WO2011148550A1 - 非水電解質二次電池用正極および非水電解質二次電池 - Google Patents
非水電解質二次電池用正極および非水電解質二次電池 Download PDFInfo
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- WO2011148550A1 WO2011148550A1 PCT/JP2011/001638 JP2011001638W WO2011148550A1 WO 2011148550 A1 WO2011148550 A1 WO 2011148550A1 JP 2011001638 W JP2011001638 W JP 2011001638W WO 2011148550 A1 WO2011148550 A1 WO 2011148550A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
- H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery including a current collector and a positive electrode mixture layer formed on the surface thereof, and more particularly to improvement of the positive electrode mixture layer.
- a non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator interposed therebetween, and a non-aqueous electrolyte.
- the positive electrode, the negative electrode, and the separator are wound to form an electrode group.
- the positive electrode includes a current collector and a positive electrode mixture layer formed on the surface of the current collector.
- the positive electrode mixture layer includes positive electrode active material particles, a binder, and a conductive material as necessary.
- a lithium-containing transition metal oxide such as LiCoO 2 , LiNiO 2 , LiNi 1-x1 Co x1 O 2 (0 ⁇ x1 ⁇ 1) is used.
- Patent Document 1 proposes that the electrode mixture layer is divided into a plurality of regions by concave portions provided at regular intervals. Patent Document 1 describes that the electrode can be greatly bent without being damaged.
- Patent Document 2 proposes that the interface between the electrode mixture layer and the current collector is easily peeled off. It is said that the fracture of the electrode can be prevented by slightly peeling the interface due to the stress at the time of winding.
- the peel strength at the interface between one electrode mixture layer and the current collector disposed inside the current collector is smaller than the peel strength at the interface between the other electrode mixture layer and the current collector. Proposal to do.
- Patent Document 3 proposes that the concentration of the binder in the central portion of the electrode mixture layer be 50 to 90% of the concentration in the vicinity of the current collector. Patent Document 3 describes that the amount of the binder can be reduced and the charge / discharge characteristics can be improved without reducing the adhesion between the current collector and the electrode mixture layer.
- Patent Document 1 since no active material is disposed in the recess, the amount of active material contained in the electrode is small. Therefore, there is a limit to increasing the capacity of the nonaqueous electrolyte secondary battery. In Patent Document 2, since the electrode mixture layer and the current collector are easily peeled off, the current collecting property tends to decrease.
- the positive electrode breaks down due to stress during winding. For this reason, it has been difficult to achieve a high balance of battery capacity, current collection, and suppression of damage to the positive electrode in a balanced manner.
- One aspect of the present invention includes a current collector and a positive electrode mixture layer formed on a surface of the current collector.
- the positive electrode mixture layer includes positive electrode active material particles and a binder.
- the curve indicating the correlation between the distance from the current collector in the thickness direction of the agent layer and the amount of the binder in the positive electrode mixture layer has the first maximum point, the minimum point, and the second maximum point, and the minimum The point corresponds to the position of the intermediate portion in the thickness direction of the positive electrode mixture layer, the first maximum point corresponds to the position on the current collector side relative to the position corresponding to the minimum point of the positive electrode mixture layer, and the second The maximum point corresponds to a position farther from the current collector than the position corresponding to the minimum point of the positive electrode mixture layer, and the amount W 1 of the binder with respect to 100 parts by weight of the positive electrode active material particles at the first maximum point , at the minimum point, a ratio W 1 / W 2 of the amount W 2 of the binder with respect to 100 parts by weight of the positive electrode active material
- Another aspect of the present invention includes the positive electrode, the negative electrode, a separator and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode, the negative electrode, and the separator are wound to form an electrode group.
- the present invention relates to a non-aqueous electrolyte secondary battery.
- the positive electrode for a non-aqueous electrolyte secondary battery of the present invention has a high density, it does not easily break even if stress is generated by winding when forming the electrode group. Therefore, the manufacture of the nonaqueous electrolyte secondary battery is facilitated.
- a positive electrode for a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a positive electrode) includes a sheet-like current collector and a positive electrode mixture layer formed on the surface of the current collector.
- the positive electrode mixture layer includes positive electrode active material particles and a binder as essential components, and includes a conductive material and the like as optional components.
- the positive electrode mixture layer only needs to be formed on at least one surface of the current collector, and may be formed on both surfaces.
- the positive electrode is produced, for example, by the following method. Positive electrode active material particles, a binder, and a dispersion medium are mixed to prepare a positive electrode mixture slurry. Optional components may be added to the positive electrode mixture slurry.
- the positive electrode mixture layer is obtained by applying the positive electrode mixture slurry to the surface of the current collector and drying it. Since the active material density is increased by rolling the positive electrode mixture layer, a high capacity positive electrode can be obtained.
- the binder contained in the positive electrode mixture slurry is likely to migrate (migrate) to the surface side portion of the positive electrode mixture layer when the positive electrode mixture slurry applied to the surface of the current collector is dried.
- the binder migration occurs, the weight ratio of the binder in the current collector side portion of the positive electrode mixture layer decreases. As a result, the interface between the positive electrode mixture layer and the current collector becomes easy to peel off, and the current collecting property may be lowered.
- FIG. 1 is a graph showing the correlation (binder distribution) between the distance from the current collector in the thickness direction of the positive electrode mixture layers a to c and the amount of the binder.
- the “amount of binder” means the binder present on the plane at a distance d from the current collector (interface between the positive electrode mixture layer and the current collector) in the positive electrode mixture layer. Is expressed as an amount (parts by weight) relative to 100 parts by weight of the positive electrode active material particles.
- weight ratio of the binder uses almost synonymously with the quantity (weight part) of the binder with respect to 100 weight part of positive electrode active material particles in the layer which has the minute thickness of the position of the distance d.
- the amount (parts by weight) of the binder with respect to 100 parts by weight of the positive electrode active material particles may be simply referred to as “weight ratio of the binder”.
- the positive electrode active material is all LiCoO 2 and the binder is all polyvinylidene fluoride (PVDF).
- the dispersion medium used in preparing the positive electrode mixture slurry is N-methyl-2-pyrrolidone (NMP).
- Curve A shows the distribution of the binder in the positive electrode mixture layer a.
- the positive electrode mixture layer a includes a positive electrode active material and a binder.
- the first positive electrode mixture slurry in which the weight ratio of the binder is 5 parts by weight is applied to the current collector, and then the current collector is heated at 190 ° C. for 1 hour, and then the binder is bonded. It is obtained by applying a second positive electrode mixture slurry in which the weight ratio of the agent is 0.9 parts by weight.
- Curve B shows the distribution of the binder in the positive electrode mixture layer b.
- the second weight ratio of the binder is 0.7 parts by weight. It is obtained by applying a positive electrode mixture slurry.
- Curve C shows the distribution of the binder in the positive electrode mixture layer c obtained by applying a positive electrode mixture slurry having a binder weight ratio of 1.7 parts by weight to the current collector.
- Each positive electrode mixture slurry is usually dried after coating. The dried coating film is usually finally rolled.
- the curve C in the positive electrode mixture layer c, the amount of the binder is small on the current collector side. This is considered due to the migration of the binder as described above.
- the curves A and B indicating the correlation between the distance from the current collector in the thickness direction and the amount of the binder are first on the current collector side, respectively. It has local maxima X A and X B. Curves A and B further have local minimum points Y A and Y B and second local maximum points Z A and Z B.
- the position corresponding to the minimum point is in the middle in the thickness direction of the positive electrode mixture layer.
- An intermediate part means the part except the collector side part and surface side part of a positive mix layer.
- the current collector side portion of the positive electrode mixture layer is defined as having a thickness of 0.00 from the current collector (interface between the current collector and the positive electrode mixture layer), where T is the thickness of the positive electrode mixture layer.
- the region up to 3T is referred to, and the surface side portion refers to a region from the surface of the positive electrode mixture layer to a thickness of 0.3T.
- the amount of the binder in the intermediate portion is relatively small.
- the particles are likely to move near the position corresponding to the minimum point where the amount of the binder is relatively small.
- the part on the electric body side and the part on the surface side are shifted.
- the positive electrode mixture layer is deformed and the stress generated by winding is relaxed. Therefore, breakage of the positive electrode such as breakage of the current collector, cracking of the positive electrode mixture layer and cracking can be suppressed.
- the first maximum point corresponds to a position closer to the current collector than a position corresponding to the minimum point of the positive electrode mixture layer.
- the positive electrode mixture layer having such a distribution contains a relatively large amount of binder in the current collector side portion. Therefore, the current collector side portion of the positive electrode mixture layer is bonded to the current collector with sufficient adhesive strength. Therefore, the positive electrode mixture layer is difficult to peel off from the current collector, and a decrease in current collecting property can be suppressed.
- the total thickness of the positive electrode mixture layer is preferably 20 to 150 ⁇ m, and more preferably 50 to 100 ⁇ m.
- the first maximum point preferably corresponds to a position at a distance of 0.1 to 10 ⁇ m from the current collector in the thickness direction of the positive electrode mixture layer, and more preferably 1 to 5 ⁇ m.
- the ratio W 1 / W 2 between the amount W 1 of the binder with respect to 100 parts by weight of the positive electrode active material particles at the first maximum point and the amount W 2 of the binder with respect to 100 parts by weight of the positive electrode active material particles at the minimum point. Must be greater than 2. Since the positive electrode satisfying such W 1 / W 2 is in a rolled state until the active material density becomes high, the amount of the binder near the position corresponding to the minimum point is relatively small. The adhesiveness of the positive electrode does not become too high, and damage to the positive electrode when stress is generated by winding can be satisfactorily suppressed.
- W 1 / W 2 is greater than 2, preferably 2.1 or more, and more preferably 2.4 or more.
- W 1 / W 2 is more preferably 10 or less, particularly preferably 6 or less, and may be 3 or less.
- These lower limit values and upper limit values can be arbitrarily combined.
- W 1 / W 2 may be greater than 2 and 3 or less, or 2.1 or more and 10 or less.
- W 1 is 1 to 8 parts by weight, preferably 1.2 to 7 parts by weight, and 2 to 5 parts by weight or 1.3 to 3.5 parts by weight per 100 parts by weight of the positive electrode active material particles. Is particularly preferred. By making W 1 in the above range, it becomes easy to maintain good binding properties between the positive electrode mixture layer and the current collector.
- the amount of the binder with respect to 100 parts by weight of the positive electrode active material particles is preferably 0.6 W. 1 to 0.99 W 1 , more preferably 0.7 W 1 to 0.98 W 1 .
- W 2 is 0.3 to 1.5 parts by weight, preferably 0.5 to 1.2 parts by weight, more preferably 0.6 to 1.1 parts by weight, per 100 parts by weight of the positive electrode active material particles. .
- W 2 is 0.3 to 1.5 parts by weight, preferably 0.5 to 1.2 parts by weight, more preferably 0.6 to 1.1 parts by weight, per 100 parts by weight of the positive electrode active material particles. .
- the second maximum point corresponds to a position (away from the current collector) on the surface side of the positive electrode mixture layer from a position corresponding to the minimum point.
- the positive electrode mixture layer having such a distribution includes more binder in the surface side portion than in the intermediate portion. Therefore, the positive electrode active material particles can be prevented from falling off from the surface side of the positive electrode mixture layer.
- the amount W 3 of the binder with respect to 100 parts by weight of the positive electrode active material particles at the second maximum point is preferably smaller than W 1 .
- W 3 is preferably 1 to 5 parts by weight, more preferably 1 to 3 parts by weight, and particularly preferably 1.1 to 2.5 parts by weight per 100 parts by weight of the positive electrode active material particles. .
- the W 3 is within the above range, it is easy to further suppress the dropping of the positive electrode active material particles from the surface side of the positive electrode mixture layer.
- the graph showing the distribution of the binder in the positive electrode mixture layer shows the distance d from the current collector in the thickness direction of the positive electrode mixture layer on the horizontal axis and the weight ratio (parts by weight) of the binder at the distance d. It is a graph which makes a vertical axis
- the local maximum point in the region closer to the current collector than the position corresponding to the determined local minimum point is set as the first local maximum point, and the local maximum point in the region far from the current collector is determined as the second local maximum point.
- the one having the maximum value can be set as the first local maximum point.
- the one having the maximum value can be set as the second maximum point.
- the straight line connecting the first maximum point and the minimum point preferably has an inclination of ⁇ 0.3 parts by weight / ⁇ m or more and ⁇ 0.05 parts by weight / ⁇ m or less. More preferably, the inclination is ⁇ 0.2 parts by weight / ⁇ m or more and ⁇ 0.05 parts by weight / ⁇ m.
- the positive electrode mixture layer becomes too thick, the distance between the first maximum point and the minimum point will be too far away, so the absolute value of the slope will be small and the distribution will be gentle, so the effect of suppressing damage to the positive electrode will be small. There is a case.
- an arbitrary measurement region including the surface of the current collector to the surface of the positive electrode mixture layer is selected, and the measurement region is divided into 255 ⁇ 255 pixels (micro regions).
- the peak intensity in each minute region is obtained by an electron probe microanalyzer (EPMA) method.
- EPMA electron probe microanalyzer
- an electron beam is scanned in the surface direction of the positive electrode, and the peak intensity in each minute region is measured. Find and average.
- the same measurement is performed along the thickness direction from the surface of the positive electrode mixture layer on one surface of the current collector to the surface of the current collector.
- the weight ratio (parts by weight) of the binder in an arbitrary region is determined.
- the relationship between the intensity of the signal and the weight ratio of the binder can be obtained by creating a calibration curve from a sample with a known weight ratio and comparing it.
- confirm the state of binder distribution in the positive electrode mixture layer by plotting the distance from the current collector in the thickness direction on the horizontal axis and the weight ratio (parts by weight) of the binder on the vertical axis. it can.
- a sample in the present invention, a cross section in the thickness direction of the positive electrode
- an accelerated electron beam to detect a characteristic X-ray spectrum.
- the binder is a fluororesin
- the elemental fluorine element may be detected.
- the element correlated with the weight ratio of the binder may be a constituent element of the binder or may not be a constituent element.
- the binder may be doped with an easily detectable element.
- the positive electrode active material particles those commonly used in the field of non-aqueous electrolyte secondary batteries can be used.
- the positive electrode active material is, for example, a lithium-containing transition metal oxide.
- the lithium-containing transition metal oxide preferably has a layered or hexagonal crystal structure or a spinel structure.
- the transition metal element include one or more elements selected from the group consisting of Co, Ni, Mn, and the like.
- 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 one or more elements selected from the group consisting of Na, Mg, Sc, Y, Fe, Cu, Zn, Al, Cr, Pb, Sb, and B. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination.
- the positive electrode active material includes the element M and another transition metal element (Ni, Co, or Mn)
- the element M is usually an element different from the transition metal element. In the above general formula, 0 ⁇ x ⁇ 1.2, 0 ⁇ y ⁇ 0.9, and 2 ⁇ z ⁇ 2.3.
- various binders usually used for positive electrodes for non-aqueous electrolyte secondary batteries for example, fluororesin, olefin resin, acrylic resin, rubber-like resin (styrene-butadiene rubber, etc.) can be used. Of these, fluororesins are preferred. Examples of the fluororesin include, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer containing vinylidene fluoride (VDF) units (for example, a copolymer containing VDF units and hexafluoropropylene (HFP) units). Polymer).
- PTFE polytetrafluoroethylene
- PVDF polyvinylidene fluoride
- VDF copolymer containing vinylidene fluoride
- HFP hexafluoropropylene
- the copolymer preferably contains 50% by weight or more of vinylidene fluoride units. These fluororesins preferably have a weight average molecular weight of 300,000 to 1,500,000.
- the amount of the binder contained in the entire positive electrode mixture layer may be, for example, 0.9 to 4 parts by weight, preferably 1 to 3 parts by weight per 100 parts by weight of the positive electrode active material.
- Examples of the conductive material include carbon black such as acetylene black and ketjen black, and graphite.
- the amount of the conductive material contained in the positive electrode mixture layer may be, for example, 0.5 to 5 parts by weight per 100 parts by weight of the positive electrode active material.
- Examples of the positive electrode current collector include sheets and foils containing metal materials such as aluminum and titanium.
- Active material density of the positive electrode mixture layer according to the present invention is 3.3 ⁇ 4g / cm 3, is preferably 3.5 ⁇ 3.8g / cm 3. With such an active material density, a high-capacity battery can be obtained.
- a positive electrode including a positive electrode mixture layer having a high active material density tends to generate stress therein and tends to be damaged.
- the active material density of the positive electrode mixture layer is the weight of the positive electrode active material particles contained per 1 cm 3 of the positive electrode mixture layer.
- the porosity of the positive electrode mixture layer is preferably 10 to 25%, more preferably 15 to 21%. In such a range, damage during winding can be more effectively suppressed, and it is advantageous in terms of increasing the capacity of the battery.
- the porosity of the positive electrode mixture layer is determined from the weight and true density of each material (positive electrode active material, conductive material, binder, etc.) contained in the positive electrode mixture layer per unit area.
- the positive electrode of the present invention is obtained, for example, by the following production method.
- (1) Preparation of slurry The distribution of the binder in the positive electrode mixture layer can be controlled by applying a plurality of slurries with different amounts (usually, weight ratios) of the binder with respect to the amount of the positive electrode active material particles.
- a positive electrode active material particle, a binder, and a dispersion medium are mixed to prepare a slurry.
- the first slurry applied to the current collector and the second slurry applied onto the coating film of the first slurry after applying the first slurry are used.
- three or more types of slurries with different binder weight ratios may be used.
- Weight ratio of the binder in each slurry may appropriately be adjusted according to the desired distribution of binder (W 1 / W 2 and the slope of the straight line or the like connecting the first local maximum and minimum points).
- the amount w 1 of the binder with respect to 100 parts by weight of the positive electrode active material particles in the first slurry is preferably 1 to 8 parts by weight, It is more preferably 2 to 5 parts by weight.
- the amount w 2 of the binder with respect to 100 parts by weight of the positive electrode active material particles is preferably 0.1 to 3 parts by weight, 0.5 to 1.5 parts by weight or 0.5 to 1 part. More preferred are parts by weight.
- the amount w 1 of the binder with respect to 100 parts by weight of the positive electrode active material particles in the first slurry is preferably 1 to 8 parts by weight. More preferred are parts by weight.
- the amount w 2 of the binder with respect to 100 parts by weight of the positive electrode active material particles is preferably 0.5 to 1.5 parts by weight, and more preferably 0.6 to 1 part by weight.
- the amount w 3 of the binder with respect to 100 parts by weight of the positive electrode active material particles is preferably 1 to 3 parts by weight, preferably 1.3 to 2.5 parts by weight or 1.5 to 2.5 parts by weight. More preferred are parts by weight.
- the ratio w 1 / w 2 between the amount w 1 of the binder with respect to 100 parts by weight of the positive electrode active material particles in the first slurry and the amount w 2 of the binder with respect to 100 parts by weight of the positive electrode active material particles in the second slurry is: It is preferably greater than 2 and 10 or less, more preferably greater than 2 and 6 or less.
- dispersion medium examples include water, organic solvents such as N-methyl-2-pyrrolidone, and mixed solvents thereof.
- the first slurry is applied to the surface of the current collector to form the first layer. Until the coating film of the first slurry applied to the surface of the current collector is dried, the binder in the first slurry migrates, and the binder moves in the direction toward the surface side. Accordingly, a binder distribution is formed in the first layer so that the amount increases as the distance from the current collector surface increases.
- the second slurry is applied to the surface of the first layer to form the second layer. Similar migration occurs in the coating film of the second slurry.
- a part of the binder contained in the first layer is eluted in the solvent contained in the second slurry.
- the eluted binder moves to the surface side when the second slurry is dried together with the binder contained in the second slurry.
- the first layer contains a relatively large amount of the binder, a large amount of the binder remains in the current collector side portion.
- a first maximum point is generated in the first layer
- a minimum point is generated at a position away from the current collector from the interface between the first layer and the second layer
- a second point is formed near the surface of the second layer.
- a binder distribution that produces a maximum point is obtained.
- a third slurry is further applied to the surface of the second layer.
- a positive electrode mixture layer is formed on the surface of the current collector.
- the first slurry, the second slurry, and the third slurry are preferably applied and then dried with hot air or the like. It is also possible to arbitrarily control the binder migration depending on the drying conditions.
- the drying temperature is, for example, less than 150 ° C., preferably 80 to 130 ° C., more preferably 90 to 125 ° C.
- the drying time can be appropriately selected according to the drying temperature and the type of the dispersion medium.
- the positive electrode mixture layer is usually rolled after drying. By rolling, the thickness of the positive electrode mixture layer (or the thickness of each layer) and / or the active material density can be controlled.
- each layer can be adjusted as appropriate according to the desired binder distribution.
- T and T 1 satisfy 0.1T ⁇ T 1 ⁇ 0.4T. It is preferable to satisfy, and it is more preferable to satisfy 0.15T ⁇ T 1 ⁇ 0.3T.
- T and T 2 preferably satisfy 0.6T ⁇ T 2 ⁇ 0.9T, and satisfy 0.7T ⁇ T 2 ⁇ 0.85T. Is more preferable.
- the minimum point can be easily controlled by a desired position.
- the thickness of the first layer may be, for example, 5 to 50 ⁇ m, and more preferably 10 to 20 ⁇ m. Such a range is advantageous in distributing a sufficient amount of the binder to the current collector side portion of the positive electrode mixture layer. Further, it is advantageous in that the minimum point can be effectively suppressed from being located away from the current collector in the thickness direction of the positive electrode mixture layer, and the minimum point can correspond to an appropriate position. In this case, even if the positive electrode mixture layer is peeled off near the minimum point, it is possible to more effectively prevent breakage in the current collector side portion of the positive electrode mixture layer.
- the thickness T 2 of the second layer By setting the thickness T 2 of the second layer in the above range, the minimum point can be easily controlled by a desired position. Further, it is advantageous for distributing a sufficient amount of the binder to the current collector side portion of the positive electrode mixture layer.
- the thickness of the second layer may be, for example, 10 to 100 ⁇ m, and more preferably 30 to 80 ⁇ m.
- the current collector on which the first layer is formed may be heated before applying the second slurry.
- the crystallinity of the binder contained in the first layer is increased.
- the heating temperature may be, for example, 150 to 250 ° C., preferably 170 to 230 ° C.
- T and T 1 satisfy 0.1T ⁇ T 1 ⁇ 0.4T. Is preferable, and it is more preferable to satisfy 0.15T ⁇ T 1 ⁇ 0.3T. This is for the same reason as in the case of the two-layer structure.
- T and T 2 preferably satisfy 0.05T ⁇ T 2 ⁇ 0.25T, and satisfy 0.1T ⁇ T 2 ⁇ 0.2T. Is more preferable.
- T and T 3 preferably satisfy 0.45T ⁇ T 3 ⁇ 0.85T, and satisfy 0.55T ⁇ T 3 ⁇ 0.75T. Is more preferable.
- the thickness of the second layer may be, for example, 5 to 25 ⁇ m, and more preferably 10 to 20 ⁇ m.
- the thickness T 3 of the third layer By setting the thickness T 3 of the third layer in the above range, the minimum point can be easily controlled by a desired position. In addition, a sufficient amount of the binder can be distributed on the current collector side portion of the positive electrode mixture layer, which is advantageous.
- the thickness of the third layer may be, for example, 10 to 100 ⁇ m, and more preferably 20 to 60 ⁇ m.
- the second slurry when the second slurry is applied, a part of the binder contained in the first layer is eluted in the solvent contained in the second slurry.
- the first layer contains a relatively large amount of the binder, a large amount of the binder remains in the current collector side portion.
- a binder distribution is obtained in which a first maximum point is generated in the first layer, a minimum point is generated in the vicinity of the second layer, and a second maximum point is generated in the vicinity of the surface of the third layer.
- the nonaqueous electrolyte secondary battery includes the positive electrode, the negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte.
- the positive electrode, the negative electrode, and the separator are wound to form an electrode group.
- the negative electrode includes a current collector and a negative electrode mixture layer formed on the surface of the current collector.
- the negative electrode mixture layer includes negative electrode active material particles and a binder as essential components, and includes a thickener, a conductive material, and the like as optional components.
- Examples of the negative electrode active material include carbon materials such as graphite particles, materials containing Si, and materials containing Sn.
- the graphite particles particles including a region having a graphite structure can be used, and examples thereof include natural graphite, artificial graphite, and graphitized mesophase carbon particles.
- Examples of the material containing Si include Si alone, an alloy containing Si, and SiO m1 (0 ⁇ m1 ⁇ 2).
- Examples of the material containing Sn include Sn alone, an alloy containing Sn, and SnO m2 (0 ⁇ m2 ⁇ 2).
- a negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.
- binder various binders exemplified as the binder for the positive electrode mixture layer can be used.
- the thickener include carboxymethyl cellulose (CMC).
- the current collector for the negative electrode include sheets and foils containing copper and nickel.
- the nonaqueous electrolyte includes a nonaqueous solvent and a solute that dissolves in the nonaqueous solvent.
- Nonaqueous solvents include, for example, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and the like.
- the cyclic carbonate include ethylene carbonate (EC) and propylene carbonate (PC).
- the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).
- Examples of the cyclic carboxylic acid ester include ⁇ -butyrolactone (GBL) and ⁇ -valerolactone (GVL).
- a non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.
- the solute is not particularly limited, and examples thereof include inorganic lithium fluoride and a lithium imide compound.
- examples of the inorganic lithium fluoride include LiPF 6 and LiBF 4
- examples of the lithium imide compound include LiN (CF 3 SO 2 ) 2 .
- a microporous film made of polyethylene, polypropylene or the like is generally used as the separator.
- the thickness of the separator is, for example, 10 to 30 ⁇ m.
- Example 1 Fabrication of positive electrode (first layer) 100 parts by weight of LiCoO 2 as a positive electrode active material, 2 parts by weight of polyvinylidene fluoride (PVDF, KF polymer L # 7208 manufactured by Kureha Corporation) as a binder, and 3 parts by weight of acetylene black as a conductive material Then, an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersion medium was mixed to prepare a first slurry having a solid content of 73% by weight. The 1st slurry was apply
- NMP N-methyl-2-pyrrolidone
- (Second layer) 100 parts by weight of the same positive electrode active material as that of the first layer, 1 part by weight of PVDF as a binder, 3 parts by weight of acetylene black as a conductive material, and an appropriate amount of NMP as a dispersion medium are mixed to obtain a solid content of 78 A weight percent second slurry was prepared. The 2nd slurry was apply
- the coating film was rolled with a roller so that the active material density of the positive electrode mixture layer was 3.55 g / cm 3 to prepare a positive electrode sheet.
- the thickness of the 1st layer after rolling was about 15 micrometers
- the thickness of the 2nd layer was about 40 micrometers
- the thickness of the whole sheet was 125 micrometers.
- the positive electrode sheet was cut into a size of 55 mm in width and 500 mm in length to obtain a positive electrode.
- the coating film was rolled with a roller so that the thickness of the whole negative electrode was 150 ⁇ m, and a negative electrode sheet was produced. Thereafter, the negative electrode sheet was cut into a size of 58 mm in width and 540 mm in length to obtain a negative electrode.
- LiPF 6 LiPF 6 was dissolved at a concentration of 1 mol / l in a non-aqueous solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 3, thereby producing non-aqueous electrolyte.
- An electrolyte was prepared.
- a nonaqueous electrolyte secondary battery shown in FIG. 2 was produced by the following procedure. One end of the positive electrode lead 5a was connected to the exposed part of the positive electrode current collector, and one end of the negative electrode lead 6a was connected to the exposed part of the negative electrode current collector.
- the positive electrode 5 and the negative electrode 6 were wound with a separator 7 made of a polypropylene microporous film having a thickness of 20 ⁇ m between them, and a winding core having an outer diameter of 3 mm was wound to produce an electrode group.
- the electrode group was sandwiched between the upper insulating ring 8a and the lower insulating ring 8b and accommodated in a cylindrical battery case 1 having an outer diameter of 18 mm and a length of 65 mm.
- the other end of the negative electrode lead 6 a was welded to the inner bottom surface of the battery case 1.
- a non-aqueous electrolyte was injected into the battery case 1, and the electrode group was impregnated with the non-aqueous electrolyte by a decompression method.
- the other end of the positive electrode lead 5 a was welded to the lower surface of the sealing body 2.
- the battery case 1 was sealed with the sealing body 2 through the gasket 3 to produce a cylindrical lithium ion secondary battery.
- Example 2 A battery was fabricated in the same manner as in Example 1 except that the amount of the binder in the first slurry was 3 parts by weight and the solid content was 68% by weight.
- Example 3 A battery was fabricated in the same manner as in Example 1 except that the amount of the binder in the first slurry was 4 parts by weight and the solid content was 60% by weight.
- Example 4 The positive electrode after forming the first layer was heated at 190 ° C. for 30 minutes. Thereafter, a battery was produced in the same manner as in Example 3 except that the second layer was formed on the surface of the first layer.
- Example 5 A battery was fabricated in the same manner as in Example 4 except that the amount of the binder in the first slurry was 5 parts by weight and the solid content was 58% by weight.
- Example 6 A battery was fabricated in the same manner as in Example 4 except that the amount of the binder in the first slurry was 7 parts by weight and the solid content was 50% by weight.
- Example 7 Fabrication of positive electrode (first layer) Mixing 100 parts by weight of LiCoO 2 as a positive electrode active material, 4 parts by weight of PVDF as a binder, 3 parts by weight of acetylene black as a conductive material, and an appropriate amount of NMP as a dispersion medium, the solid content is 62% by weight.
- % First slurry was prepared. The 1st slurry was apply
- (Second layer) Mixing 100 parts by weight of the same positive electrode active material as in the first layer, 0.7 parts by weight of PVDF as a binder, 3 parts by weight of acetylene black as a conductive material, and an appropriate amount of NMP as a dispersion medium, A second slurry having a solid content of 78% by weight was prepared. The 2nd slurry was apply
- (3rd layer) 100 parts by weight of the same positive electrode active material as in the first layer, 1.5 parts by weight of PVDF as a binder, 3 parts by weight of acetylene black as a conductive material, and an appropriate amount of NMP as a dispersion medium are mixed.
- the coating film was rolled with a roller so that the active material density of the positive electrode mixture layer was 3.55 g / cm 3 to prepare a positive electrode sheet.
- the thickness of the 1st layer after rolling was about 15 micrometers
- the thickness of the 2nd layer was about 10 micrometers
- the thickness of the 3rd layer was about 30 micrometers
- the thickness of the whole sheet was 125 micrometers.
- the positive electrode sheet was cut into a size of 55 mm in width and 500 mm in length to obtain a positive electrode.
- a battery was fabricated in the same manner as in Example 1 except that the above positive electrode was used.
- Comparative Example 1 100 parts by weight of LiCoO 2 as a positive electrode active material, 2 parts by weight of PVDF as a binder, 3 parts by weight of acetylene black as a conductive material, and an appropriate amount of NMP as a dispersion medium are mixed to obtain a solid content of 73 wt. % Positive electrode mixture slurry was prepared. The positive electrode mixture slurry was applied on both surfaces of the same positive electrode current collector as in Example 1, and dried under conditions of 110 ° C. for 5 minutes to form a positive electrode mixture layer. The second layer and the third layer were not produced.
- the coating film was rolled with a roller so that the active material density of the positive electrode mixture layer was 3.55 g / cm 3 to prepare a positive electrode sheet.
- the total thickness of the sheet after rolling was 125 ⁇ m.
- the positive electrode sheet was cut into a size of 55 mm in width and 500 mm in length to obtain a positive electrode.
- a battery was fabricated in the same manner as in Example 1 except that the above positive electrode was used.
- Comparative Example 2 A battery was fabricated in the same manner as in Example 4 except that the amount of the binder in the first slurry was 10 parts by weight and the solid content was 40% by weight.
- Comparative Example 3 A battery was fabricated in the same manner as in Example 1 except that the amount of the binder in the second slurry was 1.5 parts by weight and the solid content was 73% by weight.
- (Second layer) Mix 100 parts by weight of the same positive electrode active material as that of the first layer, 1 part by weight of PVDF as a binder, 3 parts by weight of acetylene black as a conductive material, and an appropriate amount of NMP as a dispersion medium. A 78 wt% second slurry was prepared. The 2nd slurry was apply
- (3rd layer) 100 parts by weight of the same positive electrode active material as that of the first layer, 0.5 parts by weight of PVDF as a binder, 3 parts by weight of acetylene black as a conductive material, and an appropriate amount of NMP as a dispersion medium are mixed.
- the 3rd slurry was apply
- the coating film was rolled with a roller so that the active material density of the positive electrode mixture layer was 3.55 g / cm 3 to prepare a positive electrode sheet.
- the thickness of the 1st layer after rolling was about 15 micrometers
- the thickness of the 2nd layer was about 20 micrometers
- the thickness of the 3rd layer was about 20 micrometers
- the thickness of the whole sheet was 125 micrometers.
- the positive electrode sheet was cut into a size of 55 mm in width and 500 mm in length to obtain a positive electrode.
- a battery was fabricated in the same manner as in Example 1 except that the above positive electrode was used.
- Example 1 except that the amount of the binder was 10 parts by weight and the solid content was 40% by weight in the first slurry, and the amount of the binder was 5 parts by weight and the solid content was 58% by weight in the second slurry. Thus, a battery was produced.
- Table 1 shows the layer structure of the positive electrodes in the batteries of Examples 1 to 7 and Comparative Examples 1 to 5.
- the amount of the binder indicates the amount (parts by weight) of the binder with respect to 100 parts by weight of the positive electrode active material particles in the slurry used for producing each layer.
- a graph was created with the average value of the amount of the binder on the vertical axis and the distance from the current collector on each surface on the horizontal axis.
- the amount W 1 of the binder at the first maximum point, the amount W 2 of the binder at the minimum point, the amount W 3 , W 1 / W 2 of the binder at the second maximum point, and the first maximum point and the minimum point The slope of the straight line connecting The results are shown in Table 2.
- the positive electrode, the negative electrode, and the separator were wound using a core having an outer diameter of 3 mm to produce an electrode group, and then the electrode group was disassembled. The positive electrode was observed to confirm whether the positive electrode current collector was broken. For each example and comparative example, 50 electrode groups were observed and the number of broken electrode groups was determined. The results are shown in Table 2.
- the first layer was formed and then heated, and then the second layer was formed on the surface of the first layer.
- the crystallinity of the binder contained in the first layer is increased. Therefore, it is thought that the elution to the 2nd slurry of the binder contained in a 1st layer was suppressed, and the positive mix layer which has a better binder distribution was obtained.
- Example 7 a first layer, a second layer, and a third layer were formed. Thereby, it is considered that a positive electrode mixture layer having a good binder distribution was obtained.
- the productivity of the nonaqueous electrolyte secondary battery can be increased. Therefore, it is highly useful as a power source suitable for reducing the size and weight of electronic devices such as mobile phones and notebook computers.
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Abstract
Description
特許文献2では、電極合剤層と集電体とを剥離しやすくしているため、集電性が低下しやすい。
各正極合剤スラリーは、通常、塗布後に乾燥される。乾燥された塗膜は、通常、最終的に圧延される。
一方、本発明に係る正極合剤層aおよびbでは、厚さ方向における集電体からの距離と、結着剤の量との相関を示す曲線AおよびBが、それぞれ集電体側に第1極大点XAおよびXBを有する。曲線AおよびBは、更に極小点YAおよびYBならびに第2極大点ZAおよびZBを有する。
正極の断面において、集電体表面から正極合剤層表面までを含む任意の測定領域を選択し、当該測定領域を255×255個のピクセル(微小領域)に分割する。電子線プローブマイクロアナライザー(EPMA)法により、それぞれの微小領域におけるピーク強度を求める。具体的には、正極の厚さ方向の断面の任意の位置(例えば、集電体からの距離dの位置)において、正極の面方向に電子線をスキャンし、それぞれの微小領域におけるピーク強度を求め、平均する。同様の測定を、集電体の一方の面の正極合剤層の表面から集電体表面まで厚さ方向に沿って行う。結着剤に含まれる元素に帰属されるシグナルの強度から、任意の領域における結着剤の重量割合(重量部)を求める。シグナルの強度と結着剤の重量割合との関係は、重量割合が既知のサンプルから検量線を作成し、これと対比することで求められる。その後、厚さ方向における集電体からの距離を横軸とし、結着剤の重量割合(重量部)を縦軸としてプロットすることで、正極合剤層における結着剤の分布の状態を確認できる。
(1)スラリーの調製
正極活物質粒子の量に対する結着剤の量(通常、重量割合)の異なる複数のスラリーを塗布することで、正極合剤層における結着剤の分布を制御できる。正極活物質粒子と、結着剤と、分散媒とを混合してスラリーを調製する。具体的には、集電体に塗布する第1スラリーと、第1スラリーを塗布した後に、第1スラリーの塗膜上に塗布する第2スラリーとを用いる。本発明においては、結着剤の重量割合の異なる3種類以上のスラリーを用いてもよい。
第1スラリーを集電体の表面に塗布し、第1層を形成する。集電体の表面に塗布された第1スラリーの塗膜が乾燥するまでの間に、第1スラリー中の結着剤のマイグレーションが起こり、結着剤が表面側へ向かう方向に移動する。よって、第1層には、集電体表面から離れるほど量が多くなるように結着剤の分布が形成される。
正極合剤層は、乾燥後、通常、圧延される。圧延により、正極合剤層の厚み(または各層の厚み)および/または活物質密度を制御することができる。
また、第2層の厚さをT2とするとき、TとT2は、0.05T≦T2≦0.25Tを満たすことが好ましく、0.1T≦T2≦0.2Tを満たすことがより好ましい。また、第3層の厚さをT3とするとき、TとT3は、0.45T≦T3≦0.85Tを満たすことが好ましく、0.55T≦T3≦0.75Tを満たすことがより好ましい。
負極活物質は、1種のみを単独で用いてもよく、2種以上を組み合わせて用いてもよい。
増粘剤としては、カルボキシメチルセルロース(CMC)等が挙げられる。
負極用の集電体としては、銅、ニッケルなどを含むシート、箔などが挙げられる。
(i)正極の作製
(第1層)
正極活物質である100重量部のLiCoO2、結着剤である2重量部のポリフッ化ビニリデン(PVDF、(株)クレハ製のKFポリマーL#7208)、導電材である3重量部のアセチレンブラックおよび分散媒である適量のN-メチル-2-ピロリドン(NMP)を混合して、固形分73重量%の第1スラリーを調製した。第1スラリーを厚さ15μmのアルミニウム箔からなる集電体の両面に塗布し、110℃、5分の条件で乾燥させて、第1層を形成した。
第1層と同様の正極活物質100重量部、結着剤である1重量部のPVDF、導電材である3重量部のアセチレンブラックおよび分散媒である適量のNMPを混合して、固形分78重量%の第2スラリーを調製した。第2スラリーを、第1層のそれぞれの表面に塗布し、110℃、5分の条件で乾燥させて、第2層を形成した。
負極活物質である100重量部の鱗片状黒鉛、結着剤である2重量部のスチレン-ブタジエン共重合体(SBR、日本ゼオン(株)製のBM-400B)、増粘剤である1重量部のカルボキシメチルセルロース(CMC)および分散媒である適量の水を混合して、負極合剤スラリーを調製した。負極合剤スラリーを、厚さ10μmの銅箔からなる負極集電体に塗布し、60℃、5分の条件で乾燥させて、負極集電体の表面に負極合剤層を形成した。その後、負極全体の厚さが150μmとなるようにローラで塗膜を圧延し、負極シートを作製した。その後、負極シートを幅58mm、長さ540mmの大きさに切断して、負極とした。
エチレンカーボネート(EC)とエチルメチルカーボネート(EMC)とを、1:3の体積割合で含む非水溶媒に、LiPF6を1mol/lの濃度で溶解させて非水電解質を調製した。
図2に示す非水電解質二次電池を以下の手順で作製した。
正極集電体の露出部に正極リード5aの一端を接続し、負極集電体の露出部に負極リード6aの一端を接続した。正極5と負極6とを、これらの間に厚さ20μmのポリプロピレン製の微多孔膜からなるセパレータ7を介在させて、外径3mmの巻芯を用いて捲回し、電極群を作製した。
正極リード5aの他端を封口体2の下面に溶接した。ガスケット3を介して電池ケース1を封口体2で封口し、円筒型リチウムイオン二次電池を作製した。
第1スラリーにおいて、結着剤の量を3重量部とし、固形分68重量%としたこと以外、実施例1と同様にして、電池を作製した。
第1スラリーにおいて、結着剤の量を4重量部とし、固形分60重量%としたこと以外、実施例1と同様にして、電池を作製した。
第1層を形成した後の正極を、190℃で30分間加熱した。その後、第1層の表面に第2層を形成したこと以外、実施例3と同様にして、電池を作製した。
第1スラリーにおいて、結着剤の量を5重量部とし、固形分58重量%としたこと以外、実施例4と同様にして、電池を作製した。
第1スラリーにおいて、結着剤の量を7重量部とし、固形分50重量%としたこと以外、実施例4と同様にして、電池を作製した。
(i)正極の作製
(第1層)
正極活物質である100重量部のLiCoO2、結着剤である4重量部のPVDF、導電材である3重量部のアセチレンブラックおよび分散媒である適量のNMPを混合して、固形分62重量%の第1スラリーを調製した。第1スラリーを実施例1と同様の集電体の両面に塗布し、110℃、5分の条件で乾燥させて、第1層を形成した。
第1層と同様の正極活物質100重量部と、結着剤である0.7重量部のPVDF、導電材である3重量部のアセチレンブラックおよび分散媒である適量のNMPを混合して、固形分78重量%の第2スラリーを調製した。第2スラリーを、第1層のそれぞれの表面に塗布し、110℃、5分の条件で乾燥させて、第2層を形成した。
第1層と同様の正極活物質100重量部と、結着剤である1.5重量部のPVDFを、導電材である3重量部のアセチレンブラックおよび分散媒である適量のNMPを混合して、固形分73重量%の第3スラリーを調製した。第3スラリーを、両面に形成された第2層のそれぞれの表面に塗布し、110℃、5分の条件で乾燥させて、第3層を形成した。
上記の正極を用いたこと以外、実施例1と同様にして、電池を作製した。
正極活物質である100重量部のLiCoO2、結着剤である2重量部のPVDF、導電材である3重量部のアセチレンブラックおよび分散媒である適量のNMPを混合して、固形分73重量%の正極合剤スラリーを調製した。正極合剤スラリーを、実施例1と同様の正極集電体の両面に塗布し、110℃、5分の条件で乾燥させて、正極合剤層を形成した。第2層および第3層は作製しなかった。
上記の正極を用いたこと以外、実施例1と同様にして、電池を作製した。
第1スラリーにおいて、結着剤の量を10重量部とし、固形分40重量%としたこと以外、実施例4と同様にして、電池を作製した。
第2スラリーにおいて、結着剤の量を1.5重量部とし、固形分73重量%としたこと以外、実施例1と同様にして、電池を作製した。
(i)正極の作製
(第1層)
正極活物質である100重量部のLiCoO2、結着剤である4重量部のPVDF、導電材である3重量部のアセチレンブラックおよび分散媒である適量のNMPを混合して、固形分60重量%の第1スラリーを調製した。第1スラリーを実施例1と同様の集電体の両面に塗布し、110℃、5分の条件で乾燥させて第1層を形成した。
第1層と同様の正極活物質100重量部と、結着剤である1重量部のPVDF、導電材である3重量部のアセチレンブラックおよび分散媒である適量のNMPを混合して、固形分78重量%の第2スラリーを調製した。第2スラリーを、第1層のそれぞれの表面に塗布し、110℃、5分の条件で乾燥させて、第2層を形成した。
第1層と同様の正極活物質100重量部と、結着剤である0.5重量部のPVDFを、導電材である3重量部のアセチレンブラックおよび分散媒である適量のNMPを混合して、固形分78重量%の第3スラリーを調製した。第3スラリーを、両面に形成された第2層のそれぞれの表面に塗布し、110℃、5分の条件で乾燥させて、第3層を形成した。
上記の正極を用いたこと以外、実施例1と同様にして、電池を作製した。
第1スラリーにおいて、結着剤の量10重量部、固形分40重量%とし、第2スラリーにおいて、結着剤の量5重量部、固形分58重量%としたこと以外、実施例1と同様にして、電池を作製した。
実施例1~7および比較例1~5で作製した非水電解質二次電池について、以下の評価を行った。
各実施例および比較例の正極を2cm角に切断し、エポキシ樹脂で被覆して硬化させた。その後、研磨機にて硬化物の断面研磨を実施し、正極の厚さ方向における断面を露出させた。その後、波長分散型の電子線プローブマイクロアナライザー(EPMA、日本電子(株)製のJXA-8900)により結着剤の分布を分析した。同様の分析を、正極の面方向にスキャンしながら行い、各面における正極活物質粒子100重量部に対する結着剤の量(重量部)の平均値を算出した。この結着剤の量の平均値を縦軸に、各面の集電体からの距離を横軸にしてグラフを作成した。第1極大点における結着剤の量W1、極小点における結着剤の量W2、第2極大点における結着剤の量W3、W1/W2および第1極大点と極小点とを結ぶ直線の傾きを求めた。結果を表2に示す。
一方の面の正極合剤層を取り除いた正極を、幅15mm、長さ100mmの短冊状に切断した。残した正極合剤層を水平方向へ可動できる台座へ両面テープで接着した後、引っ張り圧縮試験機のチャックで集電体の端部をつかんで90°上方へ引っ張り、剥離試験を行った。剥離後の正極の表面における集電体の露出の有無を観察し、集電体と正極合剤層の密着性を評価した。結果を表2に示す。
正極、負極およびセパレータを、外径3mmの巻芯を用いて捲回して電極群を作製した後、電極群を分解した。正極を観察して、正極集電体の破断の有無を確認した。各実施例および比較例について、50個の電極群を観察し、破断した電極群の数を求めた。結果を表2に示す。
電池の製造工程における正極合剤層の表面側からの正極活物質粒子の脱落の有無を目視で確認した。結果を表2に示す。
実施例1~3は、第1スラリーおよび第2スラリーにおける結着剤の量を変化させた。これらの実施例では、良好な結着剤の分布を有する正極合剤層が得られた。
2 封口体
3 ガスケット
5 正極
5a 正極リード
6 負極
6a 負極リード
7 セパレータ
8a 上部絶縁リング
8b 下部絶縁リング
Claims (6)
- 集電体と、前記集電体の表面に形成された正極合剤層とを備え、
前記正極合剤層が、正極活物質粒子と、結着剤とを含み、
前記正極合剤層の厚さ方向における前記集電体からの距離と、前記正極合剤層における前記結着剤の量との相関を示す曲線が、第1極大点、極小点および第2極大点を有し、
前記極小点が、前記正極合剤層の厚さ方向における中間部の位置に対応し、
前記第1極大点が、前記正極合剤層の前記極小点に対応する位置よりも集電体側の位置に対応し、
前記第2極大点が、前記正極合剤層の前記極小点に対応する位置よりも集電体から離れた位置に対応し、
前記第1極大点における、前記正極活物質粒子100重量部に対する前記結着剤の量W1と、前記極小点における、前記正極活物質粒子100重量部に対する前記結着剤の量W2との比W1/W2が、2より大きく、
前記W1が、1~8重量部であり、
前記W2が、0.3~1.5重量部であり、
前記正極活物質粒子が、リチウム含有遷移金属酸化物を含み、
前記正極合剤層の活物質密度が3.3~4g/cm3である、非水電解質二次電池用正極。 - 前記正極合剤層の厚さが、20~150μmであり、
前記結着剤が、フッ素樹脂を含み、
前記第1極大点が、前記正極合剤層の厚さ方向における前記集電体からの距離0.1~10μmの位置に対応する、請求項1記載の非水電解質二次電池用正極。 - 前記第1極大点に対応する位置と、前記集電体との中間において、前記正極活物質粒子100重量部に対する前記結着剤の量が、0.6W1~0.99W1である、請求項1または2記載の非水電解質二次電池用正極。
- 前記第1極大点と前記極小点とを結ぶ直線の傾きが、-0.3重量部/μm以上、-0.05重量部/μm以下である、請求項1~3のいずれか1項に記載の非水電解質二次電池用正極。
- 前記第2極大点における、前記正極活物質粒子100重量部に対する前記結着剤の量W3が、前記W1よりも小さい、請求項1~4のいずれか1項に記載の非水電解質二次電池用正極。
- 請求項1~5のいずれか1項に記載の正極、負極、前記正極と前記負極との間に介在するセパレータおよび非水電解質を備え、前記正極、前記負極および前記セパレータが、捲回されて電極群を構成している、非水電解質二次電池。
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CN102473900A (zh) | 2012-05-23 |
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