JP7190252B2 - Non-graphitizable carbonaceous materials for non-aqueous electrolyte secondary batteries, negative electrodes for non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries - Google Patents

Description

The present invention provides a non-graphitizable carbonaceous material suitable as a negative electrode of a fully charged non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery), a method for producing the same, a negative electrode for a non-aqueous electrolyte secondary battery, and a fully charged non-aqueous electrolyte secondary battery. It relates to a charged non-aqueous electrolyte secondary battery.

Lithium ion secondary batteries are widely used in small portable devices such as mobile phones and notebook computers. The non-graphitizable carbonaceous material is capable of doping (charging) and undoping (discharging) lithium in an amount exceeding the theoretical capacity of graphite, 372 mAh/g, and also has good input/output characteristics, cycle durability and low temperature characteristics. Because of its excellent properties, it has been developed and used as a negative electrode for lithium ion secondary batteries.

The non-graphitizable carbonaceous material can be obtained, for example, from petroleum pitch, coal pitch, phenolic resin, or plant as a carbon source. Among these carbon sources, plants are attracting attention because they are raw materials that can be sustainably and stably supplied by cultivation and are available at low cost. In addition, a carbonaceous material obtained by sintering a plant-derived carbon raw material is expected to have a good charge/discharge capacity because it has many pores.
For example, Patent Literature 1 and Patent Literature 2 describe a carbonaceous material for an electrode of a non-aqueous solvent secondary battery, and describe that the carbonaceous material is obtained by carbonizing a plant-derived organic matter. there is

In a lithium-ion secondary battery, if it goes beyond the fully charged state during charging and becomes overcharged, the decomposition reaction of the solvent will occur, the temperature of the lithium-ion secondary battery will rise, and the reaction at the positive electrode will increase Lithium ions are generated and metal lithium is deposited on the surface of the negative electrode which can no longer be received, and the thermal stability of the lithium ion secondary battery is lowered. In order to solve this problem, safety is usually ensured against overcharging. For example, Patent Document 3 describes a lithium ion secondary battery equipped with a current interrupting device, and Patent Document 4 describes an electrolyte for a lithium secondary battery containing an additive that effectively acts against overcharge. Lithium secondary batteries with liquid are described.
On the other hand, in order to ensure safety more reliably, charging a lithium-ion secondary battery is normally carried out until the negative electrode terminal potential reaches a predetermined potential of 0 mV or more (for example, 0.5 mA/ cm ² ), and after the negative terminal potential reaches a predetermined potential, constant voltage charging is performed, and charging is completed when the current value (for example, at 20 μA) becomes constant for a predetermined time (constant current constant voltage Act). In this case, even if the negative electrode still has room to accept lithium ions, the battery is not charged until it reaches a fully charged state.

JP-A-9-161801 JP-A-10-21919 JP 2015-88354 A JP-A-2001-15155

On the other hand, in recent years, due to growing interest in environmental issues, the development of lithium-ion secondary batteries for in-vehicle applications has progressed and is being put to practical use. Therefore, there is a need for a non-graphitizable carbonaceous material for producing lithium-ion batteries that have higher charge-discharge efficiency as well as higher charge capacity.

In addition to high charge capacity and high charge-discharge efficiency, the subject of the present invention is to have high output characteristics due to low electrode resistance, and to be used as a negative electrode of a non-aqueous electrolyte secondary battery (for example, a lithium ion battery) that is used after being fully charged. The object of the present invention is to provide a non-graphitizable carbonaceous material and a method for producing the same. The subject of the present invention is also a negative electrode for a non-aqueous electrolyte secondary battery comprising such a non-graphitizable carbonaceous material, and a fully charged negative electrode for a non-aqueous electrolyte secondary battery comprising such a negative electrode for a non-aqueous electrolyte secondary battery. An object of the present invention is to provide a non-aqueous electrolyte secondary battery.

As a result of intensive studies by the present inventors, the negative electrode of a non-aqueous electrolyte secondary battery used in a fully charged state has a non-graphitizable carbonaceous material that provides a specific ⁷ Li nucleus-solid NMR analysis chemical shift value and a specific electrode expansion rate. The inventors have found that the above problems can be solved by using the material, and have completed the present invention.

That is, the present invention includes the following preferred embodiments.
[1] A non-graphitizable carbonaceous material for the negative electrode of a non-aqueous electrolyte secondary battery that is used after being fully charged, and is based on lithium chloride observed by ⁷ Li nucleus-solid NMR analysis when fully charged. The main resonance peak position of the chemical shift value is greater than 115 ppm, and the expansion rate of the negative electrode containing the non-graphitizable carbonaceous material at full charge is 107% or less based on the thickness of the negative electrode before charging. A non-graphitizable carbonaceous material.
[2] The non-graphitizable carbonaceous material according to [1] above, which has an oxygen element content of 0.30% by mass or less.
[3] The non-graphitizable carbonaceous material according to the above [1] or [2], which is derived from a plant-derived carbon precursor.
[4] Any of the above [1] to [3], wherein the average interplanar spacing d ₀₀₂ of the (002) plane calculated using the Bragg formula according to the wide-angle X-ray diffraction method is 0.36 to 0.42 nm The non-graphitizable carbonaceous material described.
[5] The non-graphitizable carbonaceous material according to any one of [1] to [4], which has a potassium element content of 0.1% by mass or less and an iron element content of 0.02% by mass or less.
[6] The above [1] to [5], comprising a step of acid-treating a plant-derived carbon precursor, and a step of firing the acid-treated carbon precursor at 1050°C to 1400°C in an inert gas atmosphere. A method for producing a non-graphitizable carbonaceous material according to any one of the above.
[7] A negative electrode for a non-aqueous electrolyte secondary battery, comprising the non-graphitizable carbonaceous material according to any one of [1] to [5].
[8] A fully charged nonaqueous electrolyte secondary battery comprising a negative electrode for a nonaqueous electrolyte secondary battery comprising a non-graphitizable carbonaceous material, wherein when fully charged, ⁷ Li nucleus- The main resonance peak position of the chemical shift value based on lithium chloride observed by solid-state NMR analysis is greater than 115 ppm, and the expansion rate at full charge of the negative electrode comprising the non-graphitizable carbonaceous material is equal to that before charging A non-aqueous electrolyte secondary battery having a negative electrode thickness of 107% or less.
[9] The non-aqueous electrolyte secondary battery according to [8], wherein the oxygen element content is 0.30% by mass or less.
[10] The non-aqueous electrolyte secondary battery according to [8] or [9] above, wherein the non-graphitizable carbonaceous material is derived from a plant-derived carbon precursor.
[11] The average interplanar spacing d ₀₀₂ of the (002) plane of the non-graphitizable carbonaceous material calculated using the Bragg formula according to the wide-angle X-ray diffraction method is 0.36 to 0.42 nm, the above [8] to The non-aqueous electrolyte secondary battery according to any one of [10].
[12] The above [8] to [11], wherein the non-graphitizable carbonaceous material has a potassium element content of 0.1% by mass or less and an iron element content of the non-graphitizable carbonaceous material is 0.02% by mass or less. ] The non-aqueous electrolyte secondary battery according to any one of the above.

When the non-graphitizable carbonaceous material of the present invention is used for the negative electrode and a fully charged non-aqueous electrolyte secondary battery is produced, such a non-aqueous electrolyte secondary battery has high charge capacity and high charge-discharge efficiency. In addition, it has high output characteristics due to low electrode resistance.

1 shows a ⁷ Li nuclear-solid NMR pattern of a non-graphitizable carbonaceous material prepared according to Example 1. FIG. 7 shows a ⁷ Li nuclear-solid NMR diagram of a carbonaceous material prepared according to Comparative Example 5. FIG.

<Non-graphitizable carbonaceous material>
The non-graphitizable carbonaceous material of the present invention is a non ^- graphitizable carbonaceous material for a negative electrode of a non-aqueous electrolyte secondary battery that is used in a fully charged state. The main resonance peak position of the chemical shift value based on lithium chloride is greater than 115 ppm, and the expansion rate of the negative electrode containing the non-graphitizable carbonaceous material at full charge is based on the thickness of the negative electrode before charging 107% or less.

As used herein, the phrase “used after being fully charged” means that a non-aqueous electrolyte secondary battery is assembled using a negative electrode containing a non-graphitizable carbonaceous material and a positive electrode containing lithium, and deposition of metallic lithium is achieved. ⁷ Li nucleus - Lithium is charged (doped) to the negative electrode until just before it is confirmed by solid state NMR analysis, and is usually charged to a range of 580 to 700 mAh / g per unit mass of the negative electrode active material at a constant current value. means that Therefore, it has a completely different meaning from using the battery after charging by the conventional constant current constant voltage method as described above. The charge capacity of the negative electrode when lithium was charged to the negative electrode until immediately before the deposition of metallic lithium was confirmed by ⁷ Li nucleus-solid NMR analysis was compared to the charge capacity at which lithium deposition was confirmed, the discharge capacity and the charge capacity. From the viewpoint of maintaining a high discharge efficiency, it is preferably set at 80 to 98%, more preferably at 85 to 95%, and particularly preferably at 88 to 92%.

<Main resonance peak position of chemical shift value>
The non-graphitizable carbonaceous material of the present invention is charged (doped) with lithium to a fully charged state, and the chemical shift value based on lithium chloride observed when ⁷ Li nucleus-solid NMR analysis is performed. The main resonance peak position is greater than 115 ppm, preferably greater than 117 ppm, more preferably greater than 119 ppm.

The fact that the main resonance peak position of the chemical shift value relative to lithium chloride is greater than 115 ppm, that is, the main resonance peak position is observed on the lower magnetic field side than 115 ppm indicates that clustering in the non-graphitizable carbonaceous material A large lithium storage capacity means that the battery has a high charging capacity. The occluded clustered lithium is reversible lithium that can be discharged (dedoped) from the non-graphitizable carbonaceous material. It means that the charge/discharge efficiency calculated from "capacity/charge capacity" is high.

A high charging/discharging efficiency means that there is little loss of lithium in the negative electrode due to side reactions during charging/discharging. If the loss of lithium in the negative electrode is small, there is no need to supplement the negative electrode with lithium by using an excessive amount of the positive electrode, which is advantageous in terms of capacity per battery volume and cost.

In a carbonaceous material having a main resonance peak position of 115 ppm or less in a chemical shift value with respect to lithium chloride, the amount of clustered lithium occlusion is small. Therefore, like the non-graphitizable carbonaceous material of the present invention, high charge capacity and high charge-discharge efficiency are extremely difficult.

In order to adjust the main resonance peak position to a value larger than the above value, for example, the carbon-containing material is heated to a temperature of 1050° C. to 1400° C. while actively removing thermal decomposition gases such as carbon monoxide and hydrogen. A non-graphitizable carbonaceous material manufactured by firing in an active gas atmosphere may be used for the negative electrode. The details of the ⁷ Li nucleus-solid NMR analysis are as described in the Examples.

<Expansion rate of electrode>
The expansion rate of the negative electrode containing the non-graphitizable carbonaceous material of the present invention when fully charged is 107% or less based on the thickness of the negative electrode before charging. If the expansion rate exceeds 107%, contact failure occurs between the active materials in the electrodes and the electrode resistance increases, so a non-aqueous electrolyte secondary battery having good output characteristics (high discharge capacity retention rate) cannot be obtained. do not have.
The expansion rate is preferably 106% or less, particularly preferably 105% or less. When the expansion coefficient is equal to or less than the above upper limit, a conductive path between the active materials (non-graphitizable carbonaceous materials) in the electrode and the diffusion of lithium ions are easily ensured, so that a low electrode resistance is easily obtained. output characteristics are easily obtained.

In order to adjust the electrode expansion coefficient to the above value or less, for example, a material containing carbon is subjected to an inert gas atmosphere at 1050° C. to 1400° C. while actively removing thermal decomposition gases such as carbon monoxide and hydrogen. A non-graphitizable carbonaceous material manufactured by firing at is used for the negative electrode. In the negative electrode comprising the non-graphitizable carbonaceous material produced by the above method, many lithium ions are charged not only between the carbon crystal layers but also in the gaps between the carbon crystal layers, so that lithium ions are charged only between the carbon crystal layers. It is believed to result in a significantly lower electrode expansion rate than the conventional negative electrode that is used. The details of the measurement of the expansion rate are as described in Examples.

<Oxygen element content>
The oxygen element content of the non-graphitizable carbonaceous material of the present invention is preferably as low as possible. The oxygen element content is preferably 0.30% by mass or less, more preferably 0.28% by mass or less. More preferably, the non-graphitizable carbonaceous material contains substantially no oxygen element. Here, "substantially free of elemental oxygen" means that the elemental oxygen content is 10 ^-6 % by mass, which is the detection limit of the method for measuring the elemental oxygen content (inert gas fusion-nondispersive infrared absorption method) described later. means that: If the elemental oxygen content is less than the above value, lithium ions are consumed by the reaction between lithium ions and oxygen, resulting in a decrease in lithium ion utilization efficiency. Decrease in utilization efficiency of lithium ions due to inability to easily desorb, generation of gas in the electrode due to side reactions derived from moisture, and increase in electrode expansion rate due to the generation of gas (increase in electrode resistance, deterioration in output characteristics) is easily suppressed.

The method for adjusting the oxygen element content to the above value or less is not limited at all. For example, a plant-derived carbon precursor is acid-treated at a predetermined temperature, mixed with a volatile organic substance, and fired at a temperature of 1050° C. to 1400° C. under an inert gas atmosphere to reduce the elemental oxygen content to the above value. You can adjust below. The details of the measurement of the oxygen element content are as described in Examples.

<Carbon precursor of plant origin>
The non-graphitizable carbonaceous material of the present invention is preferably derived from a plant-derived carbon precursor. In the present invention, "plant-derived carbon precursor" means a plant-derived material before carbonization or a plant-derived material (plant-derived char) after carbonization. The plant used as the raw material (hereinafter sometimes referred to as "plant raw material") is not particularly limited. Examples include coconut husks, coffee beans, tea leaves, sugarcane, fruits (eg, oranges, bananas), straw, rice husks, hardwoods, conifers, and bamboo. Examples of this include waste after it has been put to its original use (eg, spent tea leaves), or a portion of plant material (eg, banana or orange peel). These plants can be used singly or in combination of two or more. Among these plants, coconut shells, which are easily available in large quantities, are preferred.

Coconut shells are not particularly limited. For example, coconut shells of palm (oil palm), coconut, salak or hyacinth. These coconut shells can be used alone or in combination. Particularly preferred are coconut shells of coconut palms and palm palms, which are biomass wastes generated in large amounts and are used as raw materials for foods, detergents, biodiesel oils, and the like.

The method of carbonizing plant raw materials, ie, the method of producing plant-derived char, is not particularly limited. For example, it is carried out by heat-treating the plant raw material in an inert gas atmosphere at 300° C. or higher (hereinafter sometimes referred to as “calcination”).

It is also available in the form of char (eg, coconut shell char).

As a raw material for the non-graphitizable carbonaceous material of the present invention, by using a plant-derived carbon precursor having appropriate microvoids, micropores capable of absorbing a large amount of clustered lithium are formed inside the non-graphitizable carbonaceous material. It is formed. In addition, since the expansion coefficient of the electrode containing the non-graphitizable carbonaceous material of the present invention is low, the many micropores of the non-graphitizable carbonaceous material can reduce the volume change of the electrode active material during charging and discharging. Partial absorption is thought to contribute.

<Average surface distance d ₀₀₂ >
In the non-graphitizable carbonaceous material of the present invention, the average interplanar spacing d ₀₀₂ of the (002) plane calculated using the Bragg formula according to the wide-angle X-ray diffraction method is preferably 0.36 nm to 0.42 nm, It is more preferably 0.38 nm to 0.40 nm, and particularly preferably 0.381 nm to 0.389 nm. When the average interplanar spacing d ₀₀₂ of the (002) plane is within the above range, the resistance when lithium ions are inserted into the carbonaceous material increases and the resistance during output increases, resulting in a lithium ion battery. deterioration of the input/output characteristics of the In addition, deterioration in stability as a battery material due to repeated expansion and contraction of the non-graphitizable carbonaceous material is likely to be suppressed. Furthermore, although the diffusion resistance of lithium ions is reduced, the decrease in the effective capacity per volume due to the increase in the volume of the non-graphitizable carbonaceous material can be easily avoided. In order to adjust the average interplanar spacing to the above range, for example, the carbon precursor that gives the non-graphitizable carbonaceous material may be sintered at a temperature in the range of 1050 to 1400°C. Alternatively, a method of mixing with a thermally decomposable resin such as polystyrene and firing, or a method of subjecting a non-graphitizable carbonaceous material fired at 1050 to 1400° C. to a CVD treatment using a hydrocarbon gas or the like can also be used. Here, the details of the measurement of the average interplanar spacing _d002 are as described in Examples.

<true density ρ _Bt >
The non-graphitizable carbonaceous material of the present invention preferably has a true density ρ _{Bt measured} by the butanol method of 1.40 to 1.70 g/cm ³ from the viewpoint of increasing the capacity per mass of the battery. It is more preferably 42 to 1.65 g/cm ³ , particularly preferably 1.44 to 1.60 g/cm ³ . A true density within the above range can be obtained, for example, by setting the firing temperature to 1050 to 1400° C. when producing a non-graphitizable carbonaceous material from a plant raw material. Here, the details of the measurement of the true density ρ _Bt are as described in Examples.

<Potassium element content and iron element content>
The potassium element content of the non-graphitizable carbonaceous material of the present invention is preferably 0.1% by mass or less, more preferably 0.05% by mass, from the viewpoint of increasing the dedoping capacity and decreasing the non-dedoping capacity. It is more preferably 0.03 mass % or less, more preferably 0.03 mass % or less. It is particularly preferred that the non-graphitizable carbonaceous material contains substantially no elemental potassium. In addition, the iron element content of the non-graphitizable carbonaceous material of the present invention is preferably 0.02% by mass or less, and 0.015% by mass, from the viewpoint of increasing the dedoping capacity and decreasing the non-dedoping capacity. It is more preferably 0.01% by mass or less, more preferably 0.01% by mass or less. It is particularly preferred that the non-graphitizable carbonaceous material contains substantially no elemental iron. Here, substantially free of potassium element or iron element means that the potassium element content or iron element content is determined by the fluorescent X-ray analysis described later (for example, analysis using "LAB CENTER XRF-1700" manufactured by Shimadzu Corporation). It means below the detection limit. When the potassium element content and the iron element content are equal to or less than the above values, sufficient dedoping capacity and non-dedoping capacity are likely to be obtained in the non-aqueous electrolyte secondary battery using the non-graphitizable carbonaceous material. Furthermore, the problem of safety of the non-aqueous electrolyte secondary battery caused by short-circuiting when these metal elements are eluted and re-deposited in the electrolyte can be easily avoided. The details of the measurement of the potassium elemental content and the iron elemental content are as described in Examples.

<Amount of moisture absorbed>
The moisture absorption of the non-graphitizable carbonaceous material of the present invention is preferably 10000 ppm or less, more preferably 9000 ppm or less, and particularly preferably 8000 ppm or less. The smaller the amount of moisture absorbed, the less water is adsorbed to the non-graphitizable carbonaceous material and the more lithium ions are adsorbed to the non-graphitizable carbonaceous material, which is preferable. In addition, the smaller the amount of moisture absorption, the more the self-discharge due to the reaction between the adsorbed moisture and lithium ions can be reduced, and the side reaction products and gas generation due to the reaction between the adsorbed moisture and lithium ions can be suppressed, which is preferable. The moisture absorption amount of the non-graphitizable carbonaceous material can be reduced, for example, by reducing the amount of oxygen atoms contained in the non-graphitizable carbonaceous material. The moisture absorption of the non-graphitizable carbonaceous material is measured using, for example, Karl Fischer. The details of the measurement of moisture absorption are as described in Examples.

<Specific surface area>
The non-graphitizable carbonaceous material of the present invention preferably has a specific surface area of 1 to 75 m ² /g, more preferably 2 to 60 m ² /g, as determined by the nitrogen adsorption BET three-point method. 50 m ² /g is particularly preferred. When the specific surface area is within the above range, in a non-aqueous electrolyte secondary battery manufactured using a non-graphitizable carbonaceous material, excessive side reactions between the electrolyte and the non-graphitizable carbonaceous material are suppressed while lithium ions are generated. is easily doped into the non-graphitizable carbonaceous material, and the contact area for dedoping lithium ions from the non-graphitizable carbonaceous material is likely to be kept high, so both high charge capacity and high output characteristics are easily achieved. The specific surface area can be adjusted, for example, by controlling the temperature of the deashing process described below.

<Method for producing non-graphitizable carbonaceous material>
The method for producing a non-graphitizable carbonaceous material of the present invention comprises a step of acid-treating a plant-derived carbon precursor, and a step of firing the acid-treated carbon precursor at 1050° C. to 1400° C. in an inert gas atmosphere. include.

<Carbon precursor of plant origin>
By "plant-derived carbon precursor" is meant the plant-derived material before carbonization or after carbonization (plant-derived char), as described above. The plant (plant material) used as the raw material is not particularly limited. Plants such as those exemplified above can be used alone or in combination of two or more. Among these, coconut shells, which are easily available in large quantities, are preferred.

Coconut shells are not particularly limited. Coconut shells such as those exemplified above can be used alone or in combination. Particularly preferred are coconut shells of coconut palms and palm palms, which are biomass wastes that are used as foods, raw materials for detergents, raw materials for biodiesel oil, and the like, and which are generated in large amounts.

The method of carbonizing plant raw materials, ie, the method of producing plant-derived char, is not particularly limited. For example, it is carried out by calcining the plant raw material in an inert gas atmosphere at 300° C. or higher.

It is also available in the form of char (eg, coconut shell char).

In general, plant materials include alkali metal elements (e.g. potassium and sodium), alkaline earth metal elements (e.g. magnesium and calcium), transition metal elements (e.g. iron and copper) and non-metal elements (e.g. phosphorus), etc. contains a lot of When such a non-graphitizable carbonaceous material containing a large amount of metallic elements and non-metallic elements is used as the negative electrode, it may adversely affect the electrochemical characteristics and safety of the non-aqueous electrolyte secondary battery.

<Acid treatment>
Accordingly, the method for producing a non-graphitizable carbonaceous material of the present invention includes a step of acid-treating a plant-derived carbon precursor. Here, reducing the content of metallic elements and/or non-metallic elements in the carbon precursor by subjecting the carbon precursor of plant origin to an acid treatment is hereinafter also referred to as deashing.

The acid treatment method, that is, the deashing method is not particularly limited. For example, mineral acids such as hydrochloric acid or sulfuric acid, acid water containing organic acids such as acetic acid or formic acid, etc. are used to extract and demineralize metals (liquid phase demineralization), or halogen compounds such as hydrogen chloride are used. A method of demineralizing by exposing to a high-temperature gas phase (vapor-phase demineralization) can be used.

<Liquid phase decalcification>
In the liquid phase demineralization, a plant-derived carbon precursor is immersed in an organic acid aqueous solution, and an alkali metal element, an alkaline earth metal element, a transition metal element and/or a non-metal element is removed from the plant-derived carbon precursor. Removal by elution is preferred.

When carbonizing a plant-derived carbon precursor containing these metal elements, the carbonaceous material necessary for carbonization may be decomposed. In addition, since non-metallic elements such as phosphorus are easily oxidized, the degree of oxidation of the surface of the carbide changes, which greatly changes the properties of the carbide, which is not preferable. Furthermore, when liquid phase demineralization is performed after carbonization of the carbon precursor, phosphorous, calcium, magnesium, potassium and iron may not be sufficiently removed. Further, the amount of metal elements and/or non-metal elements remaining in the carbide after liquid phase demineralization and the amount of metal elements and/or non-metal elements remaining in the carbide after liquid phase demineralization greatly differ depending on the content of metal elements and/or non-metal elements in the carbide. Therefore, it is preferable to sufficiently remove the content of metallic elements and/or non-metallic elements in the carbon precursor before carbonization. That is, in liquid-phase demineralization, it is preferable to use a plant-derived material before carbonization as the "plant-derived carbon precursor".

The organic acids used in liquid phase demineralization are preferably free of impurity source elements such as phosphorus, sulfur and halogens. When the organic acid does not contain elements such as phosphorus, sulfur and halogen, it is suitable as a carbon material even if the carbon precursor in which the organic acid remains is carbonized without washing with water after liquid phase demineralization. This is advantageous because it provides a carbide that can be used for Moreover, it is advantageous because it is possible to relatively easily treat the used organic acid waste liquid without using a special apparatus.

Examples of organic acids include saturated carboxylic acids such as formic acid, acetic acid, propionic acid, oxalic acid, tartaric acid and citric acid, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and fumaric acid, aromatic Carboxylic acids such as benzoic acid, phthalic acid and naphthoenoic acid are included. Acetic acid, oxalic acid and citric acid are preferred from the standpoint of availability, corrosion due to acidity and effects on the human body.

In the present invention, the organic acid is mixed with an aqueous solution and used as an organic acid aqueous solution from the viewpoints of the solubility of eluted metal compounds, disposal of waste, and environmental compatibility. Aqueous solutions include water and mixtures of water and water-soluble organic solvents. Water-soluble organic solvents include, for example, alcohols such as methanol, ethanol, propylene glycol or ethylene glycol.

The acid concentration in the organic acid aqueous solution is not particularly limited. The concentration can be adjusted according to the type of acid used. In the present invention, usually 0.001% by mass to 20% by mass, more preferably 0.01% by mass to 18% by mass, and particularly preferably 0.02% by mass to 15% by mass based on the total amount of the organic acid aqueous solution. An aqueous organic acid solution with a range of acid concentrations is used. If the acid concentration is within the above range, an appropriate elution rate of metallic elements and/or non-metallic elements can be obtained, so liquid phase demineralization can be performed in a practical time. In addition, since the residual amount of acid in the carbon precursor is reduced, the effect on subsequent products is also reduced.

The pH of the organic acid aqueous solution is preferably 3.5 or less, more preferably 3 or less. When the pH of the organic acid aqueous solution is equal to or less than the above value, the metallic element and/or the nonmetallic element can be efficiently removed without lowering the dissolution rate of the metallic element and/or the nonmetallic element in the organic acid aqueous solution. easy to do.

The temperature of the organic acid aqueous solution when the carbon precursor is immersed is not particularly limited. The range is preferably 45°C to 120°C, more preferably 50°C to 110°C, and particularly preferably 60°C to 100°C. If the temperature of the organic acid aqueous solution when the carbon precursor is immersed is within the above range, the decomposition of the acid used is suppressed, and the liquid phase demineralization can be performed within a practical time. It is preferable because the dissolution rate can be easily obtained. Moreover, it is preferable because liquid phase deashing can be easily performed without using a special device.

The time for immersing the carbon precursor in the organic acid aqueous solution can be appropriately adjusted according to the acid used. In the present invention, the immersion time is usually in the range of 1 to 100 hours, preferably 2 to 80 hours, more preferably 2.5 to 50 hours, from the viewpoint of economy and deashing efficiency.

The ratio of the mass of the carbon precursor to be immersed to the mass of the organic acid aqueous solution can be appropriately adjusted according to the type, concentration and temperature of the organic acid aqueous solution used, and is usually 0.1% by mass to 200% by mass. , preferably 1% to 150% by mass, more preferably 1.5% to 120% by mass. Within the above range, the metallic element and/or non-metallic element eluted into the organic acid aqueous solution is less likely to precipitate from the organic acid aqueous solution, and redeposition to the carbon precursor is likely to be suppressed, which is preferable. Moreover, if it is within the above range, it is preferable from an economical point of view because the volumetric efficiency is appropriate.

The atmosphere for liquid phase demineralization is not particularly limited, and may vary depending on the method used for immersion. In the present invention, liquid phase demineralization is normally carried out in an air atmosphere.

These operations may be repeated preferably 1 to 8 times, more preferably 2 to 5 times.

In the present invention, after liquid phase demineralization, a washing step and/or a drying step may be performed as necessary.

<Vapor phase demineralization>
As vapor phase deashing, it is preferable to heat-treat a plant-derived carbon precursor in a vapor phase containing a halogen compound. In gas-phase demineralization, if a rapid thermal decomposition reaction of plant-derived carbon precursors is involved during heat treatment, the efficiency of gas-phase demineralization will decrease due to the generation of thermal decomposition components, and the generated thermal decomposition components will cause the inside of the heat treatment equipment to become clogged. Contamination may interfere with stable operation. From these points of view, it is preferable to use a carbonized plant-origin material as the "plant-origin carbon precursor."

Halogen compounds used in gas-phase deashing are not particularly limited. For example, fluorine, chlorine, bromine, iodine, hydrogen fluoride, hydrogen chloride, hydrogen bromide, iodine bromide, chlorine fluoride (ClF), iodine chloride (ICl), iodine bromide (IBr), bromine chloride (BrCl) and mixtures thereof can be used. Compounds that generate these halogen compounds by thermal decomposition, or mixtures thereof can also be used. Hydrogen chloride is preferably used from the viewpoint of supply stability and stability of the halogen compound to be used.

In vapor phase deashing, a mixture of a halogen compound and an inert gas may be used. The inert gas is not particularly limited as long as it does not react with the carbon component constituting the plant-derived carbon precursor. For example, nitrogen, helium, argon, krypton, or mixtures thereof can be used. Nitrogen is preferably used from the viewpoint of supply stability and economy.

In vapor phase demineralization, the mixing ratio of the halogen compound and the inert gas is not limited as long as sufficient demineralization can be achieved. For example, from the viewpoint of safety, economic efficiency, and persistence in the carbon precursor, the amount of the halogen compound relative to the inert gas is preferably 0.01 to 10.0% by volume, more preferably 0.05. 8.0% by volume, particularly preferably 0.1 to 5.0% by volume.

The temperature for vapor phase demineralization may be varied depending on the plant-derived carbon precursor to be demineralized, but from the viewpoint of easily obtaining the desired oxygen element content and specific surface area, it is preferably 500 to 950°C. is 600 to 940°C, more preferably 650 to 940°C, particularly preferably 850 to 930°C. When the demineralization temperature is within the above range, good demineralization efficiency is obtained, sufficient demineralization is easily achieved, and activation by a halogen compound is easily avoided.

The time for vapor phase demineralization is not particularly limited. From the viewpoint of the economic efficiency of reaction equipment and the ability to maintain the structure of the carbon content, the time is, for example, 5 to 300 minutes, preferably 10 to 200 minutes, more preferably 20 to 150 minutes.

The average particle size of the plant-derived carbon precursor to be subjected to gas-phase demineralization is not particularly limited. If the average particle size is too small, it may be difficult to separate the gas phase containing removed potassium and the like from the plant-derived carbon precursor. Therefore, the lower limit of the average particle size is preferably 100 μm or more. , 300 μm or more, and particularly preferably 500 μm or more. Also, the upper limit of the average particle size is preferably 10000 μm or less, more preferably 8000 μm or less, and particularly preferably 5000 μm or less, from the viewpoint of the fluidity of the carbon precursor in the mixed gas stream. Here, the details of the measurement of the average particle size are as described in Examples.

The apparatus used for vapor phase deashing is not particularly limited as long as it can heat while mixing the plant-derived carbon precursor and the gas phase containing the halogen compound. For example, using a fluidized bed, a continuous or batch intralayer flow system using a fluidized bed or the like can be used. The supply amount (flow amount) of the gas phase is also not particularly limited. From the viewpoint of the fluidity of the carbon precursor in the mixed gas stream, for example, the gas phase is preferably 1 mL/min or more, more preferably 5 mL/min or more, and particularly preferably 10 mL/min or more per 1 g of the plant-derived carbon precursor. supply.

In gas phase deashing, after heat treatment in an inert gas atmosphere containing a halogen compound (hereinafter sometimes referred to as "halogen heat treatment"), further heat treatment in the absence of a halogen compound (hereinafter referred to as "gas phase (sometimes referred to as "deacidification treatment") is preferably performed. Since halogen is contained in the plant-origin carbon precursor by the halogen heat treatment, it is preferable to remove the halogen contained in the plant-origin carbon precursor by vapor-phase deoxidation treatment. Specifically, the vapor-phase deoxidation treatment is carried out in an inert gas atmosphere containing no halogen compounds, usually at 500°C to 940°C, preferably 600°C to 940°C, more preferably 650°C to 940°C, particularly preferably 850°C. This is done by heat treating at ~930°C. The temperature of this heat treatment is preferably the same as or higher than the temperature of the preceding halogen heat treatment. For example, after the halogen heat treatment, the gas phase deoxidation treatment can be performed by interrupting the supply of the halogen compound and performing the heat treatment. Moreover, the time for the vapor-phase deoxidation treatment is not particularly limited. It is preferably 5 minutes to 300 minutes, more preferably 10 minutes to 200 minutes, particularly preferably 10 minutes to 100 minutes.

The acid treatment in the present invention removes (demineralizes) potassium and/or iron contained in the plant-derived carbon precursor. The potassium element content contained in the plant-derived carbon precursor obtained after the acid treatment is preferably reduced to 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.03% by mass or less. be. Particularly preferably, the elemental potassium content is reduced to the extent that the non-graphitizable carbonaceous material is substantially free. In addition, the iron element content contained in the carbon precursor obtained after the acid treatment is preferably reduced to 0.02% by mass or less, more preferably 0.015% by mass or less, and even more preferably 0.01% by mass or less. . Particularly preferably, the elemental iron content is reduced to the extent that the non-graphitizable carbonaceous material is substantially free. Here, substantially free of potassium element or iron element means that the potassium element content or iron element content is determined by the fluorescent X-ray analysis described later (for example, analysis using "LAB CENTER XRF-1700" manufactured by Shimadzu Corporation). It means below the detection limit. When the potassium element content and the iron element content are the above values or less, as described above, sufficient dedoping capacity and non-dedoping capacity are easily obtained, and the safety problem of the non-aqueous electrolyte secondary battery is avoided. easy to be The details of the measurement of the potassium elemental content and the iron elemental content are as described in Examples.

In the acid treatment of the present invention, part of the carbon component is removed at the same time as deashing. Specifically, in the case of liquid phase demineralization, part of the carbon component is removed by elution, and in the case of gas phase demineralisation, part of the carbon component is removed by chlorine activation. This removed portion provides storage points for clustered lithium after the firing step described below.

Acid treatment is performed at least once in the present invention. Two or more acid treatments may be performed with the same or different acids.

The plant-derived carbon precursor to be acid-treated is a plant-derived substance before carbonization or a plant-derived substance after carbonization. That is, from the viewpoint of increasing the lithium absorption point, it is preferable to subject the plant raw material itself before carbonization to liquid phase demineralization.

If the acid-treated carbon precursor is a carbon precursor that has not yet been carbonized, i.e., if the carbon precursor is a carbon precursor that has been acid-treated from a plant raw material before carbonization, it is then carbonized. . The carbonization method is not particularly limited as described above. For example, it is carried out by calcining the acid-treated plant raw material before carbonization in an inert gas atmosphere at 300° C. or higher.

The plant-derived carbon precursor is optionally pulverized and classified to adjust its average particle size. The pulverization step and the classification step are preferably carried out after the acid treatment.

<Grinding>
In the pulverization step, the plant-derived carbon precursor is preferably pulverized so that the average particle size after the firing step is in the range of 1 to 30 μm, for example, from the viewpoint of coatability during electrode production. That is, the average particle diameter (Dv ₅₀ ) of the non-graphitizable carbonaceous material of the present invention is adjusted, for example, within the range of 1 to 30 μm. When the average particle size of the non-graphitizable carbonaceous material is 1 μm or more, the amount of fine powder increases, the specific surface area increases, the reactivity with the electrolytic solution increases, and the irreversible capacity is the capacity that does not discharge even when charged. increases, and the tendency for the positive electrode capacity to waste increases tends to be suppressed. In addition, when a negative electrode is produced using the obtained non-graphitizable carbonaceous material, sufficient voids are easily secured between the carbonaceous materials, ensuring good movement of lithium ions in the electrolyte. Cheap. The average particle diameter (Dv ₅₀ ) of the carbonaceous material of the present invention is preferably 1 µm or more, more preferably 1.5 µm or more, and particularly preferably 2 µm or more. On the other hand, when the average particle diameter is 30 μm or less, the diffusion free path of lithium ions in the particles is small, and rapid charge/discharge tends to be possible, which is preferable. Furthermore, in a lithium ion secondary battery, it is important to increase the electrode area in order to improve the input/output characteristics. Therefore, it is necessary to reduce the thickness of the active material applied to the current collector plate when preparing the electrode. In order to reduce the coating thickness, it is necessary to reduce the average particle size of the active material. From such a viewpoint, the average particle size is preferably 30 μm or less, more preferably 19 μm or less, still more preferably 17 μm or less, even more preferably 16 μm or less, and particularly preferably 15 μm or less.

Note that the plant-derived carbon precursor shrinks by about 0 to 20% depending on the main firing conditions described later. Therefore, in order to make the average particle size after firing 1 to 30 μm, the average particle size of the plant-derived carbon precursor should be about 0 to 20% larger than the desired average particle size after firing. It is preferable to adjust the diameter. Therefore, the average particle size after pulverization is preferably 1 to 36 μm, more preferably 1 to 22.8 μm, still more preferably 1 to 20.4 μm, still more preferably 1 to 19.2 μm, particularly preferably 1 to 18 μm. It is preferable to perform pulverization so that

The order of the pulverization steps is not particularly limited because the carbon precursor does not dissolve even when the firing step described later is performed. Considering the recovery rate (yield) of the carbon precursor in the acid treatment, it is preferably performed after the acid treatment, and from the viewpoint of sufficiently reducing the specific surface area of the carbonaceous material, it is preferably performed before the calcination step. preferable. However, it is not excluded to carry out the grinding step before the acid treatment or after the calcination step.

The pulverizer used in the pulverization step is not particularly limited. For example, jet mills, ball mills, hammer mills, mixer mills, bead mills or rod mills can be used. A jet mill with a classifying function is preferable from the viewpoint of generating less fine powder. When using a ball mill, hammer mill, mixer mill, bead mill, rod mill, or the like, fine powder can be removed by classification after the pulverization step.

<Classification>
The classification process enables the average particle size of the carbonaceous material to be adjusted more accurately. For example, particles with a particle size of less than 1 μm can be removed.

When particles with a particle size of less than 1 μm are excluded by classification, the content of particles with a particle size of less than 1 μm in the non-graphitizable carbonaceous material of the present invention is preferably 3% by volume or less. The removal of particles with a particle diameter of less than 1 μm is not particularly limited as long as it is performed after pulverization, but it is preferably performed at the same time as the classification during pulverization. In the non-graphitizable carbonaceous material of the present invention, the content of particles having a particle diameter of less than 1 μm is 3% by volume or less from the viewpoint of suppressing the side reaction between the electrolytic solution and the non-graphitizable carbonaceous material and reducing the irreversible capacity. is preferably 2.5% by volume or less, and particularly preferably 2.0% by volume or less.

A classification method is not particularly limited. Examples include classification using a sieve, wet classification, or dry classification. Examples of wet classifiers include classifiers using principles such as gravity classification, inertia classification, hydraulic classification, and centrifugal classification. Dry classifiers include classifiers using principles such as sedimentation classification, mechanical classification, and centrifugal classification.

The grinding step and the classification step can also be performed using one device. For example, a jet mill equipped with a dry classifying function can be used to perform the pulverizing step and the classifying step. Furthermore, an apparatus in which the pulverizer and the classifier are independent can also be used. In this case, pulverization and classification can be performed continuously, but pulverization and classification can also be performed discontinuously.

<Firing>
The non-graphitizable carbonaceous material of the present invention can be produced by optionally pulverizing and classifying, then calcining the acid-treated and carbonized carbon precursor. The firing step is a step in which the temperature is raised from room temperature to a predetermined firing temperature, and then firing is performed at the firing temperature. The carbon precursor may be (a) calcined at 1050-1400° C. (main calcination), or (b) calcined at 350-1050° C. (pre-calcination) and then Firing at 1400° C. (main firing), or (c) after firing at 1050 to 1400° C. (main firing), heat treatment (CVD treatment) at 500 to 1000° C. in an inert gas atmosphere containing a hydrocarbon compound. good. An example of procedures for preliminary firing, main firing, and CVD processing will be described below in order.

<Preliminary firing>
The preliminary firing step in the method for producing a non-graphitizable carbonaceous material of the present invention can be carried out by firing, for example, the acid-treated and carbonized carbon precursor at a temperature of 350 to less than 1050°C. By removing volatiles (such as CO ₂ , CO, CH ₄ and H ₂ ) and tars by pre-firing, their production in the main firing can be reduced and the load on the firing machine can be reduced. The pre-baking temperature is usually 350 to less than 1050°C, preferably 400 to less than 1050°C. Preliminary firing can be carried out according to a normal prefiring procedure. Specifically, the pre-baking can be performed in an inert gas atmosphere, and examples of the inert gas include nitrogen and argon. Preliminary firing can also be performed under reduced pressure, for example, at 10 KPa or less. The pre-baking time is not particularly limited, and is usually 0.5 to 10 hours, preferably 1 to 5 hours.

When preliminary firing is performed in the method for producing a non-graphitizable carbonaceous material of the present invention, it is considered that the carbon precursor is coated with the tar component and the hydrocarbon-based gas during the preliminary firing step. It is believed that this carbonaceous coating favorably reduces the specific surface area of the non-graphitizable carbonaceous material.

<Main firing>
The main firing step in the method for producing a non-graphitizable carbonaceous material of the present invention can be carried out according to a normal main firing procedure, and a non-graphitizable carbonaceous material is obtained after the main firing.

The main firing temperature is usually 1050 to 1400°C, preferably 1100 to 1380°C, more preferably 1150 to 1350°C. The firing can be performed in an inert gas atmosphere, and examples of the inert gas include nitrogen and argon. Moreover, it is also possible to carry out the final firing in an inert gas containing a halogen gas. Furthermore, the main firing can be performed under reduced pressure, for example, at 10 KPa or less.

When the carbon precursor is heat-treated in the main firing step, gases such as carbon monoxide and hydrogen are generated from the carbon precursor itself. These gases are highly reactive, and it is important to control the reaction between the gas and the carbon precursor during heat treatment in order to destroy the voids between the carbon crystals that can occlude clustered lithium. For example, in WO2017/022486, a non-graphitizable carbonaceous material capable of absorbing more clustered lithium during charging is obtained by performing heat treatment after performing vapor phase demineralization or liquid phase demineralization. Although WO2017/022486 certainly makes it possible to obtain a carbonaceous material for non-aqueous electrolyte secondary batteries having high charge capacity and high charge/discharge efficiency, the present invention actively removes pyrolysis gas during firing. As a result, it has been found that even higher output characteristics can be obtained. The method of firing while actively removing the pyrolysis gas from the carbon precursor is not particularly limited. There is a method of actively removing the gas remaining in the sample by reducing the stacking height. These methods allow reactive gases emanating from the carbon precursor itself to be removed prior to reacting with the carbon precursor. Therefore, a non-graphitizable carbonaceous material having a more controlled carbon structure can be produced. The time for main firing is not particularly limited, and is, for example, 0.05 to 10 hours, preferably 0.05 to 8 hours, and more preferably 0.05 to 6 hours.

In the present invention, when the carbon precursor is fired, it can be fired after being mixed with a volatile organic substance. By mixing with a volatile organic substance and firing, the specific surface area of the non-graphitizable carbonaceous material obtained from the carbon precursor is increased to a specific surface area more suitable for a negative electrode for a non-aqueous electrolyte secondary battery, such as a lithium ion secondary battery. can be

<Volatile organic matter>
The volatile organic matter that can be used in the present invention is a volatile organic matter that is solid at room temperature and has a residual carbon content of less than 5% by mass based on the weight of the volatile organic matter before incineration when incinerated at 800 ° C. Although not particularly limited, it is preferable to generate a volatile substance (eg, hydrocarbon-based gas or tar component) capable of reducing the specific surface area of the non-graphitizable carbonaceous material produced from the carbon precursor. The content of the volatile substance capable of reducing the specific surface area in the volatile organic matter is not particularly limited, but is usually 1 to 20% by mass, preferably 3 to 15% by mass, based on the mass of the volatile organic matter. %. In addition, in this specification, normal temperature refers to 25 degreeC.

Examples of volatile organic substances include thermoplastic resins and low-molecular-weight organic compounds. More specifically, thermoplastic resins include polystyrene, polyethylene, polypropylene, poly(meth)acrylic acid and poly(meth)acrylic acid esters, and low-molecular-weight organic compounds include toluene, xylene, mesitylene, Styrene, naphthalene, phenanthrene, anthracene or pyrene may be mentioned. Polystyrene, polyethylene or polypropylene is preferred as the thermoplastic resin, and naphthalene, phenanthrene, anthracene or pyrene is preferred as the low-molecular-weight organic compound, from the viewpoint of not oxidizing and activating the surface of the carbon precursor when volatilized and thermally decomposed at the baking temperature. preferable. It is more preferable to use naphthalene, phenanthrene, anthracene, or pyrene from the viewpoint of safety because of its low volatility at room temperature.

The residual carbon content can be measured by quantifying the amount of carbon in the ignition residue after the sample is ignited in an inert gas. Ignition means that approximately 1 g of a volatile organic substance [this exact mass is W ₁ (g)] is placed in a crucible, and the crucible is heated in an electric furnace at 10° C./min while flowing 20 liters of nitrogen per minute. It means that the temperature is raised to 800° C. and then held at 800° C. for 1 hour. Let the residue at this time be an ignition residue, and let the mass be W2 ₍ g).

Next, the residue on ignition is subjected to elemental analysis according to the method specified in JIS M8819 to measure the carbon mass ratio P ₁ (%). The residual coal rate P ₂ (%) is calculated by the following formula.

When the carbon precursor and the volatile organic matter are mixed and fired, the carbon precursor and the volatile organic matter are preferably mixed in a mass ratio of 97:3 to 40:60. This mixing ratio is more preferably 95:5 to 60:40, particularly preferably 93:7 to 80:20. By setting the mixing ratio within the above range, the specific surface area of the non-graphitizable carbonaceous material can be sufficiently reduced. On the other hand, it is easy to avoid wasteful consumption of volatile organic substances due to saturation of the effect of reducing the specific surface area.

Mixing of the carbon precursor and the volatile organic matter may be performed before or after pulverization of the carbon precursor. If the carbon precursor is mixed prior to milling, milling and mixing can be accomplished simultaneously by simultaneously metering the carbon precursor and the volatile organics into the milling device. It is also preferred to mix the volatile organics after grinding the carbon precursor. The mixing method in this case may be any mixing method as long as both are uniformly mixed.

The volatile organic substance is preferably mixed in the form of particles, but the particle form and average particle size are not particularly limited. From the viewpoint of uniform dispersion in the pulverized carbon precursor, the average particle size of the volatile organic substance is preferably 0.1 to 2000 μm, more preferably 1 to 1000 μm, particularly preferably 2 to 600 μm.

A mixture of a carbon precursor and a volatile organic substance can contain the carbon precursor as long as the effect of the non-graphitizable carbonaceous material of the present invention is obtained, that is, as long as the specific surface area of the non-graphitizable carbonaceous material is reduced. and may contain other components than volatile organics. For example, natural graphite, artificial graphite, metal-based materials, alloy-based materials, or oxide-based materials may be included. The content of the other components is not particularly limited, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, relative to 100 parts by mass of the mixture of the carbon precursor and the volatile organic substance, It is more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less.

<CVD treatment>
In the present invention, a CVD treatment using a hydrocarbon compound may be performed after the main firing step. The CVD treatment is a chemical vapor deposition (CVD) treatment in which the non-graphitizable carbonaceous material obtained in the main firing step is coated with a pyrolyzed hydrocarbon compound. Conditions for the CVD treatment are not particularly limited as long as the chemical vapor deposition can be achieved. For example, a method of heat treatment at 500 to 1000° C. in an inert gas atmosphere containing a hydrocarbon compound may be used. In the CVD process, the hydrocarbon compound is thermally decomposed by heat treatment at, for example, 500 to 1000° C., and the resulting thermal decomposition product adheres to the non-graphitizable carbonaceous material and coats the surface of the non-graphitizable carbonaceous material. As a result, although not limited to the following mechanism, the specific surface area can be reduced while maintaining the gaps between the carbon crystals that can absorb the clustered lithium of the non-graphitizable carbonaceous material, so the amount of moisture absorption is greatly reduced. It is thought that it is possible to Therefore, it is considered that the charge/discharge efficiency can be improved while maintaining a high charge capacity. In addition, the CVD treatment removes functional groups on the surface of the non-graphitizable carbonaceous material, such as —OH groups or —COOH groups, which can inhibit the absorption of lithium ions, by reacting with the radicals of the thermally decomposed hydrocarbon compound. It is thought that Therefore, it is believed that the oxygen element content in the carbonaceous material is reduced, and irreversible side reactions during charging and discharging are suppressed, thereby improving charge capacity and charging and discharging efficiency.

Hydrocarbon compounds used in CVD processes are compounds composed primarily of carbon and hydrogen atoms. Hydrocarbon compounds include, for example, low-molecular-weight organic hydrocarbon compounds. In the CVD process, one type of hydrocarbon compound may be used, or two or more types of hydrocarbon compounds may be used in combination. The hydrocarbon compound mainly composed of carbon atoms and hydrogen atoms means that the total amount of carbon atoms and hydrogen atoms in the hydrocarbon compound is preferably 75% by mass or more, based on the total mass of the hydrocarbon compound. It means that it is preferably 80% by mass or more, more preferably 85% by mass or more.

Low-molecular-weight organic hydrocarbon compounds include, for example, hydrocarbon compounds having 1 to 20 carbon atoms. The number of carbon atoms in the hydrocarbon compound is preferably 2-18, more preferably 3-16. The hydrocarbon compound may be a saturated hydrocarbon compound or an unsaturated hydrocarbon compound, and may be a chain hydrocarbon compound or a cyclic hydrocarbon compound. In the case of unsaturated hydrocarbon compounds, the unsaturated bond may be a double bond or a triple bond, and the number of unsaturated bonds contained in one molecule is not particularly limited. For example, a chain hydrocarbon compound is an aliphatic hydrocarbon compound and can include straight or branched alkanes, alkenes, or alkynes. Cyclic hydrocarbon compounds can include alicyclic hydrocarbon compounds (eg, cycloalkanes, cycloalkenes, cycloalkynes) or aromatic hydrocarbon compounds. Specific examples of aliphatic hydrocarbon compounds include methane, ethane, propane, butane, pentane, hexane, octane, nonane, decane, ethylene, propylene, butene, pentene, hexene, and acetylene. Examples of alicyclic hydrocarbon compounds include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclopropane, cyclopentene, cyclohexene, cycloheptene, cyclooctene, decalin, norbornene, methylcyclohexane, and norbornadiene. Furthermore, aromatic hydrocarbon compounds include benzene, toluene, xylene, mesitylene, cumene, butylbenzene, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinylxylene, p- Monocyclic aromatic compounds such as tert-butylstyrene and ethylstyrene, and 3- to 6-ring condensed polycyclic aromatic compounds such as naphthalene, phenanthrene, anthracene and pyrene can be mentioned, but condensed polycyclic aromatic compounds are preferred. group compounds, more preferably naphthalene, phenanthrene, anthracene or pyrene. Here, the hydrocarbon compound may have any substituent. Although the substituent is not particularly limited, for example, an alkyl group having 1 to 4 carbon atoms (preferably an alkyl group having 1 to 2 carbon atoms), an alkenyl group having 2 to 4 carbon atoms (preferably an alkenyl group having 2 carbon atoms, group), and a cycloalkyl group having 3 to 8 carbon atoms (preferably a cycloalkyl group having 3 to 6 carbon atoms).

In the CVD treatment step, it is preferable to continuously supply the hydrocarbon compound in a gaseous state from the viewpoint of performing the CVD treatment uniformly and easily obtaining the desired properties of the carbonaceous material. A hydrocarbon compound that becomes gaseous at the temperature at which the CVD process is performed may be used, or a hydrocarbon compound that has been gaseous in a pre-process of the CVD process may be supplied to the CVD process. For example, using a hydrocarbon compound that becomes a gaseous state at a temperature of 500 to 1000 ° C., and performing heat treatment at that temperature to perform CVD treatment, from the viewpoint of productivity and miscibility between the hydrocarbon compound and the non-graphitizable carbonaceous material. preferred from From the above point of view, the boiling point of the hydrocarbon compound is preferably below the temperature at which the CVD process is performed.

The CVD treatment step may preferably be performed in an inert gas atmosphere containing hydrocarbon compounds. Inert gases used in the CVD process include nitrogen or argon. The same inert gas or different inert gases may be used in the firing process and the CVD process. From the viewpoint of simplifying the manufacturing process and increasing manufacturing efficiency, it is preferable to use the same inert gas in the main firing process and the CVD treatment process.

When the CVD process is performed in an inert gas atmosphere containing a hydrocarbon compound, the mixing ratio of the hydrocarbon compound and the inert gas is not particularly limited. For example, from the viewpoint of safety, economy, and contamination in the firing furnace, the amount of the hydrocarbon compound relative to the inert gas is preferably 1 to 60% by volume, more preferably 5 to 50% by volume, Especially preferred is 10 to 45% by volume. According to the production method of this embodiment, in which heat treatment is performed in an inert gas atmosphere containing a hydrocarbon compound, it is easy to efficiently remove the oxygen element from the carbonaceous material.

The heat treatment temperature in the CVD treatment step may vary depending on the type of carbonaceous material and hydrocarbon compound used, but from the viewpoint of obtaining the desired carbon structure, it is preferably 500 to 1000° C., more preferably 600 to 900° C. More preferably, it is 700 to 850°C. If the heat treatment temperature is too low, the oxygen element will not be sufficiently removed from the carbonaceous material, and if the heat treatment temperature is too high, a large amount of carbon structures derived from hydrocarbon compounds that do not contribute to the charge capacity will adhere, resulting in a decrease in the charge capacity. .

When the CVD treatment step is performed in an inert gas atmosphere containing a hydrocarbon compound, the supply amount of the inert gas stream containing the hydrocarbon compound is not particularly limited, but is preferably 0.1 L/min per 50 g of the carbonaceous material. Above, more preferably 0.3 L/min or more, particularly preferably 0.5 L/min or more. It is preferable to carry out the heat treatment at a supply amount equal to or higher than the above lower limit, because the carbon coating is likely to be uniformly formed. The upper limit of the supply amount is preferably 10 L/min or less, more preferably 5 L/min or less. It is preferable to carry out the heat treatment at a supply amount of the above upper limit or less because the supplied hydrocarbon compound tends to act efficiently.

<Negative electrode for non-aqueous electrolyte secondary battery>
The negative electrode for non-aqueous electrolyte secondary batteries of the present invention comprises the non-graphitizable carbonaceous material of the present invention.

<Production of negative electrode>
The negative electrode material containing the non-graphitizable carbonaceous material of the present invention is prepared by adding a binder to the non-graphitizable carbonaceous material, adding an appropriate amount of an appropriate solvent, and kneading to form an electrode mixture, followed by It can be manufactured by applying an electrode mixture to a collector plate made of a metal plate or the like, drying it, and molding it under pressure. By using the non-graphitizable carbonaceous material of the present invention, an electrode having high conductivity can be produced without adding a conductive aid. However, in order to impart even higher conductivity, a conductive aid may be added during the preparation of the electrode mixture, if necessary.

Conductive carbon black, vapor grown carbon fiber (VGCF), nanotubes, and the like can be used as the conductive aid. The amount of the conductive aid added varies depending on the type of conductive aid used, but is preferably 0.5 to 10% by mass [here, active material (non-graphitizable carbonaceous material) amount + binder amount + conductive Amount of auxiliary agent = 100% by mass], more preferably 0.5 to 7% by mass, and particularly preferably 0.5 to 5% by mass. By setting the addition amount of the conductive aid within the above range, the expected conductivity can be easily obtained without deteriorating the dispersion of the conductive aid in the electrode mixture.

The binder to be added is not particularly limited as long as it does not react with the electrolytic solution. Examples include PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethylcellulose). Among them, PVDF is preferable because the PVDF adhering to the surface of the active material hardly inhibits the movement of lithium ions, and good input/output characteristics can be obtained. The amount of the binder to be added varies depending on the type of binder used. % by mass, more preferably 3 to 10% by mass. By setting the amount of the binder to be added within the above range, the resistance of the resulting electrode is increased, the internal resistance of the battery is increased, the battery characteristics are deteriorated, and the negative electrode particles and the negative electrode particles and the current collector plate are not easily separated. It is easy to avoid problems such as insufficient bonding.

A polar solvent such as N-methylpyrrolidone (NMP) is preferably used as a solvent for dissolving PVDF to form a slurry. Water is preferably used as a solvent to form an aqueous emulsion such as SBR or an aqueous solution such as CMC. Binders that use water as a solvent often use a mixture of binders, such as a mixture of SBR and CMC. The amount of the solvent to be added is preferably 10 to 200 parts by mass, more preferably 50 to 150 parts by mass, based on the total mass (100 parts by mass) of the non-graphitizable carbonaceous material, binder and conductive aid used. Department.

Although the electrode active material layer is basically formed on both sides of the collector plate, it may be formed on one side if necessary. The thickness of the active material layer (per side) is preferably 10 to 100 μm, more preferably 20 to 90 μm, particularly preferably 20 to 80 μm. By setting the thickness within the above range, it is easy to achieve high capacity because a small number of current collector plates and separators is required, and high input/output characteristics can be obtained because a large electrode area facing the counter electrode can be secured. Cheap.

<Non-aqueous electrolyte secondary battery>
The nonaqueous electrolyte secondary battery of the present invention includes, for example, a lithium ion secondary battery, a sodium ion secondary battery, a lithium sulfur battery, an all-solid battery, an organic radical battery, and the like. It comprises a negative electrode for a battery. A fully charged non-aqueous electrolyte secondary battery manufactured using the negative electrode for a non-aqueous electrolyte secondary battery comprising the non-graphitizable carbonaceous material of the present invention exhibits high charging capacity and high charging/discharging efficiency.

When the non-graphitizable carbonaceous material of the present invention is used to form a negative electrode for a non-aqueous electrolyte secondary battery, other materials constituting the battery such as the positive electrode material, separator, and electrolyte are not particularly limited. do not have. Various materials conventionally used or proposed for non-aqueous solvent secondary batteries can be used.

For example, the cathode material may be a layered oxide system [LiMO ₂ [M represents a metal], such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , or _LiNix Co _{y Moz} O ₂ (here where x, y, and z represent the composition ratio)], olivine-based (LiMPO ₄ [M represents a metal], such as LiFePO ₄ ), and spinel-based (LiM ₂ O ₄ [M represents a metal ] and, for example, LiMn ₂ O ₄ ) is preferred, and these chalcogen compounds may be mixed as necessary. A positive electrode is formed by molding these positive electrode materials together with a suitable binder and a carbon material for imparting electrical conductivity to the electrode and forming a layer on a conductive collector.

The non-aqueous electrolyte used in combination with these positive and negative electrodes is generally formed by dissolving the electrolyte in a non-aqueous solvent. Examples of non-aqueous solvents include organic A solvent can be used individually or in combination of 2 or more types. As the electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr, LiB(C ₆ H ₅ ) ₄ , LiN(SO ₃ CF ₃ ) ₂ or the like is used.

A non-aqueous electrolyte secondary battery generally comprises a positive electrode and a negative electrode formed as described above, which are immersed in an electrolytic solution, with a liquid-permeable separator made of non-woven fabric or other porous material, if necessary, facing each other. It is formed by As the separator, a permeable separator made of non-woven fabric or other porous material commonly used in secondary batteries can be used. Alternatively, instead of the separator or together with the separator, a solid electrolyte made of a polymer gel impregnated with an electrolytic solution can be used.

As used herein, the term “fully charged non-aqueous electrolyte secondary battery” means that the non-aqueous electrolyte secondary battery of the present invention is assembled and lithium is charged until just before deposition of metallic lithium is confirmed by ⁷ Li nuclear-solid NMR analysis. is a non-aqueous electrolyte secondary battery in which the negative electrode is charged (doped), and is usually charged at a constant current value to a range of 580 to 700 mAh / g per mass of the negative electrode active material. means that

<Main resonance peak position of chemical shift value>
The non-graphitizable carbonaceous material in the non-aqueous electrolyte secondary battery of the present invention is charged (doped) with lithium until it reaches a fully charged state, and the lithium chloride observed when ⁷ Li nucleus-solid NMR analysis is performed is The main resonance peak position of the reference chemical shift value is greater than 115 ppm, preferably greater than 117 ppm, more preferably greater than 119 ppm.

As described above, the fact that the main resonance peak position of the chemical shift value relative to lithium chloride is greater than 115 ppm means that the charge capacity of the battery is high, and the charge/discharge ratio calculated from "discharge capacity/charge capacity". It means high efficiency. High charge/discharge efficiency is advantageous in terms of capacity per battery volume and cost. A carbonaceous material having a main resonance peak position of a chemical shift value relative to lithium chloride of 115 ppm or less provides both high charge capacity and high charge/discharge efficiency like the non-graphitizable carbonaceous material of the present invention. is extremely difficult.

In order to adjust the main resonance peak position to a value larger than the above value, for example, the carbon-containing material is heated to a temperature of 1050° C. to 1400° C. while actively removing thermal decomposition gases such as carbon monoxide and hydrogen. A non-graphitizable carbonaceous material manufactured by firing in an active gas atmosphere may be used for the negative electrode. The details of the ⁷ Li nucleus-solid NMR analysis are as described in the Examples.

<Expansion rate of electrode>
In the non-aqueous electrolyte secondary battery of the present invention, the expansion rate of the negative electrode containing the non-graphitizable carbonaceous material at full charge is 107% or less based on the thickness of the negative electrode before charging. If the expansion rate exceeds 107%, contact failure occurs between the active materials in the electrodes and the electrode resistance increases, so a non-aqueous electrolyte secondary battery having good output characteristics (high discharge capacity retention rate) cannot be obtained. do not have.
The expansion rate is preferably 106% or less, particularly preferably 105% or less. When the expansion coefficient is equal to or less than the above upper limit, a conductive path between the active materials (non-graphitizable carbonaceous materials) in the electrode and the diffusion of lithium ions are easily ensured, so that a low electrode resistance is easily obtained. output characteristics are easily obtained.

In order to adjust the electrode expansion coefficient to the above value or less, for example, a material containing carbon is subjected to an inert gas atmosphere at 1050° C. to 1400° C. while actively removing thermal decomposition gases such as carbon monoxide and hydrogen. A non-graphitizable carbonaceous material manufactured by firing at is used for the negative electrode. In the negative electrode comprising the non-graphitizable carbonaceous material produced by the above method, many lithium ions are charged not only between the carbon crystal layers but also in the gaps between the carbon crystal layers, so that lithium ions are charged only between the carbon crystal layers. It is believed to result in a significantly lower electrode expansion rate than the conventional negative electrode that is used. The details of the measurement of the expansion rate are as described in Examples.

<Oxygen element content>
In the non-aqueous electrolyte secondary battery of the present invention, the oxygen element content of the non-graphitizable carbonaceous material is preferably as low as possible. The oxygen element content is preferably 0.30% by mass or less, more preferably 0.28% by mass or less. More preferably, the non-graphitizable carbonaceous material contains substantially no oxygen element. Here, "substantially free of elemental oxygen" means that the elemental oxygen content is 10 ^-6 % by mass, which is the detection limit of the method for measuring the elemental oxygen content (inert gas fusion-nondispersive infrared absorption method) described later. means that: As described above, if the oxygen element content is less than the above value, the lithium ions are consumed by the reaction between the lithium ions and oxygen, resulting in a decrease in the utilization efficiency of the lithium ions, and the oxygen attracting moisture in the air. Water is adsorbed on the surface and does not easily desorb, resulting in a decrease in the utilization efficiency of lithium ions, generation of gas in the electrode due to side reactions derived from moisture, and an increase in the expansion rate of the electrode due to the generation of gas (increase in electrode resistance). , deterioration of output characteristics) are likely to be suppressed.

Moreover, as described above, the method for adjusting the oxygen element content is not limited at all. For example, a plant-derived carbon precursor is acid-treated at a predetermined temperature, mixed with a volatile organic substance, and fired at a temperature of 1050° C. to 1400° C. under an inert gas atmosphere to reduce the elemental oxygen content to the above value. You can adjust below. The details of the measurement of the oxygen element content are as described in Examples.

<Carbon precursor of plant origin>
The non-graphitizable carbonaceous material in the non-aqueous electrolyte secondary battery of the present invention is preferably derived from a plant-derived carbon precursor. In the present invention, "plant-derived carbon precursor" means a plant-derived material before carbonization or a plant-derived material (plant-derived char) after carbonization. As mentioned above, the plant material is not particularly limited. Plants such as those described above can be used singly or in combination of two or more. Among them, coconut shells, which are easily available in large quantities, are preferred.

Coconut shells are not particularly limited. Coconut shells such as those exemplified above can be used alone or in combination. Particularly preferred are coconut shells of coconut palms and palm palms, which are biomass wastes that are used as foods, raw materials for detergents, raw materials for biodiesel oil, and the like, and which are generated in large amounts.

The method of carbonizing plant raw materials, ie, the method of producing plant-derived char, is not particularly limited. For example, it is carried out by calcining the plant raw material in an inert gas atmosphere at 300° C. or higher.

It is also available in the form of char (eg, coconut shell char).

<Average surface distance d ₀₀₂ >
The non-graphitizable carbonaceous material in the non-aqueous electrolyte secondary battery of the present invention has an average interplanar spacing d ₀₀₂ of the (002) plane calculated using the Bragg formula based on the wide-angle X-ray diffraction method of 0.36 nm to 0.36 nm. It is preferably 42 nm, more preferably 0.38 nm to 0.40 nm, and particularly preferably 0.381 nm to 0.389 nm. When the average interplanar spacing d ₀₀₂ of the (002) plane is within the above range, as described above, deterioration in input/output characteristics as a lithium ion battery is easily suppressed, and deterioration in stability as a battery material is suppressed. It is easy to use, and the decrease in effective capacity per volume is easily avoided. In order to adjust the average interplanar spacing to the above range, for example, the firing temperature of the carbon precursor that gives the non-graphitizable carbonaceous material should be in the range of 1050 to 1400°C. Alternatively, a method of mixing with a thermally decomposable resin such as polystyrene and then baking can be used. Details of the measurement of the average interplanar spacing d ₀₀₂ are as described in Examples.

<true density ρ _Bt >
The non-graphitizable carbonaceous material in the non-aqueous electrolyte secondary battery of the present invention has a true density ρ _{Bt measured} by the butanol method of 1.40 to 1.70 g/cm ³ from the viewpoint of increasing the capacity per mass of the battery. preferably 1.42 to 1.65/cm ³ , particularly preferably 1.44 to 1.60/cm ³ . The true density in the above range can be obtained by setting the firing process temperature to 1050 to 1400° C., for example. The details of the measurement of the true density ρ _Bt are as described in Examples.

<Potassium element content and iron element content>
As described above, the potassium element content of the non-graphitizable carbonaceous material in the non-aqueous electrolyte secondary battery of the present invention is preferably 0.1% by mass or less, and more preferably 0.05% by mass or less. More preferably, it is 0.03% by mass or less, and it is particularly preferable that the non-graphitizable carbonaceous material contains substantially no potassium element. In addition, as described above, the iron element content of the non-graphitizable carbonaceous material in the non-aqueous electrolyte secondary battery of the present invention is preferably 0.02% by mass or less, and is 0.015% by mass or less. More preferably, it is 0.01% by mass or less, and it is particularly preferable that the non-graphitizable carbonaceous material contains substantially no iron element. Here, substantially free of potassium element or iron element means that the potassium element content or iron element content is determined by the fluorescent X-ray analysis described later (for example, analysis using "LAB CENTER XRF-1700" manufactured by Shimadzu Corporation). It means below the detection limit. When the potassium element content and the iron element content are the above values or less, as described above, sufficient dedoping capacity and non-dedoping capacity are easily obtained, and the safety problem of the non-aqueous electrolyte secondary battery is avoided. easy to be The details of the measurement of the potassium elemental content and the iron elemental content are as described in Examples.

<Amount of moisture absorbed>
The moisture absorption of the non-graphitizable carbonaceous material in the non-aqueous electrolyte secondary battery of the present invention is preferably 10000 ppm or less, more preferably 9000 ppm or less, and particularly preferably 8000 ppm or less. As described above, the smaller the amount of moisture absorbed, the more lithium ions are adsorbed to the non-graphitizable carbonaceous material, and the less self-discharge due to the reaction between the adsorbed moisture and lithium ions, which is preferable. The moisture absorption amount of the non-graphitizable carbonaceous material can be reduced, for example, by reducing the amount of oxygen atoms contained in the non-graphitizable carbonaceous material. The moisture absorption of the non-graphitizable carbonaceous material can be measured using, for example, Karl Fischer. The details of the measurement of moisture absorption are as described in Examples.

<Specific surface area>
The non-graphitizable carbonaceous material in the non-aqueous electrolyte secondary battery of the present invention preferably has a specific surface area of 1 to 75 m ² /g, more preferably 2 to 60 m ² /g, as determined by the nitrogen adsorption BET three-point method. is more preferred, and 3 to 50 m ² /g is particularly preferred. As described above, when the specific surface area is within the above range, excessive side reactions between the electrolyte and the non-graphitizable carbonaceous material occur in the non-aqueous electrolyte secondary battery manufactured using the non-graphitizable carbonaceous material. Lithium ions are easily doped into the non-graphitizable carbonaceous material while being suppressed, and the contact area for dedoping lithium ions from the non-graphitizable carbonaceous material is easily maintained at a high level, resulting in high charge capacity and high output characteristics. is easily compatible with The specific surface area can be adjusted, for example, by controlling the temperature of the deashing process described above.

EXAMPLES The present invention will be specifically described below with reference to Examples, but these are not intended to limit the scope of the present invention. Methods for measuring the physical properties of the non-graphitizable carbonaceous material are described below, but the physical properties described in this specification, including the examples, are based on the values obtained by the following methods. .

<Measurement of main resonance peak position of chemical shift value by ⁷ Li nucleus-solid NMR analysis>
The negative electrode containing the non-graphitizable carbonaceous material doped with lithium ions in a fully charged state was taken out from the cell, and the negative electrode from which the electrolytic solution had been wiped off was all filled in an NMR sample tube. Measurement of the main resonance peak position of the chemical shift value by ⁷ Li nucleus-solid NMR analysis was performed using BRUKER's "Nuclear Magnetic Resonance Apparatus AVANCE 300". In the measurement, lithium chloride was used as a reference substance and set to 0 ppm.

<Measurement of oxygen element content>
The elemental oxygen content was measured using an "oxygen/nitrogen/hydrogen analyzer EMGA-930" manufactured by Horiba, Ltd.
The detection method of this device is oxygen: inert gas fusion-non-dispersive infrared absorption method (NDIR), nitrogen: inert gas fusion-thermal conductivity method (TCD), hydrogen: inert gas fusion-non-dispersive infrared Absorption method (NDIR) and calibration was performed with (oxygen/nitrogen) Ni capsules, TiH ₂ (H standard sample), and SS-3 (N, O standard sample). 20 mg of a sample that had been dehydrated at 250° C. for about 10 minutes as a pretreatment was weighed into a Ni capsule, degassed for 30 seconds in an elemental analyzer, and then measured. Three samples were analyzed, and the average value was used as the analytical value.

<Measurement of average interplanar spacing d002 of ( ₀₀₂ ) plane>
Using "MiniFlex II" manufactured by Rigaku Corporation, the non-graphitizable carbonaceous material powder was filled in a sample holder, and an X-ray diffraction pattern was obtained using CuKα rays made monochromatic by a Ni filter as a radiation source. The peak position of the diffraction pattern is obtained by the centroid method (a method of obtaining the centroid position of the diffraction line and obtaining the peak position with the corresponding 2θ value), and using the diffraction peak of the (111) plane of the high-purity silicon powder for standard substance corrected. The wavelength of the CuKα ray was set to 0.15418 nm, and d ₀₀₂ was calculated by the Bragg's formula shown below.

このとき、ｄは水の３０℃における比重（０．９９４６）である。 <Measurement of true density ρ _Bt by butanol method>
The true density was measured by the butanol method according to the method specified in JIS R 7212. The mass (m ₁ ) of a pycnometer with a side tube having an internal volume of about 40 mL was accurately weighed. Next, the sample was put flat on the bottom so as to have a thickness of about 10 mm, and its mass (m ₂ ) was measured accurately. 1-Butanol was gently added to this to make a depth of about 20 mm from the bottom. Next, the pycnometer was shaken lightly to confirm that no large bubbles were generated, then placed in a vacuum desiccator and gradually evacuated to 2.0 to 2.7 kPa. Keep it at that pressure for 20 minutes or more, and after the bubbles have stopped generating, take it out, fill it with 1-butanol, plug it, and immerse it in a constant temperature water bath (adjusted to 30±0.03°C) for 15 minutes or more. , and the liquid level of 1-butanol was aligned with the marked line. Next, it was taken out, the outside was thoroughly wiped, and after cooling to room temperature, the mass (m ₄ ) was measured accurately. Next, the same pycnometer was filled with only 1-butanol, immersed in a constant temperature water bath in the same manner as described above, and after matching the gauge lines, the mass (m ₃ ) was measured. Also, just before use, distilled water was boiled to remove the dissolved gas and placed in a _pycnometer .
The true density ρ _Bt was calculated by the following formula.

At this time, d is the specific gravity of water at 30°C (0.9946).

<Measurement of potassium element content and iron element content>
The potassium element content and iron element content were measured by the following methods. A carbon sample containing predetermined potassium and iron elements is prepared in advance, and a fluorescent X-ray analyzer is used to determine the relationship between the potassium Kα ray intensity and the potassium element content, and the relationship between the iron Kα ray intensity and the iron element content. A calibration curve for the relationship was created. Next, the intensities of potassium Kα line and iron Kα line in fluorescent X-ray analysis of the sample were measured, and the elemental potassium content and the elemental iron content were obtained from the previously prepared calibration curve. Fluorescent X-ray analysis was performed using Shimadzu Corporation's "LAB CENTER XRF-1700" according to the following procedure. A holder for the top irradiation method was used, and the sample measurement area was set within a circle with a diameter of 20 mm. The sample to be measured was placed by placing 0.5 g of the sample to be measured in a polyethylene container with an inner diameter of 25 mm, pressing the back with a plankton net, and covering the measurement surface with a polypropylene film. The X-ray source was set at 40 kV, 60 mA. Potassium was measured using LiF (200) as an analyzing crystal and a gas flow type proportionality coefficient tube as a detector at a scanning rate of 8°/min over the range of 2θ from 90 to 140°. For iron, LiF (200) was used as an analyzing crystal, and a scintillation counter was used as a detector.

<Measurement of moisture absorption>
10 g of a non-graphitizable carbonaceous material pulverized to a particle size of about 5 to 50 μm is placed in a sample tube, pre-dried at 120° C. for 2 hours under a reduced pressure of 133 Pa, transferred to a 50 mmφ glass petri dish, and placed at 25° C. and humidity of 50. % constant temperature and humidity chamber for a predetermined period of time. A 1 g sample was taken, heated to 250° C. in a Karl Fischer (manufactured by Mitsubishi Chemical Analytech), and the water content was measured under a nitrogen stream.

<Measurement of average particle size by laser scattering method>
The average particle size (particle size distribution) of plant-derived char, carbon precursor, and volatile organic matter was measured by the following method. The sample was put into an aqueous solution containing 0.3% by mass of a surfactant (“Toriton X100” manufactured by Wako Pure Chemical Industries, Ltd.), treated with an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution was measured using a particle size/particle size distribution analyzer ("Microtrac MT3000" manufactured by Nikkiso Co., Ltd.). Dv50 is the particle diameter at which the cumulative volume becomes ₅₀ %, and this value was taken as the average particle diameter.

Example 1 (vapor phase deashing, addition of volatile organic matter, full-cell evaluation)
<Preparation of carbon precursor>
Coconut shells were dry distilled at 500° C. and crushed to obtain coconut shell char having an average particle size of about 2 mm. 100 g of this coconut shell char was subjected to halogen heat treatment at 870° C. for 30 minutes while nitrogen gas containing 1% by volume of hydrogen chloride gas was supplied at a flow rate of 18 L/min, after which only hydrogen chloride gas was supplied. Then, while nitrogen gas was supplied at a flow rate of 18 L/min, heat treatment was performed at 870° C. for 30 minutes to perform vapor-phase deoxidation treatment to obtain a carbon precursor.
The obtained carbon precursor was pulverized using a mixer mill (MM400, manufactured by Verder Scientific Co., Ltd.) to an average particle size of 6 μm, and then classified using a nano jetmizer (manufactured by Aisin Nano Technologies Co., Ltd.). , to obtain a carbon precursor (1) having an average particle size of 5 μm.

<Preparation of non-graphitizable carbonaceous material>
5 g of the carbon precursor prepared as described above and 0.5 g of polystyrene (manufactured by Sekisui Plastics Co., Ltd., average particle size: 400 μm, residual carbon content: 1.2%) were mixed. 5.5 g of this mixture was placed in a graphite sheath so that the sample layer height was about 2 mm, and heated up to 1290° C. at a rate of 10° C./min under a nitrogen flow rate of 5 L/min in a tubular furnace manufactured by Motoyama Co., Ltd. After the temperature was raised, it was held for 30 minutes and cooled naturally. After confirming that the temperature in the furnace had decreased to 200° C. or less, the non-graphitizable carbonaceous material was taken out from the furnace. The recovered non-graphitizable carbonaceous material was 4.9 g, and the recovery rate was 89%.
For the non-graphitizable carbonaceous material prepared as described above, measurement of the main resonance peak position of the chemical shift value by ⁷ Li nucleus-solid NMR analysis, measurement of the oxygen element content, measurement of the average interplanar spacing d ₀₀₂ of the (002) plane measurement, measurement of true density ρ _Bt by the butanol method, measurement of potassium element content and iron element content, and measurement of moisture absorption. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
94 parts by mass of the non-graphitizable carbonaceous material prepared as described above, 6 parts by mass of PVDF (polyvinylidene fluoride) and 90 parts by mass of NMP (N-methylpyrrolidone) were mixed to obtain a slurry. The obtained slurry was applied to one side of a copper foil having a thickness of 14 μm, dried and pressed to obtain an electrode having a thickness of 70 to 80 μm. The density of the obtained electrodes was 0.9-1.1 g/cm ³ .
A negative electrode was used as a working electrode, and metallic lithium was used as a counter electrode and a reference electrode. As a solvent, ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 3:7 and used. LiPF ₆ was dissolved in this solvent to a concentration of 1 mol/L, and used as an electrolytic solution. A glass fiber nonwoven fabric was used for the separator. A coin cell was fabricated in a glove box under an argon atmosphere.
A charging/discharging test was performed on the negative electrode half-cell having the above configuration using a charging/discharging test apparatus (manufactured by Toyo System Co., Ltd., "TOSCAT"). Doping of lithium was performed at a rate of 30 mA/g to a predetermined capacity at which metallic lithium does not precipitate with respect to the mass of the active material, and was completed. The capacity (mAh/g) at this time was defined as the charge capacity. Here, the “predetermined capacity at which metallic lithium does not deposit” refers to the upper limit charging capacity (mAh/g) at which metallic lithium does not deposit by Li-NMR.

<Full cell evaluation>
・Preparation of positive electrode 92 parts by mass of ternary oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) as a positive electrode active material, 3 parts by mass of PVDF (polyvinylidene fluoride), 5 parts by mass of acetylene black and 120 parts by mass of NMP (N-methylpyrrolidone) was mixed to obtain a slurry. The obtained slurry was applied to one side of an aluminum foil having a thickness of 20 μm, dried and then pressed to obtain a positive electrode. The density of the obtained electrodes was 2.4-2.6 g/cm ³ . This electrode was punched into a disk shape with a diameter of 14 mm to obtain a positive electrode plate.

- Preparation of positive electrode half cell Metal lithium was used as a counter electrode and a reference electrode for the obtained positive electrode. As a solvent, ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 3:7 and used. LiPF ₆ was dissolved in this solvent to a concentration of 1 mol/L, and used as an electrolytic solution. A glass fiber nonwoven fabric was used for the separator. A coin cell was fabricated in a glove box under an argon atmosphere.
A charge/discharge test was performed on the positive electrode half-cell having the above configuration using a charge/discharge test apparatus (manufactured by Toyo System Co., Ltd., "TOSCAT"). Lithium dedoping from the positive electrode was performed at a rate of 15 mA/g with respect to the mass of the active material until the lithium potential reached 4.2 V, and the capacity at this time was taken as the charge capacity. Next, lithium doping to the positive electrode was performed at a rate of 15 mA/g with respect to the mass of the active material until the lithium potential reached 3.0 V, and the capacity at this time was taken as the discharge capacity. The resulting charge capacity was 174 mAh/g, the discharge capacity was 154 mAh/g, and the charge/discharge efficiency (initial charge/discharge efficiency) calculated as a percentage of "discharge capacity/charge capacity" was 88.5%.

- Production and Evaluation of Full Cell The mixture-coated surfaces of the negative electrode and the positive electrode were opposed to each other with a separator made of glass fiber nonwoven fabric interposed therebetween so that the positive electrode (14 mm in diameter) did not protrude from the negative electrode surface with a diameter of 15 mm. At this time, the ratio (negative electrode capacity/positive electrode capacity) of the negative electrode charge capacity (mAh) and the positive electrode charge capacity (mAh) per facing area was adjusted to be 1. As a solvent, ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 3:7 and used. LiPF ₆ was dissolved in this solvent to a concentration of 1 mol/L, and used as an electrolytic solution. A coin cell was fabricated in a glove box under an argon atmosphere.

- Charge/discharge test A charge/discharge test was performed on the coin cell (full cell) having the above configuration using a charge/discharge test apparatus (manufactured by Toyo System Co., Ltd., "TOSCAT"). First, the battery was charged at a rate of 30 mA/g with respect to the mass of the negative electrode active material until it reached 4.2 V, and the capacity at this time was taken as the charge capacity. Next, discharge was performed at a rate of 30 mA/g with respect to the mass of the negative electrode active material until the voltage reached 2.0 V, and the capacity at this time was taken as the discharge capacity. In addition, the value calculated by the difference of "charge capacity-discharge capacity" was defined as irreversible capacity, and the value calculated by the percentage of "discharge capacity / charge capacity" was defined as charge-discharge efficiency (initial charge-discharge efficiency). Table 1 shows the obtained charge capacity, discharge capacity, irreversible capacity and charge/discharge efficiency.

・Output characteristic test For the coin cell (full cell) having the above configuration, first, charging is performed at a rate of 30 mA / g with respect to the mass of the negative electrode active material until it reaches 4.2 V, and then discharging is performed on the mass of the negative electrode active material. On the other hand, the rate was 30 mA/g until the voltage reached 2.0 V, and the capacity at this time was taken as the discharge capacity (A). Further, charging is performed to 4.2 V at a rate of 30 mA/g of the negative electrode active material mass, and then discharging is performed to 2.0 V at a rate of 150 mA/g of the negative electrode active material mass. The capacity at this time was defined as the discharge capacity (B). A value calculated as a percentage of "discharge capacity (B)/discharge capacity (A)" was taken as the discharge capacity retention rate. The lower the electrode resistance, the easier it is for lithium ions to be dedoped from the negative electrode, and the higher the discharge capacity retention rate, the higher the output characteristics. Table 1 shows the obtained output characteristics (discharge capacity retention rate).

・Electrode expansion rate The coin cell (full cell) having the above configuration is charged at a rate of 30 mA/g with respect to the mass of the negative electrode active material until it reaches 4.2 V, and discharged at 30 mA/g with respect to the mass of the negative electrode active material. It went until it became 2.0V at the rate of g. After repeating this charge-discharge cycle five times, the coin cell was disassembled in a glove box under an argon atmosphere to take out the negative electrode, which was washed with diethyl carbonate and then dried. The negative electrode thickness (D) after drying was measured, and the ratio [percentage of “thickness (D)/thickness (C)”] to the negative electrode thickness (C) measured before charging/discharging was determined as the electrode expansion rate. The negative electrode thickness (C) and the negative electrode thickness (D) are each obtained by measuring the total thickness of the mixture layer and the copper foil at several points and subtracting the copper foil thickness from each total thickness. Average value. Table 1 shows the electrode expansion coefficients obtained.

Example 2 (vapor phase deashing, addition of volatile organic matter, full-cell evaluation)
<Preparation of carbon precursor>
A carbon precursor was obtained in the same manner as in Example 1 up to the vapor phase deoxidation treatment.
The resulting carbon precursor was pulverized using a dry bead mill (SDA5, manufactured by Ashizawa Finetech) under the conditions of a bead diameter of 3 mmφ, a bead filling rate of 75%, and a raw material feed rate of 1 kg/hour to obtain an average particle diameter of 2. A 0.7 μm carbon precursor (2) was obtained.

<Preparation of non-graphitizable carbonaceous material>
Firing was performed in the same manner as in Example 1, except that the carbon precursor prepared as described above was used, to prepare a non-graphitizable carbonaceous material. The recovered non-graphitizable carbonaceous material was 4.9 g, and the recovery rate was 89%.
The characteristic values of the non-graphitizable carbonaceous material prepared as described above were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that the non-graphitizable carbonaceous material prepared as described above was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. , a charge-discharge test was performed using a charge-discharge test device.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that the non-graphitizable carbonaceous material prepared as described above was used. Table 1 shows the characteristic values obtained.

Example 3 (vapor phase demineralization, CVD treatment, full-cell evaluation)
<Preparation of carbon precursor>
The same carbon precursor (2) as in Example 2 was used.

<Preparation of non-graphitizable carbonaceous material>
Main baking was carried out in the same manner as in Example 2, except that polystyrene, which is a volatile organic substance, was not used. Then, 3 g of the obtained carbonaceous material was placed in a quartz inner case and heated to 780° C. at a rate of 20° C./min under a nitrogen flow rate of 0.1 L/min in a rotary tubular furnace. After reaching 780° C., the vaporized hexane gas was mixed with nitrogen gas at a flow rate of 0.04 L/min, and the nitrogen/hexane mixed gas was passed through the tubular furnace for 30 minutes to perform CVD treatment. After that, the hexane gas stream was stopped, and heat treatment was further performed for 30 minutes under a nitrogen flow rate of 0.1 L/min, followed by natural cooling. After confirming that the temperature in the furnace had decreased to 200° C. or less, the non-graphitizable carbonaceous material was taken out from the furnace. The recovered non-graphitizable carbonaceous material was 2.95 g, and the recovery rate was 98%.
The characteristic values of the non-graphitizable carbonaceous material prepared as described above were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that the non-graphitizable carbonaceous material prepared as described above was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. , a charge-discharge test was performed using a charge-discharge test device.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that the non-graphitizable carbonaceous material prepared as described above was used. Table 1 shows the characteristic values obtained.

Example 4 (liquid phase demineralization, CVD treatment, full-cell evaluation)
<Preparation of carbon precursor>
Approximately 5 mm square 100 g of coconut shell chips from Mindanao Island in the Philippines were immersed in 150 g of a 7.4% by mass citric acid aqueous solution, heated to 80° C., and heated for 4 hours. It was then cooled to room temperature and deliquored by filtration. This operation was performed 5 times to demineralize. The decalcified coconut shells were dried at 80° C. under 1 Torr for 24 hours. 20 g of decalcified and dried coconut shell chips were placed in a crucible and heated at 10° C. using a KTF1100 furnace (inner diameter: 70 mmΦ) manufactured by Koyo Thermo Co., Ltd. under a flow rate of 3 L/min (0.012 m/sec) of nitrogen stream with an oxygen content of 15 ppm. /min to 750°C, held for 60 minutes, and then cooled over 6 hours. After confirming that the temperature in the furnace had decreased to 50°C or less, the carbon precursor was taken out from the furnace.
The resulting carbon precursor was pulverized using a dry bead mill (SDA5, manufactured by Ashizawa Finetech) under the conditions of a bead diameter of 3 mmφ, a bead filling rate of 75%, and a raw material feed rate of 1 kg/hour to obtain an average particle diameter of 2. A 7 μm carbon precursor (3) was obtained.

<Preparation of non-graphitizable carbonaceous material>
Firing and CVD treatment were performed in the same manner as in Example 3 except that the carbon precursor (3) was used to prepare a non-graphitizable carbonaceous material. The recovered non-graphitizable carbonaceous material was 2.95 g, and the recovery rate was 98%.
The characteristic values of the non-graphitizable carbonaceous material prepared as described above were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that the non-graphitizable carbonaceous material prepared as described above was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. , a charge-discharge test was performed using a charge-discharge test device.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that the non-graphitizable carbonaceous material prepared as described above was used. Table 1 shows the characteristic values obtained.

Comparative Example 1 (vapor phase demineralization, change in sample layer height, full-cell evaluation)
<Preparation of carbon precursor>
The same carbon precursor (1) as in Example 1 was used.

<Preparation of non-graphitizable carbonaceous material>
75 g of the carbon precursor prepared as described above and 7.5 g of polystyrene (manufactured by Sekisui Plastics Co., Ltd., average particle size: 400 μm, residual carbon content: 1.2%) were mixed. 82.5 g of this mixture was placed in a graphite sheath so that the sample layer height was about 30 mm, and heated to 1290 ° C. at a rate of 10 ° C./min under a nitrogen flow rate of 1 L/min in a tubular furnace manufactured by Motoyama Co., Ltd. After heating, it was held for 30 minutes and cooled naturally. After confirming that the temperature in the furnace had decreased to 200° C. or less, the non-graphitizable carbonaceous material was taken out from the furnace. The recovered non-graphitizable carbonaceous material was 73.4 g, and the recovery rate was 89%.
The characteristic values of the non-graphitizable carbonaceous material prepared as described above were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that the non-graphitizable carbonaceous material prepared as described above was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. , a charge-discharge test was performed using a charge-discharge test device.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that the non-graphitizable carbonaceous material prepared as described above was used. Table 1 shows the characteristic values obtained.

Comparative Example 2 (vapor phase demineralization, change in sample layer height, full-cell evaluation)
<Preparation of carbon precursor>
The same carbon precursor (2) as in Example 2 was used.

<Preparation of non-graphitizable carbonaceous material>
Firing was carried out in the same manner as in Comparative Example 1, except that the carbon precursor (2) was used, to prepare a non-graphitizable carbonaceous material. The recovered non-graphitizable carbonaceous material was 72 g, and the recovery rate was 87%.
The characteristic values of the non-graphitizable carbonaceous material prepared as described above were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that the non-graphitizable carbonaceous material prepared as described above was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. , a charge-discharge test was performed using a charge-discharge test device.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that the non-graphitizable carbonaceous material prepared as described above was used. Table 1 shows the characteristic values obtained.

Comparative Example 3 (vapor phase demineralization, no addition of volatile organic matter, full-cell evaluation)
<Preparation of carbon precursor>
The same carbon precursor (2) as in Example 2 was used.

<Preparation of non-graphitizable carbonaceous material>
Firing was performed in the same manner as in Example 2, except that polystyrene, which is a volatile organic substance, was not used to prepare a non-graphitizable carbonaceous material. The recovered non-graphitizable carbonaceous material was 4.75 g, and the recovery rate was 95%.
The characteristic values of the non-graphitizable carbonaceous material prepared as described above were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that the non-graphitizable carbonaceous material prepared as described above was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. , a charge-discharge test was performed using a charge-discharge test device.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that the non-graphitizable carbonaceous material prepared as described above was used. Table 1 shows the characteristic values obtained.

Comparative Example 4 (liquid phase demineralization after carbonization, CVD treatment, full cell evaluation)
<Preparation of carbon precursor>
Approximately 5 mm square of 20 g of coconut shell chips from Mindanao Island in the Philippines are placed in a crucible, and using a Koyo Thermo KTF1100 furnace (inner diameter 70 mmΦ), under a flow rate of 3 L / min (0.012 m / sec) of nitrogen stream with an oxygen content of 15 ppm. , the temperature was raised to 750° C. at 10° C./min, held for 60 minutes, cooled over 6 hours, confirmed that the temperature in the furnace had decreased to 50° C. or less, and the carbide was removed from the furnace. After the obtained charcoal was immersed in a 35% by mass hydrochloric acid aqueous solution for 1 hour, it was washed twice with water at 80° C. for 1 hour to demineralize. The decalcified coconut shells were dried at 80° C. under 1 Torr for 24 hours.
The obtained deashed and dried carbon precursor was pulverized using a dry bead mill (SDA5, manufactured by Ashizawa Finetech Co., Ltd.) under the conditions of a bead diameter of 3 mmφ, a bead filling rate of 75%, and a raw material feed amount of 1 kg/hour. , to obtain a carbon precursor (4) having an average particle size of 2.7 μm.

<Preparation of non-graphitizable carbonaceous material>
Main firing and CVD treatment were performed in the same manner as in Example 4 except that the carbon precursor (4) was used to prepare a non-graphitizable carbonaceous material. The recovered non-graphitizable carbonaceous material was 2.95 g, and the recovery rate was 98%.
The characteristic values of the non-graphitizable carbonaceous material prepared as described above were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that the non-graphitizable carbonaceous material prepared as described above was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. , a charge-discharge test was performed using a charge-discharge test device.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that the non-graphitizable carbonaceous material prepared as described above was used. Table 1 shows the characteristic values obtained.

Comparative Example 5 (Carbotron PJ, full cell evaluation)
<Measurement of characteristic values of Carbotron PJ>
The characteristic values of Carbotron PJ were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that Carbotron PJ manufactured by Kureha Corporation was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. A charge/discharge test was performed.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that Carbotron PJ manufactured by Kureha Corporation was used. Table 1 shows the characteristic values obtained.

Comparative Example 6 [Carbotron PS (F), full-cell evaluation]
<Measurement of characteristic values of Carbotron PS (F)>
Characteristic values of Carbotron PS (F) were measured in the same manner as in Example 1. Table 1 shows the results.

<Estimation of negative electrode full charge capacity for full cell>
A negative electrode was prepared in the same manner as in Example 1 except that Carbotron PS (F) manufactured by Kureha Corporation was used, and a coin cell was prepared using metallic lithium as a counter electrode and a reference electrode. A charge/discharge test was performed using the device.

<Full cell evaluation>
Full-cell evaluation was performed in the same manner as in Example 1, except that Carbotron PS (F) manufactured by Kureha Corporation was used. Table 1 shows the characteristic values obtained.

As shown in Table 1, the non-graphite of the present invention that provides a specific ⁷ Li nucleus-solid NMR analysis chemical shift value and a specific electrode expansion coefficient in the negative electrode of a non-aqueous electrolyte secondary battery that is used when fully charged. By using carbonaceous materials (Examples 1 to 4), high output characteristics were achieved in addition to high charge capacity and high charge/discharge efficiency.

On the other hand, when a non-graphitizable carbonaceous material that does not give a specific ⁷ Li nucleus-solid NMR analysis chemical shift value is used (Comparative Examples 1 to 3), a specific ⁷ Li nucleus-solid NMR analysis chemical shift value is also obtained. When a non-graphitizable carbonaceous material that does not provide a specific electrode expansion coefficient is used (Comparative Examples 4-5), and when a non-graphitizable carbonaceous material that does not provide a specific electrode expansion coefficient is used (Comparative Example 6) However, it is not possible to manufacture a non-aqueous electrolyte secondary battery having both high charge capacity and high charge-discharge efficiency and high discharge capacity retention rate, and such a non-aqueous electrolyte secondary battery suffers from low charge-discharge efficiency and low discharge. It had only capacity retention (ie low output characteristics).

A fully charged non-aqueous electrolyte secondary battery comprising the non-graphitizable carbonaceous material of the present invention has high output characteristics due to low electrode resistance in addition to high charge capacity and high charge/discharge efficiency. Therefore, it can be suitably used for in-vehicle applications such as hybrid vehicles (HEV) and electric vehicles (EV).

Claims (12)

A non-graphitizable carbonaceous material for the negative electrode of a non-aqueous electrolyte secondary battery that is used in a fully charged state, and a chemical shift relative to lithium chloride observed by ⁷ Li nucleus-solid NMR analysis when the battery is fully charged. The main resonance peak position of the value is greater than 115 ppm, and the expansion rate of the negative electrode containing the non-graphitizable carbonaceous material at full charge is 107% or less based on the thickness of the negative electrode before charging, and the expansion rate Measured on a negative electrode having a thickness of 70 to 80 μm and a density of 0.9 to 1.1 g/cm ³ with a mixture layer containing 6 parts by mass of polyvinylidene fluoride for 94 parts by mass of a non-graphitizable carbonaceous material. and the following formula:
[Thickness (D)/Thickness (C)] × 100
[In the formula, the thickness (C) is the average value of the thickness of several locations of the negative electrode measured before charging, and the thickness (D) is the thickness of several locations of the negative electrode measured after repeating the charge-discharge cycle five times. is the average of]
Non-graphitizable carbonaceous material, which is a value calculated according to 2. The non-graphitizable carbonaceous material according to claim 1, wherein the oxygen element content is 0.30% by mass or less. 3. The non-graphitizable carbonaceous material according to claim 1, which is derived from a plant-derived carbon precursor. The non-graphitizable carbon according to any one of claims 1 to 3, wherein the average interplanar spacing d ₀₀₂ of the (002) plane calculated using the Bragg formula according to the wide-angle X-ray diffraction method is 0.36 to 0.42 nm. quality material. The non-graphitizable carbonaceous material according to any one of claims 1 to 4, wherein the elemental potassium content is 0.1% by mass or less and the elemental iron content is 0.02% by mass or less. 6. The flame of any one of claims 1 to 5, comprising the steps of acid-treating the plant-derived carbon precursor and calcining the acid-treated carbon precursor at 1050°C to 1400°C under an inert gas atmosphere. A method for producing a graphitized carbonaceous material. A negative electrode for a non-aqueous electrolyte secondary battery, comprising the non-graphitizable carbonaceous material according to any one of claims 1 to 5. A fully charged nonaqueous electrolyte secondary battery comprising a negative electrode for a nonaqueous electrolyte secondary battery comprising a non-graphitizable carbonaceous material, wherein when fully charged, ⁷ Li nuclear-solid NMR analysis The main resonance peak position of the chemical shift value based on lithium chloride observed by is larger than 115 ppm, and the expansion rate at the time of full charge of the negative electrode containing the non-graphitizable carbonaceous material is the thickness of the negative electrode before charging The expansion coefficient is 107% or less based on , and the expansion coefficient is provided with a mixture layer containing 6 parts by mass of polyvinylidene fluoride with respect to 94 parts by mass of the non-graphitizable carbonaceous material . Measured on a negative electrode of 9 to 1.1 g/cm ³ , the following formula:
[Thickness (D)/Thickness (C)] × 100
[In the formula, the thickness (C) is the average value of the thickness of several locations of the negative electrode measured before charging, and the thickness (D) is the thickness of several locations of the negative electrode measured after repeating the charge-discharge cycle five times. is the average of]
Non-aqueous electrolyte secondary battery, which is a value calculated according to . 9. The non-aqueous electrolyte secondary battery according to claim 8, wherein the oxygen element content is 0.30% by mass or less. 10. The non-aqueous electrolyte secondary battery according to claim 8, wherein the non-graphitizable carbonaceous material is derived from a plant-derived carbon precursor. Any one of claims 8 to 10, wherein the average interplanar spacing d ₀₀₂ of the (002) plane of the non-graphitizable carbonaceous material calculated using the Bragg formula according to the wide-angle X-ray diffraction method is 0.36 to 0.42 nm. 3. The non-aqueous electrolyte secondary battery according to . 12. The non-graphitizable carbonaceous material according to any one of claims 8 to 11, wherein the potassium element content of the non-graphitizable carbonaceous material is 0.1% by mass or less, and the iron element content of the non-graphitizable carbonaceous material is 0.02% by mass or less. non-aqueous electrolyte secondary battery.

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