JP5715572B2 - 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 made smaller and lighter, so mobile phones, personal computers, personal digital assistants ( It is widely used as a power source for mobile electronic devices such as PDAs (Personal Digital Assistants) and handy video cameras, and the demand is expected to increase in the future.

  In addition, in response to energy and environmental problems, there are demands for electric vehicles, hybrid electric vehicles (HEVs) that combine nickel-hydrogen battery-driven motors and gasoline engines, and storage batteries for power storage. There is a growing demand for further enhancement of performance (particularly cycle characteristics and output characteristics) of lithium secondary batteries.

  In a lithium secondary battery, a carbon material that is excellent in terms of safety and life is generally used as a negative electrode material (negative electrode active material). Among carbon materials, graphite material is an excellent material having a high energy density obtained at a high temperature of at least about 2000 ° C., usually about 2600 to 3000 ° C., but has problems in high input / output characteristics and cycle characteristics. doing. For this reason, for example, for high input / output applications such as power storage and electric vehicles, the use of a low-crystalline carbon material that is fired at a temperature lower than that of the graphite material and has a low degree of graphitization is mainly studied.

  In recent years, from the viewpoint of further improving the performance of hybrid electric vehicles, further improvement in performance has been demanded for lithium secondary batteries, and there is an urgent need to improve the performance. In particular, the characteristics of the lithium secondary battery are required to sufficiently reduce the potential on the negative electrode side to improve the actual battery voltage and to exhibit sufficiently high output characteristics.

  In addition, the discharge capacity of the lithium secondary battery can be raised as an important characteristic so that a current that is an energy source of the hybrid electric vehicle can be sufficiently supplied. In addition, the ratio of the charge capacity to the discharge capacity, that is, the initial efficiency is required to be high so that the discharge current amount is sufficiently higher than the charge current amount.

  Furthermore, in order to enable charging in a short time, the lithium secondary battery preferably maintains a high charge capacity up to a high current density, and is also required to have a high capacity maintenance rate.

  That is, it is required to improve such characteristics as output characteristics, discharge capacity, initial efficiency, capacity maintenance ratio and the like in a balanced manner.

  For the purpose of such a lithium secondary battery, many carbon materials such as coke and graphite have been studied as a negative electrode material. However, although the discharge capacity described above can be increased, the initial efficiency is not sufficient. Further, the actual battery voltage is insufficient, and the recent requirements for high output characteristics and capacity maintenance ratio cannot be satisfied.

  For example, Patent Document 1 discloses a carbonaceous material that defines a specific specific surface area, an X-ray diffraction crystal thickness, and the like obtained by pyrolysis or calcining carbonization of an organic compound as a negative electrode material using intercalation or doping. However, it is still insufficient for in-vehicle applications such as HEV.

  Patent Document 2 discloses a carbon material having a relatively high discharge capacity with excellent recycling characteristics by removing impurities by heat treatment in an inert atmosphere using coke calcined as a negative electrode material. However, it has not been sufficient in terms of output characteristics and the like in in-vehicle applications such as for HEV.

  Patent Document 3 discloses that a carbonaceous material obtained by providing a specific coating layer on a carbonaceous material having a graphite-like structure and heat-treating it as a negative electrode material, and Patent Document 4 discloses a low-temperature material as a negative electrode material. Carbon materials having a relatively high discharge capacity have been disclosed by removing impurities to a higher degree by heat-treating in an inert atmosphere using coke heat-treated as a raw material. It did not have sufficient battery characteristics for in-vehicle applications.

  Patent Document 5 discloses that a lithium secondary battery having a large charge / discharge capacity can be supplied by using heat-treated coke obtained by heat-treating raw coke of petroleum or coal at 500 to 850 ° C. as a negative electrode material. However, it was not sufficient in terms of output characteristics in in-vehicle applications such as for HEV.

  Most of the researches on negative electrode materials for lithium secondary batteries using low-crystal carbon materials made from coke as described above are aimed at improving the characteristics of the negative electrode materials for secondary batteries as power sources for small portable devices. In fact, a negative electrode material having sufficient characteristics suitable for a high current input / output lithium secondary battery represented by a secondary battery for HEV has not been developed.

  On the other hand, adding various compounds to an organic material or a carbonaceous material to improve battery characteristics has also been studied.

  For example, Patent Document 6 discloses a negative electrode material obtained by carbonizing an organic material or a carbonaceous material by adding a phosphorus compound, and Patent Document 7 discloses a carbon material containing boron and silicon as graphite. Although the negative electrode material obtained by making it into a device is disclosed, as in the above, it is still not sufficient for practical use in terms of output characteristics or the like in an in-vehicle application such as for HEV.

  On the other hand, a resin binder (binder) having a function of binding active materials and the like plays a role of bonding active materials to each other and bonding a current collector that forms a negative electrode to the active material. Until now, PVDF (polyvinylidene fluoride) has been mainly used. However, the PVDF has a problem that the cycle life is shortened because it is inferior in terms of adhesion between the active materials and the current collector. In addition, if the battery temperature rises abnormally due to a short circuit or the like, PVDF decomposes and HF (hydrogen fluoride) is generated, and this HF reacts violently with Li (exothermic reaction), so that the battery may be damaged or explode. There was also a problem in terms of reliability.

  In order to solve such a problem, in Patent Document 8, polyimide resin is used as a binder. However, in Patent Document 8, sufficient input / output characteristics suitable for a lithium secondary battery that inputs and outputs a large current are used. There is no mention of whether or not.

JP 62-90863 A Japanese Patent Laid-Open No. 1-221859 JP-A-6-5287 JP-A-8-102324 JP-A-9-320602 JP-A-3-137010 Japanese Patent Laid-Open No. 11-40158 Japanese Patent No. 3311402

  The present invention can sufficiently improve the input / output characteristics of the secondary battery, including the cycle life, by binding a novel negative electrode active material with a polyimide resin, as well as the discharge capacity, initial efficiency, capacity maintenance rate. And an anode for a secondary battery having practical characteristics required for in-vehicle use such as for HEV including reliability (safety).

  The inventors of the present invention have intensively studied to achieve the above object. As a result, coal-based and / or petroleum-based (hereinafter referred to as coal-based) raw coke and the coal-based calcined coke are blended at a predetermined ratio, and i) phosphorus compound or ii) phosphorus compound and A negative electrode for a secondary battery having an active material layer formed by baking a coke material containing a boron compound to form a negative electrode active material, which is integrated with a polyimide resin. The potential of the electrode can be reduced sufficiently to improve the actual battery voltage, and the practical characteristics required for in-vehicle applications such as cycle life, input / output characteristics, discharge capacity, initial efficiency and capacity maintenance ratio can be expressed. The present invention has been completed.

That is, the present invention is a negative electrode for a secondary battery including an active material layer in which a negative electrode active material is integrated with a binder, wherein the negative electrode active material is at least one of coal-based or petroleum-based raw coke. And any one or more of calcined coke and coal-based or petroleum-based calcined coke at a mass ratio of 90:10 to 10:90, and phosphorous coke and calcined coke in total amount of 100 parts by mass with respect to 100 parts by mass. The coke material to which the compound is added in a proportion of 0.1 to 6.0 parts by mass is fired at a firing temperature in the range of 800 ° C. to 1400 ° C. at the highest temperature, and the binder is a polyimide resin. It is the negative electrode for secondary batteries characterized.

The present invention also provides a negative electrode for a secondary battery comprising an active material layer in which a negative electrode active material is integrated with a binder, wherein the negative electrode active material is at least one of coal-based and petroleum-based raw coke. And any one or more of calcined coke and coal-based or petroleum-based calcined coke at a mass ratio of 90:10 to 10:90, and phosphorous coke and calcined coke in total amount of 100 parts by mass with respect to 100 parts by mass. A coke material in which a compound and a boron compound are added at a ratio of 0.1 to 6.0 parts by mass in terms of phosphorus and boron, respectively , is fired at a firing temperature in the range of 800 ° C. to 1400 ° C. at the highest achieved temperature , The binder is also a negative electrode for a secondary battery, which is a polyimide resin.

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

  In the present invention, any one or more raw cokes of coal-based or petroleum-based may be collectively referred to as “coal-based raw coke”. For example, petroleum-based and / or coal-based heavy oil is referred to as, for example, It means a product obtained by carrying out a thermal decomposition / polycondensation reaction for about 24 hours at a temperature of about 400 ° C. to 800 ° C. using a coking facility such as a delayed coker. Similarly, any one or more calcined cokes of coal-based or petroleum-based may be collectively referred to as “coal-based calcined coke”. This means petroleum-based and / or coal-based coke that has been calcined at a maximum temperature of about 800 ° C to 1500 ° C.

  According to the present invention, the cycle life and the input / output characteristics of the secondary battery can be sufficiently improved, and for HEV including discharge capacity, initial efficiency, capacity maintenance rate, and reliability (safety), etc. It is possible to provide a negative electrode for a secondary battery having practical performance required for in-vehicle use and excellent in performance balance.

  Hereinafter, the present invention will be described in more detail based on embodiments of a negative electrode for a secondary battery.

  First, for the negative electrode active material in the present invention, first, a coal-based heavy oil, for example, a suitable coking facility such as a delayed coker is used, and the maximum temperature reached at a temperature of about 400 ° C. to 800 ° C. for 24 hours. Coking coke is obtained by advancing the thermal decomposition and polycondensation reaction to some extent. Thereafter, the obtained coal-based raw coke mass is pulverized to a predetermined size. An industrially used pulverizer can be used for the pulverization. Specific examples include an atomizer, a Raymond mill, an impeller mill, a ball mill, a cutter mill, a jet mill, and a hybridizer, but are not particularly limited thereto.

  The heavy coal oil used here may be either a heavy petroleum oil or a heavy coal oil, but the heavy heavy oil is richer in aromaticity. , S, V, Fe, etc. are less impurities and less volatile matter, so it is preferable to use heavy coal oil.

  Also, the coal-based raw coke obtained as described above is calcined at a maximum temperature of 800 ° C. to 1500 ° C. to produce coal-based calcined coke. Preferably it is 1000 to 1500 degreeC, More preferably, it is the range of 1200 to 1500 degreeC. For burning raw coke such as coal-based, equipment such as lead hammer furnace, shuttle furnace, tunnel furnace, rotary kiln, roller hearth kiln or microwave capable of mass heat treatment can be used, but it is particularly limited to this. is not. Further, these firing facilities may be either a continuous type or a batch type. Next, the obtained coal-based calcined coke lump is pulverized to a predetermined size using a pulverizer such as an industrially used atomizer in the same manner as described above.

In addition, the size of the coal-based raw coke powder after pulverization and the calcined coke powder such as coal-based calcined coke powder is not particularly limited, but the average particle size required as the median diameter is preferably 5 to 50 μm. More preferably, the thickness is 5 to 15 μm. At this time, the BET specific surface area is preferably 5 m ² / g or less, more preferably 1 m ² / g or less. If the average particle size is less than 5 μm, the specific surface area may be excessively increased. On the other hand, if the average particle size is more than 50 μm, the charge / discharge characteristics may be deteriorated. If the BET specific surface area exceeds 5 m ² / g, the energy efficiency when used in a secondary battery may be reduced. The BET specific surface area is desirably about 1 m ² / g or more from the viewpoint of forming fine pores.

  Next, the coal-based raw coke powder and the coal-based calcined coke powder obtained as described above are blended at a predetermined ratio. The blending amount of the coal-based raw coke powder and the coal-based calcined coke powder is 90:10 to 10:90, preferably 70:30 to 30:70, in mass ratio. Increasing the proportion of calcined coke such as coal will improve the output characteristics, and increasing the proportion of raw coke such as coal will improve the discharge capacity and initial characteristics. For example, from the aspect of output characteristics, it is preferable that the content of coal-based calcined coke is 50% or more.

  If the ratio of raw coke powder such as coal-based and calcined coke powder such as coal-based is out of the above range, the potential of the negative electrode made of the obtained negative electrode active material cannot be sufficiently reduced, and the actual battery voltage is improved. In some cases, sufficiently high output characteristics cannot be obtained. In addition, the resistance value of the secondary battery at the end of charge / discharge may increase, and stable charge / discharge characteristics may not be exhibited.

  In the above-mentioned coke powder, a phosphorus compound is essential, and i) a phosphorus compound or ii) a phosphorus compound and a boron compound (hereinafter, i) or ii) is also referred to as “phosphorus compound or the like”. ) To make a coke material. Addition is performed by blending the above-described coal-based raw coke powder and coal-based calcined coke powder with the following amounts of i) phosphorus compound or ii) phosphorus compound and boron compound and putting them in a predetermined mold. (First addition method).

  Addition of phosphorus compounds etc., after obtaining coal-based raw coke powder and coal-based calcined coke powder, at the time of obtaining coal-based raw coke mass and coal-based calcined coke mass It can also be carried out (second addition method). In this case, the coal-based raw coke lump and the coal-based calcined coke lump are put into a pulverizer, and at the same time, the above-mentioned phosphorus compound or the like is put into the pulverizer to pulverize the lump. Coal-based raw coke powder and coal-based calcined coke powder to which a phosphorus compound or the like is added can be obtained.

  Therefore, since the phosphorus compound can be added simultaneously with the pulverization of the coal-based raw coke lump and the coal-based calcined coke lump, the operation of adding the phosphorus compound or the like separately during the firing may be omitted. In addition, the entire manufacturing process of the negative electrode active material can be simplified.

  However, both the first addition method and the second addition method differ only in the production process of the negative electrode active material due to the difference in the specific method of addition, and the output characteristics of the negative electrode active material itself and There is almost no change in discharge capacity, initial efficiency, and capacity maintenance rate.

  The addition amount of the phosphorus compound is 0.1 to 6.0 parts by mass, preferably 0.5 to 5.5 in terms of phosphorus with respect to 100 parts by mass of the total amount of raw coke such as coal-based raw coke and coal-based calcined coke. 0 parts by mass. If the addition amount is less than the lower limit, the effect of adding the phosphorus compound may not be sufficiently obtained. On the other hand, if the addition amount exceeds the upper limit part by mass, the crystallization of the coke surface may progress and the output characteristics may deteriorate. Because.

  Moreover, the addition amount of the said boron compound is 0.1-6.0 mass parts in conversion of boron with respect to 100 mass parts of total amounts of raw coke, such as a coal system, and calcined coke, etc., Preferably 0.5- 5.0 parts by mass. If the addition amount is less than the lower limit, the effect of adding the boron compound may not be sufficiently obtained. On the other hand, if the addition amount exceeds the upper limit, carbonization of coke is excessively promoted, and unreacted boron may remain. Because there is. In the present invention, as described above, the boron compound is used in combination with the phosphorus compound, and the addition of only the phosphorus compound can achieve the object of the present invention and achieve the effect.

  As the phosphorus compound described above, phosphoric acids are preferable from the viewpoints of easily preparing an aqueous solution and having high safety. Phosphoric acid (orthophosphoric acid) is more preferably used as the phosphoric acid, but is not limited thereto, and can be appropriately selected from linear polyphosphoric acid, cyclic polyphosphoric acid, various phosphoric ester compounds, and the like. Any one of these phosphoric acids may be used alone, or two or more thereof may be used in combination.

Moreover, it is preferable to use boron carbide (B ₄ C) as the boron compound described above. This is because even if boron carbide decomposes during firing, the resulting components are only boron for achieving the object of the present invention, and carbon which is a constituent element of coke which is a base material of the negative electrode active material. And since other components are not included, it is because the bad influence to the negative electrode active material by this component can be suppressed.

  Such coke material is fired. The firing temperature is preferably 800 ° C. or higher and 1400 ° C. or lower at the maximum temperature. Preferably it is the range of 900 to 1400 degreeC. When the firing temperature exceeds the upper limit, the crystal growth of the coke material is excessively promoted and adversely affects the battery characteristic balance, which is not preferable from the viewpoint of mass productivity. On the other hand, if the firing temperature is lower than the lower limit, not only sufficient crystal growth cannot be achieved, but also the addition effect of phosphorus compound and boron compound is not sufficient in the carbonization process of coke, and it also tends to adversely affect the battery property balance. .

  The holding time at the highest temperature is not particularly limited but is preferably 30 minutes or longer. The firing atmosphere is not particularly limited, but may be an inert gas atmosphere such as argon or nitrogen, a non-oxidizing atmosphere in a non-sealed state such as a rotary kiln, or a non-oxidizing atmosphere in a sealed state such as a lead hammer furnace. An oxidizing atmosphere may be used.

The negative electrode active material obtained in this way contains 0.05 to 5 parts by mass of the phosphorus element and boron element derived from the above additive components with respect to 100 parts by mass of the active material. Is advantageous.
The phosphorus content in the negative electrode active material can be measured by ICP emission spectral analysis. Specifically, the negative electrode active material is incinerated by JIS M8814 (ash content test method), and then the obtained ash (inorganic component) is quantified by the above-described analysis method. The ICP emission spectroscopic analysis method is a method in which a sample is excited by a plasma flame generated by irradiating a high frequency to argon gas, and an element is identified and quantified from an emission spectrum when returning to a ground state.

  In the present invention, a polyimide resin is used as the binder. The polyimide resin is excellent in the binding force between the negative electrode active materials as well as PVDF which has been mainly used as a binder so far, and is excellent in adhesiveness to the current collector forming the negative electrode as compared with 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.

［式中、Ａｒ₁は、少なくとも２価の芳香族ジアミン残基を示し、Ａｒ_２は、４価の酸二無水物残基を示す。］The polyimide resin has a repeating unit represented by the following general formula (1). In general, a raw material diamine and an acid anhydride are polymerized in the presence of a solvent to obtain a polyimide precursor resin, and then heat treatment to obtain an imide. Can be manufactured. 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 polymerization solvent used at this time include dimethylacetamide, dimethylformamide, N-methylpyrrolidone, 2-butanone, diglyme, xylene, and the like, and one or more of these may be used in combination. However, it is not limited to these.

[In the formula, Ar ₁ represents at least a divalent aromatic diamine residue, and Ar ₂ represents a tetravalent acid dianhydride residue. ]

The diamine component as a polyimide resin raw material, a compound represented by H _{2 N-Ar 1} -NH 2. Examples of the Ar _1, there can be mentioned the following aromatic diamine residues.

Examples of the acid anhydride include compounds represented by O (OC) ₂ Ar ₂ (CO) ₂ O, and examples of Ar ₂ include the following aromatic acid dianhydride residues. Can do.

［式（３）において、Ｙは、直結合又は−ＣＯ−のいずれかを示す。］In the present invention, the diamine component is preferably selected so that an ether bond is included in the repeating unit structure constituting the polyimide resin for the following reasons. According to the polyimide resin in which an ether bond is included in the repeating unit structure, the cycle characteristics (life) are remarkably improved in the negative electrode using the same negative electrode active material as compared with the case where PVDF is used. From such a viewpoint, as the binder, Ar _{1 in the} above general formula (1) has an ether bond typified by diaminodiphenyl ether, preferably a divalent aromatic having at least two ether bonds. It is preferable to use a polyimide resin which is a diamine residue and Ar ₂ 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-. ]

〔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。〕

Preferred examples of the divalent aromatic diamine residue R ₁ having at least two ether bonds in the general formula (1) include the following.

[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 constituting the structural unit of the general formula (1), specifically, 2,2′-bis [4- (4-aminophenoxy) phenyl] propane (BAPP), 1,3-bis (4- Aminophenoxy) benzene (TPE-R), 1,3-bis (3-aminophenoxy) benzene (APB), 4,4′-bis (4-aminophenoxy) biphenyl (BAPB) and the like. Further, preferred acid dianhydrides constituting the repeating unit of the general formula (1) are specifically pyromellitic anhydride (PMDA), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride ( BPDA), 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and the like. In addition, the diamine and acid anhydride which are polyimide resin raw materials may use together 2 or more types of diamines and acid anhydrides, respectively, and may use other diamines and acid anhydrides other than the above.
The polyimide resin in the present invention preferably contains 50 mol% or more of the structural unit represented by the general formula (1), but the diamine and acid anhydride constituting the other structural units include the components exemplified above. Other diamines and acid anhydride components may be used.

  In the present invention, the negative electrode active material and the polyimide resin or polyimide precursor resin are mixed with a solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF), water, alcohol, or the like. A slurry is prepared by mixing, and a negative electrode provided with an active material layer is obtained by coating and drying on a current collector.

  Here, although the material of the electroconductive base material used as a collector is not specifically limited, 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.

  A solution in which a polyimide resin or a polyimide precursor resin is dissolved in an organic solvent such as NMP is mixed with a negative electrode active material and, if necessary, a conductive additive to form a slurry, followed by extrusion coating, curtain coating, roll coating, gravure The active material layer is formed by coating the current collector with a uniform thickness by a known means such as coating, drying and removing the organic solvent, followed by heating imidization. At this time, from the viewpoint of the balance between the binding property and the discharge capacity, the content ratio of the polyimide resin or the polyimide precursor resin with respect to the negative electrode active material is preferably in the range of 0.1 to 10% by 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 configured using the negative electrode of the present invention, the opposite positive electrode includes a lithium-containing transition metal oxide LiM (1) _x O ₂ (wherein x is a numerical value in the range of 0 ≦ x ≦ 1). In which M (1) represents a transition metal and consists of at least one of Co, Ni, Mn, Ti, Cr, V, Fe, Zn, Al, Sn, 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 (where 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, S Composed of at least one of _{In), 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 chalcogenide (Ti, S ₂ , NbSe, etc.), vanadium oxide (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 (wherein x is in the range 0 ≦ x ≦ 4, y is in the range 0 ≦ y ≦ 1) And a positive active material such as activated carbon, activated carbon fiber, or the like can be used. In the formula, M represents a metal including a transition metal, and Ch represents a chalcogen metal.

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, etc. 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, propionitrile , Trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethylorthoformate, 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 equivalent: 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.
Further, as a result of ICP emission spectroscopic analysis of the active material A, the phosphorus and boron contents in the active material A were 12000 ppm and 14000 ppm, respectively.

  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 in a ratio of 95% by mass and 5% by mass, respectively, and dimethylacetamide (DMAC) was used as a solvent to prepare a slurry, 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 constant current discharge and charge 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%. The capacity retention rate (cycle characteristics) after 100 cycles is shown in Table 1 as ◎ if the capacity retention rate is 80% or more, ○ if it is 70% or more and less than 80%, and Δ if it is less than 70%. Shows the results of evaluation in three stages.

(Comparative Example 1)
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. The obtained negative electrode was evaluated in the same manner as in Example 1. As a result, the discharge capacity was 352 mAh / g, the capacity maintenance ratio related to the output characteristics was 93.7%, and the capacity maintenance ratio related to the input characteristics was 4.9%. Met. The input / output balance obtained from the product of these ratios was 0.05.

(Comparative Example 2)
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. 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. The input / output balance obtained from the product of these ratios was 0.20, and the capacity retention rate after 100 cycles obtained by repeating 100 cycles of constant current discharge and charge was 63.9%.

(Examples 2 to 5)
A negative electrode was obtained in the same manner as in Example 1 except that the binder used in Example 1 was changed to polyimide resins 2 to 5 having the composition shown in Table 1. About the obtained negative electrode, it carried out similarly to Example 1, and evaluated discharge capacity, output characteristics, and cycling characteristics. The results are shown in Table 1. In addition, the meaning of the abbreviation described in Table 1 is as follows, and polyimide resins 2 to 5 polymerize precursors by the same operation as in Example 1, respectively, and heat treatment when forming an active material layer Made it.
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

(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.
Moreover, as a result of performing the ICP emission spectral analysis of the said active material B, phosphorus content in the active material B was 14000 ppm.

  A negative electrode was obtained in the same manner as in Example 1 by using the polyimide resin 1 precursor used in Example 1 as the binder. 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.

(Examples 7 and 8)
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 and 3 having the composition shown in Table 1. 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 1.

  As is clear from the results of Examples 1 to 8 and Comparative Examples 1 and 2, Comparative Example 1 using natural graphite as the negative electrode active material is compared with Examples 1 and 6 using active material A or B. Although the discharge capacity was excellent, it was found that the input / output balance was deteriorated because the input characteristics were greatly inferior. Further, it was found that Comparative Example 2 using PVDF as a binder was generally inferior in discharge capacity, input / output balance, and cycle characteristics as compared with Examples using polyimide resin. As described above, according to the present invention, it was confirmed that a negative electrode having excellent discharge capacity, input / output balance, and cycle characteristics was obtained.

Claims (5)

A negative electrode for a secondary battery having an active material layer in which a negative electrode active material is integrated with a binder,
The negative electrode active material is blended at a mass ratio of 90:10 to 10:90 in any one of coal-based or petroleum-based raw coke and any one of coal-based or petroleum-based calcined coke. A coke material in which a phosphorus compound is added in a proportion of 0.1 to 6.0 parts by mass in terms of phosphorus with respect to a total amount of 100 parts by mass of the raw coke and calcined coke is 800 ° C. Fired at a firing temperature in the range of 1400 ° C. ,
The negative electrode for a secondary battery, wherein the binder is a polyimide resin. A negative electrode for a secondary battery having an active material layer in which a negative electrode active material is integrated with a binder,
The negative electrode active material is blended at a mass ratio of 90:10 to 10:90 in any one of coal-based or petroleum-based raw coke and any one of coal-based or petroleum-based calcined coke. up with respect to the total amount 100 parts by mass of the raw coke and calcination coke, phosphorus compounds and boron compounds, the coke material has been added in a proportion of each 0.1 to 6.0 parts by weight of phosphorus and boron in terms It is fired at a firing temperature ranging from 800 ° C. to 1400 ° C. at the ultimate temperature ,
The negative electrode for a secondary battery, wherein the binder is a polyimide resin.   The negative electrode for a secondary battery according to claim 1, wherein the binder is a polyimide resin having an ether bond in a repeating unit structure.   The negative electrode for a secondary battery according to any one of claims 1 to 3, 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.   The secondary battery obtained using the negative electrode in any one of Claims 1-4.