JP5886543B2 - Negative electrode for lithium secondary battery and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a negative electrode for a secondary battery and a secondary battery using the same.

  Lithium secondary batteries, which are one of the secondary batteries, have a higher energy density than other secondary batteries, so they can be reduced in size and weight, such as mobile phones, personal computers, and personal digital assistants (PDAs). It is widely used as a power source for mobile electronic devices such as handy video cameras, and its demand is expected to increase in the future.

  In particular, in recent years, in order to deal with energy problems and environmental problems, application to electric vehicles, smart grids, and other applications has attracted attention, and lithium secondary such as initial efficiency, charge / discharge capacity and cycle life are compatible. There is a need for further improvements in battery performance.

  A lithium secondary battery (lithium ion secondary battery) has a structure in which an electrolyte containing lithium ions is filled between a positive electrode and a negative electrode. Among these, a negative electrode active material that intercalates lithium is a binder. An active material layer that is bound by (binder) and integrated on the current collector is provided. As the binder, polyvinylidene fluoride (PVDF) has been mainly used so far.

  However, PVDF has a problem in that the adhesive strength between the negative electrode active materials and the current collector is not sufficient, the adhesion gradually becomes worse, and the cycle life is shortened. Further, if the battery temperature rises abnormally due to a short circuit or the like, PVDF is decomposed to generate HF, and this HF reacts violently with Li, so that the battery is damaged.

  In view of this, a negative electrode using a polyimide resin as a binder has been proposed in order to obtain a secondary battery having a longer cycle life and excellent reliability (see Patent Document 1). Furthermore, the following improved technologies have been proposed for the negative electrode using a polyimide resin as a binder. For example, the ratio of the negative electrode active material made of carbonaceous powder and the polyimide resin is specified to improve the charge / discharge capacity (see Patent Document 2), or the active material layer made of the polyimide resin and the negative electrode active material. In addition to the technology for improving cycle characteristics (see Patent Document 3) by specifying three parameters: thickness, proportion of polyimide resin in the active material layer, and drying temperature at the time of active material layer formation, a specific acid anhydride By combining two types of polyimide resins using materials, the negative electrode active material and the binder are more reliably bonded to the current collector, and the binding force between the negative electrode active materials is increased to suppress an increase in resistance at the negative electrode. Technology (see Patent Document 4), a negative electrode active material containing silicon particles having a predetermined particle size is bound with a polyimide resin using a specific diamine to obtain a negative electrode. As withstand repeated electrodeposition, such techniques to improve the cycle characteristics (see Patent Document 5) are known.

  In addition, it is known that by using so-called hard carbon having low carbon crystallinity as an active material, it is generally known that an excellent cycle life is exhibited. It is also known that the efficiency is inferior.

Japanese Patent No. 3311402 JP 2008-252550 A JP 2008-84562 A Japanese Patent No. 4215532 JP 2008-34352 A

  In particular, when a lithium secondary battery is used as an on-vehicle power source for an electric vehicle or a storage battery for a smart grid, in addition to the discharge capacity, which is a typical performance of the secondary battery, a cycle life that shows charge / discharge repeatability is shown. It becomes important to achieve both. However, as described above, although various improvements have been made for the negative electrode using a polyimide resin as a binder, it cannot be said that the compatibility between the discharge capacity and the cycle life is still at a sufficient level. On the other hand, even when hard carbon is used as an active material, it is difficult to achieve both.

  Therefore, as a result of intensive studies on the above problems, the present inventors use a polyimide resin made of a specific acid anhydride and diamine as a raw material as a binder, and from a specific carbon material as a negative electrode active material integrated therewith By using the active material, it was found that a negative electrode for a secondary battery having both discharge capacity and cycle characteristics can be obtained, and the present invention has been completed.

  Accordingly, an object of the present invention is to provide a negative electrode capable of obtaining a secondary battery having both discharge capacity and cycle characteristics. Another object of the present invention is to provide a secondary battery that is suitable as a power source for an electric vehicle, a smart grid, or the like using such a negative electrode.

〔式中、Ａｒ₁は、少なくとも２個のエーテル結合を有した２価の芳香族ジアミン残基を示し、Ａｒ₂は、下記式（２）で表される４価の酸二無水物残基を示す。〕

That is, the present invention is a negative electrode for a lithium secondary battery including an active material layer in which a negative electrode active material is integrated with a binder, and the binder includes a repeating unit represented by the following general formula (1). Polyimide resin is used, and the negative electrode active material is a low-crystalline carbon material having a low degree of graphitization using at least one of petroleum heavy oil and coal heavy oil as a raw material. A negative electrode for a lithium secondary battery using 5 to 50 μm, a crystal surface interval d ₀₀₂ by X-ray diffraction of 0.3354 to 0.3500 nm, and a BET specific surface area of 10 m ² / g or less. .

[Wherein Ar ₁ represents a divalent aromatic diamine residue having at least two ether bonds, and Ar ₂ represents a tetravalent acid dianhydride residue represented by the following formula (2): Indicates. ]

Moreover, this invention is a lithium secondary battery using said negative electrode.

  The negative electrode of the present invention can provide a negative electrode for a secondary battery having both discharge capacity and cycle characteristics. Therefore, according to the negative electrode of the present invention, it is possible to obtain a secondary battery having a balance of practical characteristics required for an in-vehicle power source for an electric vehicle or a storage battery for a smart grid.

Hereinafter, the present invention will be described in detail based on embodiments of a negative electrode for a secondary battery.
In the present invention, a predetermined polyimide resin is used as a binder as described below. In general, the polyimide resin is excellent in the binding force between the negative electrode active materials, and more excellent in adhesiveness to the current collector forming the negative electrode than PVDF. In addition, unlike PVDF, which is a type of fluororesin, polyimide resin does not contain fluorine in the structure, and because it is thermally stable and has high heat resistance, the battery can be used even when the battery temperature rises abnormally. Low risk of breakage or rupture.

〔式（４）においてＸは、芳香環を１以上有する２価の有機基を表し、好ましくは、下記（５）に示した構造のものが挙げられる。〕

The polyimide resin used in the present invention has a repeating unit represented by the general formula (1), and Ar ₁ is a divalent aromatic diamine residue having at least two ether bonds. The following can be mentioned.

[In formula (4), X represents a divalent organic group having one or more aromatic rings, and preferably has a structure shown in the following (5). ]

  As a preferred diamine component that gives such an aromatic diamine residue, specifically, 2,2′-bis [4- (4-aminophenoxy) phenyl] propane (BAPP), 1,3-bis (4-amino) And phenoxy) benzene (TPE-R), 1,3-bis (3-aminophenoxy) benzene (APB), 4,4′-bis (4-aminophenoxy) biphenyl (BAPB), and the like.

〔式（３）において、Ｙは、直結合又は−ＣＯ−のいずれかを示す。〕 In the polyimide resin used in the present invention, Ar ₂ shown in the general formula (1) is a tetravalent acid dianhydride residue represented by the following formula (2) or formula (3).

[In Formula (3), Y shows either a direct bond or -CO-. ]

Preferred acid dianhydrides that give such acid dianhydride residues are specifically pyromellitic anhydride (PMDA), 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and the like. In addition, the diamine and acid anhydride used as the raw material for the polyimide resin may be a mixture of two or more components, respectively, and a diamine or acid anhydride other than those represented by Ar ₁ and Ar ₂ may be used in combination. However, in that case, it is desirable that the ratio of the components other than those represented by Ar ₁ and Ar ₂ is 50% or less in terms of the molar ratio of each component. As Ar ₁ and Ar ₂ constituting the polyimide structural unit other than the general formula (1), Ar ₁ is 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, m -Phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'- Diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diamino Diphenylsulfone, 3,3'-diaminodiphenylsulfone, benzidine, 3,3'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphe , 3,3′-dimethoxybenzidine, 4,4 ''-diamino-p-terphenyl, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, and the like. Two or more kinds can be mixed and used. Moreover, you may use the siloxane diamine etc. which have the siloxane chain of 1-20 repetition numbers. Furthermore, Ar ₂ may be used those comprising the formula (2) or (3) other than the acid dianhydride. Examples of the acid anhydride in which Ar ₂ gives an acid anhydride residue other than those represented by the general formulas (2) and (3) include 4,4′-oxydiphthalic dianhydride, naphthalene-2,3,6,7-tetracarboxylic Acid dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetra Carboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, 2,2-bis (2,3-dicarboxyphenyl) -propane dianhydride, 2,2-bis (3 , 4-Dicarboxyphenyl) -propane dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3.4-dicarboxyphenyl) ) Methane dianhydride, bis (2,3-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, and the like. It can also be used above.

  When the polyimide resin of the general formula (1) is obtained, it is produced by polymerizing raw material diamine and acid anhydride in the presence of a solvent to obtain a polyimide precursor resin, followed by heat treatment and imidization. Can do. In addition, when setting it as a negative electrode material binder, generally it is set as the composition for disperse-mixing with an active material, a solvent, and other required additives in the state of a polyimide precursor resin, and forming an active material layer. Examples of the reaction solvent used here include dimethylacetamide, dimethylformamide, N-methylpyrrolidone, 2-butanone, diglyme, and xylene, and one or more of these may be used. In addition, the polyimide precursor resin has a weight average molecular weight of 10,000 to 500, from the viewpoint of the balance between the binding property / adhesiveness as a binder and the viscosity of the slurry obtained by mixing with the active material. It is preferable to be in the range of 000.

The negative electrode active material in the present invention is made of a carbon material made from at least one of petroleum heavy oil and coal heavy oil, and has an average particle diameter of 5 to 50 μm and a crystal plane by X-ray diffraction. The distance d ₀₀₂ must be 0.3354 to 0.3500 nm and the BET specific surface area should be 10 m ² / g or less. For example, as a battery suitable for a lithium secondary battery (lithium ion secondary battery), any battery capable of intercalating lithium can be used. Specifically, graphite, low crystallized carbon having a low degree of graphitization, and the like can be used. Examples thereof include carbon materials. Two or more negative electrode active materials may be used in combination.

In the present invention, may be a negative electrode active material composed of a carbon material satisfying the above requirements, but furthermore, the intensity ratio 1580 cm ^-1 peak of 1360 cm ^-1 vicinity by Raman spectroscopy (R = I ₁₃₆₀ / I ₁₅₈₀ ) Is preferably in the range of 0 to 1.5, and more preferably in the range of 0.2 to 0.8. When the intensity ratio R exceeds 1.5, the carbon crystallinity is lowered, and the discharge capacity and the initial efficiency are lowered.

  The graphite material used as the negative electrode active material is a material obtained by subjecting natural graphite to surface treatment as necessary, or artificial graphite having a high energy density obtained at a high temperature of at least about 2000 ° C., usually about 2600 to 3000 ° C. By being used in combination with the specific polyimide resin used in the present invention as a material, the effect of exhibiting excellent cycle characteristics can be obtained.

As a low crystalline carbon material having a low degree of graphitization used as a negative electrode active material, for example, a petroleum-based or coal-based heavy oil is thermally decomposed and heated at a maximum temperature of about 400 ° C. to 800 ° C. for about 24 hours. Examples include raw coke obtained by performing a polycondensation reaction, calcined coke obtained by calcining this raw coke at a maximum temperature of about 800 ° C. to 1500 ° C., and mixing these at a predetermined ratio. good. In addition, a material obtained by adding a boron compound, a phosphorus compound, a nitrogen compound, or the like to these carbon materials, firing, and replacing a part of carbon with a specific element can also be used. Since such a carbon material is usually obtained in the form of a lump, it is better to pulverize it to a predetermined particle size using a pulverizer. In that case, from the viewpoint of energy efficiency when used in a secondary battery The average particle diameter determined as the median diameter is preferably 5 to 50 μm, more preferably 5 to 15 μm, and the BET specific surface area is preferably 10 m ² / g or less, more preferably. Is preferably 5 m ² / g or less. The pulverized carbon material can be used as a negative electrode active material by further firing at about 800 to 1400 ° C.

  In the present invention, the polyimide resin and the negative electrode active material are mixed by using a solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF) or water, alcohol, etc. The negative electrode provided with the active material layer can be obtained by preparing and applying and drying on the current collector.

  Here, the material of the conductive substrate used as the current collector is not particularly limited, but a metal foil such as aluminum, copper, nickel, titanium, and stainless steel can be used. Moreover, although the form of such an electroconductive base material can be made into various forms, such as a continuous sheet, a perforated sheet, and a net-like (net-like) sheet, it is particularly preferable to use a continuous sheet. Furthermore, the thickness of the conductive substrate is preferably 2 to 30 μm.

  In forming the active material layer on the current collector, a negative electrode active material and, if necessary, a conductive aid were mixed into a slurry obtained by dissolving a polyimide resin or a precursor thereof in an organic solvent such as NMP. Then, the active material layer is formed by coating the current collector with a uniform thickness by a known means such as extrusion coating, curtain coating, roll coating or gravure coating, drying to remove the organic solvent, and then heat curing. Form. At this time, from the viewpoint of the balance between the binding property and the discharge capacity, the content ratio of the polyimide resin with respect to the negative electrode active material may be in the range of 0.1 to 10% by mass, preferably 0.3 to It is good to make it the range of 8 mass%. Further, the thickness of the active material layer may be about the same as that for forming a known negative electrode for a secondary battery, and is not particularly limited, but is generally about 10 to 500 μm.

The negative electrode thus obtained can be suitably used as an electrode for a secondary battery such as a lithium secondary battery. When a lithium secondary battery is formed using the negative electrode of the present invention, the opposite positive electrode includes a lithium-containing transition metal oxide LiM (1) _x O ₂ (where x is a numerical value in the range of 0 ≦ x ≦ 1). Where M (1) represents a transition metal and is composed of at least one of Co, Ni, Mn, Ti, Cr, V, Fe, Zn, Al, Sn, and In), or LiM (1) _y M (2) _2-y O ₄ (wherein y is a numerical value in the range of 0 ≦ y ≦ 1, where M (1) and M (2) represent transition metals, Co, Ni, Mn , Ti, Cr, V, Fe, Zn, Al, Sn, In), LiM (1) _x M (2) _y M (3) _z O ₂ (wherein x, y and z are x + y + z = 1 in the range satisfying the relationship, where M (1), M (2) and M (3) represent transition metals, Co, Ni, Mn, Ti, Cr, V, Fe, Zn , Al, Sn, In at least Consisting _{types), LiM (1) x PO} 4 ( wherein x is a number in the range of 0 ≦ x ≦ 1, wherein M (1) represents a transition metal, Co, Ni, Mn, Ti , Cr , V, Fe, Zn, Al, Sn, In), transition metal chalcogenides (Ti, S ₂ , NbSe, etc.), vanadium oxides (V ₂ O ₅ , V ₆ O ₁₃ , V ₂₎ O ₄ , V ₃ O _6, etc.) and lithium compounds, general formula M _x Mo ₆ Ch _6-y (where x is a numerical value in the range of 0 ≦ x ≦ 4, y is 0 ≦ y ≦ 1, Medium M is a metal including a transition metal, Ch is a chalcogen metal), or a positive electrode active material such as activated carbon or activated carbon fiber.

Further, Examples of the electrolyte filling the space between the positive electrode and the negative electrode, and any known ones can be used, for example _{LiClO 4, LiBF 4, LiPF 6} , LiAsF 6, LiB (C 6 H 5), LiCl LiBr, Li ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, Li (CF ₃ CH ₂ OSO ₂ ) ₂ N, Li (CF ₃ CF ₂ CH ₂ OSO ₂ ) ₂ N, Li (HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ N, Li ((CF ₃ ) ₂ CHOSO ₂ ) ₂ N, LiB [C ₆ H ₃ (CF ₃ ) ₂ ] ₄ Mention may be made of mixtures of more than one species.

  Examples of the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1, 2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, anisole, diethyl ether, sulfolane, methylsulfolane, acetonitrile, chloronitrile, propio Nitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene Benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, sulfite, a single solvent or a mixture of two or more solvents such as dimethyl sulfite may be used.

  Hereinafter, the present invention will be described in more detail on the basis of examples. However, the present invention is not limited to the following examples in any way, and can be implemented with appropriate modifications without departing from the scope of the present invention. .

  In addition, the various physical-property values in a following example are each measured based on the following measuring method.

  The particle diameter was determined from the particle size distribution measured by a laser diffraction method with LA-920 manufactured by HORIBA, and the maximum particle diameter at 50% on the fine powder side with respect to the volume was determined as the average particle diameter.

Spacing of the crystal plane d ₀₀₂ was measured by a powder XRD analysis in compliance with Gakushin method.

  The BET specific surface area was measured by BET by nitrogen gas adsorption with Bellsourb-mini manufactured by Bell.

The intensity ratio (R = I ₁₃₆₀ / I ₁₅₈₀ ) of the peak near 1360 cm −1 to the peak near ₁₅₈₀ cm −1 in the Raman spectroscopy was measured by argon laser Raman spectroscopy.

Example 1
Using refined pitch from which quinoline insolubles have been removed from coal-based heavy oil, bulk coke produced by heat treatment at a temperature of 500 ° C. for 24 hours by a delayed coking method (raw coke) is obtained. The size was adjusted to obtain a raw coke powder having an average particle size of 9.9 μm.

  The bulk raw coke obtained as described above is heat-treated for 1 hour or more at a temperature from the inlet temperature of 700 ° C. to the outlet temperature of 1500 ° C. (maximum temperature reached) by a rotary kiln to obtain massive calcined coke. The powder was pulverized and sized by a mill to obtain calcined coke powder having an average particle size of 9.5 μm.

  Phosphoric acid ester (14% by mass active phosphorus solid resin: manufactured by Sanko Co., Ltd.) with respect to the total of 50 parts by mass of raw coke powder and 50 parts by mass of calcined coke powder obtained as described above (100 parts by mass of coke powder). Name HCA, chemical name: 9,10-dihydro-9-oxa-10-osfaphenanthrene-10-oxide) 17.9 parts by mass (phosphorus conversion: 2.5 parts by mass) was added to obtain a coke material.

  Next, the coke material is heated from room temperature at a rate of 600 ° C./hour, reaches 900 ° C. (maximum temperature reached), and is further held for 2 hours for carbonization treatment (firing), and a lithium secondary battery Negative electrode active material A was obtained.

When the average particle diameter of the active material A was measured, it was 15 μm, the crystal plane distance d ₀₀₂ was 0.3413 nm, and the BET specific surface area was 3 m ² / g. The intensity ratio (R = I ₁₃₆₀ / I ₁₅₈₀ ) determined by Raman spectroscopy was 1.32.

  On the other hand, for the polymerization of binder, pyromellitic anhydride (PMDA) is used as acid dianhydride and 2,2'-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) is used in approximately the same mole as diamine. Then, a precursor of polyimide resin 1 having a weight average molecular weight of 144,000 was obtained by reacting in dimethylacetamide (DMAC) at room temperature for 4 hours.

  Next, the negative electrode was prepared in the following manner using the negative electrode active material A and the polyimide resin 1 precursor obtained above, and the performance as a secondary battery was evaluated.

  As shown in Table 1 below, the negative electrode active material A and the polyimide resin 1 precursor were mixed at a ratio of 93% by mass to 7% by mass and kneaded using dimethylacetamide (DMAC) as a solvent to produce a slurry. did. This was applied to a copper foil having a thickness of 10 μm so as to have a uniform thickness, and then heat-treated at 350 ° C. for 30 minutes in a nitrogen atmosphere, thereby forming an active material layer on the copper foil. The copper foil provided with the active material layer is dried and pressed to a predetermined electrode density to produce an electrode sheet having a total thickness of 60 μm, and a negative electrode is obtained by cutting the sheet into a circle having a diameter of 15 mmΦ. It was.

For the obtained negative electrode, in order to evaluate the electrode characteristics of the negative electrode single electrode, a test lithium secondary battery was prepared as follows. As the counter electrode, metallic lithium cut out to about 15.5 mmΦ was used. In addition, a coin cell was prepared by using LiPF ₆ dissolved at a concentration of 1 mol / l in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1 mixture) as an electrolytic solution, and using a porous membrane of propylene as a separator. did.

  Using this coin cell obtained, initial discharge was performed by constant current discharge of 30 mA / g at a constant temperature of 25 ° C. in a voltage range in which the lower limit voltage of terminal voltage was 0 V and the upper limit voltage of discharge was 1.5 V. When the capacity was examined, the discharge capacity was 333 mAh / g. Also, the capacity maintenance ratio after 50 cycles obtained from the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle by repeating constant current discharge and charging at 80 mA / g for 50 cycles under the condition of 45 ° C. is 95%.

(Comparative Example 1)
A negative electrode was obtained in the same manner as in Example 1 except that the binder used in Example 1 was polyvinylidene fluoride (PVDF) and the heat treatment at 350 ° C. was omitted (Table 2). The obtained negative electrode was evaluated in the same manner as in Example 1. As a result, the discharge capacity was 329 mAh / g, and 50 cycles were obtained by repeating 50 cycles of constant current discharge and charge under the condition of 45 ° C. The subsequent capacity retention rate was 78%.

( Reference Examples 2-3)
A negative electrode according to Reference Example 2 was obtained in the same manner as in Example 1 except that the active material used in Example 1 was replaced with natural graphite B that had been subjected to a surface treatment having the characteristic values shown in Table 1. Further, a negative electrode according to Reference Example 3 was obtained in the same manner as in Example 1 except that the active material was changed to artificial graphite C having the characteristic values shown in Table 1. About the obtained negative electrode, it carried out similarly to Example 1, and evaluated discharge capacity and cycling characteristics, respectively. The results are shown in Table 1.

(Comparative Examples 2-3)
A negative electrode was obtained in the same manner as in Example 1 except that polyvinylidene fluoride (PVDF) was used as the binder used in Reference Examples 2 to 3 and the heat treatment at 350 ° C. was omitted (Table 2). About the obtained negative electrode, it carried out similarly to Example 1, and evaluated discharge capacity and cycling characteristics, respectively. The results are shown in Table 2.

(Comparative Example 4)
A negative electrode was obtained in the same manner as in Example 1 except that hard carbon D having the characteristic values shown in Table 1 was used instead of the negative electrode active material A used in Example 1 (Table 2). About the obtained negative electrode, it carried out similarly to Example 1, and evaluated discharge capacity and cycling characteristics, respectively. The results are shown in Table 2.

As is clear from the results of Example 1, Reference Examples 2 to 3 and Comparative Examples 1 to 4, according to Example 1 according to the present invention and the negative electrodes of Reference Examples 2 to 3 , Comparative Examples 1 to 4 were used. It was found that a secondary battery having both discharge capacity and cycle characteristics can be obtained as compared with the case of.

  The negative electrode of the present invention can provide a secondary battery having both discharge capacity and cycle characteristics. Therefore, by using this negative electrode, it is possible to obtain a secondary battery having a balance of practical characteristics required for an in-vehicle power source for an electric vehicle or a storage battery for a smart grid. Moreover, it is not restricted to these uses, It can utilize suitably as power supplies with which a high capacity | capacitance and a long life are requested | required, such as a power supply for electric power tools, including a power supply for fuel cell vehicles.

Claims (4)

A negative electrode for a lithium secondary battery having an active material layer in which a negative electrode active material is integrated with a binder, wherein the binder is a polyimide resin having a repeating unit represented by the following general formula (1), The negative electrode active material is composed of a low crystalline carbon material having a low degree of graphitization using at least one of petroleum heavy oil and coal heavy oil as a raw material, and has an average particle diameter of 5 to 50 μm, X-ray A negative electrode for a lithium secondary battery, wherein a crystal surface interval d ₀₀₂ by diffraction is 0.3354 to 0.3500 nm and a BET specific surface area is 10 m ² / g or less.

[Wherein Ar ₁ represents a divalent aromatic diamine residue having at least two ether bonds, and Ar ₂ represents a tetravalent acid dianhydride residue represented by the following formula (2): Indicates. ]

The negative electrode for a lithium secondary battery according to claim 1, wherein a content ratio of the polyimide resin with respect to the negative electrode active material is in a range of 0.1 to 10% by mass. A lithium secondary battery using the negative electrode according to claim 1. The lithium secondary battery according to claim 3, which is used as a power source for an electric vehicle or a smart grid.