WO2015046468A1 - リチウムイオン二次電池 - Google Patents
リチウムイオン二次電池 Download PDFInfo
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- WO2015046468A1 WO2015046468A1 PCT/JP2014/075731 JP2014075731W WO2015046468A1 WO 2015046468 A1 WO2015046468 A1 WO 2015046468A1 JP 2014075731 W JP2014075731 W JP 2014075731W WO 2015046468 A1 WO2015046468 A1 WO 2015046468A1
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- H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
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- 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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- H01M2300/0045—Room temperature molten salts comprising at least one organic ion
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- 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 lithium ion secondary battery.
- Nonaqueous electrolyte secondary batteries such as lithium ion batteries have the advantages of high energy density, low self-discharge, and good cycle performance. Therefore, in recent years, it is expected that the non-aqueous electrolyte secondary battery is used as a power source for various industrial machines and industrial instruments by increasing the size or capacity.
- the non-aqueous solvent used in the non-aqueous electrolyte of such a lithium ion secondary battery carbonate solvents such as ethylene carbonate and diethyl carbonate, which easily dissolve lithium salts and are not easily electrolyzed, are used.
- carbonate solvents such as ethylene carbonate and diethyl carbonate
- An ionic liquid is an ionic substance that is in a liquid state even at room temperature (about 30 ° C.), and not only has high ionic conductivity, but also has a low vapor pressure, non-volatility and flame retardancy, and is a lithium ion secondary. It also has excellent characteristics for battery safety.
- the non-aqueous electrolyte of the lithium ion secondary battery is required to be electrochemically stable, and the ionic liquid has a stable potential window equal to or higher than that of the carbonate-based solvent.
- an ionic liquid has a problem that it is inferior in charge / discharge characteristics of a large current because it has higher viscosity and lower conductivity than a carbonate solvent.
- Patent Document 1 achieves excellent large-current charge / discharge characteristics by using a specific separator.
- the present inventors have found that a load characteristic of a large current cannot be achieved only by using a separator having the characteristics described in Patent Document 1.
- the present invention solves these problems of the prior art, and provides a lithium ion secondary battery having excellent large current characteristics even when an ionic liquid is used as an electrolytic solution. Objective.
- the positive electrode has a first current collector and a positive electrode mixture applied to at least one surface of the first current collector, and the positive electrode on one surface of the first current collector The application amount of the mixture is 1 mg / cm 2 to 10 mg / cm 2 , and the volume porosity of the positive electrode mixture is 20% to 45% by volume.
- the negative electrode has a second current collector and a negative electrode mixture applied to at least one surface of the second current collector, and the negative electrode on one surface of the second current collector
- the application amount of the mixture is 1 mg / cm 2 to 10 mg / cm 2
- the volume porosity of the negative electrode mixture is 20% to 45% by volume.
- the separator is a nonwoven fabric containing at least one selected from the group consisting of polyolefin fibers, glass fibers, cellulose fibers, and polyimide fibers.
- the anionic component of the ionic liquid is N (C 4 F 9 SO 2 ) 2 ⁇ , CF 3 SO 3 ⁇ , N (SO 2 F) 2 ⁇ , N (SO 2 CF 3 ) 2 ⁇ , and N (SO 2 CF 2 CF 3) 2 - lithium ion secondary battery according to ⁇ 1> or ⁇ 2> made containing at least one selected from the group from.
- ⁇ 4> Any one of ⁇ 1> to ⁇ 3>, wherein the cation component of the ionic liquid includes at least one selected from the group consisting of a chain quaternary ammonium cation, a piperidinium cation, a pyrrolidinium cation, and an imidazolium cation. 2.
- ⁇ 5> The lithium ion secondary battery according to any one of ⁇ 1> to ⁇ 4>, wherein the positive electrode mixture or the negative electrode mixture includes an active material having a median diameter of 0.3 ⁇ m to 30 ⁇ m determined by a laser diffraction method. .
- the present invention it is possible to provide a lithium ion secondary battery having excellent large current characteristics even when an ionic liquid is used as the electrolytic solution.
- the lithium ion secondary battery of the present invention will be described in detail.
- numerical ranges indicated by using “to” indicate ranges including numerical values described before and after “to” as the minimum value and the maximum value, respectively.
- the amount of each component in the composition means the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition.
- the positive electrode is the side that releases (desorbs) lithium ions during charging, and the side that stores (inserts) lithium ions during discharging.
- the negative electrode stores (inserts) lithium ions during charging and releases lithium ions during discharging. (Desorption) side.
- the lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, a separator, and an electrolytic solution containing an ionic liquid and a lithium salt.
- the separator has a porosity of 80% to 98% and satisfies at least one of the following conditions (1) and (2), whereby an ionic liquid is used as the electrolyte. It has been found that a lithium-ion secondary battery excellent in large current characteristics can be provided even if is used, and the present invention has been completed.
- the positive electrode has a first current collector and a positive electrode mixture applied to at least one surface of the first current collector, and the positive electrode mixture is applied to one surface of the first current collector.
- the amount is 1 mg / cm 2 to 10 mg / cm 2 and the volume porosity of the positive electrode mixture is 20% to 45% by volume.
- the negative electrode has a second current collector and a negative electrode mixture applied to at least one surface of the second current collector, and application of the negative electrode mixture to one surface of the second current collector The amount is 1 mg / cm 2 to 10 mg / cm 2 and the volume porosity of the negative electrode mixture is 20% by volume to 45% by volume.
- the positive electrode has a first current collector and a positive electrode mixture applied to at least one surface of the first current collector.
- a positive electrode plate formed by applying a positive electrode mixture to at least one surface of the first current collector, drying and pressing the positive electrode mixture is used.
- the material of the first current collector also referred to as a positive electrode current collector
- metals such as aluminum, titanium, and tantalum, and alloys thereof are used.
- the material of the first current collector is preferably lightweight aluminum and its alloy from the viewpoint of weight energy density.
- the positive electrode mixture includes a positive electrode active material.
- the positive electrode mixture may further contain a conductive agent, a binder and the like.
- lithium transition metal compound As the positive electrode active material, a lithium transition metal compound or the like is used.
- lithium transition metal compounds include lithium transition metal oxides and lithium transition metal phosphates.
- the lithium transition metal oxide a lithium transition metal oxide represented by the chemical formula LiMO 2 (M is at least one transition metal) is used.
- M is at least one transition metal
- the lithium transition metal oxide a part of transition metals such as Mn, Ni, Co, etc. contained in lithium manganate, lithium nickelate, lithium cobaltate, etc., which are one kind of lithium transition metal oxide, are used.
- Lithium transition metal oxides substituted with two or more other transition metals are also used.
- the lithium transition metal oxide one obtained by replacing a part of the transition metal of the lithium transition metal oxide with a metal element (typical element) such as Mg or Al is also used.
- the lithium transition metal oxide includes a part of the transition metal of the lithium transition metal oxide substituted with a metal element (typical element). Specific examples of the lithium transition metal oxide include Li (Co 1/3 Ni 1/3 Mn 1/3 ) O 2 , LiNi 1/2 Mn 1/2 O 2 , LiNi 1/2 Mn 3/2 O 4. Etc.
- Lithium transition metal phosphates include LiFePO 4 , LiMnPO 4 , LiMn X M 1-X PO 4 (0.3 ⁇ x ⁇ 1, M is Fe, Ni, Co, Ti, Cu, Zn, Mg and Zr) And at least one element selected from the group consisting of:
- the positive electrode active material preferably has a median diameter determined by a laser diffraction method in the range of 0.3 ⁇ m to 30 ⁇ m, more preferably in the range of 0.5 ⁇ m to 25 ⁇ m, and in the range of 0.5 ⁇ m to 10 ⁇ m. Further preferred.
- a positive electrode active material having a median diameter in the range of 0.3 ⁇ m to 30 ⁇ m the reaction specific surface area can be increased, the internal resistance can be reduced, and the deterioration of large current characteristics can be further suppressed.
- the median diameter of the positive electrode active material refers to a value obtained by the following method.
- the positive electrode active material is put into pure water so as to be 1% by mass, dispersed with ultrasonic waves for 15 minutes, and then the particle diameter at which the volume-based cumulative distribution becomes 50% is measured by laser diffraction. And this particle diameter is made into the median diameter of a positive electrode active material.
- a known conductive agent is used as the conductive agent of the positive electrode mixture.
- carbon materials such as graphite, acetylene black, carbon black, and carbon fiber are used as the conductive agent of the positive electrode mixture.
- it is not limited to these materials.
- the binder of the positive electrode mixture a known binder is used. Specifically, polyvinylidene fluoride, styrene-butadiene rubber, isoprene rubber, acrylic rubber or the like is used as the binder for the positive electrode mixture. However, it is not limited to these materials.
- the binder for the positive electrode is preferably polyvinylidene fluoride.
- the positive electrode mixture When the positive electrode mixture is applied to one surface of the first current collector, it is preferably dispersed in a dispersion medium to form a slurry.
- a dispersion medium a known dispersion medium can be appropriately selected and used.
- the dispersion medium is preferably an organic solvent such as N-methyl-2-pyrrolidone.
- the mixing ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode mixture is, for example, 1: 0.05 in mass ratio (positive electrode active material: conductive agent: binder) when the positive electrode active material is 1. To 0.20: 0.02 to 0.10. However, it is not limited to this range.
- the application amount of the positive electrode mixture (deposition volume of the positive electrode mixture to one surface of a first current collector: also referred to as coating amount) is 1mg / cm 2 ⁇ 10mg / cm 2, 1mg / cm 2 ⁇ 7.5 mg / cm 2 is preferable, and 1 mg / cm 2 to 5.5 mg / cm 2 is more preferable.
- the applied amount of the positive electrode mixture is 1 mg / cm 2 or more, it is easy to make the thickness of the positive electrode mixture uniform during pressing, and it is advantageous because a high energy density can be achieved.
- the applied amount of the positive electrode mixture is 10 mg / cm 2 or less, it is advantageous because the distance between the positive electrode and the negative electrode (ion conduction diffusion distance) is shortened.
- the application amount of the positive electrode mixture can be obtained by subtracting the mass of the first current collector from the mass of the positive electrode cut out in a predetermined area.
- the volume porosity of the positive electrode mixture is 20% to 45% by volume, preferably 30% to 45% by volume, and more preferably 35% to 45% by volume.
- the volume porosity of the positive electrode mixture is 20% by volume or more, the impregnation property of the ionic liquid is improved, which is advantageous.
- the volume porosity of the positive electrode mixture is 45% by volume or less, the adhesion between the positive electrode current collector and the mixture is improved, which is advantageous.
- the volume porosity of a positive mix is 45 volume% or less, since the electronic network of a electrically conductive agent is formed and an electronic resistance can be reduced, it is advantageous.
- the volume porosity of the positive electrode mixture is calculated from the blending ratio of the materials used for the positive electrode mixture, the true specific gravity of each material, the thickness of the positive electrode mixture, the area of the positive electrode mixture, the density of the positive electrode mixture, and the like.
- the volume porosity of the positive electrode mixture can be calculated from the following formula when the positive electrode mixture includes a positive electrode active material, a conductive agent, and a binder.
- Formula: Volume porosity of positive electrode mixture (volume%) [1- ⁇ (i) + (ii) + (iii) / (width of positive electrode mixture ⁇ length ⁇ thickness) ⁇ ] ⁇ 100
- (i) represents the volume of the positive electrode active material in the positive electrode mixture
- (ii) represents the volume of the conductive agent in the positive electrode mixture
- (iii) represents the binding in the positive electrode mixture.
- (I), (ii), and (iii) can each be calculated from the following equations.
- Formula: (i) (total mass of positive electrode mixture ⁇ ratio of mass of positive electrode active material in positive electrode mixture) / true specific gravity of positive electrode active material
- Formula: (ii) (total mass of positive electrode mixture ⁇ conductivity Ratio of the mass of the agent in the positive electrode mixture) / true specific gravity of the conductive agent
- Formula: (iii) (total mass of the positive electrode mixture ⁇ ratio of the mass of the binder in the positive electrode mixture) / binder
- the true specific gravity can be measured by the method for measuring the density and specific gravity of chemical products described in JIS K 0061 (2001).
- the thickness of the positive electrode mixture (also referred to as coating thickness) is preferably 20 ⁇ m to 80 ⁇ m, and more preferably 20 ⁇ m to 50 ⁇ m.
- the thickness of the positive electrode mixture is 20 ⁇ m or more, it is easy to make the thickness of the positive electrode mixture uniform at the time of pressing, and it is advantageous because the Li + concentration distribution in the positive electrode accompanying charge / discharge is less likely to occur.
- the thickness of the positive electrode mixture is 80 ⁇ m or less, it is advantageous because the decrease in conductivity of the ionic liquid in the voids in the positive electrode mixture can be suppressed.
- the positive electrode When the negative electrode satisfies the condition (2), the positive electrode does not need to satisfy the condition (1).
- the positive electrode may have a known configuration using metallic lithium as the positive electrode active material.
- the negative electrode satisfying the condition (2) will be described.
- the negative electrode has a second current collector and a negative electrode mixture applied to at least one surface of the second current collector.
- a negative electrode plate formed by applying a negative electrode mixture to at least one surface of the second current collector, drying, and pressing is used as the negative electrode.
- the material of the second current collector also referred to as a negative electrode current collector
- metals such as aluminum, copper, nickel, and stainless steel, and alloys thereof are used.
- the material of the second current collector is preferably lightweight aluminum and its alloy from the viewpoint of weight energy density.
- the material of the second current collector is preferably copper from the viewpoint of easy processing into a thin film and cost.
- the negative electrode mixture includes a negative electrode active material.
- the negative electrode mixture may further contain a conductive agent, a binder and the like.
- the negative electrode active material examples include (1) lithium titanate (Li 4 Ti 5 O 12 ), (2) carbon materials such as graphite and amorphous carbon, (3) metal materials including tin, silicon, and the like (4) Metal lithium etc. are mentioned. From the viewpoint of safety, cycle characteristics, and low temperature characteristics, it is preferable to use lithium titanate as the negative electrode active material.
- the negative electrode active material preferably has a median diameter determined by a laser diffraction method in the range of 0.1 ⁇ m to 50 ⁇ m, more preferably in the range of 0.3 ⁇ m to 30 ⁇ m, and in the range of 0.3 ⁇ m to 20 ⁇ m. Further preferred.
- a negative electrode active material with a median diameter in the range of 0.1 ⁇ m to 50 ⁇ m is a median diameter measured by the same method as that for the positive electrode active material.
- a known conductive agent can be used, and specific examples and preferred materials thereof are the same as those used for the positive electrode mixture.
- a known binder can be used as the binder for the negative electrode mixture, and specific examples and preferred materials thereof are the same as those used for the positive electrode mixture.
- the negative electrode mixture When the negative electrode mixture is applied to one surface of the second current collector, it is preferably dispersed in a dispersion medium to form a slurry.
- a dispersion medium Specific examples and preferred materials of the dispersion medium are the same as those of the dispersion medium used for the positive electrode mixture.
- the mixing ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode mixture is, for example, 1: 0.01 in terms of mass ratio (negative electrode active material: conductive agent: binder) when the negative electrode active material is 1. To 0.20: 0.02 to 0.10. However, it is not limited to this range.
- the application amount of the negative electrode mixture (deposition volume of the positive electrode mixture to one surface of the second current collector: also referred to as coating amount) is 1mg / cm 2 ⁇ 10mg / cm 2, 1mg / cm 2 ⁇ 8 mg / cm 2 is preferable, and 1 mg / cm 2 to 7 mg / cm 2 is more preferable.
- the applied amount of the negative electrode mixture is 1 mg / cm 2 or more, it is easy to make the thickness of the positive electrode mixture uniform at the time of pressing, and it is advantageous because high energy density can be achieved.
- the application amount of the negative electrode mixture is 10 mg / cm 2 or less, the distance between the positive electrode and the negative electrode (ion conduction diffusion distance) is shortened, which is advantageous.
- the amount of the negative electrode mixture applied can be determined by subtracting the mass of the second current collector from the mass of the negative electrode cut out in a predetermined area.
- the volume porosity of the negative electrode mixture is 20% to 45% by volume, preferably 30% to 45% by volume, and more preferably 35% to 45% by volume. This is for the same reason as the positive electrode mixture.
- the volume porosity of the negative electrode mixture is calculated from the blending ratio of the materials used for the negative electrode mixture, the true specific gravity of each material, the thickness of the negative electrode mixture, the area of the negative electrode mixture, the density of the negative electrode mixture, and the like.
- the volume porosity of the negative electrode mixture can be calculated from the following formula when the negative electrode mixture includes a negative electrode active material, a conductive agent, and a binder.
- Formula: Volume porosity of negative electrode mixture (volume%) [1- ⁇ (i) + (ii) + (iii) / (width of negative electrode mixture ⁇ length ⁇ thickness) ⁇ ] ⁇ 100
- (i) represents the volume of the active material in the negative electrode mixture
- (ii) represents the volume of the conductive agent in the negative electrode mixture
- (iii) represents the binder in the negative electrode mixture.
- Represents the volume of. (I), (ii), and (iii) can each be calculated from the following equations.
- Formula: (i) (total mass of negative electrode mixture ⁇ ratio of mass of negative electrode active material in negative electrode mixture) / true specific gravity of negative electrode active material
- Formula: (ii) (total mass of negative electrode mixture ⁇ conductivity Ratio of the mass in the negative electrode mixture of the agent) / true specific gravity of the conductive agent:
- (iii) (total mass of the negative electrode mixture ⁇ ratio of the mass in the negative electrode mixture of the binder) / binder
- the true specific gravity can be measured by the method for measuring the density and specific gravity of chemical products described in JIS K 0061 (2001).
- the thickness of the negative electrode mixture (also referred to as coating thickness) is preferably 20 ⁇ m to 80 ⁇ m, and more preferably 20 ⁇ m to 50 ⁇ m. This is for the same reason as the positive electrode.
- the negative electrode When the positive electrode satisfies the condition (1), the negative electrode does not need to satisfy the condition (2).
- the negative electrode may have a known configuration using metallic lithium as the negative electrode active material.
- the material and shape of the separator are not particularly limited. However, as the material of the separator, it is preferable to use a material that is stable with respect to the electrolytic solution and excellent in liquid retention. Specifically, as the separator, it is preferable to use a polyolefin porous film containing polyethylene, polypropylene, etc .; a nonwoven fabric containing polyolefin fibers (polyethylene fibers, polypropylene fibers, etc.), glass fibers, cellulose fibers, polyimide fibers, etc. .
- the nonwoven fabric is preferable as the separator because it is stable with respect to the electrolytic solution and has excellent liquid retention, and at least one selected from the group consisting of polyolefin fibers, glass fibers, cellulose fibers, and polyimide fibers.
- the nonwoven fabric containing is more preferable.
- the separator is a porous substrate containing glass fiber and resin.
- the glass fiber may be alkali glass or non-alkali glass.
- the fiber diameter of the glass fiber is not particularly limited, and the number average fiber diameter is preferably 0.5 ⁇ m to 5.0 ⁇ m, more preferably 0.5 ⁇ m to 4.0 ⁇ m, and 0.5 ⁇ m to 2.0 ⁇ m. More preferably.
- the fiber diameter of the glass fiber is 0.5 ⁇ m or more, it tends to be easy to obtain a uniform pore diameter.
- the fiber diameter of the glass fiber is 5.0 ⁇ m or less, it becomes easy to produce a sufficiently thin (for example, 50 ⁇ m or less) electrochemical separator, and it tends to be easy to obtain good papermaking properties at the time of papermaking described later.
- the fiber length of the glass fiber is not particularly limited, and the number average fiber length is preferably 1.0 ⁇ m to 30 mm, more preferably 100 ⁇ m to 20 mm, and further preferably 500 ⁇ m to 10 mm.
- the fiber length of the glass fiber is 1.0 ⁇ m or more, it tends to be easy to obtain a uniform pore diameter.
- the fiber length of the glass fiber is 30 mm or less, it becomes easy to produce an electrochemical separator having a sufficiently high strength (for example, 5 MPa or more), and it tends to be easy to obtain good papermaking properties.
- the number average fiber diameter and the number average fiber length of the fibers can be obtained by direct observation using, for example, a dynamic image analysis method, a laser scanning method (for example, conforming to JIS L1081), a scanning electron microscope, or the like. Specifically, the fiber diameter and the fiber length can be obtained by observing about 50 fibers using these methods and taking the average value.
- the resin is not particularly limited as long as it is a compound that acts as a binder for inorganic materials, preferably a resin having a melting point of 100 ° C. to 300 ° C., more preferably a resin having a melting point of 100 ° C. to 180 ° C.
- a resin having a temperature of 100 ° C. to 160 ° C. is more preferable.
- the melting point of the resin is 100 ° C. or more, there is a tendency that a shutdown property at the time of short circuit is easily obtained.
- fusing point of resin is 300 degrees C or less.
- the melting point is a value measured based on JIS-K7121.
- Examples of such a resin include organic fibers and polymer particles.
- Examples of organic fibers include natural fibers, regenerated fibers, and synthetic fibers.
- As the organic fiber for example, at least one selected from the group consisting of aramid fiber, polyamide fiber, polyester fiber, polyurethane fiber, polyacrylic fiber, polyethylene fiber, and polypropylene fiber is preferably used. These organic fibers may be used alone or in combination of two or more.
- polymer particles it is possible to use at least one selected from the group consisting of polyolefin particles, polybutyl acrylate particles, crosslinked polymethyl methacrylate particles, polytetrafluoroethylene particles, benzoguanamine particles, crosslinked polyurethane particles, crosslinked polystyrene particles, and melamine particles. preferable. These polymer particles may be used alone or in combination of two or more.
- the porous substrate may contain an inorganic filler different from the glass fiber (hereinafter simply referred to as “inorganic filler”).
- the inorganic filler can function as a binding aid between the glass fiber and the resin.
- the inorganic filler itself can increase the heat resistance of the separator, trap impurities (hydrogen fluoride gas, heavy metal ions, etc.) in the non-aqueous electrolyte, and can reduce the pore size.
- inorganic fillers include fillers made of electrically insulating materials such as metal oxides, metal nitrides, metal carbides, and silicon oxides; fillers made of carbon nanotubes, carbon nanofibers, and the like. These fillers may be used alone or in combination of two or more.
- the metal oxide include Al 2 O 3 , SiO 2 (except for fibrous ones), sepiolite, attapulgite, wollastonite, montmorillonite, mica, ZnO, TiO 2 , BaTiO 3 , ZrO 2 , zeolite, Examples include imogolite. Among these, a sepiolite filler can be used suitably.
- Sepiolite is a clay mineral mainly composed of hydrous magnesium silicate and is generally represented by the following chemical formula (x). Mg 8 Si 2 O 30 (OH 2 ) 4 (OH) 4 ⁇ 6 to 8H 2 O (x)
- An inorganic filler is either a crushing filler (amorphous filler), a scale-like filler (plate-like filler), a fibrous filler (acicular filler), and a spherical filler, for example. Also good.
- the inorganic filler is preferably a fibrous filler from the viewpoint of further improving the separator strength.
- the number average fiber diameter of the fibrous filler is preferably 0.01 ⁇ m to 1.0 ⁇ m, more preferably 0.01 ⁇ m to 0.5 ⁇ m, and 0.01 ⁇ m to 0.1 ⁇ m. More preferably.
- the fiber diameter of the fibrous filler is 0.01 ⁇ m or more, it tends to be easy to obtain a uniform pore diameter.
- the fiber diameter of the fibrous filler is 1.0 ⁇ m or less, a sufficiently thin (for example, 50 ⁇ m or less) electrochemical separator tends to be easily manufactured.
- the number average fiber length of the fibrous filler is preferably 0.1 ⁇ m to 500 ⁇ m, more preferably 0.1 ⁇ m to 300 ⁇ m, and further preferably 0.1 ⁇ m to 100 ⁇ m. If the fiber length of the fibrous filler is 0.1 ⁇ m or more, it tends to be easy to obtain a uniform pore diameter. Moreover, when the fiber length of the fibrous filler is 500 ⁇ m or less, it tends to be easy to produce a sufficiently thin (for example, 50 ⁇ m or less) electrochemical separator.
- the porous substrate may contain further refined pulp.
- the pulp used as necessary may be any of wood pulp, non-wood pulp, mechanical pulp, and chemical pulp.
- the pulp beating degree (CSF value) is preferably 300 or less (also expressed as “CSF-300 ml”), more preferably 150 or less.
- the lower limit of the beating degree of a pulp is 0.
- the air permeability (Gurley value) of the separator is preferably 0.1 sec / 100 ml to 10 sec / 100 ml.
- the air permeability of the separator is more preferably 0.1 second / 100 ml to 5 seconds / 100 ml.
- the air permeability of the separator can be measured according to JIS P8142 (2005).
- the pore diameter of the separator is preferably 0.01 ⁇ m to 20 ⁇ m.
- the pore diameter of the separator is more preferably 0.01 ⁇ m to 1 ⁇ m.
- the pore diameter of the separator can be measured by a mercury intrusion method, a bubble point method (JIS K 3832 (1990)), or the like.
- the porosity of the separator is 80% to 98%.
- the porosity of the separator is preferably 85% to 98%, and more preferably 90 to 98%.
- the total pore volume of the separator is preferably 2 ml / g or more from the viewpoint of rate characteristics.
- the upper limit of the total pore volume of the separator is not particularly limited, and is preferably 10 ml / g from a practical viewpoint.
- the total pore volume of the separator is more preferably 3 ml / g to 10 ml / g, more preferably 5 ml / g to 10 ml / g, from the viewpoint of rate characteristics.
- the porosity and total pore volume of the separator are values obtained from mercury porosimeter measurement.
- Conditions for mercury porosimeter measurement are as follows. ⁇ Equipment: Shimadzu Corporation Autopore IV 9500 ⁇ Mercury pressure: 0.51 psia ⁇ Pressure holding time at each measurement pressure: 10 s ⁇ Contact angle between sample and mercury: 140 ° ⁇ Mercury surface tension: 485 dynes / cm ⁇ Mercury Density: 13.5335 g / mL
- the air permeability of the separator is preferably 10 s / 100 ml or less from the viewpoint of rate characteristics.
- the lower limit of the air permeability of the separator is not particularly limited, and is preferably 0.1 s / 100 ml from a practical viewpoint.
- the air permeability of the separator is more preferably from 0.1 s / 100 ml to 10 s / 100 ml, more preferably from 0.1 s / 100 ml to 5 s / 100 ml, from the viewpoint of rate characteristics.
- the air permeability of the separator is a value obtained from the Gurley tester method.
- the measurement conditions of the Gurley tester method are as shown below, for example.
- a B-type Gurley Densometer manufactured by Yasuda Seiki Seisakusho
- the separator is tightened into a circular hole with a diameter of 28.6 mm and an area of 645 mm 2 , and the air inside the cylinder is passed from the test hole to the outside of the cylinder by the inner cylinder (inner cylinder weight 567 g), and the time for 100 mL of air to pass is measured.
- the air permeability is obtained by doing so.
- the thickness is preferably 50 ⁇ m or less, more preferably 30 ⁇ m or less, and even more preferably 20 ⁇ m or less. In addition, as a minimum of thickness, it is preferable that it is 10 micrometers or more from a viewpoint of fully ensuring heat resistance, intensity
- the electrolyte is a non-aqueous electrolyte and includes an ionic liquid and a lithium salt. Specifically, for example, it is preferable to use an electrolytic solution obtained by dissolving a lithium salt in an ionic liquid that exhibits liquid properties at ⁇ 20 ° C. or higher.
- the electrolytic solution may include a compound having a carbonate structure.
- a compound having a carbonate structure When a compound having a carbonate structure is included, a film derived from the carbonate structure can be formed on the negative electrode mixture by lowering the charging voltage to the reductive decomposition potential of the compound having the carbonate structure at the first charge.
- the carbonate compound include ethylene carbonate, propylene carbonate, vinylene carbonate, and the like. It is more preferable to use vinylene carbonate as the carbonate compound from the viewpoint of forming a film derived from the carbonate structure on the negative electrode without increasing the charging voltage.
- the content is preferably 0.1% by mass to 10% by mass, more preferably 0.2% by mass to 5% by mass, and further preferably 0.5% by mass to 3% by mass. .
- the cation component of the ionic liquid is not particularly limited, and is at least one selected from the group consisting of a chain quaternary ammonium cation, a piperidinium cation, a pyrrolidinium cation, and an imidazolium cation. Is preferred.
- Examples of the chain quaternary ammonium cation include a chain quaternary ammonium cation represented by the following general formula [1] (X is a nitrogen atom or a phosphorus atom).
- Examples of the piperidinium cation include a piperidinium cation that is a six-membered cyclic compound containing nitrogen represented by the following general formula [2].
- Examples of the pyrrolidinium cation include a pyrrolidinium cation that is a five-membered cyclic compound represented by the general formula [3].
- Examples of the imidazolium cation include an imidazolium cation represented by the general formula [4].
- R 1 , R 2 , R 3 and R 4 in the general formulas [1] to [3] are each independently an alkyl group having 1 to 20 carbon atoms, or R 6 —O— (CH 2 ).
- an alkoxyalkyl group represented by n- R 6 represents a methyl group or an ethyl group, and n represents an integer of 1 to 4).
- the alkyl group is a chain alkyl group
- the alkoxyalkyl group is a chain alkoxyalkyl group.
- R 1 , R 2 , R 3 , R 4 and R 5 in the general formula [4] are each independently represented by an alkyl group having 1 to 20 carbon atoms, R 6 —O— (CH 2 ) n —.
- An alkoxyalkyl group R 6 represents a methyl group or an ethyl group, and n represents an integer of 1 to 4), or a hydrogen atom.
- the anion component of the ionic liquid is not particularly limited, but is an anion of a halogen such as Cl ⁇ , Br ⁇ and I ⁇ , an inorganic anion such as BF 4 ⁇ and N (SO 2 F) 2 — , and B (C 6 H 5 ) 4 ⁇ , CH 3 SO 3 ⁇ , CF 3 SO 3 ⁇ , N (C 4 F 9 SO 2 ) 2 ⁇ , N (SO 2 CF 3 ) 2 ⁇ , N (SO 2 CF 2 CF 3 ) 2 - organic anions and the like.
- a halogen such as Cl ⁇ , Br ⁇ and I ⁇
- an inorganic anion such as BF 4 ⁇ and N (SO 2 F) 2 —
- the anionic component of the ionic liquid includes B (C 6 H 5 ) 4 ⁇ , CH 3 SO 3 ⁇ , N (C 4 F 9 SO 2 ) 2 ⁇ , CF 3 SO 3 ⁇ , N (SO 2 F) 2 ⁇ , N (SO 2 CF 3 ) 2 — and N (SO 2 CF 2 CF 3 ) 2 — are preferably included, and N (C 4 F 9 SO 2 ) at least selected from the group consisting of 2 ⁇ , CF 3 SO 3 ⁇ , N (SO 2 F) 2 ⁇ , N (SO 2 CF 3 ) 2 ⁇ , and N (SO 2 CF 2 CF 3 ) 2 — More preferably, it contains one, and more preferably contains N (SO 2 F) 2 — .
- An ionic liquid containing at least one selected from the group consisting of 2 ⁇ in particular, an ionic liquid containing N (SO 2 F) 2 — has a relatively low viscosity. Will be improved.
- a preferred combination of an anionic component and a cationic component is a combination of N-methyl-N-propylpyrrolidinium and bis (fluorosulfonyl) imide (N (SO 2 F) 2 ⁇ ), N— Examples include a combination of methyl-N-propylpyrrolidinium and bis (trifluoromethylsulfonyl) imide (N (SO 2 CF 3 ) 2 ⁇ ).
- An ionic liquid may be used individually by 1 type, and may use 2 or more types together.
- Lithium salts include LiBF 4 , LiClO 4 , LiB (C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN (SO 2 F) 2 , LiN (SO 2 CF 3 ) 2 , and LiN ( And at least one selected from the group consisting of SO 2 CF 2 CF 3 ) 2 . However, it is not limited to these materials.
- the concentration of the lithium salt is preferably 0.5 mol / L to 1.5 mol / L, more preferably 0.7 mol / L to 1.3 mol / L with respect to the ionic liquid, and 0.8 mol / L to 1.2 mol / L is more preferable.
- concentration of the lithium salt By setting the concentration of the lithium salt to 0.5 mol / L to 1.5 mol / L, the charge / discharge characteristics can be further improved.
- the manufacturing method of the lithium ion secondary battery of the present invention having the positive electrode, the negative electrode, the separator, and the electrolytic solution is not particularly limited, and a known method can be used.
- the shape of the lithium ion secondary battery is not particularly limited, and a stacked type, a wound type, or the like can be used.
- Example 1 As a positive electrode active material, lithium iron phosphate (LiFePO 4 ) having a median diameter of 0.6 ⁇ m measured by laser diffraction method: 85% by mass, and acetylene black (trade name: HS-100, Denki Kagaku Kogyo Co., Ltd.) as a conductive agent ): 10% by mass and 5% by mass of polyvinylidene fluoride as a binder were added and mixed to prepare a positive electrode mixture. The positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and a slurry was applied onto an aluminum foil having a thickness of 20 ⁇ m.
- LiFePO 4 lithium iron phosphate having a median diameter of 0.6 ⁇ m measured by laser diffraction method: 85% by mass
- acetylene black trade name: HS-100, Denki Kagaku Kogyo Co., Ltd.
- the coating amount after drying of the dispersion medium was 4.25 mg / cm 2. And then dried at 120 ° C. for 1 hour. After drying, pressing was performed to produce a positive electrode having a density of the positive electrode mixture of 1.7 g / ml, a coating thickness of the positive electrode mixture of 25 ⁇ m, and a volume porosity of the positive electrode mixture of 43% by volume.
- the positive electrode was cut into a 3.0 cm ⁇ 3.5 cm rectangle, and the positive electrode mixture was scraped from the aluminum foil, leaving a 2.5 cm ⁇ 2.5 cm positive electrode mixture.
- the aluminum tab was connected to the aluminum foil after scraping off the positive electrode mixture by spot welding.
- lithium titanate Li 4 Ti 5 O 12
- acetylene black trade name: HS-100, electric Chemical Industry Co., Ltd.
- 10% by mass 5% by mass of polyvinylidene fluoride as a binder
- the negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and the resulting slurry was applied onto an aluminum foil having a thickness of 20 ⁇ m so that the coating amount after drying of the dispersion medium was 4.95 mg / cm 2. And dried at 120 ° C. for 1 hour.
- the negative electrode was cut into a 2.5 cm ⁇ 3.0 cm rectangle, and the negative electrode mixture was scraped from the aluminum foil, leaving a 2.0 cm ⁇ 2.0 cm negative electrode mixture.
- An aluminum tab was connected to the aluminum foil after scraping off the negative electrode mixture by spot welding.
- LiFSI lithium bis (fluorosulfonyl) imide
- solute lithium salt
- These positive electrode and negative electrode are inserted into an aluminum laminated bag through the glass fiber nonwoven fabric A (GE Healthcare Japan, model number: GF / A) shown in Table 1 as a separator, and heat is left leaving some openings. Sealed by welding. An electrolyte was poured from the unsealed opening, and the inside of the aluminum laminate bag was evacuated, and then the unsealed opening was sealed by thermal welding to obtain a laminate cell.
- glass fiber nonwoven fabric A GE Healthcare Japan, model number: GF / A
- Example 2 A laminate cell was prepared in the same manner as in Example 1 except that the glass fiber nonwoven fabric B (Nippon Sheet Glass Co., Ltd.) shown in Table 1 was used as the separator.
- the glass fiber nonwoven fabric B Nippon Sheet Glass Co., Ltd.
- Example 3 As a positive electrode active material, lithium nickel manganate (LiNi 0.5 Mn 1.5 O 4 ) having a median diameter measured by a laser diffraction method of 9.6 ⁇ m: 85% by mass, acetylene black (trade name: trade name: HS-100, Denki Kagaku Kogyo Co., Ltd.): 10% by mass, and 5% by mass of polyvinylidene fluoride as a binder were added and mixed to prepare a positive electrode mixture.
- lithium nickel manganate LiNi 0.5 Mn 1.5 O 4
- acetylene black trade name: trade name: HS-100, Denki Kagaku Kogyo Co., Ltd.
- the positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and the resulting slurry was coated on a 20 ⁇ m thick aluminum foil with a coating amount of 5.10 mg / cm 2 after drying the dispersion medium. And then dried at 120 ° C. for 1 hour. After drying, pressing was performed to produce a positive electrode having a positive electrode mixture density of 1.9 g / ml, a positive electrode mixture coating thickness of 27 ⁇ m, and a positive electrode mixture volume porosity of 43 vol%.
- lithium titanate Li 4 Ti 5 O 12
- acetylene black trade name: HS-100
- a conductive agent Denki Kagaku Kogyo Co., Ltd.
- 10% by mass 5% by mass of polyvinylidene fluoride as a binder
- a negative electrode mixture is dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and a slurry is applied onto an aluminum foil having a thickness of 20 ⁇ m.
- the coating amount after drying of the dispersion medium is 2.70 mg / cm 2. And dried at 120 ° C. for 1 hour. After drying, pressing was performed to produce a negative electrode having a negative electrode mixture density of 1.8 g / ml, a negative electrode mixture coating thickness of 17 ⁇ m, and a negative electrode mixture volume porosity of 44 vol%.
- Example 2 the laminate cell was produced similarly to Example 1 except having used the glass fiber nonwoven fabric B (Nippon Sheet Glass Co., Ltd.) of Table 1 as a separator with the produced said positive electrode and negative electrode.
- the glass fiber nonwoven fabric B Natural Sheet Glass Co., Ltd.
- Example 4 A laminate cell was produced in the same manner as in Example 3 except that the glass fiber nonwoven fabric C (Nippon Sheet Glass Co., Ltd.) shown in Table 1 was used as the separator.
- Example 1 A laminate cell was produced in the same manner as in Example 1 except that the cellulose fiber nonwoven fabric described in Table 1 was used as the separator.
- Example 2 A laminate cell was produced in the same manner as in Example 1 except that the polyimide fiber nonwoven fabric shown in Table 1 was used as the separator.
- Example 3 A laminate cell was produced in the same manner as in Example 3 except that the cellulose fiber nonwoven fabric shown in Table 1 was used as the separator.
- Example 5 As a positive electrode active material, lithium manganate (LiMn 2 O 4 ) having a median diameter of 5.0 ⁇ m measured by a laser diffraction method: 89% by mass, and acetylene black (trade name: HS-100, Electrochemical Industry) as a conductive agent Company): 6% by mass, and 5% by mass of polyvinylidene fluoride as a binder were added and mixed to prepare a positive electrode mixture. The positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and a slurry was applied onto an aluminum foil having a thickness of 20 ⁇ m. The coating amount after drying of the dispersion medium was 5.50 mg / cm 2.
- a positive electrode having a positive electrode mixture density of 2.2 g / ml, a positive electrode mixture coating thickness of 25 ⁇ m, and a positive electrode mixture volume porosity of 38 vol%.
- the positive electrode was cut into a 2.5 cm ⁇ 3.0 cm rectangle, and the positive electrode mixture was scraped from the aluminum foil, leaving a 2.0 cm ⁇ 2.0 cm positive electrode mixture.
- the aluminum tab was connected to the aluminum foil after scraping off the positive electrode mixture by spot welding.
- the negative electrode used was a copper mesh cut into a 3.0 cm ⁇ 3.5 cm rectangle leaving a tab weld, and a nickel tab was connected by spot welding and metallic lithium was pasted on the mesh.
- LiFSI lithium bis (fluorosulfonyl) imide
- solute lithium salt
- Example 6 A laminate cell was produced in the same manner as in Example 5 except that lithium manganate (LiMn 2 O 4 ) having a median diameter of 10.0 ⁇ m measured by a laser diffraction method was used as the positive electrode active material.
- lithium manganate LiMn 2 O 4
- Example 7 A laminate cell was produced in the same manner as in Example 5 except that lithium manganate (LiMn 2 O 4 ) having a median diameter measured by a laser diffraction method of 25.0 ⁇ m was used as the positive electrode active material.
- lithium manganate LiMn 2 O 4
- Example 8 The same as in Example 5 except that the coating amount of the positive electrode mixture was 6.00 mg / cm 2 , the density of the positive electrode mixture was 2.4 g / ml, and the volume porosity of the positive electrode mixture was 32% by volume. Thus, a laminate cell was produced.
- Example 9 Except that the coating amount of the positive electrode mixture was 6.50 mg / cm 2 , the density of the positive electrode mixture was 2.6 g / ml, and the volume porosity of the positive electrode mixture was 26% by volume, the same as in Example 5. Thus, a laminate cell was produced.
- Example 10 A laminate cell was produced in the same manner as in Example 5 except that the coating amount of the positive electrode mixture was 8.14 mg / cm 2 and the coating thickness of the positive electrode mixture was 37 ⁇ m.
- Example 11 A laminate cell was produced in the same manner as in Example 5 except that the coating amount of the positive electrode mixture was 9.90 mg / cm 2 and the coating thickness of the positive electrode mixture was 45 ⁇ m.
- lithium iron phosphate (LiFePO 4 ) having a median diameter of 0.6 ⁇ m measured by laser diffraction method: 85% by mass, and acetylene black (trade name: HS-100, Denki Kagaku Kogyo Co., Ltd.) ): 10% by mass, and 5% by mass of polyvinylidene fluoride as a binder were added and mixed to prepare a positive electrode mixture.
- the positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and a slurry was applied onto an aluminum foil having a thickness of 20 ⁇ m. The coating amount after drying of the dispersion medium was 7.65 mg / cm 2.
- a laminate cell was produced in the same manner as in Example 5.
- Example 13 Except that the coating amount of the positive electrode mixture was 8.55 mg / cm 2 , the density of the positive electrode mixture was 1.9 g / ml, and the volume porosity of the positive electrode mixture was 36% by volume, the same as in Example 12. Thus, a laminate cell was produced.
- Example 14 As a positive electrode active material, lithium nickel manganate (LiNi 0.5 Mn 1.5 O 4 ) having a median diameter measured by a laser diffraction method of 9.6 ⁇ m: 85% by mass, acetylene black (trade name: trade name: HS-100, Denki Kagaku Kogyo): 10% by mass and 5% by mass of polyvinylidene fluoride as a binder were added and mixed to prepare a positive electrode mixture. The positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and the resulting slurry was coated on a 20 ⁇ m thick aluminum foil with a coating amount of 5.10 mg / cm 2 after drying the dispersion medium.
- LiNi 0.5 Mn 1.5 O 4 lithium nickel manganate having a median diameter measured by a laser diffraction method of 9.6 ⁇ m: 85% by mass
- acetylene black trade name: trade name: HS-100, Denki Kagaku
- a laminate cell was produced in the same manner as in Example 5.
- Example 15 The positive electrode was obtained by connecting a nickel tab by spot welding to a copper mesh cut into a 3.0 cm ⁇ 3.5 cm rectangle leaving a tab weld and bonding metal lithium on the mesh.
- lithium titanate (Li 4 Ti 5 O 12 ) having a median diameter of 7.0 ⁇ m measured by a laser diffraction method: 85% by mass, acetylene black (trade name: HS-100, electric Chemical Industry Co., Ltd.): 10% by mass, and 5% by mass of polyvinylidene fluoride as a binder were added and mixed to prepare a negative electrode mixture.
- the negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and the resulting slurry was coated on a 20 ⁇ m thick aluminum foil with a coating amount of 4.80 mg / cm 2 after drying the dispersion medium. And dried at 120 ° C. for 1 hour.
- a negative electrode having a negative electrode mixture density of 1.6 g / ml, a negative electrode mixture coating thickness of 33 ⁇ m, and a negative electrode mixture volume porosity of 44 vol%.
- the negative electrode was cut into a 2.5 cm ⁇ 3.0 cm rectangle, and the negative electrode mixture was scraped from the aluminum foil, leaving a 2.0 cm ⁇ 2.0 cm negative electrode mixture.
- An aluminum tab was connected to the aluminum foil after scraping off the negative electrode mixture by spot welding.
- LiFSI lithium bis (fluorosulfonyl) imide
- solute lithium salt
- Example 16 As the negative electrode active material, lithium titanate (Li 4 Ti 5 O 12 ) having a median diameter of 1.2 ⁇ m measured by a laser diffraction method is used, and the coating amount of the negative electrode mixture is 2.70 mg / cm 2 .
- a laminate cell was prepared in the same manner as in Example 15 except that the density of the negative electrode mixture was 1.8 g / ml, the coating thickness of the negative electrode mixture was 17 ⁇ m, and the volume porosity of the negative electrode mixture was 44% by volume. Produced.
- Example 4 A laminate cell was produced in the same manner as in Example 5 except that the coating amount of the positive electrode mixture was 17.60 mg / cm 2 and the coating thickness of the positive electrode mixture was 85 ⁇ m.
- the coating amount of the positive electrode mixture is 6.50 mg / cm 2 , the density of the positive electrode mixture is 2.85 g / ml, the coating thickness of the positive electrode mixture is 23 ⁇ m, and the volume porosity of the positive electrode mixture is 19 volumes.
- a laminated cell was produced in the same manner as in Example 5 except that the percentage was changed to%.
- the coating amount of the positive electrode mixture is 8.14 mg / cm 2 , the density of the positive electrode mixture is 1.9 g / ml, the coating thickness of the positive electrode mixture is 43 ⁇ m, and the volume porosity of the positive electrode mixture is 46 volumes.
- a laminated cell was produced in the same manner as in Example 5 except that the percentage was changed to%.
- Example 7 A laminate cell was produced in the same manner as in Example 12 except that the coating amount of the positive electrode mixture was 14.45 mg / cm 2 and the coating thickness of the positive electrode mixture was 85 ⁇ m.
- Example 9 A laminate cell was produced in the same manner as in Example 14 except that the coating amount of the positive electrode mixture was 11.00 mg / cm 2 and the coating thickness of the positive electrode mixture was 58 ⁇ m.
- Example 10 A laminate cell was prepared in the same manner as in Example 14 except that the density of the positive electrode mixture was 1.6 g / ml, the coating thickness of the positive electrode mixture was 32 ⁇ m, and the volume porosity of the positive electrode mixture was 55% by volume. Produced.
- the coating amount of the negative electrode mixture was 7.20 mg / cm 2 , the density of the negative electrode mixture was 2.2 g / ml, the coating thickness of the negative electrode mixture was 33 ⁇ m, and the volume porosity of the negative electrode mixture was 18% by volume.
- a laminate cell was produced in the same manner as in Example 16 except for the above.
- Example 14 A laminate cell was produced in the same manner as in Example 16 except that the volume porosity of the negative electrode mixture was 50% by volume.
- constant current charging was performed at a constant current of 0.2 C to a charge end voltage of 2.5 V, and then constant voltage charging was performed at a charge end voltage of 2.5 V until the current value reached 0.01 C.
- constant current discharge was performed at a current value of 0.1 C and a discharge end voltage of 1.0 V.
- the discharge capacity at this time was defined as the initial discharge capacity.
- constant current charging was performed at a constant current of 0.2 C to a charging end voltage of 2.5 V, and then constant voltage charging was performed at a charging end voltage of 2.5 V until the current value reached 0.01 C. After resting for 15 minutes, constant current discharge was performed at a current value of 1 C and a discharge end voltage of 1.0 V.
- constant current charging was performed at a constant current of 0.2 C to a charge end voltage of 3.8 V, and then constant voltage charging was performed at a charge end voltage of 3.8 V until the current value reached 0.01 C.
- constant current discharge was performed at a current value of 0.1 C and a discharge end voltage of 2.0 V.
- the discharge capacity at this time was the initial discharge capacity.
- constant current charging was performed at a constant current of 0.2 C to a charging end voltage of 3.8 V, and then constant voltage charging was performed at a charging end voltage of 3.8 V until the current value reached 0.01 C.
- constant current discharge was performed at a current value of 1 C and a discharge end voltage of 2.0 V.
- Table 2 shows the initial discharge capacity, initial Coulomb efficiency, and 1C / 0.1C constant current discharge capacity ratio (rate characteristics) of the batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 3.
- constant current charging was performed at a constant current of 0.2 C to a charging end voltage of 4.3 V, and then constant voltage charging was performed at a charging end voltage of 4.3 V until the current value reached 0.01 C.
- constant current discharge was performed at a current value of 0.1 C and a discharge end voltage of 3.0 V.
- the discharge capacity at this time was defined as the initial discharge capacity.
- the initial discharge capacity was converted per unit mass of the positive electrode active material.
- constant current charging was performed at a constant current of 0.2 C to a charging end voltage of 4.3 V, and then constant voltage charging was performed at a charging end voltage of 4.3 V until the current value reached 0.01 C.
- constant current discharge was performed at a current value of 1 C and a discharge end voltage of 3.0 V.
- constant current charging was performed at a constant current of 0.2 C to a charging end voltage of 4.0 V, and then constant voltage charging was performed at a charging end voltage of 4.0 V until the current value reached 0.01 C.
- constant current discharge was performed at a current value of 0.1 C and a discharge end voltage of 2.0 V.
- the discharge capacity at this time was defined as the initial discharge capacity.
- the initial discharge capacity was converted per unit mass of the positive electrode active material.
- constant current charging was performed at a constant current of 0.2 C to a charging end voltage of 4.0 V, and then constant voltage charging was performed at a charging end voltage of 4.0 V until the current value reached 0.01 C. After resting for 15 minutes, constant current discharge was performed at a current value of 1 C and a discharge end voltage of 2.0 V.
- Example 14 and Comparative Examples 9-10 The batteries (laminate cells) produced in Example 14 and Comparative Examples 9 to 10 were charged at a constant current of 0.2 C to a charge end voltage of 4.95 V at 25 ° C., and then the current value at a charge end voltage of 4.95 V. The battery was charged at a constant voltage until the temperature reached 0.01C. After resting for 15 minutes, constant current discharge was performed at a current value of 0.2 C and a discharge end voltage of 3.5 V. Charging / discharging was repeated 3 times under the above charging / discharging conditions.
- constant current charging was performed at a constant current of 0.2 C to a charge end voltage of 4.95 V, and then constant voltage charging was performed until the current value reached 0.01 C at a charge end voltage of 4.95 V.
- constant current discharge was performed at a current value of 0.1 C and a discharge end voltage of 3.5 V.
- the discharge capacity at this time was defined as the initial discharge capacity.
- the initial discharge capacity was converted per unit mass of the positive electrode active material.
- constant current charging was performed at a constant current of 0.2 C to a charging end voltage of 4.95 V, and then constant voltage charging was performed at a charging end voltage of 4.95 V until the current value reached 0.01 C.
- constant current discharge was performed at a current value of 1 C and a discharge end voltage of 3.5 V.
- Examples 15 to 16 and Comparative Examples 11 to 14 The batteries (laminate cells) produced in Examples 15 to 16 and Comparative Examples 11 to 14 were charged at a constant current of 0.2 C to a charge end voltage of 3.4 V at 25 ° C., and then charged to a charge end voltage of 3.4 V. Constant voltage charging was performed until the current value reached 0.01C. After resting for 15 minutes, constant current discharge was performed at a current value of 0.2 C and a discharge end voltage of 2.0 V. Charging / discharging was repeated 3 times under the above charging / discharging conditions.
- constant current charging was performed at a constant current of 0.2 C to a charge end voltage of 3.4 V, and then constant voltage charging was performed until the current value reached 0.01 C at a charge end voltage of 2.0 V.
- constant current discharge was performed at a current value of 0.1 C and a discharge end voltage of 2.0 V.
- the discharge capacity at this time was defined as the initial discharge capacity.
- the initial discharge capacity was converted per unit mass of the negative electrode active material.
- constant current charging was performed at a constant current of 0.2 C to a charge end voltage of 3.4 V, and then constant voltage charging was performed at a charge end voltage of 3.4 V until the current value reached 0.01 C. After resting for 15 minutes, constant current discharge was performed at a current value of 1 C and a discharge end voltage of 2.0 V.
- Tables 2 to 4 show the initial discharge capacity, initial Coulomb efficiency, and 1C / 0.1C constant current discharge capacity ratio (rate characteristics) of the batteries prepared in Examples 1 to 16 and Comparative Examples 1 to 14, respectively.
- the batteries of Examples 1 to 4 have a rate characteristic of 80% or more, which is superior to the batteries of Comparative Examples 1 to 3.
- the batteries of Examples 1 to 4 have improved rate characteristics by including a separator having a porosity of 80% to 98%. It can also be seen that the batteries of Examples 1 to 4 have improved rate characteristics by including a separator having a total pore volume of 2 ml / g or more. It can also be seen that the batteries of Examples 1 to 4 have improved rate characteristics by including a separator having an air permeability of 10 s / 100 ml or less.
- the batteries of the examples were provided with a separator having a porosity of 80% to 98%, and (1) to one surface of the aluminum foil (positive electrode current collector).
- the amount of negative electrode mixture applied (coating amount) to one surface of the (negative electrode current collector) is 1 mg / cm 2 to 10 mg / cm 2
- the volume porosity of the negative electrode mixture is 20 volume% to 45 volume. It can be seen that the large current characteristics are improved by using at least one of the negative electrodes.
- the positive electrode mixture and the negative electrode mixture when an active material having a median diameter of 0.3 ⁇ m to 30 ⁇ m is used for the positive electrode mixture and the negative electrode mixture, and the thickness (coating thickness) of the positive electrode mixture and the negative electrode mixture is 20 ⁇ m to 80 ⁇ m, the large current characteristics It can also be seen that is improved.
- volume porosity of the positive electrode mixture and the negative electrode mixture was calculated using the following numerical values as true specific gravity.
- LiFePO 4 3.70 LiMn 2 O 4 : 4.28 Li 4 Ti 5 O 12 : 3.48 LiNi 0.5 Mn 1.5 O 4 : 4.46
- Acetylene black 1.31
- Polyvinylidene fluoride 1.77
Abstract
Description
このようなリチウムイオン二次電池の非水電解液に使用される非水溶媒としては、リチウム塩を溶解しやすく、かつ電気分解しにくいエチレンカーボネート、ジエチルカーボネート等のカーボネート溶媒が使用されている。
また、最近では、リチウムイオン二次電池の非水電解液として、安全性の観点から、イオン性液体を使用することが種々検討されている(例えば、特開2010-287380号公報参照)。
一方、イオン性液体はカーボネート溶媒に比べて、粘性が高く導電性が低いため、大電流の充放電特性に劣るという問題がある。
このような問題を解決するために、特許文献1では、特定のセパレータを用いることで優れた大電流の充放電特性を達成している。
しかしながら、本発明者らが鋭意検討した結果、特許文献1に記載されているような特性のセパレータを使用するだけでは、大電流の負荷特性を達成できないことを本発明者らは見出した。
正極と、負極と、セパレータと、イオン性液体及びリチウム塩を含む電解液とを有し、前記セパレータの空孔率が80%~98%であり、かつ下記(1)及び(2)の少なくとも一方の条件を満たすリチウムイオン二次電池。(1)前記正極は、第1集電体と前記第1集電体の少なくとも一方の面に付与された正極合剤とを有し、前記第1集電体の一方の面への前記正極合剤の付与量が1mg/cm2~10mg/cm2であり、前記正極合剤の体積空隙率が20体積%~45体積%である。(2)前記負極は、第2集電体と前記第2集電体の少なくとも一方の面に付与された負極合剤とを有し、前記第2集電体の一方の面への前記負極合剤の付与量が1mg/cm2~10mg/cm2であり、前記負極合剤の体積空隙率が20体積%~45体積%である。
前記セパレータが、ポリオレフィン繊維、ガラス繊維、セルロース繊維、及びポリイミド繊維からなる群より選択される少なくとも一種を含む不織布である<1>に記載のリチウムイオン二次電池。
前記イオン性液体のアニオン成分が、N(C4F9SO2)2 -、CF3SO3 -、N(SO2F)2 -、N(SO2CF3)2 -、及びN(SO2CF2CF3)2 -からなる群より選択される少なくとも一種を含む<1>又は<2>に記載のリチウムイオン二次電池。
前記イオン性液体のカチオン成分が、鎖状四級アンモニウムカチオン、ピペリジニウムカチオン、ピロリジニウムカチオン、及びイミダゾリウムカチオンからなる群より選択される少なくとも一種を含む<1>~<3>のいずれか1項に記載のリチウムイオン二次電池。
前記正極合剤又は前記負極合剤は、レーザー回折法によって求められるメジアン径が0.3μm~30μmの活物質を含む<1>~<4>のいずれか1項に記載のリチウムイオン二次電池。
なお、本明細書において、「~」を用いて示された数値範囲は、「~」の前後に記載される数値をそれぞれ最小値及び最大値として含む範囲を示す。また、組成物中の各成分の量は、組成物中に各成分に該当する物質が複数存在する場合、特に断らない限り、組成物中に存在する当該複数の物質の合計量を意味する。また、正極とは、充電時にリチウムイオンを放出(脱離)し、放電時にリチウムイオン吸蔵(挿入)する側とし、負極とは、充電時にリチウムイオンを吸蔵(挿入)し、放電時にリチウムイオン放出(脱離)する側とする。
そして、発明者らは、鋭意検討の結果、セパレータの空孔率を80%~98%とし、かつ下記(1)及び(2)の少なくとも一方の条件を満たすことにより、電解液としてイオン性液体を用いても、大電流特性に優れるリチウムイオン二次電池を提供することができることを見出し、本発明を完成させるに至った。(1)正極は、第1集電体と第1集電体の少なくとも一方の面に付与された正極合剤とを有し、第1集電体の一方の面への正極合剤の付与量が1mg/cm2~10mg/cm2であり、正極合剤の体積空隙率が20体積%~45体積%である。(2)負極は、第2集電体と第2集電体の少なくとも一方の面に付与された負極合剤とを有し、第2集電体の一方の面への負極合剤の付与量が1mg/cm2~10mg/cm2であり、負極合剤の体積空隙率が20体積%~45体積%である。
条件(1)を満たす正極について説明する。
正極は、第1集電体と、第1集電体の少なくとも一方の面に付与された正極合剤とを有する。具体的には、正極としては、例えば、第1集電体の少なくとも一方の面に、正極合剤を塗工した後、乾燥し、プレスして形成した正極板が用いられる。
リチウム遷移金属化合物としては、リチウム遷移金属酸化物、リチウム遷移金属リン酸塩等が挙げられる。
リチウム遷移金属酸化物としては、リチウム遷移金属酸化物の1種であるマンガン酸リチウム、ニッケル酸リチウム、コバルト酸リチウム等に含有されるMn、Ni、Co等の遷移金属の一部を1種又は2種以上の他の遷移金属で置換したリチウム遷移金属酸化物も用いられる。
リチウム遷移金属酸化物としては、リチウム遷移金属酸化物の遷移金属の一部をMg、Al等の金属元素(典型元素)で置換したものも用いられる。なお、本発明においては、リチウム遷移金属酸化物の遷移金属の一部を金属元素(典型元素)で置換されたものもリチウム遷移金属酸化物に含まれる。
リチウム遷移金属酸化物の具体例としては、Li(Co1/3Ni1/3Mn1/3)O2、LiNi1/2Mn1/2O2、LiNi1/2Mn3/2O4等が挙げられる。
純水中に1質量%となるように正極活物質を投入し、超音波で15分間分散し、その後、レーザー回折法により体積基準の累積分布が50%となる粒子径を測定する。そして、この粒子径を正極活物質のメジアン径とする。
なお、正極合剤の付与量は、所定の面積に切り出した正極の質量から、第1集電体の質量を引くことで求めることができる。
式: 正極合剤の体積空隙率(体積%)=[1-{(i)+(ii)+(iii)/(正極合剤の幅×長さ×厚さ)}] ×100
式: (i)=(正極合剤の全質量×正極活物質の正極合剤中に占める質量の割合)/正極活物質の真比重
式: (ii)=(正極合剤の全質量×導電剤の正極合剤中に占める質量の割合)/導電剤の真比重
式: (iii)=(正極合剤の全質量×結着剤の正極合剤中に占める質量の割合)/結着剤の真比重
なお、真比重は、JIS K 0061(2001年)に記載の化学製品の密度及び比重測定方法により測定することができる。
条件(2)を満たす負極について説明する。
負極は、第2集電体と、第2集電体の少なくとも一方の面に付与された負極合剤とを有する。具体的には、負極としては、例えば、第2集電体の少なくとも一方の面に、負極合剤を塗工した後、乾燥し、プレスして形成した負極板が用いられる。
安全性、サイクル特性及び低温特性の観点からは、負極活物質としてチタン酸リチウムを用いることが好ましい。
ここで、負極活物質のメジアン径とは、正極活物質と同様の方法で測定したメジアン径である。
負極合剤の結着剤には、公知の結着剤を用いることができ、その具体例及び好ましい材料は正極合剤に用いられる結着剤と同様である。
なお、負極合剤の付与量は、所定の面積に切り出した負極の質量から、第2集電体の質量を引くことで求めることができる。
式:負極合剤の体積空隙率(体積%)=[1-{(i)+(ii)+(iii)/(負極合剤の幅×長さ×厚さ)}]×100
式: (i)=(負極合剤の全質量×負極活物質の負極合剤中に占める質量の割合)/負極活物質の真比重
式: (ii)=(負極合剤の全質量×導電剤の負極合剤中に占める質量の割合)/導電剤の真比重
式: (iii)=(負極合剤の全質量×結着剤の負極合剤中に占める質量の割合)/結着剤の真比重
なお、真比重は、JIS K 0061(2001年)に記載の化学製品の密度及び比重測定方法により測定することができる。
セパレータの材質及び形状については、特に限定されない。ただし、セパレータの材料としては、電解液に対して安定であり、保液性に優れた材料を用いることが好ましい。具体的には、セパレータとしては、ポリエチレン、ポリプロピレン等を含むポリオレフィン多孔質膜;ポリオレフィン繊維(ポリエチレン繊維、ポリプロピレン繊維等)、ガラス繊維、セルロース繊維、ポリイミド繊維等を含む不織布;などを用いるのが好ましい。これらの中でも、電解液に対して安定であり、保液性に優れる点から、セパレータとしては、不織布が好ましく、ポリオレフィン繊維、ガラス繊維、セルロース繊維、及びポリイミド繊維からなる群より選択される少なくとも一種を含む不織布がより好ましい。
ガラス繊維は、アルカリガラスであっても、無アルカリガラスであってもよい。ガラス繊維の繊維径に特に制限はなく、数平均繊維径は0.5μm~5.0μmであることが好ましく、0.5μm~4.0μmであることがより好ましく、0.5μm~2.0μmであることが更に好ましい。ガラス繊維の繊維径が0.5μm以上であると均一な細孔径にし易くなる傾向にある。また、ガラス繊維の繊維径が5.0μm以下であると、充分に薄い(例えば、50μm以下)電気化学セパレータを製造し易くなり、また後述する抄造時に良好な抄造性を得易い傾向にある。
樹脂としては、無機材料の結着剤として作用する化合物であれば特に制限はなく、融点が100℃~300℃である樹脂が好ましく、融点が100℃~180℃である樹脂がより好ましく、融点が100℃~160℃である樹脂が更に好ましい。樹脂の融点が100℃以上であると、短絡時のシャットダウン性を得易い傾向がある。また、樹脂の融点が300℃以下であると、製造工程(乾燥)を簡略にできる傾向がある。ここで、融点とは、JIS-K7121に基づき測定される値である。
有機繊維としては、天然繊維、再生繊維、合成繊維等を例示することができる。有機繊維としては、例えばアラミド繊維、ポリアミド繊維、ポリエステル繊維、ポリウレタン繊維、ポリアクリル繊維、ポリエチレン繊維及びポリプロピレン繊維からなる群より選ばれる少なくとも一種を用いることが好ましい。これらの有機繊維は単独で用いてもよいし、二種以上を混合して使用してもよい。
多孔質基体は、ガラス繊維とは異なる無機フィラー(以下、単に「無機フィラー」という)を含んでいてもよい。無機フィラーはガラス繊維と樹脂との結着助剤として機能させることができる。また、無機フィラー自身がセパレータの耐熱性を高めたり、非水電解液中の不純物(フッ化水素ガス、重金属イオン等)をトラップしたり、孔径を微細化することもできる。
なお、セピオライトは、含水マグネシウム珪酸塩を主成分とする粘土鉱物であり、一般的に以下の化学式(x)で表される。
Mg8Si2O30(OH2)4(OH)4・6~8H2O ・・・(x)
多孔質基体は、更に微細化したパルプを含んでいてもよい。必要に応じ用いられるパルプとしては、木材パルプ、非木材パルプ、機械パルプ、及び化学パルプのいずれであってもよい。ただし、セパレータ強度をより良好にするために、パルプの叩解度(CSF値)は、300(「CSF-300ml」とも表記する)以下であることが好ましく、150以下であることがより好ましい。なお、パルプの叩解度の下限値は、0であることが好ましい。
セパレータの透気度(ガーレー値)は、0.1秒/100ml~10秒/100mlであることが好ましい。透気度が0.1秒/100ml以上であると、イオン伝導度を上げ易くすることができる。透気度が10秒/100ml以下であると、短絡不良をより低減することができる。このような観点から、セパレータの透気度は0.1秒/100ml~5秒/100mlであることがより好ましい。なお、セパレータの透気度はJIS P8142(2005)に準拠して測定することができる。
電解液は、非水電解液であり、イオン性液体、及びリチウム塩を含む。具体的には、例えば、電解液は、-20℃以上で液体の性質を示すイオン性液体にリチウム塩を溶解したものを用いることが好ましい。
カーボネート構造を有する化合物を含む場合の含有率は、0.1質量%~10質量%が好ましく、0.2質量%~5質量%がより好ましく、0.5質量%~3質量%が更に好ましい。
これらの中でも、イオン性液体のアニオン成分としては、B(C6H5)4 -、CH3SO3 -、N(C4F9SO2)2 -、CF3SO3 -、N(SO2F)2 -、N(SO2CF3)2 -及びN(SO2CF2CF3)2 -からなる群より選択される少なくとも1種を含むことが好ましく、N(C4F9SO2)2 -、CF3SO3 -、N(SO2F)2 -、N(SO2CF3)2 -、及びN(SO2CF2CF3)2 -からなる群より選択される少なくとも一種を含むことがより好ましく、N(SO2F)2 -を含むことが更に好ましい。
アニオン成分として、N(C4F9SO2)2 -、CF3SO3 -、N(SO2F)2 -、N(SO2CF3)2 -、及びN(SO2CF2CF3)2 -からなる群より選択される少なくとも一種を含むイオン性液体、特にN(SO2F)2 -を含むイオン性液体は比較的低粘度であるため、これを用いることで、充放電特性がより向上する。
正極活物質として、レーザー回折法により測定されたメジアン径が0.6μmのリン酸鉄リチウム(LiFePO4): 85質量%に、導電剤としてアセチレンブラック(商品名:HS-100、電気化学工業社): 10質量%、及び結着剤としてポリフッ化ビニリデン: 5質量%を加えて混合して、正極合剤を調製した。正極合剤を分散媒としてのN-メチル-2-ピロリドンに分散し、スラリー状としたものを厚さ20μmのアルミニウム箔上に、分散媒の乾燥後の塗工量が4.25mg/cm2になるように塗工して120℃で1時間乾燥した。乾燥後、プレスすることにより、正極合剤の密度が1.7g/ml、正極合剤の塗工厚が25μm、正極合剤の体積空隙率が43体積%の正極を作製した。なお、正極合剤の密度は、式:正極合剤の密度=(正極の質量-集電体[アルミニウム箔]の質量)/(正極合剤の厚み×正極合剤の面積)、から算出した。
正極は3.0cm×3.5cmの長方形に切り出し、2.5cm×2.5cmの正極合剤を残して、正極合剤をアルミ箔から削り取った。正極合剤を削り取った後のアルミニウム箔に、アルミニウムタブをスポット溶接で接続した。
負極は2.5cm×3.0cmの長方形に切り出し、2.0cm×2.0cmの負極合剤を残して、負極合剤をアルミ箔から削り取った。負極合剤を削り取った後のアルミニウム箔に、アルミニウムタブをスポット溶接で接続した。
セパレータとして、表1に記載のガラス繊維不織布B(日本板硝子社)を用いたこと以外は実施例1と同様にしてラミネートセルを作製した。
正極活物質として、レーザー回折法により測定されたメジアン径が9.6μmのニッケルマンガン酸リチウム(LiNi0.5Mn1.5O4): 85質量%に、導電剤としてアセチレンブラック(商品名:HS-100、電気化学工業社): 10質量%、及び結着剤としてポリフッ化ビニリデン: 5質量%を加えて混合して、正極合剤を調製した。正極合剤を分散媒としてのN-メチル-2-ピロリドンに分散し、スラリー状としたものを厚さ20μmのアルミニウム箔上に、分散媒の乾燥後の塗工量が5.10mg/cm2になるように塗工して120℃で1時間乾燥した。乾燥後、プレスすることにより、正極合剤の密度が1.9g/ml、正極合剤の塗工厚が27μm、正極合剤の体積空隙率が43体積%の正極を作製した。
セパレータとして、表1に記載のガラス繊維不織布C(日本板硝子社)を用いたこと以外は実施例3と同様にしてラミネートセルを作製した。
セパレータとして、表1に記載のセルロース繊維不織布を用いたこと以外は実施例1と同様にしてラミネートセルを作製した。
セパレータとして、表1に記載のポリイミド繊維不織布を用いたこと以外は実施例1と同様にしてラミネートセルを作製した。
セパレータとして、表1に記載のセルロース繊維不織布を用いたこと以外は実施例3と同様にしてラミネートセルを作製した。
正極活物質として、レーザー回折法により測定されたメジアン径が5.0μmのマンガン酸リチウム(LiMn2O4): 89質量%に、導電剤としてアセチレンブラック(商品名:HS-100、電気化学工業社): 6質量%、及び結着剤としてポリフッ化ビニリデン: 5質量%を加えて混合して、正極合剤を調製した。正極合剤を分散媒としてのN-メチル-2-ピロリドンに分散し、スラリー状としたものを厚さ20μmのアルミニウム箔上に、分散媒の乾燥後の塗工量が5.50mg/cm2になるように塗工し、120℃で1時間乾燥した。乾燥後、プレスすることにより、正極合剤の密度2.2g/ml、正極合剤の塗工厚25μm、正極合剤の体積空隙率38体積%の正極を作製した。
正極は2.5cm×3.0cmの長方形に切り出し、2.0cm×2.0cmの正極合剤を残して、正極合剤をアルミニウム箔から削り取った。正極合剤を削り取った後のアルミ箔に、アルミニウムタブをスポット溶接で接続した。
正極活物質として、レーザー回折法により測定されたメジアン径が10.0μmのマンガン酸リチウム(LiMn2O4)を用いたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極活物質として、レーザー回折法により測定されたメジアン径が25.0μmのマンガン酸リチウム(LiMn2O4)を用いたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極合剤の塗工量を6.00mg/cm2とし、正極合剤の密度を2.4g/mlとし、正極合剤の体積空隙率32体積%としたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極合剤の塗工量を6.50mg/cm2とし、正極合剤の密度を2.6g/mlとし、正極合剤の体積空隙率26体積%としたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極合剤の塗工量を8.14mg/cm2、正極合剤の塗工厚を37μmとしたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極合剤の塗工量を9.90mg/cm2、正極合剤の塗工厚を45μmとしたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極活物質として、レーザー回折法により測定されたメジアン径が0.6μmのリン酸鉄リチウム(LiFePO4): 85質量%に、導電剤としてアセチレンブラック(商品名:HS-100、電気化学工業社): 10質量%、及び結着剤としてポリフッ化ビニリデン: 5質量%を加えて混合し、正極合剤を調製した。正極合剤を分散媒としてのN-メチル-2-ピロリドンに分散し、スラリー状としたものを厚さ20μmのアルミニウム箔上に、分散媒の乾燥後の塗工量が7.65mg/cm2になるように塗工し、120℃で1時間乾燥した。乾燥後、プレスすることにより、正極合剤の密度が1.7g/ml、正極合剤の塗工厚が45μm、正極合剤の体積空隙率が43体積%の正極を作製したこと以外は実施例5と同様にしてラミネートセルを作製した。
正極合剤の塗工量を8.55mg/cm2、正極合剤の密度を1.9g/mlとし、正極合剤の体積空隙率を36体積%としたこと以外は実施例12と同様にしてラミネートセルを作製した。
正極活物質として、レーザー回折法により測定されたメジアン径が9.6μmのニッケルマンガン酸リチウム(LiNi0.5Mn1.5O4): 85質量%に、導電剤としてアセチレンブラック(商品名:HS-100、電気化学工業社): 10質量%、及び結着剤としてポリフッ化ビニリデン: 5質量%を加えて混合し、正極合剤を調製した。正極合剤を分散媒としてのN-メチル-2-ピロリドンに分散し、スラリー状としたものを厚さ20μmのアルミニウム箔上に、分散媒の乾燥後の塗工量が5.10mg/cm2になるように塗工し、120℃で1時間乾燥した。乾燥後、プレスすることにより、正極合剤の密度が1.9g/ml、正極合剤の塗工厚が27μm、正極合剤の体積空隙率が43体積%の正極を作製したこと以外は実施例5と同様にしてラミネートセルを作製した。
正極は、タブ溶接部を残して3.0cm×3.5cmの長方形に切り出した銅メッシュにニッケルタブをスポット溶接で接続し、メッシュ上に、金属リチウムを貼り付けたものを用いた。
負極は2.5cm×3.0cmの長方形に切り出し、2.0cm×2.0cmの負極合剤を残して、負極合剤をアルミニウム箔から削り取った。負極合剤を削り取った後のアルミニウム箔に、アルミニウムタブをスポット溶接で接続した。
負極活物質として、レーザー回折法により測定されたメジアン径が1.2μmのチタン酸リチウム(Li4Ti5O12)を用いると共に、負極合剤の塗工量を2.70mg/cm2とし、負極合剤の密度を1.8g/mlとし、負極合剤の塗工厚を17μmとし、負極合剤の体積空隙率を44体積%としたこと以外は実施例15と同様にしてラミネートセルを作製した。
正極合剤の塗工量を17.60mg/cm2とし、正極合剤の塗工厚を85μmとしたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極合剤の塗工量を6.50mg/cm2とし、正極合剤の密度を2.85g/mlとし、正極合剤の塗工厚を23μmとし、正極合剤の体積空隙率を19体積%としたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極合剤の塗工量を8.14mg/cm2とし、正極合剤の密度を1.9g/mlとし、正極合剤の塗工厚を43μmとし、正極合剤の体積空隙率を46体積%としたこと以外は実施例5と同様にしてラミネートセルを作製した。
正極合剤の塗工量を14.45mg/cm2とし、正極合剤の塗工厚を85μmとしたこと以外は実施例12と同様にしてラミネートセルを作製した。
正極合剤の塗工量を7.20mg/cm2、正極合剤の密度を1.6g/mlとし、正極合剤の体積空隙率を47体積%としたこと以外は実施例12と同様にしてラミネートセルを作製した。
正極合剤の塗工量を11.00mg/cm2とし、正極合剤の塗工厚を58μmとしたこと以外は実施例14と同様にしてラミネートセルを作製した。
正極合剤の密度を1.6g/mlとし、正極合剤の塗工厚を32μmとし、正極合剤の体積空隙率を55体積%としたこと以外は実施例14と同様にしてラミネートセルを作製した。
負極合剤の塗工量を7.20mg/cm2、負極合剤の密度を2.2g/ml、負極合剤の塗工厚を33μm、負極合剤の体積空隙率18体積%としたこと以外は実施例16と同様にしてラミネートセルを作製した。
負極合剤の塗工量を5.00mg/cm2、負極合剤の密度を1.5g/mlとし、負極合剤の体積空隙率47体積%としたこと以外は実施例15と同様にしてラミネートセルを作製した。
負極合剤の塗工量を11.00mg/cm2、負極合剤の塗工厚を61μmとし、負極合剤の体積空隙率43体積%としたこと以外は実施例16と同様にしてラミネートセルを作製した。
負極合剤の体積空隙率50体積%としたこと以外は実施例16と同様にしてラミネートセルを作製した。
各例で用いたセパレータの細孔分布を水銀ポロシメーター測定により求めた。水銀ポロシメーターの測定から得られた全細孔容積及び空孔率を表1に示す。また、ガーレー試験機法の測定から得られた透気度も表1に示す。
実施例1~2及び比較例1~2で作製した電池(ラミネートセル)を25℃において0.2Cの定電流で充電終止電圧2.5Vまで定電流充電し、次いで充電終止電圧2.5Vで電流値が0.01Cになるまで定電圧充電を行った。尚、電流値の単位として用いたCとは、”電流値(A)/電池容量(Ah)”を意味する。15分間休止後、電流値0.2C、放電終止電圧1.0Vで定電流放電を行った。前記の充放電条件で充放電を3回繰り返した。
その後、0.2Cの定電流で充電終止電圧2.5Vまで定電流充電し、次いで充電終止電圧2.5Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.1C、放電終止電圧1.0Vで定電流放電を行った。このときの放電容量を初回放電容量とした。
さらに、0.2Cの定電流で充電終止電圧2.5Vまで定電流充電し、次いで充電終止電圧2.5Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値1C、放電終止電圧1.0Vで定電流放電を行った。
実施例3~4と比較例3で作製した電池(ラミネートセル)を25℃において
0.2Cの定電流で充電終止電圧3.8Vまで定電流充電し、次いで充電終止電圧3.8Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.2C、放電終止電圧2.0Vで定電流放電を行った。前記の充放電条件で充放電を3回繰り返した。
その後、0.2Cの定電流で充電終止電圧3.8Vまで定電流充電し、次いで充電終止電圧3.8Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.1C、放電終止電圧2.0Vで定電流放電を行った。このときの放電容量は初回放電容量とした。
さらに、0.2Cの定電流で充電終止電圧3.8Vまで定電流充電し、次いで充電終止電圧3.8Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値1C、放電終止電圧2.0Vで定電流放電を行った。
実施例5~11と比較例4~6で作製した電池(ラミネートセル)を25℃において0.2Cの定電流で充電終止電圧4.3Vまで定電流充電し、次いで充電終止電圧4.3Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.2C、放電終止電圧3.0Vで定電流放電を行った。前記の充放電条件で充放電を3回繰り返した。
その後、0.2Cの定電流で充電終止電圧4.3Vまで定電流充電し、次いで充電終止電圧4.3Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.1C、放電終止電圧3.0Vで定電流放電を行った。このときの放電容量を初回放電容量とした。尚、初回放電容量は、正極活物質の単位質量当たりで換算した。
さらに、0.2Cの定電流で充電終止電圧4.3Vまで定電流充電し、次いで充電終止電圧4.3Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値1C、放電終止電圧3.0Vで定電流放電を行った。
実施例12~13と比較例7~8で作製した電池(ラミネートセル)を25℃において0.2Cの定電流で充電終止電圧4.0Vまで定電流充電し、次いで充電終止電圧4.0Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.2C、放電終止電圧2.0Vで定電流放電を行った。前記の充放電条件で充放電を3回繰り返した。
その後、0.2Cの定電流で充電終止電圧4.0Vまで定電流充電し、次いで充電終止電圧4.0Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.1C、放電終止電圧2.0Vで定電流放電を行った。このときの放電容量を初回放電容量とした。尚、初回放電容量は、正極活物質の単位質量当たりで換算した。
さらに、0.2Cの定電流で充電終止電圧4.0Vまで定電流充電し、次いで充電終止電圧4.0Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値1C、放電終止電圧2.0Vで定電流放電を行った。
実施例14と比較例9~10で作製した電池(ラミネートセル)を25℃において0.2Cの定電流で充電終止電圧4.95Vまで定電流充電し、次いで充電終止電圧4.95Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.2C、放電終止電圧3.5Vで定電流放電を行った。前記の充放電条件で充放電を3回繰り返した。
その後、0.2Cの定電流で充電終止電圧4.95Vまで定電流充電し、次いで充電終止電圧4.95Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.1C、放電終止電圧3.5Vで定電流放電を行った。このときの放電容量を初回放電容量とした。尚、初回放電容量は、正極活物質の単位質量当たりで換算した。
さらに、0.2Cの定電流で充電終止電圧4.95Vまで定電流充電し、次いで充電終止電圧4.95Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値1C、放電終止電圧3.5Vで定電流放電を行った。
実施例15~16と比較例11~14で作製した電池(ラミネートセル)を25℃において0.2Cの定電流で充電終止電圧3.4Vまで定電流充電し、次いで充電終止電圧3.4Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.2C、放電終止電圧2.0Vで定電流放電を行った。前記の充放電条件で充放電を3回繰り返した。
その後、0.2Cの定電流で充電終止電圧3.4Vまで定電流充電し、次いで充電終止電圧2.0Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値0.1C、放電終止電圧2.0Vで定電流放電を行った。このときの放電容量を初回放電容量とした。尚、初回放電容量は、負極活物質の単位質量当たりで換算した。
さらに、0.2Cの定電流で充電終止電圧3.4Vまで定電流充電し、次いで充電終止電圧3.4Vで電流値が0.01Cになるまで定電圧充電を行った。15分間休止後、電流値1C、放電終止電圧2.0Vで定電流放電を行った。
また、正極合剤及び負極合剤に、メジアン径0.3μm~30μmの活物質を用い、また、正極合剤及び負極合剤の厚み(塗工厚)を20μm~80μmとすると、大電流特性が向上することもわかる。
本明細書に記載された全ての文献、特許出願、および技術規格は、個々の文献、特許出願、および技術規格が参照により取り込まれることが具体的かつ個々に記された場合と同程度に、本明細書中に参照により取り込まれる。
Claims (5)
- 正極と、負極と、セパレータと、イオン性液体及びリチウム塩を含む電解液とを有し、前記セパレータの空孔率が80%~98%であり、かつ下記(1)及び(2)の少なくとも一方の条件を満たすリチウムイオン二次電池。(1)前記正極は、第1集電体と前記第1集電体の少なくとも一方の面に付与された正極合剤とを有し、前記第1集電体の一方の面への前記正極合剤の付与量が1mg/cm2~10mg/cm2であり、前記正極合剤の体積空隙率が20体積%~45体積%である。(2)前記負極は、第2集電体と前記第2集電体の少なくとも一方の面に付与された負極合剤とを有し、前記第2集電体の一方の面への前記負極合剤の付与量が1mg/cm2~10mg/cm2であり、前記負極合剤の体積空隙率が20体積%~45体積%である。
- 前記セパレータが、ポリオレフィン繊維、ガラス繊維、セルロース繊維、及びポリイミド繊維からなる群より選択される少なくとも一種を含む不織布である請求項1に記載のリチウムイオン二次電池。
- 前記イオン性液体のアニオン成分が、N(C4F9SO2)2 -、CF3SO3 -、N(SO2F)2 -、N(SO2CF3)2 -、及びN(SO2CF2CF3)2 -からなる群より選択される少なくとも一種を含む請求項1又は請求項2に記載のリチウムイオン二次電池。
- 前記イオン性液体のカチオン成分が、鎖状四級アンモニウムカチオン、ピペリジニウムカチオン、ピロリジニウムカチオン、及びイミダゾリウムカチオンからなる群より選択される少なくとも一種を含む請求項1~請求項3のいずれか1項に記載のリチウムイオン二次電池。
- 前記正極合剤又は前記負極合剤は、レーザー回折法によって求められるメジアン径が0.3μm~30μmの活物質を含む請求項1~請求項4のいずれか1項に記載のリチウムイオン二次電池。
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US15/025,446 US20160240885A1 (en) | 2013-09-30 | 2014-09-26 | Lithium ion secondary battery |
JP2015539397A JP6112213B2 (ja) | 2013-09-30 | 2014-09-26 | リチウムイオン二次電池 |
CN201480053722.1A CN105594050A (zh) | 2013-09-30 | 2014-09-26 | 锂离子二次电池 |
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JP2017073251A (ja) * | 2015-10-06 | 2017-04-13 | 株式会社日本触媒 | リチウムイオン二次電池 |
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WO2019151501A1 (ja) * | 2018-02-02 | 2019-08-08 | 日立化成株式会社 | リチウムイオン二次電池 |
CN114583386A (zh) * | 2022-03-22 | 2022-06-03 | 中国石油大学(华东) | 锂硫电池复合一体化隔膜及制备方法和锂硫电池 |
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JP6112213B2 (ja) | 2017-04-12 |
JPWO2015046468A1 (ja) | 2017-03-09 |
CN105594050A (zh) | 2016-05-18 |
TW201535843A (zh) | 2015-09-16 |
TWI624104B (zh) | 2018-05-11 |
US20160240885A1 (en) | 2016-08-18 |
KR20160064157A (ko) | 2016-06-07 |
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