methyl- 2-pyrrolidone, a dimethylformamide, isopropanol, a pure water etc. are mentioned, There is no restriction | limiting in particular in the quantity. As the current collector, for example, a foil such as nickel or copper, a mesh, or the like can be used. The integration can be performed by a molding method such as a roll or a press.

  The negative electrode thus obtained has a cycle characteristic compared to a lithium secondary battery using conventional silicon as a negative electrode material by placing the positive electrode opposite to each other through a separator and injecting an electrolytic solution. In addition, a lithium secondary battery having excellent characteristics such as high capacity and high initial efficiency can be manufactured.

The material used for the positive electrode, for example _{LiNiO 2, LiCoO 2, LiMn 2} O 4, LiNi x Mn y Co 1-x-y O 2, LiFePO 4, Li 0.5 Ni 0.5 Mn 1.5 O 4 Li ₂ MnO ₃ —LiMO ₂ (M═Co, Ni, Mn) or the like can be used alone or in combination.

As an electrolytic solution, a lithium salt such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF _{3 is used as} a non-aqueous solvent such as ethylene carbonate, diethyl carbonate, dimethoxyethane, dimethyl carbonate, tetrahydrofuran, and propylene carbonate. A so-called dissolved organic electrolyte solution can be used. Furthermore, ionic liquids using imidazolium, ammonium, and pyridinium type cations can be used. The counter anion is not particularly limited, and examples thereof include BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ^{− and the} like. The ionic liquid can be used by mixing with the organic electrolyte solvent described above. An SEI (solid electrolyte interface layer) forming agent such as vinylene carbonate or fluoroethylene carbonate can also be added to the electrolytic solution.

  In addition, a solid electrolyte obtained by mixing the above salts with polyethylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, or the like, or a derivative, mixture, or complex thereof can also be used. In this case, the solid electrolyte can also serve as a separator, and the separator becomes unnecessary. As the separator, for example, a nonwoven fabric mainly composed of polyolefin such as polyethylene or polypropylene, cloth, microporous film, or a combination thereof is used. can do.

  According to the present invention, excellent cycle characteristics by suppressing the reaction between the electrolyte and silicon by reducing the expansion volume per particle by silicon of fine particles, and by complexing the dense carbonaceous material and lithium compound, and the initial and cycle The charge / discharge efficiency is high, and the electric conduction is achieved by the doping effect of at least one element selected from the group of transition metal and group 13 or 15 elements on silicon and the solid electrolyte effect of lithium by the lithium compound. As a result, the internal impedance is lowered and the irreversible expansion due to the charge / discharge cycle is suppressed, and a lithium ion battery negative electrode with a high battery capacity secured in a long cycle is obtained. In addition, a high bulk density negative electrode active material suitable for forming a high density negative electrode can be obtained by the production method of the present invention.

2 is a secondary electron image obtained by FE-SEM of a cross section of a negative electrode active material particle obtained in Example 1. FIG. 2 is a mapping image of P (phosphorus) element by EDS (energy dispersive X-ray analysis) of a cross section of negative electrode active material particles obtained in Example 1. FIG. The change of the charging / discharging capacity | capacitance and negative electrode expansion coefficient by the charging / discharging cycle of the battery produced with the negative electrode active material obtained by the comparative example 5 is shown. The change of the charging / discharging capacity | capacitance by the charging / discharging cycle of the battery produced with the negative electrode active material obtained in Example 10 and a negative electrode expansion coefficient is shown. The SEM image (3000 time) of the negative electrode active material obtained in Example 10 is shown. The SEM image (3000 time) of the negative electrode active material obtained in Example 11 is shown.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples.

Example 1
A pulverized wet bead mill using zirconia beads having a mean particle size D ₅₀ of 7 μm and chemical grade metal Si (purity 3N) mixed with ethanol in an amount of 20% by weight and having a diameter of 0.3 mm for 5 hours, zirconia having a diameter of 0.03 mm micronization wet bead mill using beads for 5 hours, the average particle diameter _{D 50} of 0.15 [mu] m, BET surface area of the drying to obtain ultrafine particles Si slurry 100 m ² / g.

  Immerse natural graphite with a particle diameter of about 0.5 mm (width in the (200) plane direction) and a thickness of about 0.02 mm in a solution of concentrated sulfuric acid with 1 wt% sodium nitrate and 7 wt% potassium permanganate added for 24 hours. Then, it was washed with water and dried to obtain acid-treated graphite. This acid-treated graphite was placed in a vibrating powder feeder, placed on nitrogen gas at a flow rate of 10 L / min, passed through a mullite tube having a length of 1 m and an inner diameter of 11 mm heated to 850 ° C. with an electric heater, and released from the end face to the atmosphere. A gas such as sulfurous acid was exhausted at the top, and expanded graphite was collected at the bottom in a stainless steel container. The expanded graphite had a width in the (200) plane direction of about 0.5 mm and maintained the original graphite value. However, the thickness expanded to about 4 mm and about 200 times, and the appearance was coiled. It was confirmed that the layer peeled and was in the form of an accordion.

Agglomerates of lithium phosphate (Li ₃ PO ₄ , purity 3N) were pulverized for 20 seconds with a new power mill (batch type cutter mill), then mixed with ethanol at 20% by weight, and fine particles using zirconia beads having a diameter of 0.3 mm were used. milling wet bead mill for 10 hours, the average particle diameter _{D 50} was obtained slurry of the ultrafine lithium phosphate 0.05 .mu.m.

  60 g of the ultrafine Si (concentration 20% by weight) slurry, 24 g of the expanded graphite, 4 g of the ultrafine lithium phosphate (concentration 20% by weight) slurry, 10 g of resol type phenolic resin (weight after firing 4 g) Then, 1 L of ethanol was put into a stirring vessel and mixed and stirred with a homomixer for 1 hour. Thereafter, the mixed solution was transferred to a rotary evaporator, heated to 60 ° C. with a warm bath while rotating, and evacuated with an aspirator to remove the solvent. Thereafter, it was spread on a bat in a fume hood and dried for 2 hours while evacuating, passed through a mesh with a mesh opening of 2 mm, and further dried for 12 hours to obtain about 40 g of a dried product (light bulk density 80 g / L).

  This mixed dried product was passed through a three-roll mill twice, and granulated and consolidated to a particle size of about 2 mm and a light bulk density of 350 g / L.

Next, the granulated / consolidated product was placed in a new power mill and pulverized at 22000 rpm for 900 seconds while cooling with water, and spheroidized at the same time to obtain a spheroidized powder with a light bulk density of 480 g / L. The obtained powder was put into an alumina boat and fired at a maximum temperature of 900 ° C. for 1 hour while flowing nitrogen gas in a tubular furnace. Then, through the mesh of 45 [mu] m, an average particle diameter _{D 50} of 15 [mu] m, to obtain a negative electrode active material of diatomaceous bulk density 620 g / L.

In FIG. 1, the secondary electron image by the FE-SEM of the cross section which cut | disconnected the obtained negative electrode active material particle with the ion beam is shown. The inside of the negative electrode active material particles is 0.05 to 0.2 μm in length between fine graphite layers (11) having a thickness of 0.02 to 0.2 μm (13) (the gap is 0. The structure sandwiched between (05-1 μm) spreads in a mesh pattern and is laminated. The carbonaceous material was in close contact with and covered the Si fine particles. Further, near the surface of the active material particles, the graphite thin layer (12) was curved to cover the active material particles. Further, when the composition was analyzed by EDS (energy dispersive X-ray analysis), as shown in FIG. 2, P (phosphorus) was present on the graphite thin layer (21) where the carbonaceous material was present and the negative electrode active material surface (22). was detected. The specific surface area by the BET method using nitrogen gas was 18 m ² / g. In powder X-ray diffraction, a diffraction line corresponding to the (002) plane of graphite was observed, and d002 was 0.336 nm. In addition, a very broad diffraction line derived from amorphous carbonization of the carbonaceous material was observed in the vicinity thereof. A diffraction line corresponding to the (100) plane of Si was observed, and d002 was 0.314 nm.

  A lithium ion secondary battery using the obtained negative electrode active material was produced as follows.

"Preparation of negative electrode for lithium ion secondary battery"
The obtained negative electrode active material was 95.5% by weight (content in the total solid content, the same applies hereinafter), acetylene black 0.5% by weight as a conductive additive, and CMC 1.5% by weight as a binder. A negative electrode mixture-containing slurry was prepared by mixing 2.5% by weight of SBR and water.

The obtained slurry was applied to a copper foil having a thickness of 15 μm using an applicator so that the solid content was 3 mg / cm ² and dried at 110 ° C. in a stationary operation dryer for 0.5 hour. After drying, the lithium ion 2 was punched into a circle of 14 mmφ, uniaxially pressed under conditions of a pressure of 0.6 t / cm ² , and further heat-treated at 110 ° C. for 3 hours under vacuum to form a negative electrode mixture layer having a thickness of 30 μm. A negative electrode for a secondary battery was obtained.

"Production of evaluation cells"
In the glove box, the evaluation cell was prepared by dipping the negative electrode, a 24 mmφ polypropylene separator, a 21 mmφ glass filter, a 18 mmφ 0.2 mm thick metal lithium and a stainless steel foil of the base material into the electrolyte solution in the glove box. After that, the layers were laminated in this order, and finally the lid was screwed in. The electrolyte used was a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1, dissolved LiPF ₆ to a concentration of 1.2 mol / L, and added with 2% by volume of fluoroethylene carbonate. did. The evaluation cell was further placed in a sealed glass container containing silica gel, and an electrode through a silicon rubber lid was connected to the charge / discharge device.

"Evaluation conditions"
The evaluation cell was cycle tested in a constant temperature room at 25 ° C. Charging was performed after charging to 0.01 V at a constant current of 2 mA until the current value reached 0.2 mA at a constant voltage of 0.01 V. The discharge was performed at a constant current of 2 mA up to a voltage value of 1.5 V. The discharge capacity and the initial charge / discharge efficiency were the results of the initial charge / discharge test.

  In addition, the cycle characteristics were evaluated as the capacity retention rate by comparing the discharge capacity after 50 charge / discharge tests under the charge / discharge conditions with the initial discharge capacity.

Comparative Example 1
In the mixing step, a slurry of ultrafine lithium phosphate was not added, 60 g of ultrafine Si slurry, 25 g of the above expanded graphite, 10 g of a resol type phenolic resin, and 1 L of ethanol were put into a stirring vessel. Except for the above, a negative electrode active material, a negative electrode, and an evaluation cell were prepared in the same manner as in Example 1, and the cells were evaluated.

Comparative Example 2
In the mixing step, a negative electrode active material, a negative electrode, and an evaluation cell were prepared in the same order as in Example 1 except that lithium phosphate (Li ₃ PO ₄ ) was replaced with lithium silicate (Li ₄ SiO ₄ ). evaluated.

  The results of Example 1 and Comparative Examples 1 and 2 are shown in Table 1.

  As is clear from Table 1, the lithium ion secondary battery of Example 1 of the negative electrode active material in which lithium phosphate, which is a lithium compound, and Si, a carbonaceous material, and graphite are combined, has a high capacity and an initial charge / discharge efficiency. And charge / discharge cycle characteristics are good.

On the other hand, the lithium ion secondary battery of Comparative Example 1 of the negative electrode active material in which Si, a carbonaceous material, and graphite were combined without adding a lithium compound had a capacity about 20% lower than that of Example 1 and had an initial charge / discharge. Efficiency is 4% lower and charge / discharge cycle characteristics are inferior. Further, in Comparative Example 2 in which Li ₄ SiO ₄ which is a complex oxide of Group 14 element and lithium is added instead of the lithium compound, both capacity and initial charge / discharge efficiency are slightly lower than those in Comparative Example 1, and the charge / discharge cycle is reduced. Only the characteristics were good.

Example 2
60 g of ultrafine Si (concentration 20% by weight) slurry prepared under the same conditions as in Example 1, 24 g of expanded graphite prepared under the same conditions as in Example 1, and 10 g of resol type phenolic resin (4 g weight after firing) ), 1 L of ethanol was put into a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Thereafter, the mixed solution was transferred to a rotary evaporator, heated to 60 ° C. with a warm bath while rotating, and evacuated with an aspirator to remove the solvent. Thereafter, it was spread on a bat in a fume hood and dried for 2 hours while evacuating, passed through a mesh with a mesh opening of 2 mm, and further dried for 12 hours to obtain about 40 g of a dried product (light bulk density 90 g / L).

  This mixed dried product was passed through a three-roll mill twice, and granulated and consolidated to a particle size of about 2 mm and a light bulk density of 370 g / L.

Next, the granulated / consolidated product was placed in a new power mill and pulverized at 22000 rpm for 900 seconds while cooling with water, and spheroidized at the same time to obtain a spheroidized powder with a light bulk density of 490 g / L. The obtained powder was put into an alumina boat and fired at a maximum temperature of 900 ° C. for 1 hour while flowing nitrogen gas in a tubular furnace. Then, 30 g of round Si carbon composite particles having an average particle diameter D ₅₀ of 18 μm and a light bulk density of 640 g / L were obtained by passing through a mesh having an opening of 45 μm.

30 g of this Si carbon composite particle was divided into three, and 10 g was used as the negative electrode active material of Comparative Example 3. Another 10 g of Si carbon composite particles prepared under the same conditions as in Example 1 were mixed with 0.5 g of a slurry of ultrafine lithium phosphate (concentration 20% by weight) and 100 mL of ethanol in a beaker and stirred and mixed with a stirrer for 20 minutes. Then, it was dried with a rotary evaporator in a 60 ° C. warm bath. The remaining 10 g of Si carbon composite particles were mixed with 2.5 g of a slurry of ultrafine lithium phosphate (concentration 20 wt%) and 100 mL of ethanol under the same conditions and dried. Two types of samples mixed with ultrafine lithium phosphate were put in an alumina boat and fired at a maximum temperature of 850 ° C. for 1 hour while flowing nitrogen gas in a tubular furnace. Thereafter, the mixture was lightly crushed with a crusher and passed through a mesh having an opening of 45 μm. The weight of lithium phosphate in the obtained negative electrode active material was 1% by weight and 5% by weight, respectively. The average particle diameter _{D 50} is 18～19Myuemu, diatomaceous bulk density was 660~690g / L.

  Using Comparative Example 3 and the negative electrode active material of Example 2 in which the weight of the lithium phosphate was 1% by weight and 5% by weight, a negative electrode and an evaluation cell were prepared in the same manner as in Example 1, and the cell evaluated. The results of Example 2 and Comparative Example 3 are shown in Table 2.

  As is apparent from Table 2, the initial charge / discharge efficiency was improved by 2% as compared with Comparative Example 3 in which the Si carbon composite particles were coated with lithium phosphate. The 1 wt% lithium phosphate coating improved the capacity by 5% and improved the charge / discharge cycle characteristics. In addition, with the 5 wt% lithium phosphate coating, the capacity per weight was slightly reduced, but the charge / discharge cycle characteristics were further improved.

Example 3
60 g of ultrafine particle Si (concentration 20% by weight) slurry prepared under the same conditions as in Example 1, 23 g of expanded graphite prepared under the same conditions as in Example 1, and ultrafine particles prepared under the same conditions as in Example 1. 10 g of a slurry of lithium phosphate (concentration 20% by weight), 10 g of a resole type phenol resin (weight 4 g after firing), and 1 L of ethanol were placed in a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Subsequent drying, three-roll mill, spheronization, calcination, carried out under the same conditions as in Example 1 to mesh through an average particle diameter D ₅₀ of 18 [mu] m, to obtain a negative electrode active material of diatomaceous bulk density 715 g / L.

Example 4
60 g of ultrafine particle Si (concentration 20 wt%) slurry prepared under the same conditions as in Example 1, 21 g of expanded graphite prepared under the same conditions as in Example 1, and ultrafine particles prepared under the same conditions as in Example 1. 20 g of a slurry of lithium phosphate (concentration 20 wt%), 10 g of a resol type phenol resin (weight 4 g after firing), and 1 L of ethanol were placed in a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Subsequent drying, three-roll mill, spheronization, calcination, carried out under the same conditions as in Example 1 to mesh through an average particle diameter D ₅₀ of 22 .mu.m, to obtain a negative electrode active material of diatomaceous bulk density 785 g / L.

Example 5
60 g of ultrafine particle Si (concentration 20 wt%) slurry prepared under the same conditions as in Example 1, 19 g of expanded graphite prepared under the same conditions as in Example 1, and ultrafine particles prepared under the same conditions as in Example 1. 30 g of a slurry of lithium phosphate (concentration 20% by weight), 10 g of a resole type phenol resin (weight 4 g after firing), and 1 L of ethanol were placed in a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Subsequent drying, three-roll mill, spheronization, calcination, carried out under the same conditions as in Example 1 to mesh through an average particle diameter D ₅₀ of 19 .mu.m, to obtain a negative electrode active material of diatomaceous bulk density 675 g / L.

Example 6
60 g of ultrafine Si (concentration 20% by weight) slurry prepared under the same conditions as in Example 1, 24 g of expanded graphite prepared under the same conditions as in Example 1, and 10 g of resol type phenolic resin (4 g weight after firing) ), 1 L of ethanol was put into a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Subsequent drying, three-roll mill, spheronization, conducted under the same conditions as in Example 2 to a firing mesh through an average particle diameter _{D 50} of 16 [mu] m, loosed bulk density was 30g prepared Si-carbon composite particles of 610 g / L. 30 g of this Si carbon composite particle was divided into four, and 7.5 g was used as the negative electrode active material of Comparative Example 4.

  Thereafter, lithium phosphate was coated in the same manner as in Example 2 as the weight of the negative electrode active material at 5, 9, and 13% by weight to prepare three types of negative electrode active materials.

Example 7
Si carbon composite particles before being coated with a lithium compound were produced under the same conditions as in Example 6, and then a molar ratio of lithium ethoxide (Li (OEt)) and titanium tetraisopropoxide (Ti (i-Pr) ₄ ). 6: 4 In the same manner as in Example 2, the Li-Ti oxide was coated with 5, 9 and 13% by weight in terms of Li ₄ Ti ₅ O _{12 in} terms of Li ₄ Ti ₅ O ₁₂ (firing temperature 850 ° C.), Three types of negative electrode active materials were produced.

Example 8
Si carbon composite particles before being coated with a lithium compound were prepared under the same conditions as in Example 6, and then lithium ethoxide (Li (OEt)) and niobium pentaethoxide (Nb (OEt) ₅ ) in a molar ratio of 1: 1. In the same manner as in Example 2, except that the firing temperature was set to 350 ° C., the Li—Nb oxide in terms of LiNbO ₃ was coated with 5, 9 and 13% by weight as the weight in the negative electrode active material, and three types A negative electrode active material was prepared.

Example 9
60 g of ultrafine Si (concentration 20 wt%) slurry prepared under the same conditions as in Example 1, 24 g of expanded graphite prepared under the same conditions as in Example 1, and 10 g of resol type phenolic resin (weight after firing: 8 g) ), 1 L of ethanol was put into a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Subsequent drying, three-roll milling, spheronization, and firing are performed under the same conditions as in Example 2. After firing, classification is performed using a centrifugal airflow classifier (rotor rotational speed 18000 rpm), and an average particle diameter D _{50 is obtained.} 14 g of Si carbon composite particles having a particle size of 5 μm and a light bulk density of 230 g / L.

  Thereafter, in the same manner as in Example 2, 13% by weight of lithium phosphate as a weight in the negative electrode active material was coated to prepare a negative electrode active material.

Example 10
100 g of ultrafine Si (concentration 20% by weight) slurry prepared under the same conditions as in Example 1, 16 g of expanded graphite prepared under the same conditions as in Example 1, and 10 g of resole-type phenol resin (4 g weight after firing) ), 1 L of ethanol was put into a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Subsequent drying, three-roll milling, spheronization, and firing are performed under the same conditions as in Example 2. After firing, classification is performed using a centrifugal airflow classifier (rotor rotational speed 18000 rpm), and an average particle diameter D _{50 is obtained.} 14 μm of Si carbon composite particles having a particle size of 4 μm and a light bulk density of 210 g / L.

  Thereafter, in the same manner as in Example 2, 13% by weight of lithium phosphate as a weight in the negative electrode active material was coated to prepare a negative electrode active material.

Example 11
80 g of ultrafine particle Si (concentration 20% by weight) slurry prepared under the same conditions as in Example 1, 20 g of expanded graphite prepared under the same conditions as in Example 1, and 10 g of resol type phenol resin (4 g weight after firing) ), 1 L of ethanol was put into a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Subsequent drying, three-roll milling, spheronization, and firing are performed under the same conditions as in Example 2. After firing, classification is performed using a centrifugal airflow classifier (rotor rotational speed 18000 rpm), and an average particle diameter D _{50 is obtained.} 14 μm of Si carbon composite particles having a particle size of 4 μm and a light bulk density of 200 g / L.

  Thereafter, 13 wt% of lithium phosphate was coated as a weight in the negative electrode active material in the same manner as in Example 2 except that the stirring and mixing time with the slurry of ultrafine lithium phosphate was reduced to 5 minutes by the same method as in Example 2. Thus, a negative electrode active material was produced.

Comparative Example 5
80 g of ultrafine particle Si (concentration 20% by weight) slurry prepared under the same conditions as in Example 1, 20 g of expanded graphite prepared under the same conditions as in Example 1, and 10 g of resol type phenol resin (4 g weight after firing) ), 1 L of ethanol was put into a stirring vessel, and mixed and stirred with a homomixer for 1 hour. Subsequent drying, three-roll mill, spheronization, baking, mesh up through was conducted under the same conditions as in Example 1, the average particle diameter D ₅₀ of 17 .mu.m, to obtain a negative electrode active material of diatomaceous bulk density 640 g / L.

  Lithium ion secondary batteries using the negative electrode active materials obtained in Examples 3 to 11 and Comparative Examples 3 to 5 were produced as follows.

"Preparation of negative electrode for lithium ion secondary battery"
With respect to 80.0% by weight of the obtained negative electrode active material, acetylene black 5.0% by weight as a conductive auxiliary, polyimide (IST dream bond) 15% by weight (weight after curing), NMP, Were mixed to prepare a negative electrode mixture-containing slurry.

The obtained slurry was applied to a copper foil having a thickness of 18 μm using an applicator so that the solid content was 3 mg / cm ² , preliminarily dried at 80 ° C., and then dried at 200 ° C. with a vacuum dryer. Dry for hours. After drying, it was punched into a circle of 14 mmφ, uniaxially pressed under conditions of a pressure of 0.6 t / cm ² , and further heat-treated at 110 ° C. for 2 hours under vacuum to form a negative electrode mixture layer having a thickness of 20 ± 5 μm. A negative electrode for an ion secondary battery was obtained.

"Electrode displacement evaluation cell"
The amount of expansion was measured using an electrode displacement cell that measures the expansion displacement of the negative electrode. A positive electrode is used for the lower part, a negative electrode is used for the upper part, and a piston-like support is fixed to the upper part of the negative electrode with a spring so that the expansion displacement of the electrode is transmitted to the support. Further, only the expansion displacement on the negative electrode side was measured by inserting and fixing a hard glass filter between the positive electrode and the negative electrode. Furthermore, the displacement displacement of the electrode can be measured by installing a laser displacement meter on the surface of the column. A commercially available displacement meter was used as the laser displacement meter. The displacement data was connected to a data logger and recorded.

The evaluation cell was assembled in a glove box. In the evaluation cell, 16 mmφ metallic lithium, 16 mmφ glass filter, 21 mmφ hard glass filter, 21 mmφ polypropylene separator, and 13.8 mmφ negative electrode were each dipped in the electrolyte solution, and then laminated in this order. The piston-like column was fixed with a spring and sealed with a lid. The electrolyte is a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1, the additive is FEC (fluoroethylene carbonate), and LiPF ₆ is dissolved to a concentration of 1.2 mol / L. used. After assembly, the electrode was connected to a charge / discharge device.

"Evaluation conditions"
The evaluation cell was cycle tested in a constant temperature room at 25 ° C. Charging was performed after charging to 0.01 V at a constant current of 2 mA until the current value reached 0.2 mA at a constant voltage of 0.01 V. The discharge was performed at a constant current of 2 mA up to a voltage value of 1.5 V. Recording of the laser displacement meter was started simultaneously with the start of charge / discharge.

  After preparing an electrode according to the above using the negative electrode active material of Comparative Example 5 and Example 10 and measuring the initial thickness, an electrode displacement evaluation cell was assembled, and a change in electrode thickness due to charging / discharging was examined with a laser displacement meter. . Here, the expansion rate is defined with the height obtained by subtracting the initial thickness of the electrode from the initial position of the laser displacement meter as the origin (0%), the maximum position by the initial charge as 100%, the charge / discharge capacity by the charge / discharge cycle, and The change in the expansion coefficient is shown in FIGS.

  In FIG. 3 (Comparative Example 5), the irreversible expansion, in which the contraction during discharge is smaller than the expansion during charging, is significant, and the expansion rate is 195% (arrow in the figure) after the 25th charge. In FIG. 4 (Example 10), although it slightly expanded to 108% in the second charge, it hardly changed thereafter, and the expansion rate was maintained at 108% (arrow in the figure) even in the 25th charge. On the other hand, in FIG. 3 (Comparative Example 5), the charge / discharge capacity decreased by 15% after 25 charge / discharge cycles, but in FIG. 4 (Example 10), the charge / discharge capacity remained at a 6% decrease after 25 charge / discharge cycles. The characteristics were greatly improved, and the capacity was reversed after the 25th time. In the initial charge / discharge efficiency, since the irreversible capacity due to the lithiation of the polyimide binder is about 200 mAh / g, it is considerably lower than when the aqueous binder is used, but in the efficiency of the 25th charge / discharge, FIG. Although it was as low as 93% in Comparative Example 5), it was greatly improved to about 99% in FIG. 4 (Example 10).

  Table 3 shows the results of evaluation of charge / discharge capacities and expansion rates before and after the cycle test (25 times) in the same manner using the negative electrode active materials of Examples 3 to 5 and Comparative Example 4.

  From Table 3, the initial capacity and efficiency decreased by the addition of 5 wt% or more of lithium phosphate, but the capacity retention rate by the cycle increased, and the 25th efficiency increased to 99%. In addition, the expansion rate for the 25th time was 165% when lithium phosphate was not added, but when lithium phosphate was added in excess of 10% by weight, the expansion rate became 130% or less, and when 15% by weight was added, 105%. Was suppressed until.

  Table 4 shows the results obtained by similarly assembling batteries using the negative electrode active materials of Examples 6 to 8 and Comparative Example 4, and evaluating the charge / discharge capacity and the expansion rate before and after the cycle test (25 times).

  From Table 4, the capacity decrease of the negative electrode active material due to the coating is small in the order of Li—Nb oxide, Li—Ti oxide, and lithium phosphate, but the capacity retention ratio and the efficiency of the 25th time are Li—Ti oxide, Lithium phosphate was excellent. The expansion rate for the 25th time was less than 130% by adding more than 10% by weight of the coating material, and reduced to around 120% for any material by 15% by weight coating.

  Table 5 shows the results of similarly assembling batteries using the negative electrode active materials of Examples 9 to 11 and Comparative Example 5, and evaluating the charge / discharge capacity and the expansion rate before and after the cycle test (25 times).

From Table 5, the average particle diameter _{D 50} of the anode active material and following the order of 5 to 6 .mu.m 15 [mu] m, _and, by the _{D 10} or more 1 [mu] m, in Si50 weight percent, initial capacity while exceeding the 900mAh / g, In the 25th time, a high capacity retention rate of 94%, an efficiency of 99%, and a low expansion rate of 108% were secured.

The SEM images of the negative electrode active materials of Examples 10 and 11 are shown in FIGS. 5 and 6. Although the particles in FIG. 5 (Example 10) are mostly spherical, the particles in FIG. 6 (Example 11). is mixed numerous fine flaky particles D ₁₀ of cause less than 1 [mu] m, which is considered to cause a slight expansion greater in example 11. Note that the grain size of the lithium compound of the coating film is less than 0.2 μm from these SEM images and SEM images of higher magnification, and the grain size of the lithium compound is not limited to Examples 10 and 11 but in any of the Examples. Was less than 0.2 μm.

Example 12
LAGP (Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ , purity 3N) powder was pulverized for 20 seconds with a new power mill (batch type cutter mill), then mixed with ethanol in an amount of 20% by weight. the milled wet mill using 0.3mm zirconia beads for 10 hours, the average particle diameter _{D 50} was obtained slurry of the ultrafine LAGP of 0.2 [mu] m.

  7.5 g of the above ultrafine particle LAGP and 100 mL of ethanol were placed in a beaker and mixed with 10 g of the Si carbon composite particles before the lithium compound coating prepared under the same conditions as in Example 6, and then stirred and mixed with a stirrer for 20 minutes. It dried with the rotary evaporator of the hot bath of ℃. This sample was put into an alumina boat and fired at a maximum temperature of 840 ° C. for 1 hour while flowing nitrogen gas in a tubular furnace. Thereafter, the mixture was lightly crushed with a crusher and passed through a mesh having an opening of 45 μm. The weight of LAGP in the obtained negative electrode active material was 13% by weight.

Example 13
By replacing LAGP with LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ), a negative electrode active material obtained by coating 13 g by weight of LLZ as a weight of the negative electrode active material on 10 g of Si carbon composite particles in the same manner as in Example 12 Produced.

Example 14
In the same manner as in Example 12, replacing LAGP with LLT (Li _0.33 La _0.55 Ti ₃ ), negative electrode active material in which 10 g of Si carbon composite particles were coated with 13 wt% of LLT as the weight of the negative electrode active material. The material was made.

  Using the negative electrode active materials of Examples 12 to 14, the negative electrode (the negative electrode active material was 95.5% by weight, acetylene black 0.5% by weight as a conductive additive, and a binder in the same manner as in Example 1 Table 6 shows the results of cell evaluation. CMC 1.5 wt%, SBR 2.5 wt%, and water were mixed to prepare a negative electrode mixture-containing slurry.

  As is apparent from Table 6, the initial capacity was slightly lowered by coating the Si carbon composite particles with LAGP, LLZ, and LLT compared with Comparative Example 3 where the coating was not performed, but the capacity was maintained with LAGP and LLT coating. The rate improved significantly. Although the expansion rate was as large as 175% in Comparative Example 3, all the samples in Examples 12 to 14 were 130% or less.

  The negative electrode active material for lithium ion secondary battery and the method for producing the same of the present invention can be used for a lithium ion secondary battery that requires a high capacity and a long life.

11 Graphite thin layer inside negative electrode active material 12 Graphite thin layer near negative electrode active material surface 13 Si fine particle and carbonaceous material layer 21 Signal from Kα ray of P (phosphorus) element between graphite thin layers inside negative electrode active material ( White dot)
22 Signal from the Kα ray of the P (phosphorus) element on the negative electrode active material surface (white dot)

Claims (13)

And Si or Si alloy and a graphite carbonaceous material or carbonaceous material, in comprise negative active material for a lithium ion secondary battery comprising, the average particle diameter _{D 50} of the Si or Si alloy is 0.01 to 5 [mu] m, The carbonaceous material is compounded with a transition metal, a complex oxide of at least one element selected from the group of Group 13 or Group 15 elements and lithium, and a specific surface area of 0.5 to ²⁰ m ^2. / g der is, the negative active material is a composite particle having an average particle diameter D ₅₀ which shape is rounded 1 to 40 [mu] m, average particle having an average particle diameter of the negative electrode active material of the Si or Si alloy A carbonaceous material having a diameter of 1/5 or less and complexed with a complex oxide of lithium and at least one element selected from the group of transition metals, Group 13 or Group 15 elements, at least the surface of the active material Covering Negative active material for a lithium ion secondary battery, characterized Rukoto. The Si or Si alloy has a thickness of 0.2 μm or less together with a carbonaceous material compounded with a complex oxide of at least one element selected from the group of transition metals, Group 13 or Group 15 elements and lithium. The structure is sandwiched between thin graphite layers, and the structure spreads in a laminated and / or network shape. The thin graphite layer is curved near the surface of the active material particles to cover the active material particles, The surface of the outer layer is covered with a carbonaceous material complexed with a complex oxide of lithium and at least one element selected from the group of transition metal, group 13 or group 15 element of the periodic table. Item 2. The negative electrode active material for a lithium ion secondary battery according to Item 1 . At least one element selected from the group consisting of the transition metal, group 13 or group 15 element, wherein the Si or Si alloy content is 10 to 80% by weight, the carbonaceous material content is 5 to 90% by weight negative active material for a lithium ion secondary battery according to claim 1 or 2, wherein the content of the composite oxide of lithium is 0.5 to 80% by weight. The Si or Si alloy content is 10 to 60% by weight, the carbonaceous material content is 5 to 40% by weight, the graphite content is 20 to 80% by weight, the transition metal, the periodic table group 13 or 15 at least one element and the lithium ion secondary battery according to claim 1 or 2 content of the composite oxide is characterized by a 0.5 to 65 wt% of lithium selected from the group of group elements Negative electrode active material. The negative active material having an average particle diameter _{D 50} of 2 to 20 [mu] m, and 10% particle diameter _{D 10} of claim 1 lithium ion secondary battery according to any one of 4, characterized in that at 1μm or more Negative electrode active material. A step of mixing Si or a Si alloy, a carbon precursor, a transition metal, a complex oxide of lithium and at least one element selected from the group of Group 13 or 15 elements of the periodic table, and, if necessary, graphite. The method according to claim 1, comprising a step of granulating and compacting, a step of pulverizing the mixture to form composite particles, and a step of firing the composite particles in an inert gas atmosphere. A method for producing a negative electrode active material for a lithium ion secondary battery. Si or a Si alloy, a carbon precursor, and a transition metal, a complex oxide of at least one element selected from the group of Group 13 or 15 elements of the periodic table and lithium, and optionally graphite, A step of mixing and dispersing in a solvent in which the body dissolves, a step of granulating and densifying, a step of pulverizing and spheronizing to form composite particles having a round shape, and the composite particles in an inert atmosphere The method for producing a negative electrode active material for a lithium ion secondary battery according to claim 1 , further comprising a step of firing in. Si or a Si alloy, a carbon precursor, a transition metal, a complex oxide of lithium and at least one element selected from the group of Group 13 or Group 15 elements, expanded graphite, or flake graphite, A step of mixing and dispersing in a solvent that dissolves, a step of granulating and densifying, a step of forming a composite particle having a round shape by pulverization and spheronization, and a step of forming the composite particle in an inert atmosphere. The method for producing a negative electrode active material for a lithium ion secondary battery according to claim 2 , further comprising a step of firing in. The temperature of the process of baking the said composite particle in inert atmosphere is 300-1000 degreeC, The negative electrode active material for lithium ion secondary batteries of any one of Claims 6-8 characterized by the above-mentioned. Production method. At least one element selected from the group of transition metal, group 13 or group 15 element and lithium on the surface of rounded Si carbon composite particles comprising Si or Si alloy, carbonaceous material and graphite A negative electrode active material for a lithium ion secondary battery coated with a coating layer of a lithium compound that is a composite oxide with Si and a Si alloy having an average particle diameter of 0.01 to 5 μm, and the negative electrode A negative electrode active material for a lithium ion secondary battery, wherein the average particle size D ₅₀ of the negative electrode active material is 1 to 40 μm, which is 1/5 or less of the average particle size of the active material. In the Si carbon composite particles, the Si or Si alloy is sandwiched between graphite thin layers having a thickness of 0.2 μm or less together with the carbonaceous material, and the structure spreads in a laminated and / or network form. The graphite thin layer is curved near the surface of the active material particle to cover the active material particle, and the surface of the Si carbon composite particle is at least one selected from the group of transition metals, group 13 or group 15 elements 11. The negative electrode active material for a lithium ion secondary battery according to claim 10 , wherein the negative electrode active material is covered with a coating layer of a lithium compound that is a composite oxide of two elements and lithium. The negative electrode active material for a lithium ion secondary battery according to claim 10 or 11 , wherein the lithium compound is 0.5 to 65 wt% in the negative electrode active material. 13. The lithium ion secondary battery according to claim 10 , wherein the negative electrode active material has an average particle diameter D ₅₀ of 2 to 20 μm and a 10% particle diameter D ₁₀ of 1 μm or more. Negative electrode active material.

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