JP6993216B2 - Silicon-containing amorphous carbon material, lithium-ion secondary battery - Google Patents

Description

The technique disclosed herein relates to a silicon-containing amorphous carbon material used in a negative electrode or the like of a lithium ion secondary battery.

Lithium-ion secondary batteries are lighter and have higher capacity than conventional secondary batteries such as nickel-cadmium batteries, nickel-hydrogen batteries, and lead batteries. Therefore, portable electronic devices such as mobile phones and notebook computers can be used. It has been put into practical use as a power source for driving. It is also used as a power source for electric vehicles and hybrid vehicles.

As the material for the negative electrode, silicon, tin, germanium, and oxides thereof that are alloyed with lithium can be used, but these materials expand in volume during charging to occlude lithium ions and release lithium ions. The volume shrinks during discharge. Therefore, the negative electrode material may fall off or disintegrate from the electrode due to the volume change when the charge / discharge cycle is repeated.

Patent Document 1 describes an active material for a lithium ion secondary battery containing silicon oxide and a carbon material. Since this active material has voids inside, the volume change during charging and discharging is suppressed to be small.

Further, Patent Document 2 describes a technique for embedding lithium storage material particles in a carbon material and reducing the size of the lithium storage material particles to prevent electrode destruction during charging / discharging. ..

Japanese Unexamined Patent Publication No. 2013-30428 Japanese Unexamined Patent Publication No. 2005-71938

However, since the active material for a lithium ion secondary battery described in Patent Document 1 is obtained by carbonizing a sprayed resin aqueous solution together with colloidal silica, it is close to a true sphere and has a sharp particle size distribution. .. Therefore, when the electrode is manufactured, there are few indirect points of particles, and it is necessary to take measures such as mixing a large amount of conductive material. Further, according to the method described in Patent Document 1, it is considered that it is not practical because there are many steps for manufacturing an active material.

Further, in the technique described in Patent Document 2, although the volume change when lithium is stored and released in the lithium storage material particles can be suppressed to some extent, it cannot be sufficiently suppressed, so that the negative electrode is destroyed and the cycle. It is difficult to achieve sufficient improvement in properties.

In view of the above problems, an object of the present invention is to provide a material for a negative electrode such as a lithium ion secondary battery, which has a small volume change during charging and discharging and can practically improve cycle characteristics.

The silicon-containing amorphous carbon material according to the embodiment of the present invention comprises easily graphitized amorphous carbon, and is represented by SiO _x (0 <x <2) in the easily graphitized amorphous carbon. Contains silicon oxide particles.

Here, the "silicon oxide particles" include those in which the surface of the silicon particles added as a raw material is air-oxidized.

This silicon-containing amorphous carbon material contains 1% by weight or more and less than 50% by weight of silicon. Further, as the oxygen content mainly derived from silicon oxide, the silicon-containing amorphous carbon material may contain oxygen in an amount of more than 0% by weight and less than 40% by weight. Further, this silicon-containing amorphous carbon material has a circularity of 0.70 or more and 1.0 or less, and a BET specific surface area of 1.5 to 32.5 m ² / g.

Further, the silicon-containing amorphous carbon material according to the embodiment of the present invention may have a molar ratio (O / Si) of silicon content and oxygen content of 0.2 or more and less than 2.0.

The method for producing a silicon-containing amorphous carbon material according to another embodiment of the present invention includes a step of mixing raw coke powder and silicon-containing particles for dry granulation, and a step of granulating the granulated particles with an inert gas. It is equipped with a process of carbonizing in an atmosphere. In the dry granulation step, the amount of the silicon particles or the silicon oxide particles added is 2% by volume or more and 90% by volume or less when the sum of the volumes of the raw coke and the silicon particles or the silicon oxide particles is 100%. Is preferable.

The carbonization temperature in the carbonization step is preferably 800 ° C. or higher and 1200 ° C. or lower, for example.

According to the silicon-containing amorphous carbon material according to the embodiment of the present invention, it is possible to suppress the destruction of the negative electrode due to the volume change of the silicon oxide particles during charging and discharging, which can contribute to the improvement of the cycle characteristics. ..

FIG. 1 is a diagram showing a micrograph of a cross section of an amorphous carbon material according to Example 8. FIG. 2 is a diagram showing an example of a lithium ion secondary battery provided with a negative electrode using a silicon-containing amorphous carbon material according to an embodiment of the present invention. FIG. 3 is a diagram showing a micrograph of a cross section of the amorphous carbon material according to Example 10. FIG. 4 is a diagram showing a micrograph of a cross section of the amorphous carbon material according to Example 12.

A silicon-containing amorphous carbon material for a negative electrode of a lithium ion secondary battery and a lithium ion secondary battery using the material will be described below according to an embodiment of the present invention. It should be noted that the following is an example of the embodiment, and the constituent materials, the shapes of the constituent materials or members, the conditions for processing and heat treatment, and the like can be appropriately changed as long as the gist of the present invention is not deviated.

-Definition of words-
The "circularity" used in the present specification is an index of the roundness of particles and the like, and is a value obtained by the following equation (1).

(Circularity) = {4 x π x (projected area)} / {(perimeter) ² } ... (1)
Further, as an index showing the unevenness of the particle surface, the value obtained by the following equation (2) was defined as the “degree of unevenness”.

(Degree of unevenness) = (Diameter equivalent to projected area circle x π) / Perimeter ... (2)
(Embodiment)
-Explanation of silicon-containing amorphous carbon material-
FIG. 1 is a diagram showing a micrograph of a cross section of a silicon-containing amorphous carbon material according to an embodiment of the present invention.

As shown in FIG. 1, the silicon-containing amorphous carbon material 1 according to the present embodiment includes amorphous carbon 4, and the amorphous carbon 4 is represented by SiO _x (0 <x <2). Contains silicon oxide particles to be made. The silicon oxide particles in the amorphous carbon 4 exist in a dispersed state, for example. Amorphous carbon 4 is easily graphitized carbon, so-called soft carbon. Each silicon-containing amorphous carbon material 1 is composed of a plurality of carbon particles derived from the raw material.

According to this configuration, the amorphous carbon 4 contains silicon oxide particles, which improves the initial discharge capacity and has a sufficiently high level of cycle characteristics when used as a negative electrode material for a lithium ion secondary battery. Can be maintained.

Further, in the silicon-containing amorphous carbon material 1 of the present embodiment, if the molar ratio (O / Si) of the silicon content and the oxygen content is 0.2 or more and less than 2.0, the initial discharge capacity is improved. On the other hand, it is more preferable because it can provide a certain level of initial efficiency and cycle characteristics in a well-balanced manner. It is more preferable that the molar ratio (O / Si) of the silicon content and the oxygen content is 0.3 or more and 1.7 or less. The silicon-containing amorphous carbon material 1 may contain oxygen in an amount of more than 0% by weight and less than 40% by weight.

The average particle size of the silicon-containing amorphous carbon material 1 is, for example, about 5 μm or more and 40 μm or less. If the average particle size exceeds 40 μm, the strength of the carbon material may decrease, and it may be difficult to form an electrode having an appropriate film thickness when manufacturing the negative electrode. Further, with a carbon material having an average particle size of less than 5 μm, it is difficult to disperse the silicon oxide particles in the amorphous carbon particles.

The average particle size of the silicon-containing amorphous carbon material 1 is more preferably 10 μm or more and 30 μm or less. The maximum particle size of the silicon-containing amorphous carbon material 1 is about 45 μm or less.

The content of silicon in the silicon-containing amorphous carbon material 1 is 1% by weight or more and 50% by weight or less. This is because if it is 50% by weight or less, it is easy to granulate. In addition, in order to sufficiently obtain the effect of improving the capacity, the silicon content is preferably 5% by weight or more.

In the silicon-containing amorphous carbon material 1 of the present embodiment, voids 20 are formed around the silicon oxide particles. This is because the silicon-containing particles are likely to be arranged in the gaps between the carbon particles derived from the carbon raw material, and voids are likely to be formed around the silicon-containing particles when the volatile component is removed from raw coke or the like. Conceivable. Due to the presence of the voids 20 around the silicon oxide, the influence of the expansion of the volume of the silicon oxide particles is suppressed due to the presence of the voids even when lithium ions are inserted into the silicon-containing amorphous carbon material 1 during charging.

The density (true density) of the silicon-containing amorphous carbon material 1 is preferably about 1.8 g / cm ³ or more and 2.2 g / cm ³ or less. When the density of the silicon-containing amorphous carbon material 1 is in an appropriate range, it is possible to sufficiently secure the energy density per volume when used for the negative electrode of a lithium ion secondary battery.

Further, the circularity of the silicon-containing amorphous carbon material 1 of the present embodiment is preferably about 0.70 or more and 1.0 or less, and more preferably 0.80 or more and 0.98 or less. According to this configuration, the packing density and the electrode density can be increased. If the circularity is less than 0.7, the effect of the compounding cannot be sufficiently exerted, and the particles are caught by each other and the packing density and the electrode density are lowered. The circularity does not exceed 1.0, and the effect of the present invention can be obtained even with a material having a circularity of 1.0, but in order to improve the packing density and increase the contact points between particles. More preferably, the circularity is 0.98 or less. However, even when the circularity of the silicon-containing amorphous carbon material is out of the above range, it has the effect of suppressing the volume change during charging and discharging to be smaller than that of the conventional carbon material. It can be used as a negative electrode material for a secondary battery.

Further, for the silicon-containing amorphous carbon material 1 of the present embodiment, the value obtained by dividing the equal area circumference length obtained by multiplying the projected area circle equivalent diameter by the circumference ratio (π) by the circumference length of the projected particles is an index of unevenness. When used as, the degree of unevenness is 0.9 or more and less than 1.0. This indicates that the contours of the particles do not form a smooth arc, but rather have a so-called "potato" shape with many irregularities.

The amorphous carbon 4 contained in the silicon-containing amorphous carbon material 1 produced using raw coke preferably contains a transition metal of 700 ppm or more and 2500 ppm or less. The transition metal mainly includes nickel, vanadium and the like. Further, the amorphous carbon 4 may contain 250 ppm or more of vanadium.

As described above, it is considered that the effect of promoting the insertion or desorption of lithium can be obtained by containing the transition metal in the amorphous carbon 4, and the transition metal is doped in silicon oxide. The expansion or contraction of silicon oxide particles can be alleviated.

According to the silicon-containing amorphous carbon material 1 described above, since high-capacity silicon oxide particles are dispersed in the amorphous carbon 4, the initial charge capacity and the initial discharge capacity are set to the amorphous carbon 4. It can be made larger than when it is composed of only.

Here, silicon oxide particles or silicon particles are used as the silicon source of the silicon-containing amorphous carbon material 1 as described later. In each case, the above-mentioned silicon can be mixed by mixing the materials at an appropriate blending ratio. The contained amorphous carbon material 1 can be obtained.

Further, in the silicon-containing amorphous carbon material 1, the void 20 (see FIG. 1) is formed inside, so that the influence of the volume expansion of the silicon oxide particles when lithium ions are inserted can be mitigated. can. Therefore, it is possible to suppress the disintegration of the silicon-containing amorphous carbon material 1 and make it difficult for the negative electrode to be destroyed, and it is possible to improve the cycle characteristics of the lithium ion secondary battery.

Further, since the voids are contained in one carbon material particle, the diffusion path of lithium is sufficiently secured, so that lithium can be rapidly inserted and removed. In addition, the volume change during charging and discharging is also mitigated.

Further, the silicon-containing amorphous carbon material 1 of the present embodiment can be charged and discharged more quickly than graphite because the lithium ions are occluded and released in the amorphous carbon portion in the same direction. .. Further, by containing silicon oxide, it has a high capacity. Therefore, the silicon-containing amorphous carbon material 1 of the present embodiment is particularly preferably used for a lithium ion secondary battery or the like for an electric vehicle.

Further, since the lithium ions are occluded and released in the same direction, the volume change in one direction becomes small, so that the negative electrode is less likely to be destroyed as compared with the case where a graphite material having high crystallinity is used.

The silicon-containing amorphous carbon material 1 of the present embodiment can be used not only as a lithium ion secondary battery but also as a negative electrode material such as a lithium ion capacitor.

-Manufacturing method of negative electrode material-
The silicon-containing amorphous carbon material 1 of the present embodiment can be produced using raw coke such as needle (needle-shaped) coke and mosaic (non-needle-shaped) coke as a material. Raw coke is obtained by heating heavy oil to about 300 ° C. to 700 ° C. using a coking facility such as a delayed coke, and thermally decomposing and polycondensing the heavy oil.

For example, in a cross section observed with a polarizing microscope, the optically isotropic structure is evenly dispersed, the optically isotropic structure ratio is 75% or more, more preferably 85% or more, and the total transition metal content is Petroleum-based raw coke having a value of 700 ppm or more and 2500 ppm or less can be used. Since this raw coke contains a large amount of transition metals and the like as impurities, it is considered that the efficiency of Li insertion / removal is improved when it is used as a negative electrode material for a lithium ion secondary battery.

Petroleum-based raw coke is crushed with a mechanical crusher, for example, a super rotor mill (manufactured by Nisshin Engineering Co., Ltd.), a jet mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), or the like.

The average particle size (D50) after pulverization is 1 μm or more and 15 μm or less, more preferably 3 μm or more and 10 μm or less. The average particle size is based on the measurement by a laser diffraction type particle size distribution meter. If D50 is less than 1 μm, the required grinding energy will be enormous, which is not realistic. If D50 is less than 3 μm, sufficient mechanical energy cannot be applied to the particles during dry granulation. Comes out. Further, if D50 exceeds 15 μm, the number of particles having an appropriate size as a negative electrode material for the lithium ion secondary battery is reduced after granulation, which is not preferable.

The crushed product can be further classified. Examples of the classifier include a precision air classifier (manufactured by Nisshin Engineering Co., Ltd.), an elbow jet (manufactured by Nittetsu Mining Co., Ltd.), a classifier (manufactured by Seishin Enterprise Co., Ltd.), and the like.

Next, silicon particles and / or silicon oxide particles, which are silicon raw materials, are prepared. Here, the average particle size of the silicon raw material is not particularly limited, but by setting it to 1 μm or less, the expansion width of the silicon oxide particles during charging and discharging of the silicon-containing amorphous carbon material becomes small, so that the volume of the carbon layer changes. Can be suppressed.

Here, as an example, silicon oxide particles having an average particle size of 20 nm or more and 30 nm or less are used. The case of using silicon particles will be described later because the compounding ratio is different from the case of using silicon oxide particles.

Subsequently, the raw coke particles and the silicon oxide particles are well mixed to perform dry granulation. Since raw coke has adhesiveness, it is not necessary to add a binder component for wet granulation. The amount of silicon oxide particles added during granulation is not particularly limited, but the amount of silicon oxide particles added is 2 volumes when the sum of the volumes of raw coke and silicon oxide particles is 100%. It is preferably% or more and 90% by volume or less. The amount of the silicon oxide particles added is more preferably 10% by volume or more and 85% by volume or less, and even more preferably 20% by volume or more and 80% by volume or less.

For this treatment, a device capable of spheroidizing processing in which stresses such as shearing, compression, and collision are applied at the same time can be used, but the processing device is not limited to the device using such a structure and principle. ..

The devices used in this process include, for example, a ball-type kneader such as a rotary ball mill, a wheel-type kneader such as an edge runner, a hybridization system (manufactured by Nara Machinery Co., Ltd.), Mechanofusion (manufactured by Hosokawa Micron), and Nobilta. (Manufactured by Hosokawa Micron Co., Ltd.), COMPOSI (manufactured by Nippon Coke Industries Co., Ltd.) and the like. In particular, a device having a structure in which compaction stress or compressive stress is applied to the powder in the gap between the blade of the rotating blade and the housing is preferably used. If the temperature applied to the powder during processing is controlled to be 60 ° C to 300 ° C, the volatile components contained in the raw coke will cause appropriate stickiness, and the particles will instantly adhere to each other. Growth is promoted.

Since the circularity of raw coke used as a raw material is about 0.5 to 0.8, the circularity of the powder obtained after shape processing by compressive shear stress is larger than 0.70 and 1.0 or less. The circularity of the powder is preferably 0.80 or more and 0.98 or less. Even if the circularity of the powder is 1.0, the effect of alleviating the influence of expansion and contraction of the silicon oxide particles can be obtained, but the particles treated to a circularity exceeding 0.98 are close to true spheres. The number of contacts between particles is reduced. In particular, the range of circularity of the particles is preferably 0.90 or more and 0.96 or less.

Here, the entire amount of the silicon oxide particles may be mixed with the raw coke, but if the amount of the silicon oxide particles is large, it becomes difficult to granulate, so the raw coke and some of the silicon oxide particles are mixed and granulated. After starting the above, the silicon oxide particles may be added in a plurality of times (for example, 3 times or more). Further, the silicon oxide particles and raw coke may be added after the silicon oxide particles and the like are added at the start of granulation, and only the raw coke is added at the end of the granulation to cover the surface of the silicon oxide particles with the raw coke. You may. Further, in this step, a part of silicon oxide may be replaced with elemental silicon.

Furthermore, by replacing part of the raw coke used for granulation with carbon materials such as acetylene black, inorganic compounds such as transition metal compounds, and organic compounds, it is possible to combine different materials with raw coke. Is. As long as it does not interfere with granulation, a part of the raw coke to be added at the start of granulation or during granulation may be replaced with a different material, or only different materials may be added during granulation. .. The amount of different materials added is not particularly limited as long as it does not interfere with granulation. The average particle size of the dissimilar materials is not particularly limited as long as it does not interfere with granulation, but is preferably 1/2 or less of the granulated particle size at the time of addition.

Next, the granulated particles are carbonized. The carbonization method is not particularly limited, but for example, the heat treatment is carried out in an atmosphere of an inert gas such as nitrogen or argon with a maximum ultimate temperature of 800 ° C. or higher and 1200 ° C. or lower, and a holding time at the maximum ultimate temperature of longer than 0 hours and 10 hours or less. There is a way to do it.

When the carbonization temperature is 800 ° C. or higher, the amount of small molecule hydrocarbons and functional groups remaining in the coke can be reduced, so that the increase in irreversible capacity due to these impurities can be effectively suppressed. When the carbonization temperature is 1200 ° C. or lower, it is preferable because it is possible to suppress the formation of insulating silicon carbide in the material. It is particularly preferable that the carbonization temperature is about 900 ° C. or higher and 1100 ° C. or lower. By setting the carbonization temperature to 900 ° C. or higher, it is possible to more effectively suppress the increase in irreversible capacity due to the residual of small molecule hydrocarbons and the like.

In the carbonization step, the holding time at the maximum arrival time may be longer than 10 hours, but it is not economical because the heat treatment is continued after the carbonization is completed.

It is considered that the volatile components in the raw coke promote the reduction of silicon oxide by this carbonization treatment. Further, when the gas of the volatile component generated during carbonization escapes to the outside, a gas release path is formed in the particles, and the release path is used as a negative electrode material of a lithium ion secondary battery. It serves as a path for lithium to diffuse, and also has the effect of cushioning the expansion and contraction of silicon oxide particles.

According to the above method, a material used for a negative electrode of a lithium ion secondary battery can be easily manufactured as compared with the method described in Patent Document 1.

Further, as another example, a case where silicon particles are used instead of silicon oxide particles will be described.

When silicon particles are handled in air, an oxide film is likely to be formed on the surface of the particles, and in order to prevent excessive oxidation of the silicon particles, an oxide film may be formed on the surface of the silicon particles in advance. However, in the present invention, these silicon particles can also be used.

First, dry coke granulation is performed by mixing raw coke particles and silicon particles well. At the time of granulation, the amount of silicon particles added is, for example, 2% by volume or more and 90% by volume or less with respect to the amount of raw coke. In particular, since silicon particles having a low oxidation number expand and contract significantly, the amount of silicon particles added is preferably 5% by volume or more and 50% by volume or less, and more preferably 5% by volume or more and 35% by volume or less. preferable.

Similar to the above method, an apparatus capable of simultaneously applying stress such as shearing, compression, and collision can be used for this treatment.

Since the circularity of raw coke used as a raw material is about 0.5 to 0.8, the circularity of the powder obtained after shape processing by compressive shear stress is larger than 0.70 and 1.0 or less. The circularity of the powder is preferably 0.80 or more and 0.98 or less. Even if the circularity of the powder is 1.0, the effect of alleviating the influence of expansion and contraction of the silicon particles can be obtained, but the particles treated to a circularity exceeding 0.98 are close to a true sphere. , The number of contacts between particles is reduced. In particular, the range of circularity of the particles is preferably 0.90 or more and 0.96 or less.

Here, the entire amount of the silicon particles may be mixed with the raw coke, but if the amount of the silicon particles is large, it becomes difficult to granulate, so the raw coke and some of the silicon particles are mixed and granulation is started. After that, the silicon particles may be added in a plurality of times (for example, 3 times or more). Further, the silicon particles and raw coke may be added after the silicon particles or the like are added at the start of granulation, or only the raw coke may be added at the end of the granulation to coat the surface of the silicon particles with the raw coke. .. Further, in this step, a part of silicon may be replaced with silicon oxide.

Furthermore, by replacing part of the raw coke used for granulation with carbon materials such as acetylene black, inorganic compounds such as transition metal compounds, and organic compounds, it is possible to combine different materials with raw coke. Is. As long as it does not interfere with granulation, a part of the raw coke to be added at the start of granulation or during granulation may be replaced with a different material, or only different materials may be added during granulation. .. The amount of different materials added is not particularly limited as long as it does not interfere with granulation. The average particle size of the dissimilar materials is not particularly limited as long as it does not interfere with granulation, but is preferably 1/2 or less of the granulated particle size at the time of addition.

Next, the granulated particles are carbonized. The carbonization method is not particularly limited, but for example, the heat treatment is carried out in an atmosphere of an inert gas such as nitrogen or argon with a maximum ultimate temperature of 800 ° C. or higher and 1200 ° C. or lower, and a holding time at the maximum ultimate temperature of longer than 0 hours and 10 hours or less. There is a way to do it.

When the carbonization temperature is 800 ° C. or higher, the amount of small molecule hydrocarbons and functional groups remaining in the coke can be reduced, so that the increase in irreversible capacity due to these impurities can be effectively suppressed. When the carbonization temperature is 1200 ° C. or lower, it is preferable because it is possible to suppress the formation of insulating silicon carbide in the material.

It is particularly preferable that the carbonization temperature is about 900 ° C. or higher and 1100 ° C. or lower. By setting the carbonization temperature to 900 ° C. or higher, it is possible to suppress an increase in irreversible capacity due to the residual of small molecule hydrocarbons and the like.

In the carbonization step, the holding time at the maximum arrival time may be longer than 10 hours, but it is not economical because the heat treatment is continued after the carbonization is completed.

It is considered that this carbonization treatment has an action of reducing the oxide film on the surface of the silicon particles by the volatile components in the raw coke. A carbon material containing silicon particles having a small oxidation number is preferable as a negative electrode material because it exhibits a high capacity, but on the other hand, there is a problem that silicon particles having a small oxidation number have a larger expansion / contraction. According to the present invention, since the voids formed by the volatile component gas generated during carbonization escaping to the outside buffer the expansion and contraction of the silicon particles, it is possible to provide a high-capacity silicon-containing amorphous carbon material. Further, when the gas of the volatile component generated during carbonization escapes to the outside, a gas release path is formed in the particles, and the release path is used as a negative electrode material of a lithium ion secondary battery. It becomes a path for lithium to diffuse.

Also by the above method, the material used for the negative electrode of the lithium ion secondary battery can be easily manufactured.

Further, in the manufacturing method of the present embodiment, the size of the unevenness on the surface of the granulated particles can be adjusted. Specifically, in the granulation process, the granulation time is shortened, the pressure at the time of granulation is lowered, or the raw coke having a larger particle size than the raw coke particles added at the beginning of granulation during the granulation process. By adding particles, the surface irregularities can be increased. On the contrary, by adding the raw coke particles having a particle size smaller than that of the raw coke particles added at the beginning of granulation in the middle of granulation, the unevenness of the surface can be reduced.

-Structure of lithium-ion secondary battery-
FIG. 2 is a diagram showing an example of a lithium ion secondary battery provided with a negative electrode using the silicon-containing amorphous carbon material of the present embodiment.

As shown in the figure, the lithium ion secondary battery 10 according to the present embodiment has a negative electrode 11, a negative electrode current collector 12, a positive electrode 13, a positive electrode current collector 14, and a negative electrode 11 and a positive electrode 13. It is provided with a separator 15 interposed therebetween and an exterior 16 made of an aluminum laminated film or the like.

As the negative electrode 11, for example, a metal foil coated with the amorphous carbon-containing material 1 of the present embodiment on both sides or one side is used. The average particle size and circularity of the coated silicon-containing amorphous carbon material 1 were almost unchanged before and after the battery manufacturing process, and were 5 μm or more and 40 μm or less, and 0.70 or more and 1.0 or less, respectively. ing.

When producing the negative electrode, in addition to the granulated silicon-containing amorphous carbon material, an appropriate amount of a conductive auxiliary agent such as acetylene black (AB) or a binder such as polyvinylidene fluoride (PVdF) is added to N. A paste kneaded with a solvent such as -methyl - 2 - pyrrolidone (NMP) is applied onto the copper foil for current collection.

As for the shapes and constituent materials of the members other than the negative electrode 11, such as the negative electrode current collector 12, the positive electrode 13, the positive electrode current collector 14, the separator 15, and the exterior 16, general materials can be applied.

Since the lithium ion secondary battery according to the present embodiment has a negative electrode coated with the above-mentioned silicon-containing amorphous carbon material, it can be charged and discharged quickly, and has a large capacity and can be charged and discharged. Even if it is repeated, the negative electrode is less likely to collapse. Further, the energy density is high, the irreversible capacitance is kept small, and the cycle characteristics can be improved.

This is an example of a lithium ion secondary battery, and the shape, the number of electrodes, the size, and the like of each member may be appropriately changed.

Hereinafter, the invention according to the present application will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

-Explanation of measurement method-
(A) Measurement of optical isotropic structure ratio of raw material Place a small amount of observation sample in the bottom of a plastic sample container and cold-embedded resin (trade name: cold-embedded resin # 105, manufacturer: Japan Composite). (Co., Ltd.) and a curing agent (trade name: curing agent (M agent), manufacturing company: Nippon Oil & Fats Co., Ltd.) are slowly poured in and allowed to stand to solidify. Next, the solidified sample is taken out, and the surface to be measured is polished using a polishing plate rotary polishing machine. Polishing is performed so that the polished surface is pressed against the rotating surface. The rotation of the polishing plate is 1000 rpm. The number of the polishing plate is # 500, # 1000, # 2000 in this order, and finally, mirror polishing using alumina (trade name: Baikalocks type 0.3CR, particle size 0.3 μm, manufacturer: Baikowski). do. The polished sample was observed using a polarizing microscope (manufactured by Nikon Corporation) having a magnification of 500 times at observation angles of 0 degrees and 45 degrees, and each image was taken into a Keyence digital microscope VHX-2000.

For each of the two captured images, a square area (100 μm square) was cut out from the same point, and the following analysis was performed on all the particles within that range to obtain the average value.

The color of the optically anisotropic domain changes depending on the orientation of the crystallites. Optical isotropic domains, on the other hand, always show the same color. Using this property, the portion where the color does not change is extracted by a binarized image, and the area ratio of the optically isotropic portion is calculated. When binarizing, the part where the threshold value is 0 to 34 and the part where the threshold value is 239 to 255 are set as a pure macender. The black part was treated as a void.
(B) Measurement of Transition Metal Content in Raw Material The coke used as a raw material was quantitatively analyzed using a Hitachi ratio beam spectrophotometer U-5100 according to the emission spectrophotometric method.
(C) Measurement of average particle size Measurement was performed using a laser diffraction / scattering type particle size distribution measuring device LMS-2000e (manufactured by Malvern).
(D) Measurement of BET specific surface area The BET specific surface area was measured using a multi-sorb (manufactured by Malvern).
(E) Measurement of true density The true density measured by the gas substitution method was measured with a multi-volume density meter No. 1305 (manufactured by Shimadzu Corporation) using helium gas.
(F) Measurement of tap density The tap density was measured according to the method described in JIS K5101-12-2, except that the number of taps was 600.
(G) Measurement of oxygen content of amorphous carbon material The oxygen content in the sample was quantitatively analyzed by the Inert gas melting-infrared absorption method.
(H) Measurement of Silicon Content of Amorphous Carbon Material The sample was incinerated at 1050 ° C., and the remaining amount was used as the silicon content to calculate the silicon content. The O / Si ratio is determined based on the molar concentration in the sample obtained from the oxygen content and the silicon content, respectively.
(I) Measurement of circularity and degree of unevenness Scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies Corporation) disperses and fixes the sheet so that the particles are not stacked and the flat particles are arranged so that the flat surfaces are arranged in parallel with the sheet. ) Was taken from directly above the sheet, and the image was analyzed by A-kun (manufactured by Asahi Kasei Engineering Co., Ltd.). In this example and the comparative example, the projected area and the projected peripheral length were measured for 300 particles, respectively, and the circularity and the degree of unevenness were calculated to obtain the average value of the circularity and the average value of the degree of unevenness.
(J) Cross-sectional observation of particles The cross-sectional photograph of the particles was taken by treating the particles embedded in the resin with a cross-section polisher (CP) and taking a picture with a scanning electron microscope (S-4800, manufactured by Hitachi High-Tech).
(K) Measurement of transition metal content of raw coke and amorphous carbon material Transition of vanadium and the like contained in a sample by ICP (inductively coupled high frequency plasma emission spectrometry) method using SPS-5000 (manufactured by Seiko Denshi Kogyo). The metal was quantitatively analyzed.
(L) Battery fabrication and evaluation test for half-cell evaluation Single-pole battery evaluation was performed using a CR2032 coin cell.

Preparation of paste for making electrode sheet:
0.044 parts by weight of acetylene black (AB) and 0.066 parts by weight of KF polymer (polyvinylidene fluoride (PVdF)) manufactured by Kureha Chemical Co., Ltd. are added to 1 part by weight of the sample, and N-methylpyrrolidone (NMP) is used as a solvent for the planeta. After kneading with a Lee mixer, it was applied to Cu metal foil and dried. This sheet was rolled and punched to a predetermined size to prepare an electrode for evaluation. Metallic lithium was used as the counter electrode, and a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in which 1 mol / l LiPF ₆ was dissolved (1: 2 in volume ratio) was used as the electrolytic solution. The following coin cells were assembled in a dry argon atmosphere with a dew point of −80 ° C. or lower.

Unipolar charge / discharge test:
For charging, constant current charging (CC charging) was performed at 0.25 mA up to 10 mV, and charging was completed when the current decreased to 0.025 mA. The discharge was constant current discharge (CC discharge) at 0.25 mA and cut off at 1.5 V. This charging / discharging was repeated for 10 cycles.

-Preparation of silicon-containing amorphous carbon material according to Examples and Comparative Examples-
In the following examples and comparative examples, coke A, which is a petroleum-based non-needle-like coke, or coke B, which is a petroleum-based needle-like coke, was used as the raw material coke. Table 1 shows the isotropic texture of coke A and B, the transition metal content, and the vanadium content. Coke A had a much higher transition metal content and vanadium content than coke B.

Next, the manufacturing conditions in the following Examples and Comparative Examples are summarized in Table 2. Table 3 shows the results of measuring each parameter of the carbon materials produced in these Examples and Comparative Examples.

<Example 1>
Raw coke A was pulverized and classified so that D50 was 5.7 μm, and raw coke particles and silicon dioxide particles were mixed and dry granulation was performed by the above method. The particle size of the silicon dioxide particles was 20 to 30 nm. When the sum of the volumes of the silicon dioxide particles and the raw coke particles was 100%, the amount of the silicon dioxide particles added was 50% by volume.

The raw coke particles and a part of the silicon dioxide particles were charged into COMPOSI CP15 type (manufactured by Nippon Coke Industry Co., Ltd.) to start the spheroidizing treatment at a low speed, and the entire amount of the silicon dioxide particles was charged in several times. After the total amount was charged, the treatment was carried out for 120 minutes at a peripheral speed of 80 m / s to obtain granulated particles.

Next, the granulated particles were carbonized at 1000 ° C. with a holding time (carbonization time) at the maximum temperature of 5 hours.

The D50 of the amorphous carbon material according to Example 1 thus obtained is 13.5 μm, the BET is 1.5 m ² / g, the circularity is 0.970, and the value of the degree of unevenness is high. Was 0.985. The true density was 2.02 g / cm ³ , and the O / Si ratio (molar ratio) was 1.03. The Si content in the obtained carbon material was 15.0 wt%.

<Example 2>
Raw coke B was pulverized and classified so that D50 was 9.6 μm, raw coke particles and silicon dioxide particles were mixed, and dry granulation and carbonization were performed by the above-mentioned method. At this time, the amount of silicon dioxide particles added was set to 53% by volume. The whole amount of silicon dioxide particles was added in several batches. After the total amount was charged, granulation and carbonization were performed under the same conditions as in Example 1 except that the peripheral speed was set to 80 m / s and the treatment time was set to 120 minutes.

The D50 of the amorphous carbon material according to Example 2 thus obtained is 24.9 μm, the BET is 8.1 m ² / g, the circularity is 0.953, and the value of the degree of unevenness is high. Was 0.976. The true density was 2.10 g / cm ³ , and the O / Si ratio (molar ratio) was 1.21. The Si content in the obtained carbon material was 14.5 wt%.

<Example 3>
Raw coke A was pulverized and classified so that D50 was 7.9 μm, raw coke particles and silicon dioxide particles were mixed, and dry granulation and carbonization were performed by the above-mentioned method. At this time, the amount of silicon dioxide particles added was set to 53% by volume. The whole amount of silicon dioxide particles was added in several batches. After the total amount was charged, granulation and carbonization were performed under the same conditions as in Example 1 except that the peripheral speed was 70 m / s and the treatment time was 120 minutes.

The D50 of the amorphous carbon material according to Example 3 thus obtained is 27.1 μm, the BET is 10.7 m ² / g, the circularity is 0.901, and the value of the degree of unevenness is high. Was 0.949. The true density was 2.07 g / cm ³ , and the O / Si ratio (molar ratio) was 1.29. The Si content in the obtained carbon material was 14.4 wt%.

<Example 4>
Raw coke A was pulverized and classified so that D50 was 7.9 μm, raw coke particles and silicon dioxide particles were mixed, and dry granulation and carbonization were performed by the above-mentioned method. At this time, the amount of silicon dioxide particles added was set to 50% by volume. The whole amount of silicon dioxide particles was added in several batches. After the total amount was charged, granulation was carried out under the same conditions as in Example 1 except that the peripheral speed was 70 m / s and the processing time was 180 minutes.

The D50 of the amorphous carbon material according to Example 4 thus obtained is 21.1 μm, the BET is 1.6 m ² / g, the circularity is 0.947, and the value of the degree of unevenness is high. Was 0.973. The true density was 2.02 g / cm ³ , and the O / Si ratio (molar ratio) was 1.31. The Si content in the obtained carbon material was 15.0 wt%. The tap density was 1.2 g / cm ³ .

<Example 5>
Raw coke A was pulverized and classified so that D50 was 4.8 μm, raw coke particles and silicon dioxide particles were mixed, and dry granulation and carbonization were performed by the above-mentioned method. At this time, the amount of silicon dioxide particles added was set to 50% by volume. The whole amount of silicon dioxide particles was added in several batches. Granulation and carbonization were carried out under the same conditions as in Example 1 except that the peripheral speed after charging the entire amount was 80 m / s and the treatment time was 210 minutes.

The D50 of the amorphous carbon material according to Example 5 thus obtained is 9.6 μm, the BET is 2.5 m ² / g, the circularity is 0.963, and the value of the degree of unevenness is high. Was 0.981. The true density was 2.04 g / cm ³ , and the O / Si ratio (molar ratio) was 1.27. The Si content in the obtained carbon material was 15.1 wt%. The tap density was 1.17 g / cm ³ .

<Example 6>
Example 6 was an amorphous carbon material obtained by mixing the amorphous carbon material according to Example 4 and the amorphous carbon material according to Example 5 at a weight ratio of 7: 3. The tap density of the obtained carbon material was 1.27 g / cm ³ .

<Example 7>
Raw coke A was pulverized and classified so that D50 was 5.8 μm, raw coke particles and silicon dioxide particles were mixed, and dry granulation and carbonization were performed by the above-mentioned method. At this time, the amount of the silicon dioxide particles added was 61% by volume, and the total amount of the silicon dioxide particles was added in several batches. Granulation and carbonization were carried out under the same conditions as in Example 1 except that the peripheral speed after charging the entire amount was 80 m / s and the treatment time was 120 minutes.

The D50 of the amorphous carbon material according to Example 7 thus obtained is 12.1 μm, the BET is 5.0 m ² / g, the circularity is 0.967, and the value of the degree of unevenness is high. Was 0.983. The true density was 2.09 g / cm ³ , and the O / Si ratio (molar ratio) was 1.14. The Si content in the obtained carbon material was 20.0 wt%.

<Example 8>
Raw coke A was pulverized and classified so that D50 was 5.7 μm, raw coke particles and silicon dioxide particles were mixed, and dry granulation and carbonization were performed by the above-mentioned method. At this time, the amount of the silicon dioxide particles added was 80% by volume, and the total amount of the silicon dioxide particles was added in several batches. Granulation and carbonization were carried out under the same conditions as in Example 1 except that the peripheral speed after charging the entire amount was 80 m / s and the treatment time was 60 minutes.

The D50 of the amorphous carbon material according to Example 8 thus obtained is 13.6 μm, the BET is 27.2 m ² / g, the circularity is 0.967, and the value of the degree of unevenness is high. Was 0.983. The true density was 2.19 g / cm ³ , and the O / Si ratio (molar ratio) was 1.26. The Si content in the obtained carbon material was 35.0 wt%.

Note that FIG. 1 already described is a diagram showing a micrograph of a cross section of the amorphous carbon material according to the present embodiment taken by the above method. From the figure, it can be seen that the amorphous carbon material according to the present embodiment has a high circularity and has voids 20 formed inside.

<Examples 9 and 10>
Coke A was pulverized and classified so that D50 was 4.8 μm, mixed with crushed silicon particles so that the particle size was 400 nm, and dry granulation and carbonization were performed by the above-mentioned method. At this time, in Example 9, the amount of silicon particles added was 7% by volume, and in Example 10, the amount of silicon particles added was 28% by volume. The entire amount of silicon particles was added in several batches. After charging the entire amount of silicon particles, in Example 9, the peripheral speed was set to 80 m / s and the processing time was set to 420 minutes, and in Example 10, the peripheral speed was set to 80 m / s and the processing time was set to 390 minutes. Granulation and carbonization were performed under the same conditions as above.

The D50 of the amorphous carbon material according to Example 9 thus obtained is 8.8 μm, the BET is 1.8 m ² / g, the circularity is 0.966, and the value of the degree of unevenness is high. Was 0.981. The true density was 1.80 g / cm ³ , and the O / Si ratio (molar ratio) was 1.18. The Si content in the obtained carbon material was 3.0 wt%.

Further, the D50 of the amorphous carbon material according to Example 10 is 8.8 μm, the BET is 9.5 m ² / g, the circularity is 0.963, and the value of the degree of unevenness is 0.982. there were. The true density was 1.94 g / cm ³ , and the O / Si ratio (molar ratio) was 1.17. The Si content in the obtained carbon material was 11.7 wt%.

FIG. 3 is a diagram showing a micrograph of a cross section of the amorphous carbon material according to the present embodiment taken by the above method. From the figure, it can be seen that the amorphous carbon material according to the present embodiment has voids 20 formed therein and contains silicon oxide particles 5.

<Example 11>
Raw coke B was pulverized and classified so that D50 was 9.6 μm, raw coke particles and silicon dioxide particles were mixed, and dry granulation and carbonization were performed by the above-mentioned method. At this time, the amount of silicon dioxide particles added was set to 53% by volume. The whole amount of silicon dioxide particles was added in several batches. After the total amount was charged, granulation and carbonization were carried out under the same conditions as in Example 1 except that the peripheral speed was set to 80 m / s and the treatment time was set to 105 minutes.

The D50 of the amorphous carbon material according to Example 11 thus obtained is 24.8 μm, the BET is 8.8 m ² / g, the circularity is 0.921, and the value of the degree of unevenness is high. Was 0.961. The true density was 2.10 g / cm ³ , and the O / Si ratio (molar ratio) was 1.22. The Si content in the obtained carbon material was 10.0 wt%.

<Example 12>
Raw coke A was pulverized and classified so that D50 was 5.7 μm, raw coke particles and silicon dioxide particles were mixed, and dry granulation and carbonization were performed by the above-mentioned method. At this time, the amount of silicon dioxide particles added was 80% by volume. The whole amount of silicon dioxide particles was added in several batches. Granulation and carbonization were carried out under the same conditions as in Example 1 except that the peripheral speed after charging the entire amount was 80 m / s, the treatment time was 60 minutes, and the carbonization temperature was 1200 ° C.

The D50 of the amorphous carbon material according to Example 12 thus obtained is 14.0 μm, the BET is 32.5 m ² / g, the circularity is 0.965, and the value of the degree of unevenness is high. Was 0.979. The true density was 2.18 g / cm ³ , and the O / Si ratio (molar ratio) was 1.59. The Si content in the obtained carbon material was 35.2 wt%.

Further, FIG. 4 is a diagram showing a micrograph of a cross section of the amorphous carbon material according to Example 12 taken by the above method. From the figure, it can be seen that the amorphous carbon material according to the present embodiment has a high circularity and has voids 20 formed inside.

<Comparative Example 1>
Raw coke A was pulverized and classified so that D50 was 6.0 μm, and dry granulation was performed using only raw coke particles. In the granulation, the peripheral speed was set to 80 m / s and the processing time was set to 240 minutes. Next, the granulated particles were carbonized under the conditions that the holding time at 1000 ° C. and the maximum temperature reached was 5 hours.

The D50 of the amorphous carbon material according to Comparative Example 1 thus obtained is 14.6 μm, the BET is 0.3 m ² / g, the circularity is 0.963, and the value of the degree of unevenness is high. Was 0.981. Met. The true density was 1.76 g / cm ³ , and the O / Si ratio (molar ratio) was 1.44.

<Comparative Example 2>
Graphite having a D50 of 8.5 μm was mixed with silicon dioxide particles to perform dry granulation and carbonization by the method described above. At this time, the amount of silicon dioxide particles added was set to 63% by volume. The whole amount of silicon dioxide particles was added in several batches. After the total amount was charged, granulation and carbonization were performed under the same conditions as in Example 1 except that the peripheral speed was 70 m / s and the treatment time was 120 minutes.

The carbon material according to Comparative Example 2 thus obtained was not sufficiently composited, and some of the silicon dioxide particles did not adhere to graphite. The BET was 33.2 m ² / g, the circularity was 0.812, and the value of the degree of unevenness was 0.899. The true density was 2.31 g / cm ³ , and the O / Si ratio (molar ratio) was 1.96. The Si content in the obtained carbon material was 14.8 wt%.

<Comparative Example 3>
Coke A was pulverized and classified so that D50 was 4.8 μm, and raw coke particles and silicon dioxide particles were manually mixed. The amount of silicon particles added to the coke particles was 50% by volume. No granulation treatment was performed, and carbonization treatment was performed under the conditions of 1000 ° C. for 5 hours.

The BET of the amorphous carbon material according to Comparative Example 3 thus obtained was 39.1 m ² / g, the circularity was 0.745, and the value of the degree of unevenness was 0.856. The true density was 2.14 g / cm ³ , and the O / Si ratio (molar ratio) was 1.88.

For the carbon materials according to the examples and comparative examples produced as described above, the initial charge capacity and the initial discharge capacity were measured, and the initial efficiency was calculated. Further, the ratio of the discharge capacity after 10 cycles of charge / discharge to the initial discharge capacity was defined as the cycle maintenance rate.

Regarding Comparative Example 3, an attempt was made to prepare an electrode by the same method as in Examples 1 to 12 and Comparative Examples 1 and 2, but since the active material layer was peeled off from the copper foil, acetylene black was added to 1 part by weight of the sample. The composition is changed so as to add 0.047 parts by weight and 0.116 parts by weight of PVdF.

-Measurement result-
Table 4 shows the test results for the carbon materials according to Examples 1 to 10 and 12 and Comparative Examples 1 to 3.

As shown in Table 4, the carbon materials according to Examples 1 to 10 and 12 all have an initial discharge capacity sufficiently exceeding 300 mAh, a cycle maintenance rate of 80% or more, and carbon containing silicon oxide. As a material, it could be made sufficiently high.

Further, for example, since both the carbon material according to Example 1 and the carbon material according to Comparative Example 1 use raw coke as a raw material, the obtained carbon material contains easily graphitized amorphous carbon. .. However, although the initial efficiency of the carbon material according to Example 1 is slightly lower than that of the carbon material according to Comparative Example 1, the initial discharge capacity is significantly increased and the deterioration of cycle characteristics is suppressed to a small extent. It was confirmed that it was done.

On the other hand, when graphite was used as the carbon raw material (Comparative Example 2), the carbon material and the silicon material could not be combined even if the spheroidizing treatment was performed, and the effect of improving the initial discharge capacity was not observed. .. It is considered that this is because the silicon dioxide particles were not reduced in the carbonization step because the graphite did not contain a volatile component, and the effect of improving the capacity of silicon could not be sufficiently obtained.

Further, when the granulation treatment is not performed (Comparative Example 3), for example, even if the amount of silicon dioxide particles added is the same as that of Example 5, the effect of improving the capacity of silicon cannot be sufficiently obtained. Was confirmed. It is considered that this is because the raw coke particles and the silicon dioxide particles were not composited, and the volatile matter generated from the raw coke during the carbonization treatment could not effectively reduce the silicon dioxide.

Further, from the results of Example 2, it was found that even when petroleum-based needle-shaped coke is used as a carbon raw material, an excellent effect can be obtained as in the case of using petroleum-based non-needle-shaped coke as a carbon raw material. rice field.

From the results of Examples 9 and 10, even if crushed silicon particles are used as the silicon raw material, the initial discharge capacity can be increased as compared with the case where the silicon raw material is not used (Comparative Example 1), and the initial efficiency is high. It was confirmed that the cycle characteristics were maintained and the deterioration of the cycle characteristics was suppressed to a small extent.

In the amorphous carbon materials according to Examples 1 to 12, the O / Si ratio is 0.2 or more and less than 2.0, and the silicon content exceeds 1% by weight and 50% by weight. It was as follows. The true densities are 1.8 g / cm ³ or more and 2.2 g / cm ³ or less, which are larger than the case where no silicon raw material is used (Comparative Example 1), and the case where graphite is used as a carbon raw material (Comparative Example). It was smaller than 2).

Further, in Example 6 in which the carbon material according to Example 4 and the carbon material according to Example 5 were mixed at a weight ratio of 7: 3, silicon oxide was composited into graphitized amorphous carbon by granulation. By using a mixture of two types of particles having different particle sizes, it is possible to obtain a carbon material capable of increasing the tap density and increasing the electrode density without impairing the effect of improving the cycle characteristics of the present invention. rice field.

Further, the transition metal content of the amorphous carbon materials according to Examples 1 to 12 was 700 ppm or more and 2500 ppm or less in each case, but it was the same as the transition metal content contained in the carbon materials according to Comparative Examples 1 to 3. There was no significant difference between them.

The silicon-containing amorphous carbon material according to an example of the present embodiment is useful as a negative electrode material for a lithium ion secondary battery or a lithium ion capacitor used in, for example, an electric vehicle, a power storage system for solar power generation, wind power generation, and the like. Is.

1 Silicon-containing amorphous carbon material 4 Amorphous carbon 5 Silicon oxide particles 10 Lithium-ion secondary battery 11 Negative electrode 12 Negative electrode current collector 13 Positive electrode 14 Positive electrode current collector 15 Separator 16 Exterior 20 Void

Claims (7)

Equipped with easily graphitized amorphous carbon with voids ,
A silicon-containing amorphous carbon material containing silicon oxide particles represented by SiO _x (0 <x <2) in the graphitized amorphous carbon.
The silicon content is 1% by weight or more and 50% by weight or less.
A silicon-containing amorphous carbon material having a circularity of 0.70 or more and 1.0 or less and a BET specific surface area of 1.5 to 32.5 m ² / g. In the silicon-containing amorphous carbon material according to claim 1,
A silicon-containing amorphous carbon material having a molar ratio (O / Si) of silicon content to oxygen content of 0.2 or more and less than 2.0. In the silicon-containing amorphous carbon material according to claim 1 or 2.
A silicon-containing amorphous carbon material having a true density of 1.8 g / cm ³ or more and 2.2 g / cm ³ or less. The silicon-containing amorphous carbon material according to any one of claims 1 to 3.
A silicon-containing amorphous carbon material having a total transition metal content of 700 ppm or more and 2500 ppm or less. The silicon-containing amorphous carbon material according to any one of claims 1 to 4.
A silicon-containing amorphous carbon material having an average particle size of 5 μm or more and 40 μm or less. In the silicon-containing amorphous carbon material according to any one of claims 1 to 5, the SiO _x A silicon-containing amorphous carbon material, characterized in that silicon oxide particles represented by (0 <x <2) are present in a dispersed state. A lithium ion secondary battery comprising a negative electrode having the silicon-containing amorphous carbon material according to any one of claims 1 to 6 .

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