JP2011076744A - Lithium secondary battery negative electrode mixture, lithium secondary battery negative electrode, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery negative electrode mixture, a lithium secondary battery negative electrode, and a lithium secondary battery capable of further improving charging-discharging cycle properties of a lithium ion secondary battery. <P>SOLUTION: The lithium secondary battery negative electrode mixture comprises a negative electrode active material and a binder. The negative electrode active material comprises: composite particles consisting of silicon-containing particles, which contain a silicon-alloy, oxide, nitride, or carbide capable of storing/releasing lithium ions, and a resin carbon material surrounding the silicon-containing particles; and a silicon-containing grid-shaped structure binding onto the surfaces of the composite particles and comprising nanofibers and/or nanotubes surrounding the composite particles. The binder comprises alkoxy group-bonded cellulose, hydroxyalkyl group-bonded cellulose, or carboxyalkyl group-bonded cellulose. The lithium secondary battery negative electrode includes the negative electrode mixture, and the lithium secondary battery includes the negative electrode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery negative electrode mixture, a lithium secondary battery negative electrode, and a lithium secondary battery.

  As electronic devices become more portable and cordless, lithium secondary batteries are required to be smaller and lighter or have higher energy density. In order to increase the density of lithium secondary batteries, it is known to employ a negative electrode mixture that uses silicon, tin, germanium, magnesium, lead, and aluminum, or an oxide or alloy thereof, which is alloyed with lithium, as a negative electrode active material. It has been. However, the negative electrode mixture as described above expands in volume during charging when the negative electrode active material used occludes lithium ions, and conversely shrinks in volume during discharging to release lithium ions. For this reason, it is known that the volume of the negative electrode changes as the charge / discharge cycle repeats, and as a result, the negative electrode active material is pulverized and dropped from the electrode, causing the negative electrode to collapse.

  In order to overcome the above-mentioned problems, various methods and means have been studied. However, when a metal and an oxide are used as the negative electrode active material of the lithium secondary battery negative electrode mixture, stabilizing the charge / discharge characteristics is not possible. The current situation is difficult. Thus, for example, as a study on the negative electrode material, as disclosed in Japanese Patent Application Laid-Open No. 2007-214137, as a negative electrode material for a lithium secondary battery having excellent charge / discharge cycle characteristics, a metal capable of forming a lithium alloy is used. A negative electrode active material in which the particle surface is coated with an organic substance has been proposed. According to the negative electrode material described in Japanese Patent Application Laid-Open No. 2007-214137, it is described that a metal particle having an average primary particle diameter of 500 to 1 nm is used in order to suppress expansion that occurs when occlusion of lithium ions. Yes. However, it is difficult to suppress the expansion of the metal particles during lithium occlusion during charging only by reducing the primary particle size of the metal particles used.

  Further, for example, as disclosed in JP 2007-30569 A, a negative electrode comprising a metal nanocrystal having a particle size of 20 nm or less and a carbon coating layer formed on the surface of the metal nanocrystal. Active materials have been proposed. According to the negative electrode described in JP-A-2007-305569, a lithium secondary battery having a high capacity and a good capacity retention rate can be obtained. As a technique for extending the life of the described negative electrode, a metal crystal is made into nanoparticles, and an alkyl group having 2 to 10 carbon atoms, an arylalkyl group having 3 to 10 carbon atoms, or an alkylaryl having 3 to 10 carbon atoms It is characterized in that the surface of the metal crystal is coated with an organic molecule containing a group or an alkoxy group having 2 to 10 carbon atoms. The formation of the carbonized layer formed on the surface of the metal crystal described in Japanese Patent Application Laid-Open No. 2007-305569 is formed by a vapor phase growth method and is essentially different from the present invention.

  Further, for example, as disclosed in JP-A-8-241715, a negative electrode active material characterized by mixing a metal salt and an organic substance serving as a carbon source and firing in a non-oxidizing atmosphere has been proposed. However, the negative electrode active material described in JP-A-8-241715 contains only a metal content of up to 40 wt%. Therefore, the amount of the metal introduced into the negative electrode active material occludes lithium ions is small. Further, since the amount of occlusion is small, the metal does not easily expand, and the negative electrode is difficult to collapse. However, it is difficult to increase the capacity of the negative electrode active material by the method disclosed in JP-A-8-241715.

JP 2007-214137 A JP 2007-305568 A JP-A-8-241715

  The negative electrode for a lithium secondary battery using a lithium secondary battery negative electrode mixture containing a negative electrode active material using a metal and an oxide described in each of the above publications and a binder, and alloyed with lithium. By covering or treating the metal to be coated with carbon, the volume expansion / contraction of the negative electrode active material due to the charge / discharge cycle is suppressed to some extent. However, in the inventions described in the above publications, it is not possible to completely prevent the negative electrode collapse due to the pulverization of the negative electrode active material due to the charge / discharge cycle. Furthermore, none of the above examples describes an attempt to improve the charge / discharge cycle in the study of a binder that exhibits a synergistic effect with the developed negative electrode active material, and the lithium secondary described in each of the above-mentioned publications. It cannot be said that the battery negative electrode has sufficient charge / discharge cycle characteristics. The present invention provides a lithium secondary battery negative electrode mixture, a lithium secondary battery negative electrode, and a lithium secondary battery using the same, which are intended to further improve the charge / discharge cycle characteristics of the lithium ion secondary battery.

The above object is achieved by the following items (1) to (13).
(1) A lithium secondary battery negative electrode mixture comprising a negative electrode active material (A) and a binder (B), wherein the negative electrode active material (A) is silicon capable of occluding and releasing lithium ions. Composite particles comprising silicon-containing particles containing an alloy, oxide, nitride, or carbide of the above, and a resin carbon material surrounding the silicon-containing particles, and bonded to the surface of the composite particles and surrounding the composite particles The binder (B) contains alkoxy group-bonded cellulose, hydroxyalkyl group-bonded cellulose or carboxyalkyl group-bonded cellulose. What is claimed is: 1. A lithium secondary battery negative electrode mixture,

(2) The lithium secondary battery negative electrode mixture according to item (1), wherein 4 to 20 parts by mass of the binder (B) is used with respect to 100 parts by mass of the negative electrode active material (A). .

(3) The lithium secondary as described in item (1) or (2), wherein the binder (B) contains carboxymethylcellulose having an etherification degree of 0.6 to 1.5. Battery negative electrode mixture.

(4) The resin carbon material has pores and the volume of the pores having a pore diameter of 0.25 to 0.45 nm calculated by a micropore method using a nitrogen gas adsorption method is 0.00. The lithium secondary battery negative electrode mixture according to any one of Items (1) to (3), which is 0001 to 1.5 cm ² / g.

(5) Any one of items (1) to (4), wherein the volume of the pores having a pore diameter of 0.25 to 0.45 nm is 0.0005 to 1.0 cm ² / g. The lithium secondary battery negative electrode mixture as described in the paragraph.

(6) The resin carbon material has pores, and the volume of the pores having a pore diameter of 0.25 to 0.45 nm calculated by a micropore method using a nitrogen gas adsorption method is The lithium secondary battery negative electrode mixture according to any one of items (1) to (5), which is 25% by volume or more based on the total pore volume of the resin carbon material.

(7) The volume of the pores having a pore diameter of 0.25 to 0.45 nm is 30% by volume or more based on the total pore volume of the resin carbon material, The lithium secondary battery negative electrode mixture according to any one of (6).

(8) The lithium secondary battery negative electrode mixture according to any one of (1) to (7), wherein the network structure further contains carbon.

(9) The lithium secondary battery negative electrode mixture according to any one of (1) to (8), wherein the silicon-containing particles contain silicon oxide.

(10) In the negative electrode active material (A), the content of silicon alloy, oxide, nitride or carbide is in the range of 5 to 60 mass%, according to the items (1) to (9) The lithium secondary battery negative electrode mixture according to any one of the above items.

(11) The lithium secondary battery negative electrode mixture according to any one of (1) to (10), wherein the negative electrode active material (A) has an average particle diameter in the range of 3 μm to 15 μm. .

(12) A lithium secondary battery negative electrode comprising the lithium secondary battery negative electrode mixture according to any one of items (1) to (11).

(13) A lithium secondary battery including the lithium secondary battery negative electrode according to item (12).

  According to the negative electrode mixture of the lithium secondary battery of the present invention, the pulverization of the negative electrode active material due to the charge / discharge cycle is suppressed by the extremely high synergistic effect of the negative electrode active material and the binder, and nanofibers and / or nanotubes By maintaining the adhesion between the anode and the composite particles, the negative electrode active material can be prevented from falling off from the electrode, and the lithium secondary battery negative electrode mixture and lithium secondary battery exhibiting unprecedented excellent charge / discharge cycle characteristics. A secondary battery negative electrode and a lithium secondary battery using the same are provided.

1 is a scanning electron microscope (SEM) photograph of the carbon material obtained in Example 1. FIG. FIGS. 2A and 2B are graphs showing the results of elemental analysis by an energy dispersive X-ray analyzer (EDX) of different portions of the nanofibers observed by SEM.

  The present invention is a lithium secondary battery negative electrode mixture containing a negative electrode active material (A) and a binder (B), and the negative electrode active material (A) can occlude and release lithium ions. Composite particles comprising silicon-containing particles containing an alloy, oxide, nitride, or carbide of silicon, and a resin carbon material surrounding the silicon-containing particles, and bonded to the surface of the composite particles, and the composite particles It includes a silicon-containing network structure composed of surrounding nanofibers and / or nanotubes, and the binder (B) comprises alkoxy group-bonded cellulose, hydroxyalkyl group-bonded cellulose or carboxyalkyl group-bonded cellulose. It is a lithium secondary battery negative electrode mixture characterized by containing, and as described later, as a negative electrode active material for a lithium ion secondary battery, The negative electrode active material (A) of the present invention can be obtained by using a negative electrode mixture in which the binder (B) of the present invention is further combined with the negative electrode active material (A) of the present invention, which realizes the electric cycle characteristics. Disclosed is a technology relating to a lithium secondary battery negative electrode mixture, a lithium secondary battery negative electrode, and a lithium secondary battery that realize extremely excellent charge / discharge cycle characteristics by the synergistic effect of the binder (B).

First, the negative electrode active material (A) of the present invention will be described in detail.
The negative electrode active material (A) according to the present invention comprises silicon-containing particles containing a silicon alloy, oxide, nitride or carbide capable of occluding and releasing lithium ions, and a resin carbon material surrounding the silicon-containing particles. And a network structure composed of nanofibers and / or nanotubes (hereinafter referred to as “nanofibers”) bound to the surface of the composite particles and surrounding the composite particles, The network structure includes silicon. The resin carbon material and the network structure are formed by carbonizing a carbon precursor in the presence of a catalyst if necessary. Furthermore, the network structure is apparently formed starting from the surface of the composite particles composed of silicon-containing particles and a resin carbon material.

Although not intended to be bound by any particular theory, the network structure composed of nanofibers or the like in the present invention is made of a silicon alloy, oxide, nitride or carbide capable of occluding and releasing lithium ions. It is considered to be entangled with the network structure caused by another adjacent particle because it is bonded to the surface of the composite particle composed of the silicon-containing particle containing and the resin carbon material surrounding the silicon-containing particle. . For this reason, the adhesion between the nanofibers and the composite particles becomes high, and the nanofibers and the like are hardly separated from the composite particles even during the volume expansion and contraction of the silicon-containing particles due to charge and discharge. In addition, because the network structure of a plurality of adjacent particles is entangled with each other to form a stretchable network structure as a whole, the conductivity of the entire negative electrode is maintained during the volume expansion and contraction of silicon-containing particles due to charge and discharge. Is done. And by maintaining the electroconductivity of a negative electrode, the resistance change accompanying charging / discharging can be suppressed and it becomes excellent in cycling characteristics. Such a network structure peculiar to the present invention cannot be formed only by adding carbon nanofibers or the like separately formed by a vapor phase method as in the prior art. The network structure is apparently formed starting from the surface of the composite particle, but since the network structure contains silicon, the true starting point of the network structure is considered to be the surface of the silicon-containing particle.

  The nanofibers and the like constituting the network structure according to the present invention include silicon-containing fibers having a fiber diameter of less than 1 μm. Although it is not necessary to strictly distinguish between nanofibers and nanotubes, in the present specification, those having a fiber diameter of 100 nm or more are specifically defined as nanofibers, and those having a fiber diameter of 100 nm or less are defined as nanotubes. The elemental composition of the nanofiber or the like according to the present invention is assumed to be silicon carbide, silicon nitride, silicon carbonitride, or any combination thereof depending on the original composition of the silicon-containing particles. The elemental composition of the nanofiber or the like according to the present invention may be uniform throughout the nanofiber or the like, or may vary depending on the location. Furthermore, it is preferable that the nanofibers and the like constituting the network structure according to the present invention include carbon nanofibers and / or carbon nanotubes (hereinafter referred to as “carbon nanofibers”). The presence of carbon nanofibers is expected to improve the conductivity between composite particles including silicon-containing particles.

The resin carbon material according to the present invention has pores for allowing lithium ions to enter. Such pores are places where nitrogen molecules can enter and adsorb to the negative electrode active material (A) when nitrogen gas is used as a probe molecule. The size of the pores (pore diameter) is preferably in the range of 0.25 to 0.45 nm. If the pore diameter is less than 0.25 nm, the lithium ion intrusion is hindered by the shielding effect of the carbon atoms of the resin carbon material by the electron cloud, so that the charge capacity decreases. On the other hand, when the pore diameter exceeds 0.45 nm, solvated lithium ions are trapped in the pores, so that the initial efficiency (discharge capacity / charge capacity) decreases. The pore diameter is a value measured by a micropore method (apparatus: manufactured by Shimadzu Corporation; pore distribution measuring device “ASAP-2010”).

The total pore volume and pore volume of the resin carbon material according to the present invention are measured as a space where nitrogen molecules can enter when nitrogen gas is used as a probe molecule, and are calculated by a micropore method using a nitrogen gas adsorption method. The The pore volume here means the pore volume at each pore diameter. Specifically, the pore volume at each pore diameter is calculated from the amount of nitrogen gas adsorbed by each relative pressure at the time of measurement. The pore volume of the resin carbon material according to the present invention having a pore diameter of 0.25 to 0.45 nm is preferably within a range of 0.0001 to 1.5 cm ³ / g, more preferably 0.0005 to 1.0 cm. Within the range of ³ / g. When the pore volume having a pore diameter of 0.25 to 0.45 nm is 1.5 cm ³ / g or less, the decomposition reaction of the electrolytic solution in charge / discharge is suppressed, and the initial charge / discharge characteristics are hardly deteriorated. Moreover, the reduction | decrease of the true density of a resin carbon material is suppressed and it is preferable also at the point which the energy density fall as an electrode is suppressed. On the other hand, when the pore volume having a pore diameter of 0.25 to 0.45 nm is 0.0001 cm ³ / g or more, the site where lithium ions can enter does not decrease and the charge capacity does not decrease, which is preferable. In addition, the resin carbon material has an appropriate density structure, suppresses expansion of the silicon-containing particles, and exhibits good charge / discharge cycle characteristics. The pore volume having a pore diameter of 0.25 to 0.45 nm can be controlled by heat treatment conditions or carbonization treatment conditions (temperature, temperature rising rate, treatment time, treatment atmosphere, etc.) of the resin carbon material described later.

In the resin carbon material according to the present invention, the volume of the pores having a pore diameter of 0.25 to 0.45 nm is preferably 25% by volume or more, more preferably with respect to the total pore volume of the resin carbon material. 30% by volume or more. Here, the total pore volume of the resin carbon material is the pore volume of each pore diameter calculated from the nitrogen gas adsorption amount of each relative pressure in the micropore method with respect to the unit mass of the negative electrode active material (A). Refers to the sum of
When the volume of the pores having a pore diameter of 0.25 to 0.45 nm is 25% by volume or more with respect to the total pore volume, a sufficient charging capacity can be secured, which is preferable.

The shape of the negative electrode active material (A) of the present invention is not particularly limited, and may have any particle shape such as a lump shape, a scale shape, a spherical shape, and a fibrous shape. The negative electrode active material particles preferably have an average particle size of 3 μm or more and 15 μm or less in view of charge / discharge characteristics. More preferably, it is 5 μm or more and 12 μm or less. More preferably, it is 7 μm or more and 10 μm or less. When the average particle diameter is 15 μm or less, the gap between the negative electrode active material particles can be kept small, and when used as the negative electrode active material (A), the density of the negative electrode can be improved. Further, when the average particle diameter is 3 μm or more, when viewed per unit mass, the number of negative electrode active material particles does not increase greatly, and it can be prevented from becoming bulky as a whole, and handling becomes easy.

The definition of the particle diameter in the present invention is a value obtained by calculating the measured amount into the particle diameter using the particle shape and Mie theory, and is referred to as an effective diameter.
In the present invention, the average particle diameter was determined as an average particle diameter D50%, which is 50% in terms of volume measured by the laser diffraction particle size distribution measurement method.

Examples of silicon alloys, oxides, nitrides or carbides constituting the silicon-containing particles according to the present invention include silicon monoxide (SiO), silicon nitride (Si ₂ N ₄ ), silicon carbide (SiC), titanium silicon alloy ( Ti-Si type). Among these, SiO is more preferable because it has a smaller expansion coefficient during charging than the corresponding Si alone.

  The average particle size of the silicon-containing particles according to the present invention is preferably in the range of approximately 0.5 μm to 5 μm. Generally, in order to obtain a high charge / discharge capacity, it is preferable to reduce the average particle size and increase the contact area with lithium ions. However, when the average particle diameter of the silicon-containing particles is 0.5 μm or more, the occlusion amount of lithium ions does not become excessive, and the expansion and contraction of the silicon-containing particles can be suppressed by the network structure, which is preferable. On the other hand, when the average particle diameter of the silicon-containing particles is 5 μm or less, a high charge / discharge capacity can be expressed, which is preferable.

The negative electrode active material (A) in the present invention preferably contains 5 to 60% by mass of a silicon alloy, oxide, nitride or carbide with respect to the negative electrode active material (A). When the content of the silicon alloy, oxide, nitride or carbide is 5% by mass or more, it is possible to increase the occlusion of lithium ions and to obtain a high charge / discharge capacity. On the other hand, when the content is 60% by mass or less, expansion and contraction in the insertion and extraction of lithium ions of silicon can be suppressed by the network structure, and good charge / discharge cycle characteristics can be obtained. Here, the content of the silicon alloy, oxide, nitride or carbide is measured by an ash test method according to JIS K 2272: 1998.

The negative electrode active material (A) according to the present invention is obtained by mixing silicon-containing particles containing an alloy, oxide, nitride, or carbide of silicon capable of occluding and releasing lithium ions with a carbon precursor. It is produced by forming a mixture in which the contained particles are dispersed in the carbon precursor, and then subjecting the mixture to carbonization. By this carbonization treatment, the carbon precursor is converted into a resin carbon material, and a network structure composed of nanofibers or the like surrounding the composite particles composed of the converted resin carbon material and silicon-containing particles is formed on the surface of the composite particles. Formed at the starting point. Furthermore, the negative electrode active material according to the present invention is obtained by mixing silicon-containing particles containing an alloy, oxide, nitride or carbide of silicon capable of occluding and releasing lithium ions, a carbon precursor, and a catalyst. It is also produced by forming a mixture in which the silicon-containing particles and the catalyst are dispersed in the carbon precursor, and then subjecting the mixture to carbonization. By dispersing the catalyst in the carbon precursor and subjecting it to carbonization, it is possible to increase the amount of nanofibers constituting the network structure, particularly carbon nanofibers.

  Examples of the carbon precursor include an easily graphitizable material or a hardly graphitized material selected from the group consisting of petroleum pitch, coal pitch, phenol resin, furan resin, epoxy resin, and polyacrylonitrile. A mixture of an easily graphitizable material and a hardly graphitized material may be used. Moreover, you may include a hardening | curing agent (for example, hexamethylenetetramine) in a phenol resin etc., In that case, a hardening | curing agent can also be a part of carbon precursor.

  When using a catalyst, as an example, at least one element selected from the group consisting of copper (Cu), iron (Fe), cobalt (Co), nickel (Ni), molybdenum (Mo) and manganese (Mn) The thing containing is mentioned. The catalyst element may be contained as an impurity in the carbon precursor, and in that case, it may not be necessary to intentionally prepare and mix a separate catalyst. These catalytic elements are preferably mixed with the particles as a solution so as to form a mixture dispersed in the silicon-containing particles and the carbon precursor. In order to provide such a solution, the catalyst element is preferably prepared as a metal salt compound. Examples of such metal salt compounds include the above-described elements and inorganic acid radicals such as nitrates, sulfates, and hydrochlorides. And salts with organic acid radicals such as salts, carboxylic acids, sulfonic acids and phenols. Further, the solvent used in such a solution may be appropriately selected from water, an organic solvent, and a mixture of water and an organic solvent. Particularly, examples of the organic solvent include ethanol, isopropyl alcohol, toluene, benzene, hexane. , Tetrahydrofuran and the like.

  There is no particular limitation on the method of mixing the silicon-containing particles, the carbon precursor, and, if necessary, the catalyst. Melting or solution mixing with a stirrer such as a homodisper or homogenizer; centrifugal crusher, free mill, jet mill It is possible to employ pulverization and mixing using a pulverizer such as mulling, kneading and mixing using a mortar or pestle. The order of mixing the silicon-containing particles and the carbon precursor is not particularly limited, but the order of the silicon-containing particles and the carbon precursor may be used for the solvent (when used), or vice versa. In forming particles containing silicon-containing particles and resin carbon materials, and forming composite particles surrounding the silicon-containing particles with the resin carbon material, the silicon-containing particles and the carbon precursor are mixed using a solvent to form a slurry mixture. Alternatively, a carbon precursor may be mixed with the silicon-containing particles, and the carbon precursor may be cured to form a solid. Further, in the slurry, if the carbon precursor is liquid, it is not necessary to use a solvent.

  When adjusting the particle size distribution of the negative electrode active material (A) of the present invention, a known pulverization method and classification method may be employed. Examples of the pulverizer include a hammer mill, a jaw crusher, and a collision pulverizer. Moreover, as an example of the classification method, air classification and classification with a sieve are possible. Particularly, examples of the air classification apparatus include a turbo classifier and a turboplex.

  What is necessary is just to set the heating temperature for carbonization processing suitably in the range of preferably 400-1400 degreeC, More preferably, 600-1300 degreeC. There is no restriction | limiting in particular in the temperature increase rate until it reaches the said heating temperature, What is necessary is just to set suitably in the range of 0.5-600 degreeC / hour, More preferably, 20-300 degreeC / hour. The holding time at the heating temperature is suitably set within 48 hours, more preferably within a range of 1 to 12 hours. Moreover, what is necessary is just to implement carbonization processing in reducing atmosphere, such as argon, nitrogen, a carbon dioxide. Furthermore, it is preferable to control the physical properties of the obtained resin carbon material by carrying out the carbonization treatment in two or more stages. For example, after processing (primary carbonization) at a temperature of 400 to 700 ° C. for about 1 to 6 hours, a negative electrode active material having an intended average particle size is obtained by the above-described pulverization treatment, and the negative electrode active material is further heated to 1000 ° C. or more. It is preferable to perform the treatment (secondary carbonization) at a temperature of

  Thus, since the negative electrode active material (A) according to the present invention is formed by carbonizing the resin carbon material and the network structure composed of nanofibers or the like, nanofibers or the like are separately formed by vapor phase method, arc There is no need to prepare by a discharge method or a plasma treatment method, the manufacturing process is simple, and the cost can be reduced.

Next, the binder (B) of the present invention will be described.
The binder (B) of the present invention includes an alkoxy group-bonded cellulose, a hydroxyalkyl group-bonded cellulose, or a carboxyalkyl group-bonded type. As described above, the network structure composed of nanofibers or the like in the negative electrode active material (A) of the present invention is entangled with the network structure caused by other adjacent particles, so that the nanofibers and the composite particles In addition, the nanofibers and the like are hardly separated from the composite particles even during the volume expansion / contraction of the silicon-containing particles due to charge / discharge. In addition, because the network structure of a plurality of adjacent particles is entangled with each other to form a stretchable network structure as a whole, the conductivity of the entire negative electrode is maintained during the volume expansion and contraction of silicon-containing particles due to charge and discharge. The effect of improving the adhesion between the composite particles of the present invention by using the binder (B) of the present invention (this is an active material particle without nanofibers in the conventional binder) In addition to the effect of improving the adhesion between each other), the adhesion between the nanofibers and the composite particles or between the nanofibers is improved, and further, the effect of reinforcing the entangled portion between the network structures is exhibited. The cycle characteristics are remarkably improved by the synergistic effect of the negative electrode active material (A) of the present invention and the binder (B).

  Examples of the alkoxy group-bonded cellulose, hydroxyalkyl group-bonded cellulose, or carboxyalkyl group-bonded cellulose used in the present invention include alkoxy group-bonded cellulose such as methyl cellulose, ethyl cellulose, propyl cellulose, isopropyl cellulose, and butyl cellulose, hydroxyethyl cellulose, hydroxy Examples include hydroxyalkyl group-bonded cellulose such as propylcellulose, carboxyalkyl group-bonded cellulose such as carboxymethylcellulose, carboxyethylcellulose, and carboxyethylmethylcellulose. These cellulose compounds can be used alone or in combination of two or more. The binder (B) of the present invention containing alkoxy group-bonded cellulose, hydroxyalkyl group-bonded cellulose, or carboxyalkyl group-bonded cellulose is used in an amount of 4 to 20 parts by weight with respect to 100 parts by weight of the negative electrode active material (A). It is preferable. Moreover, it is 6-14 mass parts more preferably. If it is 4 parts by mass or more, it is difficult for the active material to fall off due to the charge / discharge cycle, and the adhesion between the active material and the pyroelectric material is less likely to be generated. The amount is sufficient, and the charge / discharge characteristics, particularly the capacity per negative electrode volume, is sufficient. The binder (B) used in the present invention only needs to contain an alkoxy group-bonded cellulose, a hydroxyalkyl group-bonded cellulose, or a carboxyalkyl group-bonded cellulose. Among them, the degree of etherification is 0.6 to 1. .5 is preferred in terms of workability and adhesion, and when the degree of etherification of carboxymethyl cellulose is 0.6 or more, the aforementioned adhesion is sufficient, and when charging and discharging are repeated, the active materials Phenomenon such as dropout is unlikely to occur and suppresses capacity reduction. On the other hand, when the degree of etherification is 1.5 or less, the viscosity of the electrode slurry does not extremely increase and can be smoothly applied to the pyroelectric material. Further, the binder (B) of the present invention may be any one containing alkoxy group-bonded cellulose, hydroxyalkyl group-bonded cellulose, or carboxyalkyl group-bonded cellulose, but the binder of the present invention described in the above description. As long as the effect of the binder (B) is not lowered, other binders such as polyvinylidene fluoride resin may be used in combination as needed.

By using the negative electrode active material (A) obtained as described above and the binder (B), the lithium secondary battery negative electrode according to the present invention can be produced. The lithium secondary battery negative electrode according to the present invention can be produced by a conventionally known method. For example, a suitable solvent is added to the negative electrode active material (A) and the binder (B) of the present invention by adding a conductive agent or the like. Alternatively, a slurry having a predetermined viscosity is prepared with a dispersion medium, and this is applied to a current collector such as a metal foil to form a coating having a thickness of several μm to several hundred μm. The negative electrode according to the present invention can be obtained by heat-treating the coating at about 50 to 200 ° C. to remove the solvent or the dispersion medium.
The conductive agent used for producing the negative electrode according to the present invention may be any material that is usually used as a conductive auxiliary material, and examples thereof include graphite, acetylene black, and ketjen black. Furthermore, the solvent or dispersion medium used in the production of the negative electrode according to the present invention may be any material that can uniformly mix the negative electrode active material, the binder, the conductive agent, and the like. As an example, N-methyl-2-pyrrolidone, Examples include methanol, acetonitrile, water and the like.

  Furthermore, the lithium secondary battery according to the present invention can be produced by using the lithium secondary battery negative electrode according to the present invention. The lithium secondary battery according to the present invention can be produced by a conventionally known method. In general, the lithium secondary battery includes a negative electrode according to the present invention, a positive electrode, and an electrolyte, and further includes a separator that prevents the negative electrode and the positive electrode from being short-circuited. Including. When the electrolyte is a solid electrolyte combined with a polymer and has the function of a separator, an independent separator is not necessary.

The positive electrode used for the production of the lithium secondary battery according to the present invention can be produced by a conventionally known method. For example, a positive electrode active material is added with a binder, a conductive agent and the like to prepare a slurry having a predetermined viscosity with an appropriate solvent or dispersion medium, and this is applied to a current collector such as a metal foil, and a thickness of several μm to What is necessary is just to remove a solvent or a dispersion medium by forming several hundred micrometers coating and heat-processing the coating at about 50-200 degreeC. The positive electrode active material may be a conventionally known material, for example, a cobalt composite oxide such as LiCoO ₂ , a manganese composite oxide such as LiMn ₂ O ₄ , a nickel composite oxide such as LiNiO ₂ , and a mixture of these oxides. , LiNiO ₂ in which part of nickel is replaced with cobalt or manganese, iron composite oxides such as LiFeVO ₄ and LiFePO ₄ , and the like can be used.

  As the electrolyte, a known electrolytic solution, a room temperature molten salt (ionic liquid), an organic or inorganic solid electrolyte, and the like can be used. Examples of the known electrolyte include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as ethyl methyl carbonate and diethyl carbonate. Examples of the room temperature molten salt (ionic liquid) include imidazolium salts, pyrrolidinium salts, pyridinium salts, aliphatic salts, ammonium salts, phosphonium salts, sulfonium salts, and the like. Examples of the solid electrolyte include polyether polymers, polyester polymers, polyimine polymers, polyvinyl acetal polymers, polyacrylonitrile polymers, polyfluorinated alkene polymers, polyvinyl chloride polymers, poly (vinyl chloride-fluoride). Vinylidene) -based polymers, poly (styrene-acrylonitrile) -based polymers, and organic polymer gels represented by linear polymers such as nitrile rubber; inorganic ceramics such as zirconia; silver iodide, silver iodide sulfur compounds, iodine And inorganic electrolytes such as silver rubidium compounds. Moreover, in order to reduce ionic conductivity, what melt | dissolved lithium salt in the said electrolyte can be used as an electrolyte for secondary batteries. A flame retardant electrolyte solubilizer can also be added to impart flame retardancy to the electrolyte. Similarly, a plasticizer can be added to reduce the viscosity of the electrolyte.

Examples of the lithium salt dissolved in the electrolyte include LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiBF ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiC ( CF ₃ SO ₂ ) _{3 and the} like. The lithium salts may be used alone or in combination of two or more. The lithium salt is generally used in a content of 0.1% by mass to 89.9% by mass, preferably 1.0% by mass to 79.0% by mass, based on the entire electrolyte. Components other than the lithium salt of the electrolyte can be added in an appropriate amount on condition that the content of the lithium salt is within the above range.

  The polymer used for the electrolyte is not particularly limited as long as it is electrochemically stable and has high ionic conductivity. For example, an acrylate polymer, polyvinylidene fluoride, or the like can be used. In addition, polymers synthesized from those containing a salt monomer composed of an onium cation having a polymerizable functional group and an organic anion having a polymerizable functional group have particularly high ionic conductivity, which further improves charge / discharge characteristics. It is more preferable at the point which can contribute. The polymer content in the electrolyte is preferably in the range of 0.1 mass% to 50 mass%, more preferably 1 mass% to 40 mass%.

  The flame retardant electrolyte solubilizer is not particularly limited as long as it is a compound that exhibits self-extinguishing properties and can dissolve the electrolyte salt in the presence of the electrolyte salt. For example, phosphate ester, halogen compound Phosphazene etc. can be used.

  Examples of the plasticizer include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as ethyl methyl carbonate and diethyl carbonate. The above plasticizers may be used alone or in combination of two or more.

  When a separator is used in the lithium secondary battery according to the present invention, a conventionally known material that can prevent a short circuit between the positive electrode and the negative electrode and is electrochemically stable may be used. Examples of the separator include a polyethylene separator, a polypropylene separator, a cellulose separator, a nonwoven fabric, an inorganic separator, a glass filter, and the like. When a polymer is included in the electrolyte, the electrolyte may also have a separator function, and in that case, an independent separator is unnecessary.

  As a method for producing the secondary battery of the present invention, a known method can be applied. For example, the positive electrode and the negative electrode obtained above are first prepared by cutting them into a predetermined shape and size, and then bonded via a separator so that the positive electrode and the negative electrode are not in direct contact with each other. And Next, an electrolyte is injected between the electrodes of the single-layer cell by a method such as injection. A secondary battery is obtained by inserting and sealing the thus obtained cell into an exterior body made of a laminate film having a three-layer structure of polyester film / aluminum film / modified polyolefin film, for example. The obtained secondary battery may be used as a single cell or a module in which a plurality of cells are connected depending on the application.

  Hereinafter, an example for explaining the present invention more concretely is provided.

<Example 1>
135 parts by weight of a novolak type phenolic resin (PR-50237 manufactured by Sumitomo Bakelite Co., Ltd.) and 25 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.) are dissolved in a four-necked flask to which 20 parts by weight of methanol is added. 50 parts by mass of silicon monoxide (average particle size: 1.2 μm) was added and stirred for 2 hours. After stirring, the resulting slurry was cured at 200 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 1 hour after reaching 500 ° C. The obtained carbide is pulverized until the average particle size becomes 11 μm, and the carbide obtained by the pulverization is further heated, and after reaching 1100 ° C., carbonized for 10 hours to obtain a negative electrode active for secondary battery. Obtained material. When the obtained negative electrode active material was measured by the following measurement method, the pore volume of 0.25 to 0.45 nm was 0.85 cm ³ / g, which was 55% by volume with respect to the total pore volume. It was. Moreover, when the obtained negative electrode active material was observed using the scanning electron microscope (SEM), the production | generation of the nanofiber etc. with a fiber diameter of 50 nm was confirmed on the negative electrode active material particle surface. Further, the obtained negative electrode active material contained 36.7% by mass of silicon monoxide.

The result (electron micrograph) of observing the obtained negative electrode active material with a scanning electron microscope (SEM) is shown in FIG. As can be seen from FIG. 1, it was confirmed that nanofibers and the like were generated from the surface of the composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles, and surrounded these particles. . In addition, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, carbon was obtained as shown in FIGS. 2 (A) and (B). Oxygen and silicon peaks were confirmed.

Evaluation of negative electrode active material Measurement of pore volume and pore distribution Using a Shimadzu Corporation pore distribution measuring device “ASAP-2010”, the sample was vacuum-heated and pretreated at 623 K to desorb the adsorbed gas, and probe Using N ₂ as the gas, the adsorption isotherm was measured at 77.3 K in the range of absolute pressure 760 mmHg and relative pressure 0.005 to 0.86. From the specific surface area and adsorption amount of the obtained adsorption medium, the adsorption layer Through the thickness t, the average pore hydraulic radius was calculated based on the thickness formula of Halsey and Halsey and Jura, and the pore volume was calculated based on the following formula.
The thickness formulas of Halsey and Halsey and Jura are as described below.
t = (M × Vsp / 22414) × (Va / S)
[Wherein, t: statistical thickness of the adsorption layer, M: molecular weight of the adsorbate, Va: adsorption amount per unit mass of the adsorbent, Vsp: specific volume of the adsorbate gas, S: specific surface area of the adsorbent]
t _I = HP1 × [HP2 / ln (Prel _I )] HP3
[Where, t _I : thickness of I ^th point, HP1: Halsey parameter # 1, HP2: Halsey parameter # 2, HP3: Halsey parameter # 3, Prel _I : relative pressure (mmHg) of I ^th point]
Average hydraulic radius (nm): R _I = (t _I + t _I-1 ) / 20
Increment of pore surface area blocked at the Ith point ΔS: ΔS = S _I-1 −S _I
Integrated pore surface area (m ² / g) blocked at the Ith point S: S = S ₁ + S ₂ + S ₃ +... Sn
Pore volume increment ΔV blocked at the Ith point:
ΔV = (S × 10 ⁴ cm ² / m ² ) × (R _I × 10 ⁻⁸ cm / Å)
Ith point pore volume ΔV / ΔR _I (cm ³ / g): ΔV / ΔR _I = ΔV / t _I −t _I−1
The Ith point refers to an individual measurement point by each relative pressure.
Pore volume blocked at the Ith point (cm ³ / g): V = V ₁ + V ₂ + V ₃ +... Vn.

  The particle size of the negative electrode active material was measured using a laser diffraction diffraction scattering particle size distribution analyzer (LS-230 manufactured by Beckman Coulter, Inc.). The average particle diameter was converted to volume, and the place where the frequency reached 50% cumulatively was defined as the average particle diameter.

Evaluation of charge / discharge characteristics (1) Preparation of negative electrode mixture and negative electrode Using 100 parts by mass of the negative electrode active material obtained above, carboxymethylcellulose (manufactured by Daicel Chemical Industries, Ltd .: product number 1160), etherification as a binder A degree of 0.6 to 0.8) was mixed at a ratio of 10 parts by mass and 3 parts by mass of acetylene black, and 200 parts by mass of water was further added and mixed as a diluent solvent to prepare a slurry-like negative electrode mixture.
This negative electrode mixture was applied to both sides of a 10 μm copper foil, and then vacuum-dried at 110 ° C. for 1 hour. After vacuum drying, the electrode was pressure molded to 100 μm by a roll press. This was cut into a size of 40 mm in width and 290 mm in length to produce a negative electrode. Using this negative electrode, a negative electrode was punched out with a diameter of 13 mm as an electrode for a lithium ion secondary battery.

(2) Production of Lithium Ion Secondary Battery The negative electrode, separator (polypropylene porous film: diameter φ16, thickness 25 μm), and lithium metal (diameter φ12, thickness 1 mm) as working electrodes in order of Hosen 2032 The coin cell was placed at a predetermined position in the coin cell. Further, an electrolytic solution in which lithium perchlorate is dissolved at a concentration of 1 [mol / liter] in a mixed solution of ethylene carbonate and diethylene carbonate (volume ratio is 1: 1) is injected into a lithium ion secondary solution. A battery was produced.

(3) Evaluation of battery characteristics <Evaluation of initial charge / discharge characteristics>
Regarding the charging capacity, constant current charging is performed with the current density at the time of charging being 25 mA / g, and from the time when the potential reaches 0 V, constant voltage charging is performed at 0 V until the current density reaches 1.25 mA / g. The amount of electricity charged was taken as the charge capacity.
On the other hand, with respect to the discharge capacity, constant current discharge was performed with a current density at the time of discharge of 25 mA / g, and constant voltage discharge was performed at 2.5 V from the time when the potential reached 2.5 V, and the current density was 1.25 mA. The amount of electricity discharged up to / g was taken as the discharge capacity.
In addition, evaluation of the charging / discharging characteristic was performed using the charging / discharging characteristic evaluation apparatus (Hokuto Denko Co., Ltd. product: HJR-1010mSM8).
The initial charge / discharge efficiency was defined by the following equation.
Initial charge / discharge efficiency (%) = initial discharge capacity (mAh / g) / initial charge capacity (mAh / g) × 100

<Cycle evaluation>
The discharge capacity obtained after repeatedly measuring the initial charge / discharge characteristic evaluation conditions 300 times was defined as the discharge capacity at the 300th cycle. In addition, the cycle property (300 cycle capacity maintenance rate) was defined by the following equation.
Cycle performance (%, 300 cycle capacity retention rate) = 300th cycle discharge capacity (mAh / g) / initial discharge capacity (mAh / g) × 100

<Evaluation of load characteristics>
The discharge capacity obtained by the initial charge / discharge characteristic evaluation is defined as the reference capacity (C ₀ ), and after charging the reference capacity, discharging is performed at a current density that discharges the charged amount in 1 hour. The capacity. Similarly, after charging the reference capacity, discharging was performed at a current density that discharges the charged amount in 2 minutes, and the obtained discharge capacity was set to 30 C capacity. Also, the load characteristic (%, capacity at 30 C vs. capacity at 1 C) was defined by the following equation.
Load characteristics (%, capacity at 30 C vs. capacity at 1 C) = 30 C capacity (mAh / g) / 1 C capacity (mAh / g) × 100

<Example 2> A four-necked flask in which 135 parts by mass of novolak-type phenolic resin (PR-50237 manufactured by Sumitomo Bakelite Co., Ltd.) and 25 parts by mass of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.) were added with 30 parts by mass of acetone. Further, 30 parts by mass of silicon monoxide (average particle size: 3.3 μm) was added, and the mixture was stirred for 3 hours. After stirring, the resulting slurry was cured at 200 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 1 hour after reaching 550 ° C. The obtained carbide is pulverized until the average particle size becomes 7 μm. The carbide obtained by the pulverization is further heated, and after reaching 1150 ° C., carbonization is performed for 10 hours to obtain a negative electrode active for secondary battery. Obtained material. The obtained negative electrode active material had a pore volume of 0.25 to 0.45 nm of 0.75 cm ³ / g, and 75% by volume with respect to the total pore volume. Further, when SEM observation of the obtained negative electrode active material was performed, nanofibers having a fiber diameter of 40 nm were generated from the surface of composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles. It was confirmed that these particles were surrounded. Further, as in Example 1, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, peaks of carbon, oxygen and silicon were confirmed. It was done. Further, the obtained negative electrode active material contained 26.0% by mass of silicon monoxide.

  Next, carboxymethyl cellulose (manufactured by Daicel Chemical Industries, product number: 1160, degree of etherification: 0.6 to 0.8) as a binder with respect to 100 parts by mass of the negative electrode active material, and a ratio of 3 parts by mass of acetylene black, respectively. Further, 250 parts by weight of water was added as a diluent solvent and mixed to obtain a negative electrode mixture and a negative electrode for a lithium ion secondary battery. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Example 3>
135 parts by mass of a novolac type phenolic resin (PR-50237 manufactured by Sumitomo Bakelite Co., Ltd.) and 25 parts by mass of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.) are dissolved in a four-necked flask to which 45 parts by mass of acetone is added. 45 parts by mass of silicon monoxide (average particle size: 0.7 μm) was added and stirred for 5 hours. After stirring, the resulting slurry was cured at 200 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 500 ° C. The obtained carbide is pulverized until the average particle size becomes 11 μm. The carbide obtained by the pulverization is further heated, and after reaching 1100 ° C., carbonization is performed for 5 hours to obtain a negative electrode active for secondary battery. Obtained material. When the obtained negative electrode active material was evaluated in the same manner as in Example 1, the pore volume of 0.25 to 0.45 nm was 0.65 cm ³ / g, and 55 volumes with respect to the total pore volume. %Met. Further, when SEM observation of the obtained negative electrode active material was performed, nanofibers having a fiber diameter of 40 nm were generated from the surface of composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles. It was confirmed that these particles were surrounded. Further, as in Example 1, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, peaks of carbon, oxygen and silicon were confirmed. It was done. Furthermore, the obtained negative electrode active material contained 35.3% by mass of silicon monoxide.

  Next, carboxymethyl cellulose (manufactured by Daicel Chemical Industries, product number: 1160, degree of etherification: 0.6 to 0.8) as a binder with respect to 100 parts by mass of the negative electrode active material, and at a ratio of 3 parts by mass of acetylene black, respectively. Further, 160 parts by mass of water was added as a diluent solvent and mixed to obtain a negative electrode mixture and a lithium ion secondary battery negative electrode. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Example 4>
135 parts by mass of a novolac type phenolic resin (PR-50237 manufactured by Sumitomo Bakelite Co., Ltd.) and 25 parts by mass of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.) are dissolved in a four-necked flask to which 25 parts by mass of acetone is added, and 30 parts by mass of silicon monoxide (average particle size 1.3 μm) and 0.1 part by mass of iron nitrate as a catalyst were added and stirred for 3 hours. After stirring, the resulting slurry was cured at 200 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 450 ° C. The obtained carbide is pulverized until the average particle size becomes 12 μm, the temperature of the carbide obtained by the pulverization is further increased, and after reaching 1100 ° C., carbonization is performed for 10 hours. Obtained material. When the obtained negative electrode active material was evaluated in the same manner as in Example 1, the pore volume of 0.25 to 0.45 nm was 0.80 cm ³ / g, and 50 volumes with respect to the total pore volume. %Met. Further, when SEM observation of the obtained negative electrode active material was performed, nanofibers having a fiber diameter of 20 nm were generated from the surface of composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles. It was confirmed that these particles were surrounded. Further, as in Example 1, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, peaks of carbon, oxygen and silicon were confirmed. It was done. Furthermore, the obtained negative electrode active material contained 28.4% by mass of silicon monoxide.

Next, carboxymethyl cellulose (manufactured by Daicel Chemical Industries, product number: 1350, degree of etherification: 1.0 to 1.5) as a binder with respect to 100 parts by mass of the negative electrode active material, and 3 parts by mass of acetylene black, respectively. Further, 200 parts by mass of water was added as a diluent solvent and mixed to obtain a negative electrode mixture and a negative electrode for a lithium ion secondary battery. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Example 5> 100 parts by mass of β-naphthol, 53.3 parts by mass of a 43% formaldehyde aqueous solution, and 3 parts by mass of oxalic acid were placed in a three-necked flask equipped with a stirrer and a condenser, and reacted at 100 ° C for 3 hours. The temperature was dehydrated to obtain 90 parts by mass of β-naphthol resin. A mixture of 10 parts by mass of hexamethylenetetramine with respect to 100 parts by mass of the β-naphthol resin obtained by repeating the above operation was pulverized and mixed, and then added with 30 parts by mass of dimethylsulfamide. It was made to melt | dissolve in a flask, 60 mass parts (average particle diameter of 3.3 micrometers) of silicon monoxide was further added, and it stirred for 3 hours. After stirring, the resulting slurry was cured at 200 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 6 hours after reaching 450 ° C. The obtained carbide is pulverized until the average particle size becomes 7 μm. The carbide obtained by the pulverization is further heated, and after reaching 1100 ° C., carbonization is performed for 10 hours. Obtained material. When the obtained negative electrode active material was evaluated in the same manner as in Example 1, the pore volume of 0.25 to 0.45 nm was 0.65 cm ³ / g, and 65 volumes with respect to the total pore volume. %Met. Further, when SEM observation of the obtained negative electrode active material was performed, nanofibers having a fiber diameter of 20 nm were generated from the surface of composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles. It was confirmed that these particles were surrounded. Further, as in Example 1, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, peaks of carbon, oxygen and silicon were confirmed. It was done. Further, the obtained negative electrode active material contained 56.2% by mass of silicon monoxide.

  Next, carboxymethyl cellulose (manufactured by Daicel Chemical: product number 2280, degree of etherification 0.6 to 0.8) as a binder with respect to 100 parts by mass of the negative electrode active material, respectively, at a ratio of 3 parts by mass of acetylene black, respectively. Further, 200 parts by mass of water was added as a diluent solvent and mixed to obtain a negative electrode mixture and a negative electrode for a lithium ion secondary battery. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Example 6>
100 parts by mass of a resol-type phenolic resin (PR-51723 manufactured by Sumitomo Bakelite Co., Ltd.) was dissolved in a four-necked flask to which 30 parts by mass of acetone was added, and 20 parts by mass of silicon monoxide (average particle size 1.1 μm) was further added. The mixture was further stirred for 3 hours. After stirring, the resulting slurry was cured at 200 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 2 hours after reaching 550 ° C. The obtained carbide is pulverized until the average particle size becomes 10 μm, the temperature of the carbide obtained by the pulverization is further increased, and carbonization is performed for 18 hours after reaching 1200 ° C. Obtained material. When the obtained negative electrode active material was evaluated in the same manner as in Example 1, the pore volume of 0.25 to 0.45 nm was 0.012 cm ³ / g, and 40 volumes with respect to the total pore volume. %Met. Further, when SEM observation of the obtained negative electrode active material was performed, nanofibers having a fiber diameter of 35 nm were generated from the surface of composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles. It was confirmed that these particles were surrounded. Further, as in Example 1, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, peaks of carbon, oxygen and silicon were confirmed. It was done. Furthermore, the obtained negative electrode active material contained 33.1% by mass of silicon monoxide.

  Next, carboxymethyl cellulose (manufactured by Daicel Chemical Industries, product number: 1160, degree of etherification: 0.6 to 0.8) as a binder with respect to 100 parts by mass of the negative electrode active material, and at a ratio of 3 parts by mass of acetylene black, respectively. Further, 200 parts by mass of water was added as a diluent solvent and mixed to obtain a negative electrode mixture and a negative electrode for a lithium ion secondary battery. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Example 7>
135 parts by weight of a novolak type phenolic resin (PR-50237 manufactured by Sumitomo Bakelite Co., Ltd.) and 25 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.) are dissolved in a four-necked flask to which 20 parts by weight of methanol is added. 50 parts by mass of silicon monoxide (average particle size: 1.2 μm) was added and stirred for 2 hours. After stirring, the obtained slurry was cured at 150 ° C. for 5 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 600 ° C. The obtained carbide is pulverized until the average particle size becomes 9 μm, the carbide obtained by the pulverization is further heated, and after reaching 1250 ° C., carbonization is performed for 3 hours. Obtained material. The obtained negative electrode active material had a pore volume of 0.25 to 0.45 nm of 1.2 cm ³ / g, and was 80% by volume based on the total pore volume. Moreover, when the obtained negative electrode active material SEM observation was performed, nanofibers having a fiber diameter of 40 nm were generated from the surface of the composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles, It was confirmed to surround these particles. Further, as in Example 1, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, peaks of carbon, oxygen and silicon were confirmed. It was done. Furthermore, the obtained negative electrode active material contained 35.9% by mass of silicon monoxide.

  Next, 20 parts by mass of methyl cellulose (manufactured by Sigma-Aldrich, number average molecular weight 14000) and 3 parts by mass of acetylene black are blended with respect to 100 parts by mass of the negative electrode active material, respectively, and water 400 as a diluent solvent. Part by mass was added and mixed to obtain a negative electrode mixture and a negative electrode for a lithium ion secondary battery. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Example 8>
135 parts by weight of a novolak type phenolic resin (PR-50237 manufactured by Sumitomo Bakelite Co., Ltd.) and 25 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.) are dissolved in a four-necked flask to which 20 parts by weight of methanol is added. 40 parts by mass of silicon monoxide (average particle size: 1.2 μm) was added and stirred for 2 hours. After stirring, the resulting slurry was cured at 175 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 1 hour after reaching 650 ° C. The obtained carbide is pulverized until the average particle size becomes 9 μm, and the carbide obtained by the pulverization is further heated, and after reaching 1100 ° C., carbonization is performed for 18 hours to obtain a negative electrode active for secondary battery. Obtained material. The obtained negative electrode active material had a pore volume of 0.25 to 0.45 nm of 0.85 cm ³ / g and 25 volume% with respect to the total pore volume. Further, when SEM observation of the obtained negative electrode active material was performed, nanofibers having a fiber diameter of 35 nm were generated from the surface of composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles. It was confirmed that these particles were surrounded. Further, as in Example 1, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, peaks of carbon, oxygen and silicon were confirmed. It was done. Furthermore, the obtained negative electrode active material contained 36.2% by mass of silicon monoxide.

  Next, hydroxypropylmethylcellulose (manufactured by Sigma-Aldrich, 2% by weight aqueous solution) is blended as a binder to 100 parts by weight of the negative electrode active material so that the solid content is 4 parts by weight, and further 3 parts by weight of acetylene black is added. The mixture was mixed to obtain a negative electrode mixture and a lithium ion secondary battery negative electrode. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Example 9>
100 parts by mass of a resol type phenolic resin (PR-51723, manufactured by Sumitomo Bakelite Co., Ltd.) was dissolved in a four-necked flask to which 30 parts by mass of acetone was added, and 45 parts by mass of silicon monoxide (average particle size 1.3 μm) was further added. The mixture was further stirred for 3 hours. After stirring, the resulting slurry was cured at 200 ° C. for 3 hours. After the curing treatment, the temperature was raised in a nitrogen atmosphere, and carbonization was performed for 3 hours after reaching 450 ° C. The obtained carbide is pulverized until the average particle size becomes 10 μm, the temperature of the carbide obtained by the pulverization is further increased, and carbonization is performed for 3 hours after reaching 1050 ° C. Obtained material. The obtained negative electrode active material had a pore volume of 0.25 to 0.45 nm of 0.0003 cm ³ / g, and was 30% by volume with respect to the total pore volume. Further, when SEM observation of the obtained negative electrode active material was performed, nanofibers having a fiber diameter of 50 nm were generated from the surface of composite particles composed of silicon-containing particles and a resin carbon material surrounding the silicon-containing particles. It was confirmed that these particles were surrounded. Further, as in Example 1, when elemental analysis was performed using an energy dispersive X-ray analyzer (EDX) at two locations such as nanofibers observed by SEM, peaks of carbon, oxygen and silicon were confirmed. It was done. Furthermore, the obtained negative electrode active material contained 34.1% by mass of silicon monoxide.

  Next, hydroxypropylmethylcellulose (manufactured by Sigma-Aldrich, 2% by weight aqueous solution) is blended as a binder to 100 parts by weight of the negative electrode active material so that the solid content is 4 parts by weight, and further 3 parts by weight of acetylene black is added. The mixture was mixed to obtain a negative electrode mixture and a lithium ion secondary battery negative electrode. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Comparative example 1> It mix | blends in the ratio of 10 mass parts of polyvinylidene fluoride resin as a binder with respect to 100 mass parts of negative electrode active materials produced in Example 1, and 3 mass parts of acetylene black, respectively, Furthermore, as a dilution solvent 120 parts by mass of N-methyl-2-pyrrolidone was added and mixed to obtain a negative electrode mixture and a negative electrode for a lithium ion secondary battery. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Comparative Example 2>
100 parts by mass of the negative electrode active material produced in Example 5 were blended in a proportion of 10 parts by mass of polyvinylidene fluoride resin as a binder and 3 parts by mass of acetylene black, respectively, and further N-methyl-2 as a diluent solvent -Pyrrolidone 120 mass part was added and mixed, and the negative electrode mixture and the lithium ion secondary battery negative electrode were obtained. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

Comparative Example 3 A four-necked flask in which 135 parts by mass of a novolak-type phenolic resin (PR-50237 manufactured by Sumitomo Bakelite Co., Ltd.) and 25 parts by mass of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.) were added with 20 parts by mass of methanol. In addition, 20 parts by mass of silicon (average particle size of 54 μm) was added and stirred for 2 hours. After completion of the stirring, the obtained slurry was cured at 200 ° C. for 3 hours, and the negative electrode active material was obtained in the same manner as in Example 1 except that carbonization was performed for 10 hours after reaching 1000 ° C. Got. The average particle diameter of the obtained negative electrode active material was adjusted to 8 μm. The obtained negative electrode active material was evaluated in the same manner as in Example 1. As a result, the pore volume of 0.25 to 0.45 nm was 0.65 cm ³ / g, and 20 volumes with respect to the total pore volume. %Met. When SEM observation of the obtained negative electrode active material was performed, a network structure was not confirmed on the surface of the composite particles. The obtained negative electrode active material contained 23.1% by mass of silicon.

  Next, carboxymethyl cellulose (manufactured by Daicel Chemical Industries, product number: 1160, degree of etherification: 0.6 to 0.8) as a binder with respect to 100 parts by mass of the negative electrode active material, and at a ratio of 3 parts by mass of acetylene black, respectively. Further, 200 parts by mass of water was added as a diluent solvent and mixed to obtain a negative electrode mixture and a negative electrode for a lithium ion secondary battery. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

<Comparative example 4>
135 parts by weight of a novolac type phenolic resin (PR-50237 manufactured by Sumitomo Bakelite Co., Ltd.) and 25 parts by weight of hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Co., Inc.) are dissolved in a four-necked flask to which 30 parts by weight of methanol is added. 40 parts by mass of silicon (average particle size: 25 μm) was added and stirred for 3 hours. After completion of the stirring, the obtained slurry was cured at 200 ° C. for 3 hours, and the negative electrode active material was obtained in the same manner as in Example 1 except that carbonization was performed for 5 hours after reaching 900 ° C. Got. The average particle diameter of the obtained negative electrode active material was adjusted to 10 μm. When the obtained negative electrode active material was evaluated in the same manner as in Example 1, the pore volume of 0.25 to 0.45 nm was 1.25 cm ³ / g, and 25 volumes with respect to the total pore volume. %Met. When SEM observation of the obtained negative electrode active material was performed, a network structure was not confirmed on the surface of the composite particles. Moreover, the obtained negative electrode active material contained 32.3 mass% of silicon.

  Next, carboxymethyl cellulose (manufactured by Daicel Chemical Industries, product number: 1160, degree of etherification: 0.6 to 0.8) as a binder with respect to 100 parts by mass of the negative electrode active material, and at a ratio of 3 parts by mass of acetylene black, respectively. Further, 200 parts by mass of water was added as a diluent solvent and mixed to obtain a negative electrode mixture and a negative electrode for a lithium ion secondary battery. Further, in the same manner as in Example 1, a lithium ion secondary battery was produced, and charge / discharge characteristics were evaluated.

  Table 1 shows the evaluation results of the negative electrode active material and Table 2 shows the evaluation results of the battery characteristics for each of the above Examples and Comparative Examples.

As is clear from Tables 1 and 2, the lithium ion secondary batteries of Examples 1 to 9 have a discharge capacity maintenance rate of 80% or more after 300 cycles, compared with Comparative Examples 1, 2, 3, and 4, The charge / discharge cycle characteristics were remarkably improved. This is because, in the examples, nanofibers or the like are generated from the surface of the composite particles composed of the silicon-containing particles of the present invention and the resin carbon material surrounding the silicon-containing particles, and other particles surrounding and adjoining these particles. In addition to the effect of improving the adhesion between the composite particles of the present invention by using the binder (B) of the present invention by entanglement with the network structure resulting from the above, the nanofibers and the composite particles, or Cycle characteristics are remarkably improved by the synergistic effect of the carbon material (A) and the binder (B) in order to improve the adhesion between the nanofibers and to reinforce the entangled part between the network structures. It is what. In Comparative Example 1 and Comparative Example 2, although the negative electrode active material (A) of the present invention is used, since the binder of the present invention is not used, there is no synergistic effect with the negative electrode active material, and cycle characteristics Inferior to In Comparative Example 3 and Comparative Example 4, there is no nanofiber or the like surrounding the particles of the negative electrode active material (A), so that the pulverization accompanying the expansion and contraction of the negative electrode active material due to the charge / discharge cycle proceeds substantially. The electrode collapsed. In particular, in Examples 1 to 6, the volume of the pores having a pore diameter of 0.25 to 0.45 nm is 0.0005 to 1.0 cm ² / g, and the volume of the resin carbon material has In each case, the discharge capacity retention rate after 300 cycles was recorded as 85% or more by being 30% by volume or more with respect to the total pore volume.

Claims (13)

  A lithium secondary battery negative electrode mixture comprising a negative electrode active material (A) and a binder (B), wherein the negative electrode active material (A) is a silicon alloy capable of occluding and releasing lithium ions, Composite particles comprising silicon-containing particles containing oxides, nitrides or carbides, and resin carbon material surrounding the silicon-containing particles, and nanofibers bonded to the surface of the composite particles and surrounding the composite particles And / or a silicon-containing network structure composed of nanotubes, and the binder (B) contains an alkoxy group-bonded cellulose, a hydroxyalkyl group-bonded cellulose, or a carboxyalkyl group-bonded cellulose. A lithium secondary battery negative electrode mixture.   The lithium secondary battery negative electrode mixture according to claim 1, wherein 4 to 20 parts by mass of the binder (B) is used with respect to 100 parts by mass of the negative electrode active material (A).   The lithium secondary battery negative electrode mixture according to claim 1 or 2, wherein the binder (B) contains carboxymethyl cellulose having an etherification degree of 0.6 to 1.5. The resin carbon material has pores, and the pore volume having a pore diameter of 0.25 to 0.45 nm calculated by a micropore method using a nitrogen gas adsorption method is 0.0001 to 1 The lithium secondary battery negative electrode mixture according to claim 1, which is 0.5 cm ² / g. The lithium secondary battery negative electrode according to any one of claims 1 to 4, wherein a volume of the pores having a pore diameter of 0.25 to 0.45 nm is 0.0005 to 1.0 cm ² / g. Mixture.   The resin carbon material has pores, and the volume of the pores having a pore diameter of 0.25 to 0.45 nm calculated by a micropore method using a nitrogen gas adsorption method is the resin carbon material. The lithium secondary battery negative electrode mixture according to any one of claims 1 to 5, which is 25% by volume or more based on the total pore volume of the lithium secondary battery.   The volume of the pores having a pore diameter of 0.25 to 0.45 nm is 30% by volume or more based on the total pore volume of the resin carbon material. The lithium secondary battery negative electrode mixture as described in 1.   The lithium secondary battery negative electrode mixture according to any one of claims 1 to 7, wherein the network structure further contains carbon.   The lithium secondary battery negative electrode mixture according to any one of claims 1 to 8, wherein the silicon-containing particles contain silicon oxide.   In the said negative electrode active material (A), content of a silicon alloy, an oxide, a nitride, or a carbide | carbonized_material is in the range of 5-60 mass%, Lithium 2 of any one of Claims 1-9. Secondary battery negative electrode mixture.   11. The lithium secondary battery negative electrode mixture according to claim 1, wherein an average particle diameter of the negative electrode active material (A) is in a range of 3 μm to 15 μm.   The lithium secondary battery negative electrode containing the lithium secondary battery negative electrode mixture of any one of Claims 1-11.   The lithium secondary battery containing the lithium secondary battery negative electrode of Claim 12.