KR20050057491A - Lithium polymer battery and method for manufacturing same - Google Patents

Abstract

Conventional lithium polymer batteries obtained by impregnating a graphite negative electrode with a precursor of polymer solid electrolyte and then conducting polymerization, have a problem that radicals generated during the polymerization are consumed by the graphite. Consequently, some monomers remain unreacted, thereby hindering the thus-obtained polymer battery from having an excellent long- term reliability. Conventional polymer batteries using physically crosslinked gel have a problem that a leakage occurs on abnormal occasions since the gel liquefies at high temperatures. A lithium polymer battery of the invention comprises a positive electrode, a negative electrode containing a negative electrode active material that is a carbon material powder, and a chemically crosslinked gel electrolyte. The carbon material powder is a mixture of at least two composite graphite material powders wherein a low-crystalline carbon material adheres to the surface of high-crystalline graphite particles. The composite graphite material powders are different from each other in values of physical properties. Accordingly, a battery having a high energy density and an excellent long-term reliability (excellent cycle characteristics) can be obtained.

Description

Lithium polymer battery and manufacturing method therefor {LITHIUM POLYMER BATTERY AND METHOD FOR MANUFACTURING SAME}

TECHNICAL FIELD This invention relates to a lithium polymer battery and its manufacturing method. More specifically, the present invention provides a lithium polymer battery using a negative electrode having a composite carbon material powder composed of two or more kinds of graphite material powders having a low crystalline carbon material adhered to a surface of a high crystalline graphite powder as an active material, and the production thereof. It is about a method.

In recent years, instead of using metallic lithium or an alloy thereof as a negative electrode, matrix materials such as carbon materials and conductive polymers have been developed using occlusion and release processes of lithium ions. As a result, the generation of dendrites which occurred when metal lithium or its alloy was used did not occur in principle, and the problem of short circuit inside the battery was reduced. In particular, it is known that carbon materials have a lithium occlusion-release potential closer to that of lithium than that of other materials. Among them, the graphite material can theoretically inject lithium into the crystal lattice at a ratio of one lithium atom to six carbon atoms. For this reason, a graphite material is a carbon material which has high capacity per unit weight and unit volume. In addition, since the graphite material has a flat and chemically stable potential of insertion-desorption of lithium, a battery having good cycle stability can be obtained by using the graphite material.

For example, J. Electronchm. Soc., Vol. 137, 2009 (1990), Japanese Patent Laid-Open Publication No. 4-115457, Japanese Patent Laid-Open Publication No. 4-115458, Japanese Patent Laid-Open Publication No. 4-237971, and the like, have graphite-based carbon materials as a negative electrode active material. In addition, Japanese Patent Laid-Open Publication No. Hei 4-368778, Japanese Patent Laid-Open Publication No. 5-28996, Japanese Patent Laid-Open Publication No. 5-114421, and the like have a battery using a surface-treated graphite carbon material as a negative electrode active material. It is described.

By using the organic electrolytic solution mainly composed of ethylene carbonate (EC), the graphite-based carbon material obtains a discharge capacity almost close to the theoretical capacity. In addition, the potential of the charge and discharge is slightly higher than the potential of the dissolution-precipitation of lithium and is also very flat. For this reason, when a battery is manufactured using the graphite-based carbon material as the negative electrode active material, a secondary battery having a high capacity and a high flatness of battery voltage can be realized, thereby achieving high battery capacity.

However, there remains a problem that graphite-based carbon materials cause decomposition of organic electrolytic solutions because of their high crystallinity. For example, propylene carbonate (PC), which is a solvent for organic electrolytes, has been widely used as a solvent for electrolytes for lithium secondary batteries from a wide potential window, low freezing point (-70 ° C), and high chemical stability. However, when the graphite-based carbon material is used as the negative electrode active material, decomposition reaction of the PC occurs remarkably, and the negative electrode made of the graphite-based carbon material cannot charge and discharge as much as 10% of the PC exists in the electrolyte solution. Electrochem. Soc., Vol. 142,1746 (1995).

As a solution, (1) a method in which an additive such as vinylene carbonate is added to the electrolyte, an active film is formed on the graphite-based carbon material as the negative electrode active material, and the decomposition of the subsequent electrolyte is suppressed by the film, or ( 2) A method of coating the surface of a high crystalline graphite carbon material with a low crystalline carbon material has been proposed. In the latter method, a composite graphite material having a high capacity characteristic of the high crystalline graphite carbon material and no selectivity of the electrolyte solution which is a characteristic of the low crystalline carbon material is obtained.

In recent years, various researches on the ion conductive polymer which has high ion conductivity are aimed at improving the leakage resistance, high stability, and long-term storage property of the battery which used the liquid electrolyte solution. As ion conductive polymers, homopolymers or copolymers of linear polymers, network crosslinked polymers or comb polymers based on ethylene oxide are currently proposed and practically used.

The battery using the ion conductive polymer is widely described in patent documents and the like. For example, US Pat. Nos. 4, 303, 748 to Armand et al., US Pat. Nos. 4, 589, 197 to North, and US Pat. Nos. 4, 547, 440 to Hooper et al. The battery described in a patent document is mentioned.

As a characteristic of these batteries, an ion conductive polymer containing a solution in which an electrolyte salt is dissolved in a polymer material having a polyether structure is used. These ion-conducting polymers have low ion conductivity at room temperature or lower, and thus are particularly compact and lightweight required for batteries for driving power supplies and memory backup power supplies for portable electronic devices, and high energy density cannot be realized.

Therefore, as a method for improving the ion conductivity more than the ion conductive polymer, a method of mixing a monomer, an organic solvent (especially a high dielectric constant organic solvent such as EC or PC) and an electrolyte salt and a method of polymerizing the monomer Is proposed. By the above method, an electrolyte solution is held in a polymer network, and a gel-like polymer electrolyte (hereinafter referred to as chemically crosslinked gel) in which a solid state is maintained can be obtained.

The chemically crosslinked gel has a high holding power of the electrolyte solution and may not be melted even at a high temperature (for example, about 100 ° C.), and is effective from the viewpoint of leakage of liquid at the time of binomiing. However, there are still many problems to be solved, such as poor performance at low temperatures, and an initiator added to the precursor of the ion conductive polymer to crosslink to remain in the battery, causing deterioration in battery performance.

On the other hand, Japanese Patent Application Laid-Open No. 8-507407 proposes a gel electrolyte (hereinafter referred to as a physical crosslinked gel) in which an electrolyte solution is maintained by physically crosslinking a copolymer of hexafluoropropylene-vinylidene fluoride.

The gel of this type forms a battery element by melting the electrolyte solution and then melting it by heating and forming a gel after the battery element is formed. For this reason, it has the advantage that it can manufacture by the method similar to the manufacturing method of the lithium ion battery using liquid electrolyte solution, and the like.

The physically crosslinked gel is in the form of a gel at room temperature, and the effect of preventing leakage to some extent can be expected. However, when the temperature is high, the gel phase is melted and the state of the gel cannot be maintained, and therefore, it is not sufficient from the viewpoint of leakage prevention during battery binomial. Based on the above situation, a high-performance lithium polymer battery using a chemically crosslinked gel that can sufficiently anticipate the effect of leakage prevention is strongly desired.

1 is a cross-sectional view showing an example of the composite graphite material powder of the present invention.

An object of the present invention is to provide a high performance lithium polymer battery having no load leakage, temperature characteristics, and energy density comparable to a lithium ion battery without causing leakage of the electrolyte even when the temperature of the battery rises during the binomial of the battery. To provide.

According to the present invention, there is provided an anode comprising an anode, an anode containing a cathode active material made of a carbon material powder, and an electrolyte using a chemically crosslinked gel, wherein the carbon material powder has a low crystalline carbon material attached to the surface of the high crystalline graphite powder, There is also provided a lithium polymer battery comprising a mixture of at least two or more kinds of composite graphite material powders having different physical properties.

In addition, according to the present invention, a carbon material powder that is a negative electrode active material, wherein a low crystalline carbon material adheres to the surface of the high crystalline graphite powder, and further includes at least two or more composite graphite material powders having different physical properties. The manufacturing method of the lithium polymer battery containing the process of impregnating the precursor of a chemically crosslinked gel, and the process of gelatinizing a precursor and obtaining an electrolyte are provided.

Although composite graphite material powder is excellent as a negative electrode active material, the lubricity inherent in high crystalline graphite powder (henceforth a graphite powder) is hindered by the low crystalline carbon material of a surface. For this reason, filling property is bad and a high density negative electrode may not be obtained. About this filling property, the inventors of this invention etc. examined in detail and found that filling property is largely influenced by the physical-property value of the composite graphite material powder, such as a coating ratio or the kind of core material.

Moreover, the inventors of this invention etc. discovered from the said viewpoint that the high efficiency crosslinking is performed when hardening the precursor of a chemically crosslinked gel by using two or more types of composite graphite material powders from which a physical property value differs as a negative electrode active material. The reason why crosslinking is performed with high efficiency is estimated as follows. The graphite powder consumes radicals generated from the initiator by means such as heat or UV at its active site and inhibits the polymerization reaction. By coating the surface with a low crystalline carbon material, consumption of radicals by the graphite powder is suppressed, and it is considered that the generated radicals are used for the polymerization reaction with high efficiency.

The inclusion of at least two or more kinds of composite graphite material powders having different physical properties in the present invention includes at least two kinds of composite graphite material powders as main active materials and composite graphite material powders for improving their filling properties. it means. By such a negative electrode containing at least two or more kinds of composite graphite material powders, a high performance secondary battery having a high capacity density and excellent load characteristics can be produced.

Since the composite graphite material powder is an aggregate of powder, and strictly speaking, it is difficult to obtain a completely uniform aggregate of powder, it has a physical property value of each particle and a physical property value (average value) as an aggregate of particle | grains. In the present invention, two or more kinds means that two or more kinds of composite graphite material powders having different physical properties are present as the latter aggregates. Here, the physical properties include crystallinity (interface gap, crystal size, etc.), specific surface area, particle size distribution, coverage ratio, Raman strength ratio, true density, size density, purity, shape, and the like.

In the present invention, it is preferable to use two or more kinds of composite graphite material powders having different coverage ratios. Specifically, different coverage ratios mean that the average value (hereinafter referred to as coverage ratio) of the amount of the low crystalline carbon material / (the amount of the high crystalline graphite powder + the amount of the low crystalline carbon material) is different. By varying the coating ratio, a higher capacity density and a high performance secondary battery can be produced.

In addition, a coverage ratio does not mean the value of each particle, but means the value as an aggregate of composite graphite material powder, ie, an average value. This value is computed by the weight change of the graphite powder in a manufacturing process, and the weight change of the finally obtained composite graphite material powder.

It is preferable that the coating ratio of the composite graphite material powder with the larger coating ratio exists in the range of 0.03-0.3, and it is still more preferable if it is 0.1-0.25. If the coating ratio is larger than 0.3, the low crystal component becomes too large and the charge / discharge capacity is lowered, which is not preferable. Moreover, since it is low in the inhibitory effect to decomposition | disassembly of electrolyte solution, when it becomes less than 0.03, it is not preferable.

Moreover, it is preferable that it is 0.1 or less, and, as for the coverage ratio of the composite graphite material powder with a smaller coverage ratio, 0.01-0.1 are more preferable. More preferably, it is 0.01-0.05. In a material of less than 0.01, it is not preferable to suppress the inhibitory factor of the polymerization, and at a coating ratio greater than 0.1, the performance is excellent and a negative electrode having a high filling density is not easily obtained.

Moreover, it is preferable that the quantity of the composite graphite material powder with a small coating ratio with respect to the quantity of the composite graphite material powder with a large coating ratio is 50% or less by weight ratio, More preferably, it is about 10 to 30%. If the amount to be added is too large, the properties of the material become dominant, and the effect of suppressing the factor that inhibits the polymerization cannot be sufficiently obtained, or the material itself is oriented, and the salting of the electrolyte is deteriorated. The load characteristic becomes worse. Moreover, when the amount added is not enough, the problem that the effect of a filler improvement is not fully acquired arises.

In addition, by changing the type of graphite powder instead of varying the coating ratio, it is possible to obtain a battery having high capacity and high performance. Even when two or more kinds of graphite powders having different crystallinity evaluations defined by X-ray diffraction, Raman spectroscopy, true density, etc. are used and the low crystalline carbonaceous material is coated at an equivalent coating ratio, It is clear that the filling properties are different. It is estimated that the microstructure which cannot be judged by the evaluation means such as the X-ray diffraction method is lined up, and the difference in the filling property is caused by the difference in the shape, the balance of the particle size, etc. of the composite graphite material powder derived from the shape of the core material. do.

The coating ratio in the case where the graphite powder is different is not particularly limited. However, the coating ratio of the composite graphite material powder having a large coating ratio is preferably 0.03 to 0.3, and the coating ratio of the composite graphite material powder having a small coating ratio is 0.01 to more, as the filling ratio is increased. It is preferable that it is 0.1. More preferable latter coverage ratio is 0.01-0.05.

Moreover, it is preferable that the quantity of the composite graphite material powder with a small coating ratio with respect to the quantity of the composite graphite material powder with a large coating ratio is 50% or less by weight ratio, More preferably, it is about 10 to 30%. If the amount added is too large, the property of the material becomes dominant, and the effect of suppressing the factor that inhibits the polymerization is not sufficiently obtained, or the material itself is oriented, and the salting of the electrolyte becomes bad, for example. The characteristics become worse. Moreover, when the amount added is not enough, the problem that the effect of a filler improvement is not fully acquired arises.

In the present invention, good results are obtained when bulky artificial graphite is used as the graphite powder of the composite graphite material powder having a large coverage ratio and natural graphite powder is used as the graphite powder of the composite graphite material powder having a small coverage ratio.

In the present invention, as an index indicating the degree of filling, a parameter called a compression ratio is defined to define physical properties of the composite graphite material powder. Here, the compression ratio is a slurry obtained by adding 7.5 parts by weight of PVDF (vinylidene fluoride) to the composite graphite material powder as a target, based on 100 parts by weight of the composite graphite material powder, and mixing with a solvent. It means the thickness change at the time of apply | coating in thin shape and pressing at 300 kg / cm of linear pressures. Specifically,

Compression ratio = thickness of coating after press / thickness of coating before press

Is defined as

Moreover, the coating film density at the time of producing a coating film is also important. In other words, the higher the coating film density before pressing and the smaller the compression ratio, the higher density of the negative electrode can be obtained. Even if the compression ratio is sufficiently small, when the coating film density before press is too small, the graphite powder may be easily oriented when the press is pressed to obtain a high-density negative electrode, and the negative electrode may have poor load characteristics. In addition, even in a material having a sufficiently large coating film density before pressing, a large compression ratio is not preferable because a cathode having a high energy density is not obtained.

In this invention, 2 or more types of composite graphite material powders are mixed so that the coating film density before press may be 0.7 g / cm <^3> or more, a compression ratio is 0.4-0.7, and the coating film density after press will be 1.5 g / cm <^3> or more. It is desirable to. The higher the coating film density after pressing, the higher the capacity of the negative electrode. However, the high-density load obtained when the coating film density before press is low and a compression ratio is small may worsen load characteristics by the orientation of a material, etc., and is unpreferable. Moreover, it is preferable that the coating film density after press is suppressed to about 1.8 g / cm <^3> . In the case of higher than this, since the space | gap in a negative electrode is not enough, the quantity of electrolyte in a negative electrode is not enough, and battery characteristics, such as load characteristics, may not be fully acquired.

The composite graphite material powder in the present invention is obtained by attaching the low crystalline carbon material 2 to the surface of the high crystalline graphite powder 1 by a method such as a gas phase method, a liquid phase method, or a solid phase method. Can be obtained.

The graphite powder used for the core material is natural graphite, artificial graphite in the form of particles (flakes, blocks, fibers, whiskers, spheres, fractures, etc.), or mesocarbon microbeads, mesophase pitch powders, isotropic pitch powders, or the like. One kind or two or more kinds of graphitized products may be used.

Here, as the graphite powder serving as the core material, more preferably, the average plane spacing d002 of the (002) plane by X-ray wide-angle diffraction method is 0.335 to 0.340 nm, and the crystal lattice thickness Lc of the (002) plane direction is 10 nm or more (more preferably, 40 nm or more), crystal lattice thickness La in the (110) plane direction is 10 nm or more (more preferably, 50 nm or more), and peak intensity around 1580 cm ^-1 by argon laser Raman It is preferable that the peak intensity ratio (hereinafter referred to as R value) in the vicinity of 1360 cm ⁻¹ to the ratio is 0.5 or less (more preferably, 0.4 or less). When the average interplanar spacing is larger than 0.340 nm, or when Lc and La are smaller than 10 nm, or when the R value exceeds 0.5, the crystallinity of the graphite powder is not sufficient. For this reason, when producing a composite graphite material powder, since the capacity | capacitance of the electrolytic part (0-300 mV based on the potential potential of Li) which is close to the dissolution precipitation of lithium is not enough, it is unpreferable.

It is preferable that the particle size distribution of the graphite powder used as a core material is about 0.1-150 micrometers. The particle size of the composite graphite material powder in which the low crystalline carbon material adheres to the surface of the graphite powder is substantially dependent on the particle size of the graphite powder which is a core material. For this reason, by the particle diameter of a core material, the particle size of a final written matter is also almost prescribed. When the particle diameter of the core material is smaller than 0.1 mu m, the risk of causing an internal short circuit through the hole of the separator of the battery increases, which is not preferable. When larger than 150 micrometers, since the uniformity of a negative electrode, the packing density of an active material, the operability in the process of manufacturing a negative electrode, etc. fall, it is unpreferable.

The particle size here is an average value of the powder, and in the particle size distribution measured by a laser diffraction particle size distribution meter, a value indicating a peak is defined as the particle size.

In the method of forming a low crystalline carbon material on the surface of the graphite powder, the vapor phase method is to transport a gaseous raw material or a liquid raw material into the reaction system by a method such as spraying or bubbling, and thermal decomposition of the raw material It is a method of forming carbon from the gas phase on the surface of graphite powder. As pyrolysis temperature, although it changes with a raw material, it can be performed in the temperature range of about 450-1500 degreeC.

As a raw material, aliphatic saturated hydrocarbons, such as methane, ethane, and propane, aliphatic unsaturated hydrocarbons, such as propylene, aromatic hydrocarbons, such as benzene, toluene, xylene, naphthalene, and perylene, are mentioned. Moreover, it is also possible to use suitable inert gas, such as argon and nitrogen, as a carrier gas. Moreover, the method of adding hydrogen, and suppressing generation | occurrence | production of the soot in a gaseous phase can also be considered.

In the method of forming a low crystalline carbon material on the surface of the graphite powder, the liquid phase method is a method of forming carbon on the surface by adhering a raw material having a carbonization degree to the surface of graphite via a liquid phase and firing them. . Examples of the raw material include aromatic hydrocarbons such as naphthalene, phenanthrene, acenaphthylene, anthracene, triphenylene, pyrene, glycene, and perylene, and tar, pitch, asphalt, and oil obtained by polycondensing these under heat and pressure. The origin of these raw materials is irrespective of a petroleum system and a coal system.

In addition, before firing, the graphite powder coated with the carbon precursor may be provided to the washing step. By applying the washing step, the low molecular component of the carbon precursor can be removed, and the carbonization rate from the carbon precursor can be improved, and the effect of suppressing fusion or aggregation when the particles are calcined can be obtained. . Here, toluene, chinoline, acetone, hexane, benzene, xylene, methyl naphthalene, alcohols, coal-based oil, petroleum-based oil etc. are mentioned as an organic solvent used for washing | cleaning here. Among these, toluene, chinoline, acetone, benzene, xylene, methanol, petroleum light oil and heavy oil, petroleum light oil and heavy oil and the like are more preferable.

In the method for forming a low crystalline carbon material on the surface of the graphite powder, the solid phase method is a method of forming carbon on the surface by attaching a raw material to which the carbon precursor is carbonized via a solid phase to the surface of graphite and firing them It is a way. In general, the resin is carbonized through a solid phase, but in order to adhere such a resin to the surface of the graphite powder, the resin is made into a liquid phase by heating to a temperature above the melting point of dissolving the resin in a solvent. The method of mixing by the method as described in description of a liquid phase method, and making it adhere to a surface is mentioned. Moreover, it is also possible to mix resin and graphite powder, and to hold | maintain near melting | fusing point at the time of baking.

As a specific raw material, Polyamide-imide resin; Polyamide resins; Conjugated resins such as polyacetylene, poly (p-phenylene) and poly (p-phenylene vinylene); Phenolic resins; Furopril alcohol resin; Cellulose; Acrylic resins such as polyacrylonitrile and poly (α-halogenated acrylonitrile); Vinyl halide resins such as polyvinyl chloride, polyvinylidene chloride and chlorinated polyvinyl chloride; Etc. can be mentioned. In addition, as baking conditions, the baking method described in the said liquid layer method, and baking atmosphere are applicable.

The low crystalline carbon material obtained by the above method is more preferably an average interplanar spacing (d002) of the (002) plane by the X-ray wide-angle diffraction method is larger than 340 nm, and the crystal lattice in the (002) plane direction The thickness Lc is smaller than 40 nm (more preferably smaller than 10 nm), the crystal lattice thickness La in the (110) plane direction is smaller than 50 nm (more preferably smaller than 10 nm), and the R value is 0.4. Greater (more preferably greater than 0.5).

1 to 30 parts by weight of the binder is mixed with respect to the active material 100 parts by weight to form a negative electrode. Examples of the binder include, but are not limited to, fluoropolymers such as polytetrafluoroethylene and polyvinylidene fluoride, polyolefin-based polymers such as polyethylene and polypropylene, synthetic rubbers, and the like. If the binder is more than 30 parts by weight, a practical lithium polymer battery cannot be produced because the resistance or polarization of the negative electrode is increased and the discharge capacity is reduced. Conversely, when the binder is smaller than 1 part by weight, the binding capacity disappears and is not practical. In the preparation of the negative electrode, in order to increase the binding property, heat treatment may be performed at a temperature before and after the melting point of the binder.

In order to obtain the negative electrode which has the said compression ratio, it is preferable to use synthetic rubbers as a binder among the said binders. The negative electrode having the above compression ratio and having a physical property of 1.5 g / cc or more after pressing has a tendency of cycle deterioration due to repeated expansion and contraction of the negative electrode depending on charge and discharge. Since a rubber binder has strong binding capacity and rubber elasticity, it is thought that it can follow the expansion shrinkage of an active material, and can suppress cycle deterioration of a negative electrode.

The polymerizable monomer as a raw material of the chemically crosslinked gel in the present invention is not particularly limited as long as it is a compound having affinity with the solvent solution of the electrolyte and having a polymerizable functional group. For example, single or 2 or more types of use of the polymerizable monomer which provides polymers, such as a thing which has a polyether structure and an unsaturated double bond group, oligoester acrylate, polyester, polyimine, polythioether, polysulfone, etc. are mentioned. Can be. Moreover, it is preferable to have a polyether structure and an unsaturated double bond group from affinity with a solvent. Examples of the polyether structural unit include ethylene oxide, propylene oxide, butylene oxide, glycidyl ether, and the like, and these alone or in combination of two or more thereof are preferably used. In the case of a combination of two or more kinds, the form can be appropriately selected regardless of block or random. Especially, the use of the polymerizable monomer which consists of a polyfunctional monomer and a monofunctional monomer as an acrylate material is preferable because it provides the gel which has the strength and elasticity which follow the volume change of a negative electrode.

As an acrylate-type monomer, what esterified the terminal hydroxyl group of polyether polyol with acrylic acid can be used preferably. Polyfunctional monomers are polyhydric alcohols such as ethylene glycol, glycerin, and trimetholpropane as initiators, and terminal hydroxides of polyether polyols obtained by addition polymerization of ethylene oxide (EO) alone or EO and propylene oxide (PO). Obtained by esterifying a siloxane group with acrylic acid. The monofunctional monomer is a terminal of a polyether polyol obtained by addition polymerization of ethylene oxide (EO) alone or EO and propylene oxide (PO) to monohydric alcohols such as methanol, ethanol and propanol as an initiator. Obtained by esterifying a hydroxyl group with acrylic acid.

Here, a polyfunctional monomer shows an important role for the liquid-retaining property of the electrolyte solution of a gel electrolyte, and it is more preferable that average molecular weight is the range of 5,000-10,000. In the case where the polyfunctional monomer in the above range is employed, the precursor can be easily dissolved in the electrolyte when the precursor is adjusted, and has excellent liquid retention properties when preparing the gel electrolyte.

On the other hand, as for the monofunctional monomer, the one with less average molecular weight can improve the flexibility of a gel electrolyte, and it is preferable that average molecular weight is about 200-3,000.

Moreover, as electrolyte solution used for electrolyte, cyclic carbonates, such as PC, EC, butyl carbonate, chain carbonates, such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, (gamma) -butyrolactone, (gamma)- Lactones, such as valerolactone, Furan, such as tetrahydrodofuran and 2-methyl tetrahydrodofuran, diethyl ether, 1,2-dimethoxyethane, 1,2- diethoxyethane, ethoxymethoxyethane And ethers such as dioxane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl succinate, methyl nitrate and the like can be used.

Examples of electrolyte salts include lithium perchlorate (LiClO ₄ ), lithium borofluoride (LiBF ₄ ), lithium phosphide (LiPF ₆ ), lithium hexafluorophosphate (LiAsF ₆ ), lithium hexafluorophosphate (LiSbF ₆ ), trifluoromethane Lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ), lithium trifluorouronitrate (LiCF ₃ COO), and trifluorofluoromethanesulfonate imide lithium (LiN (CF ₃ SO ₂ ) ₂ ); One or more kinds of can be mixed and used.

The electrolyte is obtained by preparing an electrolyte by dissolving an electrolyte salt in the selected solvent, mixing with the polymerizable monomer and polymerizing.

The ratio of the polymerizable monomer and the electrolyte solution is preferably 70:30 to 99: 1, more preferably 80:20 from the viewpoint of the performance comparable to the electrolyte solution and the retention of the electrolyte solution without causing leakage. ~ 97: 3.

In addition, when mixing and using a monofunctional monomer and a polyfunctional monomer, it is preferable that the mixture ratio of a monomer mixes polyfunctional monomer: monofunctional monomer in the range of 4: 6-9: 1.

As a crosslinking method of a polymer solid electrolyte, the method of using optical energy, such as an ultraviolet-ray, an electron beam, and visible light, and the method by heating can be used. It is also important to use a polymerization initiator if necessary. Especially in the crosslinking method by ultraviolet rays or heating, it is preferable to add a polymerization initiator of several% or less. Examples of the polymerization initiator include photopolymerization initiators such as trimethylsilylbenzophenone, benzoin, 2-methylbenzoin, 4-methoxybenzophenone, benzoin methyl ether anthraquinone and benzyl dimethyl ketal, benzyl peroxide, methyl ethyl ketone, You may add polymerization initiators, such as (alpha), (alpha) '-azo bizisobutyronitrile.

In addition, as for the ultraviolet-ray polymerization and the wavelength of an ultraviolet-ray, 250-360 nm is suitable. Also when using an initiator, according to this invention, a favorable polymer can be obtained with few initiators. The by-product by the residual polymerization initiator and the polymerization initiator may adversely affect the battery characteristics, and it is preferable to leave it in the required minimum amount. Although the quantity of an initiator is based also on the kind of initiator, it is preferable to suppress to 3000 ppm or less normally with respect to the precursor which consists of a polymerizable monomer and electrolyte solution.

As the positive electrode in the lithium polymer secondary battery of the present invention, for example, an oxide containing lithium can be used as the positive electrode active material. Specific examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , or materials substituted with a part of these transition metals. Accordingly, a positive electrode is formed by mixing a conductive material, a binder and, in some cases, a solid electrolyte and the like.

This mixing ratio can make 5-50 weight part of electrically conductive materials and 1-30 weight part of binders with respect to the active material 100 weight part. Although carbons, such as a carbon block (acetylene block, a thermal block, a channel block, etc.), graphite powder, a metal powder, etc. can be used for this electrically conductive material, it is not limited to this.

Examples of the binder include fluorine-based polymers such as polytetrafluoroethylene and polyvinylidene fluoride, polyolefin-based polymers such as polyethylene and polypropylene, synthetic rubbers, and the like, but are not limited thereto.

If the conductive material is less than 5 parts by weight, or the binder is more than 30 parts by weight, a practical lithium polymer battery cannot be produced because the resistance or polarization of the positive electrode increases and the discharge capacity is reduced. When the conductive material is more than 50 parts by weight (weight part varies depending on the kind of mixed conductive material), the amount of active material contained in the positive electrode decreases, so that the discharge capacity as the positive electrode becomes small. If the binder is less than 1 part by weight, the binding capacity is lost. If the amount is more than 30 parts by weight, the amount of active material contained in the positive electrode decreases as in the case of the conductive material, and as described above, the resistance or polarization of the positive electrode increases and the discharge capacity decreases, which is not practical. In the production of the positive electrode, in order to increase the binding property, heat treatment is preferably performed at a temperature before and after the melting point of each binder.

(Example)

Example 1, Comparative Example 1

In order to see the effect on the curing of the precursor of the polymer solid electrolyte, the curing experiment of the precursor was conducted in the state of mixing the graphite material powder.

Adjustment of the precursor

A mixed solvent of EC and γ-butyrolactone in which 1 mol / liter of LiBF ₄ was dissolved was used as an electrolyte solution. Monofunctional acrylate monomers having an average molecular weight of 7500 to 9000 and monofunctional acrylate monomers having an average molecular weight of 200 to 300 containing a copolymer of ethylene oxide and propylene oxide are monomers having a weight ratio of 7: 3. It mixed with electrolyte solution so that it became this 95: 5. A thermal initiator was added to the solution in an amount of 200 ppm with respect to the total weight of the precursor. The thermal polymerization initiator used is t-butyloxy neodecanoate.

Both were mixed so that the ratio of graphite powder and precursor became a weight ratio 1:10, it hold | maintained for 24 hours in the 80 degreeC thermostat, and the hardening state of the precursor was confirmed.

A composite graphite material powder containing artificial crystalline graphite (KS25) manufactured by Timcal Co., Ltd. as a graphite powder and having a low crystalline carbon material attached thereto, and the average value of low crystalline carbon material / (high crystalline graphite powder + low crystalline carbon material). The hardening experiment was done using the thing which changed (Example 1). In addition, the case where a low crystalline carbon material is not coat | covered was made into the comparative example 1. The results are shown in Table 1. In Table 1, ◎ means that the liquid is sufficiently cured and there is no liquid part, and ○ means that the gel is slightly soft but the liquid part is not left, and × means that the liquid part is not sufficiently cured. Means.

In Table 1, the curing condition was good as the coating ratio was large.

Similarly, when experiment was performed by changing the amount of initiator, even if it changed, the tendency of the degree of hardening is the same, and the one with a large coating ratio hardens favorably.

In addition, when the initiator was increased to about 5000 ppm relative to the total amount of the precursor, some degree of curing was obtained only by the graphite powder. Therefore, the composite graphite material powder cured irrespective of the initiator concentration, and in particular, it was found that the effect was greater than that of the core material alone in the region of 5000 ppm or less.

(Example 2)

(Production of the anode)

Lithium cobaltate (LiCoO ₂ ) was used as the positive electrode active material. A paste was prepared by dispersing a mixture of the positive electrode active material and the acetylene block in a binder solution in which a polyvinylidene fluoride as a binder was once dissolved in a mortar with a solvent N-methyl-2-pyrrolidone.

The paste thus obtained was applied onto an aluminum foil current collector, which was temporarily dried at 60 deg. C and heat-treated at 150 deg. The cathode size was made 3.5 x 3 cm (coating part 3 x 3 cm), and aluminum foil (50 micrometers) was welded to the non-coating part. Furthermore, the thing dried under reduced pressure at 180 degreeC for water removal was used as a test anode. The film density was 2.9 g / cm <^3> .

(Production of the cathode)

A composite graphite material powder having a low crystalline carbon material adhered to the surface using artificial graphite (KS25) manufactured by Timcal Co., Ltd. as a negative electrode active material (particle size 12 μm, d (002) = 0.337 nm, R value = 0.4, low 80 parts by weight of the amount of crystalline carbon material / (amount of high crystalline graphite powder + amount of low crystalline carbon material) = 0.18), and low crystalline carbon attached to the surface by using natural graphite (Madagascaric acid) as a core material. Composite graphite material powder (particle size 16μm, d (002) = 0.336nm, R value = 0.21, amount of low crystalline carbon material / (amount of high crystalline graphite powder + amount of low crystalline carbon material) = 0.05) A mixture of parts by weight was used as the negative electrode active material. This was dispersed in a solution dissolved in solvent N-methyl-2-pyrrolidone using polyvinylidene fluoride as a fluid as a fluid, and the paste was applied to 20 µm copper foil, which was then dried at 60 ° C. And pressed after heat treatment at 240 ℃. A nickel foil (50 μm) lead was welded to the non-coated portion, with a cathode size of 3.5 × 3 cm (coating part 3 × 3 cm). In addition, vacuum drying at 150 DEG C was used as the cathode for water removal. The coating film density was 1.58 g / cm <^3> .

(Adjustment of precursor)

A mixed solvent of EC and γ-butyrolactone in which 1.8 mol / liter of LiBF ₄ is dissolved is used as an electrolyte solution. Monofunctional acrylate monomers having an average molecular weight of 7500 to 9000 and monofunctional acrylate monomers having an average molecular weight of 200 to 300 containing a copolymer of ethylene oxide and propylene oxide are monomers having a weight ratio of 7: 3. It mixed in electrolyte solution so that ratio might be 97: 3. The thermal polymerization initiator was added to the solution with respect to the total weight of 200 ppm to make a precursor.

(Production of battery)

Using a nonwoven fabric made of polyester as a separator, the electrodes obtained as described above are polymerized so as to face each other and inserted into a bag of alumina laminate processed into a bag shape. The precursor is put therein, and heat sealing is performed under reduced pressure. Then, the mixture was kept at 80 ° C for 4 hours to thermally polymerize to manufacture a polymer battery. The obtained battery was repeatedly charged and discharged under the conditions of a current value of 4 mA, charging 4.1 V-CCCV (current voltage constant), and discharge 2.75 V-CC (current constant), and cycle characteristics were measured. Table 2 shows the used materials, the mixing ratios, and the like, and the coating film density (before press), the compression ratio, the coating film density (after the press), the volume energy density around the negative electrode active material layer, and the capacity retention rate at the cycle.

Comparative Example 2

A composite graphite material powder having a low crystalline carbon material adhered to the surface by using artificial graphite (KS25) manufactured by Timcal Co., Ltd. as a negative electrode active material (particle size 12 μm, d (002) = 0.337 nm, R value = 0.4, low A negative electrode was prepared in the same manner as in Example 2, except that the amount of crystalline carbon material / (amount of high crystalline graphite powder + amount of low crystalline carbon material) = 0.18) was used alone. The coating film density of the obtained negative electrode was 1.46 g / cm ³ . A battery was produced in the same manner as in Example 2 except that the obtained negative electrode was used, and a charge / discharge test was performed. Table 2 shows the coating materials density (before press), the compression ratio, the coating film density (after pressing), the volume energy density around the negative electrode active material layer, and the capacity retention rate at the cycle.

Comparative Example 3

A composite graphite material powder having a low crystalline carbon material adhered to the surface by using artificial graphite (KS25) manufactured by Timcal Co., Ltd. as a negative electrode active material (particle size 12 μm, d (002) = 0.337 nm, R value = 0.4, low 80 parts by weight of the amount of crystalline carbon material / (amount of high crystalline graphite powder + amount of low crystalline carbon material) = 0.18), and natural graphite (Madagascaric acid, particle diameter 14 μm, d (002) = 0.3358 nm, R A negative electrode was prepared in the same manner as in Example 2, except that 20 parts by weight of the mixture (q = 0.1) was used. The coating film density of the obtained negative electrode was 1.65 g / cm ³ . A battery was produced in the same manner as in Example 2 except that the obtained negative electrode was used, and a charge / discharge test was performed. Table 2 shows the coating materials density (before press), the compression ratio, the coating film density (after pressing), the volume energy density around the negative electrode active material layer, and the capacity retention rate at the cycle.

Examples 3-5 and Comparative Examples 4-5

A negative electrode and a battery were produced in the same manner as in Example 2 except that the graphite material powder shown in Table 2 was used as the carbon material as the active material. The results (coating film density (before press), compression ratio, coating film density (after pressing), volume energy density around the negative electrode active material layer, capacity retention rate at the cycle) are shown in Table 3. In Table 2, MCMB is an abbreviation for mesocarbon microbeads, which are spherical carbon materials.

As the above result shows, according to the Example, the lithium polymer battery excellent in high capacity density and cycling characteristics can be obtained. When the composite graphite material powder alone was used (Comparative Examples 2 and 5), the capacity density of the electrode was low, and when natural graphite was used as the filler (Comparative Example 3), sufficient cycle characteristics were not obtained. This is because when the graphite alone is used, since the pressability is low, the density does not increase, and when natural graphite is used as the filler, the result of Example 1 shows that the It is estimated that superposition | polymerization is inhibited and the unreacted monomer which remained in the battery has a bad influence.

(Example 6)

A positive electrode and a negative electrode were produced in the same manner as in Example 2 except that the composite graphite material powder shown in Table 4 was used.

(Adjustment of Precursor for Anode)

2.5 mol / liter of the lactone and the PC LiBF ₄ dissolved in EC and γ- butyric 1: 1 was dissolved in a mixed solvent of the electrolyte: 2. A monofunctional acrylate monomer having an average molecular weight of 7500 to 9000 and a monofunctional acrylate monomer having an average molecular weight of 200 to 300 containing a copolymer of ethylene oxide and propylene oxide are monomers having a weight ratio of 9: 1 by weight of an electrolyte solution and a monomer. It mixed in electrolyte solution so that ratio might be 97: 3. 2000 ppm of UV initiators were added to the solution to form a precursor.

(Adjustment of precursor for cathode)

A 1: 2: 1 mixed solvent of ethylene carbonate (EC) and γ-butyrolactone and propylene carbonate (PC) in which 1 mol / liter of LiBF ₄ was dissolved was used as an electrolytic solution. A monofunctional acrylate monomer having an average molecular weight of 7500 to 9000 and a monofunctional acrylate monomer having an average molecular weight of 200 to 300, containing a copolymer of ethylene oxide and propylene oxide, has a monomer of 8: 2 in a weight ratio of an electrolyte solution and a monomer. It mixed in electrolyte solution so that ratio might be 95: 5. 2000 ppm of UV initiators were added to the solution to obtain a precursor.

(Production of battery)

Polymerized by using a nonwoven fabric made of polyester as a separator on the positive electrode, impregnated with a precursor for positive electrode, and then embedded in a quartz plate, irradiated with 30 m of UV light at 30 mW / cm ² , and the separator and the positive electrode and electrolyte layer Unified.

The negative electrode was impregnated with a precursor for the negative electrode, similarly irradiated with UV light, and the negative electrode and the electrolyte layer were integrated. The obtained electrode was bonded so that an active material layer faced, it inserted in the alumina laminate processed into the bag shape, and heat-sealed under reduced pressure, and produced the lithium polymer battery. The obtained battery was repeatedly charged and discharged under the conditions of a current value of 4 mA, charge 4.1 V-CCCV, and discharge 2.75 V-CC, and cycle characteristics were measured. Table 4 shows the used materials, the mixing ratio, and the like, and the coating film density (before pressing), the compression ratio, the coating film density (after pressing), the volume energy density per negative electrode active material layer, and the capacity retention rate at the cycle are shown in Table 5.

(Example 7)

As a binder for the negative electrode, a lithium polymer battery was produced and evaluated in the same manner as in Example 6 except that SBR (styrene butadiene rubber): 2 parts and CMC-NH 4: 2 parts were used, and water was used as the dispersion medium. Table 4 shows the mixing ratio and the like, and the coating film density (before press), the compression ratio, the coating film density (after the press), the volume energy density per negative electrode active material layer, and the capacity retention rate at the cycle.

(Comparative Example 6)

A polymer battery was produced in the same manner as in Example 6 except that the composite graphite material powder shown in Table 4 was used. The results are shown in Table 5.

From the above results, it can be seen that the cycle characteristics differ greatly as the composite graphite material powder is different. It is thought that this is because in the composite graphite material powder of the comparative example, radicals generated by the initiator are consumed by the graphite powder and many unreacted monomers remain in the negative electrode. Further, it can be seen that better performance can be obtained when SBR (styrene butadiene rubber) is used as the binder of the negative electrode.

According to the present invention, a lithium polymer battery having a high energy density and excellent long-term reliability (cycle characteristics) can be obtained by using a negative electrode active material in which at least two kinds of composite graphite material powders are mixed.

In addition, since the lithium polymer battery provided by the present invention uses a chemically crosslinked gel, even when the battery is irradiated at a high temperature, the gel does not dissolve and liquefy. Therefore, it is difficult to cause expansion of the battery and the like, and a highly reliable battery can be obtained.

The feature of the lithium polymer battery is that the thickness can be reduced and the shape is free, and the feature of the lithium polymer battery can be utilized more effectively by incorporating it between the poles of the electronic device. In the usage method which a user cannot replace easily, long-term reliability and prevention of expansion of a battery are very important, and the industrial meaning is large.

Claims (8)

A cathode comprising an anode, a cathode active material consisting of a carbon material powder, and an electrolyte using a chemically crosslinked gel, wherein the carbon material powder has a low crystalline carbon material attached to the surface of the highly crystalline graphite powder, and has different physical properties. A lithium polymer battery comprising a mixture of at least two or more kinds of composite graphite material powders. The method of claim 1, The two or more types of composite graphite material powders have different coverage ratios as physical properties, which are expressed as an average value of the amount of the low crystalline carbon material / (the amount of the high crystalline graphite powder + the amount of the low crystalline carbon material). The method of claim 1, The two or more types of composite graphite material powders have different physical property values due to different kinds of high crystalline graphite powders. The method of claim 1, Said two or more types of composite carbon materials consist of two types of composite graphite material powder whose coverage ratio is 0.03-0.3, and composite graphite material powder whose coverage ratio is 0.1 or less. The method of claim 4, wherein Said two or more types of composite carbon materials consist of two types of composite graphite material powder whose compound ratio is 0.1-0.25, and composite graphite material powder whose coverage ratio is 0.01-0.05. The method of claim 4, wherein A lithium polymer battery, wherein the amount of the composite graphite material powder having a coverage ratio of 0.1 or less to the amount of the composite graphite material powder having a coverage ratio of 0.03 to 0.3 is 50% or less by weight ratio. The method of claim 6, The weight ratio is 10-30% the lithium polymer battery. A carbon material powder as a negative electrode active material, wherein a low crystalline carbon material adheres to the surface of a high crystalline graphite powder and is a precursor of a chemically crosslinked gel to a negative electrode including at least two or more composite graphite material powders having different physical properties. A method of manufacturing a lithium polymer battery, comprising the step of impregnating with and gelling a precursor to obtain an electrolyte.