KR20120105019A - Negative electrode for secondary battery, and secondary battery using same - Google Patents

Abstract

In addition to the cycle life, the input and output characteristics of the secondary battery can be sufficiently improved, and practical characteristics required for vehicle applications such as HEV, which include discharge capacity, initial efficiency, capacity retention rate, and reliability (safety), are provided. Provided is a negative electrode for a secondary battery. A negative electrode for a secondary battery provided with an active material layer in which a negative electrode active material is integrated with a binder, wherein the negative electrode active material is 100 parts by mass in a total amount of at least one raw coke of coal or petroleum and calcined coke of coal or petroleum. On the other hand, a phosphorus compound is essential, and a coke material to which a phosphorus compound or a phosphorus compound and a boron compound are added is fired, and the binder is a negative electrode for secondary batteries, wherein the binder is a polyimide resin.

Description

A negative electrode for a secondary battery and a secondary battery using the same {NEGATIVE ELECTRODE FOR SECONDARY BATTERY, AND SECONDARY BATTERY USING SAME}

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, and thus can be miniaturized and lightened. Therefore, a mobile phone, a personal computer, a personal digital assistant (PDA), and a handy video camera are available. It is widely used as a power source for mobile electronic devices, and the like is expected to gradually increase in the future.

In addition, in order to cope with energy problems and environmental problems, demand for electric power storage batteries as well as hybrid electric vehicles (HEVs) in which a motor of a nickel hydride battery and a gasoline engine are combined is increasing. Further high performance (especially cycle characteristics and output characteristics) of a lithium secondary battery is calculated | required.

Lithium secondary batteries are generally used as negative electrode materials (cathode active materials), and carbon materials excellent in terms of safety and lifespan. Among the 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 a problem in high input / output characteristics and cycle characteristics. For this reason, the use of the low crystalline carbon material which bakes at the temperature lower than graphite material and is low in graphitization grade, for example for high power input / output applications, such as an electric power storage and an electric vehicle, is mainly studied.

In recent years, from the standpoint of further improving the performance of hybrid electric vehicles, higher performance has also been required for lithium secondary batteries, and improvement of the characteristics is urgently required. 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 show sufficiently high output characteristics.

Moreover, the discharge capacity of a lithium secondary battery emerges as an important characteristic so that the electric current which is an energy source of a hybrid electric vehicle can fully be supplied. In addition, it is also required that the ratio of the charge capacity to the discharge capacity, that is, the initial efficiency is high, so that the discharge current amount is sufficiently high compared with the charge current amount.

In addition, in order to enable charging for a short time, the lithium secondary battery preferably maintains a high charge capacity up to a high current density, and a high capacity retention rate is also required.

In other words, it is required to balance such characteristics as output characteristics, charging capacity, initial efficiency, capacity retention rate and the like.

Although many carbon materials, such as coke and graphite, are examined as a negative electrode material for the purpose of such a lithium secondary battery, although the discharge capacity mentioned above can be increased, initial stage efficiency is not enough. In addition, the actual battery voltage is insufficient, and the requirements of the recent high output characteristics and capacity retention rate cannot be satisfied.

For example, Patent Document 1 discloses a carbonaceous material that defines a specific specific surface area and X-ray diffraction crystal thickness obtained by thermal decomposition or plastic carbonization of an organic compound as an anode material using intercalation or doping. Although disclosed, it is still insufficient for vehicle use, such as for HEV.

Further, Patent Document 2 discloses a carbon material having a relatively high discharge capacity excellent in recycling characteristics by removing impurities by heat treatment in an inert atmosphere using calcined coke as a raw material as a raw material, but for vehicles such as HEVs. In use, it was not enough in terms of output characteristics.

Patent Document 3 discloses the use of a carbonaceous material obtained by forming a specific coating layer on a carbonaceous material having a graphite-like structure and heat treatment as a negative electrode material, and Patent Document 4 uses coke heat-treated at low temperature as a negative electrode material as a raw material. By heat treatment in an inert atmosphere, it is possible to remove impurities more highly, and a carbon material having a relatively high discharge capacity has been disclosed, but not all have sufficient battery characteristics in vehicle applications such as HEV.

In addition, 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 heating raw coke of petroleum or coal at 500 to 850 ° C as a negative electrode material. It was not enough in the aspect of an output characteristic in vehicle use, such as these.

Most of the studies on the cathode materials for lithium secondary batteries of low crystalline carbon materials using coke or the like as described above are mostly for improving the characteristics of the anode materials for secondary batteries as power sources for small portable devices, and the large current input / output lithium secondary batteries represented by HEV secondary batteries. There is no development of a negative electrode material having sufficient characteristics suitable for a battery.

On the other hand, addition of various compounds to organic materials or carbonaceous materials 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 carbonaceous material by adding a phosphorus compound, and Patent Document 7 discloses a negative electrode material obtained by graphitizing a carbon material containing boron and silicon. However, all of them are still not sufficient for practical use in terms of output characteristics in vehicle applications such as HEV.

On the other hand, a resin binder (binder) having a function of binding an active material or the like serves to bond the active materials to each other and to bond the current collector forming the negative electrode with the active material, and so far PVDF (polyvinylidene fluoride) ) Has been used mainly. By the way, in this PVDF, there existed a problem that an active material jumped in the adhesive point with respect to an electrical power collector, and a cycle life became short. In addition, when the battery temperature rises ideally due to a short circuit or the like, PVDF decomposes to generate HF (hydrogen fluoride), and the HF reacts rapidly with Li (exothermic reaction), which may cause the battery to break or burst. There was also a problem in terms of reliability.

In order to solve such a problem, in patent document 8, although polyimide resin is used as a binder, it is not mentioned in this patent document 8 whether it has sufficient input / output characteristics suitable for the lithium secondary battery which inputs and outputs a large current. not.

Japanese Laid-Open Patent Publication No. 62-90863 Japanese Patent Application Laid-open No. Hei 1-221859 Japanese Unexamined Patent Publication No. Hei 6-5287 Japanese Patent Application Laid-Open No. 8-102324 Japanese Patent Laid-Open No. 9-320602 Japanese Patent Laid-Open No. 3-137010 Japanese Patent Application Laid-Open No. 11-40158 Japanese Patent Publication No. 3311402

The present invention binds a novel negative electrode active material with a polyimide resin to sufficiently improve the input and output characteristics of a secondary battery, including cycle life, and includes discharge capacity, initial efficiency, capacity retention rate, and reliability (safety). An object of the present invention is to obtain a secondary battery negative electrode having practical characteristics required for vehicle use such as HEV.

The present inventors conducted an in-depth study to achieve the above object. As a result, coke and / or petroleum (hereinafter referred to as coal-based) raw coke and calcined coke such as coal-based are blended in a predetermined ratio, and coke containing i) phosphorus compound or ii) compound and boron compound. By firing the material to form a negative electrode active material, which is a negative electrode for a secondary battery having an active material layer formed by integrating a polyimide resin, the potential of the negative electrode of the lithium secondary battery can be sufficiently reduced to improve the actual battery voltage. The present invention has been completed by discovering that the practical characteristics required for vehicle use, such as cycle characteristics, input / output characteristics, discharge capacity, initial efficiency, and capacity retention rate, can be expressed.

That is, the present invention is a negative electrode for a secondary battery having an active material layer in which a negative electrode active material is integrated with a binder, wherein the negative electrode active material has at least one of coke-based or petroleum-based calcined coke and coal-based or petroleum-based calcined coke. It is made by baking the coke material which mix | blends the phosphorus compound with the ratio of 0.1-6.0 mass part with respect to 100 mass parts of said total cokes, and said calcined coke, together with the 90: 10-10: 90 furnace, It is a negative electrode for secondary batteries, It is a polyimide resin.

The present invention also provides a negative electrode for a secondary battery having an active material layer in which a negative electrode active material is integrated with a binder, wherein the negative active material is calcined coke of at least one of coke-based or petroleum-based coke and petroleum-based coke. It is mix | blended in 90: 10-10: 90 by mass ratio, and phosphorus compound and a boron compound were added in the ratio of 0.1-6.0 mass parts respectively in conversion of phosphorus and boron with respect to 100 mass parts of said total coke and calcined coke. It is made by baking a coke material, and the said binder is polyimide resin, It is a negative electrode for secondary batteries characterized by the above-mentioned.

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

In addition, in the present invention, at least one of the coke-based or petroleum-based coke may be referred to as "coal-like coke", but this may refer to petroleum and / or coal-based heavy oil, for example, a delayed coker. It means that it is obtained by performing a thermal decomposition-polycondensation reaction for about 24 hours at the temperature which the highest achieved temperature is about 400 degreeC-800 degreeC using the coking apparatus, etc.). In addition, similarly, calcined coke of at least one of coal or petroleum may be collectively referred to as "calcined coke, such as coal," but this means that calcination is performed on fresh coke, such as coal, and the highest achieved temperature is 800 ° C to It means petroleum and / or coal-based coke calcined at about 1500 ℃.

According to the present invention, it is possible to sufficiently improve the input / output characteristics of the secondary battery as well as the cycle life, and is required for vehicle applications such as for HEV including discharge capacity, initial efficiency, capacity retention rate, and reliability (safety). A negative electrode for a secondary battery having practical characteristics and excellent in performance balance can be provided.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail based on embodiment of the negative electrode for secondary batteries.

First, about the negative electrode active material in this invention, first, heavy oils, such as a coal system, are used for 24 hours at the temperature which the highest achieved temperature is about 400 degreeC-800 degreeC, respectively using appropriate coking apparatus, such as a delayed coker. Raw coke, such as a coal system, is obtained by carrying out the degree, thermal decomposition, and polycondensation reaction. Thereafter, the obtained coal-based lump or the like is pulverized to a predetermined size. Industrially used grinders can be used for grinding. Specifically, an atomizer, a raymond mill, an impeller mill, a ball mill, a cutter mill, a jet mill, a hybridizer, etc. can be illustrated, but it is not specifically limited to this.

The heavy oil such as coal-based oil may be petroleum-based heavy oil or coal-based heavy oil, but coal-based heavy oil is used because coal-based heavy oil is rich in aromaticity, contains less impurities such as S, V, and Fe, and has less volatile matter. It is desirable to.

In addition, the raw coke such as coal-based obtained as described above is calcined at a maximum achieved temperature of 800 ° C to 1500 ° C to produce calcined coke such as coal. Preferably it is 1000 degreeC-1500 degreeC, More preferably, it is the range of 1200 degreeC-1500 degreeC. The firing of coal-based fresh coke can be carried out with a large amount of heat-treated leaded hammer kilns, shuttle kilns, tunnel kilns, rotary kilns, roller hearth kilns or microwaves. Although facilities, such as these, can be used, it is not specifically limited to this. In addition, these baking facilities may be either a continuous type or a batch type. Subsequently, the obtained lumps of calcined coke, such as coal-based, are pulverized to a predetermined size using a grinder such as an atomizer used industrially as in the above.

In addition, the size of fresh coke powder such as coal-based grinder and calcined coke powder such as coal-based is not particularly limited, but the average particle diameter obtained as the median diameter is preferably 5 to 50 µm, more preferably 5 to 15 µm, At this time, the BET specific surface area is preferably 5 m 2 / g or less, and more preferably 1 m 2 / g or less. If the average particle diameter is less than 5 μm, the specific surface area may be excessively increased. On the other hand, if the average particle diameter is more than 50 μm, the charge and discharge characteristics may be deteriorated. When BET specific surface area exceeds 5 m <2> / g, there exists a possibility that the energy efficiency at the time of using for a secondary battery may fall. The BET specific surface area is preferably about 1 m 2 / g or more from the viewpoint of forming fine pores.

Subsequently, raw coke powders such as coal-based and calcined coke powders such as coal crabs obtained as described above are each blended in a proportion of a predetermined amount. The compounding quantity of fresh coke powder, such as a coal system, and calcined coke powder, such as a coal system, is 90: 10-10: 90 by mass ratio, Preferably it is 70: 30-30: 70. Increasing the ratio of calcined coke such as coal-based improves the output characteristics. Increasing the ratio of fresh coke such as coal-based improves the discharge capacity and initial characteristics. Although it depends on which characteristic is highly requested | required, For example, in terms of an output characteristic, it is good to contain content of calcination coke etc. 50% or more.

When the ratio of the 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 composed of the obtained negative electrode active material cannot be sufficiently reduced, and the actual battery voltage cannot be improved, and sufficiently high output characteristics are obtained. You may not lose. In addition, the resistance value of the secondary battery at the end of the charge / discharge increases, so that stable charge and discharge characteristics may not be exhibited.

A phosphorus compound is essential to the coke powder mentioned above, and i) compound or ii) compound and a boron compound (henceforth i) or ii) are also called "phosphorus compound etc.", and it is set as a coke material. The addition is carried out by mixing the above-described raw coke powder such as coal-based and calcined coke powder such as coal-based with the following amounts of i) phosphorus compound or ii) compound and boron compound in a predetermined mold (first Addition method).

Phosphorus compounds and the like may be added after obtaining coke powders such as coal and calcined coke powders such as coal. Alternatively, the phosphorus compounds may be added at the point of time when agglomerates of fresh coke such as coal and chunks of calcined coke such as coal are obtained (second addition method). In this case, the phosphorus compound and the like are added by putting a lump of fresh coke such as coal-based and calcined coke such as coal-based into the pulverizer and simultaneously putting the above-mentioned phosphorus compound into the pulverizer and pulverizing the lump. Raw coke powder, such as a coal system, and calcined coke powder, such as a coal system, can be obtained.

Therefore, since the phosphorus compound and the like can be added simultaneously with the pulverization of the lump of fresh coke such as coal-based and calcined coke such as coal-based, the operation of adding the phosphorus compound and the like separately during firing can be omitted, and the process of producing the negative electrode active material The whole can be simplified.

However, since the specific method of addition differs in both the said 1st addition method and the 2nd addition method, only the manufacturing process of a negative electrode active material differs, and the output characteristics, discharge capacity, initial efficiency, and capacity retention of the negative electrode active material itself change substantially. There is no.

The addition amount of the said phosphorus compound is 0.1-6.0 mass parts in conversion of phosphorus with respect to 100 mass parts of total amounts of fresh coke, such as a coal system, and calcined coke, such as a coal system, Preferably it is 0.5-5.0 mass parts. It is because there exists a possibility that the effect of adding a phosphorus compound may not be fully acquired when addition amount is less than a lower limit, On the other hand, when the addition amount exceeds an upper limit mass part, the crystallization of the surface of a coke advances and there exists a possibility that output characteristics may fall.

In addition, the addition amount of the said boron compound is 0.1-6.0 mass parts in conversion of boron, Preferably it is 0.5-5.0 mass parts with respect to 100 mass parts of total amounts of fresh coke, such as a coal system, and calcined coke, such as a coal system. 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 accelerated excessively, and unreacted boron may remain. to be. In addition, in the present invention, as described above, the boron compound is used in combination with the phosphorus compound, and it is also possible to achieve the object of the present invention and to exert the effect only by adding only the phosphorus compound.

As a phosphorus compound mentioned above, an aqueous solution can be manufactured easily, In addition, phosphoric acid is preferable from a viewpoint of having high safety. As phosphoric acid, it is more preferable to use phosphoric acid (ortho phosphoric acid), but it is not limited to this, It can select suitably from linear polyphosphoric acid, cyclic polyphosphoric acid, various phosphate ester compounds, etc., and can use. These phosphoric acids may be used alone or in combination of two or more thereof.

Further, as the above-mentioned boron compound it is preferable to use a boron carbide (B ₄ C). This is because even if boron carbide is decomposed during firing, the resultant component is only boron for achieving the object of the present invention, and carbon, which is a constituent element of coke, which is the base material of the negative electrode active material, and does not include other components. It is because the bad influence to the negative electrode active material by this can be suppressed.

Firing is performed on such coke material. This firing temperature is preferably at least 800 ° C and not more than 1400 ° C as the highest achieved temperature. Preferably, it is the range of 900 degreeC-1400 degreeC. When the firing temperature exceeds the upper limit, crystal growth of the coke material is excessively promoted, adversely affecting the battery characteristic balance, and it is not preferable from the viewpoint of mass productivity. On the other hand, when the firing temperature is lower than the lower limit, not only sufficient crystal growth is possible, but also the effect of adding the phosphorus compound and the boron compound in the carbonization process of coke is not sufficient, and it tends to adversely affect the battery characteristic balance.

In addition, the holding time at the highest achieved temperature is not particularly limited, but 30 minutes or more is preferable. The firing atmosphere is not particularly limited, but may be an inert gas atmosphere such as argon or nitrogen, and may be a non-oxidizing atmosphere in a non-closed state such as a rotary kiln, and a non-oxidizing atmosphere in a closed state such as a lead hammer kiln. It may be.

Thus, it is advantageous that the obtained negative electrode active material contains phosphorus element and boron element derived from the said addition component in the ratio of 0.05-5 mass parts with respect to 100 mass parts of active materials, respectively.

Phosphorus content in a negative electrode active material can be measured by ICP emission spectroscopy. Specifically, after carbonizing the negative electrode active material by JIS M8814 (ash test method), the obtained ash (inorganic component) is quantified by the above-described analysis method. ICP emission spectroscopy is a method of exciting and quantifying an element from an emission spectrum when returning to a ground state by exciting a sample by plasma flame generated by irradiating argon gas with high frequency.

In the present invention, polyimide resin is used as the binder. Like PVDF which has been mainly used as a binder until now, polyimide resin is excellent in the binding force of negative electrode active materials, and is excellent in adhesiveness to the electrical power collector which forms a negative electrode compared with PVDF. In addition, unlike PVDF, which is a kind of fluorine resin, polyimide resin does not contain fluorine in its structure, and is thermally stable and has high heat resistance, and thus there is a low risk of breakage and rupture of the battery even when the battery temperature rises ideally.

A polyimide resin has a repeating unit represented by following General formula (1), and is generally manufactured by superposing | polymerizing diamine and an acid anhydride which are raw materials in presence of a solvent, making it a polyimide precursor resin, and then imidating by heat processing. Can be. In the case of using a negative electrode material binder, the composition is generally used to form an active material layer dispersed and mixed with an active material, a solvent, and other necessary additives in the state of a polyimide precursor resin. As a polymerization catalyst used at this time, dimethyl acetoamide, dimethylformamide, N-methylpyrrolidone, 2-butanone, diglyme, xylene, etc. are illustrated, for example, and these 1 type, or 2 or more types are used together, Although it can use, it is not limited to this.

[Wherein Ar ₁ represents at least a divalent aromatic diamine residue and Ar ₂ represents a tetravalent acid dianhydride residue.]

For the diamine component being a raw material of the polyimide resin, the compound represented by H ₂ N-Ar ₁ -NH ₂ and illustrated, as the Ar ₁ may be mentioned the following aromatic diamine residues of.

Further, as the acid _{anhydride, O (OC) 2 Ar 2} (CO) are illustrated compounds represented by the ₂ O, as Ar ₂ may be an aromatic acid is shown in the following example the anhydride residue.

Moreover, in this invention, it is preferable to select a diamine component so that an ether bond may be contained in the repeating unit structure which comprises a polyimide resin for the following reasons. According to the polyimide resin in which an ether bond is contained in a repeating unit structure, in the negative electrode using the same negative electrode active material, compared with the case of using PVDF, cycling characteristics (life time) are improved significantly. In view of this, as the binder, Ar ₁ in the general formula (1) having an ether bond represented by diaminodiphenyl ether, preferably a divalent aromatic diamine residue having at least two ether bonds, Ar it may be that the _second formula (2) or tetravalent acid represented by the formula (3) to use a polyimide resin, an anhydride moiety.

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

As bivalent aromatic diamine residue R <_1> which has at least 2 ether bond in this general formula (1), The following can be illustrated preferably.

[In Formula (4), X represents the bivalent organic group which has one or more aromatic rings, Preferably the thing of the structure shown to the following (5) is illustrated.]

As a preferable diamine component which comprises the structural unit of General formula (1), 2,2'-bis [4- (4-amino phenoxy) phenyl] propane (BAPP), 1, 3-bis (4-) specifically, Aminophenoxy) benzene (TPE-R), 1,3-bis (3-aminophenoxy) benzene (APB), 4,4'-bis (4-aminophenoxy) biphenyl (BAPB) and the like are exemplified. . Moreover, as a preferable acid dianhydride which comprises the repeating unit of General formula (1), specifically, pyromellitic dianhydride (PMDA), 3,3 ', 4,4'- fiphenyl tetracarboxylic dianhydride (BPDA) 3 , 3 ', 4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and the like are exemplified. In addition, the diamine and acid anhydride which become a polyimide resin raw material may use together 2 or more types of diamine and an acid anhydride, respectively, and may use other diamine and acid anhydride other than the above.

It is preferable that the polyimide resin in this invention contains 50 mol% or more of structural units represented by General formula (1), The diamine and acid anhydride which comprise other structural units may use the component illustrated above. You may use other diamine and an acid anhydride component other than that.

In the present invention, a solvent such as N-methylpyrrolidone (NMP), dimethylacetoamide (DMAC), dimethylformamide (DMF) or water or alcohol is used as the negative electrode active material and the polyimide resin or polyimide precursor resin. A slurry is produced by mixing using a mixture, and coated and dried on a current collector to obtain a negative electrode having an active material layer.

Here, although the material of the electrically conductive base material used as an electrical power collector is not specifically limited, Metal foil, such as aluminum, copper, nickel, titanium, stainless steel, can be used. In addition, although the form of such an electroconductive base material can be made into various forms, such as a continuous sheet, a punching sheet, a net-shaped (net-shaped) sheet, it is preferable to set it as a continuous sheet especially. In addition, it is preferable that the thickness of an electroconductive base material shall be 2-30 micrometers.

After mixing a negative electrode active material and a conductive support agent into a slurry in the solution which melt | dissolved polyimide resin or polyimide precursor resin in organic solvents, such as NMP, as an slurry, extrusion coating, curtain coating, roll coating, gravure An active material layer is formed by coating with a uniform thickness on an electrical power collector by well-known means, such as application | coating, drying, removing an organic solvent, and heat-imidizing. At this time, it is good to make it the content ratio of the polyimide resin or polyimide precursor resin with respect to a negative electrode active material into the range of 0.1-10 mass parts from a balance of binding property and discharge capacity. In addition, about the thickness of an active material layer, if it is about the same as when forming the well-known negative electrode for secondary batteries, it does not have a restriction | limiting in particular, although it is about 10-500 micrometers generally.

The negative electrode thus obtained can be preferably used as an electrode of secondary batteries including lithium secondary batteries. In the case of constituting a lithium secondary battery using the negative electrode of the present invention, as a positive electrode to be opposed, a lithium-containing transition metal oxide LiM (1) _x O ₂ (wherein x is a numerical value in the range of 0 ≦ x ≦ 1 and M in the formula (1) represents a transition metal and comprises 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, wherein M (1) and M (2) represent transition metals, and Co, Ni, Mn, Ti, Cr, V, Fe, Zn, At least one of Al, Sn, and In, LiM (1) _x M (2) _y M (3) _z O ₂ (wherein x, y and z satisfy the relationship of x + y + z = 1 In the formula, M (1), M (2) and M (3) represent transition metals and include at least one of Co, Ni, Mn, Ti, Cr, V, Fe, Zn, Al, Sn, and In. LiM (1) _x PO ₄ (wherein x is a numerical value in the range of 0 ≦ _x ≦ 1, wherein M (1) represents a transition metal, and Co, Ni, Mn, Ti, Cr, V, Consists of at least one of 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 oxides, general formula M _x Represented by Mo ₆ Ch _6-y (wherein x is a value in the range of 0 ≦ x ≦ 4, y is 0 ≦ y ≦ 1, wherein M represents a metal including a transition metal, and Ch represents a chalcogen metal). Chevrel compounds, or cathode active materials such as activated carbon and activated carbon fibers may be used.

In addition, as the electrolyte filling between the positive electrode and the negative electrode, all conventionally 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 One or a mixture of two or more such as (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 will be exemplified. Can be.

As the non-aqueous electrolyte, for example, propylene carbonate, ethylene carbonate, butylene carbonate, chloroethane carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,1-dimethoxyethane, 1,2-dimethoxyethane , 1,2-diethoxyethane, γ-butylolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,2-dioxolane, anisole, diethyl ether , Sulfolane, methyl sulfolane, acetonitrile, chloronitrile, propionitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethylorthoformate, nitrobenzene , Sole solvents such as benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, sulfite, dimethyl sulfite or two or more kinds of mixed solvents can be used. There.

(Example)

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to the following Example, It is possible to change suitably and to implement in the range which does not change the summary.

(Example 1)

Using a refined pitch from which quinoline insolubles were removed from coal-based heavy oil, a coke (raw coke) prepared by heat treatment at a temperature of 500 ° C. by a delayed coking method was obtained for 24 hours, and finely pulverized and sized with a jet mill. (Iii) to obtain fresh coke powder having an average particle diameter of 9.9 μm.

The bulk raw coke obtained as mentioned above is heat-treated by a rotary kiln at the temperature of the inlet temperature of 700 degreeC from the outlet temperature of 1500 degreeC (maximum reached temperature) for 1 hour or more, and obtains the calcination calcination coke, and similarly it is fine with a jet mill. It pulverized and sintered and the calcined coke powder whose average particle diameter is 9.5 micrometers was obtained.

Phosphoric acid ester (14 mass% active solid resin: Sankosha brand name HCA,) with respect to the sum total (50 mass parts of calcination coke powder and 50 mass parts of calcined coke powder) obtained as mentioned above. Chemical Name: 17.9 parts by mass (in terms of phosphorus: 2.5 parts by mass), and 3.2 parts by mass of boron carbide (in terms of boron: 2.5 parts by mass) 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) Was added to make a coke material.

Subsequently, the said coke material was heated up at the speed | rate of 600 degree-C / hour from room temperature, reached 900 degreeC (maximum reached temperature), hold | maintained again for 2 hours, and carbonized (baking), and the negative electrode active material A for lithium secondary batteries was obtained. .

Further, as a result of performing ICP emission spectroscopy on the active material A, phosphorus and boron contents in the active material A were 12000 rpm and 14000 rpm, respectively.

On the other hand, the polymerization of the binder was performed using pyromellitic anhydride (PMDA) as the acid dianhydride and 2,2'-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) as diamine, in about the same molar amount. By reacting in acetoamide (DMAC) at room temperature for 4 hours, the precursor of the polyimide resin 1 whose weight average molecular weight is 144,000 was obtained.

Next, the negative electrode was produced by the following method using the negative electrode active material A and precursor of polyimide resin 1 obtained above, and the performance as a secondary battery was evaluated.

As shown in Table 1 below, the precursors of the negative electrode active material A and the polyimide resin 1 were used in the proportions of 95% by mass and 5% by mass, respectively, and kneaded using dimethylacetoamide (DMAC) as a solvent to prepare a slurry. This was apply | coated so that thickness might be uniform on the copper foil of thickness 10micrometer, and then heat-processed at 350 degreeC for 30 minutes in nitrogen atmosphere, and the active material layer was formed on the copper foil. The copper foil provided with the active material layer was dried, pressed to a predetermined electrode density, a 60 μm electrode sheet was produced as a total thickness, and a negative electrode was obtained by cutting the sheet into a circular shape having a diameter of 15 mm.

In order to evaluate the electrode characteristics in a negative electrode monopolar with respect to the obtained negative electrode, the test lithium secondary battery was produced as follows. The metal lithium cut out to about 15.5 mm (phi) was used for the counter electrode. In addition, a mixed solvent of ethylene carbonate and diethyl carbonate as an electrolytic solution: to prepare a coin cell with a porous polypropylene film is used that obtained by dissolving LiPF ₆ in (volume ratio 1: 1 mix) at a concentration of 1mol / l, and the separator.

Using this obtained coin cell, the initial discharge capacity was determined by a constant current discharge of 0.5 mA / cm 2 in a voltage range where the lower limit voltage of the terminal voltage was 0 V and the upper limit voltage of the discharge was 1.5 V at a constant temperature of 25 ° C., The output characteristics and input characteristics of the constant current discharge and charging at 5 mA / cm 2 were examined at the capacity retention rate, and the discharge capacity was 313 mAh / g, and the capacity retention ratio at the output characteristic was 78.2%, The capacity retention rate was 56.2%. Moreover, when the product of these ratios was evaluated as input / output balance, it was 0.44. Here, the capacity retention rate for the output characteristics is obtained from the ratio of the discharge capacity at the time of 5 mA / cm 2 constant current discharge to the initial discharge capacity, and the capacity retention rate for the input characteristics is 5 mA / cm 2 constant current charge at the initial charge capacity. It calculated | required from the ratio of the filling capacity of. The constant current discharge and charge were repeated 100 cycles, and the capacity retention rate after 100 cycles determined from the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle was 87.7%. Oh, about capacity retention rate (cycle characteristics) after 100 cycles, if capacity retention rate is 80% or more, (◎), 70% or more and less than 80%, ○, and 70% or less, and △, Table 1 lists the results evaluated in three steps. It was.

(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 cathode electrode was evaluated in the same manner as in Example 1, and the discharge capacity was 352 mAh / g, the capacity retention rate of the output characteristic was 93.7%, and the capacity retention rate of the input characteristic was 4.9%. In addition, 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 made of polyvinylidene fluoride (PVDF) and the heat treatment at 350 ° C. was omitted. The obtained cathode electrode was evaluated in the same manner as in Example 1, and the discharge capacity was 291 mAh / g, the capacity retention rate of the output characteristic was 61.2%, and the capacity retention rate of the input characteristic was 32.8%. In addition, 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 charging was 63.9%.

(Examples 2-5)

A negative electrode was obtained in the same manner as in Example 1 except that the binder used in Example 1 was replaced with polyimide resins 2 to 5 having the compositions shown in Table 1. About the obtained cathode electrode, discharge capacity, the output characteristic, and the cycle characteristic were evaluated like Example 1. The results are shown in Table 1. In addition, the meaning of abbreviated-name of Table 1 is as follows. The polyimide resins 2-5 superimposed each precursor by the operation similar to Example 1, and imidated by the heat processing at the time of forming an active material layer.

BTDA: 3.3 ', 4,4'-benzophenonetetracarboxylic 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 a refined pitch from which quinoline insolubles were removed from coal-based heavy oil, a coke (raw coke) prepared by heat treatment at a temperature of 500 ° C. by a delayed coking method was obtained for 24 hours, pulverized and sized with a jet mill, and average particle diameter. This 9.9 micrometers raw coke powder was obtained.

The bulk raw coke obtained as mentioned above is heat-treated by a rotary kiln at the temperature of the inlet temperature of 700 degreeC from the outlet temperature of 1500 degreeC (maximum reached temperature) for 1 hour or more, and obtains the calcination calcination coke, and similarly it is fine with a jet mill. It pulverized and sintered and the calcined coke powder whose average particle diameter is 9.5 micrometers was obtained.

Phosphoric acid ester (14 mass% active solid resin: Sankosha brand name HCA,) with respect to the sum total (50 mass parts of calcination coke powder and 50 mass parts of calcined coke powder) obtained as mentioned above. Chemical name: 17.9 mass parts (9 mass parts of phosphorus conversion: phosphorus conversion: 2.5 mass parts) of 9,10-dihydro-9-oxa-10-phosphafaphenanthrene-10-oxide) were added, and it was set as the coke material.

Subsequently, the said coke material was heated up at the speed | rate of 600 degree-C / hour from room temperature, reached 900 degreeC (maximum reached temperature), hold | maintained again for 2 hours, and carbonized (baking), and the negative electrode active material B for lithium secondary batteries was obtained. .

In addition, the ICP emission spectroscopic analysis of the said active material B showed that the phosphorus content in the active material B was 14000 rpm.

A negative electrode was obtained in the same manner as in Example 1 using the precursor of polyimide resin 1 used in Example 1 as the binder. The obtained cathode electrode was evaluated in the same manner as in Example 1, and the discharge capacity was 313 mAh / g, the capacity retention rate of the output characteristic was 80.1%, and the capacity retention rate of the input characteristic was 57.0%. Moreover, when the product of these ratios was evaluated as input / output balance, it 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 replaced with polyimide resins 2 and 3 having the compositions shown in Table 1. The discharge capacity, the output characteristic, and the cycle characteristic were evaluated like Example 6 about the obtained cathode electrode. The results are shown in Table 1.

As is clear from the results of the above Examples 1 to 8 and Comparative Examples 1 to 2, in Comparative Example 1 using natural graphite as the negative electrode active material, the discharge capacity was lower than that of Examples 1 and 6 using the active material A or B. Although excellent in input characteristics, the input / output balance was found to deteriorate. Moreover, in the comparative example 2 which used PVDF as a binder, compared with the Example which used polyimide resin, it turned out that discharge capacity, input / output balance, and cycling characteristics are inferior generally. As described above, according to the present invention, it was confirmed that a cathode having excellent overall discharge capacity, input / output balance, and cycle characteristics was obtained.

Claims (5)

As a negative electrode for secondary batteries provided with the active material layer which integrated the negative electrode active material into the binder,
In the negative electrode active material, at least one raw coke of coal or petroleum and calcined coke of coal or petroleum are blended in a mass ratio of 90:10 to 10:90, and the fresh coke and calcined coke It is made by baking the coke material which added the phosphorus compound in the ratio of 0.1-6.0 mass parts with respect to 100 mass parts of total amounts of,
The binder for secondary batteries, characterized in that the binder is a polyimide resin. As a negative electrode for secondary batteries provided with the active material layer which integrated the negative electrode active material into the binder,
In the negative electrode active material, at least one raw coke of coal or petroleum and calcined coke of coal or petroleum are blended in a mass ratio of 90:10 to 10:90, and the total amount of the fresh coke and calcined coke is 100 A phosphorus compound and a boron compound are baked by baking the coke material added in the ratio of 0.1-6.0 mass part, respectively, with respect to a mass part,
The binder for secondary batteries, characterized in that the binder is a polyimide resin. The method according to claim 1 or 2,
Said binder is polyimide resin which has an ether bond in a repeating unit structure, The negative electrode for secondary batteries characterized by the above-mentioned. 4. The method according to any one of claims 1 to 3,
The content rate of the polyimide resin with respect to a negative electrode active material is the range of 0.1-10 mass%, The negative electrode for secondary batteries characterized by the above-mentioned. The secondary battery obtained using the negative electrode of any one of Claims 1-4.