KR20080112142A - Lithium secondary battery - Google Patents

Abstract

A high-capacity secondary lithium battery with excellent productivity is provided to be used for the power source of a mobile unit, vehicle, bicycle and autobicycle. A high-capacity secondary lithium battery containing a negative electrode(2) is formed with a negative layer containing a carbonaceous material at one side or both side of a negative collector. The negative layer has a density of 1.7 g / cm^3 or greater and a diameter measured by a mercury porosimeter of 0.9mum. The carbonaceous material comprises a carbonaceous material (A) having D50 of 15-25 mum and the compressive strength of 16 MPa or more and a carbonaceous material (B) having D50 of 15-25 mum and the compressive strength of 15 MPa or less.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

The present invention relates to a lithium secondary battery having a high capacity and excellent productivity.

Since lithium secondary batteries have high voltage and high energy density, there is a tendency to increase demand as driving power sources for portable devices and the like. At present, as a negative electrode active material of this lithium ion secondary battery, a carbonaceous material having a large capacity and good reversibility is mainly used.

The current lithium secondary battery is required to have a higher capacity according to the improvement of the device to be applied. Therefore, the examination which improves electrode density, fills an active material, and enlarges the capacity density of a battery is performed (for example, patent document 1). As disclosed in Patent Literature 1, by increasing the electrode density, high capacity of the lithium secondary battery can be achieved.

[Patent Document 1]

Japanese Patent Application Laid-Open No. 2007-95402

By the way, in the lithium secondary battery disclosed by patent document 1, as a negative electrode, the porous negative electrode mixture layer containing active materials, such as a carbonaceous material, binder, etc. is an electrical power collector. The one formed on the surface of the body is used.

The lithium secondary battery is, for example, a laminated electrode body in which a negative electrode as described above and a positive electrode (for example, a positive electrode having a porous positive electrode mixture layer) are stacked on each other via a separator, or After the spirally wound wound electrode body is further configured, and after the electrode body is loaded in the exterior body, the nonaqueous electrolyte is injected into the exterior body in the electrolyte injection step, and the negative electrode mixture layer of the negative electrode or the positive electrode mixture layer of the positive electrode, It is manufactured through the process of infiltrating electrolyte into the empty hole of a separator, and then sealing an exterior body.

By the way, in the electrode which densified for the high capacity of a battery, since the penetration rate of a nonaqueous electrolyte liquid becomes slow, it may take time in the electrolyte solution pouring process at the time of manufacturing a battery, and may reduce the production speed of a battery.

This invention is made | formed in view of the said situation, and the objective is to provide the lithium secondary battery which is high capacity and was excellent in productivity.

The lithium secondary battery of the present invention, which has achieved the above object, has a negative electrode mixture layer in which a negative electrode mixture layer containing a carbonaceous material is formed on one or both surfaces of a negative electrode current collector, wherein the negative electrode mixture layer Silver is 1.7 g / cm <3> or more, and the mode of the pore diameter measured by a mercury porosimeter is 0.9 micrometer or more, It is characterized by the above-mentioned.

In the lithium secondary battery of the present invention, high capacity is achieved by setting the density of the negative electrode mixture layer containing the carbonaceous material to 1.7 g / cm 3 or more.

On the other hand, when the negative electrode mixture layer has a high density of 1.7 g / cm 3 or more, the empty pores of the porous negative electrode mixture layer decreases, so that the non-aqueous electrolyte solution (hereinafter simply referred to as 'electrolyte solution') for the negative electrode mixture layer is reduced. Penetration rate is reduced. Therefore, in the lithium secondary battery of the present invention, the pore size of the negative electrode mixture layer is made 0.9 m or more in the negative electrode mixture layer to increase the pore of the negative electrode mixture layer, thereby increasing the penetration rate of the electrolyte solution into the negative electrode mixture layer, The shortening of the electrolyte solution injection | pouring process at the time of manufacture is achieved, and the productivity is improved.

According to the present invention, a lithium secondary battery having high capacity and excellent productivity can be provided.

The negative electrode of the lithium secondary battery of the present invention is formed by forming a negative electrode mixture layer containing a carbonaceous material as a negative electrode active material on one side or both sides of a negative electrode current collector, but the negative electrode mixture layer is carbon which is a negative electrode active material. In addition to the quality material, it is a porous layer containing a binder etc. which bind this.

The negative electrode mixture layer has a density of 1.7 g / cm 3 or more, preferably 1.73 g / cm 3 or more. In the battery of the present invention, by making the negative electrode mixture layer high density in this way, the amount of charge in the negative electrode mixture layer of the carbonaceous material as the active material is increased to achieve high capacity of the negative electrode, that is, high capacity of the battery. In addition, the density of the negative electrode mixture layer is preferably 1.85 g / cm 3 or less, because if too high, metallic lithium precipitates on the surface of the negative electrode, causing deterioration of charge / discharge capacity and charge / discharge cycle characteristics. More preferably 1.82 g / cm 3 or less.

In addition, the density of the negative mix layer demonstrated in this specification is a value measured by the following method. The negative electrode is cut out to a predetermined area, the mass thereof is measured using a minimum scale 1 mg electronic balance, and the mass of the negative electrode mixture layer is calculated by subtracting the mass of the current collector. On the other hand, all the thicknesses of the negative electrode were measured at 10 points by a micrometer with a minimum scale of 1 μm, and the volume of the negative electrode mixture layer was calculated from the average value of the values obtained by subtracting the thickness of the current collector from these measured values. do. The density of the negative electrode mixture layer is calculated by dividing the mass of the negative electrode mixture layer by the volume.

Moreover, the mode of the pore diameter by a mercury porosimeter of the negative electrode mixture layer is 0.9 micrometer or more, Preferably it is 0.92 micrometer or more. In the present invention, by increasing the pore diameter of the negative electrode mixture layer while increasing the negative electrode mixture layer as described above, the penetration rate of the electrolyte solution is increased, thereby improving battery productivity. The larger the pore diameter in the negative electrode mixture layer is, the more preferable the larger the value is. However, in the present invention, since the density of the negative electrode mixture layer is 1.7 g / cm 3 or more, the upper limit of the mode of the pore diameter is also limited. . Specifically, about 5 micrometers becomes an upper limit of the mode of pore diameter, for example.

In addition, the mode of the pore diameter of the negative electrode material mixture layer described in the present specification uses a mercury porosimeter ("Poresizer 9310" manufactured by Micromeritic) to cut the negative electrode into 2 x 4 cm, and directly to the cell. In the log differential pore volume distribution curve calculated by the measurement, the pore diameter (pore diameter) at the maximum peak is meant.

As described above, the negative electrode mixture layer having a high density and having a large pore diameter can be formed by adopting the following configuration, for example.

In the lithium secondary battery of the present invention, a carbonaceous material is used as the negative electrode active material, but at least the following carbonaceous material (A) and carbonaceous material (B) are preferably used as the carbonaceous material. These carbonaceous materials do not contain lithium at the time of negative electrode production, but when they act as negative electrode active materials, they are in a state containing lithium by chemical means, electrochemical means or the like.

The carbonaceous material (A) has a D ₅₀ of preferably 15 µm or more, more preferably 17 µm or more, preferably 25 µm or less, more preferably 23 µm or less, and a compressive strength, preferably Is at least 16 MPa, more preferably at least 18 MPa.

The carbonaceous material (B) has a D ₅₀ of preferably 15 µm or more, more preferably 16 µm or more, preferably 25 µm or less, more preferably 22 µm or less, and a carbonaceous material. It is preferable to have a compressive strength lower than (A), It is more preferable that compressive strength is 15 MPa or less, It is more preferable that it is 14 MPa or less.

By combining the carbonaceous material (A) and the carbonaceous material (B) as described above to form a negative electrode mixture layer, the pore diameter is greatly increased as indicated by the mode of the above pore diameters while maintaining the high density as described above. can do.

The negative electrode which concerns on this invention prepares the paste mixture composition of the paste form or slurry which contains said carbonaceous material, a late binder, etc., for example, and this is an electrical power collector, After apply | coating to and drying it, it is made through the process of performing a press process and adjusting the thickness and density of a negative electrode mixture layer. When a high press pressure is added in order to increase the density of the negative electrode mixture layer during the press treatment, deformation of the carbonaceous material in the negative electrode mixture layer occurs, the filling proceeds, the density of the negative electrode mixture layer increases, and It is thought that the pore diameter becomes small.

As described above, however, the negative electrode mixture layer is formed by combining the high-compressive carbonaceous material (A) and the lower-compressive carbonaceous material (B) to form a negative electrode mixture layer. By controlling the degree of deformation and filling, the density of the negative electrode mixture layer can be increased while keeping the pore diameter large.

If the compressive strength of the carbonaceous material (A) is too small, it may be difficult to increase the mode of the pore diameter as described above. In addition, the compressive strength of the carbonaceous material (A) is preferably 50 MPa or less, and more preferably 30 MPa or less. By using the carbonaceous material (A) of such compressive strength, not only can the battery be increased in capacity or productivity, but also the load characteristics of the battery can be improved.

Further, the compressive strength of the carbonaceous material (B) is more preferably 3 MPa or more, more preferably 5 MPa or more, as described above, more preferably 15 MPa or less, and still more preferably 14 MPa or less. . When the compressive strength of the carbonaceous material (B) is too small, it may be difficult to increase the mode of the pore diameter as described above, and when too large, the load characteristics of the battery may decrease. For example, when setting the density of a negative electrode mixture layer relatively low, even if the compressive strength is used for a carbonaceous material (B), the mode of pore diameter can be enlarged easily as mentioned above. On the other hand, when the density of the negative electrode mixture layer is set high, it is preferable to use a relatively high compressive strength for the carbonaceous material (B), whereby the mode of the pore diameter can be easily enlarged as described above. Become.

The compressive strengths of the carbonaceous material (A) and the carbonaceous material (B) described in the present specification are each obtained by extracting arbitrary ten particles, and using a Shimadzu Seisakusho microcompression testing machine "MCT-W500". Particles were placed on the lower pressure plate one by one, and a compression test was performed by pressing the upper pressure plate with a diameter of 50 μm, where St = 2.8 P / πd ² where St: compressive strength (MPa) and P: fracture test force ( N), d: particle diameter (µm)] is a mean value calculated from the compressive strength of each particle and calculated from all these measured values.

In addition, D ₅₀ of the carbonaceous material (A) and the carbonaceous material (B) described in the present invention is dispersed by performing a sonication process by putting a predetermined amount of the carbonaceous material in a liquid in which a surfactant is added to water. 50% diameter in the integral ratio based on the volume when the integrated volume is obtained from particles having a small particle size distribution measured by a laser diffraction scattering type particle size distribution measuring device (MICROTRAC, manufactured by Honeywell) using the dispersion liquid. Value [median diameter].

In the negative electrode mixture layer, as the ratio of the carbonaceous material (A) and the carbonaceous material (B), when the total of the carbonaceous material (A) and the carbonaceous material (B) is 100 mass%, the carbonaceous material (A ) Is preferably at least 3 mass%, more preferably at least 10 mass% (that is, the carbonaceous material (B) is preferably at most 97 mass%, more preferably at most 90 mass%). If the proportion of the carbonaceous material (A) is too small, the effect of using the carbonaceous material (A) (particularly, the effect of increasing the pore diameter of the negative electrode mixture layer) may be reduced. Moreover, when the ratio of the carbonaceous material (A) in the sum total of a carbonaceous material (A) and a carbonaceous material (B) is too large, it will become difficult to enlarge the density of a negative mix layer. Therefore, when the total of carbonaceous material (A) and carbonaceous material (B) is 100 mass%, it is preferable that carbonaceous material (A) is 80 mass% or less, and it is more preferable that it is 60 mass% or less [that is, , The carbonaceous material (B) is preferably 20% by mass or more, and more preferably 40% by mass or more].

As the carbonaceous material (A), Raman (Raman) the ratio R of the peak value of the intensity of 1580cm ^-1 to 1360cm ^-1 to the intensity of the peak by spectroscopy, preferably 0.15 or more, more preferably from 0.2 bar The above is preferable, Preferably it is 1.5 or less, More preferably, it is 1 or less. When using the carbonaceous material (A) which satisfy | fills the said R value, the time required for the electrolyte solution pouring process at the time of battery manufacture can be further reduced. Although it is not clear about the said reason, the carbonaceous material (A) which satisfy | fills the said R value is considered that affinity with the electrolyte solution of the surface is favorable, and it is guessed whether this is related. The time-cutting effect of the electrolyte solution pouring step by the carbonaceous material (A) satisfying the above R value is obtained when the ratio of the carbonaceous material (A) and the carbonaceous material (B) satisfies the above suitable values. Especially noticeable.

In addition, R value demonstrated in this specification is a Raman Spectrum obtained using "T-5400" by a Ramanaor company (light source: Ar laser, wavelength: 514.5 nm, laser power: 1 mW). in is a value calculated from the intensity of the peak of the obtained 1360cm ^-1 and 1580cm ^-1 peak intensity.

As a carbonaceous material (B) which has said compressive strength, natural graphite, artificial graphite, etc. are mentioned, for example.

Moreover, as carbonaceous material (A) which has said compressive strength and satisfy | fills said R value, for example, besides the carbonaceous material which has a hard-layered structure, graphite of natural graphite, artificial graphite, etc. By attaching an amorphous carbonaceous material to part or all of the surface, a carbonaceous material having a different crystallinity between the surface and the central portion may be mentioned. As a method of attaching an amorphous carbonaceous material to the surface of graphite, for example, an amorphous carbonaceous material formed by thermal decomposition of a gas of hydrocarbons at a relatively low temperature (for example, 800 to 1200 ° C) is used. A method of depositing on the surface of graphite; A method of forming amorphous carbonaceous material on the surface of graphite by attaching a pitch, tar, a polymer compound, etc. to the surface of graphite, and then baking at a relatively low temperature (for example, 800 to 1300 ° C). ; Etc. can be illustrated.

As the negative electrode active material, only the above carbonaceous material (A) and carbonaceous material (B) may be used, but other carbonaceous materials (carbon not corresponding to carbonaceous material (A) and carbonaceous material (B)) Quality materials] may also be used in combination. When using the said other carbonaceous material, from the viewpoint of ensuring the above-mentioned effect by using together a carbonaceous material (A) and a carbonaceous material (B) more reliably, out of the whole carbonaceous material used for a negative electrode, It is preferable to make the said other carbonaceous material into 30 mass% or less, and it is more preferable to set it as 20 mass% or less.

The negative electrode, as described above, adds a binder to the carbonaceous material that is the negative electrode active material, and if necessary, adds a solvent to prepare a negative electrode mixture-containing composition (paste, slurry, and the like), which is prepared on one side of the current collector or After apply | coating to both surfaces and drying, it manufactures through the process of forming a negative mix layer, adjusting thickness and density by a press process. As a solvent used for a negative electrode mixture containing composition, For example, Water; Organic solvents such as N-methyl-2-pyrrolidone (N-methyl 2-pyrroridone NMP), toluene and xylene; Etc. can be mentioned. In preparation of the negative electrode mixture-containing composition, the binder is preferably mixed with solid particles such as an anode active material, using a solution previously dissolved in an organic solvent or water or a dispersed suspension.

As the binder used for the negative electrode, for example, a polyvinylidene fluoride polymer, a rubber polymer, a cellulose polymer and the like are suitable. Only 1 type may be used for these binders and they may use 2 or more types together.

As a fluorine-containing monomer group for synthesize | combining said polyvinylidene fluoride system polymer, Vinylidene fluoride; A mixture of vinylidene fluoride and another monomer, the monomer mixture containing at least 80% by mass of vinylidene fluoride; Etc. can be mentioned. Examples of the other monomers include vinyl fluoride, trifluoroethylene, trifluorochloro ethylene, tetra fluoroethylene, and hexafluoropropylene. fluoropropylen, fluoroalkylvinylether, and the like.

As said rubber type polymer, a styrene butadiene rubber SBR, ethylene propylene diene rubber, a fluoro rubber etc. are mentioned, for example. Moreover, as said cellulose polymer, For example, carboxy methyl cellulose CMC, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose (hydroxylethyl methyl cellulose), hydroxypropyl methyl cellulose, and the like.

As a method of apply | coating a negative electrode mixture containing composition to an electrical power collector, various well-known coating methods, including an extrusion coater, a reverse coater, a doctor blade, an applicator, etc. are mentioned, for example. Can be adopted.

As the negative electrode current collector, for example, metallic conductive materials such as aluminum, stainless steel, nickel, titanium, copper, and the like, and a net, punched metal, and foam metal (foam metal), foil processed into plate shape, etc. are used. It is preferable that the thickness of a negative electrode electrical power collector is 5-12 micrometers, for example.

The thickness of the negative electrode mixture layer formed on the surface of the negative electrode current collector is preferably the thickness after drying, for example, 40 to 160 µm. Moreover, when making a negative electrode mixture layer contain a carbonaceous material and a binder, for example, it is preferable to make content of a negative electrode active material into 90-99.8 mass%, for example.

When the negative electrode mixture layer contains, for example, a carbonaceous material and a binder, the content of the binder is preferably, for example, 0.2% by mass or more, and preferably 0.5% by mass or more. More preferably, it is preferable to set it as 10 mass% or less, and it is more preferable to set it as 3 mass% or less. If the content of the binder is too small, the mechanical strength of the negative electrode mixture layer is insufficient, and the negative electrode mixture layer may be peeled off from the current collector. Moreover, when there is too much content of a binder, there exists a possibility that the amount of active materials (amount of carbonaceous material) in a negative electrode material mixture layer may decrease, and the high capacity | capacitance effect of the battery in this invention may become small.

In the press treatment at the time of producing the negative electrode, if the density of the negative electrode mixture layer can be 1.7 g / cm 3 or more, the condition is not particularly limited. For example, the linear pressure at the time of pressing is 15. It is preferable to set it as 500-500 kg / cm.

The lithium secondary battery of this invention should just have said negative electrode, and does not restrict | limit especially about other structure / structure, The structure / structure employ | adopted by the conventionally well-known lithium secondary battery can be applied.

As a positive electrode, what is formed by forming the positive electrode mixture layer containing a positive electrode active material, an electron conduction adjuvant, a binder, etc. on one or both surfaces of a positive electrode electrical power collector can be used, for example. Examples of the positive electrode active material include lithium cobalt oxide, lithium nickel cobalt oxide, lithium nickel oxide, lithium manganese oxide, and nickel cobalt manganese lithium. Cobalt manganese oxide), and the like, nickel compound, cobalt, manganese compounds of each of the compounds substituted with other elements, such as an olivine compound, such as a positive electrode active material used in conventional lithium secondary batteries in particular Can be used without limitation. Only 1 type may be used for these positive electrode active materials, and 2 or more types may be used together.

As an electron conduction aid used for a positive electrode, carbonaceous materials, such as carbon black, acetylene black, ketjen black, graphite, a carbon fiber, etc. Is preferred. Among the carbonaceous materials described above, acetylene black, Ketjen black, and graphite are particularly preferable in terms of the added amount, the effect of conductivity, and the manufacturability of the positive electrode mixture layer-containing composition (to be described later).

As a binder used for a positive electrode, polyvinylidene fluoride type polymer (polymer of the fluorine-containing monomer group containing 80 mass% or more of vinylidene fluoride which is a main component monomer), rubber type polymer, etc. are used suitably, for example. Only 1 type may be used for these binders and they may use 2 or more types together. In addition, the binder may be provided in the form of a solution dissolved in a dispersion or a solvent dispersed in a dispersion medium, for example, in a powder form.

As a fluorine-containing monomer group for synthesize | combining said polyvinylidene fluoride system polymer, Vinylidene fluoride; Monomer mixtures containing at least 80% by mass of vinylidene fluoride as a mixture of vinylidene fluoride and other monomers; Etc. can be mentioned. As said other monomer, vinyl fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, fluoroalkyl vinyl ether, etc. are mentioned, for example.

As said rubber type polymer, styrene butadiene rubber (SBR), ethylene propylene diene rubber, fluororubber etc. are mentioned, for example.

The content of the positive electrode active material in the positive electrode mixture layer is preferably 96% by mass or more, more preferably 97.0% by mass or more, preferably 99.4% by mass or less, and more preferably 98.0% by mass or less.

The content of the carbonaceous material as the electron conduction aid in the positive electrode mixture layer is, for example, preferably 0.5% by mass or more, more preferably 0.8% by mass or more, preferably 18% by mass or less, and more preferably. Preferably it is 15 mass% or less. If the amount of electron conduction adjustment in the positive electrode mixture layer is too small, the electron conductivity of the positive electrode may become insufficient, and the load characteristics of the battery may decrease. If the amount of electron conduction preparation in the positive electrode mixture layer is too large, the amount of active material charged in the positive electrode mixture layer may be reduced. Since it reduces, there exists a possibility that the high capacity | capacitance effect of the battery in this invention may become small.

The content of the binder in the positive electrode mixture layer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, preferably 5% by mass or less, and more preferably 2% by mass or less. If the content of the binder in the positive electrode mixture layer is too small, the mechanical strength of the positive electrode mixture layer may be insufficient, and the positive electrode mixture layer may peel off from the current collector. If the content of the binder in the positive electrode mixture layer is too large, There is a concern that the amount of the active material decreases and the effect of increasing the capacity of the battery in the present invention is reduced.

The positive electrode having the positive electrode mixture layer is, for example, a positive electrode mixture-containing composition (paste, slurry, etc.) prepared by dispersing the above positive electrode active material, an electron conduction aid, a binder, and the like in a solvent (some components may be dissolved). After apply | coating to one side or both surfaces of an electrical power collector, and drying, it can produce by pressing as needed and adjusting the thickness and density of a positive mix layer. In addition, the manufacturing method of the positive electrode which concerns on this invention is not limited to this, You may employ | adopt another method. As a solvent which can be used for a positive electrode mixture containing composition, it is water; Organic solvents such as NMP, toluene and xylene; Can be mentioned.

As a method of apply | coating a positive electrode mixture containing composition to the surface of a positive electrode electrical power collector, the various methods illustrated as a method of apply | coating said negative electrode mixture containing composition to the surface of a negative electrode electrical power collector can be employ | adopted.

As the positive electrode current collector, for example, a mesh, a punched methyl, a foam metal, a foil processed into a plate shape, or the like of a metal conductive material such as aluminum, stainless steel, or titanium is used. It is preferable that the thickness of a positive electrode electrical power collector is 8-16 micrometers, for example.

Moreover, it is preferable that the thickness of the positive mix layer formed on the surface of a positive electrode collector is 40-150 micrometers in thickness after drying, for example.

It is preferable that it is 3.75 g / cm <3> or more, and, as for the density of a positive mix layer, it is more preferable that it is 3.8Og / cm <3> or more. By using the positive electrode having such a high-density positive electrode mixture layer and the negative electrode having the high-density negative electrode mixture layer in combination, it is possible to further increase the battery capacity. However, when the density is too large also in the positive electrode mixture layer, it becomes difficult to get wet with the electrolytic solution and the productivity of the battery may decrease, so that the density is preferably 4.1 g / cm 3 or less. The density of the positive mix layer can be adjusted by adjustment of the press conditions in the said press process at the time of positive electrode manufacture, for example. The density of the positive mix layer described here is a value measured by the same measuring method as the density of the said negative mix layer.

The lithium ion secondary battery of the present invention includes, for example, a laminated electrode body laminated through a separator between the positive electrode and the negative electrode and a wound electrode body wound around the laminated electrode body in a spiral shape. It is manufactured through the process of inserting into a battery case made of aluminum, an aluminum alloy, nickel plating iron, stainless steel, etc., inject | pouring electrolyte solution, and then sealing. In addition, in the battery of the present invention, a conventionally known explosion-proof mechanism for discharging the gas generated inside the battery to the outside of the battery in a step of raising to a certain pressure and preventing the battery from rupturing under high pressure is introduced.

There is no restriction | limiting in particular about the separator interposed between an anode and a cathode, A conventionally well-known thing can be applied. For example, a microporous polyethylene film, a microporous polypropylene film, a polyethylene polypropylene composite film, or the like having a thickness of 5 to 30 µm and a porosity of 30 to 70% is suitably used.

As electrolyte solution, what melt | dissolved electrolyte, such as lithium salt, in the organic solvent is used. As the electrolyte, for example, in general formula LiXF _n ( _wherein X is P, As, Sb or B, n is 6 when X is P, As or Sb, and 4 when X is B). The inorganic lithium salt, fluorine-containing organic lithium imide salt, etc. which are shown are mentioned. These electrolytes can be used independently, respectively and may use 2 or more types together.

-부티로락톤(

-butyrolactone), 디에틸카보네이트(diethyl carbonate), 디메틸카보네이트(dimethyl carbonate), 에틸메틸카보네이트(ethyl methyl carbonate) 등의 에스테르(ester)류 ; 술포란(sulfolane) 등의 함황화합물 ; 불화 비환식 카보네이트(fluorated acyclic carbonate(트리플루오로메틸에틸 카보네이트(trifluromethyl ethyl carbonate 등), 불화 환식 카보네이트 fluorated cyclic carbonate(퍼플루오로에틸렌 카보네이트 perfluoroethylene carbonate 등), 불화 비환식 에테르 fluorated ether(퍼플루오로부틸메틸에테르 perfluorobuty methyl ether 등)등의 함불소 용매 ; 를 들 수 있다. 이들 유기용매는, 각각 단독으로 사용해도 되고, 2종 이상을 함유하는 혼합 용매로서 사용하여도 된다. 상기 유기용매 중에서도, 에테르류는, 고전압하에서도 양극 활물질과의 반응성이 적고 저장 특성을 향상시키는 효과가 크기 때문에 바람직하다. 충전시의 전해액의 안정성 향상의 관점에서, 이 에스테르류는, 모든 전해액 용매 중 20 체적% 이상인 것이 바람직하다. Although it does not specifically limit as an organic solvent used for dissolving the said electrolyte, For example, 1, 2- dimethoxyethane (1, 2-dimethoxyethane), 1, 2- diethoxyethane (1, 2-diethoxyethane) ), Ethers such as dimethoxypropane, 1, 3-dioxolane, 1, 3-dioxolane, tetrahydrofuran and 2-methyl tetrahydrofuran; Propylene carbonate, ethylene carbonate,

Butyrolactone (

esters such as butyrolactone, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; Sulfur-containing compounds such as sulfolane; Fluorinated acyclic carbonates (such as trifluoromethylethyl carbonate), fluorinated cyclic carbonates (such as perfluoroethylene carbonate), fluorinated acyclic ethers (perfluorobutyl) Fluorine-containing solvents, such as methyl ether perfluorobuty methyl ether etc. These organic solvents may be used independently, respectively, and may be used as a mixed solvent containing 2 or more types. The esters are preferable because of their low reactivity with the positive electrode active material and a high effect of improving storage characteristics even under high voltage, and from the viewpoint of improving the stability of the electrolyte solution at the time of filling, the esters are not less than 20% by volume in all the electrolyte solvents. desirable.

The concentration of the electrolyte in the electrolyte is preferably 0.4 to 1.8 mol / l, and particularly preferably 0.6 to 1.6 mol / l, even if two or more different electrolytes are contained.

Since the lithium ion secondary battery of the present invention has high productivity in addition to excellent productivity, the lithium ion secondary battery utilizes such characteristics to utilize conventionally known lithium secondary batteries including power supplies for mobile devices, power supplies for automobiles, bicycles, motorcycles, and the like. It can be used suitably for the various uses to which a battery is employ | adopted.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail based on an Example. However, the following examples do not limit the present invention.

In addition, the compressive strengths of the carbonaceous material (A) and the carbonaceous material (B) used in the present Example were compressed by one of the above-described methods for each of 10 particles having a diameter of 20 µm extracted using a microscope. It is the value which measured intensity and averaged all the measured values.

(Example 1)

<Production of Cathode>

As the negative electrode active material, D ₅₀ is 17 µm, graphite has a compressive strength of 20 MPa, and R is 0.34 (carbonaceous material (A)), and D ₅₀ is 21 µm, has a compressive strength of 7 MPa, and R is 0.14. The carbonaceous material (B) was mixed with a carbonaceous material (A): carbonaceous material (B) = 40:60 (mass ratio). Moreover, the suspension of SBR and CMC aqueous solution of 15 mass% concentration were used for the binder. SBR suspension and CMC aqueous solution were prepared so that solid content might be 1 mass part (that is, 2 mass parts as whole binder solid content), respectively, and it mixed with 98 mass parts of said active materials, and prepared the negative mix mixture containing composition. The negative electrode mixture-containing composition is uniformly applied to both surfaces of a copper foil having a thickness of 8 µm using an applicator, and then rolled by a roll press to apply a negative electrode mixture layer to both surfaces of the current collector. And a sheet-shaped negative electrode of 125 micrometers in total thickness was produced. The negative electrode mixture layer density of the negative electrode thus produced was 1.75 g / cm 3, and the mode of pore diameter measured by a mercury porosimetry was 1.1 μm.

<Production of Anode>

As active material, a mean particle size of 13 ㎛ of lithium cobalt oxide (a) and the mean particle size of 12 ㎛ of _{LiNi 0 .81 Co 0 .16 Al 0} .03 O 2 (b), (a) / (b ) Was mixed so that the ratio was 0.25 (mass ratio). A positive electrode mixture-containing composition was prepared using 98 parts by mass of this active material mixture, 1 part by mass of acetylene black as an electron conduction aid, 1 part by mass of polyvinylidene fluoride (PVDF) as a binder, and NMP as a solvent. Preparation of the positive electrode mixture-containing composition was performed by dissolving PVDF in NMP in advance, adding the active material mixture and acetylene black to this solution, adding NMP again while stirring, and adjusting the viscosity while dispersing sufficiently. The positive electrode mixture-containing composition was uniformly coated on both sides of an aluminum foil having a thickness of 15 μm using an applicator, and then rolled by a roll press to have a positive electrode mixture layer on both sides of the current collector, and the overall thickness. The sheet-like positive electrode of 130 micrometers was obtained. The positive electrode mixture layer density of the positive electrode thus produced was 3.85 g / cm 3.

<Assembly of battery>

A lead body is provided in the positive electrode and the negative electrode, and these are laminated through a separator made of a microporous polyethylene polypropylene composite film having a thickness of 14 μm, wound in a spiral shape, and then pressurized to form a flat shape. The wound electrode body of was obtained. After the insulating tape was attached to the wound electrode body, the outer dimension was inserted into a battery case of a rectangular shape (angular tubular shape) having a height of 50 mm × width of 34 mm × thickness of 4 mm to weld the lead body and the battery. Laser welding of the lid | cover for sealing to the opening edge part of the case was performed. After that, the electrolyte was injected into the battery case from the electrolyte injection opening provided in the sealing cover plate, and the electrolyte was sufficiently infiltrated into the separator or the like, and the electrolyte injection opening was sealed to be in a sealed state. Further, the electrolytic solution contains ethylene carbonate and methyl ethyl carbonate in 1: 2 (volume ratio) mixed solvent, was used by dissolving LiPF ₆ at a concentration of 1.0 mol / l. Thereafter, preliminary charging and aging were performed to obtain a rectangular lithium secondary battery having an appearance shown in FIG. 2 with the structure shown in FIG. 1.

1 and 2, the positive electrode 1 and the negative electrode 2 are wound in a spiral shape through the separator 3 as described above, and then pressurized to have a flat shape and wound in a flat shape. As the electrode body 6, it is housed together with the electrolyte solution in a rectangular battery case 4. However, in FIG. 1, in order to avoid the complicated, the metal foil, electrolyte solution, etc. which are used as an electrical power collector used in manufacture of the positive electrode 1 and the negative electrode 2 are abbreviate | omitted.

The battery case 4 is made of aluminum alloy to constitute a battery packaging material, and the battery case 4 also serves as a positive electrode terminal. And the insulator 5 which consists of polyethylene sheets is arrange | positioned at the bottom part of the battery case 4, and from the wound electrode body 6 of the flat shape which consists of the positive electrode 1, the negative electrode 2, and the separator 3, The positive electrode lead 7 and the negative electrode lead 8 connected to one end of each of the positive electrode 1 and the negative electrode 2 are drawn out. In addition, an aluminum alloy encapsulation cover plate 9 for enclosing the opening of the battery case 4 is provided with a terminal 11 made of stainless steel via a polypropylene insulating packing 10. The terminal 11 is provided with a stainless steel lead plate 13 via an insulator 12.

And the cover plate 9 is inserted in the opening part of the battery case 4, and the opening part of the battery case 4 is enclosed by welding the junction part of both, and the inside of a battery is sealed. In addition, in the battery of FIG. 1, an electrolyte injection hole 14 is provided in the cover plate 9, and the electrolyte injection hole 14 is weld-sealed by, for example, laser welding in a state where a sealing member is inserted. The sealing property of the battery is ensured (hence, in the battery of FIGS. 1 and 2, the electrolyte injection hole 14 is actually represented as the electrolyte injection hole 14 and the sealing member, for ease of explanation. have]. In addition, the cover plate 9 is provided with an explosion-proof vent 15.

In the battery of this Example 1, the battery case 4 and the cover plate 9 function as the positive electrode terminal by directly welding the positive electrode lead body 7 to the cover plate 9, and lead the negative electrode lead body 8 to the lead. Although the terminal 11 functions as a negative electrode terminal by welding to the plate 13 and conducting the negative electrode lead body 8 and the terminal 11 via the lead plate 13, the material of the battery case 4 In some cases, the yin and yang may be reversed.

Fig. 2 is a perspective view schematically showing the appearance of the battery shown in Fig. 1, and Fig. 2 is shown for the purpose of showing that the battery is a rectangular battery. Fig. 2 schematically shows a battery. Only specific components of the battery are shown. 1, the part of the inner peripheral side of an electrode body is not made into the cross section.

(Example 2)

The carbonaceous material (A), which is a negative electrode active material, was graphite having a D ₅₀ of 16 μm, a compressive strength of 25 MPa, and an R value of 0.48, and a carbonaceous material (B) of D ₅₀ of 22 μm and a compressive strength. A lithium secondary battery was produced in the same manner as in Example 1 except that each of 14 MPa and graphite having an R value of 0.13 was changed. Moreover, the negative electrode mixture layer which concerns on the lithium secondary battery of Example 2 had a density of 1.72 g / cm <3>, and the mode of the pore diameter measured with the mercury porosimeter was 1.6 micrometers.

(Example 3)

The carbonaceous material (A) as the negative electrode active material is graphite having a D ₅₀ of 18 μm, a compressive strength of 16 MPa, and an R value of 0.14. The carbonaceous material (B) is a D ₅₀ of 20 μm and a compressive strength. A lithium secondary battery was produced in the same manner as in Example 1 except that each of 4 MPa and R having a R value of 0.12 was changed. Moreover, the negative electrode mixture layer which concerns on the lithium secondary battery of Example 3 had a density of 1.77 g / cm <3>, and the mode of the pore diameter measured with the mercury porosimeter was 0.9 micrometer.

(Example 4)

The carbonaceous material (A), which is the negative electrode active material, was graphite having a D ₅₀ of 20 μm, a compressive strength of 57 MPa, and an R value of 1.5, and a carbonaceous material (B) having a D ₅₀ of 21 μm and a compressive strength. A lithium secondary battery was produced in the same manner as in Example 1 except that 7 MPa and graphite having an R value of 0.14 were changed. Moreover, the negative electrode mixture layer which concerns on the lithium secondary battery of Example 4 had a density of 1.70 g / cm <3>, and the mode of the pore diameter measured with the mercury porosimeter was 1.9 micrometers.

(Example 5)

The carbonaceous material (A), which is the negative electrode active material, was changed to graphite having a D ₅₀ of 17 µm, a compressive strength of 20 MPa, and an R value of 0.34, and further, a mixing ratio of the carbonaceous material (A) and the carbonaceous material (B). The lithium secondary battery was produced like Example 1 except having changed to carbonaceous material (A): carbonaceous material (B) = 30: 70 (mass ratio). Moreover, the negative electrode mixture layer which concerns on the lithium secondary battery of Example 5 had a density of 1.70 g / cm <3>, and the mode of the pore diameter measured with the mercury porosimeter was 1.3 micrometers.

(Comparative Example 1)

The carbonaceous material (A), which is a negative electrode active material, was graphite having a D ₅₀ of 19 μm, a compressive strength of 16 MPa, and an R value of 0.14, and a carbonaceous material (B) having a D ₅₀ of 20 μm and a compressive strength. A lithium secondary battery was produced in the same manner as in Example 1 except that 3 MPa and R were 0.12 graphite, respectively. The negative electrode mixture layer of the lithium secondary battery of Comparative Example 1 had a density of 1.77 g / cm 3 and a mode of pore diameter measured by a mercury porosimeter of 0.8 μm.

(Comparative Example 2)

The carbonaceous material (A) serving as the negative electrode active material is graphite having a D ₅₀ of 20 μm, a compressive strength of 18 MPa, and an R value of 0.16, and a carbonaceous material (B) having a D ₅₀ of 18 μm and a compressive strength. A lithium secondary battery was produced in the same manner as in Example 1 except that 2 MPa and R were 0.11 graphite, respectively. In addition, the negative electrode mixture layer of the lithium secondary battery of Comparative Example 2 had a density of 1.77 g / cm 3 and a mode of pore diameter measured by a mercury porosimeter of 0.7 μm.

(Comparative Example 3)

The carbonaceous material (A), which is a negative electrode active material, was graphite having D ₅₀ of 18 μm, compressive strength of 14 MPa, and R value of 0.15, and the carbonaceous material (B) of D ₅₀ of 20 μm. A lithium secondary battery was produced in the same manner as in Example 1 except that the strengths were 4 MPa and graphite having an R value of 0.12, respectively. In addition, the negative electrode mixture layer of the lithium secondary battery of Comparative Example 3 had a density of 1.78 g / cm 3 and a mode of pore diameter measured by a mercury porosimeter of 0.7 μm.

The permeability of electrolyte solution was measured about the negative electrode produced in Examples 1-5 and Comparative Examples 1-3 by the following method. First, the negative electrode was vacuum-dried at 60 ° C. for 15 hours, followed by further windproofing in a glove box having a dew point of −50 ° C. or lower, and 1 μL of the same electrolyte solution used for producing a lithium secondary battery was dropped on the negative electrode. And the time until electrolyte solution penetrated was measured.

In addition, to the negative electrode used in the lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 3, 1 μL of the electrolyte solution used for the production of the lithium secondary battery was dropped on the negative electrode mixture layer, until the electrolyte was completely soaked. The time of [liquid pouring time (A) of electrolyte solution] was measured. In addition, the injection time (injection time (B) of electrolyte solution) of the electrolyte solution at the time of preparation of the lithium secondary battery of Examples 1-5 and Comparative Examples 1-3 was also measured.

Moreover, the discharge capacity and the load characteristic were evaluated about the lithium secondary batteries of Examples 1-5 and Comparative Examples 1-3. For each battery, when the charge / discharge current was indicated by C, 1000 mA was 1C, a 1C current limiting circuit was provided, and the first charge was performed at a constant voltage of 4.2V, and then discharged to 3.0V at 1C. The charge / discharge was made into the 1st cycle, the charge and discharge was repeated on the same conditions, it discharged to 3.0V at 0.2C in 3rd cycle, and it discharged at 2C in the 4th cycle after charging on the conditions similar to the above. The discharge capacity of the third cycle was taken as the discharge capacity of the lithium secondary battery, and the value (%) obtained by dividing the discharge capacity of the second cycle by the fourth cycle by the discharge capacity of the second cycle by 0.2C at the third cycle was multiplied by 100 (%). It was set as the load characteristic of a secondary battery.

Table 1 shows each of the above evaluation results. In addition, about the injection time (B) of electrolyte solution, it shows by the relative value (%) at the time of the injection time of the battery of the comparative example 1.

Cathode Mixture Layer Lithium secondary battery Density (g / cm 3) Mode of Pore Diameter (μm) Injection time of electrolyte Discharge Capacity (mAh) Load characteristic (%) A (seconds) B (%) Example 1 1.75 1.1 50 55.5 1000 96 Example 2 1.72 1.6 40 52.8 1005 94 Example 3 1.77 0.9 60 57.2 995 96 Example 4 1.70 1.9 30 50 995 89 Example 5 1.70 1.3 45 58.7 995 94 Comparative Example 1 1.77 0.8 100 100 985 95 Comparative Example 2 1.77 0.7 110 104 980 93 Comparative Example 3 1.78 0.7 105 102 980 94

Table 1 shows the following things. The lithium secondary batteries of Examples 1 to 5 have a high capacity, have a short pouring time of the electrolyte solution, and are excellent in productivity. In contrast, in any of the lithium secondary batteries of Comparative Examples 1 to 3, the pouring time of the electrolyte solution was long, and the productivity was inferior.

In addition, in the lithium secondary batteries of Examples 1 to 3 and 5, a carbonaceous material (A) having a more suitable compressive strength is used, and the load characteristics are superior to those of the lithium secondary battery of Example 4.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows typically an example of the lithium secondary battery of this invention, (a) is the top view, (b) the partial longitudinal cross-sectional view,

FIG. 2 is a perspective view of the lithium secondary battery shown in FIG. 1. FIG.

※ Explanation of code for main part of drawing

1 anode 2 cathode

3: separator

Claims (9)

In a lithium secondary battery provided with a negative electrode in which the negative electrode mixture layer containing a carbonaceous material is formed in one or both surfaces of a negative electrode collector, The negative electrode mixture layer has a density of at least 1.7 g / cm 3 and a mode of a pore diameter measured by a mercury porosimeter of 0.9 μm or more. Primary battery. The method of claim 1, As the carbonaceous material at the cathode, a carbonaceous material (A) having a D ₅₀ of 15 to 25 μm, a compressive strength of 16 MPa or more, a carbonaceous material having a D ₅₀ of 15 to 25 μm and a compressive strength of 15 MPa or less Lithium secondary battery characterized by using (B). The method of claim 2, The compressive strength of a carbonaceous material (A) is 50 MPa or less, The lithium secondary battery characterized by the above-mentioned. The method of claim 2, The lithium secondary battery, wherein the amount of the carbonaceous material (A) in the carbonaceous material whole quantity of the negative electrode is 3 to 80 mass%. The method of claim 3, wherein The amount of the carbonaceous material (A) in the carbonaceous material whole quantity of the negative electrode is 3 to 80 mass%, the lithium secondary battery characterized by the above-mentioned. The method of claim 2, Carbonaceous material (A) is the Raman peak intensity for the 1580㎝ (peak) of 1360㎝ ^-1 by spectral analysis ^- the ratio R of the peak intensity value of ^1, a lithium secondary battery, characterized in that 0.15 to 1.5 . The method of claim 3, wherein Carbonaceous material (A) is the Raman peak intensity for the 1580㎝ (peak) of 1360㎝ ^-1 by spectral analysis ^- the ratio R of the peak intensity value of ^1, a lithium secondary battery, characterized in that 0.15 to 1.5 . The method of claim 2, Carbonaceous material (A) is a lithium secondary battery, characterized in that the amorphous carbonaceous material is graphite attached to part or all of the surface. The method of claim 3, wherein Carbonaceous material (A) is a lithium secondary battery, characterized in that the amorphous carbonaceous material is graphite attached to part or all of the surface.

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