WO2015181940A1 - Negative electrode active material for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Abstract

Provided is a negative electrode active material for lithium ion secondary batteries, which enables the production of a lithium ion secondary battery having high capacity. A negative electrode active material for lithium ion secondary batteries, which comprises a base and silicon nanoparticles formed on the surface of the base. The base comprises a base for amorphous carbon layer formation and an amorphous carbon layer that is formed on the surface of the base for amorphous carbon layer formation. The base for amorphous carbon layer formation is configured of an active material that is capable of absorbing and desorbing lithium ions. The silicon nanoparticles are bonded to the carbon base through the amorphous carbon layer.

Description

Negative electrode active material for lithium ion secondary battery and lithium ion secondary battery

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

Graphite-based carbon materials are widely used as negative electrode active materials of lithium ion secondary batteries. The stoichiometric composition when lithium is charged into graphite is LiC ₆ , and its theoretical capacity can be calculated to be 372 mAh / g.

On the other hand, when the silicon is filled with lithium ions, the stoichiometric composition is Li ₁₅ Si ₄ or Li ₂₂ Si ₅ , and its theoretical capacity can be calculated to be 3577 mAh / g or 4197 mAh / g. Thus, silicon is an attractive material that can store 9.6 times or 11.3 times more lithium than graphite. However, when the silicon particles are filled with lithium ions, the volume expands to about 3.1 times or about 4.1 times, so that the silicon particles are mechanically broken while repeating the lithium ion charging and discharging. The destruction of the silicon particles electrically isolates the broken fine silicon particles, and the formation of a new electrochemical coating layer on the fracture surface increases the irreversible capacity and significantly reduces the charge-discharge cycle characteristics.

By making silicon particles into nano particles as a negative electrode active material of a lithium ion secondary battery, mechanical destruction associated with charging and discharging of lithium ions can be prevented. In this case, in order to ensure the electrical conductivity between each silicon nanoparticle and the current collector, it is necessary to mix materials having electrical conductivity. Moreover, it is necessary to be strong between each silicon nanoparticle and the electrically conductive material. As a prior art, Patent Document 1 describes an example in which silicon nanoparticles are attached to the surface of dendritic carbon particles.

Japanese Patent Application Publication No. 2013-506264

Patent Document 1 describes that the conductive material of dendritic particles to which silicon nanoparticles are attached is amorphous carbon or graphite carbon. When dendritic particles are amorphous carbon alone, dendritic particles can not be used as an active material, and when a nanocomposite containing dendritic particles is used for the negative electrode of a lithium ion secondary battery, a high capacity lithium ion secondary battery is obtained It may not be possible.

An object of the present invention is to provide a negative electrode active material for a lithium ion secondary battery capable of producing a high capacity lithium ion secondary battery.

The features of the present invention for solving the above problems are, for example, as follows.

A negative electrode active material for a lithium ion secondary battery, comprising: a base material; and silicon nanoparticles formed on the surface of the base material, wherein the base material is a base material for forming an amorphous carbon layer and a group for forming an amorphous carbon layer The base material for forming an amorphous carbon layer has an amorphous carbon layer formed on the surface of the material, and the base material for forming an amorphous carbon layer is made of an active material capable of inserting and extracting lithium ions; Negative electrode active material for lithium ion secondary batteries joined to metal materials.

ADVANTAGE OF THE INVENTION By this invention, the negative electrode active material for lithium ion secondary batteries which can produce a high capacity | capacitance lithium ion secondary battery can be provided. Problems, configurations, and effects other than those described above will be apparent from the description of the embodiments below.

It is the figure which represented typically the silicon nanoparticle which concerns on one Embodiment of this invention. It is the figure which represented typically the silicon nanoparticle which concerns on one Embodiment of this invention. It is the figure which represented typically the silicon nanoparticle which concerns on one Embodiment of this invention. It is the figure which represented typically the silicon nanoparticle which concerns on one Embodiment of this invention. It is the figure which represented typically the silicon nanoparticle which concerns on one Embodiment of this invention. It is a calculation result regarding the relationship between the specific surface area of a base material, and the radius of a silicon nanoparticle when close packing is assumed. It is a calculation result regarding the relationship between the specific surface area of a base material, and the radius of a silicon nanoparticle when close packing is assumed. FIG. 1 is a schematic view of a thermal vapor deposition apparatus for forming carbon-coated silicon nanoparticles on the surface of a carbon substrate. It is a scanning electron micrograph of carbon covering silicon nanoparticles formed in the surface of a carbon substrate. It is a scanning electron micrograph of carbon covering silicon nanoparticles formed in the surface of a carbon substrate. It is a scanning electron micrograph of carbon covering silicon nanoparticles formed in the surface of a carbon substrate. It is a calculation result regarding the relation between electric capacity and silicon weight ratio. It is an internal structure of the lithium ion secondary battery which concerns on one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described using the drawings and the like. The following description shows specific examples of the content of the present invention, and the present invention is not limited to these descriptions, and various modifications by those skilled in the art can be made within the scope of the technical idea disclosed herein. Changes and modifications are possible. Moreover, in all the drawings for explaining the present invention, what has the same function may attach the same numerals, and may omit explanation of the repetition. Further, in the present specification, a numerical range indicated using “to” indicates a range including numerical values described before and after “to” as the minimum value and the maximum value, respectively.

A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a view schematically representing the structure of a silicon nanoparticle according to an embodiment of the present invention.

The negative electrode active material 1000 for a lithium ion secondary battery has a structure in which silicon nanoparticles 102 are formed on the surface of a carbon substrate 110. Specifically, the amorphous carbon layer 103 is formed on the surface of the graphite particles 101 (also referred to as a base for forming an amorphous carbon layer), and the silicon nanoparticles 102 are formed on the surface of the amorphous carbon layer 103. The silicon nanoparticles 102 are in contact with the surface of the carbon substrate 110 via flat portions having a curvature smaller than the average curvature. In other words, the silicon nanoparticles 102 are bonded to the carbon base 110 via the amorphous carbon layer 103. The carbon substrate 110 has crystallinity, and an amorphous carbon layer 103 having an amorphous structure is formed at least near the surface. The carbon substrate 110 is also simply referred to as a substrate. The carbon base 110 having such a structure can be easily formed by coating the surface of the graphite particle 101 with the amorphous carbon layer 103.

In one embodiment of the present invention, the graphite particles 101 are made of an active material capable of absorbing and desorbing lithium ions. Since the graphite particles 101 can be used as an active material, when the negative electrode active material 1000 for a lithium ion secondary battery in this example is applied to a lithium ion secondary battery, a high capacity lithium ion secondary battery can be obtained.

The thickness of the amorphous carbon layer 103 is desirably 1 to 100 nm, preferably 1 to 30 nm. If it is smaller than 1 nm, it is technically difficult to uniformly cover the surface of the graphite particles 101. If the thickness is larger than 100 nm, the possibility of the amorphous carbon layer 103 peeling off from the surface of the graphite particle 101 increases. By providing the amorphous carbon layer 103, the silicon nanoparticles 102 can be formed on the surface of the carbon substrate 101 with high density.

In one embodiment of the present invention, silicon nanoparticles 102 are grown directly on the surface of the carbon substrate 110 by vapor deposition, as described later. In this case, when the surface of the carbon substrate 110 has crystallinity, the silicon nanoparticles 102 grown on the surface slide on the crystalline carbon surface, move to aggregate, and then grow into larger and larger silicon particles 102. Do. Therefore, it is difficult to grow the silicon nanoparticles 102 at a high density. On the other hand, in the case where the amorphous carbon layer 103 is present, the aggregation of the silicon nanoparticles 102 is unlikely to occur, and it becomes possible to form the silicon nanoparticles 102 having a relatively high diameter and a uniform diameter. This is considered to be because the silicon nanoparticles 102 are less likely to move on the amorphous carbon layer 103 than on the crystalline carbon layer. Further, as shown in FIG. 1, the silicon nanoparticles 102 formed by the vapor deposition method have a shape bonded to the carbon base 110 through a flat surface to some extent. At the bonding interface, the carbon atom of the carbon base 110 and the silicon atom of the silicon nanoparticle 102 form a chemical bond, and the bond between the carbon base 110 and the silicon nanoparticle 102 is very strong.

A second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram schematically representing the structure of a silicon nanoparticle according to an embodiment of the present invention.

The negative electrode active material 1000 for a lithium ion secondary battery is composed of an amorphous carbon layer forming substrate 201, silicon nanoparticles 202, and an amorphous carbon layer 203. Amorphous carbon layer 203 is formed on the surface of base material 201 for forming amorphous carbon layer, and silicon nanoparticles 202 are formed thereon. In the present embodiment, the base 210 includes an amorphous carbon layer forming base 201 and an amorphous carbon layer 203 formed on the surface of the amorphous carbon layer forming base 201.

As the base material 201 for forming an amorphous carbon layer, it is possible to use a metal active material capable of inserting and extracting lithium ions such as silicon and tin, and various composite materials including them. In other words, the amorphous carbon layer forming base material 201 is made of an active material capable of inserting and extracting lithium ions.

A third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a view schematically representing the structure of silicon nanoparticles according to an embodiment of the present invention.

The negative electrode active material 1000 for a lithium ion secondary battery is composed of a carbon base 310, silicon nanoparticles 302, and a carbon coating layer 304. In the structure, silicon nanoparticles 302 are formed on the surface of the carbon substrate 310, and a carbon coating layer 304 is formed on the surface of the silicon nanoparticles 302. The carbon base 310 is composed of graphite particles 301 (base for forming an amorphous carbon layer) and an amorphous carbon layer 303. The carbon substrate 310 is also simply referred to as a substrate. The only difference from the first embodiment is that the carbon coating layer 304 is formed.

The carbon coating layer 304 is a coating layer containing carbon as a main component, and desirably has a nanographene structure. In the case of having a nanographene structure, it has an electrical conductivity of 1000 S / m or more, preferably 10000 S / m or more. Thereby, since the silicon nanoparticles 302 can be imparted with electrical conductivity, in particular, high-speed charge and discharge characteristics can be significantly improved.

The thickness of the carbon coating layer 304 is desirably 1 to 100 nm. If it is smaller than 1 nm, it is technically difficult to uniformly cover the surface of silicon nanoparticles. In addition, when the diameter is larger than 100 nm, the carbon covering layer 304 is likely to exfoliate from the surface of silicon nanoparticles.

The fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a view schematically representing the structure of silicon nanoparticles according to an embodiment of the present invention.

The negative electrode active material 1000 for a lithium ion secondary battery comprises an amorphous carbon layer forming substrate 401, silicon nanoparticles 402, an amorphous carbon layer 403, and a carbon coating layer 404. Amorphous carbon layer 403 is formed on the surface of a substrate 401 for forming amorphous carbon layer, silicon nanoparticles 402 are formed thereon, and a carbon coating layer 404 is formed on the surface of silicon nanoparticles 402. . The only difference from the second embodiment is that the carbon coating layer 404 is formed. In the present embodiment, the base 410 has an amorphous carbon layer forming base 401 and an amorphous carbon layer 403 formed on the surface of the amorphous carbon layer forming base 201.

The carbon coating layer 404 is a coating layer containing carbon as a main component, and desirably has a nanographene structure. In the case of having a nanographene structure, it has an electrical conductivity of 1000 S / m or more, preferably 10000 S / m or more. Thereby, since the silicon nanoparticles 402 can be imparted with electrical conductivity, in particular, high-speed charge and discharge characteristics can be significantly improved.

The thickness of the carbon coating layer 404 is desirably 1 to 100 nm. If it is smaller than 1 nm, it is technically difficult to uniformly cover the surface of the silicon nanoparticles 402. In addition, when the thickness is larger than 100 nm, the carbon covering layer 404 is likely to exfoliate from the surface of the silicon nanoparticle 402.

The fifth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram schematically representing the structure of a silicon nanoparticle according to an embodiment of the present invention.

The substrate 501 has a structure in which an amorphous carbon layer is coated on the surface of potato-like natural graphite. The negative electrode active material 1000 for a lithium ion secondary battery has a structure in which silicon nanoparticles 502 are densely formed on the surface of a substrate 501. As the substrate 501, any substrate or carbon substrate shown in Examples 1 to 4 can be used. The silicon nanoparticles 502 can also form a carbon coating layer as shown in Examples 2 and 4.

<Silicon nanoparticles>
Next, the relationship between the specific surface area of the substrate and the size of the silicon nanoparticles formed on the surface, which is a matter common to all the above-described Examples 1 to 5, the method for producing silicon nanoparticles, The morphology of silicon nanoparticles and the relationship between silicon weight ratio and capacitance will be described.

First, the relationship between the specific surface area of the substrate and the size of the silicon nanoparticles formed on the surface will be described. The diameter of the silicon nanoparticles produced on the surface of the substrate is desirably 1 to 100 nm, more desirably 1 to 30 nm. If the diameter is smaller than 1 nm, the bonding strength with the substrate is weak and the possibility of peeling from the substrate is high. Also, if the diameter is larger than 100, it is likely to be broken due to mechanical strain associated with lithium ion charging and discharging. The diameter is preferably 30 nm or less in order not to destroy mechanical strain caused by high-speed charge and discharge. Further, as described later, in order to realize a high electrical capacity negative electrode active material, it is necessary to increase the weight ratio of silicon. That is, it is desirable to form silicon nanoparticles on the surface of the base material as densely as possible.

First, when silicon nanoparticles are closely packed on the surface of a substrate, the specific surface area of the substrate required is calculated. Here, for physical use using units other than the MKSA unit system, the units are shown in square brackets. The weight of one silicon nanoparticle is w. However, the silicon nanoparticle is assumed to be a hemisphere, and its radius is r. w can be expressed by equation (1).

Here, D is the density of silicon. The number n of silicon nanoparticles formed on the surface of 1 kg of substrate can be expressed by equation (2).

Here, R is a weight ratio of silicon nanoparticles. The occupied area of n silicon nanoparticles is represented by equation (3), and the specific surface area of the substrate is s, and equation (4) holds when the silicon nanoparticles are closely packed.

4) Formula (5) is obtained by arranging formula. However, D = 2.33 × 10 ³ [kgm ⁻³ ], R = 0.20 was used.

Next, the results of calculation of the specific surface area of the required substrate are shown in FIGS. 6 and 7 when the silicon nanoparticles are close-packed and formed on the substrate surface using Equation (5). FIG. 6 and FIG. 7 show calculation results on the relationship between the specific surface area of the substrate and the radius of the silicon nanoparticles, assuming close packing. In addition to the silicon weight ratio R = 0.20 (20 wt%), the calculation results for R = 0.30 (30 wt%) and R = 0.40 (40 wt%) are also shown simultaneously. FIG. 6 shows the calculation results when the radius of the silicon nanoparticles is 0 to 30 nm, and FIG. 7 shows the results when the radius of the silicon nanoparticles is 30 to 100 nm.

When the radius of silicon nanoparticles is 15 nm (diameter is 30 nm), a substrate specific surface area of 11.9 [m ² / g] or more is necessary to achieve a weight ratio of 20 wt% of silicon. In practice, it is difficult to achieve close packing, and two to four times the specific surface area is required. That is, a specific surface area of 20 to 40 m ² / g is required. However, actually, from the viewpoint of design latitude, a specific surface area of 1 to 8 times is required. That is, a specific surface area of 10 to 80 m ² / g is required. When the carbon substrate to which silicon nanoparticles are attached is a dendritic carbon particle such as carbon black, the specific surface area of the carbon substrate is generally as large as several hundred m ² / g, and the electrochemical coating on the surface is The irreversible capacity associated with layer formation may be large. On the other hand, the irreversible capacity can be suppressed by setting the specific surface area to 10 to 80 m ² / g, preferably 20 to 40 m ² / g as described above.

Next, a method of producing silicon nanoparticles will be described. FIG. 8 is a schematic view of a thermal vapor deposition apparatus for forming carbon-coated silicon nanoparticles on the surface of a carbon substrate.

As a silicon raw material, liquid silicon tetrachloride was introduced into the reactor by bubbling with hydrogen gas. The vapor pressure of silicon tetrachloride at 20 ° C. is 30 kPa, and when bubbling is introduced, the amount of silicon tetrachloride introduced is 34%. Therefore, in the case of introducing silicon tetrachloride in an amount smaller than that, it is necessary to cool the silicon tetrachloride or to provide a separate line of hydrogen gas. In FIG. 8, a hydrogen line not bubbling was separately provided, joined with the bubbling line, and introduced into the reactor. The procedure for the growth of carbon-coated silicon nanoparticles is as follows.

Place the substrate in the sample boat and place it near the center of the reactor. The reactor is made of quartz and has a diameter of 5 cm and a length of 40 cm. With the hydrogen line flowing at a flow rate of 200 mL / min flowing in the upper hydrogen line in FIG. 8 and the bubbling hydrogen line below closed, the growth furnace is heated from room temperature to 1000 ° C. at a rate of 10 ° C./min. did.

Next, when reaching 1000 ° C., the flow rate of the upper hydrogen line was changed to 150 mL / min, and the flow rate of the hydrogen line of the lower bubbling hydrogen line was set to 50 mL / min. Under this condition, 8.5% silicon tetrachloride can be introduced. After growing at 1000 ° C. for 1 hour, the lower bubbling hydrogen line was closed, and the flow rate of the upper hydrogen line was changed to 200 mL / min and held at 1000 ° C. for 30 minutes. This makes it possible to produce silicon nanoparticles with a diameter of 30 nm on the substrate surface.

Thereafter, both hydrogen lines were closed, argon gas was flowed at a flow rate of 200 mL / min, the temperature was decreased at a rate of 10 ° C./min, and the temperature was decreased to 800 ° C. When reaching 800 ° C., a carbon coating layer was grown for 1 hour by introducing propylene gas at a flow rate of 10 mL / min and simultaneously setting the flow rate of argon gas to 190 mL / min.

After that, the propylene gas line was closed, argon gas was flowed at a flow rate of 200 mL / min, and was kept for 30 minutes and then naturally cooled. Thereby, it is possible to produce a carbon coating layer (film thickness of 10 nm) having a nanographene multilayer structure on the surface of silicon nanoparticles. As described above, by continuously performing the preparation of silicon nanoparticles and the subsequent preparation of a carbon coating layer, the formation of a natural oxide film is prevented, and the process of reducing and removing the natural oxide film becomes unnecessary.

In addition, in FIG. 8, in order to prevent the surface oxidation of a silicon nanoparticle, preparation of a silicon nanoparticle and subsequent preparation of the carbon coating layer were performed continuously. After growing the silicon nanoparticles, they are once taken out into the air and then heat-treated in a reducing atmosphere to remove the natural oxide film on the surface of the silicon nanoparticles, and subsequently to form a carbon coating layer. Productivity is improved by performing the growth of silicon nanoparticles and the preparation of the carbon coating layer in separate reactors. In addition, it is possible to change the diameter and growth weight of silicon nanoparticles by changing the temperature at the time of silicon nanoparticle growth, the amount of silicon tetrachloride introduced, and the growth time. In addition, it is possible to control the film thickness of the carbon coating layer by changing the growth time of the carbon coating layer. In addition to propylene gas, it is possible to use various hydrocarbon gases such as acetylene gas, propane gas, methane gas and the like for producing the carbon coating layer.

9, 10, and 11 show scanning electron micrographs of negative electrode materials in which silicon nanoparticles are grown on the surface of amorphous carbon-coated potato-like natural graphite. It can be seen from FIGS. 9 and 10 that silicon nanoparticles can be produced at a very high density. Further, it can be seen from the enlarged photograph of FIG. 11 that the diameter of the silicon nanoparticles is 20 to 30 nm.

Finally, the relationship between the silicon weight ratio and the electric capacity will be described. FIG. 12 shows the results of calculating the dependence of the negative electrode electric capacity on the weight ratio Si / (Si + C) of silicon to the total weight, for the negative electrode active material for lithium ion secondary batteries. For carbon, assuming that the stoichiometric composition when charged with lithium ions is LiC ₆ , its electric capacity was 372 mAh / g. In addition, for silicon, assuming that the stoichiometric composition at the time of charging with lithium ions is Li ₁₅ Si ₄ and assuming that the electric capacity is 3577 mAh / g, it is assumed that Li ₂₂ Si ₅ , It calculated about the case where the electric capacity was 4197 mAh / g.

From the balance with the positive electrode electric capacity, if 1000 mAh / g or more can be realized as the negative electrode electric capacity, it is considered that the performance is sufficient for the time being. From the calculation results of FIG. 12, in order to realize 1000 mAh / g or more as the negative electrode electric capacity, the weight ratio is 20% or more, particularly 40% or more, and further 80% with respect to the negative electrode active material for lithium ion secondary battery. It is desirable to contain% or more of silicon.

Although the case where a carbon material was used as a base material was calculated as an example in the above, when base materials other than carbon are used, the same calculation can be performed using the specific electrical capacity of the base material.

FIG. 13 is an internal structure of a lithium ion secondary battery according to an embodiment of the present invention. In FIG. 13, 1401 is a positive electrode, 1402 is a separator, 1403 is a negative electrode, 1404 is a battery can, 1405 is a positive electrode current collecting tab, 1406 is a negative electrode current collecting tab, 1407 is an inner lid, 1408 is an internal pressure release valve, 1409 is a gasket, 1410 is a positive temperature coefficient (PTC) resistive element, and 1411 is a battery cover. The battery lid 1411 is an integrated component including an inner lid 1407, an internal pressure release valve 1408, a gasket 1409, and a positive temperature coefficient resistance element 1410.

For example, the positive electrode 1401 can be manufactured by the following procedure. LiMn ₂ O ₄ is used as the positive electrode active material. To 85.0 wt% of the positive electrode active material, 7.0 wt% and 2.0 wt% of a graphite powder and acetylene black are added as a conductive material, respectively. Further, a solution dissolved in 6.0 wt% of polyvinylidene fluoride (hereinafter abbreviated as PVDF) and 1-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) as a binder is added and mixed by a planetary mixer. Further, the bubbles in the slurry are removed under vacuum to prepare a homogeneous positive electrode mixture slurry. This slurry is uniformly and evenly applied on both sides of a 20 μm thick aluminum foil using a coater. After application, it is compression molded by a roll press so that the electrode density is 2.55 g / cm ³ . This is cut with a cutting machine to produce a positive electrode 1401 having a thickness of 100 μm, a length of 900 mm, and a width of 54 mm.

For example, the negative electrode 1403 can be manufactured by the following procedure. As the negative electrode active material, the negative electrode active material for a lithium ion secondary battery in the present invention such as the negative electrode active material for a lithium ion secondary battery in any of FIGS. 1 to 5 can be used. To 95.0 wt% of the negative electrode active material, a solution of 5.0 wt% of PVDF dissolved in NMP as a binder is added. It is mixed with a planetary mixer, and bubbles in the slurry are removed under vacuum to prepare a homogeneous negative electrode mixture slurry. This slurry is uniformly and uniformly applied on both sides of a 10 μm-thick rolled copper foil with a coating machine. After application, the electrode is compression molded by a roll press to an electrode density of 1.3 g / cm ³ . This is cut with a cutting machine to produce a negative electrode 1303 having a thickness of 110 μm, a length of 950 mm, and a width of 56 mm.

The positive electrode current collecting tab 1405 and the negative electrode current collecting tab 1406 are ultrasonically welded to the positive electrode 1401 and the uncoated part (current collector plate exposed surface) of the negative electrode 1403 which can be manufactured as described above. The positive electrode current collection tab 1405 can be an aluminum lead piece, and the negative electrode current collection tab 1406 can be a nickel lead piece.

Thereafter, a separator 1402 made of a porous polyethylene film with a thickness of 30 μm is inserted into the positive electrode 1401 and the negative electrode 1403, and the positive electrode 1401, the separator 1402, and the negative electrode 1403 are wound. The wound body is housed in a battery can 1404, and the negative electrode current collection tab 1406 is connected to the can bottom of the battery can 1404 by a resistance welder. The positive electrode current collection tab 1405 is connected to the bottom surface of the inner lid 1407 by ultrasonic welding.

Before attaching the upper battery lid 1411 to the battery can 1404, a non-aqueous electrolyte is injected. The solvent of the electrolytic solution is, for example, composed of ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC), and there is a volume ratio of 1: 1: 1 or the like. The electrolyte is LiPF ₆ at a concentration of 1 mol / L (about 0.8 mol / kg). Such an electrolytic solution is dropped from above the wound body, and the battery lid 1411 is crimped and sealed in the battery can 1404 to obtain a lithium ion secondary battery.

101 301 Graphite particles 102 202 302 402 502 Silicon nanoparticles 103 203 303 403 Amorphous carbon layer 304 404 Carbon coating layer 110 310 carbon substrate 201 401 Substrate for forming amorphous carbon layer 210 410 501 Substrate 1000 For lithium ion secondary battery Negative electrode active material 1401 Positive electrode 1402 Separator 1403 Negative electrode 1404 Battery can 1405 Positive electrode current collection tab 1406 Negative electrode current collection tab 1407 Inner lid 1408 Pressure release valve 1409 Gasket,
1410 Positive temperature coefficient resistance element 1411 Battery cover

Claims (8)

A substrate,
A negative electrode active material for a lithium ion secondary battery, comprising: silicon nanoparticles formed on the surface of the base material,
The base includes an amorphous carbon layer forming base and an amorphous carbon layer formed on the surface of the amorphous carbon layer forming base,
The base for forming the amorphous carbon layer is made of an active material capable of absorbing and releasing lithium ions,
The negative electrode active material for lithium ion secondary batteries in which the said silicon nanoparticle is joined to the said carbon base material via the said amorphous carbon layer. In claim 1,
The substrate is a carbon substrate,
A negative electrode active material for a lithium ion secondary battery, wherein the specific surface area of the carbon substrate is 10 to 80 m ² / g. In any one of claims 1 to 2,
The negative electrode active material for a lithium ion secondary battery, wherein the thickness of the amorphous carbon layer is 1 to 100 nm. In any one of claims 1 to 3,
The negative electrode active material for a lithium ion secondary battery, wherein the diameter of the silicon nanoparticles is 1 to 100 nm. In any one of claims 1 to 4,
The negative electrode active material for lithium ion secondary batteries by which the carbon coating layer is formed in the surface of the said silicon nanoparticle. In claim 5,
The said carbon coating layer is a negative electrode active material for lithium ion secondary batteries which has a nano graphene structure. In any one of claims 1 to 6,
The negative electrode active material for lithium ion secondary batteries whose weight ratio of the said silicon nanoparticle with respect to the said active material for lithium ion secondary batteries is 20% or more. A lithium ion secondary battery comprising the negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 7.

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