JP5655396B2 - Carbon material for negative electrode of lithium secondary battery, negative electrode mixture for lithium secondary battery, negative electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Description

  The present invention relates to a carbon material for a lithium secondary battery negative electrode, a negative electrode mixture for a lithium secondary battery, a negative electrode for a lithium secondary battery, 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 a lithium secondary battery, it is known to employ silicon, tin, germanium, magnesium, lead, aluminum, or an oxide or alloy thereof, which is alloyed with lithium, as a negative electrode material. However, the negative electrode material as described above expands in volume during charging to occlude lithium ions, and conversely shrinks in volume during discharge 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 material is pulverized and falls off the electrode, causing the negative electrode to collapse.

  In order to overcome the above problems, various methods and means have been studied, but it is difficult to stabilize the charge / discharge characteristics when using metals and oxides as the negative electrode material for lithium secondary batteries. is there. Therefore, for example, Patent Document 1 is characterized by comprising silicon oxide (A) represented by SiOx (0.5 ≦ x <2) and a conductive substance (B) capable of adsorbing and desorbing lithium ions. A complex has been proposed. According to Patent Document 1, it is stated that the composite is suitable as an electrode material for an electricity storage device and exhibits a high discharge capacity and good cycle characteristics, so that it is particularly preferably used as a negative electrode material for a lithium ion secondary battery. . However, it is difficult to suppress the volume expansion and contraction of the negative electrode active material during lithium occlusion and release during charge and discharge in a composite (precursor) in which silicon oxide and a conductive material are made homogeneous without phase separation. There may be.

  Further, for example, as disclosed in Patent Document 2, as a negative electrode material for a lithium secondary battery having excellent charge / discharge cycle characteristics, a negative electrode active material in which a metal particle surface capable of forming a lithium alloy is coated with an organic substance is used. Proposed. According to the negative electrode material described in Patent Document 2, 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 lithium ions are occluded. 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.

JP 2007-220411 A JP 2007-214137 A

  Both of the negative electrodes (electrode materials) for lithium secondary batteries described in the above two patent documents are coated with carbon or treated with a metal that is alloyed with lithium, so that the volume expansion of the negative electrode active material due to the charge / discharge cycle And volume shrinkage is suppressed to some extent. However, in the inventions described in the above two patent documents, the negative electrode collapse due to the pulverization of the negative electrode active material due to the charge / discharge cycle cannot be completely prevented, and the charge / discharge cycle characteristics of the negative electrode for a lithium secondary battery are That's not enough. Therefore, the present invention further improves the charge / discharge cycle characteristics of the lithium ion secondary battery, and further improves the initial charge / discharge efficiency (initial discharge capacity / initial charge capacity), and the carbon material for a lithium secondary battery negative electrode, lithium secondary battery A secondary battery negative electrode mixture, a lithium secondary battery negative electrode, and a lithium secondary battery are provided.

The above object is achieved by the following items (1) to (8).
(1) Composite particles composed of particles containing silicon oxide represented by SiO _x (0 <X ≦ 2) and a resin carbon material, and silicon dioxide contained in the entire surface of the composite particles ( X = 2) has an average content of 0.2 or more and 0.6 or less, and (the average content of silicon dioxide (X = 2) contained in the entire surface of the composite particle) / ( The value of silicon dioxide (average content of X = 2) contained in the region from the surface of the composite particle to the cross section appearing at a depth point of 100 nm of the composite particle is 0.3 or more and 0.7 or less A carbon material for a lithium secondary battery negative electrode, comprising the composite particles.
(2) (the average content of silicon dioxide (X = 2) contained in the entire surface of the composite particle) / (appears at a depth point of 100 nm of the composite particle from the surface of the composite particle) The lithium secondary battery negative electrode according to item (1), wherein a value of silicon dioxide (X = 2) in the region up to the cross section is 0.4 or more and 0.6 or less. Carbon material.
(3) The carbon material for a lithium secondary battery negative electrode according to (1) or (2), wherein an average particle diameter of the particles containing silicon oxide is 3 μm or less.
(4) Charcoal for lithium secondary battery negative electrode according to any one of (1) to (3), wherein the content of the particles containing silicon oxide is 5% by mass or more and 60% by mass or less. Material.
(5) The carbon material for a lithium ion secondary battery negative electrode according to any one of (1) to (4), wherein the composite particles have an average particle diameter of 3 μm or more and 15 μm or less.
(6) A negative electrode mixture for a lithium secondary battery comprising the carbon material for a lithium secondary battery negative electrode according to any one of items (1) to (5).
(7) A negative electrode for a lithium secondary battery comprising the negative electrode mixture for a lithium secondary battery according to (6).
(8) A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to item (7).

  ADVANTAGE OF THE INVENTION According to this invention, the carbon material for negative electrode by the charging / discharging cycle is suppressed, and the carbon material for lithium secondary battery negative electrodes which shows the outstanding charge / discharge cycling characteristic which is not in the past is provided. Moreover, according to this invention, the carbon material for lithium secondary battery negative electrodes excellent in initial stage charge / discharge efficiency (initial stage discharge capacity / initial stage charge capacity) is provided.

  Hereinafter, the present invention will be described in more detail.

(1) Carbon Material for Lithium Secondary Battery Negative Electrode A carbon material for a lithium secondary battery negative electrode according to the present invention is composed of particles containing silicon oxide represented by SiO _x (0 <X ≦ 2) and a resin carbon material. The average content of silicon dioxide (X = 2) contained in the entire surface of the composite particle is 0.2 or more and 0.6 or less, and (the surface of the composite particle (The average content of silicon dioxide contained in the whole (X = 2)) / (silicon dioxide contained in a region from the surface of the composite particle to a cross section appearing at a depth point of 100 nm of the composite particle) It is characterized by comprising composite particles having a value of (average content of (X = 2)) of 0.3 or more and 0.7 or less.

The composite particles contained in the carbon material for a negative electrode of a lithium secondary battery according to the present invention are composed of particles containing silicon oxide represented by SiO _x (0 <X ≦ 2) and a resin carbon material. The particles containing silicon oxide may be completely surrounded by the resin carbon material, or may not be completely surrounded by protruding partly from the surface of the resin carbon material, or separately from the resin carbon material. May be present.

The silicon oxide of the particles containing silicon oxide constituting the composite particles is silicon oxide represented by the chemical formula: SiO _x , and X can take any value as long as 0 <X ≦ 2. That is, the silicon oxide of the particles containing silicon oxide constituting the composite particles may be composed of at least two types of silicon oxides in which X has at least two values. When the silicon oxide of the particle containing silicon oxide constituting the composite particle is composed of at least two types of silicon oxide, the composite particle has an inclined structure in which X of silicon oxide increases from the surface of the composite particle toward the center. It is preferable. The rate of increase of X of silicon oxide in the tilted structure is (X of the region up to the cross section appearing at a depth point of 100 nm of the composite particle−X of silicon oxide on the surface of the composite particle) / (the surface of the composite particle) The silicon oxide is represented by the formula X).

Here, the method for deriving X is as follows.
(Method for deriving X)
Monovalent: 1 × monovalent peak area / total peak area = A1
Divalent: 2 × 2 peak area / total peak area = A2
Trivalent: 3 x trivalent peak area / total peak area = A3
Tetravalent: 4 × 4 valence peak area / total peak area = A4
X = (A1 + A2 + A3 + A4) / 2

  The increase rate of X is preferably 3 or less, and more preferably 2.5 or less.

  The shape of the carbon material for a lithium secondary battery negative electrode according to the present invention is not particularly limited, and can have any particle shape such as a lump shape, a scale shape, a spherical shape, or a fibrous shape. The carbon 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 13 μm or less. More preferably, it is 7 μm or more and 11 μm or less. When the average particle diameter is larger than 15 μm, the gap between the carbon material particles becomes large, and when used as a carbon material for a lithium secondary battery negative electrode, the density of the negative electrode may not be improved. On the other hand, when the average particle size is smaller than 3 μm, when viewed per unit mass, the number of carbon material particles increases, and as a result, there is a possibility that problems such as increase in bulk and difficulty in handling.

  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.

The average content of silicon dioxide (X = 2, SiO ₂ ) contained in the entire surface of the composite particles is 0.2 or more and 0.6 or less, and when it is less than 0.2, for negative electrode accompanying charge / discharge When the carbon material expands and contracts, particle collapse occurs, resulting in a problem that the cycle characteristics deteriorate. When the carbon material exceeds 0.6, the discharge capacity of the negative electrode carbon material is small. Here, the average content of silicon dioxide (X = 2, SiO ₂ ) contained in the entire surface of the composite particle is a zero valence peak obtained when an electrode produced by the procedure described later is measured by ESCA. It means the area of the tetravalent peak / the total area of all peaks when waveform separation is performed at the monovalent, divalent, trivalent, and tetravalent peaks. The average content of silicon dioxide (X = 2, SiO ₂ ) contained in the entire surface of the composite particles is preferably 0.20 or more and 0.50 or less, and is 0.25 or more and 0.45 or less. More preferably, it is more preferably 0.25 or more and 0.40 or less.

  (Average content of silicon dioxide (X = 2) contained in the entire surface of the composite particle) / (region from the surface of the composite particle to a cross section appearing at a depth point of 100 nm of the composite particle) The value of the silicon dioxide (X = 2 average content) contained in is 0.3 or more and 0.7 or less, and a cross section appearing at a depth point of 100 nm of the composite particles when it is less than 0.3 The problem is that the amount of silicon dioxide contained in the region up to this point is large and the discharge capacity is not sufficient, and if it exceeds 0.7, the problem is that the amount of silicon dioxide on the surface of the composite particles is large and the discharge capacity is not sufficient.

  Here, the average content of silicon dioxide (X = 2) contained in the entire surface of the composite particles is a zero-valence peak derived from Si obtained when an electrode produced by the procedure described below is measured by ESCA. The area of the tetravalent peak / the total area of all peaks when waveform separation is performed for each of the monovalent, divalent, trivalent, and tetravalent peaks. From the surface of the composite particle, 100 nm of the composite particle The average content of silicon dioxide (X = 2) contained in the region up to the cross section appearing at the depth point is that the surface of the electrode prepared by the procedure described later is processed by Ar etching treatment of 100 nm in the depth direction. The peak obtained when the surface is measured by ESCA is the sum of the tetravalent peak area / all peaks when waveform separation is performed for each of the zero-valent, monovalent, bivalent, trivalent, and tetravalent peaks. It is an area.

  (Average content of silicon dioxide (X = 2) contained in the entire surface of the composite particle) / (from the surface of the composite particle to a cross section appearing at a depth point of 100 nm of the composite particle) The value of silicon dioxide (average content of X = 2) contained in the region is preferably 0.35 or more and 0.65 or less, more preferably 0.40 or more and 0.65 or less, More preferably, it is 0.45 or more and 0.60 or less.

The composite particles contained in the carbon material for a lithium secondary battery negative electrode according to the present invention are formed by mixing particles containing silicon oxide and a carbon precursor to form a mixture in which the particles are dispersed in the carbon precursor, The mixture is then produced by subjecting it to carbonization. By this carbonization treatment, the carbon precursor is converted into a resin carbon material, and a reduction reaction occurs preferentially from the vicinity of the surface of the particles containing silicon oxide, and the converted resin carbon material and SiO _X (0 Composite particles composed of particles containing silicon oxide represented by <X ≦ 2) are produced.

  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.

There is no particular limitation on the method of mixing the silicon oxide particles represented by SiO _x (0 <X ≦ 2) and the carbon precursor, and melting or solution mixing with a stirrer such as a homodisper or a homogenizer; centrifugal crusher In addition, pulverization and mixing using a pulverizer such as a free mill and a jet mill; kneading and mixing using a mortar and pestle can be employed. There is no restriction | limiting in particular also in the order which mixes the said particle | grain and a carbon precursor. In forming the composite particles composed of the resin carbon material and the particles in the particles composed of the particles and the resin carbon material, the particles and the carbon precursor are mixed using a solvent to form a slurry mixture. Alternatively, a carbon precursor may be mixed into the 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.

  In order to adjust the particle size distribution of the carbon material for a lithium secondary battery negative electrode 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 carbon material having an intended average particle diameter is obtained by the above-described pulverization treatment, and the carbon material is further heated to a temperature of 1000 ° C. or more. It is preferable to process (secondary carbonization) by.

  It is preferable that the average particle diameter of the particle | grains containing the silicon oxide which comprises the composite particle contained in the carbon material for lithium secondary battery negative electrodes by this invention is 3 micrometers or less. When the average particle size of the particles containing silicon oxide is more than 3 μm, there is no practical problem, but the particles containing silicon oxide accompanying the charge and discharge are collapsed and the cycle characteristics are deteriorated. May arise. The average particle size of the particles containing silicon oxide is more preferably 1 μm or less, and even more preferably 500 nm or less.

  The content of the particles containing silicon oxide constituting the composite particles contained in the carbon material for a lithium secondary battery negative electrode according to the present invention is preferably 5% by mass or more and 60% by mass or less, and preferably 10% by mass or more and 50% by mass. % Or less, more preferably 15% by mass or more and 40% by mass or less. If the content of the silicon oxide-containing particles is less than 5% by mass, there is no practical problem, but there is a problem that the discharge capacity is small. If it exceeds 60% by mass, there is no practical problem, but charging / discharging. In some cases, there is a problem that the particle characteristics are collapsed due to the expansion and contraction of the carbon material for the negative electrode, and the cycle characteristics are deteriorated. Here, content of the particle | grains containing a silicon oxide is calculated | required from the ash content of the carbon material for lithium secondary battery negative electrodes by this invention after carbonizing. Specifically, the content of particles containing silicon oxide is measured by an ash content test method according to JIS K 2272: 1998.

  The average particle size of the composite particles contained in the carbon material for a lithium secondary battery negative electrode according to the present invention is preferably 3 μm or more and 15 μm or less, more preferably 5 μm or more and 13 μm or less, and 7 μm or more and 11 μm or less. Is more preferable. When the average particle size of the composite particles is less than 3 μm, there is no practical problem, but when viewed per unit mass, the total number of carbon material particles increases, resulting in an increase in bulk and difficulty in handling. If it exceeds 15 μm, there is no practical problem, but the gap between carbon material particles becomes large, and when used as a carbon material for a negative electrode of a lithium secondary battery, the density of the negative electrode is improved. There is a risk that it will not be possible.

(2) Negative electrode mixture for lithium secondary battery The negative electrode mixture for lithium secondary battery according to the present invention contains a carbon material for negative electrode of lithium secondary battery, and the negative electrode for lithium secondary battery according to the present invention obtained as described above. By using the carbon material for an anode as a negative electrode active material, the negative electrode mixture for a lithium secondary battery according to the present invention can be produced. For the negative electrode mixture for lithium secondary batteries according to the present invention, a conventionally known method may be used. The carbon material according to the present invention as a negative electrode active material is added with a binder, a conductive agent, etc. It can be prepared as a slurry having a viscosity.

  The binder used for preparation of the negative electrode mixture according to the present invention may be any conventionally known material, such as polyvinylidene fluoride resin, polytetrafluoroethylene, styrene / butadiene copolymer, polyimide resin, polyamide resin, polyvinyl alcohol. Polyvinyl butyral can be used. In addition, 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 for 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. Examples thereof include N-methyl-2-pyrrolidone, methanol, Examples include acetonitrile.

(3) Negative electrode for lithium secondary battery The negative electrode for lithium secondary battery according to the present invention includes the negative electrode mixture for lithium secondary battery according to the present invention, and the negative electrode for lithium secondary battery according to the present invention obtained as described above. By using the mixture, the negative electrode for a lithium secondary battery according to the present invention can be produced. Specifically, the negative electrode for a lithium secondary battery according to the present invention is formed by coating the negative electrode mixture for a lithium secondary battery according to the present invention on a current collector such as a metal foil to have a thickness of several μm to several hundred μm. And the coating is heat-treated at about 50 to 200 ° C. to remove the solvent or the dispersion medium.

(4) Lithium secondary battery Furthermore, the lithium secondary battery by this invention is producible by using the lithium secondary battery negative electrode by this 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, etc. 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 a several hundred micrometer 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 a 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, 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, 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. In addition, this invention is not limited to a following example in the range which does not deviate from the objective and the main point.

<Example 1>
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 20 parts by mass of methanol is added. Further, 25 parts by mass (average particle size 50 nm) of silicon dioxide (manufactured by Admatechs Co., Ltd.) 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 carbon material was pulverized, and the carbon material obtained by the pulverization treatment was further heated and carbonized for 8 hours after reaching 1050 ° C. to obtain a carbon material for a negative electrode of a lithium secondary battery. The average particle size of the composite particles was 9 μm. The carbon material for a lithium secondary battery negative electrode obtained in Example 1 was subjected to the following battery characteristic evaluation, ESCA valence evaluation, and content evaluation of particles containing silicon oxide. The obtained evaluation results are shown in Table 1 below.

Evaluation of Battery Characteristics (1) Preparation of Negative Electrode Mixture and Negative Electrode The carbon material for a lithium secondary battery negative electrode obtained in Example 1 above was used, and as a binder, 10% polyvinylidene fluoride and acetylene black were used as binders. Each was blended at a ratio of 3%, and an appropriate amount of N-methyl-2-pyrrolidone as a diluent solvent was added and mixed to prepare a slurry-like negative electrode mixture (negative electrode mixture). This negative electrode mixture (negative electrode slurry-like 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-formed 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 secondary battery.

(2) Production of lithium secondary battery The negative electrode, the separator (polypropylene porous film: diameter φ16, thickness 25 μm), and lithium metal (diameter φ12, thickness 1 mm) as the working electrode in this order, Hosen 2032 type It was arranged at a predetermined position in the coin cell. Furthermore, a lithium secondary battery was injected by dissolving lithium perchlorate at a concentration of 1 [mol / liter] in a mixed solution of ethylene carbonate and diethylene carbonate (volume ratio of 1: 1) as an electrolytic solution. Was made.

(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 the initial charge / discharge characteristic evaluation conditions were repeatedly measured 200 times was defined as the discharge capacity at the 200th cycle. Moreover, the cycle property (200 cycle capacity maintenance rate) was defined by the following formula.

  Cycle performance (%, 200 cycle capacity retention rate) = 200th cycle discharge capacity (mAh / g) / initial discharge capacity (mAh / g) × 100

Evaluation of ESCA Valency ESCA was measured as an evaluation of the valence of SiOx in the composite particles of the carbon material for the negative electrode of the lithium secondary battery obtained in Example 1. Using Escalab-220iXL (Thermo Fisher Scientific Co., Ltd.), the measurement was carried out, and the peak derived from Si in which Binding Energy appears at 96 to 106 eV was separated at each valence of 0 to 4 (each valence) The number peak area / total peak area) was defined as the content of each valence of silicon oxide (SiOx).

<Si-derived peak separation>
The positions of the 0-valent, 1-valent, 2-valent, 3-valent, and 4-valent peak tops do not consider the separation of Si _2P1 and Si _2P3 , and the peak top positions of the respective valences are Binding Energy = 98.6 eV, 99. 9eV, 101.1eV, 102.3eV, and 103.4eV were set, and the half width of each peak was 1.1, 1.2, 1.3, 1.5, and 1.7, respectively, and peak separation was performed.

  Here, the average content of silicon dioxide (X = 2) contained in the entire surface of the composite particle is zero valence, and the peak obtained when the electrode prepared by the above procedure is measured by ESCA. The area of the tetravalent peak / the total area of all peaks when waveform separation is performed for each of the monovalent, divalent, trivalent, and tetravalent peaks. From the surface of the composite particle, The average content of silicon dioxide (X = 2) contained in the region up to the cross section appearing at a depth point of 100 nm is 100 nm Ar etching treatment in the depth direction on the electrode surface prepared by the above procedure, The peak obtained when the treated surface is measured by ESCA is the tetravalent peak area / total peak when waveform separation is performed for each of the zero, monovalent, divalent, trivalent, and tetravalent peaks. Is the total area.

Evaluation of the content of particles containing silicon oxide (Method of obtaining from ash content of carbon material)
According to JIS K 2272: 1998, the ash content of the carbon material for a lithium secondary battery negative electrode obtained in Example 1 was measured, and the content of particles containing silicon oxide was measured.

<Example 2>
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 20 parts by mass of methanol is added. Further, 25 parts by mass (average particle diameter: 1 μm) of silicon dioxide (manufactured by Admatechs Co., Ltd.) 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 carbon material was pulverized, the carbon material obtained by the pulverization was further heated, and carbonized for 8 hours after reaching 1050 ° C. to obtain a carbon material for a negative electrode of a lithium secondary battery. The average particle size of the composite particles was 11 μm. About the carbon material for lithium secondary battery negative electrodes obtained in this Example 2, the battery characteristic evaluation method implemented in Example 1 above, the ESCA valence evaluation method, and the evaluation of the content of particles containing silicon oxide The method was evaluated in exactly the same way. The obtained evaluation results are shown in Table 1 below.

<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 20 parts by mass of methanol is added. Further, 25 parts by mass (average particle diameter: 1 μm) of silicon dioxide (manufactured by Admatechs Co., Ltd.) 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 carbon material was pulverized, the carbon material obtained by the pulverization was further heated, and carbonized for 3 hours after reaching 1050 ° C. to obtain a carbon material for a lithium secondary battery negative electrode. The average particle size of the composite particles was 10 μm. Regarding the carbon material for a lithium secondary battery negative electrode obtained in Example 3, the battery characteristic evaluation method performed in Example 1 above, the ESCA valence evaluation method, and the evaluation of the content of particles containing silicon oxide The method was evaluated in exactly the same way. The obtained evaluation results are shown in Table 1 below.

<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 20 parts by mass of methanol is added. Furthermore, 55 parts by mass of silicon dioxide (manufactured by Admatechs Co., Ltd.) (average particle size 1 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 carbon material was pulverized, the carbon material obtained by the pulverization was further heated, and carbonized for 8 hours after reaching 1050 ° C. to obtain a carbon material for a negative electrode of a lithium secondary battery. The average particle size of the composite particles was 11 μm. About the carbon material for lithium secondary battery negative electrodes obtained in this Example 4, the battery characteristic evaluation method implemented in said Example 1, the evaluation method of the valence of ESCA, and the evaluation of the content of particles containing silicon oxide The method was evaluated in exactly the same way. The obtained evaluation results are shown in Table 1 below.

<Example 5>
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 20 parts by mass of methanol is added. Further, 25 parts by mass (average particle size 50 nm) of silicon dioxide (manufactured by Admatechs Co., Ltd.) 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 carbon material is pulverized, and the carbon material obtained by the pulverization treatment is further heated and carbonized for 0.5 hours after reaching 1050 ° C. to obtain a carbon material for a negative electrode of a lithium secondary battery. It was. The average particle size of the composite particles was 9 μm. About the carbon material for lithium secondary battery negative electrodes obtained in this Example 5, the battery characteristic evaluation method implemented in Example 1 above, the ESCA valence evaluation method, and the evaluation of the content of particles containing silicon oxide The method was evaluated in exactly the same way. The obtained evaluation results are shown in Table 1 below.

<Comparative Example 1>
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 20 parts by mass of methanol is added. Further, 10 parts by mass (average particle size: 50 nm) of silicon (Nanostructured & Amorphous Materials, Inc.) 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 carbon material was pulverized, the carbon material obtained by the pulverization was further heated, and carbonized for 8 hours after reaching 1050 ° C. to obtain a carbon material for a negative electrode of a lithium secondary battery. The average particle size of the composite particles was 9 μm. The carbon material for a lithium secondary battery negative electrode obtained in Comparative Example 1 was evaluated in exactly the same manner using the battery characteristic evaluation method and ESCA valence evaluation method implemented in Example 1 above, and contained silicon. The content of the particles was evaluated according to the method for evaluating the content of particles containing silicon oxide, which was performed in Example 1. The obtained evaluation results are shown in Table 1 below.

<Comparative example 2>
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 20 parts by mass of methanol is added. Further, 25 parts by mass (average particle size: 7 μm) of silicon dioxide (manufactured by Admatechs Co., Ltd.) 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 carbon material was pulverized, the carbon material obtained by the pulverization was further heated, and carbonized for 8 hours after reaching 1050 ° C. to obtain a carbon material for a negative electrode of a lithium secondary battery. The average particle size of the composite particles was 10 μm. Regarding the carbon material for a lithium secondary battery negative electrode obtained in Comparative Example 2, the battery characteristic evaluation method implemented in Example 1 above, the ESCA valence evaluation method, and the content evaluation method of particles containing silicon oxide Was evaluated in exactly the same manner. The obtained evaluation results are shown in Table 1 below.

<Comparative 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 20 parts by mass of methanol is added. Further, 25 parts by mass (average particle size 50 nm) of silicon dioxide (manufactured by Admatechs Co., Ltd.) 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 carbon material is pulverized, and the carbon material obtained by the pulverization treatment is further heated and carbonized for 8 hours after reaching 1050 ° C., followed by treatment at 300 ° C. for 10 hours in an air atmosphere. It implemented and obtained the carbon material for lithium secondary battery negative electrodes. The average particle size of the composite particles was 11 μm. Regarding the carbon material for a lithium secondary battery negative electrode obtained in Comparative Example 3, the battery characteristic evaluation method implemented in Example 1 above, the ESCA valence evaluation method, and the content evaluation method of particles containing silicon oxide Was evaluated in exactly the same manner. The obtained evaluation results are shown in Table 1 below.

<Comparative 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 20 parts by mass of methanol is added. Further, 25 parts by mass (average particle diameter: 5 μm) of silicon dioxide (manufactured by Admatechs Co., Ltd.) 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 carbon material is pulverized, and the carbon material obtained by the pulverization treatment is further heated and carbonized for 0.1 hour after reaching 1050 ° C. to obtain a carbon material for a negative electrode of a lithium secondary battery. It was. The average particle size of the composite particles was 11 μm. Regarding the carbon material for a lithium secondary battery negative electrode obtained in Comparative Example 4, the battery characteristic evaluation method implemented in Example 1 above, the ESCA valence evaluation method, and the content evaluation method of particles containing silicon oxide Was evaluated in exactly the same manner. The obtained evaluation results are shown in Table 1 below.

  As is clear from the results shown in Table 1, the initial discharge capacities of the respective lithium secondary batteries produced using the carbon materials for the negative electrodes of the lithium secondary batteries obtained in Examples 1 to 5, respectively, 689 mAh / g, 536 mAh / g, 562 mAh / g, 677 mAh / g, and 507 mAh / g, and the cycle capacity maintenance rates after 200 cycles were 89%, 91%, 90%, 87%, and 85%, respectively. It was. On the other hand, the initial discharge capacity of the lithium secondary battery produced using the carbon material for the negative electrode of the lithium secondary battery obtained in Comparative Example 1 was 936 mAh / g, but the cycle capacity retention rate after 200 cycles was remarkable. Decreased (12%). The 200 cycle capacity retention rates of the lithium secondary batteries produced using the carbon materials for the negative electrodes of the lithium secondary batteries obtained in Comparative Examples 2 to 4 were 95%, 93%, and 94%, respectively. However, the discharge capacity was remarkably low (respectively 376 mAh / g, 311 mAh / g, 341 mAh / g). From the above results, those having a high initial discharge capacity and a high 200 cycle capacity retention rate were prepared using the carbon materials for lithium secondary battery negative electrodes obtained in Examples 1 to 5, respectively. It was a secondary battery.

Claims (8)

Composite particles composed of particles containing silicon oxide represented by SiO _x (0 <X ≦ 2) and a resin carbon material, and silicon dioxide (X = 2) contained in the entire surface of the composite particles ) Is 0.2 or more and 0.6 or less, and (the average content of silicon dioxide (X = 2) contained in the entire surface of the composite particles) / (the composite particles) A composite having a value of silicon dioxide (average content of X = 2) contained in a region from the surface to a cross section appearing at a depth of 100 nm of the composite particle is 0.3 or more and 0.7 or less In a carbon material for a lithium secondary battery negative electrode comprising particles ,
The average content of silicon dioxide (X = 2) contained in the entire surface of the composite particle is calculated by performing waveform separation of peaks obtained when an electrode made of the composite particle is measured by ESCA. The average content of deposited silicon dioxide (X = 2), and
The average content of silicon dioxide (X = 2) contained in the region from the surface of the composite particle to the cross section appearing at a depth point of 100 nm of the composite particle is the average content of the electrode made of the composite particle. The average content of silicon dioxide (X = 2) calculated by etching the surface in the depth direction to 100 nm and performing waveform separation of peaks obtained when the treated surface is measured by ESCA. A carbon material for a negative electrode of a lithium secondary battery.   (The average content of silicon dioxide (X = 2) contained in the entire surface of the composite particle) / (From the surface of the composite particle to the cross section appearing at a depth point of 100 nm of the composite particle) The carbon material for a lithium secondary battery negative electrode according to claim 1, wherein a value of silicon dioxide (X = 2) contained in the region is 0.4 or more and 0.6 or less.   The carbon material for a lithium secondary battery negative electrode according to claim 1 or 2, wherein an average particle diameter of the particles containing silicon oxide is 3 µm or less.   The carbon material for a lithium secondary battery negative electrode according to any one of claims 1 to 3, wherein a content of the particles containing silicon oxide is 5 mass% or more and 60 mass% or less.   The carbon material for a lithium ion secondary battery negative electrode according to any one of claims 1 to 4, wherein an average particle diameter of the composite particles is 3 µm or more and 15 µm or less.   The negative electrode mixture for lithium secondary batteries containing the carbon material for lithium secondary battery negative electrodes of any one of Claim 1 to 5.   The negative electrode for lithium secondary batteries containing the negative electrode mixture for lithium secondary batteries of Claim 6.   A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to claim 7.