WO2012023199A1 - 非水電解液二次電池 - Google Patents
非水電解液二次電池 Download PDFInfo
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- WO2012023199A1 WO2012023199A1 PCT/JP2010/064032 JP2010064032W WO2012023199A1 WO 2012023199 A1 WO2012023199 A1 WO 2012023199A1 JP 2010064032 W JP2010064032 W JP 2010064032W WO 2012023199 A1 WO2012023199 A1 WO 2012023199A1
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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
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/626—Metals
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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
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
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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
- H01M10/058—Construction or manufacture
- H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
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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
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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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
- H01M50/431—Inorganic material
- H01M50/434—Ceramics
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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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- 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
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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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery in which a porous layer is formed between a separator sheet and at least one of a positive electrode sheet and a negative electrode sheet.
- lithium ion batteries, nickel metal hydride batteries and other non-aqueous electrolyte secondary batteries have become increasingly important as on-vehicle power supplies or personal computers and portable terminals.
- a lithium ion battery that is lightweight and obtains a high energy density is expected to be preferably used as a high-output power source mounted on a vehicle.
- a polyolefin-based porous film is used as a separator interposed between a positive electrode and a negative electrode.
- the polyolefin-based porous film is made of a synthetic resin, it is easily deformed when the temperature inside the battery becomes high, and the risk of occurrence of an internal short circuit (short circuit) is improved. Therefore, as one of means for more reliably preventing the occurrence of defects such as short-circuiting, for example, it is considered to form a heat-resistant porous layer made of an inorganic filler on the surface of any one of the positive electrode, the negative electrode, and the separator. (For example, Patent Document 1). According to this configuration, even when the separator is deformed, the heat-resistant porous layer can prevent the contact between the positive electrode and the negative electrode, and the occurrence of a short circuit can be suppressed.
- Patent Document 1 discloses a lithium secondary battery in which a second separator layer (porous layer) having a filler having a heat resistant temperature of 150 ° C. or higher is formed on the surface of the first separator layer.
- the filler constituting the heat-resistant porous layer is preferably plate-like particles, and typical examples thereof include plate-like alumina and plate-like boehmite.
- the porous layer is crushed by the pressure of expansion and contraction of the electrode accompanying charging and discharging, and the porosity of the porous layer is reduced. If the porosity of the porous layer decreases, the electrolyte and ions cannot pass through the porous layer, and the performance (load characteristics and high-rate durability) of the lithium secondary battery constructed using this becomes insufficient. It is not preferable.
- the present invention has been made in view of such a point, and a main object thereof is to provide a non-aqueous electrolyte secondary battery in which performance deterioration due to a decrease in porosity of a porous layer is suppressed.
- the non-aqueous electrolyte secondary battery provided by the present invention is a lithium secondary battery including an electrode body in which a positive electrode sheet and a negative electrode sheet are overlapped via a separator sheet.
- a porous layer having filler particles and a binder is formed between at least one of the positive electrode sheet and the negative electrode sheet and the separator sheet.
- the median value in the circularity distribution of the filler particles contained in the porous layer is 0.85 to 0.97.
- the circularity of the filler particles can be obtained, for example, by calculating the perimeter length and area from a projected image (particle image) of the filler particles and by the following equation (1).
- Circularity a L0 / L1 (1)
- L0 in the above formula (1) is the perimeter of an ideal circle (perfect circle) having the same area as the area calculated from the actually measured projection image (particle image) of the target particle
- the circularity distribution typically, the number distribution
- Such circularity distribution can be easily measured by, for example, a commercially available particle image analyzer, for example, a flow type particle image analyzer.
- the median value in the circularity distribution of filler particles obtained by the particle image analyzer approximately 0.85 to 0.97 is appropriate.
- the filler particles become more spherical, so that the filler particles can be filled more easily and it is difficult to increase the porosity of the porous layer.
- the porous layer may be compressed under the pressure of expansion and contraction of the electrode accompanying charge / discharge, and cycle deterioration may occur.
- the porosity of the porous layer can be increased, but the amount of filler contained per volume of the porous layer is reduced, so that the contact between the positive electrode and the negative electrode Preventive action may not be obtained. Moreover, since the strength of the porous layer tends to be insufficient, the porous layer may be crushed due to the pressure of expansion and contraction of the electrode accompanying charge / discharge, and cycle deterioration may occur.
- the median value in the circularity distribution of the filler particles contained in the porous layer is generally 0.85 to 0.97, preferably 0.85 to 0.96, and more preferably 0.85 to 0.96. 0.93, particularly preferably 0.85 to 0.9.
- the porosity for example, 50 to 70%, preferably 56 to 70
- the porosity suitable for the porous layer is maintained while appropriately maintaining the amount of filler contained per volume of the porous layer. %, Particularly preferably 60 to 70%), and a porous layer having high electrolyte permeability and mechanical strength can be obtained.
- a porous layer it is possible to construct a non-aqueous electrolyte secondary battery having high safety and good battery characteristics (load characteristics and high-rate durability).
- the circularity value corresponding to a cumulative 10% from the side with the smaller circularity (Hereinafter referred to as the lower value) is 0.7 to 0.9.
- irregular and angular particles are included in a certain ratio, and the angular particles suppress slippage between filler particles, and filler filling ability is appropriately reduced. Therefore, it is possible to stably obtain an optimal porous layer that achieves both high mechanical strength and good electrolyte solution permeability as described above at a high level.
- the filler particles are alumina or alumina hydrate.
- Alumina or alumina hydrate is preferable in that the circularity distribution can be easily adjusted by processing such as grinding.
- alumina or alumina hydrate has a relatively high Mohs hardness, it is preferable in that the mechanical strength and durability of the porous layer can be improved.
- the porous layer is formed on the surface of the separator sheet.
- the manufacturing cost is reduced, and a porous layer can be formed between the separator sheet and the electrode sheet without adversely affecting the battery performance.
- the porous layer is preferably formed on a surface of the separator sheet facing the negative electrode sheet.
- the electrode body is a wound electrode body in which the positive electrode sheet and the negative electrode sheet are wound through the separator sheet.
- the electrode body is a wound electrode body, it is particularly useful to apply the present invention because performance deterioration due to a decrease in the porosity of the porous layer is particularly likely to occur.
- any of the non-aqueous electrolyte secondary batteries disclosed herein has performance suitable as a battery mounted on a vehicle (for example, high output can be obtained), and is particularly excellent in durability against high-rate charge / discharge. It can be. Therefore, according to this invention, the vehicle provided with one of the non-aqueous electrolyte secondary batteries disclosed here is provided.
- a vehicle for example, an automobile
- the non-aqueous electrolyte secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.
- FIG. 1 is a side view schematically showing a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.
- 2 is a cross-sectional view taken along line II-II in FIG.
- FIG. 3 is a diagram schematically showing an electrode body of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.
- FIG. 4 is an enlarged cross-sectional view showing a main part of the nonaqueous electrolyte secondary battery according to one embodiment of the present invention.
- FIG. 5 is a diagram for explaining a film resistance measurement method according to one test example.
- FIG. 6 is a side view schematically showing a vehicle including a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.
- non-aqueous electrolyte lithium secondary battery in which a wound electrode body (rolled electrode body) and a non-aqueous electrolyte are housed in a cylindrical container
- the present invention will be described in detail by taking (lithium ion battery) as an example.
- FIG. 1 to 3 show a schematic configuration of a lithium ion battery according to an embodiment of the present invention.
- an electrode body (winding electrode body) 80 in which a long positive electrode sheet 10 and a long negative electrode sheet 20 are wound through a long separator 40 is illustrated. It has the structure accommodated in the container 50 of the shape (cylindrical type) which can accommodate this winding electrode body 80 with the non-aqueous electrolyte solution which does not.
- the container 50 includes a bottomed cylindrical container main body 52 having an open upper end and a lid 54 that closes the opening.
- a metal material such as aluminum, steel, or Ni-plated SUS is preferably used (Ni-plated SUS in the present embodiment).
- a positive electrode terminal 70 that is electrically connected to the positive electrode 10 of the wound electrode body 80 is provided on the upper surface (that is, the lid body 54) of the container 50.
- a negative electrode terminal 72 (in this embodiment also serves as the container main body 52) that is electrically connected to the negative electrode 20 of the wound electrode body 80 is provided.
- a wound electrode body 80 is accommodated together with a non-aqueous electrolyte (not shown).
- the wound electrode body 80 according to the present embodiment is the same as the wound electrode body of a normal lithium ion battery except for the configuration of the separator 40 described later, and as shown in FIG. It has a long (strip-shaped) sheet structure at the stage before assembly.
- the positive electrode sheet 10 has a structure in which a positive electrode active material layer 14 containing a positive electrode active material is held on both surfaces of a long sheet-like foil-shaped positive electrode current collector 12. However, the positive electrode active material layer 14 is not attached to one side edge (the lower side edge portion in the figure) along the edge in the width direction of the positive electrode sheet 10, and the positive electrode current collector 12 has a constant width. An exposed positive electrode active material layer non-forming portion is formed.
- the negative electrode sheet 20 has a structure in which a negative electrode active material layer 24 containing a negative electrode active material is held on both surfaces of a long sheet-like foil-shaped negative electrode current collector 22.
- the negative electrode active material layer 24 is not attached to one side edge (the upper side edge portion in the figure) along the edge in the width direction of the negative electrode sheet 20, and the negative electrode current collector 22 is exposed with a certain width.
- a negative electrode active material layer non-formed portion is formed.
- the positive electrode sheet 10 and the negative electrode sheet 20 are laminated via the separator sheet 40 as shown in FIG. At this time, the positive electrode sheet 10 and the negative electrode sheet 20 are formed such that the positive electrode active material layer non-formed portion of the positive electrode sheet 10 and the negative electrode active material layer non-formed portion of the negative electrode sheet 20 protrude from both sides in the width direction of the separator sheet 40. Are overlapped slightly in the width direction.
- the wound electrode body 80 can be manufactured by winding the laminated body thus superposed.
- a wound core portion 82 (that is, the positive electrode active material layer 14 of the positive electrode sheet 10, the negative electrode active material layer 24 of the negative electrode sheet 20, and the separator sheet 40) is densely arranged in the central portion of the wound electrode body 80 in the winding axis direction. Laminated portions) are formed. In addition, the electrode active material layer non-formed portions of the positive electrode sheet 10 and the negative electrode sheet 20 protrude outward from the wound core portion 82 at both ends in the winding axis direction of the wound electrode body 80.
- a positive electrode lead terminal 74 and a negative electrode lead terminal 76 are respectively provided on the protruding portion 84 (that is, a portion where the positive electrode active material layer 14 is not formed) 84 and the protruding portion 86 (that is, a portion where the negative electrode active material layer 24 is not formed) 86. Attached and electrically connected to the above-described positive electrode terminal 70 and negative electrode terminal 72 (here, the container body 52 also serves).
- the constituent elements of the wound electrode body 80 may be the same as those of the conventional wound electrode body of the lithium ion battery except for the separator sheet 40, and are not particularly limited.
- the positive electrode sheet 10 can be formed by applying a positive electrode active material layer 14 mainly composed of a positive electrode active material for a lithium ion battery on a long positive electrode current collector 12.
- a positive electrode active material layer 14 mainly composed of a positive electrode active material for a lithium ion battery on a long positive electrode current collector 12.
- an aluminum foil or other metal foil suitable for the positive electrode is preferably used.
- the positive electrode active material one type or two or more types of materials conventionally used in lithium ion batteries can be used without any particular limitation.
- lithium and a transition metal element such as lithium nickel oxide (LiMn 2 O 4 ), lithium cobalt oxide (LiCoO 2 ), and lithium manganese oxide (LiNiO 2 ) are used.
- a positive electrode active material mainly containing an oxide containing a constituent metal element (lithium transition metal oxide) can be given.
- the negative electrode sheet 20 can be formed by applying a negative electrode active material layer 24 mainly composed of a negative electrode active material for a lithium ion battery on a long negative electrode current collector 22.
- a negative electrode active material layer 24 mainly composed of a negative electrode active material for a lithium ion battery on a long negative electrode current collector 22.
- a copper foil or other metal foil suitable for the negative electrode is preferably used.
- the negative electrode active material one or more of materials conventionally used in lithium ion batteries can be used without any particular limitation.
- Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium-containing transition metal oxides and transition metal nitrides.
- the separator sheet 40 has a large number of pores inside the separator, and the non-aqueous electrolyte and lithium ions can pass through the inside of the separator sheet by the connection of the pores. ing. Further, when the battery abnormally generates heat due to overcharging or the like, the separator sheet 40 closes the pores (shuts down) and blocks electrical contact between the positive and negative electrodes.
- porous resin constituting the separator sheet examples include porous polyolefin resins.
- Preferable examples include a single layer structure of porous polyethylene (PE) and a three layer structure of polypropylene (PP) / polyethylene (PE) / polypropylene (PP).
- a porous layer 42 is formed between the separator sheet 40 and at least one of the positive electrode sheet 10 and the negative electrode sheet 20.
- the porous layer 42 is formed on the surface of the separator sheet 40 that faces the negative electrode sheet 20.
- FIG. 4 is a schematic cross-sectional view showing an enlarged part of a cross section along the winding axis of the wound electrode body 80, and includes a separator sheet 40 and a porous layer formed on the surface of the separator sheet 40. 42 and the negative electrode sheet 20 facing the porous layer 42 are shown.
- the porous layer 42 is composed of filler particles 44 and a binder (not shown), and the filler particles and the filler particles and the separator sheet are bonded by the binder.
- the porous layer has a large number of pores 48 at sites not bonded by a binder, and the electrolyte solution and ions can pass through the porous layer by the connection of the pores 48.
- the porous layer 42 has a heat resistance that does not melt in a temperature range higher than the melting point of the separator sheet 40 (for example, 150 ° C. or higher), and is porous even when the separator sheet is deformed when the battery generates heat.
- the layer 42 can avoid electrical contact between the positive electrode and the negative electrode.
- the porosity of the porous layer 42 is usually preferably 50% or more (for example, 50 to 70%) at which the electrolyte and ion permeability are good, for example, 52% or more (for example, 52 to 70%).
- the range is appropriate, more preferably 56% or more (for example, 56 to 70%), particularly preferably 60% or more (for example, 60 to 70%).
- the electrolyte solution and ion permeability of the porous layer are sufficient, and battery characteristics (load characteristics, cycle characteristics) can be improved.
- the film thickness can be appropriately selected depending on the application, but in order to ensure the effect of preventing contact between the positive electrode and the negative electrode, it is generally 1 ⁇ m to 20 ⁇ m, preferably 2 to The thickness is 10 ⁇ m, more preferably 3 to 6 ⁇ m, and particularly preferably 3 to 5 ⁇ m.
- the filler particles constituting the porous layer are preferably those having heat resistance (for example, 150 ° C. or more) and electrochemically stable within the battery use range.
- examples of such an inorganic filler include filler particles made of an inorganic metal compound.
- Preferable examples include alumina (Al 2 O 3 ), alumina hydrate (eg boehmite (Al 2 O 3 .H 2 O), magnesium hydroxide (Mg (OH) 2 ), magnesium carbonate (MgCO 3 ), etc.
- Inorganic metal compounds are exemplified, and one or more of these inorganic metal compound materials can be used, among which alumina or alumina hydrate is easy to adjust the circularity distribution by processing such as grinding.
- the particle diameter of the filler particles for example, the D50 diameter based on the laser diffraction scattering method is not particularly limited, but for example, when alumina is used, it is preferably in the range of about 0.2 ⁇ m to 1.2 ⁇ m. When using boehmite, it is preferably within a range of about 0.4 ⁇ m to 1.8 ⁇ m, and the specific surface area of the filler particles based on the BET method. For example, when alumina is used, generally it is preferably in the range of 1.3 m 2 / g ⁇ 18m 2 / g.
- examples of alumina hydrates that can provide similar effects include pseudo-boehmite, ⁇ -alumina (about 900 ° C.), ⁇ -alumina (about 800 ° C.), ⁇ -alumina (about 800 ° C.), ⁇ -alumina (about 500 C), ⁇ alumina (about 500 ° C.), ⁇ alumina (about 500 ° C.), pseudo- ⁇ alumina (about 500 ° C.), ⁇ alumina (about 250 ° C.), and the like.
- the numerical value in the said parenthesis has shown the suitable calcination temperature when synthesize
- the molar ratio of H 2 O / Al 2 O 3 of these alumina hydrates is 2: 1 for pseudoboehmite, and other alumina hydrates.
- Objects can be in the range of 0-1.
- the filler particles may have various shapes ranging from a plate shape to a spherical shape.
- the median value in the circularity distribution of the filler particles is 0.85 to 0.97. It is. When the median value of the circularity distribution is larger than 0.97, the filler particles become more spherical, so that the filler particles can be filled more easily and it is difficult to increase the porosity of the porous layer.
- the porous layer is compressed (rolled) under the pressure of expansion and contraction of the electrode accompanying charge / discharge, and cycle deterioration may occur.
- the porosity of the porous layer can be increased, but the amount of filler contained per volume of the porous layer is reduced, so that the contact between the positive electrode and the negative electrode Preventive action may not be obtained. Moreover, since the strength of the porous layer tends to be insufficient, the porous layer may be crushed due to the pressure of expansion and contraction of the electrode accompanying charge / discharge, and cycle deterioration may occur.
- the median value in the circularity distribution of the filler particles contained in the porous layer is generally about 0.85 to 0.97 (eg, 0.9 to 0.97), preferably 0.85 to 0.96. (For example, 0.91 to 0.96), more preferably 0.85 to 0.93, and particularly preferably 0.85 to 0.9.
- the porosity for example, 50 to 70%, preferably 56 to 70
- the porous layer is maintained while appropriately maintaining the amount of filler contained per volume of the porous layer. %, Particularly preferably 60 to 70%), and a porous layer having high electrolyte permeability and mechanical strength can be obtained.
- a porous layer it is possible to construct a non-aqueous electrolyte lithium secondary battery having high safety and good battery characteristics (load characteristics and high-rate durability).
- the circularity value (hereinafter referred to as the lower value) corresponding to a cumulative 10% from the low circularity side is 0.7 to 0.9.
- the lower value of the circularity distribution is greater than 0.9, the majority of the particles are nearly spherical, so that the particles are more highly filled and the porosity of the porous layer is significantly reduced.
- the lower value of the circularity distribution is set to 0.7 to 0.9, irregular and angular particles are included in a certain ratio (about 10% of the total number). The slippage of the filler is suppressed, and the filler filling property is appropriately reduced. Therefore, it is possible to stably obtain an optimal porous layer that achieves both high mechanical strength and good electrolyte solution permeability as described above at a high level.
- the lower value of the circularity distribution is generally about 0.7 to 0.9, preferably 0.73 to 0.88, more preferably 0.75 to 0.85, and particularly preferably. It is 0.78 to 0.82. Within this range, it is possible to obtain an optimal porous layer that achieves both high mechanical strength and good ion permeability while appropriately maintaining the amount of filler contained per volume of the porous layer.
- the binder used for the porous layer is for bonding between the filler particles, and the material itself constituting the binder is not particularly limited, and various materials can be widely used.
- Preferable examples include acrylic resins.
- acrylic resin monomers such as acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, methacrylate, methyl methacrylate, ethylhexyl acrylate, butyl acrylate, etc. were polymerized in one kind.
- a homopolymer is preferably used.
- the acrylic resin may be a copolymer obtained by polymerizing two or more of the above monomers.
- polyvinylidene fluoride polytetrafluoroethylene (PTFE)
- PTFE polytetrafluoroethylene
- polyacrylonitrile polymethyl methacrylate
- the ratio of the filler particles in the entire porous layer is preferably about 90% by mass or more (typically 95% to 99% by mass), preferably about 96% to 99% by mass. It is preferable that it is mass%. Further, the ratio of the binder in the porous layer is preferably about 5% by mass or less, more preferably about 4.9% by mass (for example, about 0.5% to 3% by mass). Moreover, when it contains porous layer formation components (for example, thickener etc.) other than a filler particle and a binder, it is preferable that the total content rate of these arbitrary components shall be about 3 mass% or less, and about 2 mass% or less ( For example, it is preferably about 0.5% by mass to 1% by mass).
- This porous layer forming method is: (A) preparing a metal compound powder as filler particles (a commercially available metal compound powder may be purchased or synthesized by itself); (B) crushing or spheroidizing the metal compound powder so that the median value in the circularity distribution of the prepared metal compound powder is 0.85 to 0.97; and (C) After the pulverization treatment or spheronization treatment, a coating material for forming a porous layer in which the metal compound powder and a binder are dispersed in a solvent is prepared, and this is at least one of a positive electrode sheet, a negative electrode sheet, and a separator sheet Forming a porous layer by applying to one surface and drying; Is included.
- a metal compound powder used for the porous layer is prepared.
- This metal compound powder is synthesized from a predetermined raw material compound powder.
- a powder of a raw material compound (that is, a starting material) containing a part of a metal element constituting the metal compound powder is prepared, It can be synthesized by firing.
- a raw material compound (ie, starting material) powder containing a part of the metal element constituting the metal compound powder is dissolved or dispersed in an appropriate solvent and held in a thermostatic bath, and the resulting reaction product is filtered. It can be synthesized by washing, drying. Or you may purchase and use the metal compound powder (commercially available product) marketed.
- a powder of a raw material compound for example, aluminum hydroxide
- a metal element (Al) constituting the alumina powder is prepared, and the raw material compound powder is richer in the atmosphere or in the atmosphere than oxygen. It is good to bake in an oxygen gas atmosphere.
- a desired alumina powder can be obtained by pulverizing the obtained fired product until it has an appropriate size (particle size).
- the firing temperature in the firing treatment may be a temperature range in which the reaction of the raw material compound into alumina proceeds, and is usually fired at 1000 ° C. or higher (eg 1000 to 1200 ° C., eg 1150 ° C. ⁇ 50 ° C.). Is preferred.
- the firing time may be a time until the reaction of the raw material compound into alumina sufficiently proceeds, and usually 90 hours or longer (for example, 90 to 120 hours, for example, approximately 96 hours) is sufficient. .
- 90 hours or longer for example, 90 to 120 hours, for example, approximately 96 hours.
- Boehmite powder can be synthesized by a hydrothermal method.
- a powder of a raw material compound (for example, alumina trihydrate) containing a metal element (Al) constituting the boehmite powder is prepared, and the raw material compound powder, calcium hydroxide and water are put in a pressure vessel, and a thermostatic bath It is good to hold at.
- the desired boehmite powder is obtained by filtering, washing, and drying the obtained reaction product.
- the holding temperature in the thermostatic bath may be in the temperature range where a reaction product is generated, and it is usually preferable to hold at 180 ° C. or higher (eg 180 to 220 ° C., eg 200 ° C. ⁇ 10 ° C.).
- the holding time may be a time until the reaction product is sufficiently formed, and usually 60 hours or longer (for example, 60 to 100 hours, for example, approximately 72 hours) is sufficient. Since boehmite particles grow greatly by the addition of calcium hydroxide, it becomes easy to adjust the circularity distribution of the boehmite powder by pulverization or spheroidization, which will be described later.
- the metal compound powder is pulverized or crushed so that the median value in the circularity distribution of the obtained metal compound powder is 0.85 to 0.97.
- a spheroidizing process is performed.
- the metal compound powder is pulverized so that the median value of the circularity distribution is 0.85 to 0.97. Processing should be done.
- the pulverizing apparatus used for the pulverization process is not particularly limited as long as it can appropriately adjust the median value of the circularity distribution in the range of 0.85 to 0.97.
- a pulverizer such as a jet mill, a ball mill, or a vibrating ball mill can be preferably used.
- the use of a jet mill is preferable in that the circularity distribution can be adjusted more appropriately.
- the circularity distribution of the metal compound powder can be adjusted by changing pulverization conditions such as wind pressure (pulverization gas pressure) and pulverization time. That is, by appropriately selecting grinding conditions such as wind pressure (grinding gas pressure) and grinding time, a metal compound powder satisfying a median value of circularity distribution of 0.85 to 0.97 can be formed.
- the wind pressure (pulverized gas pressure) of the jet mill is preferably about 0.2 to 0.4 MPa.
- the degree of circularity distribution also depends on the time for which the pulverization process is performed.
- the grinding time is preferably about 5 to 20 minutes.
- the metal compound powder is spherical with respect to the metal compound powder so that the median value of the circularity distribution is 0.85 to 0.97. It is advisable to perform processing.
- the processing apparatus used for the spheroidizing process is not particularly limited as long as the median value of the circularity distribution can be appropriately adjusted in the range of 0.85 to 0.97.
- a particle processing apparatus such as Kryptron Orb (manufactured by Earth Technica Co., Ltd.) and Faculty (manufactured by Hosokawa Micron Co., Ltd.) can be preferably used.
- the use of kryptron orb is preferable in that it can be spheroidized without changing the particle size of the filler particles.
- the circularity distribution of the metal compound powder can be adjusted by changing processing conditions such as the number of rotations and the number of processing times. That is, a metal compound powder satisfying a median value of circularity distribution of 0.85 to 0.97 can be formed by appropriately selecting processing conditions such as the number of rotations and the number of processing times.
- the rotational speed of the kryptron orb is preferably about 6000 to 10000 rpm.
- the degree of circularity distribution also depends on the number of times of spheroidization processing. The number of treatments is preferably about 2 to 5 times.
- a metal compound powder satisfying a median value of circularity distribution of 0.85 to 0.97 can be easily formed. It should be noted that which condition is changed in adjusting the circularity distribution of the metal compound powder may be appropriately determined according to the processing apparatus to be used.
- the spheroidizing treatment can also be performed using a jet mill. The jet mill can take the corners of the particles by controlling the air volume and increase the circularity.
- the metal compound powder A coating material for forming a porous layer in which a binder and a binder are dispersed in a solvent is prepared. And the porous layer is formed by apply
- Examples of the solvent used in the coating material for forming the porous layer include organic solvents such as N-methylpyrrolidone (NMP), pyrrolidone, methyl ethyl ketone, methyl isobutyl ketone, ixahexanone, toluene, dimethylformamide, dimethylacetamide, and the like. A combination of more than one species can be mentioned. Alternatively, water or a mixed solvent mainly composed of water may be used. As 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 content of the solvent in the coating material for forming a porous layer is not particularly limited, but is preferably about 30 to 60% by mass of the whole coating material.
- the said coating material for porous layer formation can contain the 1 type, or 2 or more types of material which can be used as needed other than a metal compound powder (filler particle) and a binder.
- a material is a polymer that functions as a thickening agent for a coating material for forming a porous layer.
- the polymer that functions as a thickener for example, carboxymethyl cellulose (CMC) is preferably used.
- the operation of applying such a porous layer-forming coating material to the separator sheet surface can be performed in the same manner as in the case of producing a porous layer provided in a conventional general lithium secondary battery.
- a suitable coating device gravure coater, slit coater, die coater, comma coater, dip coat, etc.
- the separator is coated with a predetermined amount of the porous layer forming paint to a uniform thickness.
- a suitable coating device gravure coater, slit coater, die coater, comma coater, dip coat, etc.
- the coating material is dried by a suitable drying means (typically at a temperature lower than the melting point of the separator sheet, for example, 110 ° C. or less, for example, 30 to 80 ° C.) to thereby remove the solvent in the coating material for forming the porous layer. Remove.
- a suitable drying means typically at a temperature lower than the melting point of the separator sheet, for example, 110 ° C. or less, for example, 30 to 80 ° C.
- the obtained porous layer is formed using a metal compound powder (filler particle) satisfying a median value of circularity distribution of 0.85 to 0.97. Therefore, an optimal porous layer that achieves both high mechanical strength and good ion permeability can be obtained while appropriately maintaining the amount of filler per volume of the porous layer.
- a lithium secondary battery that satisfies at least one (preferably all) of high-rate cycle durability, good charge / discharge characteristics, and excellent safety is constructed. Can do.
- a lithium secondary battery can be constructed by adopting the same materials and processes as in the prior art except that the porous layer disclosed herein is used.
- the positive electrode sheet 10 and the negative electrode sheet 20 are wound through the two separator sheets 40 as shown in FIG.
- the electrode body 80 may be manufactured. Then, as shown in FIG. 2, the wound electrode body 80 may be accommodated in the container main body 52, and an appropriate nonaqueous electrolytic solution may be disposed (injected) into the container main body 52.
- non-aqueous electrolyte accommodated in the container main body 52 together with the wound electrode body 80 the same non-aqueous electrolyte as used in conventional lithium ion batteries can be used without any particular limitation.
- a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent.
- ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC) etc. can be used, for example.
- the supporting salt for example, LiPF 6, LiBF 4, LiAsF 6, LiCF 3 SO 3, can be preferably used a lithium salt of LiClO 4 and the like.
- a nonaqueous electrolytic solution in which LiPF 6 as a supporting salt is contained at a concentration of about 1 mol / liter in a mixed solvent containing EC, EMC, and DMC at a volume ratio of 3: 4: 3 can be preferably used.
- the non-aqueous electrolyte is housed in the container main body 52 together with the wound electrode body 80, and the opening of the container main body 52 is sealed with the lid body 54, thereby constructing (assembling) the lithium ion battery 100 according to the present embodiment. Is completed.
- positioning (injection) process of electrolyte solution can be performed similarly to the method currently performed by manufacture of the conventional lithium ion battery. Thereafter, the battery is conditioned (initial charge / discharge). You may perform processes, such as degassing and a quality inspection, as needed.
- test examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the following test examples.
- boehmite powder was produced as filler particles.
- 100 g of alumina trihydrate as a starting material and 150 g of water were put into a pressure vessel, 17 mg of calcium hydroxide was added, and then kept in a thermostat bath at 200 ° C. for 72 hours.
- Boehmite was synthesized by filtration, washing and drying.
- the obtained boehmite composite was put into a jet mill (manufactured by Hosokawa Micron Corporation: Model 100AFG) and pulverized at a wind pressure of 0.3 MPa for 15 minutes to prepare boehmite powder.
- the median value of the circularity distribution of the obtained boehmite powder was 0.85, and the lower value was 0.7.
- the median value and the lower value of the circularity distribution were calculated using a flow type particle image analyzer (manufactured by Sysmex Corporation: model FPIA-3000: the number of imaged particles was about 2000).
- Example 2 a commercially available titania powder (manufactured by Kanto Chemical Co., Inc.) was put into a jet mill and pulverized under the conditions shown in Table 1 to produce a titania powder.
- the median value of circularity distribution of the obtained titania powder was 0.89, and the lower value was 0.73.
- the median value of the circularity distribution of the titania powder before pulverization was about 0.985.
- alumina powder was produced as filler particles.
- aluminum hydroxide as a starting material was baked at 1050 ° C. for 96 hours in an air atmosphere to synthesize ⁇ -alumina.
- the obtained alumina composite was put into a jet mill and pulverized under the conditions shown in Table 1 to produce alumina powder.
- the median values of the circularity distribution of the obtained alumina powder were 0.91, 0.93, 0.95, and 0.96, and the lower values were 0.82, 0.85, 0.88 and 0.89.
- Example 7 commercially available magnesium hydroxide powder (manufactured by Kanto Chemical Co., Inc.) was put into a jet mill and pulverized under the conditions shown in Table 1 to produce magnesium hydroxide powder.
- the median value of circularity distribution of the obtained magnesium hydroxide powder was 0.965, and the lower value was 0.9.
- the median value of the circularity distribution of the magnesium hydroxide powder before pulverization was about 0.84.
- Example 8 a commercially available magnesium carbonate powder (manufactured by Kanto Chemical Co., Inc.) was put into a jet mill and pulverized under the conditions shown in Table 1 to produce a magnesium carbonate powder.
- the median value of the circularity distribution of the obtained magnesium carbonate powder was 0.97, and the lower value was 0.9 (1).
- the median value of the circularity distribution of the magnesium carbonate powder before pulverization was about 0.98.
- a titania powder was produced in the same manner as in Example 2, except that pulverization by a jet mill was changed to the conditions shown in Table 1.
- the median value of circularity distribution of the obtained titania powder was 0.8, and the lower value was 0.68.
- alumina powder was produced in the same manner as in Examples 3 to 6, except that the grinding by the jet mill was changed to the conditions shown in Table 1.
- the median value of the circularity distribution of the obtained alumina powder was 0.82, and the lower value was 0.66.
- Comparative Example 3 a commercially available titania powder (manufactured by Kanto Chemical Co., Inc.) was put into a kryptron orb (manufactured by Earth Technica Co., Ltd .: model CSH0), and the titania powder was prepared by processing three times at a rotational speed of 8000 rpm. The median value of circularity distribution of the obtained titania powder was 0.98, and the lower value was 0.92.
- Comparative Example 4 a commercially available alumina powder (manufactured by Kanto Chemical Co., Inc.) was put into a kryptron orb and processed under the conditions shown in Table 1 to produce an alumina powder.
- the median value of circularity distribution of the obtained alumina powder was 0.983, and the lower value was 0.92.
- a porous layer-forming coating material was prepared by mixing in NMP, and this was applied to one side of a long separator sheet 40 and dried to form a porous layer 42.
- the coating amount of the coating material for forming a porous layer was adjusted to be about 0.7 mg / cm 2 (based on solid content).
- the atmospheric temperature in the hot air drying furnace was set to 80 ° C., and the wind speed was set to 16.2 m / s.
- separator sheets two types are used: a single layer structure of polyethylene (PE) and a three layer structure of polypropylene-polyethylene-polypropylene (PP / PE / PE). did. All the separator sheets had a thickness of 20 ⁇ m and a porosity of 47%.
- PE polyethylene
- PP / PE / PE polypropylene-polyethylene-polypropylene
- the porosity of various porous layers obtained above was calculated.
- the porosity (%) of the porous layer was calculated by (1 ⁇ W / ⁇ V) ⁇ 100.
- W is the mass of the porous layer, and was measured with an electronic balance.
- V is the apparent volume of the porous layer, and was calculated from the outer dimensions (thickness x area) of the porous layer by SEM observation.
- ⁇ is the true density (theoretical density) of the material constituting the porous layer. The results are shown in Table 1.
- the porous layers of Examples 1 to 8 in which the median value of the circularity distribution was 0.85 to 0.97 had a porosity of 51 to 70%, which is suitable as a porous layer. there were.
- the median value of the circularity distribution was 0.85 to 0.91, a porous layer in which both electrolyte permeability and mechanical strength of 60 to 70% were realized at a high level could be obtained. From this result, it is desirable that the median value of the circularity distribution is 0.85 to 0.91 from the viewpoint of improving electrolyte permeability and mechanical strength of the porous layer.
- a cell for measurement was constructed using the prepared separator sheets with a porous layer, and the membrane resistance (Rs) was evaluated.
- the porous layer 42 and the separator sheet 40 were impregnated with a nonaqueous electrolytic solution and sandwiched between two copper plates 62 having an area of 35 mm 2 and a thickness of 1 mm.
- a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of 3: 4: 3 was mixed with about 1 mol / L LiPF 6 as a supporting salt.
- the one contained at a concentration of 1 liter was used.
- Such cells 60 were prepared so that there were 1, 2, 3 separator sheets, respectively.
- Each cell was placed in a constant temperature bath at 25 ° C., and the resistance value (Rs) of the cell was measured by an AC impedance method while applying a torque pressure of 50 cN ⁇ m from the upper and lower sides of the two copper plates 62.
- the AC impedance measurement conditions were an AC applied voltage of 5 mV and a frequency range of 10000 Hz to 1 Hz.
- the obtained resistance value of each cell was plotted against the number of separators, and the membrane resistance per separator was determined by linear approximation. The results are shown in Table 1.
- the cells of Examples 1 to 8 having a median value of circularity distribution of 0.85 to 0.97 have much higher membrane resistance than the cells of Comparative Examples 3 and 4. Declined.
- the median value of the circularity distribution was set to 0.91 or less, an extremely low film resistance of 1.5 ⁇ ⁇ cm 2 or less was realized.
- the cells of Examples 1 to 7 in which the lower value of the circularity distribution was 0.7 to 0.9 further reduced the film resistance as compared with the cell of Example 8.
- a lithium secondary battery was constructed using the obtained separator sheets with various porous layers, and the battery characteristics were evaluated.
- the lithium secondary battery was produced as follows.
- the positive electrode active material layer 14 is provided on both surfaces of the positive electrode current collector 12 by applying the positive electrode active material layer paste on both surfaces of the long sheet-like aluminum foil (positive electrode current collector 12) and drying it.
- the obtained positive electrode sheet 10 was produced.
- the coating amount of the positive electrode active material layer paste was adjusted so as to be about 17.2 mg / cm 2 (solid content basis) for both surfaces.
- Graphite powder as a negative electrode active material, styrene butadiene rubber (SBR) as a binder and carboxymethyl cellulose (CMC) as a thickener have a mass ratio of these materials of 98.6: 0.7: 0.7.
- SBR styrene butadiene rubber
- CMC carboxymethyl cellulose
- the paste for negative electrode active material layers was prepared by dispersing in water. This negative electrode active material layer paste is applied to both sides of a long sheet-like copper foil (negative electrode current collector 22), and a negative electrode sheet 20 having a negative electrode active material layer 24 provided on both sides of the negative electrode current collector 22 is produced. did.
- the coating amount of the negative electrode active material layer forming paste was adjusted so that the both surfaces were combined to be about 11.1 mg / cm 2 (based on solid content).
- a wound electrode body 80 was produced by winding the positive electrode sheet 10 and the negative electrode sheet 20 through two separator sheets 40 with a porous layer. At that time, when the separator sheet was PE, the porous layer and the positive electrode sheet were arranged to face each other. Moreover, when the separator sheet was PP / PE / PP, the porous layer and the negative electrode sheet were arranged to face each other.
- the wound electrode body 80 thus obtained was housed in a battery container 50 (18650 type cylindrical shape) together with a non-aqueous electrolyte, and the opening of the battery container 50 was sealed airtight.
- a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3: 4: 3 contains about 1 mol / liter of LiPF 6 as a supporting salt.
- the non-aqueous electrolyte solution contained at a concentration of was used. In this way, the lithium secondary battery 100 was assembled.
- ⁇ High-rate durability test> A charge / discharge pattern in which CC discharge for 10 seconds at 20C was repeated was applied to each of the obtained lithium secondary batteries, and a charge / discharge cycle test was performed. Specifically, in a room temperature (about 25 ° C.) environment, a charge / discharge cycle in which CC discharge is performed for 10 seconds at 20 C, CC is charged for 40 seconds at 5 C after a pause of 5 seconds, is repeated 10,000 times continuously. It was. And the resistance increase rate was computed from IV resistance (initial resistance of a lithium secondary battery) before the said charging / discharging cycle test and IV resistance after a charging / discharging cycle test.
- the IV resistance before and after the charge / discharge cycle was calculated from the voltage drop after 10 seconds of discharge when pulse discharge was performed at 25 ° C. and 30 C, respectively.
- the rate of increase in resistance (%) was determined by [(IV resistance after charge / discharge cycle test ⁇ IV resistance before charge / discharge cycle test) / IV resistance before charge / discharge cycle test] ⁇ 100. The results are shown in Table 1.
- the porous layer 42 is formed on the surface of the separator sheet 40 facing the negative electrode sheet 20 is shown, but the present invention is not limited to this, and the separator sheet 40 faces the positive electrode sheet.
- the shape (outer shape and size) of the lithium secondary battery to be constructed is not particularly limited.
- the outer package may be a thin sheet type constituted by a laminate film or the like, and the battery outer case may be a cylindrical or cuboid battery, or may be a small button shape.
- any of the lithium secondary batteries 100 disclosed herein has a performance suitable for a battery mounted on a vehicle (for example, high output can be obtained), and is particularly excellent in durability against high-rate charge / discharge. It can be. Therefore, according to the present invention, as shown in FIG. 6, a vehicle 1 including any of the lithium secondary batteries 100 disclosed herein is provided.
- a vehicle 1 for example, an automobile
- the lithium secondary battery 100 as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.
- the technology can be used in a charge / discharge cycle including a high rate discharge of 50 A or more (for example, 50 A to 250 A), and further 100 A or more (for example, 100 A to 200 A).
- a high-performance nonaqueous electrolyte secondary battery excellent in high-rate durability can be provided.
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Abstract
Description
円形度a=L0/L1 (1)
ここで、上記式(1)中のL0は実際に測定した対象の粒子の投影像(粒子画像)から算出された面積と同一の面積を有する理想円(真円)の周囲長であり、L1は当該測定対象の粒子の粒子投影像(粒子画像)から測定した実際の周囲長である。
即ち、測定対象とする粉体の円形度分布(典型的には個数分布)は、当該粉体を構成する個々のフィラー粒子について上記式(1)により算出される円形度を測定することにより求められる。かかる円形度分布は、例えば、市販される粒子画像分析装置、例えばフロー式の粒子像分析装置によって容易に測定され得る。
また、ベーマイト以外にも同様の効果が得られるアルミナ水和物として、擬ベーマイト、θアルミナ(約900℃)、δアルミナ(約800℃)、κアルミナ(約800℃)、γアルミナ(約500℃)、χアルミナ(約500℃)、ηアルミナ(約500℃)、擬γアルミナ(約500℃)、ρアルミナ(約250℃)、等が例示される。なお、上記括弧内の数値は上記アルミナ水和物を合成するときの好適な焼成温度を示している。なお、典型的には、これらアルミナ水和物(非水和物であり得る。)のH2O/Al2O3のモル比は、擬ベーマイトが2:1であり、その他のアルミナ水和物が0~1の範囲内であり得る。
(A)フィラー粒子としての金属化合物粉末を用意する(市販の金属化合物粉末を購入してもよく、自ら合成してもよい。)こと;
(B)前記用意した金属化合物粉末の円形度分布におけるメジアン値が0.85~0.97となるように前記金属化合物粉末に対して粉砕処理もしくは球状化処理を行うこと;および、
(C)前記粉砕処理もしくは球状化処理の後、前記金属化合物粉末とバインダとを溶媒中に分散した多孔層形成用塗料を調製し、これを正極シート、負極シート及びセパレータシートのうちの少なくともいずれか一つの表面に塗布し、乾燥することにより多孔層を形成すること;
を包含する。
実施例1では、フィラー粒子としてベーマイト粉末を作製した。まず、出発原料であるアルミナ三水和物100gと水150gとを圧力容器に投入し、水酸化カルシウム17mgを添加した後、200℃の恒温槽で72時間保持し、得られた反応生成物をろ過、洗浄、乾燥してベーマイトを合成した。次いで、得られたベーマイト合成物をジェットミル(ホソカワミクロン株式会社製:型式100AFG)に投入し、風圧0.3MPaで15分間、粉砕することによりベーマイト粉末を作製した。得られたベーマイト粉末の円形度分布のメジアン値は0.85であり、ロワー値は0.7であった。なお、円形度分布のメジアン値およびロワー値はフロー式粒子像分析装置(シスメックス株式会社製:型式FPIA-3000:撮像粒子数約2000個とした。)を用いて算出した。
上記得られた各種の金属化合物粉末(フィラー粒子)とアクリル系バインダとを、金属化合物粉末とバインダとの質量比が97.4:2.6となりかつ固形分率が40質量%となるようにNMP中で混合して多孔層形成用塗料を調製し、これを長尺状のセパレータシート40の片面に塗布し、乾燥することにより多孔層42を形成した。多孔層形成用塗料の塗布量は約0.7mg/cm2(固形分基準)となるように調節した。乾燥条件としては熱風乾燥炉内の雰囲気温度を80℃とし、風速を16.2m/sとした。なお、本例では、表1に示すように、セパレータシートとして、ポリエチレン(PE)の単層構造と、ポリプロプレンーポリエチレンーポリプロプレン(PP/PE/PE)の3層構造の2種類を使用した。いずれのセパレータシートも厚み20μm、空孔率47%とした。
上記作製した各種の多孔層付きセパレータシートを用いて測定用セルを構築し、その膜抵抗(Rs)を評価した。具体的には、図5に模式的に示すように、多孔層42およびセパレータシート40に非水電解液を含浸させ、これを面積35mm2、厚み1mmの2枚の銅板62に挟み込んだ。非水電解液としては、エチレンカーボネート(EC)とジメチルカーボネート(DMC)とエチルメチルカーボネート(EMC)とを3:4:3の体積比で含む混合溶媒に支持塩としてのLiPF6を約1mol/リットルの濃度で含有させたものを用いた。このようなセル60を、セパレータシートが1枚、2枚、3枚となるようにそれぞれ作製した。そして、各セルを25℃の恒温槽に入れ、2枚の銅板62の上下から50cN・mのトルク圧を加えつつ、交流インピーダンス法により、セルの抵抗値(Rs)を測定した。交流インピーダンスの測定条件については、交流印加電圧5mV、周波数範囲10000Hz~1Hzとした。得られた各セルの抵抗値をセパレータの枚数に対してプロットし、直線近似してセパレータ1枚当たりの膜抵抗を求めた。結果を表1に示す。
上記得られた各種の多孔層付きセパレータシートを用いてリチウム二次電池を構築し、その電池特性を評価した。リチウム二次電池は、以下のようにして作製した。
正極活物質としてのLi1.15Ni0.33Mn0.33Co0.33O2粉末と導電材としてのアセチレンブラック(AB)とバインダとしてのポリフッ化ビニリデン(PVdF)とを、これらの材料の質量比が88:10:2となるようにN-メチルピロリドン(NMP)中で混合して、正極活物質層用ペーストを調製した。この正極活物質層用ペーストを長尺シート状のアルミニウム箔(正極集電体12)の両面に帯状に塗布して乾燥することにより、正極集電体12の両面に正極活物質層14が設けられた正極シート10を作製した。正極活物質層用ペーストの塗布量は、両面合わせて約17.2mg/cm2(固形分基準)となるように調節した。
負極活物質としての黒鉛粉末とバインダとしてのスチレンブタジエンゴム(SBR)と増粘剤としてのカルボキシルメチルセルロース(CMC)とを、これらの材料の質量比が98.6:0.7:0.7となるように水に分散させて負極活物質層用ペーストを調製した。この負極活物質層用ペーストを長尺シート状の銅箔(負極集電体22)の両面に塗布し、負極集電体22の両面に負極活物質層24が設けられた負極シート20を作製した。負極活物質層形成用ペーストの塗布量は、両面合わせて約11.1mg/cm2(固形分基準)となるように調節した。
正極シート10及び負極シート20を2枚の多孔層付きセパレータシート40を介して捲回することによって捲回電極体80を作製した。その際、セパレータシートがPEのものは多孔層と正極シートとが対向するように配置した。また、セパレータシートがPP/PE/PPのものは多孔層と負極シートとが対向するように配置した。このようにして得られた捲回電極体80を非水電解液とともに電池容器50(18650型円筒型)に収容し、電池容器50の開口部を気密に封口した。非水電解液としてはエチレンカーボネート(EC)とエチルメチルカーボネート(EMC)とジメチルカーボネート(DMC)とを3:4:3の体積比で含む混合溶媒に支持塩としてのLiPF6を約1mol/リットルの濃度で含有させた非水電解液を使用した。このようにしてリチウム二次電池100を組み立てた。
上記得られたリチウム二次電池のそれぞれに対し、20Cで10秒間のCC放電を繰り返す充放電パターンを付与し、充放電サイクル試験を行った。具体的には、室温(約25℃)環境下において、20Cで10秒間のCC放電を行い、5秒間の休止後、5Cで40秒間のCC充電を行う充放電サイクルを10000回連続して繰り返した。そして、上記充放電サイクル試験前におけるIV抵抗(リチウム二次電池の初期の抵抗)と、充放電サイクル試験後におけるIV抵抗とから抵抗増加率を算出した。ここで、充放電サイクルの前後におけるIV抵抗は、それぞれ、25℃、30Cでパルス放電を行ったときの放電10秒後の電圧降下から算出した。なお、抵抗増加率(%)は、[(充放電サイクル試験後のIV抵抗-充放電サイクル試験前のIV抵抗)/充放電サイクル試験前のIV抵抗]×100により求めた。結果を表1に示す。
また、上記手順と同様の方法でリチウム二次電池を構築し、異物内部短絡試験を実施した。異物内部短絡試験は、高さ0.2mm×幅0.1mmで各辺1mmのL字形のニッケル小片を用いてJISC8714に準じて行い、発煙に至ったNG品の有無を調べた。結果を表1に示す。表1では発煙が認められなかった電池を○、発煙が認められた電池を×で表わしている。
Claims (6)
- 正極シートと負極シートとがセパレータシートを介して重ね合わされてなる電極体を備えた非水電解液二次電池であって、
前記正極シート及び前記負極シートの少なくとも一方と前記セパレータシートとの間には、フィラー粒子とバインダとを有する多孔層が形成されており、
前記多孔層に含有されるフィラー粒子の円形度分布におけるメジアン値が0.85~0.97である、非水電解液二次電池。 - 前記フィラー粒子の円形度分布において、円形度が小さい側からの累積10%に相当する円形度の値が0.7~0.9である、請求項1に記載の非水電解液二次電池。
- 前記フィラー粒子は、アルミナまたはアルミナ水和物である、請求項1または2に記載の非水電解液二次電池。
- 前記多孔層は、少なくとも前記セパレータシートの表面に形成されている、請求項1から3の何れか一つに記載の非水電解液二次電池。
- 前記多孔層は、前記セパレータシートの負極シートに対向する面に形成されている、請求項4に記載の非水電解液二次電池。
- 前記電極体は、前記正極シートと前記負極シートとが前記セパレータシートを介して捲回されてなる捲回電極体である、請求項1から5の何れか一つに記載の非水電解液二次電池。
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