JP3430706B2 - Carbon material for negative electrode and non-aqueous electrolyte secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon material for a negative electrode and a non-aqueous electrolyte secondary battery using the carbon material.

[0002]

2. Description of the Related Art Recent remarkable advances in electronic technology have made electronic devices smaller and lighter one after another. Along with this, batteries, which are portable power sources, are required to be smaller and lighter and have higher energy density.

Conventionally, an aqueous solution type secondary battery such as a lead battery or a nickel-cadmium battery has been mainly used as a secondary battery for general use. However, although these aqueous secondary batteries can satisfy cycle characteristics to some extent, they cannot be said to be sufficient in terms of battery weight and energy density.

On the other hand, recently, research on a non-aqueous electrolyte secondary battery using lithium or a lithium alloy as a negative electrode material
Development is actively done. This non-aqueous electrolyte secondary battery has high energy density, little self-discharge, and is lightweight.

However, in this non-aqueous electrolyte secondary battery, lithium is dendrite-like crystal grown on the negative electrode at the time of charging as the charging / discharging cycle progresses, and finally reaches the positive electrode to cause an internal short circuit. Therefore, it is difficult to put it into practical use.

Therefore, a non-aqueous electrolyte secondary battery using a carbon material as a negative electrode material has been proposed. This non-aqueous electrolyte secondary battery utilizes the fact that lithium is doped / dedoped between carbon layers of a carbon material in a negative electrode reaction, and dendrite-like lithium remains on the negative electrode even if a charge / discharge cycle proceeds. No phenomenon such as precipitation is observed, it has a high energy density, is lightweight, and exhibits excellent charge / discharge cycle characteristics.

[0007]

There are various carbon materials that can be used as the negative electrode material in such a non-aqueous electrolyte secondary battery. First, the carbon material practically used as the negative electrode material is coke or glass. It is a carbon material having low crystallinity obtained by heat-treating an organic material at a relatively low temperature, such as a non-graphitizable carbon material such as linear carbon. Non-aqueous electrolyte secondary batteries using a negative electrode composed of these non-graphitizable carbon materials and an electrolyte containing propylene carbonate (PC) as a main solvent have already been commercialized.

More recently, graphites having a developed crystal structure have been used as a negative electrode material.

It has been considered difficult to use this graphite as a negative electrode material because it decomposes PC, which has been widely used as a main solvent of non-aqueous solvents. But the PC
It has been found that such inconvenience can be eliminated by using ethylene carbonate (EC) instead of, and it can be used for the negative electrode in the form of a combination with this EC.

Here, comparing the characteristics of the non-graphitizable carbon material and the graphites as the negative electrode material, the charge-discharge mechanism of the non-graphitizable carbon material has been analyzed, and it is generally said. In addition to the existing carbon layers, a theory has been published that many pores in the material serve as storage places for lithium (21st Annual Meeting of the Carbon Material Society, p190, 194, 196). A non-graphitizable carbon material having a high discharge capacity of 480 mAh / g by controlling such a pore structure has been developed and announced (the 35th Annual Meeting of the Battery Symposium p47).

However, when observing the lithium de-doping curve (de-doping amount vs potential) for this non-graphitizable carbon material, the initial potential of de-doping is low, but the latter half of the curve shows a smooth shape. It rises and does not give a flat curve as with graphites. This gentle increase in the electric potential corresponds to pseudo deintercalation similar to coke, and in the case of the non-graphitizable carbon material, such an increase in the electric potential causes the discharge end voltage of the battery to be set high. However, there is a problem that the improved capacity cannot be fully utilized.

On the other hand, in the case of graphites, it is generally believed that lithium is mainly stored between the graphite layers, and theoretically 3
A capacity of 72 mAh / g is obtained. Since the graphites have a higher true density than the non-graphitizable carbon material, they have an advantage that a high electrode filling property can be obtained when used as a negative electrode material.

However, in order to smoothly carry out the reaction at the electrodes, it is necessary to provide a certain amount of voids in the electrodes so that the electrolytic solution can be spread throughout the electrodes, and it is not possible to improve the electrode filling property without fail. For this reason, it is difficult to fully utilize the advantage of graphites having a high electrode filling property.

In the non-aqueous electrolyte secondary battery, the final voltage for constant voltage charging is set to, for example, 4.2V. When charging is terminated at such a cutoff voltage, the potential of the negative electrode made of non-graphitizable carbon can be suppressed to 50 mV or less, but the potential of the negative electrode made of graphite can reach 100 to 150 mV. .

That is, although the charging is completed at the same final voltage, the potential of the negative electrode made of graphite is 50 to 100 mV higher than that of the negative electrode made of the non-graphitizable carbon material. Become. When the potential of the negative electrode alone is high at the end of charging, a large amount of lithium is extracted from the positive electrode active material. As a result, the structural stability of the positive electrode is impaired, and the reliability of the environmental resistance and the like is impaired.

As described above, the graphites and the non-graphitizable carbon that have been used as the negative electrode material have weak points, and cannot be said to be sufficiently satisfactory.

Therefore, the present invention has been proposed in view of such a conventional situation, and is for a negative electrode having a high electrode filling property, a high capacity, an excellent potential flatness, and a low potential at the end of charging. The purpose is to provide a carbon material. It is another object of the present invention to provide a non-aqueous electrolyte secondary battery having high energy density, good cycle characteristics, and excellent reliability by using such a carbon material for a negative electrode.

[0018]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies and found that a unique carbon material having both a graphite crystal structure and pores has a high capacity and potential. It has been found that the requirements for the negative electrode material such as excellent flatness and low potential at the end of charging are satisfied. Then, by using such a carbon material for the negative electrode, it has been found that a non-aqueous electrolyte secondary battery having high energy density and good cycle characteristics and excellent reliability is realized. .

The carbon material for a negative electrode of the present invention has been completed on the basis of such findings, and is made of a graphite material and a resin.
The carbon material obtained by mixing and firing the organic compound as the raw material of is a (002) plane spacing of 0.34 nm or less measured by an X-ray diffraction method, and a (002) plane. Is mainly composed of a graphite structure having a C-axis crystallite thickness of 14.0 nm or more, and the difference between the density measured by the helium substitution method and the density measured by the butanol solvent method is 0.1 g.
/ Cc or more and 0.30 g / cc or less.
Furthermore, carbon materials are organic materials that are the raw materials for graphite materials and resins.
900 to 150 in an inert gas stream by mixing with a compound
Desirably a carbon material obtained by heat treatment at 0 ° C
Good

Further, the non-aqueous electrolyte secondary battery of the present invention comprises a negative electrode made of a carbon material for a negative electrode having the above characteristics, a positive electrode made of a transition metal composite oxide containing lithium, and a non-aqueous solvent. And an electrolytic solution in which an electrolyte is dissolved.

[0021]

Here, a method of measuring the density by the butanol solvent method and the helium substitution method will be described.

First, the measurement of the density by the butanol solvent method is specified in JIS-R7222, and is basically performed by the following procedure.

That is, in order to measure the density of the carbon material, the weight of the carbon material is measured in advance. The measured weight of the carbon material is defined as x.

Then, the carbon material having the weight x is immersed in butanol filled in the container, and the volume of butanol removed by the immersion of the carbon material is measured. The excluded volume of this butanol is y ₁ . The ratio x / y _l for the x and y _l corresponds to the density ρq in butanol solvent method.

On the other hand, in order to measure the density of the carbon material by the helium substitution method, the weight of the carbon material is measured in advance as in the case of the butanol solvent method. The measured weight of the carbon material is defined as x.

Then, the carbon material having the weight x is left to stand in a container filled with helium gas, and the volume of helium removed by the standing of the carbon material is measured. The excluded volume of helium is y _g . This ratio of x and y _g x / y
_g corresponds to the density ρHe in the helium substitution method.

As described above, ρHe and ρq of the carbon material are obtained by measuring x, y _g , x, and y ₁ , respectively. Of these, y _g and y _l are He and butanol at the molecular level. Since the bulks are different and the carbon material surface has pores of various sizes, the values are usually different.

That is, when a carbon material is immersed in butanol, butanol has a molecular length of about 0.
Since it is about 7 nm, it is considered difficult to diffuse into the pores (so-called sub-micropores) having a diameter of about 0.8 nm or less in the opening and inside even if the thermal motion of molecules is taken into consideration. That is, it can be said that the volume y _{l of} n-butanol eliminated by the immersion of the carbon material is approximately equivalent to the value obtained by adding the volume of the pores to the volume of the carbon material itself, because butanol cannot diffuse into the pores.

On the other hand, when the carbon material is left to stand in helium gas, the He atom has an atomic radius of about 0.15 nm and a diameter of 0.3 to such that n-butanol cannot penetrate.
Diffusion into 0.4 nm pores is possible. That is, the volume y of the helium gas that is removed by leaving the carbon material unattended
_Since He can diffuse into the pores as well, it can be said that _g is substantially the same as the value in which the pores are present on the surface of the carbon material, that is, the volume of the carbon material itself excluding the volume of the pores.

Therefore, for the density ρp (x / y _l ) of the carbon material obtained by the butanol solvent method and the density ρHe (x / y _g ) of the carbon material obtained by the helium substitution method, the carbon material obtained by the helium substitution method is used. The density ρHe is usually larger than the density ρp of the carbon material obtained by the butanol solvent method. The value ρHe-ρp obtained by subtracting ρp from ρHe reflects the proportion of pores present in the carbon material, and the larger this difference ρHe-ρp is,
It means that it has many pores per unit volume.

The carbon material for the negative electrode of the present invention is the same as the above-mentioned X material.
The crystal structure parameter measured by the line diffraction method is mainly composed of a graphite structure satisfying a predetermined condition, and the difference ρHe-ρp between the density measured by the helium substitution method and the density measured by the butanol solvent method is 0. It is 1 g / cc or more.
Therefore, it has pores of a certain size or more.

As described above, the negative electrode carbon material having both the graphite structure and the fine pores exhibits the characteristics of combining the advantages of both the non-graphitizable carbon material and the graphites, and functions very well as the negative electrode material. To do.

That is, the carbon material for the negative electrode has a high capacity because it has pores of a certain size or more, and since it is mainly composed of a graphite structure, it has a high true density and a high electrode packing property.

When the lithium dedoping curve is measured, it shows a low potential as seen in the non-graphitizable carbon material in the early stage of dedoping. Then, even if the discharge proceeds, this low potential is maintained for a long time, and excellent potential flatness is obtained as seen in graphites. Therefore, even when the discharge end voltage is set high, the capacity of the material can be fully utilized and the energy density of the battery can be improved.

Further, in this carbon material for the negative electrode, the potential at the end of charging when constant current charging is performed is lower than that of commonly used graphites. Therefore, the structural stability of the positive electrode is not impaired, and it greatly contributes to the reliability improvement of the battery.

Here, ρHe-ρp is 0.1 g /
Although it is regulated to be ³ cm ³ or more, a more preferable value of ρHe-ρp is 0.3 g / cm ³ or more.

The carbon material for the negative electrode having the above characteristics can be synthesized by mixing the graphite material and the organic compound, polymerizing, and then firing. Here, in order to obtain the desired carbon material, it is desirable to set the material type and synthesis conditions to some extent strictly.

First, the raw materials of this carbon material are a graphite material and an organic compound. Of these, the graphite material that constitutes the skeleton of the carbon material needs to be considered in terms of crystallinity and particle size. There is.

That is, as the graphite material, in order to give the finally synthesized carbon material a graphite structure having a predetermined crystal structure parameter, the same crystal structure parameter as that of the graphite structure, that is, measured by the X-ray diffraction method. Done (00
2) The ones satisfying the conditions that the interplanar spacing of the faces is 0.340 nm or less and the C-axis crystallite thickness of the (002) face is 14.0 nm or more. When a graphite material having relatively high crystallinity is used among those having such crystal structure parameters, it is preferable to select one having a small particle size. However, a graphite material that is too fine, such as a particle diameter of 1 μm or less, is unsuitable. This is because a carbon material synthesized using a fine graphite material has a large side reaction at the time of charging / discharging and produces an irreversible capacity that is not discharged even when charged.

On the other hand, as the organic compound, a compound which gives non-graphitizable carbon when heat treated alone is suitable. Such an organic compound produces a volatile substance in the firing process, and the appropriate volatilization process forms a pore in the material.

As typical examples, compounds having a furan ring such as furfuryl alcohol and furfural, which are raw materials for thermosetting resins, and phenol compounds are suitable.

In addition to those which give these thermosetting resins, it is also possible to use those which, after being mixed with a graphite material, become a resin by a secondary treatment and become solid-phase carbonized. For example, condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphene and pentacene, other derivatives (for example, carboxylic acid thereof, carboxylic acid anhydride, carboxylic acid imide, etc.), or a mixture thereof, Acenaphthylene, indole, isoindole, quinoline, isoquinoline,
Fused heterocyclic compounds such as quinoxaline, phthalazine, carbazole, acridine, phenazine, and phenanthridine, derivatives thereof, pitches obtained from so-called coal and petroleum, and the like can also be used.

The petroleum pitch is tars obtained by high-temperature thermal decomposition of coal tar, ethylene bottom oil, crude oil, etc.
It can be obtained from asphalt or the like by operations such as distillation (vacuum distillation, atmospheric distillation, steam distillation), thermal polycondensation, extraction, chemical polycondensation and the like. In addition, other coal pitch is obtained as a liquid material during heat treatment of coal. At this time, the pitch H /
The C atomic ratio is important, and H must be H in order to form pores.
The / C atomic ratio needs to be 0.6 to 0.8.

To synthesize the carbon material for the negative electrode, first, the above graphite material and the organic compound are mixed. Here, in order to obtain a carbon material having appropriate pores, the mixing ratio is important. For example, when the amount of the organic compound mixed is too small, the pores are not sufficiently formed in the carbon material. When a carbon material having a small number of pores is used for the negative electrode as described above, the potential at the end of charging is increased, which may impair the structural stability of the positive electrode. On the contrary, if the amount of the organic compound mixed is too large, the carbon material will have too many pores formed therein. In the carbon material with excessively formed pores, the latter half of the lithium dedoping curve rises in a slope shape, and the energy density of the battery cannot be sufficiently increased. It should be noted that the specific appropriate range of the mixing ratio varies depending on the type of the organic compound and is therefore not uniformly determined, and it is desirable to appropriately select the appropriate range according to the degree of formation of volatiles generated during the heat treatment.

The mixture of the graphite material and the organic compound mixed in such an appropriate mixing ratio is then subjected to polymerization treatment. In this polymerization treatment, an organic compound is reactively linked to the surface of the graphite material, and further the organic chains of the reactively linked organic compound and other organic compounds are polymerized.

In this polymerization, an acid catalyst may be added if necessary. As the acid catalyst, inorganic acids such as sulfuric acid, nitric acid and perchloric acid, and organic acids such as paratoluenesulfonic acid can be used.

The polymerization treatment is usually carried out in an inert atmosphere, but when an acid catalyst is used in combination, the polymerization atmosphere may be temporarily set to an oxidizing gas atmosphere. Air, sulfur dioxide, nitrogen dioxide or the like is used as the oxidizing gas.

The processing temperature, time and pressure for the polymerization are appropriately selected depending on the kind of the organic compound or the catalyst as the raw material.
As a guide, for example, at the treatment temperature, it is desirable to set the temperature to 500 ° C. or lower at which solidification of the organic compound starts. The time and the pressure are decided in consideration of the temperature. The longer the polymerization time and the higher the pressure, the higher the degree of polymerization.

The above are the basic processing conditions for polymerization.
When the polymerization reaction is not sufficiently carried out, it is possible to accelerate the polymerization reaction by subjecting the graphite material to surface treatment such as oxidation in advance. This is because when the graphite material is subjected to the surface treatment, the functional group provided thereby acts as a polymerization initiation point.

The means for surface treatment is not particularly limited,
For example, a wet method using an aqueous solution of nitric acid, mixed acid, sulfuric acid, hypochlorous acid, etc., a dry method using an oxidizing gas (eg, air, oxygen, etc.), and a solid reagent such as sulfur, ammonium nitrate, ammonium persulfate, ferric chloride, etc. There is a method.

The polymer obtained by such a polymerization treatment is then calcined to produce the desired carbon material.

At this time, the obtained polymer may be calcined as it is, or the polymer may be calcined as it is, or may be molded by pressing with a binder pitch or the like, and then calcined. Is also good.

This calcination is carried out, for example, by carbonizing the above-mentioned polymer at a temperature of 500 to 700 ° C. in an inert gas stream such as nitrogen, and then in an inert gas stream, a heating rate of 1 to 100 per minute.
The heat treatment is performed at a temperature of 900 ° C., a reached temperature of 900 to 1500 ° C., and a holding time at the reached temperature of 0 to 30 hours. The carbonization operation may be omitted depending on the case.

The produced carbon material can be crushed and classified to be used as a negative electrode material. This pulverization may be performed before or after carbonization or firing, or during the temperature rising process.

In the non-aqueous electrolyte secondary battery of the present invention, the negative electrode is composed of the carbon material for negative electrode thus obtained,
The following are suitable as the positive electrode material and the non-aqueous electrolyte.

That is, the positive electrode material preferably contains a sufficient amount of Li, for example, the general formula LiMO.
A lithium-containing transition metal composite oxide represented by ₂ (wherein M represents at least one of Co, Ni, Mn, and Fe) and an intercalation compound containing Li are preferable.

Further, since the non-aqueous electrolyte secondary battery of the present invention is aimed at achieving a high capacity, the positive electrode is
In a steady state (for example, after repeating charging for about 5 times), it is necessary to contain 250 mAh or more of charge / discharge capacity equivalent Li per 1 g of the negative electrode carbon material, and 300 mAh or more of charge / discharge capacity equivalent Li. Is desirable 330
It is more preferable to include Li corresponding to the charge / discharge capacity of mAh or more.

However, it is not always necessary to supply all the Li from the positive electrode material, and the point is that Li corresponding to the charge / discharge capacity of 250 mAh or more per 1 g of the carbon material should be present in the battery system. The amount of Li in the battery system is determined by measuring the discharge capacity of the battery.

On the other hand, the non-aqueous electrolytic solution is prepared by dissolving an electrolyte in a non-aqueous solvent.

This non-aqueous solvent includes ethylene carbonate (EC)
A solvent mixture mainly composed of a solvent having a relatively high dielectric constant, such as, and a solvent having a plurality of low viscosity solvents added to this high dielectric constant solvent is used.

As the high dielectric constant solvent, propylene carbonate (PC), butylene carbonate, vinylene carbonate, sulfolanes, butyrolactones, valerolactones and the like are suitable in addition to EC.

As the low-viscosity solvent, a symmetric chain carbonate or an asymmetric chain carbonate such as diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate and methyl propyl carbonate is suitable, and two or more of them are mixed and used. However, a good effect can be obtained.

As the electrolyte, any of those used in this type of battery can be used. Specifically, LiP
F ₆ is preferred, but LiClO ₄ , LiAsF ₆ , Li
BF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, (CH ₃
SO ₃ ) ₂ NLi, (CH ₃ SO ₃ ) ₃ CLi, CF ₃ SO ₃
Li, LiCl, LiBr, etc. can also be used.

[0065]

The carbon material for a negative electrode of the present invention has a (002) plane spacing of 0.340 nm or more as measured by X-ray diffraction,
The (002) plane is mainly composed of a graphite structure having a C-axis crystallite thickness of 14.0 nm or more, and the difference between the density by the helium substitution method and the density by the butanol solvent method is 0.1 g / cm ^3.
That is all. Here, the difference between the density by the helium substitution method and the density by the butanol solvent method reflects the ratio of the pores existing in the material.

This value is 0.1 g / cm ³ or more, and in the carbon material for negative electrode where the crystal structure parameter measured by the X-ray diffraction method satisfies the above-mentioned conditions, the pores are present at an appropriate ratio. Since it has a graphite structure, it exhibits characteristics that combine the advantages of both the non-graphitizable carbon material and graphites, and it functions very well as a negative electrode material.

That is, this carbon material for a negative electrode has a high capacity, a high true density, and a high electrode filling property.

Further, when the lithium dedoping curve is measured, it shows a low potential in the early stage of dedoping as seen in the non-graphitizable carbon material. Then, even if the discharge progresses, this low potential is maintained for a long time, and a curve excellent in potential flatness as seen in graphites can be obtained. Therefore, even when the discharge end voltage is set high, the capacity of the material can be fully utilized.

Furthermore, in this carbon material for negative electrode, the potential at the end of charging when constant current charging is performed is a value lower than that of commonly used graphites. Therefore, the structural stability of the positive electrode is not impaired.

Therefore, in a battery using such a carbon material for a negative electrode, high energy density can be obtained, good cycle characteristics can be exhibited, and high reliability can be obtained.

[0071]

EXAMPLES The present invention will be described below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Example 1 30 g of artificial graphite powder (trade name KS-6 manufactured by Lonza)
And furfuryl alcohol (special grade manufactured by Wako Pure Chemical Industries) 1
0 g, 1 g of paratoluenesulfonic acid and 50 g of water serving as a dispersion medium were mixed and filled in a side-armed measuring flask, and a polymerization reaction was carried out at a temperature of 200 ° C. for 50 hours in a nitrogen stream. Then, the obtained reaction product was washed with water and then vacuum dried. Next, 10 g of the reaction product was filled in a crucible and kept at a temperature of 500 ° C. for 5 hours in a nitrogen stream, and then 1
The temperature was raised to 200 ° C. and heat treatment was performed for 1 hour. A carbon material powder was obtained by crushing the obtained fired product.

Comparative Example 1 100 parts by weight of furfuryl alcohol and 85% phosphoric acid of 0.
A viscous polymer (furfuryl alcohol resin: PFA) was obtained by mixing 5 parts by weight and 10 parts by weight of water and heating on a hot water bath for 5 hours.

After water and unreacted alcohol remaining in the furfuryl alcohol resin were removed by vacuum distillation, the resin was carbonized in a nitrogen stream at a temperature of 500 ° C. for 5 hours and ground. Then, 1 g of this pulverized product was filled in a crucible, heated to a temperature of 1200 ° C., and heat-treated for 1 hour. A carbon material powder was obtained by crushing the obtained fired product.

Comparative Example 2 A carbon material powder was obtained by crushing artificial graphite powder (Lonza Co., Ltd., trade name KS-6).

Comparative Example 3 A carbon material powder was obtained by pulverizing the coal pitch coke obtained at a heat treatment temperature of 1200 ° C.

With respect to the various carbon material powders obtained as described above, the interplanar spacing of the (002) plane and the C-axis crystallite thickness of the (002) plane were determined by the powder X-ray diffraction method, and the butanol solvent method and helium were used. The density was measured by the substitution method. The results are shown in Table 1.

The density was measured by the butanol solvent method according to the method specified in JIS-R7222. The density was measured by the helium substitution method using a dry automatic densimeter (trade name: Accupic 1330 type) manufactured by Micromeritics, and the equilibrium determination pressure was 0.05 psi.
g, sample pretreatment temperature 150 ° C., pretreatment time 15 hours.

Further, a working electrode was prepared by using the synthesized carbon material powder, and the working electrode was incorporated into a coin-type test cell shown in FIG. 1 and its negative electrode characteristics were examined.

The working electrode was manufactured as follows.

Immediately before preparation of the negative electrode mix, the carbon material powder was preheated in an Ar atmosphere under the conditions of a temperature rising rate of about 30 ° C./minute, an ultimate temperature of 600 ° C., and an ultimate temperature holding time of 1 hour. Then, polyvinylidene fluoride serving as a binder is added to the pretreated carbon material powder in an amount of 10%.
An amount corresponding to wt% was added, and dimethylformamide was mixed as a solvent and dried to prepare a negative electrode mix.

A working electrode was prepared by molding 37 mg of the thus prepared negative electrode mix into a pellet having a diameter of 15.5 mm together with Ni mesh as a current collector.

Then, as shown in FIG. 1, the working electrode 1 is housed in the electrode can 2, and the counter electrode (Li metal) 4 is housed in the electrode cup 3, respectively. 4 were opposed to each other, and the separator 5 was sandwiched between them. Then, after impregnating each of the electrodes 1 and 4 with the electrolytic solution,
The outer peripheral edges of the electrode can 2 and the electrode cup 3 are covered with a sealing gasket 6.
A coin type test cell was assembled by caulking and sealing via. The counter electrode 4, the separator 5, the material of the electrolytic solution, and the dimensions of the cell are as follows.

Test cell configuration Coin cell (diameter 20 mm, thickness 2.5 mm) Counter electrode: Li metal separator: Polypropylene porous membrane Electrolyte: LiPF in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1). 1 mol of ₆
The test cell thus prepared was charged / discharged, and the capacity and capacity loss per 1 g of the carbon material were examined.

Doping of lithium into the working electrode (charging: strictly speaking, in this test method, the process in which the carbon material is doped with lithium is not charging but discharging, but for convenience, according to the actual condition of the actual battery, This doping process is called charging, and the dedoping process is called discharging.
It was carried out at a constant current of 2 mA until it reached 0 mV (Li / Li ⁺ ). Further, dedoping (discharging) of lithium was performed with a terminal voltage of 1.5 V as a cutoff voltage and a constant current of 0.2 mA per cell.

The measured capacity and capacity loss per 1 g of the carbon material are shown in Table 1 together with the crystal structure parameters obtained by the powder X-ray analysis method, the density by the butanol solvent method, and the density by the helium substitution method. . The discharge (lithium dedoping) curve of the test cell is shown in FIG.

[0087]

[Table 1]

As shown in Table 1, the (002) plane spacing measured by X-ray diffractometry is 0.340 nm or less, and (00
2) The carbon material powder of Example 1 having a C-axis crystallite thickness of 14.0 nm or more and a difference between the helium substitution method density and the butanol solvent method density of 0.1 g / cc or more has a volume of Is large and the capacity loss is small. Further, as can be seen from FIG. 2, a flat portion is seen in the lithium dedoping curve, and the potential flatness is excellent.

On the other hand, the difference between the density by the helium substitution method and the density by the butanol solvent method is 0.1 g / cc or more, but the crystal structure parameters obtained by the powder X-ray diffraction method satisfy the predetermined conditions. The carbon material powder of Comparative Example 1, which is not present, has a smaller capacity and a larger capacity loss than the carbon material powder of Example 1. Moreover, since the latter half of the lithium dedoping curve rises in a slope shape, good potential flatness cannot be obtained.

On the contrary, the crystal structure parameters obtained by the powder X-ray diffraction method satisfy the predetermined conditions, but the difference between the density by the helium substitution method and the density by the butanol solvent method is 0.1 g / In the carbon material powder of Comparative Example 2, which is less than cc, a flat portion is observed in the lithium dedoping curve, but the capacity is remarkably lower than that of the carbon material powder of Example 1, and the capacity loss is large.

Furthermore, the carbon material powder of Comparative Example 3 in which both the crystal structure parameter obtained by the powder X-ray diffraction method and the difference in the density by the helium substitution method and the density by the butanol solvent method do not satisfy the predetermined conditions, However, the amount is less than half that of the carbon material powder of Example 1, and the shape of the lithium dedoping curve is also poor.

From this fact, the interplanar spacing of the (002) plane, the C-axis crystallite thickness of the (002) plane measured by the X-ray diffraction method, and the difference between the density by the helium substitution method and the density by the butanol solvent method are regulated. It was found that this is effective in improving the negative electrode characteristics of the carbon material.

As is clear from the above description, the carbon material for the negative electrode according to the present invention is a raw material for the graphite material and the resin.
The carbon material obtained by mixing with an organic compound and firing is X.
Mainly composed of a graphite structure having a (002) plane spacing of 0.34 nm or less and a (002) plane C-axis crystallite thickness of 14.0 nm or more measured by a line diffraction method, and measured by a helium substitution method. The difference between the measured density and the density measured by the butanol solvent method is 0.1 g / cc or more .
Since it is 0.30 g / cc or less, it has a high capacity, a high electrode filling property, an excellent potential flatness, and a low potential at the end of charging. By using such a carbon material for a negative electrode in a battery, it is possible to obtain a battery having high energy density, good cycle characteristics, and excellent reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a coin type test cell for investigating negative electrode characteristics of a carbon material.

FIG. 2 is a characteristic diagram showing a lithium dedoping curve of a carbon material.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-7-122300 (JP, A) JP-A-8-115723 (JP, A) JP-A-6-275270 (JP, A) JP-A-1- 161675 (JP, A) JP-A-5-307959 (JP, A) JP-A-6-295744 (JP, A) JP-A-61-277157 (JP, A) JP-A-5-290889 (JP, A) JP-A-7-230804 (JP, A) JP-A-7-230803 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40 C01B 31/04 101

Claims (3)

(57) [Claims] 1. An organic compound as a raw material for a graphite material and a resin.
The carbon material obtained by mixing and firing and has a (002) plane spacing of 0.34 nm measured by an X-ray diffraction method.
Below, the C-axis crystallite thickness of the (002) plane was 14.0 nm.
Mainly composed of the above graphite structure, and the difference between the density measured by the helium substitution method and the density measured by the butanol solvent method is 0.10 g / cc or more and 0.30 g / cc.
A carbon material for a negative electrode, which is cc or less . 2. The carbon material is a graphite material and a resin raw material.
Mixed with an organic compound to become 900
It is a carbon material obtained by heat treatment at ℃ ~ 1500 ℃
The carbon material for a negative electrode according to claim 1, wherein 3. A negative electrode comprising the carbon material for a negative electrode according to claim 1, a positive electrode comprising a transition metal composite oxide containing lithium, and an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent. Characteristic non-aqueous electrolyte secondary battery.