JP6747281B2 - Negative electrode active material, negative electrode active material manufacturing method, negative electrode and battery - Google Patents

Description

The present invention relates to a negative electrode active material, a method for producing a negative electrode active material, a negative electrode, and a battery.

In recent years, small electronic devices such as home video cameras, notebook computers, and smartphones have become widespread. Secondary batteries typified by lithium-ion batteries are used for these small electronic devices. Along with further miniaturization and higher performance of small electronic devices, secondary batteries are required to have improved charge/discharge capacity, improved quick charge performance, and longer life.

Graphite powder is used as a negative electrode active material in secondary batteries. For example, in a lithium ion battery, it is common to use an electrolytic solution in which a LiPF ₆ salt is dissolved in a mixed solvent of ethylene carbonate and dialkyl carbonate. The graphite crystal (hexagonal mesh plane) end portion has high reactivity with the electrolytic solution, and the decomposition reaction of the electrolytic solution is likely to occur. Due to this decomposition reaction, decomposition products are deposited on the electrode surface or decomposition gas is generated. Therefore, irreversible capacity is generated, and the initial charge/discharge efficiency is reduced. Therefore, the negative electrode active material is required to have a property of low irreversible capacity, that is, excellent initial charge/discharge efficiency.

Therefore, in order to suppress the decomposition of the electrolytic solution, composite particles in which the surface of graphite is coated with pitch have been proposed.

Japanese Unexamined Patent Publication No. 11-273676 (Patent Document 1) and Japanese Unexamined Patent Publication No. 2012-94505 (Patent Document 2) propose a technique of coating the surface of graphite with a pitch to improve the characteristics of the battery.

Specifically, the lithium ion secondary battery described in Patent Document 1 is obtained by firing a mixture of a graphite material and an organic substance in a mixed gas atmosphere containing an oxidizing gas in an inert gas in an amount of 50 ppm or more and 8000 ppm or less. The composite carbonaceous material obtained by crushing is used as a negative electrode. As a result, it is described in Patent Document 1 that a high capacity can be maintained even during charge/discharge at a high current density.

The carbon material for a non-aqueous electrolyte secondary battery negative electrode described in Patent Document 2 has an aspect ratio of the carbon material of 10 or less, and has a temperature of up to 900° C. measured by a thermal decomposition mass spectrometer (TPD-MS) of the carbon material. The amount of desorbed CO is 2 μmol/g or more and 15 μmol/g or less. In Patent Document 2, a multi-layered carbon material in which spherical graphite is coated with amorphous carbon is subjected to a mechanical treatment, and a carbon material having an oxygen functional group introduced on the surface of the multi-layered carbon material is treated with a non-aqueous electrolyte. Used as an electrode for secondary batteries. As a result, the non-aqueous electrolyte secondary battery using the carbon material for the non-aqueous electrolyte secondary battery negative electrode of Patent Document 2 as an electrode exhibits excellent characteristics having both rapid charge/discharge characteristics and high cycle characteristics. It is described in Patent Document 2.

JP-A-11-273676 JP 2012-94505 A

However, even with the negative electrode active material materials disclosed in the above-mentioned patent documents, compatibility between rapid charge performance (charge acceptability) and initial charge/discharge efficiency was insufficient. The reason for this is as follows. In the conventional graphite material, there is a correlation between the crystallinity (desorbed CO amount) of graphite and the specific surface area as in the material described in Patent Document 2, and when the crystallinity is low (the desorbed CO amount is large), the specific surface area is large. Is large, the charge acceptance is improved, but the initial charge/discharge efficiency is reduced. On the other hand, when the crystallinity is high (the amount of desorbed CO is small), the specific surface area is small and the initial charge/discharge efficiency is improved, but the charge acceptability is reduced. Therefore, it was difficult to achieve both charge acceptability and initial charge/discharge efficiency.

An object of the present invention is to provide a negative electrode active material that can achieve both excellent charge acceptability and initial charge/discharge efficiency.

The negative electrode active material according to the present embodiment includes graphite particles and an amorphous carbon layer on the surface of at least a part of the graphite particles. In the negative electrode active material according to the present embodiment, the specific surface area is 1.5 to ⁵ m ² /g. The CO desorption amount at 150 to 1400° C. in the temperature programmed desorption method is 5 to 20 μmol/g. The ratio R of the CO desorption amount to the specific surface area is 2.5 to 5.0. The substance amount ratio O/H of the oxygen desorption amount to the hydrogen desorption amount at 150 to 1400° C. in the temperature programmed desorption method is 0.25 to 0.35.

The negative electrode active material of the present embodiment can achieve both excellent charge acceptability and initial charge/discharge efficiency.

FIG. 1 is a diagram showing the relationship between the ratio R of the amount of CO desorbed to the specific surface area of the negative electrode active material and the reaction resistance (index of charge acceptability). FIG. 2 is a diagram showing the relationship between the ratio R of the CO desorption amount to the specific surface area and the initial charge/discharge efficiency of the negative electrode active material. FIG. 3 is a diagram showing a relationship between an O/H ratio, which is a substance amount ratio of an oxygen desorption amount to a hydrogen desorption amount at 150 to 1400° C., and a first charge/discharge efficiency by a temperature programmed desorption method. FIG. 4 is a diagram showing the relationship between the initial charge/discharge efficiency and the reaction resistance.

The present inventors have conducted various studies on a method of making the negative electrode active material material have both excellent charge acceptability and initial charge/discharge efficiency. As a result, the inventors have obtained the following findings.

When the crystallinity of the negative electrode active material is high, the number of lithium ion receiving ports is small. In this case, since lithium ions are less likely to be occluded by the negative electrode active material in the electrode, the reaction resistance increases. As a result, charge acceptability is reduced. Graphite has high crystallinity. Therefore, if the graphite particles are coated with an amorphous carbon layer having a functional group, the number of lithium ion inlets increases, and lithium is likely to be occluded by the negative electrode active material in the electrode. As a result, the reaction resistance decreases and the charge acceptability increases.

The above-mentioned functional groups contained in the amorphous carbon layer are, for example, a hydroxy group and an oxo group. Graphite particles coated with an amorphous carbon layer having a functional group are obtained by mixing an epoxy resin having these functional groups, pitch, and graphite particles, and heat-treating the mixture.

The more functional groups contained in the amorphous carbon layer, the lower the crystallinity of the surface of the negative electrode active material. That is, charge acceptability is improved. On the other hand, if the number of functional groups is too large, the reaction with the electrolytic solution is likely to occur, and the initial charge/discharge efficiency decreases. Therefore, the present inventors have found that the charge acceptability and the initial charge/discharge efficiency can be made compatible by adjusting the amount and type of the functional group contained in the amorphous carbon layer.

However, it was difficult to specify the amount and type of functional groups on the surface of the negative electrode active material. Therefore, the present inventors have further studied and found a measurement method by the thermal desorption method. The thermal desorption method has hitherto been used for a substance having a large specific surface area. This is because the measurement of a substance having a small specific surface area was not expected. The substance having a large specific surface area is, for example, activated carbon. The specific surface area of the negative electrode active material according to the present embodiment is smaller than that of activated carbon or the like. Therefore, the conventional device for thermal desorption method has not been used for the negative electrode active material. In this embodiment, the amount and type of the functional group contained in the amorphous carbon layer are specified by the temperature programmed desorption method.

Specifically, the specific surface area is 1.5 to ⁵ m ² /g, the CO desorption amount at 150 to 1400° C. in the temperature programmed desorption method is 5 to 20 μmol/g, and the CO desorption with respect to the specific surface area is The amount ratio R is 2.5 to 5.0, and the substance amount ratio O/H of the oxygen desorption amount to the hydrogen desorption amount at 150 to 1400° C. in the temperature programmed desorption method is 0.25 to 0. If it is 35, the amount and kind of the functional group contained in the amorphous carbon layer are appropriately adjusted. As a result, both charge acceptability and initial charge/discharge efficiency can be achieved.

The reasons for each of the above provisions will be described as follows.

(1) Specific surface area means the surface area per unit mass. When the specific surface area is large, the reaction with the electrolytic solution is enhanced. This improves the acceptability of lithium ions. That is, the reaction resistance is reduced and the charge acceptance is improved. This effect cannot be obtained when the specific surface area is small. On the other hand, if the specific surface area is too large, the irreversible capacity increases. The reason for this is considered as follows. If the specific surface area is too large, the reaction with the electrolytic solution is too high. In this case, lithium is consumed in the irreversible reaction and the initial charge/discharge efficiency decreases. Therefore, in this embodiment, the specific surface area is 1.5 to ⁵ m ² /g.

(2) The amount of CO desorption measured by the temperature programmed desorption method is correlated with the amount of functional groups in the amorphous carbon layer existing on the surface of the negative electrode active material. This is because the functional group of the amorphous carbon layer is decomposed during the measurement by the temperature programmed desorption method. The substances produced by the decomposition are, for example, CO, CO ₂ , H ₂ O. In the present embodiment, among the substances produced by decomposition, the amount of CO produced during the measurement by the temperature programmed desorption method is the CO desorption amount. In the present embodiment, the CO desorption amount is 5 to 20 μmol/g at 150 to 1400° C.

(3) By making the ratio of the CO desorption amount to the above-mentioned specific surface area appropriate, it is possible to achieve both excellent charge acceptability and initial charge/discharge efficiency. The value of (CO desorption amount at 150 to 1400° C.)/(specific surface area) is taken as the ratio R.

FIG. 1 is a diagram showing the relationship between the ratio R and the reaction resistance (index of charge acceptability). FIG. 2 is a diagram showing the relationship between the ratio R and the initial charge/discharge efficiency. 1 and 2 were obtained by the examples described below. In FIGS. 1 and 2, a black circle indicates an example of the present invention that satisfies all the regulations in the present embodiment. In FIGS. 1 and 2, x indicates a comparative example in which any one or more of the rules in the present embodiment are not satisfied. Referring to FIG. 1 and FIG. 2, if the ratio R is 2.5 to 5.0 and the other regulations are satisfied, the reaction resistance is 120Ω or less and the initial charge/discharge efficiency is 93.6% or more. A negative electrode active material can be obtained. Therefore, in this embodiment, the ratio R is set to 2.5 to 5.0.

(4) Furthermore, the substance amount ratio of the oxygen desorption amount to the hydrogen desorption amount (hereinafter referred to as the O/H ratio) measured by the temperature programmed desorption method is the amorphous carbon existing on the surface of the negative electrode active material. Correlates to the type of functional group in the layer. The O/H ratio is the ratio of the amount of oxygen to hydrogen in the total desorption amount of H ₂ , H ₂ O, CO and CO _{2 in} the temperature programmed desorption method. That is, the O/H ratio shows the quantitative relationship between the O-containing functional group and the H-containing functional group. If the O/H ratio is too low, it means that there are few O-containing functional groups. In this case, the initial charge/discharge efficiency decreases. If the O/H ratio is too high, it means that there are too many O-containing functional groups. In this case, functional groups are bound to each other and aggregate during the manufacturing process. When aggregated, the reaction resistance increases and the initial charge/discharge efficiency also decreases.

FIG. 3 is a diagram showing the relationship between the O/H ratio at 150 to 1400° C. and the initial charge/discharge efficiency. FIG. 3 was obtained by the example described below. In FIG. 3, a black circle indicates an example of the present invention that satisfies all the regulations in the present embodiment. In FIG. 3, x indicates a comparative example in which any one or more of the regulations in the present embodiment are not satisfied. Referring to FIG. 3, if the O/H ratio is 0.25 to 0.35 and the other regulations are satisfied, a negative electrode active material having an initial charge/discharge efficiency of 93.6% or more can be obtained. .. Therefore, in this embodiment, the O/H ratio is 0.25 to 0.35 at 150 to 1400°C.

FIG. 4 is a diagram showing the relationship between the initial charge/discharge efficiency and the reaction resistance. FIG. 4 was obtained by the example described below.

In FIG. 4, a black circle indicates an example of the present invention that satisfies all of the above-described specific surface area, CO desorption amount, ratio R and O/H ratio defined in this embodiment. In FIG. 4, x indicates a comparative example in which any one or more of the above-mentioned rules is not satisfied.

With reference to FIG. 4, in the example of the present invention satisfying all the above-described requirements, it is possible to achieve both low reaction resistance and high initial charge/discharge efficiency. Reaction resistance is an index of charge acceptability. That is, the example of the present invention can achieve both excellent charge acceptability and initial charge/discharge efficiency.

(5) In order to satisfy all the above-mentioned requirements, as an example, in the method for producing the negative electrode active material, the pitch and the epoxy resin are mixed so that the mass ratio of the epoxy resin to the pitch is 25 to 750%. The mixture is heat-treated at 900 to 1300° C. under an inert atmosphere. By using this manufacturing method, it is possible to manufacture a negative electrode active material that satisfies all of the above-described specific surface area, CO desorption amount, ratio R and O/H ratio defined in this embodiment.

The negative electrode active material material according to the present embodiment completed based on the above findings includes graphite particles and an amorphous carbon layer on the surface of at least a part of the graphite particles. In the present negative electrode active material, the specific surface area is 1.5 to ⁵ m ² /g. The CO desorption amount at 150 to 1400° C. in the temperature programmed desorption method is 5 to 20 μmol/g. The ratio R of the CO desorption amount to the specific surface area is 2.5 to 5.0. The substance amount ratio O/H of the oxygen desorption amount to the hydrogen desorption amount at 150 to 1400° C. in the temperature programmed desorption method is 0.25 to 0.35.

The negative electrode active material of the present embodiment can achieve both excellent charge acceptability and initial charge/discharge efficiency.

The average particle diameter of the negative electrode active material of this embodiment is, for example, 1 to 50 μm. When the average particle size is 1 μm or more, the specific surface area is appropriately large. In this case, the reaction between the negative electrode and the electrolytic solution can be reduced. Therefore, the irreversible capacity is small, and the initial charge/discharge efficiency is improved. On the other hand, when the average particle size of the negative electrode active material is 50 μm or less, the specific surface area is appropriately small. In this case, since the reaction between the negative electrode and the electrode liquid is moderate, the initial charge/discharge efficiency is further increased.

In the negative electrode active material of the present embodiment, the mass ratio of the amorphous carbon layer in the negative electrode active material is preferably 0.5 to 8%. In this case, the specific surface area becomes more appropriate, and the charge acceptability and the initial charge/discharge efficiency are further improved.

The method for manufacturing the negative electrode active material according to the present embodiment includes a step of preparing graphite particles, a pitch, and an epoxy resin, and the prepared material such that the mass ratio of the epoxy resin to the pitch is 25 to 750%. The method includes the steps of mixing and forming a mixture, and subjecting the mixture to a heat treatment at 900 to 1300° C. under an inert atmosphere.

According to the method for manufacturing the negative electrode active material of the present embodiment, the charge acceptability and the initial charge/discharge efficiency of the negative electrode active material are improved.

The “negative electrode active material material” referred to in the present specification is, for example, a negative electrode active material material for a non-aqueous electrolyte secondary battery typified by a lithium ion secondary battery.

Hereinafter, the negative electrode active material and the method for producing the negative electrode active material of the present embodiment will be described in detail.

[Negative electrode active material]
The negative electrode active material of the present embodiment includes graphite particles and an amorphous carbon layer that covers at least a part of the surfaces of the graphite particles.

[Graphite particles]
The graphite particles may be natural graphite or artificial graphite. Preferred is natural graphite. A mixture of natural graphite and artificial graphite may be used as the graphite particles. The graphite particles are preferably graphite granules having a shape formed by aggregating a plurality of scale-like graphite. The flake graphite is, for example, natural graphite, artificial graphite, mesophase calcined carbon (bulk mesophase) using tar/pitch as a raw material, cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.), etc. Is graphitized. More preferably, the graphite particles are granulated using a plurality of natural graphite having high crystallinity.

Usually, one graphite granule is formed from 2 to 100 scale-like graphite. Preferably, one graphite granule is formed by assembling 3 to 20 scale-like graphite. However, one piece of graphite may be folded into a spherical shape.

As a method of forming a plurality of graphite aggregates to form a graphite granule, for example, a method of mixing a plurality of flake graphite in the coexistence of a binder of graphite raw material, a method of applying a mechanical external force to a plurality of flake graphite, And a method in which the above two methods are used in combination. Preferred is a method of granulating by applying a mechanical external force without using a binder component. As a device for applying a mechanical external force, for example, a counter jet mill AFG (manufactured by Hosokawa Micron Co., Ltd., registered trademark), a current jet (manufactured by Nisshin Engineering Co., Ltd., registered trademark), ACM Pulverizer (manufactured by Hosokawa Micron Co., Ltd.). (Registered trademark), a pulverizer, a hybridization system (manufactured by Nara Machinery Co., Ltd., registered trademark), and a mechano hybrid (manufactured by Nippon Coke Industry Co., Ltd., registered trademark).

The carbon layer plane spacing of the graphite particles is preferably 0.336 nm or less. In this case, high capacity and easy deformability can be obtained.

[Amorphous carbon layer]
The amorphous carbon layer is composed of turbostratic carbon or amorphous carbon. Here, “turbulent layer structure carbon” refers to a carbon substance composed of carbon atoms having a laminated structure parallel to the hexagonal net plane direction but whose crystallographic regularity cannot be measured in the three-dimensional direction. "Amorphous carbon" refers to carbon having a short-range order (several atoms to a dozen or more atoms order) but not a long-range order (several hundreds to thousands of atoms order). In the turbostratic carbon or the amorphous carbon, the development of crystallites called carbon hexagonal mesh plane is smaller than that of graphite. If the hexagonal mesh surface is small, the charge acceptance of lithium is improved. The reason for this is considered as follows. The end portion of the bond between the carbon atoms on the hexagonal network has a functional group. Functional groups have, for example, O and H. By controlling the number, type and composition ratio of this functional group, charge acceptability can be improved.

The amorphous carbon layer may cover at least a part of the surface of the above graphite particles. This increases the number of lithium ion inlets. If the number of lithium ion inlets is large, lithium easily enters and leaves the negative electrode active material in the electrode. As a result, the reaction resistance decreases and the charge acceptability increases.

In the present embodiment, the amorphous carbon layer can be formed on the surface of the graphite particles by manufacturing the negative electrode active material using the above-mentioned graphite particles, pitch and epoxy resin by the manufacturing method described below. .. Therefore, the amorphous carbon layer is derived from pitch and epoxy resin. By mixing the pitch and the epoxy resin, the amorphous carbon layer of the present embodiment has lower crystallinity than the coating layer composed of only the pitch. As a result, it has excellent charge acceptance.

[pitch]
A known pitch can be used. The pitch is, for example, a coal pitch or a petroleum pitch. Coal-based pitch has a relatively low impurity content. Therefore, the coal pitch is preferable.

Preferably, the softening point of the pitch is 50 to 150°C. When the softening point is 50 to 150° C., the compatibility between the pitch and the epoxy resin is increased during the heat treatment in the method for producing the negative electrode active material material described later. Therefore, the amorphous carbon layer has lower crystallinity. As a result, the reaction resistance is reduced and the charge acceptance is further enhanced.

The particle size of the pitch is preferably 5 to 50 μm.

[Epoxy resin]
A known epoxy resin can be used. The epoxy resin has a functional group. Functional groups are, for example, hydroxy groups and oxo groups.

Preferably, the softening point of the epoxy resin is 50 to 150°C. More preferably, the softening point of the epoxy resin is about the same as the softening point of the pitch. In this case, the compatibility between the epoxy resin and the pitch increases during the heat treatment in the method for manufacturing the negative electrode active material described later. Therefore, the amorphous carbon layer has lower crystallinity. As a result, the reaction resistance is reduced and the charge acceptance is further enhanced.

Preferably, the epoxy equivalent of the epoxy resin is 500 to 1500 g/eq. When the epoxy equivalent of the epoxy resin is 1500 g/eq or less, the amorphous carbon layer contains more functional groups. As a result, the reaction resistance is reduced and the charge acceptance is further enhanced. When the epoxy equivalent of the epoxy resin is 500 g/eq or more, the amount of functional groups contained in the amorphous carbon layer is appropriate, and aggregation is less likely to occur during the production of the negative electrode active material.

The negative electrode active material of the present embodiment can be obtained by mixing the graphite particles, the pitch, and the epoxy resin described above with a manufacturing method described below and performing heat treatment.

[Specific surface area: 1.5 to ⁵ m ² /g]
When the specific surface area is large, lithium ion acceptance is enhanced. That is, the reaction resistance is reduced and the charge acceptance is improved. If the specific surface area is less than 1.5 m ² /g, this effect cannot be obtained. On the other hand, when the specific surface area exceeds 5 m ² /g, the irreversible capacity increases. That is, the initial charge/discharge efficiency is reduced. Therefore, in this embodiment, the specific surface area is 1.5 to ⁵ m ² /g.

In this embodiment, the specific surface area is obtained by the BET method. Specifically, gas molecules of nitrogen (N ₂ ) are adsorbed on the negative electrode active material. The specific surface area of the negative electrode active material is measured from the amount of adsorbed gas molecules. More specifically, first, the single molecule adsorption amount (Vm) is obtained from the relationship between the pressure (P) and the adsorption amount (V) using the BET formula (Brunauer, Emmet and Teller's equation). Vm is the mass of gas molecules adsorbed on the surface of the negative electrode active material. Then, the specific surface area of the negative electrode active material is obtained using the adsorption cross-sectional area (Am) of gas molecules. Am means the occupied area per molecule. The specific surface area is calculated by the formula (1).
Specific surface area = (Vm x N/M) x Am/w (1)
Here, N is Avogadro's number (6.02×10 ²³ /mol), M is the molecular weight of gas molecule (=mass of one gas molecule×N), and w is sample weight (g).
In the case of nitrogen (N ₂ ), Am is 0.162 nm ² .

[CO desorption amount: 5 to 20 μmol/g]
The amount of CO desorption measured by the temperature programmed desorption method is correlated with the amount of functional groups present on the surface of the negative electrode active material. In the negative electrode active material of this embodiment, the CO desorption amount at 150 to 1400° C. is 5 to 20 μmol/g. When the CO desorption amount is less than 5 μmol/g, it means that the amount of functional groups existing on the surface of the negative electrode active material is small. If the amount of functional groups present on the surface of the negative electrode active material is small, the reaction resistance increases. As a result, charge acceptability is reduced. If the CO desorption amount exceeds 20 μmol/g, it means that the amount of functional groups present on the surface of the negative electrode active material is too large. If the amount of functional groups present on the surface of the negative electrode active material is too large, the decomposition reaction of the electrolytic solution proceeds. As a result, the initial charge/discharge efficiency decreases. Therefore, in this embodiment, the CO desorption amount is 5 to 20 μmol/g at 150 to 1400° C.

[Method of measuring CO desorption amount: temperature programmed desorption method]
In the present embodiment, the CO desorption amount is measured by the temperature programmed desorption method. Specifically, the negative electrode active material is heated at a constant heating rate, and the desorbed gas is measured by a mass spectrometer. For the measurement by the temperature programmed desorption method, for example, a product name TDS1200-II manufactured by Electronic Science Co., Ltd. can be used. For example, quartz can be used for the sample table.

More specifically, first, as a pretreatment condition of the device, a baking process of the device is performed before measurement. After baking, as a background measurement, the ion current value is measured without a sample (only on the sample table). In this embodiment, the measurement conditions are as follows. First, heat from room temperature to 150°C. After reaching 150°C, hold for 5 minutes. After holding, it is heated from 150°C to 1400°C. After reaching 1400°C, hold for 10 minutes. During this thermal history, the ionic current value is continuously measured. Then, the ionic current value is measured under the same conditions with the negative electrode active material placed on the sample table. The ionic current value obtained by subtracting the ionic current value of only the sample table from the ionic current value of the negative electrode active material and the sample table is the ionic current value of the negative electrode active material. Each desorbed gas has a unique mass-to-charge ratio (M/z). Therefore, each gas is detected as an ion current value for each M/z. The M/z of H ₂ , H ₂ O, CO and CO ₂ are ₂ , 18, 28 and 44, respectively. The ionic current value from 150 to 1400° C. is integrated and multiplied by each gas type. The obtained value is converted into the number of molecules to calculate the desorption amount of each gas.

[Ratio of CO desorption amount to specific surface area R: 2.5 to 5.0]
By appropriately adjusting the ratio of the CO desorption amount to the specific surface area described above, it is possible to achieve both charge acceptability and initial charge/discharge efficiency. The ratio of the CO desorption amount to the specific surface area, that is, the value of (CO desorption amount)/(specific surface area) is defined as a ratio R. If the ratio R is less than 2.5, the initial charge/discharge efficiency is increased, but the reaction resistance is increased and the charge acceptability is decreased. When the ratio R exceeds 5.0, the reaction resistance decreases, so the charge acceptability increases, but the initial charge/discharge efficiency decreases. Therefore, in this embodiment, the ratio R of the CO desorption amount to the specific surface area is 2.5 to 5.0.

[O/H ratio: 0.25 to 0.35]
The substance amount ratio (O/H ratio) of the oxygen desorption amount to the hydrogen desorption amount measured by the temperature programmed desorption method correlates with the type of functional group present on the surface of the negative electrode active material. The O/H ratio is a substance amount ratio of an oxygen desorption amount to a hydrogen desorption amount in the total desorption amount of H ₂ , H ₂ O, CO and CO _{2 in} the temperature programmed desorption method. That is, the O/H ratio shows the quantitative relationship between the O-containing functional group and the H-containing functional group. When the O/H ratio is less than 0.25, it means that there are few O-containing functional groups. In this case, the initial charge/discharge efficiency decreases. If the O/H ratio exceeds 0.35, it means that there are too many O-containing functional groups. In this case, agglomeration occurs during the heat treatment in the manufacturing process. Therefore, in this embodiment, the O/H ratio is 0.25 to 0.35 at 150 to 1400°C.

The O/H ratio is calculated as follows. The amounts of H ₂ , H ₂ O, CO, and CO ₂ to be desorbed are calculated by the above-mentioned temperature programmed desorption method. From the total substance amount, the O and H substance amounts are calculated. The obtained ratio of the substance amounts of O and H is defined as the O/H ratio.

[Particle size of negative electrode active material]
The average particle diameter of the negative electrode active material of this embodiment is, for example, 1 to 50 μm. When the average particle size is 1 μm or more, the specific surface area is appropriately large. In this case, the reaction between the negative electrode and the electrolytic solution can be reduced. Therefore, the irreversible capacity is small, and the initial charge/discharge efficiency is improved. On the other hand, when the average particle size of the negative electrode active material is 50 μm or less, the specific surface area is appropriately small. In this case, since the reaction between the negative electrode and the electrode liquid is moderate, the initial charge/discharge efficiency is further increased. If the particle size is 50 μm or less, a flat and thin electrode can be produced. When the particle size is 50 μm or less, the specific surface area of the negative electrode active material is further appropriately small. In this case, since the reaction between the negative electrode and the electrode liquid is moderate, the initial charge/discharge efficiency is further increased. A more preferable lower limit of the particle size of the negative electrode active material is 5 μm. A more preferable upper limit of the particle size of the negative electrode active material is 20 μm.

The method for measuring the particle size of the negative electrode active material is not particularly limited. In the present embodiment, for example, a laser diffraction/scattering particle size distribution meter (model LA-910) manufactured by Horiba Ltd. is used, and the particle size at a volume fraction of 50% is taken as the particle size of the negative electrode active material.

The negative electrode active material material of the present embodiment can be used as an active material forming an electrode, particularly a negative electrode of a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery is, for example, a lithium ion secondary battery.

[Method for producing negative electrode active material]
Next, a method for manufacturing the negative electrode active material will be described. The manufacturing method of the negative electrode active material is a step of preparing the above graphite particles, a pitch, and an epoxy resin, and mixing the prepared materials so that the mass ratio of the epoxy resin to the pitch is 25 to 750%. A step of forming a mixture, and a step of subjecting the mixture to a heat treatment at 900 to 1300° C. under an inert atmosphere.

[Preparation process]
First, the above-mentioned graphite particles, pitch, and epoxy resin are prepared.

[Mixing process]
The prepared graphite particles, pitch, and epoxy resin are mixed. The mixing method is not particularly limited. The mixing method may be, for example, a physical mixing method in which powders of the prepared materials are simply mixed and ground in a mortar. Alternatively, the pitch and the epoxy resin may be dissolved in a solvent and mixed, and further graphite particles may be added and mixed. The solvent used at this time is, for example, tetrahydrofuran. In this case, a proper amount of functional groups are formed on the surface of the graphite particles.

[Mass ratio of epoxy resin to pitch: 25 to 750%]
Preferably, the mass ratio of the epoxy resin to the pitch ((mass of epoxy resin/mass of pitch)×100) is 25 to 750%. If the mass ratio of the epoxy resin to the pitch is less than 25%, the amount of functional groups existing on the surface of the negative electrode active material will be insufficient. In this case, the CO desorption amount and/or the O/H ratio are out of the range of the present invention. On the other hand, if the mass ratio of the epoxy resin to the pitch exceeds 750%, the amount of functional groups present on the surface of the negative electrode active material is too large. In this case, the negative electrode active material cannot be obtained due to aggregation during the manufacturing process. Therefore, the mass ratio of the epoxy resin to the pitch is 25 to 750%. The lower limit of the mass ratio of the epoxy resin to the pitch is preferably 55%, more preferably 88%. The upper limit of the mass ratio of the epoxy resin to the pitch is preferably 500%, more preferably 200%.

[Heat treatment process]
The temperature is raised to and maintained at a temperature not lower than the softening point of the pitch and the epoxy resin and not higher than 300° C. under an inert atmosphere with respect to the mixture. The holding time is 60 minutes, for example. Thereby, the pitch and the epoxy resin are sufficiently compatible with each other. After maintaining this temperature, the mixture is subjected to heat treatment at 900 to 1300°C. The heat treatment causes the mixture to carbonize. The inert atmosphere is, for example, nitrogen and argon. After heat treatment, pulverization and classification may be performed if necessary. If the heat treatment temperature is lower than 900°C, the amount of CO desorbed from the negative electrode active material becomes too large. If the heat treatment temperature exceeds 1300° C., the amount of CO desorbed from the negative electrode active material will be insufficient. The preferable lower limit of the heat treatment temperature is 1000°C. The preferable upper limit of the heat treatment temperature is 1200°C.

The heat treatment time is not particularly limited, but is 1 hour, for example.

The atmosphere during the heat treatment is preferably nitrogen.

[Mass ratio of amorphous carbon layer in negative electrode active material: 0.5 to 8%]
Preferably, the mass ratio of the amorphous carbon layer in the negative electrode active material is 0.5 to 8%. If this ratio is 0.5% or more, the amorphous carbon layer is sufficiently formed. In this case, the amount of functional groups on the surface of the amorphous carbon is moderately large and the entrance of lithium ions is moderate, so that the acceptability of lithium ions is enhanced. That is, the reaction resistance is reduced and the charge acceptance is improved. When the mass ratio of the amorphous carbon layer in the negative electrode active material is 8% or less, the amorphous carbon layer does not increase too much and the initial charge/discharge efficiency is further increased. Therefore, the mass ratio of the amorphous carbon layer in the negative electrode active material is 0.5 to 8%. The preferable lower limit of the mass ratio of the amorphous carbon layer in the negative electrode active material is 1%. The preferable upper limit of the mass ratio of the amorphous carbon layer in the negative electrode active material is 6%.

The mass ratio of the amorphous carbon layer in the negative electrode active material is calculated by the formula (2) by obtaining the mass before heat treatment and the mass after heat treatment of the sample.
Mass ratio (%) of the amorphous carbon layer in the negative electrode active material = ((weight after heat treatment (graphite + carbon)-weight before heat treatment (graphite))/weight after heat treatment (graphite)) x 100 (2)

The negative electrode active material is manufactured by the above manufacturing process.

[Negative electrode and battery manufacturing method]
An example of the method of manufacturing the negative electrode according to the present embodiment is as follows. A binder is mixed with the above-mentioned powder of the negative electrode active material to prepare a negative electrode mixture. The binder is, for example, a water-insoluble resin such as polyvinylidene fluoride (PVDF), polymethylmethacrylate (PMMA), polytetrafluoroethylene (PTFE), etc., which is insoluble in the solvent used for the non-aqueous electrolyte of the battery. Examples thereof include water-soluble resins such as carboxymethyl cellulose (CMC) and vinyl alcohol (PVA), and styrene butadiene rubber (SBR).

A solvent such as water is added to the negative electrode mixture, and if necessary, the mixture is sufficiently stirred using a homogenizer and glass beads to produce a negative electrode mixture slurry. This slurry is applied to an active material support such as rolled copper foil or electrodeposited copper foil and dried. Then, if necessary, the dried product is pressed. The negative electrode is manufactured through the above steps.

[battery]
The battery of this embodiment is a non-aqueous electrolyte secondary battery. The battery includes the negative electrode described above. The battery includes, for example, the negative electrode of this embodiment, a positive electrode, a separator, and an electrolytic solution or electrolyte.

The shape of the battery may be cylindrical, prismatic, coin-shaped, sheet-shaped, or the like. The battery of this embodiment may be a battery using a solid electrolyte such as a polymer battery.

The positive electrode preferably contains a transition metal compound containing a metal ion as an active material. More preferably, the positive electrode contains a transition metal compound containing lithium (Li) as an active material. The Li-containing transition metal compound is, for example, LiM ₁ -xM′xO ₂ or LiM ₂ yM′O ₄ . Here, in the formula, 0≦x, y≦1, M and M′ are barium (Ba), cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), titanium (Ti), respectively. , Vanadium (V), iron (Fe), zinc (Zn), aluminum (Al), indium (In), tin (Sn), scandium (Sc), and yttrium (Y).

The battery of the present embodiment includes a transition metal chalcogenide; a vanadium oxide and a lithium (Li) compound thereof; a niobium oxide and a lithium compound thereof; a conjugated polymer using an organic conductive substance; a Sheprel phase compound; activated carbon, activated carbon. Other positive electrodes such as fibers may also be used.

The electrolytic solution is generally a non-aqueous electrolytic solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. The lithium salt is, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiB(C ₆ H ₅ ), LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO. ₃ , Li(CF ₂ SO ₂ ) ₂ , LiCl, LiBr, LiI and the like. These may be used alone or in combination. As the organic solvent, carbonic acid esters such as propylene carbonate, ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate are preferable. However, various other organic solvents such as carboxylic acid ester and ether can also be used. These organic solvents may be used alone or in combination.

The separator is installed between the positive electrode and the negative electrode. The separator acts as an insulator. The separator also contributes significantly to the retention of the electrolyte. The battery of this embodiment may include a known separator. The separator is, for example, a polyolefin material such as polypropylene, polyethylene, or a mixed cloth of both materials, or a porous body such as a glass filter.

A laminate in which a separator and a positive electrode are sequentially laminated on the negative electrode is manufactured. The laminate is put in a case to manufacture a battery.

[Preparation of negative electrode active material]
[Preparation process]
In the negative electrodes of Test Nos. 1 to 36, the product name CS5S 1412-1 manufactured by Chuo Denki Kogyo was used as the graphite particles. The average particle size of the graphite particles was as shown in Table 1. Pitch powder manufactured by C-Chem was used for the negative electrodes of Test Nos. 1 to 31, 35 and 36. The pitch powder had an average particle diameter of 35 μm and a softening point of 85° C. No pitch was used for the negative electrodes of Test No. 32 to Test No. 34. An epoxy resin was used for the negative electrodes of test numbers 1 to 21, 32, 33, 35, and 36. Epoxy resin Epotote YD-014 manufactured by Nippon Steel & Sumikin Chemical Co., Ltd. was used as the epoxy resin. The epoxy equivalent of the epoxy resin was 900 to 1000 g/eq, and the average softening point was 100°C. No epoxy resin was used for the negative electrodes of test numbers 22 to 31 and 34.

[Average particle size of pitch powder]
The average particle diameter of the pitch powder is a particle diameter at a volume fraction of 50%, which is obtained by using a laser diffraction/scattering type particle size distribution meter (model LA-910) manufactured by Horiba Ltd. The dispersion medium in the measurement was water containing 0.1% by mass of a surfactant containing alkylglycoxide, the dispersion method was ultrasonic wave for 5 minutes, and the laser light transmittance in the measurement was 85 to 95%. And

[Mixing process]
The epoxy resin was ground in a coffee mill. The ground epoxy resin and pitch were mixed. Further, graphite particles were physically mixed with the mixture of the epoxy resin and the pitch. The compounding amount, the compounding ratio, and the mass ratio of the epoxy resin to the pitch were as shown in Table 1.

[Measurement of Mass Ratio of Amorphous Carbon Layer in Negative Electrode Active Material]
The mass ratio of the amorphous carbon layer in the negative electrode active material was calculated by the formula (2) by calculating the mass before heat treatment and the mass after heat treatment of the sample.

[Heat treatment process]
The temperature of the obtained mixture was raised to 200° C. in 1 hour. Then, the temperature was maintained at 200° C. for 1 hour. At this time, since 200° C. was higher than the softening point of the pitch and the epoxy resin, the pitch and the epoxy resin were compatible with each other. The temperature was further raised to 600° C. in 4 hours, and further raised to the heat treatment temperature shown in Table 1 in 2.5 hours. The heat treatment temperature shown in Table 1 was maintained for 1 hour. Then, it cooled to 100 degrees C or less, and manufactured the negative electrode active material. The average particle size of the obtained negative electrode active material was 8 to 20 μm.

[Specific surface area measurement]
The specific surface area was measured and calculated by the BET method as described above. For the measurement, a product name Kantosorb manufactured by Yuasa Ionics Co., Ltd. was used. The measurement conditions were nitrogen gas adsorption, degassing temperature of 200° C., and 1 hour.

[Measurement of CO desorption amount]
The CO desorption amount was measured by the temperature programmed desorption method. The product name TDS1200-II manufactured by Electronic Science Co., Ltd. was used for the measurement. Quartz was used for the sample stage. As a pretreatment condition of the device, a baking process of the device was performed before the measurement. After the baking treatment, as the background measurement, the measurement was performed without the sample (only the sample table), and the ion current value was measured. Next, 100 mg of the negative electrode active material was placed on the sample stand as a sample, and the ion current value was measured in the same manner. In the background measurement and sample measurement, the measurement conditions were as follows using the MID mode. Regarding the temperature history, the temperature was raised from room temperature to 150° C., and after reaching 150° C., it was held for 5 minutes. After the holding, the temperature was raised to 150 to 1400°C, and after reaching 1400°C, the temperature was held for 10 minutes. In each heating process, the heating rate was 0.5° C./s in all cases. The measurement pressure was 5×10 ⁻⁵ Pa to 1×10 ⁻⁷ Pa. The ion current of the sample was calculated by subtracting the ion current of only quartz (background measurement) from the ion current of sample+quartz (sample evaluation). The quantitative value was calculated as follows. For the ion current values from 150 to 1400° C., the ion current values at the mass-to-charge ratio M/z=2, 18, 28, 44 were integrated. The obtained integrated value was multiplied by a coefficient for each gas type and converted into the number of molecules. The calculated value was used as the desorption amount of each gas. The mass-to-charge ratio M/z= ₂ , 18, 28, 44 was specified as H ₂ , H ₂ O, CO, and CO ₂ .

[Calculation of ratio R of CO desorption amount to specific surface area]
The ratio R was calculated from the specific surface area and CO desorption amount obtained in the above test.

[Calculation of O/H ratio]
The amounts of desorbed H ₂ , H ₂ O, CO, and CO ₂ were calculated by the above-mentioned temperature programmed desorption method. The amounts of O and H were calculated from the total amount of substances. The ratio of the substance amount of O to H thus obtained was defined as the O/H ratio.

[Manufacture of negative electrode]
A mixture was prepared by mixing 1 part by mass of carboxymethylcellulose (CMC) (binder) powder with 98 parts by mass of the manufactured negative electrode active material (powder). Further, 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (SBR) was added to the mixture and then stirred to prepare a negative electrode mixture slurry. The compounding ratio was a mass ratio of negative electrode active material material: CMC:SBR=98:1:1.

The negative electrode mixture slurry was thinly applied onto one surface of an electrolytic copper foil having a thickness of 17 μm using a doctor blade (75 μm) and dried to form a coating film. The coating amount of the negative electrode material mixture slurry on the copper foil was 4.0 to 5.0 mg/cm ² . The coating film was punched out using a punch having a diameter of 13 mm to obtain pellets. A negative electrode was manufactured by pressing the pellets using a press molding machine. The pressure applied by the press molding machine was adjusted so that the density of the obtained negative electrode was about 1.20 g/cm ³ .

The density of the obtained electrode was determined by measuring the thickness with a micrometer and measuring the mass. Specifically, by subtracting the thickness and mass values of the copper foil measured in advance from those measured values, the thickness and mass of the portion other than the copper foil are determined, and the density of the electrode is determined from these numerical values. It was

[Preparation of coin cell (for initial charge/discharge efficiency measurement)]
[Counter electrode]
Li metal foil was used for the counter electrode.

[Battery manufacturing]
A coin type non-aqueous test cell was manufactured using the prepared counter electrode, negative electrode, electrolyte and separator. A non-aqueous solution was used as the electrolytic solution. The non-aqueous solution was prepared by dissolving LiPF ₆ as a supporting electrolyte in a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC)=1:3 (volume ratio) so that the concentration was 1M. A polyolefin separator (φ19 mm) was used as the separator. Negative electrode and counter electrode lithium metal foils were placed on both sides of the separator in a stainless coin cell containing an electrolytic solution.

In the evaluation with the counter electrode Li, originally, the doping of Li into the graphite negative electrode is treated as discharge. However, in this example, since the negative electrode material was evaluated, the “charge capacity” and the “discharge capacity”, which are not mentioned below, mean the capacity on the doped side and the capacity on the dedoped side, respectively.

[Evaluation of initial charge and discharge efficiency]
The initial charging/discharging efficiency of the battery of each test number was evaluated by the following method. A charge/discharge device manufactured by Electrofield was used for the measurement of the initial charge/discharge efficiency. The temperature at the time of measurement was measured at room temperature (23°C).

Constant current charging was performed on the coin type non-aqueous test cell with a current value of 0.2 mA until the potential difference became 0 V with respect to the counter electrode. Then, while maintaining 0 V, the counter electrode was continuously charged with a constant voltage until the current reached 0.005 mA, and the charge capacity was measured.

Next, discharge was performed at a current value of 0.2 mA until the potential difference became 1.5 V, and the discharge capacity was measured. The initial charge/discharge efficiency was calculated as (initial discharge capacity)/(initial charge capacity)×100.

[Preparation of 3-electrode type laminated cell (for reaction resistance measurement)]
The reaction resistance was calculated by fitting a resistance component corresponding to the resistance of the negative electrode by an electrochemical impedance method using an equivalent circuit. The product name modulab manufactured by Solartron was used for the electrochemical measurement. The structure of the electrochemical cell was measured using a three-electrode type laminated cell, using a surface-treated graphite-coated electrode as the negative electrode, lithium cobalt oxide as the counter electrode, and a LiAl wire as the reference electrode. A non-aqueous solution was used as the electrolytic solution. The non-aqueous solution was prepared by dissolving LiPF ₆ as a supporting electrolyte in a mixed solvent of ethylene carbonate (EC):ethyl methyl carbonate (EMC)=1:3 (volume ratio) so that the concentration was 1M. As for the reaction resistance, the resistance of only the negative electrode was calculated by connecting the negative electrode and the reference electrode with a terminal and measuring the electrochemical impedance. The measurement was carried out in a constant temperature bath at a reaction temperature of -30°C.

[Manufacture of positive electrode]
LiCoO ₂ was used for the positive electrode. The positive electrode was manufactured as follows.

A mixture was prepared by mixing 10 parts by mass of acetylene black powder with 80 parts by mass of the positive electrode active material (powder). Further, 10 parts by mass of PVDF dispersion liquid was added to the mixture and then stirred to prepare a positive electrode mixture slurry. The compounding ratio was a mass ratio, and the positive electrode active material material: acetylene black: PVDF=80:10:10.

The positive electrode mixture slurry was thinly applied on one side of a 17 μm thick aluminum foil using a doctor blade (150 μm) and dried to form a coating film. The amount of the positive electrode mixture slurry applied on the copper foil was 11.7 to 12.5 mg/cm ² . The coating film was punched out using a punch having a diameter of 13 mm to obtain pellets. The pellet was pressed using a press molding machine to manufacture a positive electrode. The pressure applied by the press molding machine was adjusted to be 100 kgf/cm ² .

[Production of laminated cell]
As the negative electrode, the same negative electrode used in the initial charge/discharge efficiency evaluation was used. The electrode was cut out so that the negative electrode was 2.5 cm×2.5 cm and the positive electrode was 2.3 cm×2.3 cm, and two separators (Celguard 2100) were sandwiched between the negative electrode and the positive electrode. An aluminum wire (0.25 mmφ) was placed between the two separators.

[Lamicelle pretreatment (pretreatment before reaction resistance calculation)]
As a pretreatment for calculating the reaction resistance, a charge/discharge test was carried out at room temperature (23° C.) so that the laminate cell had a state of charge (SOC) of 50%. A charging/discharging device manufactured by Electrofield was used.

The specific processing method is described below. The charging conditions were constant current charging and then constant potential charging. After constant current charging at 0.2 mA/cm ² to 4.2 V, constant potential charging was performed at 4.2 V until the current value became 0.02 mA/cm ² . The discharge conditions were constant current discharge. Specifically, constant current discharge was performed at 0.2 mA/cm ² to 3.0 V. The above charging/discharging was repeated for 2 cycles. After that, constant current charging was performed so that the SOC became 50%.

[Preparation of reference electrode]
In the pre-processed Lamicelle, the positive electrode and the reference electrode were connected by a terminal, and the Al wire was alloyed with Li. Specifically, it was charged with a constant current of 0.03 mA so that the amount of electricity was 0.3 mAh.

[Method of evaluating reaction resistance]
The pre-treatment and the preparation of the reference electrode were completed, and the Lamicelle was kept in a constant temperature bath at a set temperature of -30°C for 3 hours or more. After that, AC impedance was measured using a product name modulab manufactured by Solartron. At this time, the impedance between the negative electrode and the reference electrode was measured using the negative electrode as the working electrode. The measurement conditions were an amplitude of 5 mV and a frequency range of 0.1 Hz to 10 kHz. ZPlot (registered trademark) (manufactured by Scribner Associates, Inc.) was used as the analysis software. From the arc component obtained by the Nyquist plot of the AC impedance measurement, the reaction resistance was determined by fitting with an equivalent circuit (Instant fit Rs (CPE-Rp)) with a built-in ZPlot (registered trademark).

[Measurement result]
The results are shown in Table 2. In Table 2, "No" in the "Aggregation" column indicates that the material did not aggregate during the manufacturing process, and "Yes" indicates that the material aggregated during the manufacturing process.

With reference to Table 1 and Table 2, the method for producing the graphite particles, the amorphous carbon layer, and the negative electrode active material of Test No. 1 to Test No. 15 was appropriate. As a result, the reaction resistance was 120Ω or less, and the initial charge/discharge efficiency was 93.6% or more. That is, it was possible to achieve both excellent charge acceptability and initial charge/discharge efficiency.

On the other hand, in the test number 16, the heat treatment temperature was low. Therefore, the CO desorption amount became too large, and the ratio R exceeded the upper limit. As a result, the initial charge/discharge efficiency was low.

Test No. 17 had a high heat treatment temperature. Therefore, the ratio R was less than the lower limit, the reaction resistance was high, and the initial charge/discharge efficiency was low.

In Test No. 18, the mass ratio of the epoxy resin to the pitch exceeded 750%, so the CO desorption amount was too high. Therefore, the ratio R and the O/H ratio exceeded the upper limits, and they aggregated. As a result, the initial charge/discharge efficiency was low.

In Test No. 19, the mass ratio of the epoxy resin to the pitch exceeded 750%, so the O/H ratio exceeded the upper limit. Therefore, it aggregated. As a result, the reaction resistance was high and the initial charge/discharge efficiency was low.

Test number 20 and test number 21 had a specific surface area of less than 1.5 m ² /g. Therefore, the ratio R exceeds the upper limit. As a result, the reaction resistance was high.

Test No. 22 had no epoxy resin added. Therefore, the CO desorption amount and the ratio R were less than the lower limit. As a result, the initial charge/discharge efficiency was low.

Test number 23 did not add epoxy resin. Therefore, the ratio R and the O/H ratio were less than the lower limits. As a result, the initial charge/discharge efficiency was low.

Test number 24 did not add epoxy resin. Therefore, the O/H ratio was less than the lower limit. As a result, the initial charge/discharge efficiency was low.

Test number 25 did not add an epoxy resin. Therefore, the CO desorption amount and the ratio R were less than the lower limit. As a result, the reaction resistance was high.

Test No. 26 had no epoxy resin added. Therefore, the CO desorption amount, the ratio R, and the O/H ratio were less than the lower limits. As a result, the reaction resistance was high.

Test number 27 did not add an epoxy resin. Furthermore, the specific surface area was less than 1.5 m ² /g. Therefore, the CO desorption amount, the ratio R, and the O/H ratio were less than the lower limits. As a result, the reaction resistance was high.

Test No. 28 had no epoxy resin added. Furthermore, the heat treatment temperature was low. Therefore, the CO desorption amount exceeded the upper limit, the ratio R exceeded the upper limit, and the O/H ratio was less than the lower limit. As a result, the reaction resistance was high and the initial charge/discharge efficiency was low.

Test number 29 did not add an epoxy resin. Therefore, the O/H ratio was less than the lower limit. As a result, the reaction resistance was high and the initial charge/discharge efficiency was low.

Test number 30 and test number 31 did not add the epoxy resin. Therefore, the ratio R and the O/H ratio were less than the lower limits. As a result, the initial charge/discharge efficiency was low.

Test number 32 did not add pitch. Therefore, the ratio R and the O/H ratio were less than the lower limits. As a result, the reaction resistance was high and the initial charge/discharge efficiency was low.

Test number 33 did not add pitch. Therefore, the O/H ratio exceeded the upper limit and the particles aggregated. As a result, the reaction resistance was high and the initial charge/discharge efficiency was low.

Test number 34 did not add pitch and epoxy resin. Therefore, the CO desorption amount and the ratio R were less than the lower limit, and the O/H ratio exceeded the upper limit. As a result, the reaction resistance was high and the initial charge/discharge efficiency was low.

In Test No. 35, the mass ratio of the amorphous carbon layer in the negative electrode active material was less than 0.5%. Therefore, the specific surface area exceeded 5 m ² /g and the ratio R was less than the lower limit. As a result, the initial charge/discharge efficiency was low.

In Test No. 36, the mass ratio of the amorphous carbon layer in the negative electrode active material exceeded 8%. Therefore, the specific surface area was less than 1.5 m ² /g, the ratio R exceeded the upper limit, and the particles aggregated. As a result, the reaction resistance was high.

The embodiments of the present invention have been described above. However, the above-described embodiments are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit thereof.

Claims (6)

Graphite particles,
An amorphous carbon layer is provided on the surface of at least a part of the graphite particles,
The specific surface area is 1.5 to 5 m ² /g, the CO desorption amount at 150 to 1400° C. in the temperature programmed desorption method is 5 to 20 μmol/g, and the ratio of the CO desorption amount to the specific surface area is R is 2.5 to 5.0, and the substance amount ratio O/H of the oxygen desorption amount to the hydrogen desorption amount at 150 to 1400° C. in the temperature programmed desorption method is 0.25 to 0.35. There is a negative electrode active material. The negative electrode active material according to claim 1, wherein
A negative electrode active material having an average particle size of 1 to 50 μm. The negative electrode active material according to claim 1 or 2, wherein the mass percentage of the amorphous carbon layer in the negative electrode active material is 0.5 to 8%. It is a manufacturing method of the negative electrode active material according to any one of claims 1 to 3,
A step of preparing the graphite particles, pitch, and an epoxy resin,
A step of mixing the graphite particles, the pitch, and the epoxy resin so that a mass ratio of the epoxy resin to the pitch is 25 to 750% to form a mixture;
A step of subjecting the mixture to a heat treatment at 900 to 1300° C. in an inert atmosphere, a method for producing a negative electrode active material. A negative electrode, comprising the negative electrode active material material according to any one of claims 1 to 3. A battery comprising the negative electrode according to claim 5.

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