JP5653185B2 - Secondary battery negative electrode and 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, demand for electric vehicles and hybrid electric vehicles (HEVs) that combine nickel-metal hydride battery-powered motors and gasoline engines to increase energy and environmental issues has increased. In addition to initial efficiency and charge / discharge capacity, further improvements in lithium secondary battery performance such as input / output characteristics and cycle life are required.

  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 described above, 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.

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

  In particular, when lithium secondary batteries are used as in-vehicle power sources for hybrid vehicles and electric vehicles, in addition to the discharge capacity, which is a typical performance of secondary batteries, cycle life that shows repeated charge / discharge performance, It is important to have excellent input / output characteristics that show a balance between energy recovery and energy recovery. However, as described above, although various improvements have been made on the negative electrode using a polyimide resin as a binder, the cycle life and output characteristics are still not at a sufficient level.

  Therefore, as a result of intensive studies on the above problems, the present inventors were excellent in the balance of discharge capacity, output characteristics, and cycle characteristics by using a polyimide resin made from a specific acid anhydride and diamine as a raw material. It discovered that the negative electrode for secondary batteries could be obtained, and completed this invention.

  Accordingly, an object of the present invention is to provide a negative electrode capable of obtaining a secondary battery that exhibits a good balance of performance such as discharge capacity, output characteristics, and cycle characteristics. Another object of the present invention is to provide a secondary battery suitable as a power source for a hybrid vehicle or an electric vehicle, using such a negative electrode.

〔式中、Ａｒ₁は、２,２'-ビス[４-(４-アミノフェノキシ)フェニル]プロパン、１,３-ビス（４-アミノフェノキシ）ベンゼン、及び１,３-ビス（３-アミノフェノキシ）ベンゼンから選ばれるいずれかによって与えられて、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５０モル％以上含有するものであり、Ａｒ₂は、下記式（２）又は式（３）で表される４価の酸二無水物残基を示す。〕

〔式（３）において、Ｙは、直結合又は−ＣＯ−のいずれかを示す。〕 That is, this invention is a negative electrode for secondary batteries provided with the active material layer which integrated the negative electrode active material using a carbon material with the binder, Comprising: As said binder, it represents with following General formula (1). A negative electrode for a secondary battery using a polyimide resin having a repeating unit.

[ Wherein Ar ₁ represents 2,2′-bis [4- (4-aminophenoxy) phenyl] propane, 1,3-bis (4-aminophenoxy) benzene, and 1,3-bis (3-amino Phenoxy) containing 50 mol% or more of a divalent aromatic diamine residue having at least two ether bonds , given by any one selected from benzene , and Ar ₂ is represented by the following formula (2): Or the tetravalent acid dianhydride residue represented by Formula (3) is shown. ]

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

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

  The negative electrode of the present invention can provide a negative electrode for a secondary battery having an excellent balance of discharge capacity, output characteristics, 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 a power source for in-vehicle use such as a hybrid vehicle or an electric vehicle.

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.

  Moreover, the negative electrode active material in this invention can be suitably selected according to the kind of secondary battery, for example, in the case of a lithium secondary battery (lithium ion secondary battery), lithium can be intercalated. Specifically, in addition to carbon materials such as graphite and amorphous carbon, lithium-transition metal compounds, lithium-titanium composite oxides, metal materials, and lithium aluminum alloys, lithium tin An alloy, a lithium alloy such as a lithium silicon alloy, or the like can be used. In some cases, these two or more negative electrode active materials may be used in combination. Of these, carbonaceous materials are generally used, and in particular, the graphite material is an excellent material having a high energy density, which is obtained at a high temperature of at least about 2000 ° C., usually about 2600 to 3000 ° C. However, because it has problems with input / output characteristics and cycle characteristics, it is fired at a temperature lower than that of graphite materials for in-vehicle power sources such as hybrid cars and electric cars, and high input / output applications used for power storage. A low crystalline carbon material having a low degree of graphitization is preferably used.

As a low crystalline carbon material having a low degree of graphitization, for example, a petroleum-based or coal-based heavy oil is obtained by performing a thermal decomposition / polycondensation reaction at a maximum temperature of about 400 ° C. to 800 ° C. for about 24 hours. The raw coke produced and calcined coke obtained by calcining this raw coke at a maximum reached temperature of about 800 ° C. to 1500 ° C. may be mentioned, and these may be mixed at a predetermined ratio. 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 5 m ² / g or less, more preferably. Is preferably 1 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. .

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), and 3.2 parts by mass of boron carbide (Boron 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.

  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 95% by mass and 5% 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, a constant current discharge of 0.5 mA / cm ^{2 was performed at} a constant temperature of 25 ° C., with a terminal voltage lower limit voltage of 0 V and a discharge upper limit voltage of 1.5 V. When the initial discharge capacity was examined for output characteristics and input characteristics at a constant current discharge of 5 mA / cm ² and charging with the capacity maintenance ratio, the discharge capacity was 313 mAh / g, and the capacity maintenance ratio related to the output characteristics. Was 78.2%, and the capacity retention rate related to the input characteristics was 56.2%. The product of these ratios was evaluated as the input / output balance and found to be 0.44. Here, the capacity maintenance rate related to the output characteristics is obtained from the ratio of the discharge capacity during 5 mA / cm ² constant current discharge to the initial discharge capacity, and the capacity maintenance ratio related to the input characteristics is 5 mA / cm ² constant relative to the initial charge capacity. It calculated | required from ratio of the charge capacity at the time of electric current charge. The capacity maintenance rate after 3 cycles obtained from the ratio of the discharge capacity at the 3rd cycle to the discharge capacity at the 1st cycle by repeating constant current discharge and charging at 0.5 mA / cm ² for 3 cycles was 95.2%. Met. Furthermore, constant capacity discharge and charging were repeated 100 cycles, and the capacity retention rate after 100 cycles, which was obtained from the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle, was 87.7%. As for the capacity retention ratio (cycle characteristics) after 100 cycles, ◎ if the capacity retention ratio is 80% or more, ◯ if it is 70% or more and less than 80%, △ if it is 60% or more and less than 70%. If less than 60%, the result of evaluation in four stages is shown in Table 1 as x.

(Comparative Example 1)
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 Example 1 and the heat treatment at 350 ° C. was omitted (Table 3). The obtained negative electrode was evaluated in the same manner as in Example 1. As a result, the discharge capacity was 291 mAh / g, the capacity maintenance ratio related to output characteristics was 61.2%, and the capacity maintenance ratio related to input characteristics was 32.8%. Met. Moreover, the input / output balance obtained from the product of these ratios is 0.20, the capacity retention rate after 3 cycles obtained by repeating 3 cycles of constant current discharge and charge is 88.0%, and constant current discharge The capacity retention rate after 100 cycles obtained by repeating 100 cycles of charging was 63.9%.

(Examples 2-5, Comparative Examples 2-5)
Negative electrodes according to Examples 2 to 5 were obtained in the same manner as in Example 1 except that the binders used in Example 1 were changed to polyimide resins 2 to 5 having the compositions shown in Table 1. Moreover, except having changed the binder into the polyimide resin 9-12 of the composition shown in Table 3, it carried out similarly to Example 1, and obtained the negative electrode which concerns on Comparative Examples 2-5. About the obtained negative electrode, it carried out similarly to Example 1, and evaluated discharge capacity, output characteristics, and cycling characteristics, respectively. The results are shown in Tables 1 and 3. In addition, the meaning of the abbreviation described in Table 1-Table 3 is as follows, and polyimide resin 2-5 and 9-12 respectively polymerize a precursor by the same operation as Example 1, and an active material layer is formed. It was imidized by heat treatment during formation.
BTDA: 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride
BPDA: 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride
TPE-R: 1,3-bis (4-aminophenoxy) benzene
APB: 1,3-bis (3-aminophenoxy) benzene
DSDA: 3,3 ', 4,4'-diphenylsulfonetetracarboxylic dianhydride
BPADA: 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane dianhydride
PDA: p-Phenylenediamine
DAPE: 4,4'-diaminodiphenyl ether

(Example 6)
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 B was obtained.

  As the binder, the precursor of polyimide resin 1 used in Example 1 was used, and a negative electrode was obtained in the same manner as in Example 1 (Table 2). The obtained negative electrode was evaluated in the same manner as in Example 1. As a result, the discharge capacity was 313 mAh / g, the capacity maintenance ratio related to output characteristics was 80.1%, and the capacity maintenance ratio related to input characteristics was 57.0%. Met. The input / output balance obtained from the product of these ratios was 0.46. Further, the capacity retention rate after 3 cycles was 95.8%, and the evaluation of the cycle characteristics related to the capacity retention rate after 100 cycles was ◎.

(Examples 7 to 11)
A negative electrode was obtained in the same manner as in Example 6 except that the binder used in Example 6 was changed to polyimide resins 2, 3 and 6-8 having the composition shown in Table 2. About the obtained negative electrode, it carried out similarly to Example 6, and evaluated discharge capacity, output characteristics, and cycling characteristics. The results are shown in Table 2. In addition, the meaning of the new abbreviation described in Table 2 is as follows, and others are as above-mentioned. In addition, polyimide resins 6 to 8 were respectively imidized by heat treatment in forming an active material layer by polymerizing precursors by the same operation as in Example 1.
m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl

(Example 12)
A negative electrode was obtained in the same manner as in Example 1 except that natural graphite was used instead of the negative electrode active material A used in Example 1 (Table 2). The obtained negative electrode was evaluated in the same manner as in Example 1. As a result, the discharge capacity was 352 mAh / g, and the capacity retention rate related to output characteristics was 93.7%. Moreover, the capacity retention rate after 3 cycles was 98.6%, and the evaluation of the cycle characteristics related to the capacity retention rate after 100 cycles was ◯.

  As is clear from the results of Examples 1 to 12 and Comparative Examples 1 to 5, according to the negative electrodes of Examples 1 to 12 according to the present invention, Comparative Example 1 using PVDF as a binder and the general formula ( It was found that a secondary battery excellent in the balance of discharge capacity, output characteristics, and cycle characteristics can be obtained as compared with Comparative Examples 2 to 5 using polyimide resins other than those represented by 1). .

  The negative electrode of the present invention can provide a secondary battery having an excellent balance of discharge capacity, output characteristics, 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 a power source for in-vehicle use such as a hybrid vehicle or an electric vehicle. Moreover, it is not restricted to these uses, It can utilize suitably as a power supply by which high output, 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 secondary battery comprising an active material layer in which a negative electrode active material using a carbon material is integrated with a binder, the polyimide resin having a repeating unit represented by the following general formula (1) as the binder The negative electrode for secondary batteries characterized by using.

[ Wherein Ar ₁ represents 2,2′-bis [4- (4-aminophenoxy) phenyl] propane, 1,3-bis (4-aminophenoxy) benzene, and 1,3-bis (3-amino Phenoxy) containing 50 mol% or more of a divalent aromatic diamine residue having at least two ether bonds , given by any one selected from benzene , and Ar ₂ is represented by the following formula (2): Or the tetravalent acid dianhydride residue represented by Formula (3) is shown. ]

[In Formula (3), Y shows either a direct bond or -CO-. ]   The negative electrode for a 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 secondary battery using the negative electrode according to claim 1.   The secondary battery according to claim 3, which is used as an in-vehicle power source for a hybrid vehicle or an electric vehicle.