WO2014068905A1 - 非水電解質二次電池用電極板及びこれを用いた非水電解質二次電池並びにその製造方法 - Google Patents
非水電解質二次電池用電極板及びこれを用いた非水電解質二次電池並びにその製造方法 Download PDFInfo
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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- 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
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- 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
- H01M4/139—Processes of manufacture
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- H—ELECTRICITY
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- 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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
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- 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
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- 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
- H01M4/622—Binders being polymers
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- H—ELECTRICITY
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/70—Carriers or collectors characterised by shape or form
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- H—ELECTRICITY
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- 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
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2220/00—Batteries for particular applications
- H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
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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
- H01M2220/00—Batteries for particular applications
- H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
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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
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Definitions
- the present invention relates to improvement of cycle characteristics of a non-aqueous electrolyte secondary battery.
- Non-aqueous electrolyte secondary batteries have high energy density and high capacity, and are therefore widely used as drive power sources for portable devices such as mobile phones, smartphones, and notebook computers. In recent years, further improvement in the cycle characteristics of nonaqueous electrolyte secondary batteries has been demanded.
- An electrode plate used for such a non-aqueous electrolyte secondary battery has an electrode active material slurry obtained by mixing an electrode active material, a binder, and a solvent from the viewpoint of enhancing productivity and discharge characteristics. It is applied by a method in which it is applied onto the substrate, dried, and then rolled.
- the binder does not directly contribute to charging / discharging, if the amount is excessive, the discharge capacity is lowered. On the other hand, when the amount of the binder is too small, the peel strength of the electrode active material layer is lowered, and the electrode active material is easily detached from the core.
- Patent Documents 1 to 5 as techniques relating to the binder of the nonaqueous electrolyte secondary battery.
- Japanese Patent Laid-Open No. 5-89871 JP 2011-192539 A Japanese Patent Laid-Open No. 9-147834 JP 2008-258055 A Japanese Patent Laid-Open No. 10-284059
- Patent Document 1 is a secondary battery electrode in which a coating layer of an active material is provided on a metal current collector, and the binder in the active material layer is in the range of a binder distribution coefficient of 0.5 to 5.0.
- the technology distributed in is disclosed. According to this technique, excellent battery characteristics are obtained.
- Patent Document 2 is an electrode having a current collector, a first mixture layer formed on the surface of the current collector, and a second mixture layer formed on the surface of the first mixture layer.
- the technique which makes a 2nd mixture layer contain a smaller amount of binders than a 1st mixture layer is disclosed. According to this technique, an electrode for a non-aqueous electrolyte secondary battery having excellent rate characteristics and cycle characteristics and high capacity can be provided.
- the negative electrode active material layers are first, second, and third negative electrode active material layers 7a, 7b, and 7c in which the amount of binder decreases stepwise from the interface with the current collector.
- the technology which comprises is disclosed. According to this technology, a battery having a high capacity and a high energy density can be provided.
- Patent Document 4 includes a positive electrode current collector plate and a plurality of positive electrode mixture layers that are stacked on the positive electrode current collector plate and include a positive electrode raw material powder and a positive electrode binder. Disclosed is a technique using a positive electrode in which the content of the positive electrode binder in the innermost positive electrode mixture layer located on the electric plate side is higher than that of other positive electrode mixture layers and is 4 wt% or more and 7 wt% or less. ing. According to this technique, a secondary battery having good output characteristics and good cycle life characteristics can be obtained.
- Patent Document 5 an organic solvent and a binder made of a fluororesin are mixed, and a binder solution is applied to both sides of a current collector made of copper foil and semi-dried to form a semi-dry binder layer. Then, a carbon material solution obtained by wet-mixing an organic solvent and this mixture is applied onto each of the semi-dry binder layers and dried to form a negative electrode material layer on the current collector.
- the technology is disclosed. According to this technique, the adhesion between the negative electrode material layer and the negative electrode current collector can be sufficiently increased without reducing the discharge capacity.
- An object of the present invention is to provide a nonaqueous electrolyte secondary battery excellent in cycle characteristics.
- This invention concerning the electrode plate for nonaqueous electrolyte secondary batteries for solving the above-mentioned subject is constituted as follows.
- the binder is disposed in a central region in the thickness direction of the electrode active material layer.
- the binder has the smallest amount, and the binder is included so that the amount of the binder contained in the electrode active material layer continuously increases from the portion toward the core and the outer surface.
- the adhesive is distributed.
- the present inventors studied the relationship between the binder and the cycle characteristics and found out the following.
- the binder covers the surface of the electrode active material and the lithium ion acceptability of the electrode active material is deteriorated, while the retention ability of the nonaqueous electrolyte is increased.
- the cycle characteristics can be improved by balancing the lithium ion acceptability with the nonaqueous electrolytic mass during the charge / discharge cycle.
- the nonaqueous electrolyte since the amount of the binder on the core side where the nonaqueous electrolyte tends to be insufficient is large, a large amount of nonaqueous electrolyte is retained on the core side. Also, from the outer surface side where a large amount of binder is held and a large amount of non-aqueous electrolyte is held, the non-aqueous electrolyte has a small amount of binder (less non-aqueous electrolyte is held) during the charge / discharge cycle. To be supplied.
- the non-aqueous electrolytic mass in the entire electrode active material layer is balanced, and the charge / discharge cycle proceeds smoothly in the entire electrode active material layer, so that the cycle characteristics are improved and the resistance of the electrode plate is low.
- the effect of abundant supply of the nonaqueous electrolyte can be increased rather than the adverse effect of the decrease in lithium ion acceptability, so that a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be realized.
- there are many binders by the side of a core it can also prevent that an electrode active material layer peels from a core by impact etc.
- the central region of the electrode active material layer means a region of 10 to 90% in the thickness direction of the electrode active material layer with the core surface of the electrode active material layer as a base point. More preferably, the core of the electrode active material layer has a portion where the amount of the binder is the smallest in a region of 20 to 80% in the thickness direction of the electrode active material layer, starting from the back surface. Further, it is more preferable that the core of the electrode active material layer has a portion where the amount of the binder is the smallest in a region of 45 to 55% in the thickness direction of the electrode active material layer starting from the back surface.
- the distribution of the amount of the binder changes continuously, and there is no interface in which the amount of the binder per unit thickness changes discontinuously in the electrode active material layer.
- the binder concentration gradient in the central region is preferably smaller than the binder concentration gradient on the outer surface side or the core side.
- the amount of the binder per unit thickness of the electrode active material layer is 10 when it is assumed that the binder is uniformly distributed, the core of the electrode active material layer is facing As a starting point, the amount of the binder per unit thickness in the region of 90 to 100% in the thickness direction of the electrode active material layer can always be greater than 10.
- the amount of the binder per unit thickness of the electrode active material layer does not mean the amount of the binder present in a specific thickness region of the electrode active material layer, but the thickness of the electrode active material layer. It means a value that differentially captures the amount of binder present in the direction.
- the core of the electrode active material layer “The amount of the binder per unit thickness in the region of 90 to 100% in the thickness direction of the electrode active material layer is more than 10 as a base point” means that the core of the electrode active material layer is based on the back surface. In the region of 90-100% in the thickness direction of the substance layer (10% region on the outer surface side), it means that there is no portion where the amount of binder is 10 or less.
- the electrode active material when the amount of the binder per unit thickness of the electrode active material layer when the binder is assumed to be uniformly distributed in the electrode active material layer is 10, the electrode active material The amount of the binder per unit thickness in the region of 45 to 55% in the thickness direction of the electrode active material layer with the core of the layer as the starting point is less than 10, and the thickness of the electrode active material layer in the thickness direction of 0 to The amount of the binder per unit thickness in the 10% region can be greater than 10.
- the amount of the binder in the 10% thickness region (0 to 10% thickness direction) of the core body can be regulated as described above. preferable. In order to further improve the cycle characteristics, the amount of the binder in the region near the center (region of 45 to 55% in the thickness direction) is preferably regulated as described above.
- the lower limit of the amount distribution of the binder in the region of 45 to 55% in the thickness direction is preferably set to a minimum amount necessary for forming the electrode active material layer.
- a contact area ratio between the electrode active material included in the electrode active material layer and the core body may be 30% or more.
- the active material particles bite into the core.
- binder known binders such as polyvinylidene fluoride, polytetrafluoroethylene, and styrene butadiene rubber can be used.
- styrene-butadiene rubber and its modified products are preferable because water that does not adversely affect the environment can be used at low cost as a solvent for forming the electrode active material layer.
- modified body of styrene butadiene rubber styrene butadiene rubber subjected to carboxyl modification or amino modification is suitable.
- the mass ratio of the binder to the mass of the electrode active material layer can be appropriately set according to the type of the binder.
- the mass ratio of the binder to the mass of the electrode active material layer is 0.1 to 3.0 mass% for polyvinylidene fluoride, 0.1 to 5.0 mass% for polytetrafluoroethylene, styrene
- the content may be 0.1 to 5.0% by mass.
- the present invention according to a nonaqueous electrolyte secondary battery for solving the above problems is configured as follows.
- This invention concerning the manufacturing method of the nonaqueous electrolyte secondary battery for solving the above-mentioned subject is constituted as follows.
- a second electrode active material slurry having a mass ratio of the solvent lower than that of the first electrode active material slurry and applied on the undried layer of the first electrode active material slurry
- a step of evaporating and removing the solvent after the second step and having a portion with the smallest amount of the binder in the central region in the thickness direction of the electrode active material layer,
- the non-aqueous electrolyte secondary in which the binder is distributed so that the amount of the binder contained in the electrode active material layer continuously increases from the portion toward the core body side and the outer surface side. Battery manufacturing method.
- the first electrode active material slurry is applied onto the core, and the solvent ratio is lower than that of the first electrode active material slurry on the layer of the undried first electrode active material slurry (solid content (electrode active When the second electrode active material slurry is applied, the ratio of the material, the binder, and the thickener as needed) is high.
- the binder Sedimentation occurs and the lifting of the binder is suppressed.
- the binder floats with the volatilization of the solvent inside the electrode active material layer.
- the drying rate is preferably 5 g (solvent) / m 2 ⁇ s or less, and more preferably 4 g (solvent) / m 2 ⁇ s or less. Further, if the drying rate is too slow, the working efficiency is lowered and the binder may not be sufficiently lifted. Therefore, the amount is preferably 2 g (solvent) / m 2 ⁇ s or more, and preferably 3 g (solvent). ) / M 2 ⁇ s or more.
- the drying speed can be adjusted by controlling the atmospheric temperature, pressure and the like of the drying process.
- the binder of the first and second electrode active material slurries is preferably the same.
- the compositions of the first and second electrode active material slurries may be the same or different.
- a third electrode active material layer may be further formed on the undried second electrode active material layer.
- the ratio of the solid content mass of the first electrode active material slurry to the solid content mass of the second electrode active material slurry before the drying step is preferably 0.1 to 10, preferably 0.5 to 2 is more preferable.
- a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be obtained.
- FIG. 1 is a binder distribution diagram in the negative electrode active material layers of Examples 1 and 2 and Comparative Example 1.
- FIG. 1 is a binder distribution diagram in the negative electrode active material layers of Examples 1 and 2 and Comparative Example 1.
- Example 1 [Production of positive electrode] 100 parts by mass of lithium cobaltate (LiCoO 2 ) as a positive electrode active material, 2 parts by mass of acetylene black as a conductive agent, 2 parts by mass of polyvinylidene fluoride (PVdF) as a binder, and N-methyl-2- Pyrrolidone was mixed to obtain a positive electrode active material slurry.
- LiCoO 2 lithium cobaltate
- acetylene black as a conductive agent
- PVdF polyvinylidene fluoride
- N-methyl-2- Pyrrolidone N-methyl-2- Pyrrolidone
- the positive electrode active material slurry was applied to both sides of a 15 ⁇ m thick aluminum core by the doctor blade method and dried. Then, it compressed to 170 micrometers in thickness using the compression roller, and cut
- a part of the negative electrode active material slurry A is taken out, an appropriate amount of water is further added so that the total solid content is 40 to 48%, and the mixture is mixed with a double-arm kneader to prepare the negative electrode active material slurry B (first Electrode active material slurry). That is, the negative electrode active material slurry A and the negative electrode active material slurry B have the same constituent ratio in the solid content, and the mass ratio of moisture (solvent) is negative electrode active material slurry A ⁇ negative electrode active material slurry B. Yes.
- This negative electrode active material slurry B is applied to both surfaces of a copper core having a thickness of 10 ⁇ m by the doctor blade method, and then the negative electrode active material slurry A is applied on the layer of the undried negative electrode active material slurry B by the doctor blade method. Applied. At this time, the solid mass ratio was such that the layer made of the negative electrode active material slurry A was twice the layer made of the negative electrode active material slurry B.
- FIG. 1 shows the binder distribution in the thickness direction of the active material layer.
- the binder distribution is shown as a relative value when the amount of the binder per unit thickness of the negative electrode active material layer is 10 when it is assumed that the binder is uniformly distributed.
- the electrode active material is based on the back surface of the core of the electrode active material layer.
- the amount of binder per unit thickness in the region of 90 to 100% in the thickness direction of the layer is always 12 to 15, and the amount of binder per unit thickness in the region of 45 to 55% in the thickness direction of the electrode active material layer However, it was always 5.5 to 7, and the amount of the binder per unit thickness of the negative electrode active material layer in the region of 0 to 10% in the thickness direction of the electrode active material layer was always 12 to 15.
- the contact area ratio between the active material (artificial graphite) particles contained in the active material layer and the core was 30% before compression and 30% or more after compression.
- the positive electrode plate and the negative electrode plate were wound through a separator (thickness 20 ⁇ m) made of a polyethylene microporous film, and a tape was attached to the outermost periphery to produce a cylindrical electrode body.
- Nonaqueous electrolyte adjustment Ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 80: 5: 15 (25 ° C., 1 atm), and LiPF 6 as an electrolyte salt was dissolved to 1.0 M (mol / liter). Vinylene carbonate was added so that it might become 3 mass%, and it was set as the nonaqueous electrolyte.
- the solid content mass ratio of the layer made of the negative electrode active material slurry A and the layer made of the negative electrode active material slurry B was set to be one time that the layer made of the negative electrode active material slurry A was made larger than the layer made of the negative electrode active material slurry B.
- a nonaqueous electrolyte secondary battery according to Example 2 was fabricated in the same manner as in Example 1 (total solid content was the same as in Example 1) except that drying was performed at (solvent) / m 2 ⁇ s. .
- the distribution of the binder (SBR) in the negative electrode plate in the thickness direction of the active material layer was analyzed in the same manner as described above.
- the electrode active material is based on the back surface of the core of the electrode active material layer.
- the amount of binder per unit thickness in the region of 90 to 100% in the thickness direction of the layer is always 14 to 18, and the amount of binder per unit thickness in the region of 45 to 55% in the thickness direction of the electrode active material layer
- the contact area ratio between the active material (artificial graphite) particles contained in the active material layer and the core was 30% before compression and 30% or more after compression.
- Example 1 The same as in Example 1 above except that only the negative electrode active material slurry C having a total solid content of 50% was used and drying was performed at an average drying rate of 4 g (solvent) / m 2 ⁇ s (the total solid content was In the same manner as in Example 1, a nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced.
- the distribution of the binder (SBR) in the negative electrode plate in the thickness direction of the active material layer was analyzed in the same manner as described above. Then, the binder was uniformly distributed (see FIG. 1)). Further, the contact area ratio between the active material (artificial graphite) particles contained in the active material layer and the core was 30% before compression and 30% or more after compression.
- the binder distribution in the negative electrode active material layer is shown in FIG.
- the binder distribution of the negative electrode active material layer increases from the portion with the smallest amount of binder in the central region in the thickness direction of the electrode active material layer toward the outer surface side and the core body side.
- the cycle capacity retention at ⁇ 5 ° C. is 88% and 90%
- the cycle capacity retention at 25 ° C. is 62% and 73%
- the internal resistance is 95 and 91.
- the cycle capacity retention rate at ⁇ 5 ° C. is 83%
- the cycle capacity retention rate at 25 ° C. is 56%
- the internal resistance is better than 100.
- the amount of the binder contained in the electrode active material layer continuously increases from the portion having the smallest amount of the binder in the central region toward the outer surface side and the core side. As such, the binder is distributed.
- the binder on the core side where the nonaqueous electrolyte tends to be insufficient is large, a large amount of nonaqueous electrolyte is retained on the core side.
- the non-aqueous electrolyte has a small amount of binder (less non-aqueous electrolyte is held) during the charge / discharge cycle. To be supplied.
- the non-aqueous electrolysis mass in the entire electrode active material layer is balanced, and the charge / discharge cycle proceeds smoothly in the entire electrode active material layer, so that the cycle characteristics are improved and the resistance is lowered.
- the cycle characteristics are improved and the resistance is lowered.
- there are many binders by the side of a core it can also prevent that an electrode active material layer peels from a core by impact etc.
- the present invention is applied only to the negative electrode plate.
- the present invention can be applied to only the positive electrode plate or to both electrode plates.
- binder examples include styrene butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and the like. These may be appropriately selected according to the type of electrode active material, the type of solvent, and the like.
- spinel type lithium manganate Li x Mn 2 O 4
- carbonaceous materials that can occlude / desorb lithium ions eg, graphite, acetylene black, carbon black, amorphous carbon
- siliceous materials metallic lithium, lithium alloys, lithium ion occlusion / desorption.
- Separable metal oxides can be used alone or in combination of two or more.
- water can be used when styrene butadiene rubber is used, and N-methyl-2-pyrrolidone is used when polyvinylidene fluoride or polytetrafluoroethylene is used. Can do.
- carbonates, lactones, ketones, ethers, esters, etc. can be used as the nonaqueous solvent used in the nonaqueous electrolyte.
- ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ⁇ -butyrolactone, ⁇ -valerolactone, ⁇ -dimethoxyethane, tetrohydrofuran, 1,4-dioxane, etc. are used. be able to.
- electrolyte salts used for non-aqueous electrolytes include LiBF 4 , LiAsF 6 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiClO.
- One kind or a mixture of plural kinds such as 4 can be used.
- the amount dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / liter.
- pure aluminum or aluminum alloy can be used on the positive electrode side, and pure copper or copper alloy can be used on the negative electrode side.
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Abstract
Description
電極活物質と結着剤とを有する電極活物質層が芯体表面に設けられた非水電解質二次電池用電極板において、前記電極活物質層の厚み方向の中央領域に、前記結着剤の量が最も少ない部分を有し、且つ、当該部分から前記芯体側及び外表面側に向かって、前記電極活物質層に含まれる前記結着剤の量が連続的に増大するように前記結着剤が分布することを特徴とする。
上記のいずれかの非水電解質二次電池用電極板を、正極板、負極板の少なくとも一方として用いてなる非水電解質二次電池。
電極活物質と、結着剤と、溶剤と、を有する第1の電極活物質スラリーを、芯体上に塗布する第1塗布工程と、電極活物質と、結着剤と、溶剤と、を有し、前記第1の電極活物質スラリーよりも前記溶剤の質量比率が低い第2の電極活物質スラリーを、未乾燥の前記第1の電極活物質スラリーによる層の上に塗布する第2塗布工程と、前記第2工程の後、前記溶剤を揮発除去する乾燥工程と、を備え、前記電極活物質層の厚み方向の中央領域に、前記結着剤の量が最も少ない部分を有し、且つ、当該部分から前記芯体側及び外表面側に向かって、前記電極活物質層に含まれる前記結着剤の量が連続的に増大するように前記結着剤が分布する非水電解質二次電池の製造方法。
[実施例1]
〔正極の作製〕
正極活物質としてのコバルト酸リチウム(LiCoO2)100質量部と、導電剤としてのアセチレンブラック2質量部と、結着剤としてのポリフッ化ビニリデン(PVdF)2質量部と、N-メチル-2-ピロリドンとを混合して、正極活物質スラリーとした。
負極活物質としての人造黒鉛100質量部と、増粘剤としてのカルボキシメチルセルロース1質量部と、結着剤としてのスチレンブタジエンゴム(SBR)の水ディスパージョン(固形分比率40%)をスチレンブタジエンゴム換算で1質量部と、合計固形分が48~55%となるように適量の水とを、双腕式練合機にて混合して、負極活物質スラリーA(第2の電極活物質スラリー)とした。
すなわち、負極活物質スラリーAと、負極活物質スラリーBとは、固形分内での構成比率は同一で、水分(溶剤)の質量比率が負極活物質スラリーA<負極活物質スラリーBとなっている。
上記正極板及び負極板を、ポリエチレン製微多孔膜からなるセパレータ(厚み20μm)を介して巻回し、最外周にテープを貼り付けて、円筒状の電極体を作製した。
エチレンカーボネートとジエチルカーボネートとエチルメチルカーボネートを体積比80:5:15(25℃、1気圧)で混合し、電解質塩としてのLiPF6を1.0M(モル/リットル)となるように溶解し、ビニレンカーボネートを3質量%となるように添加して、非水電解質となした。
上記電極体および非水電解質5.5gを、円筒形外装缶内に収容した。この後、封口体により外装缶の開口を封止して、実施例1に係る非水電解質二次電池(高さ65mm、直径18mm)を作製した。
合計固形分が50%である負極活物質スラリーCのみを用い、平均乾燥速度4g(溶媒)/m2・sで乾燥を行ったこと以外は、上記実施例1と同様(総固形分量は実施例1と同一)にして、比較例1にかかる非水電解質二次電池を作製した。
実施例1、2、比較例1と同様にして作製した電池を以下の条件で充放電を2回行い、45℃の恒温槽で7日保存した。この電池を再度以下の条件で充放電を500サイクル行った。下記式により容量維持率を算出しこの結果を下記表1に示す。
放電:定電流2000mAで電圧が3.0Vとなるまで、25℃
容量維持率(%)=500サイクル目放電容量÷1サイクル目放電容量×100
実施例1、2、比較例1と同様にして作製した電池を以下の条件で充放電を100サイクル行った。下記式により容量維持率を算出しこの結果を下記表1に示す。
放電:定電流2000mAで電圧が3.0Vとなるまで、-5℃
容量維持率(%)=100サイクル目放電容量÷1サイクル目放電容量×100
実施例1、2、比較例1と同様にして作製した電池を20℃の環境に30分放置した後、定電流0.2It(440mA)で充電深度(SOC)が50%になるまで充電した。この後、25℃の環境に30分放置した。この後、定電流1It(2200mA)での10秒間の充電及び放電を行った。このときの充放電終止電圧とSOC50%の状態における開回路電圧との差を、流した電流値で除することにより、電圧勾配dV/dAを求めた。この結果を、比較例1を100とした相対値で下記表1に示す。
上記実施例では、負極板のみに本発明を適用したが、正極板のみに適用する構成や、両電極板に適用する構成とすることができる。
Claims (7)
- 電極活物質と結着剤とを有する電極活物質層が芯体表面に設けられた非水電解質二次電池用電極板において、
前記電極活物質層の厚み方向の中央領域に、前記結着剤の量が最も少ない部分を有し、且つ、当該部分から前記芯体側及び外表面側に向かって、前記電極活物質層に含まれる前記結着剤の量が連続的に増大するように前記結着剤が分布する、
ことを特徴とする非水電解質二次電池用電極板。 - 請求項1に記載の非水電解質二次電池用電極板において、
前記結着剤が均一に分布していると仮定した場合の前記電極活物質層単位厚み当たりの結着剤量を10とするとき、前記電極活物質層の芯体がわ面を基点として、前記電極活物質層の厚み方向90~100%の領域における単位厚み当たりの結着剤量が10より多い、
ことを特徴とする非水電解質二次電池用電極板。 - 請求項2に記載の非水電解質二次電池用電極板において、
前記結着剤が前記電極活物質層内に均一に分布していると仮定した場合の前記電極活物質層単位厚み当たりの結着剤量を10とするとき、
前記電極活物質層の芯体がわ面を基点として、前記電極活物質層の厚み方向45~55%の領域における単位厚み当たりの結着剤量が10未満であり、前記電極活物質層の厚み方向0~10%の領域における単位厚み当たりの結着剤量が10より多い、
ことを特徴とする非水電解質二次電池用電極板。 - 請求項1、2又は3に記載の非水電解質二次電池用電極板において、
前記電極活物質層に含まれる前記電極活物質と、前記芯体との接触面積比率が、30%以上である、
ことを特徴とする非水電解質二次電池用電極板。 - 請求項1ないし4のいずれか1項に記載の非水電解質二次電池用電極板において、
前記結着剤が、スチレンブタジエンゴム及び/又はその変性体である、
ことを特徴とする非水電解質二次電池用電極板。 - 請求項1ないし5のいずれか1項に記載の非水電解質二次電池用電極板を、正極板、負極板の少なくとも一方として用いてなる非水電解質二次電池。
- 電極活物質と、結着剤と、溶剤と、を有する第1の電極活物質スラリーを、芯体上に塗布する第1塗布工程と、
電極活物質と、結着剤と、溶剤と、を有し、前記第1の電極活物質スラリーよりも前記溶剤の質量比率が低い第2の電極活物質スラリーを、未乾燥の前記第1の電極活物質スラリーによる層の上に塗布する第2塗布工程と、
前記第2工程の後、前記溶剤を揮発除去する乾燥工程と、を備え、
前記電極活物質層の厚み方向の中央領域に、前記結着剤の量が最も少ない部分を有し、
且つ、当該部分から前記芯体側及び外表面側に向かって、前記電極活物質層に含まれる前記結着剤の量が連続的に増大するように前記結着剤が分布する、
非水電解質二次電池の製造方法。
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US10326141B2 (en) | 2015-09-16 | 2019-06-18 | Kabushiki Kaisha Toshiba | Nonaqueous electrolyte secondary battery and battery pack |
US11081700B2 (en) | 2018-08-30 | 2021-08-03 | Sanyo Electric Co., Ltd. | Nonaqueous electrolyte secondary battery and method for producing nonaqueous electrolyte secondary battery |
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