WO2013005329A1 - 二次電池 - Google Patents
二次電池 Download PDFInfo
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- WO2013005329A1 WO2013005329A1 PCT/JP2011/065609 JP2011065609W WO2013005329A1 WO 2013005329 A1 WO2013005329 A1 WO 2013005329A1 JP 2011065609 W JP2011065609 W JP 2011065609W WO 2013005329 A1 WO2013005329 A1 WO 2013005329A1
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- porous
- layer
- secondary battery
- separator
- conductive material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/50—Current conducting connections for cells or batteries
- H01M50/572—Means for preventing undesired use or discharge
- H01M50/574—Devices or arrangements for the interruption of current
- H01M50/581—Devices or arrangements for the interruption of current in response to temperature
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a secondary battery.
- it is related with a secondary battery provided with the separator of a multilayer structure.
- Lithium-ion secondary batteries, nickel-metal hydride batteries, and other secondary batteries are important as, for example, power sources mounted on vehicles that use electricity as a drive source, or power sources used in personal computers, portable terminals, and other electrical products. It is growing.
- a lithium ion secondary battery that is lightweight and obtains a high energy density is preferable as a high-output power source mounted on a vehicle.
- a separator for preventing a short circuit between both electrodes is disposed between the positive electrode and the negative electrode.
- the separator plays a role of forming an ion conduction path (conduction path) between both electrodes by impregnating an electrolyte (electrolytic solution) in the pores (pores) of the separator.
- separators having a porous layer made of a polyolefin polymer such as polyethylene or polypropylene have been used.
- Such a separator has a so-called shutdown function, and also plays a role of preventing temperature rise inside the battery.
- a separator having a porous layer made of such a thermoplastic polymer has pores that melt or soften when the temperature inside the battery rises due to overcharging or the like and reaches the melting point (shutdown temperature) of the polymer. Is blocked, and ion conduction between both electrodes is blocked. Therefore, charging / discharging of the battery is forcibly stopped, and further temperature rise can be prevented.
- Patent document 1 is mentioned as a prior art regarding a separator.
- the present invention has been created to solve the above-described problems, and its purpose is to obviate the occurrence of defects in the battery even when the temperature inside the battery rises due to overcharging or the like. It is an object of the present invention to provide a secondary battery excellent in safety that can be prevented.
- the present invention provides a secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. That is, in the secondary battery disclosed herein, the separator has a laminated structure including at least two porous layers mainly composed of different or the same polymers, and one of the layers is A porous conductive layer in which a conductive material is dispersed in the porous layer is formed.
- the secondary battery of the present invention includes a separator having a laminated structure in which a conductive material is contained in one of at least two porous layers.
- the separator of the secondary battery according to the present invention includes the porous layer that does not include the conductive material, it is possible to prevent a short circuit that occurs due to direct contact between the positive electrode and the negative electrode.
- the polymer melts to exhibit a shutdown function and the conductive material in the porous conductive layer Moves into the pores (pores) of the porous layer containing no conductive material together with the molten polymer.
- the moved conductive material is connected from the positive electrode end of the separator to the negative electrode end, and a plurality of minute conductive paths connecting the positive electrode and the negative electrode are formed.
- a minute conductive path By forming such a minute conductive path, a minute short circuit occurs between the positive electrode and the negative electrode, and heat energy is dispersed and consumed, so that an increase in temperature inside the battery can be suppressed. Therefore, according to the present invention, it is possible to provide a secondary battery excellent in safety and reliability without causing a problem due to a temperature rise inside the battery in the event of battery abnormality such as overcharge.
- the separator is composed mainly of the same polymer without including the one porous conductive layer and the conductive material laminated on both sides of the porous conductive layer. It has a three-layer structure including a porous layer.
- the melting point of the polymer constituting the porous conductive layer is higher than the melting point of the polymer constituting the porous layer not including the conductive material. Is also low. According to this configuration, since the layers have different melting points, two-stage shutdown is possible. In addition, since the polymer of the porous conductive layer melts first when the temperature inside the battery rises, the porous layer does not contain the conductive material before the porous layer melts (that is, the porous layer keeps its shape). The conductive material of the conductive layer can move to a porous layer that does not contain the conductive material to form a plurality of minute conductive paths.
- the polymer constituting the porous conductive layer is polyethylene (PE), and the polymer constituting the porous layer not containing the conductive material is polypropylene (PP).
- the shutdown temperature can be set in two stages: the melting point of PE (generally about 125 to 135 ° C.) and the melting point of PP (generally about 155 to 165 ° C.). Therefore, the separator is superior in safety.
- the content of the conductive material contained in the porous conductive layer is 3% by mass. Larger than 50% by mass. In a more preferred embodiment, the content ratio of the conductive material is 8% by mass or more and 40% by mass or less. According to this configuration, it is possible to form a plurality of minute conductive paths that have sufficient strength as a separator and are required to suppress a temperature rise inside the battery.
- the conductive material is a carbon material. Since carbon materials such as carbon powder and carbon fiber are excellent in conductivity, they can be suitably used for forming minute conductive paths.
- the porous layer not containing the conductive material has an average pore diameter of 0.05 ⁇ m to 0.5 ⁇ m, and the conductive material contained in the porous conductive layer is The average particle diameter of the material is 0.01 ⁇ m to 0.1 ⁇ m, and is an average particle diameter that does not exceed the average pore diameter.
- the “average pore diameter” is an abbreviation when the pores formed in the porous layer (including the porous conductive layer) have a substantially circular shape (including a substantially elliptical shape).
- the average value of the diameters of the circles (the major axis in the case of a substantially ellipse).
- the hole has a substantially rectangular shape (including a substantially rectangular shape)
- one side of the substantially rectangular shape Is the average value of the long side
- the “average particle diameter” means a median diameter (d50) and can be easily measured by a commercially available particle size distribution measuring apparatus based on various laser diffraction / scattering methods.
- a positive electrode including a positive electrode active material for a lithium ion secondary battery, a negative electrode including a negative electrode active material for a lithium ion secondary battery, and an electrolyte solution are used.
- lithium ion secondary batteries are used.
- Such a secondary battery is suitable as a battery mounted on a vehicle such as an automobile. Therefore, according to the present invention, a vehicle including any of the secondary batteries disclosed herein is provided.
- the secondary battery is a lithium ion secondary battery, and the lithium ion secondary battery is used as a power source (typically, a power source of a hybrid vehicle or an electric vehicle).
- a vehicle for example, an automobile provided as is suitable.
- FIG. 1 is a perspective view schematically showing the outer shape of a lithium ion secondary battery according to an embodiment of the present invention.
- FIG. 2 is a cross-sectional view taken along line II-II in FIG.
- FIG. 3 is a cross-sectional view schematically showing the structure of the separator according to one embodiment of the present invention.
- FIG. 4A is an explanatory view schematically showing a state in which the conductive material in the porous conductive layer moves to the pores of the porous layer when the temperature inside the battery rises.
- FIG. 4B is an explanatory diagram schematically illustrating a state in which a minute conductive path is formed by a conductive material from one surface of the separator to the other surface.
- FIG. 5 is a cross-sectional view schematically showing the structure of a separator according to another embodiment.
- FIG. 6 is a side view schematically showing a vehicle (automobile) provided with the secondary battery according to the present invention.
- a lithium ion secondary battery will be described in detail as an example, but the application target of the present invention is limited to such a type of secondary battery. Not intended.
- the present invention is applied to other types of secondary batteries (including, for example, secondary batteries using metal ions other than lithium ions as charge carriers, and electric double layer capacitors (physical batteries) such as lithium ion capacitors). can do.
- the separator has a laminated structure including at least two porous layers different from each other or mainly composed of the same polymer, and one of the layers has the porous structure. It is characterized by forming a porous conductive layer in which a conductive material is dispersed in the porous layer.
- FIG. 3 is a cross-sectional view schematically showing the structure of the separator 70 according to this embodiment.
- the separator 70 according to the present embodiment has a three-layer structure in which three porous layers 76A, 72, and 76B are laminated, and the conductive material 74 is dispersed in the porous layer.
- the separator 70 is typically formed in a long sheet shape, but is not limited to such an embodiment, and can be processed into various shapes depending on the shape of the secondary battery in which the separator 70 is used.
- the polymer in the porous layers 76A and 76B and the porous conductive layer 72 for example, a polyolefin-based thermoplastic polymer such as polyethylene (PE) or polypropylene (PP) can be suitably used.
- the melting point of the polymer constituting the porous conductive layer 72 is preferably lower than the melting point of the polymer constituting the porous layers 76A and 76B not including the conductive material.
- the two-stage shutdown is possible due to the difference in melting point of the polymer constituting each layer, and as described later, the polymer in the porous conductive layer 72 is melted so that the inside of the porous conductive layer 72 A plurality of minute conductive paths that flow (move) into the pores (pores) 78A and 78B (see FIG. 4A) of the porous layers 76A and 76B in which the conductive material 74 dispersed in them is maintained in shape. 79 (see FIG. 4B) can be formed.
- the porous layers 76A and 76B are preferably made of PP having a melting point of about 150 ° C. to 170 ° C. (eg, about 155 ° C. to 165 ° C.).
- PP include isotactic polypropylene and syndiotactic polypropylene.
- the melting points of both porous layers 76A and 76B may be the same or different from each other. Typically, the melting points of both porous layers 76A and 76B are substantially equal.
- the porous conductive layer 72 is preferably composed of PE having a melting point of about 120 ° C. to 140 ° C. (eg, about 125 ° C. to 135 ° C.). Examples of PE include high-density polyethylene and polyethylene called linear (linear) low-density polyethylene.
- a long porous polymer film that is uniaxially or biaxially stretched can be suitably used.
- a porous polymer film uniaxially stretched in the longitudinal direction is particularly preferable because it has a suitable strength and has little heat shrinkage in the width direction.
- thermal contraction in the longitudinal direction can be suppressed in an aspect wound with a long positive electrode sheet and a negative electrode sheet. Accordingly, a porous polymer film uniaxially stretched in the longitudinal direction is particularly suitable as a material for a separator constituting such a wound electrode body.
- the thickness of the separator 70 (that is, the total thickness of the porous layer and the porous conductive layer) is preferably, for example, about 10 ⁇ m to 30 ⁇ m (for example, about 16 ⁇ m to 20 ⁇ m).
- the thickness of the porous layer and the thickness of the porous conductive layer are each about 4 ⁇ m to 10 ⁇ m, for example, and the thicknesses may be the same or different. If the thickness of the separator 70 is too larger than 30 ⁇ m, the ion conductivity of the separator 70 may be reduced. On the other hand, if the thickness of the separator 70 is too smaller than 10 ⁇ m, the separator 70 itself may be damaged (film breakage) during charge / discharge.
- the thickness of the separator 70 can be obtained by image analysis of the SEM image.
- the total porosity of the separator 70 is preferably about 40% to 65% (preferably about 45% to 55%).
- the porosity is expressed by volume% (vol%), but is simply expressed as% below.
- the porosity of the porous layers 76A and 76B is preferably about 35% to 50%, and the porosity of the porous conductive layer 72 is preferably about 45% to 65%. If the total porosity is too small, the amount of the electrolyte solution that can be held in the separator 70 is reduced, and the ionic conductivity may be lowered. On the other hand, if the total porosity is too large, the strength of the separator 70 is insufficient, and there is a possibility that film breakage is likely to occur.
- the “porosity” can be calculated as follows.
- the porous layer 76A will be described as an example.
- the apparent volume occupied by the porous layer 76A having a unit area (size) is V1 [cm 3 ], and the mass of the porous layer 76A having the unit area is W [g].
- the ratio between the mass W and the true density ⁇ [g / cm 3 ] of the polymer constituting the porous layer 76A, that is, W / ⁇ is V0.
- V0 is a volume occupied by a dense polymer of mass W.
- the porosity of the porous layer 76A can be calculated by (V1 ⁇ V0) / V1 ⁇ 100.
- the “porosity” is a value that can be measured by, for example, an X-ray CT scanner.
- the average pore diameter of the porous layers 76A and 76B not containing the conductive material is preferably about 0.05 ⁇ m to 0.5 ⁇ m (for example, about 0.1 ⁇ m to 0.2 ⁇ m). If the average pore diameter is too larger than 0.5 ⁇ m, the strength of the separator 70 may be reduced. On the other hand, if the average pore diameter is too smaller than 0.05 ⁇ m, there is a possibility that sufficient ion conductivity cannot be obtained. Further, the average pore diameter of the porous conductive layer 72 containing a conductive material is set so that the porosity of the porous conductive layer 72 is higher than the porosity of the porous layers 76A and 76B. It is preferably larger than the average pore diameter of 76A and 76B, preferably about 0.1 ⁇ m to 1 ⁇ m (for example, about 0.15 ⁇ m to 0.3 ⁇ m).
- a carbon material such as carbon powder can be preferably used as the conductive material 74 included in the porous conductive layer 72 of the separator 70 disclosed herein.
- a carbon material such as carbon powder
- various carbon blacks for example, acetylene black, furnace black, ketjen black, etc.
- carbon powders such as graphite powder
- conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and the like can be contained alone or as a mixture thereof. Among these, only 1 type may be used or 2 or more types may be used together.
- the average particle diameter of the conductive material 74 is approximately 0.01 ⁇ m to 0.1 ⁇ m (for example, approximately 0.04 ⁇ m to 0.06 ⁇ m), and the average pore diameter of the porous layers 76A and 76B not including the conductive material is determined. The average particle size does not exceed.
- the average particle diameter of the conductive material 74 greatly exceeds the average pore diameter of the porous layers 76A and 76B, the temperature inside the battery rises due to overcharge or the like, and the porous conductive layer 72 is formed into a porous shape.
- the conductive material 74 cannot move to the holes 78A and 78B (see FIG. 4A) formed in the porous layers 76A and 76B, and the minute amount connecting the positive electrode and the negative electrode inside the separator 70. There is a possibility that the conductive path 79 (see FIG. 4B) cannot be formed.
- the content ratio (content) of the conductive material 74 included in the porous conductive layer 72 is preferably larger than 3 mass% and smaller than 50 mass% when the porous conductive layer is 100 mass%. More preferably, it exists in the range of 8 mass% or more and 40 mass% or less.
- the strength of the porous conductive layer 72 is not sufficient when forming the porous conductive layer 72 from the thermoplastic polymer and the conductive material 74. There is a possibility that the separator 70 does not function.
- the content ratio of the conductive material 74 is too smaller than 3% by mass, the polymer constituting the porous conductive layer 72 is melted so that the conductive material 72 has pores 78A and 78B of the porous layers 76A and 76B ( Even if it moves to (refer FIG. 4A), there exists a possibility that the quantity of the electrically conductive material 72 may run short and it may become impossible to form the fine conductive path 79 (refer FIG. 4B) which connects a positive electrode and a negative electrode.
- the separator 70 disclosed herein can be manufactured according to a conventionally known method. For example, a mixture containing a thermoplastic polymer (for example, polyethylene) as a component for forming a porous conductive layer and a conductive material (acetylene black) is prepared, and a thermoplastic polymer (for example, polypropylene) as a component for forming the porous layer And a film having a laminated structure can be formed by simultaneously melt-extruding these components. By stretching the formed film uniaxially or biaxially, each layer can be made porous to form a separator 70 having a laminated structure including the porous conductive layer 72 and the porous layer 76A (76B).
- a thermoplastic polymer for example, polyethylene
- a conductive material acetylene black
- a thermoplastic polymer for example, polypropylene
- the function (action, effect) of the separator 70 according to the present embodiment when the temperature inside the battery rises due to overcharging or the like will be described.
- the porous conductive layer 72 of the separator 70 when the temperature inside the battery 10 increased due to overcharging or the like, first, the porous conductive layer 72 of the separator 70 was formed into a porous shape. The polymer melts. As the polymer melts, the pores in the porous conductive layer 72 are closed (that is, shut down), and the movement of lithium ions between the positive and negative electrodes is suppressed. Further, as shown in FIG.
- the conductive material 74 included in the porous conductive layer 72 moves together with the molten polymer, and the holes 78A of the porous layer 76A and the holes of the porous layer 76B that do not include the conductive material. It flows into 78B.
- the conductive material 74 that has flowed into the holes 78A and 78B is from one end (the surface in contact with the positive electrode sheet 64) in the stacking direction of the separator 70 to the other end (the negative electrode sheet 84). And a small conductive path 79 is formed between the positive electrode sheet 64 and the negative electrode sheet 84.
- a minute short circuit occurs at a plurality of positions between the positive electrode 64 and the negative electrode 84, and heat energy is dispersed and consumed. An increase in temperature inside the battery can be suppressed.
- An inorganic filler layer having an inorganic filler and a binder (binder) may be provided on at least one surface of the porous layers 76A and 76B of the separator 70.
- the inorganic filler layer is composed of an inorganic filler and a binder, and the inorganic filler particles and the inorganic filler particles and the porous layers 76A and 76B are bonded by the binder.
- the inorganic filler layer has a large number of holes in a portion not bonded by the binder, and ions can pass through the inorganic filler layer by the connection of the holes.
- the inorganic filler layer has heat resistance that does not melt in a higher temperature range (for example, 300 ° C. to 1000 ° C. or higher) than the porous layers 76A and 76B and the porous conductive layer 72.
- the inorganic filler used in the inorganic filler layer is preferably one having a high melting point (for example, a melting point of 1000 ° C. or higher), excellent heat resistance, and electrochemically stable within the battery use range.
- examples of such inorganic fillers include metal oxides such as alumina (Al 2 O 3 ), boehmite (Al 2 O 3 .H 2 O), magnesia (MgO), and zirconia (ZrO 2 ).
- metal oxides such as alumina (Al 2 O 3 ), boehmite (Al 2 O 3 .H 2 O), magnesia (MgO), and zirconia (ZrO 2 ).
- alumina Al 2 O 3
- boehmite Al 2 O 3 .H 2 O
- MgO magnesia
- ZrO 2 zirconia
- the inorganic filler has a high melting point and excellent heat resistance, by forming an inorganic filler layer made of the inorganic filler on at least one surface of the porous layers 76A and 76B, the thermal contraction (thermal deformation) of the separator 70 is achieved. Is suppressed.
- the volume-based average particle diameter (d50) of the inorganic filler is suitably about 0.05 ⁇ m to 1.5 ⁇ m, preferably about 0.1 ⁇ m to 1 ⁇ m.
- the binder used in the inorganic filler layer is for bonding between the inorganic fillers, and the material itself constituting the binder is not particularly limited, and various materials can be used widely.
- Preferable examples include acrylic polymers.
- the acrylic polymer a homopolymer obtained by polymerizing monomers such as acrylic acid, methacrylic acid, acrylamide, methacrylamide and the like is preferably used.
- the acrylic polymer may be a copolymer obtained by polymerizing two or more of the above monomers. Further, a mixture of two or more of the above homopolymers and copolymers may be used.
- the said inorganic filler layer can contain a thickener as needed.
- the thickener include carboxymethyl cellulose (CMC) and polyethylene oxide (PEO) when an aqueous solvent is used.
- the proportion of the inorganic filler in the entire inorganic filler layer is preferably about 90% by mass or more (typically 90% by mass to 99% by mass), preferably about 95% by mass to 99% by mass. %, Preferably about 97% by mass to 99% by mass. If the proportion of the inorganic filler is too small, the heat resistance of the inorganic filler layer is lowered, and thus thermal contraction of the separator 70 may not be suppressed. On the other hand, if the proportion of the inorganic filler is too large, the amount of the binder in the inorganic filler layer is relatively reduced, so that the strength of the inorganic filler layer is lowered or the adhesion with the separator 70 is lowered. Sometimes.
- the proportion of the binder in the entire inorganic filler layer is suitably about 10% by mass or less, usually 5% by mass or less (typically 1 to 5% by mass). Preferably there is. Furthermore, in the inorganic filler layer having a composition containing a thickener, the proportion of the thickener in the inorganic filler layer can be about 5% by mass or less, for example, 2% by mass or less (typically 0.5% or less). ⁇ 2% by mass).
- the porosity of the inorganic filler layer is generally 40% to 70%, preferably 45% to 60%. By having the porosity within such a predetermined range, an inorganic filler layer satisfying both good ion permeability and high mechanical strength can be obtained.
- the thickness of the inorganic filler layer can be appropriately selected according to the use, but for example, 1 ⁇ m to 20 ⁇ m is appropriate, preferably 3 ⁇ m to 10 ⁇ m, and particularly preferably 2 ⁇ m to 8 ⁇ m.
- the inorganic filler layer is too thin, there is a possibility that the thermal shrinkage of the separator 70 cannot be suppressed.
- the inorganic filler layer is too thick, the resistance after the high-rate charge / discharge cycle may increase.
- the method for forming the inorganic filler layer will be described.
- a paste-like composition in which an inorganic filler, a binder and a solvent for example, N-methylpyrrolidone (NMP)
- NMP N-methylpyrrolidone
- An appropriate amount of this composition is applied to the surface of at least one of the porous layers 76 and 76B of the separator 70 and further dried to remove the solvent, whereby an inorganic filler layer can be formed.
- the present invention is not intended to be limited to such an embodiment. That is, as long as the separator 70 is employed, the shape (outer shape and size) of the lithium ion secondary battery to be constructed is not particularly limited.
- a lithium ion secondary battery having a configuration in which a wound electrode body and an electrolytic solution are housed in a rectangular battery case will be described as an example.
- symbol is attached
- the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.
- FIG. 1 is a perspective view schematically showing a lithium ion secondary battery (secondary battery) 10 according to the present embodiment.
- FIG. 2 is a longitudinal sectional view taken along line II-II in FIG.
- the lithium ion secondary battery 10 according to this embodiment includes a battery case 15 made of metal (a resin or a laminate film is also suitable).
- the case (outer container) 15 includes a flat cuboid case main body 30 having an open upper end, and a lid body 25 that closes the opening 20.
- the lid body 25 seals the opening 20 of the case main body 30 by welding or the like.
- a positive electrode terminal 60 electrically connected to the positive electrode sheet (positive electrode) 64 of the wound electrode body 50 and a negative electrode terminal electrically connected to the negative electrode sheet 84 of the electrode body. 80 is provided on the upper surface of the case 15 (that is, the lid body 25).
- the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal, as in the case of the conventional lithium ion secondary battery. .
- a positive electrode sheet 64 and a negative electrode sheet 84 are laminated and wound together with a total of two separator sheets 70, and then the obtained wound body is crushed from the side surface direction.
- a flat wound electrode body 50 and an electrolyte (for example, a non-aqueous electrolyte) produced by bending are accommodated.
- the positive electrode mixture layer non-formed portion of the positive electrode sheet 64 that is, the portion where the positive electrode current collector 62 is exposed without forming the positive electrode mixture layer 66
- the negative electrode composite material layer non-formed portion 84 protrudes from both sides in the width direction of the separator sheet 70. And the negative electrode sheet 84 are overlapped with a slight shift in the width direction.
- the electrode composite material layer non-forming portions of the positive electrode sheet 64 and the negative electrode sheet 84 are respectively wound core portions (that is, the positive electrode composite material layer forming portion of the positive electrode sheet 64). And a portion where the negative electrode mixture layer forming portion of the negative electrode sheet 84 and the two separator sheets 70 are wound tightly).
- the positive electrode terminal 60 is joined to the protruding portion on the positive electrode side, and the positive electrode sheet 64 and the positive electrode terminal 60 of the wound electrode body 50 formed in the flat shape are electrically connected.
- the negative electrode terminal 80 is joined to the negative electrode side protruding portion, and the negative electrode sheet 84 and the negative electrode terminal 80 are electrically connected.
- the positive and negative electrode terminals 60 and 80 and the positive and negative electrode current collectors 62 and 82 can be joined by, for example, ultrasonic welding, resistance welding, or the like.
- Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent (organic solvent).
- suitable nonaqueous solvent include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like.
- EC ethylene carbonate
- PC propylene carbonate
- DMC dimethyl carbonate
- DEC diethyl carbonate
- EMC ethyl methyl carbonate
- the supporting salt for example, it can be used lithium salts such as LiPF 6, LiBF 4.
- difluorophosphate (LiPO 2 F 2 ) or lithium bisoxalate borate (LiBOB) may be dissolved in the non-aqueous electrolyte.
- the positive electrode mixture layer 66 is, for example, a paste-like composition in which a positive electrode active material, a conductive material, a binder (binder) and the like are dispersed in an appropriate solvent and kneaded (a slurry-like composition is included in the paste-like composition). And an ink-like composition are prepared, and the composition is preferably applied to the positive electrode current collector 62 and dried.
- the positive electrode active material examples include materials capable of inserting and extracting lithium ions, and include lithium-containing compounds (for example, lithium transition metal composite oxides) containing a lithium element and one or more transition metal elements.
- lithium-containing compounds for example, lithium transition metal composite oxides
- lithium nickel composite oxide for example, LiNiO 2
- lithium cobalt composite oxide for example, LiCoO 2
- lithium manganese composite oxide for example, LiMn 2 O 4
- lithium nickel cobalt manganese composite oxide for example, LiNi 1).
- LiNi 1.1 lithium nickel composite oxide
- LiCoO 2 lithium manganese composite oxide
- LiMn 2 O 4 lithium manganese composite oxide
- a polyanionic compound for example, LiFePO 4 whose general formula is represented by LiMPO 4, LiMVO 4, or Li 2 MSiO 4 (wherein M is at least one element of Co, Ni, Mn, and Fe), etc. 4 , LiMnPO 4 , LiFeVO 4 , LiMnVO 4 , Li 2 FeSiO 4 , Li 2 MnSiO 4 , Li 2 CoSiO 4 ) may be used as the positive electrode active material.
- the conductive material is not limited to a specific conductive material as long as it is conventionally used in this type of lithium ion secondary battery.
- the same conductive material contained in the porous conductive layer 72 can be suitably used.
- the same binder as that used for the positive electrode of a general lithium ion secondary battery can be appropriately adopted.
- a solvent-based paste is used as the composition for forming the positive electrode mixture layer 66, it dissolves in an organic solvent (non-aqueous solvent) such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC).
- PVDF polyvinylidene fluoride
- PVDC polyvinylidene chloride
- Polymer materials can be used.
- a polymer material that can be dissolved or dispersed in water can be preferably used.
- PTFE polytetrafluoroethylene
- CMC carboxymethyl cellulose
- the polymer material illustrated above may be used as a thickener and other additives in the above composition in addition to being used as a binder.
- the “solvent-based paste composition” is a concept indicating a composition in which the dispersion medium of the positive electrode active material is mainly an organic solvent.
- the organic solvent for example, N-methylpyrrolidone (NMP) can be used.
- NMP N-methylpyrrolidone
- the “aqueous paste-like composition” is a concept indicating a composition using water or a mixed solvent mainly containing water as a dispersion medium of the positive electrode active material.
- a solvent other than water constituting such a mixed solvent one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.
- the positive electrode current collector 62 a conductive member made of a metal having good conductivity is preferably used, like the current collector used in the positive electrode of a conventional lithium ion secondary battery.
- a conductive member made of a metal having good conductivity is preferably used, like the current collector used in the positive electrode of a conventional lithium ion secondary battery.
- an aluminum material or an alloy material mainly composed of an aluminum material can be used.
- the shape of the positive electrode current collector may vary depending on the shape of the lithium ion secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape.
- the technique disclosed here can be preferably applied to manufacture of an electrode using, for example, a sheet-shaped or foil-shaped current collector.
- the negative electrode mixture layer 90 is prepared, for example, by preparing a paste-like composition in which a negative electrode active material, a binder (binder), and a thickener as necessary are dispersed in a suitable solvent and kneaded.
- the composition can be preferably produced by applying it to the negative electrode current collector 82 and drying it.
- the negative electrode active material one type or two or more types of materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. Examples thereof include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal composite oxides (lithium titanium composite oxides, etc.), lithium transition metal composite nitrides, and the like.
- a negative electrode active material typically, a negative electrode active material substantially composed of natural graphite (or artificial graphite), which is mainly composed of natural graphite (or artificial graphite).
- spheroidized natural graphite (or spheroidized artificial graphite) having an average particle diameter in the range of about 5 ⁇ m to 30 ⁇ m can be preferably used as the negative electrode active material.
- Carbonaceous powder having a surface coated with amorphous carbon (amorphous carbon) may be used.
- the binder As the binder (binder), the same binder as that used for the negative electrode of a general lithium ion secondary battery can be appropriately employed.
- a polymer material that is dissolved or dispersed in water can be preferably used.
- Polymer materials that can be dispersed in water include rubbers such as styrene butadiene rubber (SBR) and fluororubber; fluoropolymers such as polyethylene oxide (PEO) and polytetrafluoroethylene (PTFE); vinyl acetate Examples thereof include copolymers.
- a polymer material that is dissolved or dispersed in water or a solvent (organic solvent) can be employed as the thickener.
- water-soluble (water-soluble) polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropylmethyl cellulose (HPMC); polyvinyl alcohol ( PVA); and the like.
- the negative electrode current collector 82 a conductive member made of a metal having good conductivity is preferably used, as in the case of the current collector used in the negative electrode of a conventional lithium ion secondary battery.
- a copper material, a nickel material, or an alloy material mainly composed of them can be used.
- the shape of the negative electrode current collector can be the same as the shape of the positive electrode current collector.
- the separator 70 according to the first embodiment described above has a three-layer structure in which three porous layers are laminated.
- the separator is not limited to a three-layer separator, and even if there are two layers, there are four or more layers. It may be.
- FIG. 5 is a cross-sectional view schematically showing the structure of a two-layer separator 170 in which two porous layers 172 and 176 are laminated. As shown in FIG.
- the separator 170 has a two-layer structure in which two porous layers 176 and 172 mainly composed of different or the same polymers are laminated, A porous conductive layer 172 in which a conductive material 174 is dispersed in a porous layer, and a porous layer 176 that does not include a conductive material laminated on the surface of the porous conductive layer 172 are provided. According to this configuration, the same effect as in the first embodiment can be obtained. In addition, when forming an inorganic filler layer on the surface of the separator 170 which concerns on this embodiment, forming on the surface of the porous conductive layer 172 at least is preferable.
- Example 1 A component for preparing a porous layer by preparing a mixture having a mass ratio of 97: 3 between polyethylene (thermoplastic polymer) as a component for forming a porous conductive layer and acetylene black (conductive material) having an average particle size of 40 ⁇ m As a polypropylene (thermoplastic polymer), and melt-extruding these components simultaneously using a T-die extruder, so that both sides of a porous conductive layer (hereinafter also referred to as “conductive layer”) are porous.
- conductive layer a porous conductive layer
- the formed film was stretched (uniaxially stretched) in the longitudinal direction of the film to produce a separator sheet according to Example 1.
- the total porosity of the separator was 52%.
- the porous conductive layer had a thickness of 7 ⁇ m and an average pore diameter of 0.2 ⁇ m, and the porous layer had a thickness of 7 ⁇ m and an average pore diameter of 0.1 ⁇ m.
- alumina powder average particle size (d50) 0.3 ⁇ m; purity 99.99%) as an inorganic filler, an acrylic polymer as a binder, and carboxymethyl cellulose (CMC) as a thickener are used.
- a composition for forming an inorganic filler layer was prepared by dispersing in water such that the mass ratio was 96: 3: 1. This inorganic filler layer forming composition was applied to the surface of the porous layer with a gravure roll and dried to form an inorganic filler layer. The thickness of the inorganic filler layer was 5 ⁇ m, and the porosity was 60%. From the above, a separator sheet with an inorganic filler layer according to Example 1 having a thickness of 26 ⁇ m was produced.
- Example 2> With an inorganic filler layer according to Example 2 except that a mixture of polyethylene as a component for forming the porous conductive layer and acetylene black having an average particle size of 40 ⁇ m in a mass ratio of 92: 8 was used. A separator sheet was produced.
- Example 3> With an inorganic filler layer according to Example 3, except that a mixture of polyethylene as a component for forming the porous conductive layer and acetylene black having an average particle size of 40 ⁇ m in a mass ratio of 80:20 was used. A separator sheet was produced.
- Example 4> With the inorganic filler layer according to Example 4 except that a mixture of polyethylene as a component for forming the porous conductive layer and acetylene black having an average particle diameter of 40 ⁇ m in a mass ratio of 60:40 was used. A separator sheet was produced.
- Example 5> With an inorganic filler layer according to Example 5 in the same manner as in Example 1, except that a mixture of polyethylene as a component for forming the porous conductive layer and acetylene black having an average particle diameter of 40 ⁇ m in a mass ratio of 40:60 was used. A separator sheet was produced.
- Example 6 Prepare polyethylene as a component to form a porous conductive layer, prepare polypropylene as a component to form a porous layer, and melt and extrude these components at the same time using a T-die extruder.
- the formed film was stretched (uniaxially stretched) in the longitudinal direction of the film to produce a separator sheet according to Example 6.
- a separator sheet with an inorganic filler layer according to Example 6 was produced in the same manner as in Example 1 except that this separator sheet was used.
- Example 7 Prepare polyethylene as a component to form a porous layer (PE layer) and melt extrude the component using a T-die extruder to form a film with a single layer structure consisting of a porous layer (PE layer) did.
- the molded film was stretched (uniaxially stretched) in the longitudinal direction of the film to produce a separator sheet according to Example 7 having a thickness of 21 ⁇ m.
- a separator sheet with an inorganic filler layer according to Example 7 was produced in the same manner as in Example 1 except that this separator sheet was used.
- Example 8> A separator sheet with an inorganic filler layer according to Example 8 was produced in the same manner as in Example 7, except that polypropylene as a component for forming the porous layer (PP layer) was used.
- [Positive electrode sheet] The mass ratio of LiNi 1/3 Co 1/3 Mn 1/3 O 2 as the positive electrode active material, acetylene black (AB) as the conductive material, and PVDF as the binder is 90: 5: 5. Thus, these materials were dispersed in NMP to prepare a paste-like composition for forming a positive electrode mixture layer. The paste was applied onto a positive electrode current collector (aluminum foil) having a thickness of 15 ⁇ m at a coating amount of 6 mg / cm 2 per side and dried, followed by press treatment to form a positive electrode mixture layer on the positive electrode current collector. A positive electrode sheet was produced.
- a positive electrode current collector aluminum foil
- a paste-like composition for forming a negative electrode mixture layer was prepared by dispersing in ion-exchanged water.
- the negative electrode current collector layer (copper foil) was coated on a negative electrode current collector (copper foil) at a coating amount of 4 mg / cm 2 and dried, and then subjected to press treatment to form a negative electrode mixture layer on the negative electrode current collector.
- a sheet was produced.
- the prepared positive electrode sheet, the negative electrode sheet, and two separator sheets with an inorganic filler layer according to Example 1 were overlapped and wound into a cylindrical shape to obtain a wound electrode body according to Example 1.
- the wound electrode body and the electrolyte solution according to Example 1 are accommodated in a bottomed cylindrical case body made of nickel-plated mild steel having a diameter of 18 mm, a length of 65 mm, and a thickness of 0.5 mm.
- the next battery was built.
- As the electrolytic solution a solution obtained by dissolving 1 mol / L LiPF 6 in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 was used.
- lithium ion secondary batteries according to Examples 2 to 8 were constructed in the same manner as the lithium ion secondary battery according to Example 1.
- the separator sheet with an inorganic filler layer according to Example 5 did not have sufficient strength, a lithium ion secondary battery could not be constructed.
- Each lithium ion secondary battery after the above adjustment is charged at a constant current of 4% at a charge rate of 4C with an SOC of 300% as the upper limit (that is, the lithium ion secondary battery after charging is completed). This is a test that continues to forcibly pass the charging current.) The presence or absence of malfunction (opening or smoking) of each battery was confirmed. The results are shown in Table 1.
- the secondary battery according to Example 8 is slow to shut down and emits smoke. Further, in the secondary batteries according to Examples 6 and 7, although the shutdown occurred, the heat release was not sufficient, so that the separator sheet itself thermally contracted, and it was considered that smoke was generated. On the other hand, in the secondary batteries according to Examples 2 to 4, it was confirmed that the result was only valve opening. This is because the conductive material contained in the porous conductive layer forms multiple conductive paths that generate minute shorts between the positive electrode sheet and the negative electrode sheet, so heat generation is reduced and temperature rise inside the battery is suppressed. It is thought that it was because it was done. As described above, the lithium ion secondary batteries according to Examples 2 to 4 have excellent safety and reliability without causing problems in the secondary battery even if the temperature inside the battery rises due to overcharge or the like. It was shown to be an ion secondary battery.
- the secondary battery for example, lithium ion secondary battery 10
- a motor electric motor
- the present invention provides a vehicle (typically, a lithium-ion secondary battery 10 (typically, an assembled battery formed by connecting a plurality of the batteries 10 in series) as a power source (typically Provides a motor vehicle, particularly a motor vehicle equipped with an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel vehicle.
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Abstract
Description
そこで、本発明は、上述した課題を解決すべく創出されたものであり、その目的は、過充電等によって電池内部の温度が上昇した場合であっても電池に不具合が発生することを未然に防止できる安全性に優れた二次電池を提供することである。
このように、本発明に係る二次電池のセパレータは、導電材を含まない多孔質層を備えているため、正極と負極とが直接接触することによって発生する短絡を防止することができる。また、過充電等によって電池内部の温度が上昇して多孔質導電層を構成するポリマーの融点に達すると、該ポリマーが溶融してシャットダウン機能が発揮されると共に該多孔質導電層中の導電材が溶融したポリマーと共に導電材を含まない多孔質層の空孔(細孔)内へと移動する。移動した導電材は、セパレータの正極側の端部から負極側の端部へと繋がり、正極と負極とを結ぶ複数の微小な導電経路が形成される。かかる微小な導電経路が形成されることにより、正極と負極との間に微小な短絡が発生し熱エネルギーが分散して消費されるため、電池内部の温度の上昇を抑制することができる。
従って、本発明によると、過充電等の電池異常の際に電池内部の温度上昇による不具合が発生することなく安全性と信頼性に優れた二次電池を提供することができる。
好ましい一態様では、上記セパレータは、上記1つの多孔質導電層と、該多孔質導電層の両面にそれぞれ積層された上記導電材を含まないで相互に異なるか若しくは同じポリマーを主体に構成された多孔質層とを備える三層構造を有している。
かかる構成によると、互いに融点の異なる層を有するため、二段階シャットダウンが可能となる。また、電池内部の温度が上昇すると多孔質導電層のポリマーが先に溶融するため、導電材を含まない多孔質層が溶融する前に(即ち多孔質層が形状を保った状態で)多孔質導電層の導電材が該導電材を含まない多孔質層へと移動して複数の微小な導電経路を形成することができる。従って、正極と負極との直接接触による短絡を防止しながら電池内部の温度上昇を確実に抑制することができる。
好ましい一態様では、上記多孔質導電層を構成しているポリマーはポリエチレン(PE)であり、上記導電材を含まない多孔質層を構成しているポリマーはポリプロピレン(PP)である。
かかるセパレータによると、シャットダウン温度を、PEの融点(一般的には概ね125~135℃程度)およびPPの融点(一般的には概ね155~165℃程度)の二段階に設定することができるため、より安全性に優れるセパレータとなる。
より好ましい一態様では、上記導電材の含有割合は、8質量%以上40質量%以下である。
かかる構成によると、セパレータとして十分な強度を有すると共に電池内部の温度上昇を抑制するのに必要な複数の微小な導電経路を形成することができる。
かかる構成によると、電池内部の温度が上昇したときに正極と負極との間に微小な短絡を発生させることが可能な導電経路を形成することができる。
なお、本明細書において「平均空孔径」とは、多孔質層(多孔質導電層を含む)に形成された空孔が略円形状(略楕円形状を含む。)の場合には、その略円の直径(略楕円の場合にはその長径)の平均値をいい、上記空孔が略方形状(略長方形状を含む。)の場合には、その略方形状の一辺(略長方形の場合にはその長辺)の平均値をいい、SEM(走査型電子顕微鏡)画像等により、多孔質層(多孔質導電層を含む)の表面の少なくとも一部を観察することによって測定することができる。
また、本明細書において「平均粒径」とは、メジアン径(d50)をいい、市販されている種々のレーザー回折・散乱法に基づく粒度分布測定装置によって容易に測定することができる。
図3に示すように、本実施形態に係るセパレータ70は、3つの多孔質層76A,72,76Bが積層された3層構造であって、多孔質層中に導電材74が分散されている多孔質導電層72と、該多孔質導電層72の両面にそれぞれ積層された導電材を含まないで相互に異なるか若しくは同じポリマーを主体に構成された多孔質層76A,76Bとを備えている。かかるセパレータ70は、典型的には長尺なシート状に形成されるが、かかる態様に限定されず、該セパレータ70が用いられる二次電池の形状に応じて種々の形状に加工され得る。
また、多孔質導電層72は、融点が凡そ120℃~140℃(例えば凡そ125℃~135℃)のPEから構成されることが好ましい。PEとしては、例えば、高密度ポリエチレン、あるいは直鎖状(線状)低密度ポリエチン等と称されるポリエチレンが挙げられる。
ここで「空孔率」は、以下のようにして算出することができる。多孔質層76Aを一例として説明する。単位面積(サイズ)の多孔質層76Aが占める見かけの体積をV1[cm3]とし、上記単位面積の多孔質層76Aの質量をW[g]とする。この質量Wと上記多孔質層76Aを構成するポリマーの真密度ρ[g/cm3]との比、すなわちW/ρをV0とする。なお、V0は、質量Wのポリマーの緻密体が占める体積である。このとき、多孔質層76Aの空孔率は、(V1-V0)/V1×100によって算出することができる。また、「空孔率」は、例えばX線CTスキャナーによって計測することができる値である。
また、導電材を含む多孔質導電層72の平均空孔径は、該多孔質導電層72の空孔率を多孔質層76A,76Bの空孔率よりも高くするという目的から、多孔質ポリマー層76A,76Bの平均空孔径よりも大きいことが好ましく、凡そ0.1μm~1μm(例えば凡そ0.15μm~0.3μm)であることが好ましい。
リチウムイオン二次電池(二次電池)10(図2参照)において、過充電等により電池10内部の温度が上昇すると、まずセパレータ70の多孔質導電層72を構成する多孔質状に形成されたポリマーが溶融する。該ポリマーが溶融することで多孔質導電層72中の空孔が塞がれて(即ちシャットダウン)正負極間のリチウムイオンの移動を抑制する。さらに、図4Aに示すように、多孔質導電層72に含まれる導電材74は、溶融したポリマーと共に移動して導電材を含まない多孔質層76Aの空孔78A及び多孔質層76Bの空孔78Bへと流れ込む。そして、図4Bに示すように、空孔78A,78Bへと流れ込んだ導電材74は、セパレータ70の積層方向の一方の端部(正極シート64と接する面)から他方の端部(負極シート84と接する面)へと繋がり、正極シート64と負極シート84との間に微小な導電経路79が形成される。セパレータ70において、このような微小な導電経路79が複数形成されることによって、正極64と負極84との間の複数個所において微小な短絡が発生し、熱エネルギーが分散して消費されるため、電池内部の温度の上昇を抑制することができる。
また、上記無機フィラー層には、必要に応じて増粘材を含有することができる。かかる増粘材としては、例えば、水系溶媒を使用する場合、カルボキシメチルセルロース(CMC)やポリエチレンオキサイド(PEO)等が挙げられる。
図1に示すように、本実施形態に係るリチウムイオン二次電池10は、金属製(樹脂製又はラミネートフィルム製も好適である。)の電池ケース15を備える。このケース(外容器)15は、上端が開放された扁平な直方体状のケース本体30と、その開口部20を塞ぐ蓋体25とを備える。溶接等により蓋体25は、ケース本体30の開口部20を封止している。ケース15の上面(すなわち蓋体25)には、捲回電極体50の正極シート(正極)64と電気的に接続する正極端子60および該電極体の負極シート84と電気的に接続する負極端子80が設けられている。また、蓋体25には、従来のリチウムイオン二次電池のケースと同様に、電池異常の際にケース15内部で発生したガスをケース15の外部に排出するための安全弁40が設けられている。ケース15の内部には、図2に示すように、正極シート64および負極シート84を計二枚のセパレータシート70とともに積層して捲回し、次いで得られた捲回体を側面方向から押しつぶして拉げさせることによって作製される扁平形状の捲回電極体50及び電解質(例えば非水電解液)が収容されている。
また、一般式がLiMPO4或いはLiMVO4或いはLi2MSiO4(式中のMはCo、Ni、Mn、Feのうちの少なくとも一種以上の元素)等で表記されるようなポリアニオン系化合物(例えばLiFePO4、LiMnPO4、LiFeVO4、LiMnVO4、Li2FeSiO4、Li2MnSiO4、Li2CoSiO4)を上記正極活物質として用いてもよい。
図5に示すように、本実施形態に係るセパレータ170は、相互に異なるか若しくは同じポリマーを主体に構成された2つの多孔質層176,172が積層された2層構造であって、該多孔質層中に導電材174が分散されている多孔質導電層172と、該多孔質導電層172の表面に積層された導電材を含まない多孔質層176とを備えている。
かかる構成によると、第1実施形態の場合と同様の効果が得られる。なお、本実施形態に係るセパレータ170の表面に無機フィラー層を形成する場合には、少なくとも多孔質導電層172の表面に形成することが好ましい。
<例1>
多孔質導電層を形成する成分としてのポリエチレン(熱可塑性ポリマー)と平均粒径40μmのアセチレンブラック(導電材)との質量比が97:3である混合物を用意し、多孔質層を形成する成分としてのポリプロピレン(熱可塑性ポリマー)を用意し、Tダイ押出機を用いてこれらの成分を同時に溶融押出することによって、多孔質導電層(以下、「導電層」ともいう。)の両面に多孔質層(以下、「PP層」ともいう。)が形成された三層構造のフィルムを成形した。成形後のフィルムを該フィルムの長手方向に延伸(一軸延伸)して例1に係るセパレータシートを作製した。本例では、セパレータの総空孔率52%であった。また、多孔質導電層の厚みは7μm、平均空孔径は0.2μmであり、多孔質層の厚みは7μm、平均空孔径は0.1μmであった。
そして、無機フィラーとしてのアルミナ粉末(平均粒径(d50)0.3μm;純度99.99%)とバインダとしてのアクリル系ポリマーと増粘材としてのカルボキシルメチルセルロース(CMC)とを、それらの材料の質量比が96:3:1となるように水中で分散し、無機フィラー層形成用組成物を調製した。この無機フィラー層形成用組成物を、多孔質層の表面にグラビアロールにより塗布、乾燥することにより、無機フィラー層を形成した。無機フィラー層の厚みを5μmとし、空孔率を60%とした。以上より、厚み26μmの例1に係る無機フィラー層付セパレータシートを作製した。
<例2>
多孔質導電層を形成する成分としてのポリエチレンと平均粒径40μmのアセチレンブラックとの質量比が92:8である混合物を用いた他は例1と同様にして、例2に係る無機フィラー層付セパレータシートを作製した。
<例3>
多孔質導電層を形成する成分としてのポリエチレンと平均粒径40μmのアセチレンブラックとの質量比が80:20である混合物を用いた他は例1と同様にして、例3に係る無機フィラー層付セパレータシートを作製した。
<例4>
多孔質導電層を形成する成分としてのポリエチレンと平均粒径40μmのアセチレンブラックとの質量比が60:40である混合物を用いた他は例1と同様にして、例4に係る無機フィラー層付セパレータシートを作製した。
<例5>
多孔質導電層を形成する成分としてのポリエチレンと平均粒径40μmのアセチレンブラックとの質量比が40:60である混合物を用いた他は例1と同様にして、例5に係る無機フィラー層付セパレータシートを作製した。
多孔質導電層を形成する成分としてのポリエチレンを用意し、多孔質層を形成する成分としてのポリプロピレンを用意し、Tダイ押出機を用いてこれらの成分を同時に溶融押出することによって、ポリエチレンを主体とする多孔質層(以下、「PE層」ともいう。)の両面にポリプロピレンを主体とする多孔質層(PP層)が形成された三層構造のフィルムを成形した。成形後のフィルムを該フィルムの長手方向に延伸(一軸延伸)して例6に係るセパレータシートを作製した。かかるセパレータシートを用いた他は例1と同様にして、例6に係る無機フィラー層付セパレータシートを作製した。
<例7>
多孔質層(PE層)を形成する成分としてのポリエチレンを用意し、Tダイ押出機を用いて該成分を溶融押出することによって、多孔質層(PE層)からなる単層構造のフィルムを成形した。成形後のフィルムを該フィルムの長手方向に延伸(一軸延伸)して厚み21μmの例7に係るセパレータシートを作製した。かかるセパレータシートを用いた他は例1と同様にして、例7に係る無機フィラー層付セパレータシートを作製した。
<例8>
多孔質層(PP層)を形成する成分としてのポリプロピレンを用いた他は例7と同様にして、例8に係る無機フィラー層付セパレータシートを作製した。
正極活物質としてのLiNi1/3Co1/3Mn1/3O2と、導電材としてのアセチレンブラック(AB)と、結着材としてのPVDFとの質量比が90:5:5となるように秤量し、これら材料をNMPに分散させてペースト状の正極合材層形成用組成物を調製した。該ペーストを厚さ15μmの正極集電体(アルミニウム箔)上に片面当たり塗布量6mg/cm2で塗布し乾燥させた後、プレス処理を行って正極集電体上に正極合材層が形成された正極シートを作製した。
また、表面を非晶質炭素膜で被覆した天然黒鉛と、結着材としてのSBRと、増粘材としてのCMCとの質量比が98:1:1となるように秤量し、これら材料をイオン交換水に分散させてペースト状の負極合材層形成用組成物を調製した。該組成物を負極集電体(銅箔)上に片面当たり塗布量4mg/cm2塗布して乾燥させた後、プレス処理を行って負極集電体上に負極合材層が形成された負極シートを作製した。
上記作製した正極シートと負極シートと例1に係る無機フィラー層付セパレータシート2枚とを重ね合わせて円筒状に捲回し、例1に係る捲回電極体を得た。直径18mm、長さ65mm、厚さ0.5mmのニッケルメッキ軟鋼製の有底円筒状のケース本体に例1に係る捲回電極体と電解液とを収容することにより例1に係るリチウムイオン二次電池を構築した。電解液としては、エチレンカーボネート(EC)とジエチルカーボネート(DEC)との体積比3:7の混合溶媒に1mol/LのLiPF6を溶解させたものを使用した。また、例2から例8に係る無機フィラー層付セパレータシートを用いて、上記例1に係るリチウムイオン二次電池と同様にして例2から例8に係るリチウムイオン二次電池を構築した。なお、例5に係る無機フィラー層付セパレータシートは十分な強度を有していなかったためリチウムイオン二次電池は構築できなかった。
上記構築した例1~例8(例5を除く)に係るリチウムイオン二次電池に適当なコンディショニング処理(例えば、正極理論容量の1/10Cの充電レートで3時間の定電流(CC)充電を行い、さらに1/3Cの充電レートで4.1Vまで定電流で充電する操作と、1/3Cの放電レートで3.0Vまで定電流放電させる操作とを2~3回繰り返す初期充放電処理)を行った後、60℃の恒温槽においてSOC80%の充電状態に調整した。ここで1Cとは、正極の理論容量より予測した電池容量(Ah)を1時間で充電できる電流量を意味する。
上記調整後の各リチウムイオン二次電池に対して60℃の温度条件下において4Cの充電レートでSOC300%を上限として定電流充電を行い(即ち、充電が完了した後のリチウムイオン二次電池に強制的に充電電流を流し続ける試験である。)各電池の不具合(開弁若しくは発煙)の発生の有無を確認した。その結果を表1に示す。
15 電池ケース
20 開口部
25 蓋体
30 ケース本体
40 安全弁
50 捲回電極体
60 正極端子
62 正極集電体
64 正極シート(正極)
66 正極合材層
70 セパレータシート(セパレータ)
72 多孔質導電層(多孔質層)
74 導電材
76A,76B 多孔質層
78A,78B 空孔
79 導電経路
80 負極端子
82 負極集電体
84 負極シート(負極)
90 負極合材層
100 車両(自動車)
170 セパレータシート(セパレータ)
172 多孔質導電層(多孔質層)
174 導電材
176 多孔質層
Claims (9)
- 正極と、負極と、前記正極と前記負極との間に介在するセパレータとを備えた二次電池であって、
前記セパレータは、相互に異なるか若しくは同じポリマーを主体に構成された少なくとも2つの多孔質層を備える積層構造を有しており、そのうちの1つの層は、当該多孔質層中に導電材が分散されてなる多孔質導電層を形成している、二次電池。 - 前記セパレータは、前記1つの多孔質導電層と、該多孔質導電層の両面にそれぞれ積層された前記導電材を含まないで相互に異なるか若しくは同じポリマーを主体に構成された多孔質層とを備える三層構造を有している、請求項1に記載の二次電池。
- 前記多孔質導電層を構成しているポリマーの融点は、前記導電材を含まない多孔質層を構成しているポリマーの融点よりも低い、請求項1又は2に記載の二次電池。
- 前記多孔質導電層を構成しているポリマーはポリエチレンであり、前記導電材を含まない多孔質層を構成しているポリマーはポリプロピレンである、請求項3に記載の二次電池。
- 前記多孔質導電層を100質量%としたときに、該多孔質導電層に含まれる前記導電材の含有割合は、3質量%よりも大きく50質量%よりも小さい、請求項1から4のいずれか一項に記載の二次電池。
- 前記導電材の含有割合は、8質量%以上40質量%以下である、請求項5に記載の二次電池。
- 前記導電材はカーボン材料である、請求項1から6のいずれか一項に記載の二次電池。
- 前記導電材を含まない多孔質層の平均空孔径は0.05μm~0.5μmであり、前記多孔質導電層に含まれる導電材の平均粒径は0.01μm~0.1μmであって前記平均空孔径を上回らない平均粒径である、請求項1から7のいずれか一項に記載の二次電池。
- リチウムイオン二次電池用の正極活物質を含む正極と、リチウムイオン二次電池用の負極活物質を含む負極と、電解液とを用いてリチウムイオン二次電池として構築された、請求項1から8のいずれか一項に記載の二次電池。
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JP2016146263A (ja) * | 2015-02-06 | 2016-08-12 | 株式会社日本触媒 | セパレータ及びそれを含んで構成される電池 |
JP2018195475A (ja) * | 2017-05-18 | 2018-12-06 | 株式会社Gsユアサ | 蓄電素子 |
JP2019029299A (ja) * | 2017-08-03 | 2019-02-21 | 大日本印刷株式会社 | 電池用包装材料、その製造方法、及び電池 |
CN109560237A (zh) * | 2018-10-15 | 2019-04-02 | 福建冠城瑞闽新能源科技有限公司 | 一种锂离子电池复合隔离膜及二次锂离子电池 |
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US20140162109A1 (en) | 2014-06-12 |
EP2731169A4 (en) | 2014-05-14 |
JPWO2013005329A1 (ja) | 2015-02-23 |
EP2731169A1 (en) | 2014-05-14 |
CN103650203A (zh) | 2014-03-19 |
JP5761582B2 (ja) | 2015-08-12 |
US9660240B2 (en) | 2017-05-23 |
CN103650203B (zh) | 2017-03-01 |
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