WO2013031226A1 - 非水電解質二次電池 - Google Patents
非水電解質二次電池 Download PDFInfo
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- WO2013031226A1 WO2013031226A1 PCT/JP2012/005486 JP2012005486W WO2013031226A1 WO 2013031226 A1 WO2013031226 A1 WO 2013031226A1 JP 2012005486 W JP2012005486 W JP 2012005486W WO 2013031226 A1 WO2013031226 A1 WO 2013031226A1
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- 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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- 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
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- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
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- 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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- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M2010/4292—Aspects relating to capacity ratio of electrodes/electrolyte or anode/cathode
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- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
- H01M2300/0028—Organic electrolyte characterised by the solvent
- H01M2300/0037—Mixture of solvents
- H01M2300/004—Three solvents
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
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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
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- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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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
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Definitions
- the present invention relates to a non-aqueous electrolyte secondary battery, and specifically relates to improvement of a mixture layer of a positive electrode and a negative electrode.
- Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are expected to be used as a power source for various devices because of high voltage and high energy density and capacity.
- Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are expected to be used as a power source for various devices because of high voltage and high energy density and capacity.
- applications such as driving power sources for mobile devices, hybrid electric vehicles, electric vehicles, etc., there is a strong demand for higher capacity in order to further improve the operating time and travel distance.
- Patent Document 1 discloses that, from the viewpoint of cycle characteristics and safety, in a nonaqueous electrolyte secondary battery having a volume energy density of about 300 Wh / L, nonaqueous electrolysis is performed with respect to the total pore volume of the positive electrode, the negative electrode, and the separator. It discloses that the occupied volume of the liquid is controlled to 120 to 140%.
- the volume energy density is the battery energy density per volume normalized by the battery case size.
- Patent Document 2 discloses that such a combination of solvents reduces the viscosity of the nonaqueous electrolytic solution, improves the permeability to the separator, and provides a sufficient discharge capacity.
- the volume energy density is about 300 Wh / L, but in applications such as a driving power source, a higher capacity, for example, a volume energy density of 650 Wh / L or more is required.
- a method of using an electrode group in which the positive electrode and the negative electrode are wound with a separator interposed therebetween, and further improving the active material density in the mixture layer of the positive electrode and the negative electrode can be considered.
- the active material density of the mixture layer of the positive electrode or the negative electrode is increased, the porosity of the mixture layer is decreased, and thus the nonaqueous electrolyte is less likely to penetrate into the mixture layer.
- the nonaqueous electrolyte has low permeability, it is difficult to obtain high discharge characteristics.
- the amount of the nonaqueous electrolyte that can be accommodated in the battery is reduced, the amount of the nonaqueous electrolyte that can participate in the battery reaction is reduced.
- the amount of the non-aqueous electrolyte is small, the difference in permeability of the non-aqueous electrolyte between the positive electrode and the negative electrode tends to be remarkable. Therefore, it is considered that the nonaqueous electrolyte is unevenly distributed in one electrode having high permeability, and the amount of the nonaqueous electrolyte in the other electrode becomes insufficient. Therefore, it is difficult to suppress uneven distribution of the nonaqueous electrolyte only by reducing the viscosity of the nonaqueous electrolyte. Therefore, it is not possible to sufficiently extract the capacity, and it is not possible to suppress a decrease in capacity maintenance rate when charging and discharging are repeated.
- An object of the present invention is to provide a non-aqueous electrolyte secondary battery having an improved cycle life even with a high capacity.
- One aspect of the present invention includes a positive electrode, a negative electrode, an electrode group in which a separator interposed between the positive electrode and the negative electrode is wound, and a nonaqueous electrolyte.
- the volume energy density is 650 Wh / L or more
- the positive electrode is A positive electrode current collector and a positive electrode mixture layer attached to a surface of the positive electrode current collector; a negative electrode including a negative electrode current collector and a negative electrode mixture layer attached to the surface of the negative electrode current collector;
- the porosity P p of the mixture layer is 22% or less
- the porosity P n of the negative electrode mixture layer is 25% or less
- the ratio V E / V T of the non-aqueous electrolyte of the volume V E to the total V T of the pore volume of the separator is, 1 to 1.5 or less, the contact angle CA p of the positive electrode for non-aqueous electrolyte
- a non-aqueous electrolyte secondary battery with improved cycle life is provided by suppressing uneven distribution of the non-aqueous electrolyte. it can.
- FIG. 1 is a longitudinal sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.
- 2a is a top view schematically showing a positive electrode used in the nonaqueous electrolyte secondary battery of FIG. 2b is a cross-sectional view schematically showing the positive electrode of FIG. 2a.
- FIG. 2c is a bottom view schematically showing the positive electrode of FIG. 2a.
- 3a is a top view schematically showing a negative electrode used in the nonaqueous electrolyte secondary battery of FIG.
- FIG. 3b is a cross-sectional view schematically showing the negative electrode of FIG. 3a.
- FIG. 3c is a bottom view schematically showing the negative electrode of FIG. 3a.
- the non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, an electrode group in which a separator interposed between the positive electrode and the negative electrode is wound, and a non-aqueous electrolyte.
- the positive electrode includes a positive electrode current collector and a positive electrode mixture layer attached to the surface of the positive electrode current collector.
- the negative electrode includes a negative electrode current collector and a negative electrode mixture layer attached to the surface of the negative electrode current collector.
- the non-aqueous electrolyte secondary battery has a high capacity with a volume energy density of 650 Wh / L or more. Therefore, the active material is highly filled in both the positive electrode and the negative electrode, and the porosity of the mixture layer of the positive electrode and the negative electrode is lowered. Specifically, the porosity P p of the positive electrode mixture layer is 22% or less, and the porosity P n of the negative electrode mixture layer is 25% or less. When the porosity P p and P n are in such a range, the difference in permeability of the non-aqueous electrolyte between the positive electrode and the negative electrode tends to become remarkable, and the problem that the non-aqueous electrolyte is unevenly distributed on one electrode is a problem. Arise.
- the ratio V E / V T of the volume V E of the nonaqueous electrolyte to the total V T of the pore volume of the positive electrode mixture layer, the pore volume of the negative electrode mixture layer, and the pore volume of the separator is 1 or more and 1 .5 or less.
- the ratio V E / V T is less than 1, it becomes difficult to spread the nonaqueous electrolyte over the entire electrode group, and the battery reaction cannot be performed efficiently.
- a non-aqueous electrolyte with a ratio V E / V T exceeding 1.5 it is difficult to increase the capacity of the battery.
- is 23 ° or less.
- the contact angle of the positive electrode and the negative electrode with respect to the non-aqueous electrolyte is an indicator of the permeability of the non-aqueous electrolyte into each mixture layer.
- the non-aqueous electrolyte is prevented from being unevenly distributed on either the positive electrode or the negative electrode. Can do.
- CA p -CA n represents the absolute value of the difference between the contact angle CA n contact angle CA p, may be larger which of the CA p and CA n, but than CA p of CA n It is preferable that it is larger.
- the contact angle difference between the positive electrode and the negative electrode exceeds 23 °, the difference in the permeability of the nonaqueous electrolyte between the positive electrode and the negative electrode becomes significant, and the nonaqueous electrolyte tends to be unevenly distributed on the electrode with the smaller contact angle. .
- the electrode on the side with the larger contact angle lacks the non-aqueous electrolyte and the efficiency of the battery reaction decreases.
- the highly filled active material cannot be effectively used, and the capacity cannot be sufficiently extracted. Such a defect becomes larger as charge / discharge is repeated, and as a result, the capacity maintenance rate is lowered.
- the nonaqueous electrolyte secondary battery including the wound electrode group having a volume energy density of 650 Wh / L or more, the porosity P p and P n of the mixture layer of the positive electrode and the negative electrode,
- of the positive electrode and the negative electrode with respect to the non-aqueous electrolyte are controlled to the specific ranges as described above, respectively. To do.
- the volume energy density of the nonaqueous electrolyte secondary battery is preferably 680 Wh / L or more, more preferably 700 Wh / L or more, or 720 Wh / L or more. In the present invention, even when the volume energy density of the battery is thus high, the cycle life characteristics can be improved.
- is 23 ° or less, preferably 22 ° or less, and more preferably 21 ° or less.
- may be 0, but is preferably 3 or more, more preferably 10 or more, or 18 or more. These upper limit value and lower limit value can be appropriately selected and combined.
- may be, for example, 3 to 23 ° or 18 to 21 °.
- the contact angle CA p of the positive electrode is, for example, 1 to 20 °, preferably 5 to 18 ° or 7 to 16 °.
- the contact angle CA n of the negative electrode is, for example, 10 to 45 °, preferably 15 to 40 ° or 25 to 37 °.
- the contact angle between the positive electrode and the negative electrode can be measured by the ⁇ / 2 method. Specifically, a non-aqueous electrolyte droplet is dropped on the surfaces of the sheet-like positive electrode and negative electrode before winding, and the contact angle of the droplet after a predetermined time is measured.
- the contact angle between the positive electrode and the negative electrode is adjusted by selecting or adjusting the type of active material, the active material density in the mixture layer, the porosity, the rolling pressure when forming the mixture layer, the number of rollings, etc. Can do.
- the porosity P p of the positive electrode mixture layer is 22% or less, preferably 21% or less, more preferably 20% or less or 19% or less.
- the porosity P p is, for example, 10% or more, preferably 13% or more, and more preferably 15% or more. These upper limit value and lower limit value can be appropriately selected and combined.
- the porosity P p may be, for example, 10-22% or 15-20%.
- the porosity P p is in such a range, on easily increase the filling factor of the active material, it can be prevented from becoming low in more than necessary permeability of the non-aqueous electrolyte, under the control of the CA p, positive and negative electrodes It is easy to reduce the difference in the permeability of the nonaqueous electrolyte.
- the porosity P n of the negative electrode mixture layer is 25% or less, preferably 23% or less, and more preferably 22% or less.
- the porosity P n is, for example, 15% or more, preferably 17% or more or 18% or more. These upper limit value and lower limit value can be appropriately selected and combined.
- the porosity P n may be, for example, 15 to 25% or 18 to 22%.
- between the porosity P p of the positive electrode mixture layer and the porosity P n of the negative electrode mixture layer is, for example, 7% or less, preferably 5.5% or less, more preferably 5% or less or 4% or less. Further, the porosity difference
- the porosity can be calculated based on the true density, thickness and weight of the mixture layer.
- the true density of the mixture layer can be calculated by a gas phase substitution method or a liquid phase substitution method.
- select or adjust the type and ratio of the components of the mixture layer, the active material density in the mixture layer, the rolling pressure when forming the mixture layer, the number of rollings, etc. Can be adjusted.
- the ratio V E / V T of the volume V E of the non-aqueous electrolyte to the total V T of the pore volume of the separator is 1 or more, Preferably it is 1.2 or more, More preferably, it is 1.3 or more.
- the ratio V E / V T is 1.5 or less, preferably 1.46 or less.
- FIG. 1 is a longitudinal sectional view schematically showing a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.
- the nonaqueous electrolyte secondary battery has an electrode group 4 in which a long strip-shaped positive electrode 5, a long strip-shaped negative electrode 6, and a separator 7 interposed between the positive electrode 5 and the negative electrode 6 are wound.
- a non-aqueous electrolyte (not shown) is accommodated.
- a positive electrode lead 9 is electrically connected to the positive electrode 5, and a negative electrode lead 10 is electrically connected to the negative electrode 6.
- the electrode group 4 is housed in the battery case 1 together with the lower insulating ring 8b with the positive electrode lead 9 led out.
- the sealing plate 2 is welded to the end of the positive electrode lead 9, and the positive electrode 5 and the sealing plate 2 are electrically connected.
- the lower insulating ring 8 b is disposed between the bottom surface of the electrode group 4 and the negative electrode lead 10 led out from the electrode group 4.
- the negative electrode lead 10 is welded to the inner bottom surface of the battery case 1, and the negative electrode 6 and the battery case 1 are electrically connected.
- An upper insulating ring 8 a is mounted on the upper surface of the electrode group 4.
- the electrode group 4 is held in the battery case 1 by an inwardly protruding step 11 formed on the upper side surface of the battery case 1 above the upper insulating ring 8a.
- a sealing plate 2 having a resin gasket 3 on the periphery is placed, and the opening end of the battery case 1 is caulked and sealed inward.
- FIG. 2a, 2b, and 2c are a top view, a cross-sectional view, and a bottom view, respectively, schematically showing the positive electrode 5 used in the nonaqueous electrolyte secondary battery in FIG. 3a, 3b, and 3c are a top view, a cross-sectional view, and a bottom view, respectively, schematically showing the negative electrode 6 used in the nonaqueous electrolyte secondary battery of FIG.
- the positive electrode 5 includes a long strip-shaped positive electrode current collector 5a and a positive electrode mixture layer 5b formed on both surfaces of the positive electrode current collector 5a. On both surfaces of the positive electrode current collector 5a, current collector exposed portions 5c and 5d that do not have the positive electrode mixture layer 5b on the surface are formed at the center portion in the longitudinal direction so as to cross in the lateral direction. . And the one end part of the positive electrode lead 9 is welded to the collector exposed part 5c.
- the negative electrode 6 includes a long strip-shaped negative electrode current collector 6a and a negative electrode mixture layer 6b formed on both surfaces of the negative electrode current collector 6a. At one end in the longitudinal direction of the negative electrode 6, current collector exposed portions 6 c and 6 d having the same size and having no negative electrode mixture layer 6 b are formed on both surfaces of the negative electrode 6. Further, current collector exposed portions 6e and 6f that do not have the negative electrode mixture layer 6b are formed on both surfaces of the negative electrode 6 at the other end in the longitudinal direction of the negative electrode 6. The width of the current collector exposed portions 6e and 6f (the length in the longitudinal direction of the negative electrode 6) is greater in the current collector exposed portion 6f than in the current collector exposed portion 6e. One end of the negative electrode lead 10 is welded in the vicinity of the other end in the longitudinal direction of the negative electrode 6 on the current collector exposed portion 6f side.
- the nonaqueous electrolyte can be efficiently permeated from the longitudinal center portion of the positive electrode and the longitudinal end portion of the negative electrode.
- the positive electrode mixture layer may be attached to both surfaces of the positive electrode current collector, or may be attached to one surface.
- the positive electrode current collector may be a non-porous conductive substrate or a porous conductive substrate having a plurality of through holes.
- a metal foil, a metal sheet, or the like can be used as the non-porous conductive substrate.
- the porous conductive substrate include a metal foil having a communication hole (perforation), a mesh body, a net body, a punching sheet, an expanded metal, and a lath body.
- Examples of the metal material used for the positive electrode current collector include stainless steel, titanium, aluminum, and an aluminum alloy.
- the thickness of the positive electrode current collector can be selected from the range of 3 to 50 ⁇ m, for example, and is preferably 5 to 30 ⁇ m.
- the positive electrode mixture layer includes, for example, a positive electrode active material, a conductive auxiliary agent, and a binder.
- the positive electrode mixture layer may contain a thickener and the like as necessary.
- a positive electrode slurry containing a component of the positive electrode mixture layer such as a positive electrode active material, a conductive additive, and a binder and a dispersion medium is applied to the surface of the positive electrode current collector, and a pair of the formed coating films is applied. It can be obtained by rolling with a roll or the like and further heating to form a positive electrode mixture layer. If necessary, the coating film may be dried before rolling.
- the positive electrode active material a known positive electrode active material capable of occluding and releasing lithium ions can be used.
- the positive electrode active material those containing a sufficient amount of lithium are preferable, and specific examples include lithium-containing transition metal oxides.
- the lithium-containing transition metal oxide preferably has a layered or hexagonal crystal structure or a spinel structure.
- the positive electrode active material is usually used in a particulate form.
- transition metal elements include Co, Ni, and Mn.
- the transition metal may be partially substituted with a different element.
- the surface of the lithium-containing transition metal oxide particles may be coated with a different element.
- the different elements include Na, Mg, Sc, Y, Cu, Zn, Al, Cr, Pb, Sb, and B.
- a positive electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.
- M Li x Mn 2-y M y O 4
- the conductive auxiliary agent (or conductive agent) known materials such as carbon black such as acetylene black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride and the like can be used.
- a conductive support agent can be used individually by 1 type or in combination of 2 or more types.
- the amount of the conductive aid is not particularly limited, and may be, for example, 10 parts by volume or less with respect to 100 parts by volume of the active material. From the viewpoint of increasing the active material density to increase the capacity of the battery and reducing the difference in permeability between the positive electrode and the negative electrode, the amount of the conductive auxiliary is preferably 5 parts by volume or less, more preferably 3 Below the volume.
- the minimum of the quantity of a conductive support agent is not restrict
- a known binder for example, a fluororesin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), vinylidene fluoride (VDF) -hexafluoropropylene (HFP) copolymer;
- PTFE polytetrafluoroethylene
- PVDF polyvinylidene fluoride
- VDF vinylidene fluoride
- HFP hexafluoropropylene
- a binder can be used individually by 1 type or in combination of 2 or more types.
- the amount of the binder may be, for example, 10 parts by volume or less with respect to 100 parts by volume of the active material. From the viewpoint of increasing the capacity of the battery by increasing the active material density and reducing the difference in permeability between the positive electrode and the negative electrode, the amount of the binder is preferably 5 parts by volume or less, more preferably 3 Below the volume. The lower limit of the amount of the binder is not particularly limited, and may be 0.01 part by volume or more with respect to 100 parts by volume of the active material, for example.
- the thickener examples include cellulose derivatives such as carboxymethyl cellulose (CMC); C 2-4 polyalkylene glycol such as polyethylene glycol and ethylene oxide-propylene oxide copolymer; polyvinyl alcohol; solubilized modified rubber and the like. .
- a thickener can be used individually by 1 type or in combination of 2 or more types.
- the ratio of the thickener is not particularly limited, and is, for example, 0 to 10 parts by volume, preferably 0.01 to 5 parts by volume with respect to 100 parts by volume of the active material.
- the dispersion medium is not particularly limited, and examples thereof include water, alcohols such as ethanol, ethers such as tetrahydrofuran, amides such as dimethylformamide, N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof. .
- Rolling can be performed by passing a current collector having a coating film on the surface between a pair of rolls.
- the rolling pressure may be linear pressure, for example, 5 to 40 kN / cm, preferably 10 to 35 kN / cm, or 12 to 32 kN / cm.
- the diameter of the roll can be appropriately selected from the range of 500 to 1000 mm, for example.
- the number of rollings can be appropriately selected according to the rolling pressure, and may be, for example, 1 to 5 times, preferably 1 to 3 times.
- the active material particles may be broken and the wettability with respect to the non-aqueous electrolyte may be lowered. Therefore, it is preferable to adjust the permeability of the nonaqueous electrolyte while appropriately adjusting the rolling pressure and the number of times.
- a positive electrode mixture layer can be formed by heating the coated film after rolling.
- the heating temperature is, for example, 170 to 250 ° C., preferably 180 to 220 ° C.
- the thickness of the positive electrode mixture layer thus formed is, for example, 10 to 60 ⁇ m, preferably 12 to 50 ⁇ m, and more preferably 15 to 35 ⁇ m.
- the active material density of the positive electrode mixture layer is, for example, 3.3 to 3.9 g / cm 3 on the average of the entire positive electrode mixture layer, preferably It is 3.5 to 3.85 g / cm 3 , more preferably 3.6 to 3.8 g / cm 3 .
- the negative electrode mixture layer may be attached to both surfaces of the negative electrode current collector, or may be attached to one surface.
- a nonporous or porous conductive substrate can be used as the negative electrode current collector.
- the thickness of the negative electrode current collector can be selected from the same range as the thickness of the positive electrode current collector.
- the metal material used for the negative electrode current collector include stainless steel, nickel, copper, copper alloy, aluminum, and aluminum alloy. Of these, copper or a copper alloy is preferable.
- the negative electrode mixture layer includes, for example, a negative electrode active material and a binder, and may include a conductive additive, a thickener, and the like as necessary in addition to these components.
- the negative electrode can be formed according to the method for forming the positive electrode. Specifically, on the surface of the negative electrode current collector, a negative electrode slurry containing a component of the negative electrode mixture layer such as an active material and a binder and a dispersion medium is applied, and the formed coating film is rolled and heated. Can be formed.
- the negative electrode active material a known negative electrode active material capable of occluding and releasing lithium ions can be used.
- the negative electrode active material include various carbonaceous materials such as graphite (natural graphite, artificial graphite, graphitized mesophase carbon, etc.), coke, graphitized carbon, graphitized carbon fiber, and amorphous carbon.
- a chalcogen compound such as a transition metal oxide or transition metal sulfide capable of inserting and extracting lithium ions at a lower potential than the positive electrode; silicon; silicon oxide SiO ⁇ (0.05 ⁇ ⁇ 1.95), silicon-containing compounds such as silicide; lithium alloys containing at least one selected from the group consisting of tin, aluminum, zinc and magnesium, and various alloy composition materials can also be used.
- These negative electrode active materials can be used singly or in combination of two or more.
- a carbonaceous material mainly composed of graphite such as natural graphite or artificial graphite
- the problem of uneven distribution of the nonaqueous electrolyte is likely to occur.
- uneven distribution of the nonaqueous electrolyte can be suppressed.
- the binder As the binder, the dispersion medium, the conductive additive, and the thickener, those exemplified for the positive electrode can be used.
- the amount of each component relative to the active material can also be selected from the same range as that of the positive electrode.
- the thickness of the negative electrode mixture layer can also be selected from the same range as that of the positive electrode mixture layer.
- the active material is a carbonaceous material such as graphite
- the active material density in the negative electrode is, for example, 1.3 to 1.9 g / cm 3 , preferably 1.5 to 1.8 g in average for the entire mixture layer. / Cm 3 , more preferably 1.6 to 1.8 g / cm 3 .
- the separator a resin-made microporous film, nonwoven fabric or woven fabric can be used.
- the resin constituting the separator include polyolefins such as polyethylene and polypropylene; polyamide resins such as polyamide; polyimide resins such as polyamideimide and polyimide.
- the thickness of the separator is, for example, 5 to 50 ⁇ m.
- Non-aqueous electrolyte includes a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent.
- Nonaqueous solvents include, for example, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and the like. Examples of the cyclic carbonate include EC and PC. Examples of the chain carbonate include diethyl carbonate, EMC, and DMC. Examples of the cyclic carboxylic acid ester include ⁇ -butyrolactone and ⁇ -valerolactone.
- a non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.
- the non-aqueous solvent preferably contains a cyclic carbonate and a chain carbonate.
- the cyclic carbonate particularly preferably contains EC
- the chain carbonate particularly preferably contains EMC and DMC. Since the capacity of the nonaqueous electrolyte secondary battery of the present invention is increased, the porosity of the mixture layer of the positive electrode and the negative electrode is low. When the porosity of the mixture layer is lowered, the permeability of the non-aqueous electrolyte is lowered. Therefore, the viscosity of the non-aqueous electrolyte is preferably lowered.
- the non-aqueous solvent contains DMC
- DMC has a high melting point
- ion conductivity at low temperatures tends to be low.
- the melting point of EMC is as low as ⁇ 55 ° C., so that the melting point (or freezing point) of the non-aqueous electrolyte can be lowered even when a large amount of DMC is contained.
- DMC has a low dielectric constant and low oxidation resistance
- the polarity and oxidation resistance can be improved by incorporating EC in a non-aqueous solvent.
- the non-aqueous solvent contains EC, the dissociation property of the lithium salt can be improved.
- the EC content in the non-aqueous solvent is, for example, 10 to 25% by volume, preferably 18 to 23% by volume, and more preferably 19 to 22% by volume.
- the EMC content is, for example, 2 to 7% by volume, preferably 3 to 7% by volume, and more preferably 4 to 6% by volume.
- the DMC content is, for example, 68 to 88% by volume, preferably 70 to 79% by volume, and more preferably 72 to 77% by volume.
- the non-aqueous solvent may contain other non-aqueous solvents (the non-aqueous solvents exemplified above) in addition to EC, EMC, and DMC.
- a lithium salt of a fluorine-containing acid LiPF 6 , LiBF 4 , LiCF 3 SO 3 and the like
- a lithium salt of a fluorine-containing acid imide LiN (CF 3 SO 2 ) 2 and the like
- a lithium salt can be used individually by 1 type or in combination of 2 or more types.
- a lithium salt of a fluorine-containing acid, particularly LiPF 6 is preferable because it has high dissociation properties and is chemically stable in a non-aqueous electrolyte.
- the concentration of the lithium salt in the nonaqueous electrolyte is, for example, 0.5 to 2 mol / L, preferably 1.2 to 1.6 mol / L.
- the viscosity of the nonaqueous electrolyte at 25 ° C. is, for example, 5 mPa ⁇ s or less, preferably 4 mPa ⁇ s or less.
- the viscosity can be measured using a falling ball viscometer based on JIS Z 8803.
- the non-aqueous electrolyte may contain a known additive, for example, vinylene carbonate, cyclohexylbenzene, diphenyl ether and the like, if necessary.
- the amount of the non-aqueous electrolyte accommodated in the battery case is, for example, a cylindrical lithium ion secondary battery having a nominal capacity of 3.4 Ah (720 Wh / L), preferably 4.3 to 5.5 g, more preferably 4 .4 to 5.3 g.
- the amount of nonaqueous electrolyte tends to decrease, but when the amount of nonaqueous electrolyte decreases, the amount of decomposition of the nonaqueous electrolyte also decreases.
- the generation of gas is suppressed, and from this point of view, it is possible to suppress a decrease in capacity maintenance rate when charging and discharging are repeated.
- the shape of the electrode group may be a cylindrical shape and a flat shape having an oval end surface perpendicular to the winding axis, depending on the shape of the battery or battery case.
- Examples of the material of the positive electrode lead and the negative electrode lead include the same materials as the metal materials of the positive electrode current collector and the negative electrode current collector, respectively. Specifically, an aluminum plate or the like can be used as the positive electrode lead, and a nickel plate or a copper plate can be used as the negative electrode lead. A clad lead can also be used as the negative electrode lead.
- the battery case may be made of metal or laminate film.
- the metal material forming the battery case aluminum, an aluminum alloy (such as an alloy containing a trace amount of a metal such as manganese or copper), a steel plate, or the like can be used.
- the battery case may be plated by nickel plating or the like, if necessary.
- the shape of the battery case may be a cylindrical shape, a square shape, or the like depending on the shape of the electrode group.
- Example 1 The positive electrode 5 and the negative electrode 6 shown in FIGS. 2a to 2c and FIGS. 3a to 3c were produced as follows, and the cylindrical lithium ion secondary battery shown in FIG. 1 was produced using these.
- the obtained positive electrode paste was applied to both surfaces of a long strip-shaped aluminum foil (thickness 15 ⁇ m) as the positive electrode current collector 5a, and the positive electrode active material density of the positive electrode mixture layer was 3.63 g / ml (porosity 18 0.9%), the rolling process was repeated three times at a linear pressure of 30.4 kN / cm using a pair of rolls (roll diameter: 750 mm), and further heated at 195 ° C. The heated one was cut into dimensions of 58.2 mm in width and 562.1 mm in length, thereby producing a positive electrode 5 having a positive electrode mixture layer 5b on both surfaces of the positive electrode current collector 5a.
- current collector exposed portions 5c and 5d to which a positive electrode paste having a width of 6.5 mm was not applied, were formed on both sides at the center in the longitudinal direction of the positive electrode 5.
- a negative electrode paste was produced by stirring 100 parts by volume of graphite as a negative electrode active material and 2.3 parts by volume of styrene butadiene rubber as a binder together with an appropriate amount of CMC in a kneader. did.
- the obtained negative electrode paste was applied to both sides of a long strip copper foil (thickness 10 ⁇ m) as the negative electrode current collector 6a, and the negative electrode active material density was 1.69 g / cc (porosity 21.7%). As such, it was rolled once using a pair of rolls and then dried. The dried product was cut into a size of 59.2 mm in width and 635.5 mm in length to produce a negative electrode 6 in which the negative electrode mixture layer 6b was formed on both surfaces of the negative electrode current collector 6a.
- current collector exposed portions 6c and 6d having a width of 2.0 mm were formed on both sides at one end portion of the negative electrode 6 in the longitudinal direction. Further, at the other end of the negative electrode 6 in the longitudinal direction, a current collector exposed portion 6e having a width of 28.0 mm is formed on one surface, and a current collector exposed portion 6f having a width of 81.0 mm is formed on the other surface. did.
- Electrode group 4 was produced.
- the size of the separator 7 was 61.6 mm in width, 650.1 mm in length, and 16.5 ⁇ m in thickness.
- the obtained electrode group 4 was accommodated in a bottomed cylindrical metal battery case 1 having an inner diameter of 18.25 mm and a height of 64.97 mm.
- the other end of the positive electrode lead 9 drawn out from the electrode group 4 was welded to the sealing plate 2, and the other end of the negative electrode lead 10 was welded to the inner bottom surface of the battery case 1.
- the electrode group 4 was held in the battery case 1 by forming a stepped portion 11 protruding inward on the side surface of the battery case 1 above the upper end portion of the electrode group 4.
- the nonaqueous electrolyte was prepared by dissolving LiPF 6 in a mixed solvent obtained by mixing EC, EMC, and DMC at a volume ratio of 20: 5: 75 so that the concentration becomes 1.40 mol / L.
- the viscosity of the nonaqueous electrolyte at 25 ° C. was measured using a falling ball viscometer based on JIS Z 8803, it was 3.1 mPa ⁇ s.
- Examples 2 to 8 and Comparative Example 1 A positive electrode and a negative electrode were produced in the same manner as in Example 1 except that the linear pressure during rolling and / or the number of rolling operations were appropriately adjusted so that the active material density (and porosity) shown in Table 1 was obtained.
- the number of rolling of the positive electrode mixture layer was 3 times in Examples 2 to 7 and Comparative Example 1, and 1 time in Example 8.
- the number of rollings of the negative electrode mixture layer was all one.
- Example 1 Using the obtained positive electrode and negative electrode, a cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the nonaqueous electrolyte having the composition shown in Table 1 was used in the weight shown in Table 1.
- the viscosity of the nonaqueous electrolyte of Example 4 was measured in the same manner as in Example 1, it was 2.9 mPa ⁇ s.
- the thickness of the mixture layer is different when the active material density is different, the width and / or length of the positive electrode, the negative electrode, and / or the separator is appropriately adjusted in order to make the tension rate in the battery uniform.
- Weight evaluation The contact angles of the surfaces of the positive electrode and negative electrode before winding were measured by the ⁇ / 2 method. Specifically, in a dry air environment with a dew point of ⁇ 30 ° C. or less, one drop of a non-aqueous electrolyte is dropped on the surface of each of the positive electrode and the negative electrode, and the contact angle of the droplet 2.1 seconds after the landing (positive electrode) : CA p , negative electrode: CA n ).
- the nonaqueous electrolyte was prepared by dissolving LiPF 6 in a mixed solvent in which EC, EMC and DMC were mixed at a volume ratio of 15: 5: 80 so that the concentration would be 1.40 mol / L. Things were used.
- Table 1 shows positive electrode and negative electrode active material densities D p and D n , porosity P p and P n , porosity difference
- Example 1 a high cycle maintenance rate exceeding 80% was achieved.
- Example 1 in Example 1, a cycle retention rate of nearly 90% was obtained.
- the contact angle difference is relatively small, the positive electrode and the This is probably because the difference in the permeability of the nonaqueous electrolyte in the negative electrode was reduced, and the uneven distribution of the nonaqueous electrolyte was suppressed.
- Example 2 compared with Example 3, the difference in porosity and the contact angle difference between the positive electrode and the negative electrode are larger, but the cycle retention rate is higher.
- Example 2 since the ratio of the nonaqueous electrolyte is larger than that in Example 3, it can be understood that the ratio of the nonaqueous electrolyte is also effective in suppressing the uneven distribution of the nonaqueous electrolyte.
- Example 3 compared with Example 4, the high cycle maintenance factor is obtained. This is presumably because the battery of Example 3 had a higher EC content than the battery of Example 4, so that LiPF 6 as the electrolyte was sufficiently dissociated and the cycle retention rate was improved.
- Example 6 the cycle maintenance rate is higher than that in Example 7. This is considered to be because in Example 6, since the injection weight of the nonaqueous electrolyte is smaller than in Example 7, the amount of gas generated is small, or the change in the electrolyte composition accompanying the decomposition of the electrolyte is small. . Further, in Example 8, the cycle maintenance rate is higher than that in Example 6.
- non-aqueous electrolyte secondary battery of the present invention can provide a high cycle capacity maintenance rate despite its high capacity. Therefore, non-aqueous electrolyte secondary batteries are used in various types of portable electronic devices such as hybrid electric vehicles (especially for plug-in hybrid vehicles), motor driving power sources for electric vehicles, mobile phones, notebook personal computers, video camcorders, etc. It is useful for applications such as a driving power source and a large power source in a household power storage device.
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Abstract
Description
例えば、特許文献1は、サイクル特性と安全性の観点から、体積エネルギー密度が300Wh/L程度の非水電解質二次電池において、正極、負極およびセパレータの総空孔体積に対して、非水電解液の占有体積を120~140%に制御することを開示している。なお、体積エネルギー密度とは、電池ケースサイズで規格化した体積当たりの電池のエネルギー密度である。
しかし、体積エネルギー密度が650Wh/L以上の非水電解質二次電池では、多くの活物質を充填する必要があるため、電池内の残空間(空電池ケース内部の空間体積から、電極群の実体積を差し引いた空間体積)が減少する。そのため、電池内に収容できる非水電解質の量自体が少なくなる。
なお、正極および負極の接触角は、θ/2法により測定できる。具体的には、捲回前のシート状の正極および負極の表面に非水電解質の液滴を滴下し、所定時間経過後の液滴の接触角を測定する。
なお、|Pp-Pn|は、空孔率Ppと空孔率Pnとの差の絶対値を示し、PpとPnとのどちらが大きくてもよいが、PpよりもPnの方が大きいことが好ましい。
正極および負極の空孔率は、合剤層の構成成分の種類およびその割合、合剤層における活物質密度、合剤層を形成する際の圧延の圧力、圧延回数などを選択または調整することにより調節することができる。
図1は、本発明の一実施形態に係る非水電解質二次電池を模式的に示す縦断面図である。非水電解質二次電池は、長尺帯状の正極5と、長尺帯状の負極6と、正極5と負極6との間に介在するセパレータ7とが捲回された電極群4を有する。有底円筒型の金属製の電池ケース1内には、電極群4とともに、図示しない非水電解質が収容されている。
電極群4は、正極リード9を導出した状態で、下部絶縁リング8bとともに電池ケース1に収納される。正極リード9の端部には封口板2が溶接され、正極5と封口板2とは電気的に接続されている。
(正極)
非水電解質二次電池の正極において、正極合剤層は、正極集電体の両方の表面に付着していてもよく、一方の表面に付着していてもよい。
正極集電体は、無孔の導電性基板であってもよく、複数の貫通孔を有する多孔性の導電性基板であってもよい。無孔の導電性基板としては、金属箔、金属シートなどが利用できる。多孔性の導電性基板としては、連通孔(穿孔)を有する金属箔、メッシュ体、ネット体、パンチングシート、エキスパンドメタル、ラス体などが例示できる。
正極集電体の厚みは、例えば、3~50μmの範囲から選択でき、好ましくは5~30μmである。
正極は、正極集電体の表面に、正極活物質、導電助剤、結着剤などの正極合剤層の構成成分と分散媒とを含む正極スラリーを塗布し、形成された塗膜を一対のロールなどにより圧延し、さらに加熱して、正極合剤層を形成することにより得ることができる。塗膜は、必要により、圧延の前に乾燥させてもよい。
導電助剤の量は、特に制限されず、活物質100体積部に対して、例えば、10体積部以下であればよい。活物質密度を高めて電池を高容量化するとともに、正極と負極との浸透性の差を低減させる観点からは、上記の導電助剤の量は、好ましくは5体積部以下、さらに好ましくは3体積部以下である。導電助剤の量の下限は、特に制限されず、例えば、活物質100体積部に対して、0.01体積部以上であってもよい。
増粘剤の割合は、特に制限されず、例えば、活物質100体積部に対して0~10体積部、好ましくは0.01~5体積部である。
負極において、負極合剤層は、負極集電体の両方の表面に付着していてもよく、一方の表面に付着していてもよい。
負極集電体としては、正極集電体と同様に、無孔のまたは多孔性の導電性基板が使用できる。負極集電体の厚みは、正極集電体の厚みと同様の範囲から選択できる。負極集電体に使用される金属材料としては、例えば、ステンレス鋼、ニッケル、銅、銅合金、アルミニウム、アルミニウム合金などが例示できる。なかでも、銅または銅合金などが好ましい。
セパレータとしては、樹脂製の、微多孔フィルム、不織布または織布などが使用できる。セパレータを構成する樹脂としては、例えば、ポリエチレン、ポリプロピレンなどのポリオレフィン;ポリアミドなどのポリアミド樹脂;ポリアミドイミド、ポリイミドなどのポリイミド樹脂などが例示できる。
セパレータの厚みは、例えば、5~50μmである。
非水電解質は、非水溶媒と、非水溶媒に溶解したリチウム塩を含む。
非水溶媒は、例えば、環状カーボネート、鎖状カーボネート、環状カルボン酸エステルなどを含む。環状カーボネートとしては、EC、PCなどが挙げられる。鎖状カーボネートとしては、ジエチルカーボネート、EMC、DMCなどが挙げられる。環状カルボン酸エステルとしては、γ-ブチロラクトン、γ-バレロラクトンなどが挙げられる。非水溶媒は、一種を単独で用いてもよく、二種以上を組み合わせて用いてもよい。
なお、非水溶媒は、EC、EMCおよびDMC以外に、他の非水溶媒(前記例示の非水溶媒)を含有してもよい。
これらのリチウム塩のうち、フッ素含有酸のリチウム塩、特に、LiPF6は、解離性が高く、非水電解質中で化学的に安定であるため、好ましい。
電極群の形状は、電池または電池ケースの形状に応じて、円筒型、捲回軸に垂直な端面が長円形である扁平形状であってもよい。
電池ケースの形状は、電極群の形状に応じて、円筒型、角型などであってもよい。
次のようにして、図2a~図2cおよび図3a~図3cに示す正極5および負極6を作製し、これらを用いて、図1に示す円筒型リチウムイオン二次電池を作製した。
正極活物質としてのニッケル酸リチウム100体積部、導電助剤であるアセチレンブラック3.6体積部、および結着剤であるPVDF2.5体積部を、適量のNMPとともに練合機にて攪拌し、正極ペーストを調製した。得られた正極ペーストを、正極集電体5aとしての長尺帯状のアルミニウム箔(厚み15μm)の両面に塗布し、正極合剤層の正極活物質密度が3.63g/ml(空孔率18.9%)となるように、一対のロール(ロール直径:750mm)を用いて、線圧30.4kN/cmで、圧延処理を3回繰り返し、さらに195℃で加熱した。加熱したものを、幅58.2mm、長さ562.1mmの寸法に裁断することにより、正極集電体5aの両面に正極合剤層5bを有する正極5を作製した。
負極活物質としての黒鉛100体積部、および結着剤としてのスチレンブタジエンゴム2.3体積部を、適量のCMCとともに練合機にて攪拌することにより、負極ペーストを作製した。得られた負極ペーストを、負極集電体6aとしての長尺帯状の銅箔(厚み10μm)の両面に塗布し、負極活物質密度が1.69g/cc(空孔率21.7%)となるように、一対のロールを用いて1回圧延し、次いで乾燥させた。乾燥したものを、幅59.2mm、長さ635.5mmの寸法に裁断することにより、負極集電体6aの両面に負極合剤層6bが形成された負極6を作製した。
上記(1)および(2)で得られた正極5および負極6を、これらの間にポリエチレン製の微多孔膜セパレータ7を介在させた状態で渦捲状に捲回して電極群4を作製した。セパレータ7のサイズは、幅61.6mm、長さ650.1mm、厚み16.5μmであった。
表1に示す活物質密度(および空孔率)となるように、圧延時の線圧および/または圧延の回数を適宜調整した以外は、実施例1と同様に正極および負極を作製した。なお、正極合剤層の圧延回数は、実施例2~7および比較例1では3回、実施例8では1回とした。負極合剤層の圧延回数は、すべて1回とした。
なお、活物質密度が異なると、合剤層の厚みが異なるため、電池内の緊迫率を揃えるために、正極、負極および/またはセパレータの、幅および/または長さを適宜調整した。
(濡れ性評価)
θ/2法により、捲回前の正極および負極のそれぞれの表面の接触角を測定した。具体的には、露点-30℃以下のドライエア環境下で、正極および負極のそれぞれの表面に、非水電解質を1滴滴下し、着滴から2.1秒後の液滴の接触角(正極:CAp、負極:CAn)を測定した。
なお、非水電解質としては、EC、EMCおよびDMCを、体積比15:5:80で混合した混合溶媒に、濃度が1.40mol/Lとなるように、LiPF6を溶解させることにより調製したものを用いた。
45℃環境下、リチウムイオン二次電池を、1595mA(0.5時間率)で電圧が4.2Vになるまで定電流充電し、電圧4.2Vで終止電流が70mAとなるまで定電圧充電し、10分間休止した後、放電電流3190mA(1時間率)で定電流放電を行い、10分間休止した。このような充放電サイクルを、200サイクル繰り返し、1サイクル目の放電容量に対する200サイクル目の放電容量の比率(容量維持率)を求めた。得られた容量維持率を、サイクル維持率として表1に示す。
一方、接触角差|CAp-CAn|が21°を超える比較例1の電池では、著しくサイクル維持率が低下した。正極と負極との接触角の差が大きすぎると、正極合剤層と負極合剤層とで、電解液の浸透性の差が大きくなりやすい。そのため、電解液が偏在して反応ムラが生じ、これにより、比較例1では、サイクル維持率が低下したと考えられる。
2 封口板
3 ガスケット
4 電極群
5 正極
5a 正極集電体
5b 正極合剤層
5c、5d 正極集電体露出部
6 負極
6a 負極集電体
6b 負極合剤層
6c、6d、6e、6f 負極集電体露出部
7 セパレータ
8a 上部絶縁リング
8b 下部絶縁リング
9 正極リード
10 負極リード
11 段部
Claims (7)
- 正極、負極、前記正極および前記負極の間に介在するセパレータが捲回された電極群と、非水電解質とを備え、
体積エネルギー密度が650Wh/L以上であり、
前記正極が、正極集電体と、前記正極集電体の表面に付着した正極合剤層とを含み、
前記負極が、負極集電体と、前記負極集電体の表面に付着した負極合剤層とを含み、
前記正極合剤層の空孔率Ppが22%以下で、前記負極合剤層の空孔率Pnが25%以下であり、
前記正極合剤層の空孔体積と、前記負極合剤層の空孔体積と、前記セパレータの空孔体積との合計VTに対する前記非水電解質の体積VEの比率VE/VTが、1以上1.5以下であり、
前記非水電解質に対する前記正極の接触角CApと前記負極の接触角CAnとの差が23°以下である、非水電解質二次電池。 - 前記正極の接触角CApと前記負極の接触角CAnとの差が21°以下である、請求項1記載の非水電解質二次電池。
- 前記非水電解質が、非水溶媒と、前記非水溶媒に溶解したリチウム塩とを含み、
前記非水溶媒が、エチレンカーボネート、エチルメチルカーボネートおよびジメチルカーボネートを含み、
前記非水溶媒中の、前記エチレンカーボネートの含有量が10~25体積%、前記エチルメチルカーボネートの含有量が2~7体積%、および前記ジメチルカーボネートの含有量が68~88体積%である、請求項1または2項記載の非水電解質二次電池。 - 前記非水溶媒中の、前記エチレンカーボネートの含有量が18~23体積%、前記エチルメチルカーボネートの含有量が3~7体積%、および前記ジメチルカーボネートの含有量が70~79体積%である、請求項3記載の非水電解質二次電池。
- 前記正極合剤層の空孔率Ppと前記負極合剤層の空孔率Pnとの差が7%以下である、請求項1~4のいずれか1項記載の非水電解質二次電池。
- 前記正極合剤層の空孔率Ppと前記負極合剤層の空孔率Pnとの差が、2.2~5.5%である、請求項1~5のいずれか1項記載の非水電解質二次電池。
- 25℃における前記非水電解質の粘度が5mPa・s以下である、請求項1~6のいずれか1項記載の非水電解質二次電池。
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