JP5017834B2 - Lithium ion secondary battery - Google Patents

Description

The present invention relates to lithium ion secondary batteries.

  Lithium ion secondary batteries are highly expected from the industry to be used as mobile batteries because of their high capacity and high energy density. These batteries have a configuration in which a separator made of an electrically insulating polymer porous film is interposed between a positive electrode layer and a negative electrode layer. In the lithium ion secondary battery, various devices are applied to the separator in order to prevent a problem caused by a high capacity and a high energy density, for example, an increase in temperature due to an internal short circuit of the battery.

  In addition, there are a shutdown characteristic and a short-circuit resistance characteristic required for the separator. The shutdown means that the polymer porous film (separator) is melted when the battery temperature rises due to troubles such as overcharge and external short circuit inside the battery, the holes are closed and the current is cut off. The short circuit means that the temperature of the shut-down battery further increases and the separator is completely melted to form a hole, or the positive electrode layer and the negative electrode layer are brought into contact with each other due to the shrinkage of the separator. When such a short circuit occurs, a large current flows between the positive electrode layer and the negative electrode layer, and the battery generates heat.

  As described above, in a lithium ion secondary battery, it is important to make both shutdown characteristics and short circuit resistance compatible, and the following methods are disclosed.

As a separator for a lithium ion secondary battery of the prior art, a heat-resistant nitrogen-containing aromatic polymer and a ceramic powder are used and have heat resistance. Moreover, thermal runaway can be suppressed by making this separator contain the thermoplastic resin which melts at 260 degrees C or less (for example, refer patent document 1).
JP 2000-30686 A

  However, in the said conventional structure, a separator and a negative electrode layer are not integrated, and by repeating charging / discharging, a negative electrode layer repeats expansion and contraction, and a clearance gap arises between a negative electrode layer and a separator. In such a form, lithium deposits on the negative electrode layer at the end of the charge / discharge cycle, and the reaction area of the negative electrode layer decreases, leading to deterioration of the charge / discharge cycle.

Accordingly, the present invention is to solve the above problems, and its object is to provide a lithium ion secondary batteries.

In order to achieve the above object, the lithium ion secondary battery of the present invention comprises a separator comprising a mixture of at least two kinds of filler A having a melting point of 250 ° C. or higher and filler B having a melting point of 80 ° C. or higher and 120 ° C. or lower. The primary particle diameter of the filler A is 0.1 μm or more and 20 μm or less, and the primary particle diameter of the filler B is 0.01 μm or more and 5 μm or less,
The primary particle size of the filler A is larger than the primary particle size of the filler B, and the separator B contains 5% by weight or more and 25% by weight or less of the filler B with respect to 100% by weight of the filler A. By integrating the negative electrode layer with the negative electrode layer, both shutdown characteristics and short circuit resistance characteristics can be achieved, and the charge / discharge cycle can be improved.

As described above, according to the lithium ion secondary battery of the present invention, that Do is possible to achieve both the shutdown function and resistance to short characteristics.

(Embodiment)
Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram schematically showing a cross section of the lithium ion secondary battery according to Embodiment 1 of the present invention. A separator is formed between the polymer porous membrane and the negative electrode layer, and these batteries may be stacked or wound.

  FIG. 2 is a schematic view of the separator, and a filler having a heat resistant temperature of 250 ° C. or higher is indicated as filler A, and a filler having a melting point of 80 ° C. or higher and 120 ° C. or lower is indicated as filler B. The primary particle diameter of the filler A is 0.1 μm or more and 20 μm or less, and the primary particle diameter of the filler B is 0.01 μm or more and 5 μm or less. Furthermore, the content rate of the said filler B is 5 to 25 weight% with respect to 100 weight% of the said filler A.

  FIG. 3 is a schematic diagram showing a method for manufacturing an electrode plate of a lithium ion secondary battery. A negative electrode layer is formed on the surface of a current collector 2 made of a strip-shaped metal foil fed from a feeding mechanism 1 by a coating device 3. 4 is formed. Next, the separator 6 is formed on the negative electrode layer 4 by the coating device 5, and the volatile components contained in the negative electrode layer 4 and the separator 6 are removed in the drying furnace 7. Similarly, after the negative electrode layer 9 is formed on the surface of the current collector 2 opposite to the surface on which the negative electrode layer 4 and the separator 6 are formed by the coating device 8, the coating device 10 forms the negative electrode layer 9. The separator 11 is formed thereon, and the volatile components contained in the negative electrode layer 9 and the separator 11 are removed by the drying furnace 12. As described above, the negative electrode layers 4 and 9 and the separators 6 and 11 formed on both surfaces of the current collector 2 are pressed by the press device 13 so that the porosity of the negative electrode layer becomes a desired value. 15 is manufactured.

  Here, as the current collector 2, an aluminum foil is generally used for the positive electrode layer and a copper foil is used for the negative electrode layer. However, in the present invention, the current collector 2 is particularly limited as long as it has good conductivity. Instead, for example, another metal foil such as nickel, a metal film deposited on the surface of a polymer film such as PET, or a conductive polymer film may be used.

  The negative electrode layers 4 and 9 are composed of a positive electrode or negative electrode active material capable of occluding and releasing lithium ions, a conductive additive, a binder, a solvent, and the like.

The absorbing and desorbing active material capable of lithium ion, e.g., lithium cobalt acid, lithium nickel acid, composite oxide of lithium and transition metal such as lithium manganate and, FeS, transition metal sulfides such as TiS _2, Examples thereof include organic compounds such as polyaniline and polypyrrole, and these compounds may be partially element-substituted.

  Examples of the negative electrode active material capable of occluding and releasing lithium ions include carbon-based active materials such as graphite and coke, metallic lithium, lithium transition metal nitride, and silicon. The binder is used to bind between the current collector and the active material, and the active material, for example, a fluororesin such as polyvinylidene fluoride and polytetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, and tetrafluoro. Examples thereof include fluorine rubber such as a copolymer with ethylene, latex such as styrene-butadiene copolymer latex, acrylonitrile-butadiene copolymer latex, and cellulose derivatives such as carboxymethyl cellulose.

  Examples of the conductive aid include carbon powders such as acetylene black, carbon black, and graphite.

  The solvent is not particularly limited as long as it can dissolve or disperse the binder. For example, water, N-methyl-2-pyrrolidone, methyl ethyl ketone, acetone, cyclohexanone, butyl acetate, methanol, ethanol and the like can be used. Can be used.

  In addition to these active materials, binders, conductive assistants, and solvents, various additives such as dispersants, surfactants, and rheology modifiers may be used as necessary.

  The material constituting the separators 6 and 11 may be any material as long as lithium ions can move in the material constituting the layer or in the voids in the layer after coating, drying, and pressing. For example, but not limited to, inorganic particles such as alumina, silica, magnesium oxide, titanium oxide, zirconia, silicon carbide, silicon nitride, or polyethylene, polypropylene, polystyrene, polyacrylonitrile, polymethyl methacrylate, polyfluoride Organic particles such as vinylidene, polytetrafluoroethylene, and polyimide, and a mixture of the inorganic particles and the organic particles, a binder, a solvent, various additives, and the like can be used. Here, as the binder, the solvent, and various additives, those similar to those contained in the negative electrode layer can be used.

  Furthermore, when the separators 6 and 11 are formed on the negative electrode layers 4 and 9, it is desirable that these two layers do not enter and mix too much. For example, selection of materials of each layer and adjustment of the blending amount Can be realized by adjusting the surface tension, viscosity, etc. of each layer.

  In the present invention, the coating devices 3, 5, 8, and 10 may be any one that can form the negative electrode layers 4 and 9 on the current collector 2 and the separators 6 and 11 on the negative electrode layers 4 and 9. For example, a forward roll, a reverse roll, a gravure, a doctor blade, a slot die and the like can be used.

  The drying ovens 7 and 12 are not particularly limited in the present invention as long as the volatile components in the negative electrode layers 4 and 9 and the separators 6 and 11 can be removed. For example, hot air, various infrared rays can be used. , Microwaves, electromagnetic induction, and the like, and a drying device combining these can be used.

  The press device 13 is not particularly limited to the configuration shown in FIG. 3 as long as the porosity of the negative electrode layers 4 and 9 can be set to a desired value. Alternatively, after pressing the electrode plate 15 that has passed through the drying furnace 12, the electrode plate 15 may be pressed by an independent press device.

  FIG. 3 shows a method of sequentially forming the negative electrode layers 4 and 9 and the separators 6 and 11 on each side of the current collector 2. For example, the negative electrode layer is simultaneously formed on both sides of the current collector 2. 4, 9 and the separators 6 and 11, and after the negative electrode layer 4 and the separator 6 are formed on one side of the current collector 2, they are wound up once, and the same device is used on the opposite side of the current collector 2. A method of forming the negative electrode layer 9 and the separator 11 may be used.

  Furthermore, the negative electrode layers 4 and 9 and the separators 6 and 11 do not necessarily need to contain a volatile component. For example, each layer may be formed by electrostatic powder coating. 3 shows a method of forming the separator 6 on the negative electrode layer 4 after the formation of the negative electrode layer 4, that is, before removing the volatile components in the negative electrode layer 4, The separator 6 may be formed on the negative electrode layer 4 after removing the volatile components.

  However, it is desirable that both the negative electrode layer 4 and the separator 6 are configured to include a volatile component, and the separator 6 is formed on the negative electrode layer 4 including the volatile component. Thereby, since the distribution state of the material at the interface between the two layers becomes more ideal, a higher effect can be obtained for the charge / discharge cycle and the battery capacity, and the adhesion between the two layers becomes higher. Defects such as peeling and sliding are less likely to occur.

  In addition, the method for producing an electrode plate for a lithium ion secondary battery of the present invention can be used for either the positive electrode layer and the negative electrode layer, or both, and in either case, the difference in degree is different, An effect is obtained.

  Hereinafter, preferred examples and comparative examples of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples.

  Example 1 A positive electrode paint obtained by mixing 3% by weight of carbon black, 3% by weight of polyvinylidene fluoride, and 40% by weight of N-methyl-2-pyrrolidone with 100% by weight of lithium cobaltate is a positive electrode current collector. A 0.02 mm thick aluminum foil was applied to a thickness of 0.15 mm using a doctor blade, and a separator was applied to a thickness of 0.02 mm using a doctor blade on the positive electrode layer before drying. Thereafter, the positive electrode layer and the separator were dried in a hot air drying oven at 100 ° C. Similarly, a positive electrode layer and a separator were formed on the opposite surface of the aluminum foil. Thus, the electrode plate in which the positive electrode layer and the separator were formed on both surfaces of the aluminum foil was pressed by a pressing device so that the total thickness of the positive electrode layer was 0.2 mm.

  The separator paint was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (filler B: primary particle size of 0.05 μm) is 100% by weight of zirconia (filler A) having a primary particle size of 0.2 μm and a melting point of 2700 ° C. using a Henschel mixer manufactured by Mitsui Mining. The mixture was mixed and stirred with a dissolver in a solution consisting of 5% by weight of polyvinylidene difluoride and 50% by weight of N-methyl-2-pyrrolidone to obtain a separator coating. Table 1 shows the composition ratio, particle size, and melting point of the separators of Examples 1 to 13 and Comparative Examples 1 to 9.

グラファイト１００重量％に対し、ポリフッ化ビニリデン５重量％、Ｎ−メチル−２−ピロリドン５０重量％を混合した負極塗料を、負極集電体である厚み０．０２ｍｍの銅箔の片面に、ドクターブレードを用いて、厚み０．１５ｍｍに塗布し、乾燥前の負極層上に、セパレーター塗料を、ドクターブレードを用いて、厚み０．０２ｍｍに塗布した。この後、負極層およびセパレーターを１００℃の熱風乾燥炉で乾燥させた。同様にして、銅箔の反対の面にも、負極層およびセパレーターを形成した。このようにして、銅箔の両面に負極層およびセパレーターが形成された電極板を、プレス装置によって、負極層の総厚みが０．２ｍｍとなるようにプレスした。

A doctor blade containing a negative electrode paint in which 5% by weight of polyvinylidene fluoride and 50% by weight of N-methyl-2-pyrrolidone are mixed with 100% by weight of graphite is applied to one side of a 0.02 mm thick copper foil as a negative electrode current collector. Was applied to a thickness of 0.15 mm, and a separator paint was applied to a thickness of 0.02 mm using a doctor blade on the negative electrode layer before drying. Thereafter, the negative electrode layer and the separator were dried in a hot air drying oven at 100 ° C. Similarly, a negative electrode layer and a separator were formed on the opposite surface of the copper foil. Thus, the electrode plate in which the negative electrode layer and the separator were formed on both surfaces of the copper foil was pressed by a pressing device so that the total thickness of the negative electrode layer was 0.2 mm.

As described above, a polymer porous membrane (made of polyethylene) having a thickness of 0.02 mm and a porosity of 40% is sandwiched between the produced positive electrode layer and separator, and the wound power generation element is placed in a cylindrical stainless steel case. Then, an electrolytic solution in which LiPF ₆ was added to a mixed solution of ethylene carbonate and diethyl carbonate was injected to assemble a cylindrical lithium ion secondary battery.

  (Example 2) A separator coating was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle size of 0.05 μm) is mixed with 100% by weight of zirconia having a primary particle size of 15 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the resulting mixture is 5% by weight of polyvinylidene difluoride. A battery was prepared in the same manner as in Example 1 except that a solution comprising 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  Example 3 A separator paint was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 3 μm) is mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining, and the mixture is mixed with 5% by weight of polyvinylidene difluoride, A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Example 4) A paint for a separator was prepared as follows. 24% by weight of polyethylene beads (primary particle size 3 μm) having a melting point of 110 ° C. was mixed with 100% by weight of zirconia having a primary particle size of 15 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the mixture was mixed with 5% by weight of polyvinylidene difluoride. A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Example 5) A paint for a separator was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 3 μm) are mixed with 100% by weight of fluororesin beads having a primary particle diameter of 15 μm (melting point: 250 ° C.) using a Henschel mixer manufactured by Mitsui Mining Co., Ltd. A battery was prepared in the same manner as in Example 1 except that a solution containing 5% by weight of vinylidene difluoride and 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a paint for a separator.

  (Example 6) A paint for a separator was prepared as follows. 7% by weight of polyethylene beads having a melting point of 80 ° C. (primary particle diameter of 3 μm) are mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the mixture is mixed with 5% by weight of polyvinylidene difluoride, A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Example 7) A paint for a separator was prepared as follows. 7% by weight of polyethylene beads having a melting point of 120 ° C. (primary particle diameter of 3 μm) is mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining, and the mixture is mixed with 5% by weight of polyvinylidene difluoride, A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Example 8) A paint for a separator was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 3 μm) are mixed with 100% by weight of zirconia having a primary particle diameter of 0.1 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the resulting mixture is 5% by weight of polyvinylidene difluoride. %, N-methyl-2-pyrrolidone A battery was prepared in the same manner as in Example 1 except that a separator paint was obtained by stirring with a dissolver.

  (Example 9) A paint for a separator was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 3 μm) is mixed with 100% by weight of zirconia having a primary particle diameter of 20 μm by a Henschel mixer manufactured by Mitsui Mining, and the mixture is mixed with 5% by weight of polyvinylidene difluoride, A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Example 10) A paint for a separator was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 0.01 μm) are mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining Co., Ltd., and the mixture is 5 weights of polyvinylidene difluoride. %, N-methyl-2-pyrrolidone A battery was prepared in the same manner as in Example 1 except that a separator paint was obtained by stirring with a dissolver.

  (Example 11) A paint for a separator was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 5 μm) are mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining, and the mixture is mixed with 5% by weight of polyvinylidene difluoride, A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Example 12) A paint for a separator was prepared as follows. 5% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 3 μm) is mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining, and the mixture is mixed with 5% by weight of polyvinylidene difluoride, A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Example 13) A paint for a separator was prepared as follows. 25% by weight of polyethylene beads (primary particle diameter 3 μm) having a melting point of 110 ° C. are mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining, and the mixture is mixed with 5% by weight of polyvinylidene difluoride. A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Comparative Example 1) The separator paint was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 0.02 μm) is mixed with 100% by weight of zirconia having a primary particle diameter of 0.05 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the resulting mixture is polyvinylidene difluoride. A battery was prepared in the same manner as in Example 1 except that a solution containing 5% by weight and 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a paint for a separator.

  (Comparative example 2) The coating material for separators was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 0.005 μm) is mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining Co., Ltd., and the mixture is 5% by weight of polyvinylidene difluoride. %, N-methyl-2-pyrrolidone A battery was prepared in the same manner as in Example 1 except that a separator paint was obtained by stirring with a dissolver.

  (Comparative Example 3) A paint for a separator was prepared as follows. 3% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 3 μm) is mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining, and the mixture is mixed with 5% by weight of polyvinylidene difluoride, A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Comparative Example 4) A separator coating was prepared as follows. 30% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 3 μm) are mixed with 100% by weight of zirconia having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the mixture is mixed with 5% by weight of polyvinylidene difluoride. A battery was prepared in the same manner as in Example 1 except that a solution consisting of 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Comparative Example 5) A separator coating was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 0.05 μm) are mixed with 100% by weight of polyimide beads having a primary particle diameter of 0.2 μm and a melting point of 200 ° C. using a Henschel mixer manufactured by Mitsui Mining Co., Ltd. A battery was prepared in the same manner as in Example 1 except that a solution comprising 5% by weight of polyvinylidene difluoride and 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a paint for a separator.

  (Comparative Example 6) A separator coating was prepared as follows. Acrylic beads having a melting point of 50 ° C. (primary particle size 0.05 μm) are mixed with 100% by weight of zirconia having a primary particle size of 0.2 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the mixture is polyvinylidene difluoride. A battery was prepared in the same manner as in Example 1 except that a solution containing 5% by weight and 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a paint for a separator.

  (Comparative Example 7) A paint for a separator was prepared as follows. 7% by weight of fluororesin beads (primary particle size 0.05 μm) having a melting point of 150 ° C. are mixed with 100% by weight of zirconia having a primary particle size of 0.2 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the mixture is mixed with polyvinylidene difluoride. A battery was prepared in the same manner as in Example 1 except that a solution consisting of 5% by weight of a ride and 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a paint for a separator.

  (Comparative Example 8) A paint for a separator was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 0.05 μm) are mixed with 100% by weight of zirconia beads having a primary particle diameter of 25 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the mixture is polyvinylidene difluoride 5 A battery was prepared in the same manner as in Example 1 except that a solution containing 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

  (Comparative Example 9) A separator paint was prepared as follows. 7% by weight of polyethylene beads having a melting point of 110 ° C. (primary particle diameter of 10 μm) are mixed with 100% by weight of zirconia beads having a primary particle diameter of 15 μm by a Henschel mixer manufactured by Mitsui Mining Co., and the resulting mixture is 5% by weight of polyvinylidene difluoride. A battery was prepared in the same manner as in Example 1 except that a solution comprising 50% by weight of N-methyl-2-pyrrolidone was stirred with a dissolver to obtain a separator coating.

実施例１〜実施例１３においては５００サイクル後の容量維持率も良好で、またシャットダウン温度も１１０℃〜１１５℃であり、更に昇温を継続させても電気抵抗の低下が見られなかったことからショートは生じなかった。 A voltage of 1 volt was applied to these obtained batteries at 1 kHz, and the battery internal electrical resistance was measured to obtain a battery internal electrical resistance of 20 ° C. The battery was placed on a hot plate and heated from 20 ° C. to 300 ° C. at a rate of 5 ° C./min. In this process, the temperature at which the internal electric resistance of the battery is increased is defined as the shutdown temperature, and the temperature at which the positive electrode and the negative electrode are short-circuited by further increasing the temperature is defined as the short-circuit temperature. Moreover, the capacity | capacitance at the time of battery initial discharge and the capacity | capacitance maintenance factor at 500 cycles were also measured, and these results were shown in Table 2.

In Examples 1 to 13, the capacity retention rate after 500 cycles was good, the shutdown temperature was 110 ° C. to 115 ° C., and no further decrease in electrical resistance was observed even if the temperature increase was continued. No short circuit occurred.

  In Comparative Example 1, since the particle size of the heat-resistant filler (filler A) was small, the particles were close-packed and the intercalation of lithium ions was inhibited, so that the cycle life was reduced.

  In Comparative Example 2, since the particle diameter of the filler having a low melting point (filler B) is small, a film is formed on the surface of the heat resistant filler (filler A) when the filler melts at the time of temperature rise. For this reason, the gap between the fillers could not be closed, and shutdown did not occur.

  In Comparative Example 3, the amount of filler B was small and no shutdown occurred. In Comparative Example 4, the ratio of filler B in the separator was large, and the heat resistance was reduced, so that a short circuit occurred.

  In Comparative Example 5, a short circuit occurred because the melting point of the filler A was low and the heat resistance was lowered.

  In Comparative Example 6, the filler B has a low melting point, melts when the separator paint is applied and dried, and closes the pores, thus reducing the battery capacity.

  In Comparative Example 7, shutdown did not occur because the melting point of filler B was high.

  In Comparative Examples 8 and 9, due to the large size of each filler, missing (streaks) occurred during coating, and a part of the negative electrode layer was exposed to cause a short circuit.

  The lithium ion secondary battery of the present invention is excellent in characteristics and has excellent cycle charge / discharge characteristics, but can also be applied to uses of energy storage elements such as solid electrolyte lithium secondary batteries and nickel metal hydride batteries.

Schematic diagram of the lithium ion secondary battery of the present invention Schematic diagram of the separator used in the present invention The schematic diagram which shows the manufacturing method of the electrode plate of the lithium ion secondary battery of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Feeding mechanism 2 Current collector 3, 5, 8, 10 Coating device 4, 9 Negative electrode layer 7, 12 Drying furnace 11 Separator 13 Press device 14 Winding mechanism 15 Electrode plate

Claims (1)

In the structure of lithium ion secondary battery which arranged separator between the negative electrode layer and positive electrode layer, the separator, melting point 250 ° C. or more fillers A and melting point 80 ° C. or higher, at least two filler B is 120 ° C. or less Ri Do not from a mixture of the above,
The primary particle diameter of the filler A is 0.1 μm or more and 20 μm or less,
The primary particle size of the filler B is 0.01 μm or more and 5 μm or less,
The primary particle size of the filler A is larger than the primary particle size of the filler B,
The lithium ion secondary battery, wherein the separator B contains 5% by weight to 25% by weight of the filler B with respect to 100% by weight of the filler A.

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