WO2016147409A1 - リチウムイオン二次電池の製造方法 - Google Patents
リチウムイオン二次電池の製造方法 Download PDFInfo
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- WO2016147409A1 WO2016147409A1 PCT/JP2015/058363 JP2015058363W WO2016147409A1 WO 2016147409 A1 WO2016147409 A1 WO 2016147409A1 JP 2015058363 W JP2015058363 W JP 2015058363W WO 2016147409 A1 WO2016147409 A1 WO 2016147409A1
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- separator
- heat
- insulating layer
- resistant insulating
- drying
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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
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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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/443—Particulate material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
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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 method for manufacturing a lithium ion secondary battery.
- a lithium ion secondary battery has a configuration in which a positive electrode and a negative electrode are arranged to face each other with an electrolyte layer holding an electrolyte solution or electrolyte gel in a separator.
- a resin porous film is often used as the separator.
- a resin porous membrane may cause thermal shrinkage due to a rise in battery temperature and a short circuit associated therewith.
- an object of the present invention is to provide a method for manufacturing a lithium ion secondary battery in which the occurrence of curling is suppressed in a separator with a heat resistant insulating layer.
- the present invention provides a non-aqueous electrolyte comprising a positive electrode, a separator with a heat-resistant insulating layer having a heat-resistant insulating layer made of oxide particles on one surface of a porous resin substrate, and a negative electrode. It is a manufacturing method of the lithium ion secondary battery which makes the said separator with a heat-resistant insulating layer impregnate.
- the amount of water contained in the separator with a heat-resistant insulating layer remains within a predetermined range. It has the drying process which dries the separator with a heat-resistant insulating layer, It is characterized by the above-mentioned.
- the moisture content of the separator with a heat resistant insulating layer is left so as to be within a predetermined range.
- the curling due to the shrinkage of the separator with the heat-resistant insulating layer can be suppressed.
- stacking a positive electrode, a separator with a heat-resistant insulating layer, and a negative electrode can be improved.
- FIG. 1 is a perspective view showing the appearance of a flat lithium ion secondary battery as an example of a secondary battery that can be manufactured according to the present embodiment.
- the flat lithium ion secondary battery 10 has a rectangular flat shape, and a positive electrode tab 27 and a negative electrode tab 25 for extracting electric power are drawn out from both sides thereof. Yes.
- the power generation element 21 is wrapped by a battery exterior material 29 of the lithium ion secondary battery 10, and the periphery thereof is heat-sealed. The power generation element 21 is sealed with the positive electrode tab 27 and the negative electrode tab 25 pulled out.
- the tab take-out position shown in FIG. 1 is not particularly limited.
- the positive electrode tab 27 and the negative electrode tab 25 may be drawn out from the same side, or the positive electrode tab 27 and the negative electrode tab 25 may be divided into a plurality of parts and taken out from each side. It is not limited to.
- the ratio of the battery area (the total area including the exterior material) to the rated capacity is 5 cm 2 / Ah or more, and the rated capacity is 3 Ah or more.
- FIG. 2 is a schematic cross-sectional view showing the internal configuration of the lithium ion secondary battery.
- a substantially rectangular power generation element 21 in which a charge / discharge reaction proceeds is sealed inside a battery exterior material 29 that is an exterior body.
- the power generation element 21 has a configuration in which the positive electrode 150, the separator 17, and the negative electrode 130 are stacked.
- the separator 17 contains a nonaqueous electrolyte (for example, a liquid electrolyte).
- the positive electrode 150 has a structure in which the positive electrode active material layers 15 are disposed on both surfaces of the positive electrode current collector 12.
- the negative electrode 130 has a structure in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11.
- the separator 17 of the present embodiment is a separator with a heat-resistant insulating layer provided with a heat-resistant insulating layer on one side of a resin porous substrate (simply referred to as the separator 17 in the description of the present embodiment).
- the laminated structure has a negative electrode 130 (negative electrode current collector 11 and negative electrode active material layer 13), a separator 17 (containing a non-aqueous electrolyte as an electrolyte), and a positive electrode 150 (positive electrode current collector 12 and positive electrode active material layer 15) laminated in this order.
- the negative electrode 130, the separator 17, and the positive electrode 150 constitute one single battery layer 19.
- the lithium ion secondary battery 10 shown in FIG. 1 indicates that six cell layers 19 are stacked. Of course, an actual battery is not limited to such a number of layers. As a result, each unit cell is configured to be electrically connected in parallel.
- the positive electrode current collector 12 and the negative electrode current collector 11 are each provided with a positive electrode current collector plate (tab) 27 and a negative electrode current collector plate (tab) 25 that are electrically connected to the respective electrodes (positive electrode 150 and negative electrode 130).
- the battery 29 has a structure that is led out of the battery exterior material 29 so as to be sandwiched between the end portions of the material 29.
- the positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.
- the positive electrode active material layer 15 includes a positive electrode active material.
- Any positive electrode active material may be used as long as it is generally used in the lithium ion secondary battery 10.
- lithium-transition metal composite oxides such as LiMn 2 O 4 , LiCoO 2 , LiNiO 2 , Li (Ni—Co—Mn) O 2 and a part of these transition metals substituted by other elements, Examples thereof include lithium-transition metal phosphate compounds and lithium-transition metal sulfate compounds.
- two or more positive electrode active materials may be used in combination.
- a lithium-transition metal composite oxide is used as the positive electrode active material.
- positive electrode active materials other than those described above may be used.
- the positive electrode active material layer 15 includes a surfactant, a conductive auxiliary agent, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), a lithium salt for increasing ion conductivity, and the like as necessary. be able to.
- a surfactant e.g., a surfactant for increasing ion conductivity, and the like.
- the negative electrode active material layer 13 includes a negative electrode active material.
- a negative electrode active material what is generally used for the lithium ion secondary battery 10 should just be used. Examples thereof include carbon materials such as graphite (graphite), soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li 4 Ti 5 O 12 ), metal materials, lithium alloy negative electrode materials, and the like. In some cases, two or more negative electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. Of course, negative electrode active materials other than those described above may be used.
- the negative electrode active material layer 13 may include a surfactant, a conductive auxiliary agent, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and other salts such as a lithium salt for increasing ionic conductivity. Further includes an additive. As these materials, those used in the well-known lithium ion secondary battery 10 can be used.
- the electrolyte layer in the present embodiment has a configuration in which the separator 17 is impregnated with an electrolytic solution.
- the separator 17 has a function of holding an electrolyte to ensure lithium ion conductivity between the positive electrode 150 and the negative electrode 130 and a function as a partition wall between the positive electrode 150 and the negative electrode 130.
- This separator 17 is a separator with a heat-resistant insulating layer provided with a heat-resistant insulating layer on one surface of a porous resin substrate. Details of the separator 17 itself will be described later.
- the electrolyte impregnated in the separator 17 is not particularly limited as long as it is a non-aqueous electrolyte used in the lithium ion secondary battery 10.
- a liquid electrolyte is used, and a lithium salt as a supporting salt is dissolved in an organic solvent.
- the organic solvent to be used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, and the like. You may mix and use.
- Li (CF 3 SO 2) 2 N Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF 3 SO 3
- LiPF 6 LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF 3 SO 3
- LiPF 6 LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF 3 SO 3
- examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, and other alloys. Further, combinations of these metals and plating materials can also be preferably used.
- the current collector is not particularly limited as long as it is used in the lithium ion secondary battery 10.
- the positive electrode lead and the negative electrode lead are made of the same metal as the current collector, and are not particularly limited.
- a laminate film containing aluminum is used as the battery outer body 29 .
- a laminate film having a three-layer structure in which polypropylene, aluminum, and nylon (registered trademark) are laminated in this order can be used as the laminate film.
- polypropylene, aluminum, and nylon registered trademark
- a known metal can case may be used.
- the separator 17 of this embodiment is a separator with a heat-resistant insulating layer.
- the separator 17 is provided with a heat-resistant insulating layer 172 on one surface of a resin porous substrate 171 (see FIG. 3).
- the resin porous substrate 171 may be a conventionally known one such as a porous sheet containing an organic resin that absorbs and holds an electrolytic solution, a woven fabric, or a non-woven fabric, and is not particularly limited.
- the porous sheet is, for example, a microporous film made of a microporous polymer.
- a polymer include a single layer film of polyolefin such as polyethylene (PE) and polypropylene (PP), or a multilayer film of these, polyimide, aramid, and the like.
- PE polyethylene
- PP polypropylene
- a polyolefin-based microporous membrane is preferable because it has a property of being chemically stable with respect to an organic solvent and can reduce the reactivity with an electrolytic solution.
- the thickness of the porous sheet cannot be uniquely defined because it varies depending on the application. However, in the use of a secondary battery for driving a motor of a vehicle, it is desirable that the thickness is 4 to 35 ⁇ m in a single layer or multiple layers. It is desirable that the fine pore diameter of this porous sheet is 1 ⁇ m or less (usually a pore diameter of about 10 nm) and the porosity is 20 to 80%.
- the woven fabric or non-woven fabric for example, polyester such as polyethylene terephthalate (PET); polyolefin such as PP or PE; polyimide, aramid, or the like can be used.
- the bulk density of the woven or non-woven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated electrolyte.
- the porosity of the woven or non-woven fabric is preferably 50 to 90%.
- the thickness of the woven or non-woven fabric is preferably 5 to 35 ⁇ m, and if the thickness is 5 ⁇ m or more, the electrolyte retention is good and the resistance is unlikely to increase excessively.
- Heat resistant insulation layer Conventionally known oxide particles are also used for the heat-resistant insulating layer 172, and are not particularly limited.
- a material having a high heat resistance having a melting point or a heat softening point of 150 ° C. or higher, preferably 240 ° C. or higher is used as the material of the oxide particles. By using such a material having high heat resistance, shrinkage due to heat of the separator 17 can be effectively prevented.
- the oxide particles have electrical insulation properties, are stable to a solvent used in the production of the electrolytic solution and the heat-resistant insulating layer 172, and are electrochemically stable that are not easily oxidized and reduced in the operating voltage range of the battery. It is preferable.
- Such oxide particles are preferably inorganic particles from the viewpoint of stability.
- the oxide particles are preferably fine particles from the viewpoint of dispersibility, and fine particles having a secondary particle size of, for example, 100 nm to 4 ⁇ m, preferably 300 nm to 3 ⁇ m, more preferably 500 nm to 3 ⁇ m can be used.
- the shape of the oxide particles is not particularly limited, and may be a nearly spherical shape, or may be a plate shape, a rod shape, or a needle shape.
- the inorganic particles (inorganic powder) having a melting point or thermal softening point of 150 ° C. or higher are not particularly limited.
- Inorganic nitrides such as aluminum nitride and silicon nitride; Slightly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate; Covalent crystals such as silicon and diamond Particles such as clay such as montmorillonite;
- the inorganic oxide may be a material derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or an artificial product thereof.
- the inorganic particles are electrically insulated from the surface of a conductive material exemplified by a metal; a conductive oxide such as SnO 2 or tin-indium oxide (ITO); a carbonaceous material such as carbon black or graphite; It is also possible to use particles having electrical insulation properties by coating with a material having a property, for example, the above-described inorganic oxide.
- a conductive oxide such as SnO 2 or tin-indium oxide (ITO)
- a carbonaceous material such as carbon black or graphite
- the separator 17 can be produced by a simple method, which is preferable.
- the inorganic oxides Al 2 O 3 , SiO 2 and aluminosilicate (aluminosilicate) are particularly preferable.
- grains may be used individually by 1 type, and may be used in combination of 2 or more types.
- the thickness of the heat-resistant insulating layer 172 is appropriately determined according to the type and application of the battery and is not particularly limited.
- the heat-resistant insulating layer 172 with the heat-resistant insulating layer 172 is attached.
- the total thickness of the entire separator is preferably about 10 to 35 ⁇ m. With such a thickness, the electrolyte retainability of the resin porous substrate 171 is maintained as it is, and an increase in resistance can be suppressed.
- FIG. 3 is a schematic side view for explaining the planar shape of the separator with a heat-resistant insulating layer.
- FIG. 4 is a schematic side view for explaining the curled shape of the separator with a heat-resistant insulating layer.
- FIG. 4 is a schematic side view of the curl seen from the direction in which the curl is seen.
- the separator 17 includes a heat-resistant insulating layer 172 on one side of the resin porous substrate 171. As shown in FIG. 3, the separator 17 is in a planar state where the length of one side of the separator 17 is L and the thickness is D. However, the length L of one side of the separator 17 is a side in a curling direction, for example, a short side direction of the rectangular separator 17. Of course, when the long side direction is more likely to curl due to the environment in the manufacturing process, the length in the long side direction is set to L.
- the size of the separator 17 is a rectangular shape having a length of at least one side of 100 mm or more (the thickness is as already described).
- the size of the separator 17 is related to the size of the electrode. For example, when the aspect ratio of the electrode, which is defined as the aspect ratio of the positive electrode active material layer, is in the range of 1 to 3, the separator 17 is also set to have a corresponding aspect ratio.
- FIG. 4 The state where the curls CL1 and CL2 are generated in the separator 17 is shown in FIG.
- the phantom line (two-dot chain line) in FIG. 4 shows a flat state (the state of FIG. 3) before the occurrence of curling.
- the curls CL1 and CL2 are generated at the end of the separator 17.
- the cause of the occurrence of such curling is that the non-aqueous electrolyte system cannot sufficiently exhibit its performance when there is a large amount of water. Therefore, it is necessary to remove the water from the separator 17 and dry it. For this reason, the separator 17 that has arrived is laminated after the moisture is removed by the drying process.
- the degree of shrinkage during drying differs between the resin porous substrate 171 of the separator 17 and the heat-resistant insulating layer 172 formed on one surface thereof. This is because the material of the resin porous substrate 171 and the heat resistant insulating layer 172 are different. Curling occurs due to the difference in the degree of contraction. Therefore, in the present embodiment, the shrinkage is reduced by leaving a predetermined amount of moisture in the separator 17 in the drying step.
- the preferable range of the curl amount can be defined by the length ratio Y after shrinkage, which is the shrinkage ratio between the resin porous substrate 171 and the heat-resistant insulating layer 172.
- a preferable range of the length ratio Y after shrinkage is to make the shape of the separator 17 satisfying the following expression (1). Therefore, in the drying process, the curl amount is controlled to be in the range of the equation (1).
- FIG. 5 is a diagram for explaining how to obtain the center angle of the curl arc and the length ratio Y after contraction.
- the length ratio Y after shrinkage is the ratio of shrinkage between the resin porous substrate 171 and the heat-resistant insulating layer 172. That is, it is the ratio between the amount of shrinkage of the resin porous substrate 171 due to drying and the amount of shrinkage of the heat resistant insulating layer. Therefore, if these contracted values can be measured, the ratio is defined as the length ratio Y after contraction.
- the length ratio Y after contraction is determined from the center angle of the arc of the curled portion caused by the contraction.
- the perpendicular line p1 with respect to the separator plane is set from the curl start point cs of the separator 17.
- a perpendicular line p2 with respect to the separator plane is set from the end point ce of the curl (that is, the end of the separator 17).
- the point where these perpendicular lines p1 and p2 intersect is determined as the center o of the arc, and the angles are determined as center angles ⁇ 1 and ⁇ 2.
- FIG. 6 is a schematic diagram for explaining the starting point cs of the curl.
- the starting point cs of the curl is a position where the start of the curl can be seen.
- a line L is drawn from the line Q extending the separator plane (planar extension line) Q along the curl to obtain the plane extension line Q and the line. This is the position where the angle ⁇ formed by L begins to be approximately 1 ° to 2 °.
- the length ratio Y after shrinkage is calculated by the following equation (2) using the obtained center angles ⁇ 1 and ⁇ 2 of the curl arc.
- FIG. 7 is a graph showing the relationship between the length ratio Y after shrinkage and the ratio X between the thickness D and the length L of the separator 17.
- FIG. 7 shows the range of the expression (1).
- the amount of water contained in the separator 17 is left in a predetermined range.
- the amount of water remaining in a predetermined range is determined so that the water content ratio W satisfies the following expression (3) using the water content ratio before and after drying.
- the water content ratio W is calculated by the following equation (4), where the water content before drying is w1 and the water content after drying is w2.
- the upper limit of the moisture content of the entire separator with a heat-resistant insulating layer is 950 ppm. This is because if the separator 17 has too much moisture, moisture remains in the battery after the battery is manufactured (sealed). Water generates gas by the reaction and electrolysis of the electrolyte components. This gas component hinders the formation of the electrode film at the time of initial charge, which leads to a decrease in battery performance. If the maximum value of the water content of the separator 17 is about 950 ppm, it does not lead to performance degradation. In the present embodiment, this 950 ppm is set as a target value in the drying process. That is, drying is performed so that the moisture content is equal to or less than the target value (however, the moisture content within a predetermined range remains).
- the lower limit value of the water content of the separator 17 is not particularly limited, and is set to the range of the above formula (3) so that curling does not occur as already described.
- the degree of curl also depends on the moisture reduction rate in the drying process. In order to suppress the occurrence of curling, it is preferable to define ((1-W) / T) as the moisture reduction rate so that the following formula (5) is satisfied.
- the moisture reduction rate is calculated using the above equations (4) and (5) by measuring the moisture content of the separator 17 at certain time intervals.
- the drying process is carried out until the target value is reached, but the moisture is easily removed at an early time from the start of drying. Therefore, the moisture reduction rate is determined by the amount of moisture in the first 30 minutes.
- the moisture reduction rate in the initial drying stage where moisture is most likely to escape is related to the occurrence of curling.
- the heat-resistant insulating layer is formed by satisfying the above expression (1) as the shape of the separator 17 and controlling the moisture content so as to satisfy at least one of the expressions (3) and (5).
- the curling of the attached separator 17 can be suppressed.
- FIG. 8 is a schematic exploded perspective view for explaining the manufacturing method of the manufacturing method of the stacked battery. In the figure, details such as current collectors, active materials, leads, and exterior materials are omitted.
- the stacked battery is formed by sequentially stacking a positive electrode 150, a separator 17, and a negative electrode 130 that are formed into a sheet shape.
- the separator 17 is curled, the curled and warped end of the separator 17 is pressed by the negative electrode 130 (or the positive electrode 150) laminated thereon and folded. And when it completes as a battery laminated body, it will be in the state laminated
- Example preparation A slurry using alumina as the heat-resistant particles was applied to one side of the PP base material, and then dried with warm air to form a heat-resistant insulating layer. A separator having a heat-resistant insulating layer on one side formed into a roll shape while being formed to a width of 200 mm was produced. The thickness D of this separator with a heat-resistant insulating layer was measured with a thickness measuring machine.
- Example 1 For each example and comparative example, the drying process was carried out by controlling the environmental temperature and humidity so as to have different dew points. In Example 1, the dew point was lowered as compared with Examples 2 and 3 and Comparative Example 2 under the conditions of the highest dew point (high humidity). In Comparative Example 1, the drying process was not performed. Table 1 shows the dew point, which is a drying condition.
- Sample collection A plurality of separators with a heat-resistant insulating layer (200 ⁇ 200 mm) prepared by the above sample preparation were prepared for each example and comparative example.
- one sheet was used for moisture content measurement, and the rest was used for length ratio after drying, evaluation of stackability, and cell performance evaluation.
- a sample was cut out to have a width of about 0.5 cm and a length of about 2.5 cm. The moisture content before drying was measured by the following measuring method.
- a sample (width of about 0.5 cm ⁇ length of about 2.5 cm) was cut out from the separator with a heat-resistant insulating layer at intervals of 30 minutes, and measured by the following measurement method. The water content was measured at 30 minute intervals until 8 hours after the start of drying.
- the moisture content was measured by the coulometric titration method using the Karl Fischer method.
- the measurement is carried out by using a Karl Fischer moisture meter CA-200 (Mitsubishi Chemical Analytech), a moisture vaporizer VA-236S (Mitsubishi Chemical Analytech), a reagent Aquamicron (registered trademark) AX, and Aquamicron (registered trademark). ) CXU was used.
- the heating temperature of the moisture vaporizer was set to 120 ° C. After the moisture vaporizer reached the target temperature, the moisture vaporizer was purged using dry nitrogen as the carrier gas. The exact weight of the sample for moisture measurement was measured. Thereafter, the sample was packed in a vial, capped, the vial was set in a moisture vaporizer, and heated to measure the moisture in the sample.
- Laminate 20 layers were alternately laminated with the positive electrode, the separator of each example comparative example, and the negative electrode so that the heat-resistant layer was directed to the positive electrode side, and the occurrence of breakage at the end of the separator was evaluated. Those that did not fold and could be laminated were regarded as having good lamination properties, and those that had been broken were regarded as defective. The results are shown in Table 2.
- FIG. 9 is a graph in which examples and comparative examples are plotted on a graph showing the relationship between the length ratio Y after shrinkage and the ratio X between the thickness and length of the separator.
- Examples 1, 2, and 3 and Comparative Example 1 are within the range in which the length ratio Y after shrinkage represented by the expression (1) is good, that is, 1-4 ⁇ X ⁇ Y ⁇ 1 + 4 ⁇ X. . From this graph and the results of the stackability and cell performance in Table 2, it can be seen that if the length ratio Y after shrinkage expressed by the formula (1) is within a good range, both the stackability and the cell performance are improved. .
- FIG. 10 is a graph showing the water content ratio W and the drying time T in Examples and Comparative Examples.
- Examples 1, 2, and 3 in which the water content ratio W is within the range of the formula (3) indicate that the stackability and cell performance are good. I understand that In addition, it is better that the rate of moisture reduction is slow, and it can be seen that when the formula (5) is satisfied, the stackability and the cell performance are improved.
- the separator with a heat-resistant insulating layer when the separator with a heat-resistant insulating layer is dried, the separator with the heat-resistant insulating layer is not completely dried, but is left so that the moisture amount falls within a predetermined range. As a result, the curling due to the shrinkage of the separator with the heat-resistant insulating layer can be suppressed. For this reason, the yield of the lithium ion secondary battery manufactured by laminating
- the length ratio after shrinkage between the porous resin substrate and the heat-resistant insulating layer in the separator with the heat-resistant insulating layer after the drying step is defined as Y, and the equation (1) already described It was made to satisfy. As a result, even if curling occurs as the shape of the separator 17, by setting the length ratio Y after contraction in the formula (1), the end of the separator due to curling does not occur.
- the moisture reduction rate in the drying process is defined as (1-W) / T, and this moisture reduction rate satisfies the formula (5) already described. .
- the occurrence of curling can be suppressed, and the length ratio Y after shrinkage can satisfy the expression (1).
- the embodiment and the example are suitable for a secondary battery in which the ratio of the battery area to the rated capacity is 5 cm 2 / Ah or more and the rated capacity is 3 Ah or more.
- Lithium ion secondary battery 11 negative electrode current collector, 12 positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 Separator, 19 cell layer, 21 power generation elements, 130 negative electrode, 150 positive electrode, 171 resin porous substrate, 172 heat-resistant insulating layer.
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Abstract
Description
図1は、本実施形態により製造し得る二次電池の1例としての扁平なリチウムイオン二次電池の外観を表した斜視図である。
正極活物質層15は、正極活物質を含む。正極活物質としては、一般的にリチウムイオン二次電池10に使用されているものであればよい。たとえば、LiMn2O4、LiCoO2、LiNiO2、Li(Ni-Co-Mn)O2およびこれらの遷移金属の一部が他の元素により置換されたもの等のリチウム-遷移金属複合酸化物、リチウム-遷移金属リン酸化合物、リチウム-遷移金属硫酸化合物などが挙げられる。場合によっては、2種以上の正極活物質が併用されてもよい。好ましくは、容量、出力特性の観点から、リチウム-遷移金属複合酸化物が、正極活物質として用いられる。なお、上記以外の正極活物質が用いられてもよいことは勿論である。
負極活物質層13は、負極活物質を含む。負極活物質としては、一般的にリチウムイオン二次電池10に使用されているものであればよい。たとえば、グラファイト(黒鉛)、ソフトカーボン、ハードカーボン等の炭素材料、リチウム-遷移金属複合酸化物(例えば、Li4Ti5O12)、金属材料、リチウム合金系負極材料などが挙げられる。場合によっては、2種以上の負極活物質が併用されてもよい。好ましくは、容量、出力特性の観点から、炭素材料またはリチウム-遷移金属複合酸化物が、負極活物質として用いられる。なお、上記以外の負極活物質が用いられてもよいことは勿論である。
本実施形態における電解質層は、セパレーター17に電解液が含浸されてなる構成を有する。
セパレーター17は、電解質を保持して正極150と負極130との間のリチウムイオン伝導性を確保する機能、および正極150と負極130との間の隔壁としての機能を有する。このセパレーター17は、樹脂多孔質基体の片面に耐熱絶縁層を備えた耐熱絶縁層付セパレーターである。セパレーター17そのものの詳細は後述する。
セパレーター17に含浸させる電解質は、リチウムイオン二次電池10に使用されている非水系電解質であれば、特に限定されない。たとえば、液体電解質が用いられ、有機溶媒に支持塩であるリチウム塩が溶解した形態を有する。用いられる有機溶媒としては、たとえば、エチレンカーボネート(EC)、プロピレンカーボネート(PC)、ジメチルカーボネート(DMC)、ジエチルカーボネート(DEC)、エチルメチルカーボネート等のカーボネート類が例示され、これらは2種類以上を混合して用いてもよい。また、リチウム塩としては、Li(CF3SO2)2N、Li(C2F5SO2)2N、LiPF6、LiBF4、LiClO4、LiAsF6、LiTaF6、LiCF3SO3等の電極の活物質層に添加されうる化合物が同様に採用されうる。
集電体(負極集電体11および正極集電体12)を構成する材料に特に制限はないが、好適には金属が用いられる。
電池外装体29としては、アルミニウムを含むラミネートフィルムが用いられる。ラミネートフィルムには、たとえば、ポリプロピレン、アルミニウム、ナイロン(登録商標)をこの順に積層してなる3層構造のラミネートフィルム等を用いることができる。そのほかリチウムイオン二次電池10において使用されるものであれば特に限定されない。また、公知の金属缶ケースを用いてもよい。
本実施形態におけるセパレーター17について説明する。
樹脂多孔質基体171としては、たとえば、電解液を吸収保持する有機樹脂を含む多孔性シート、織布または不織布など従来公知のものでよく、特に限定されない。一例を挙げると、多孔性シートとしては、たとえば、微多孔質のポリマーで構成される微多孔質膜である。このようなポリマーとしては、たとえば、ポリエチレン(PE)、ポリプロピレン(PP)などのポリオレフィンの単層膜、またはこれらの多層膜、ポリイミド、アラミドなどが挙げられる。特に、ポリオレフィン系微多孔質膜は、有機溶媒に対して化学的に安定であるという性質があり、電解液との反応性を低く抑えることができることから好ましい。
できない。しかし、車両のモータ駆動用二次電池の用途においては、単層あるいは多層で4~35μmであることが望ましい。この多孔性シートの微細孔径は、最大で1μm以下(通常、十nm程度の孔径である)、その空隙率は20~80%であることが望ましい。
耐熱絶縁層172についても従来公知の酸化物粒子が用いられ、特に限定されない。たとえば、酸化物粒子の材質としては、たとえば融点または熱軟化点が150℃以上、好ましくは240℃以上である耐熱性の高いものを用いる。このような耐熱性の高い材質を用いることで、セパレーター17の熱による収縮を有効に防止することができる。
耐熱絶縁層付セパレーターの形状について説明する。図3は耐熱絶縁層付セパレーターの平面状態の形状を説明するための概略側面図である。図4は耐熱絶縁層付セパレーターのカールした状態の形状を説明するための概略側面図である。この図4はカールが発生した状態でそのカールが見える方向から見た概略側面図である。
なお(1)式中、Xは、平面状態(カールが発生していない状態)におけるセパレーター17全体の厚さDと、カールが発生する方向の辺の長さLの比であり、X=D/Lである。
図7は、収縮後の長さ比Yと、セパレーター17の厚さDと長さLの比Xの関係を示すグラフである。図7には(1)式の範囲を示している。
ここで、水分量比Wは、乾燥前水分量をw1、乾燥後水分量をw2として、下記(4)式により算出する。
ここでセパレーター17のカールを抑制し得る水分量を水分量比として示した理由を説明する。セパレーター17に含まれる水分は、セパレーター17を製造する工程やその後保管していた場所の温度および湿度によって変化する。一方、積層電池の製造工程では、セパレーター17の水分量の最大値が規定範囲となるように乾燥させる。セパレーター17がカールするかどうかは、この乾燥の前後における水分の絶対量ではなく、どれだけ水分が減少したかによって違う。このためセパレーター17のカールを抑制し得る水分量は、水分量比として制御することが好ましいものとなるのである。
ここで、Wは上記水分量比である。Tは時間0.5hrである。
積層型電池の製造方法の製造方法について説明する。
耐熱粒子としてアルミナを用いたスラリーをPP基材の片面に塗工し、その後、温風乾燥して耐熱絶縁層を形成した。幅200mmに成形しつつロール状にした片面に耐熱絶縁層が付いたセパレーターを作製した。この耐熱絶縁層付セパレーターの厚さDを厚さ測定機で測定した。
各実施例および比較例ごとに、異なる露点となるように環境温度および湿度を制御して乾燥工程を実施し乾燥させた。実施例1が最も露点が高い(湿度が高い)条件で実施例2、3、および比較例2と露点を下げている。なお比較例1は乾燥工程を行っていない。乾燥条件である露点は表1に示した。
水分量は乾燥前と、乾燥開始後30分間隔で8時間後まで水分量を測定した。経過時間ごとの水分量から水分減少速度を得た。
収縮後の長さ比の確認
乾燥後の各実施例および比較例の耐熱絶縁層付セパレーター(200×200mm×厚さD)を耐熱層を上にして置き、除電ブラシを2回かけ除電して、24時間放置した。この耐熱絶縁層付セパレーターの収縮後の長さ比Yを求めた。収縮後の長さ比Yを求める際は、カールした状態が見える方向の側面からセパレーターを写真撮影して、画像からカールの中心角度θを定規、分度器を使用して測定した。収縮後の長さ比Yの値は表2に示した。
正極側に耐熱層が向くように正極、各実施例比較例のセパレーター、負極と交互に20層積層し、セパレーター端部の折れの発生を評価した。折れが発生せず、積層できたものを積層性良好、折れが発生したものを不良とした。結果は表2に示した。
積層性の確認の際に作製した20層の電池の各正極および負極に電極を付け、ラミネート封止材により外装し、電解液を入れて封止して二次電池を作製した。この二次電池を用いて各1サイクル充放電を行った。その後45℃恒温槽で300サイクル充放電を行いて容量維持率を求め、比較例1の容量維持率を1とした場合の値を算出し、1より大きいものを良好、1以下を不良とした。なお、比較例2は積層不良があるため二次電池を製作することができなかったので、充放電は行っていない。結果は表2に示した。
11 負極集電体、
12 正極集電体、
13 負極活物質層、
15 正極活物質層、
17 セパレーター、
19 単電池層、
21 発電要素、
130 負極、
150 正極、
171 樹脂多孔質基体、
172 耐熱絶縁層。
Claims (5)
- 正極と、
樹脂多孔質基体の一方の表面に酸化物粒子からなる耐熱絶縁層を有する耐熱絶縁層付セパレーターと、
負極とを積層し、
非水系電解質を前記耐熱絶縁層付セパレーターに含浸させるリチウムイオン二次電池の製造方法であって、
前記積層の前に、前記耐熱絶縁層付セパレーターに含まれる水分量が所定の範囲で残るように前記耐熱絶縁層付セパレーターを乾燥させる乾燥工程を有することを特徴とするリチウムイオン二次電池の製造方法。 - 前記乾燥工程は、
乾燥後の前記耐熱絶縁層付セパレーターの形状が
前記乾燥工程後の前記耐熱絶縁層付セパレーターにおける前記樹脂多孔質基体と耐熱絶縁層の収縮後の長さ比をYと定義して、
1-4πX≦Y≦1+4πX
(ただし、Xは、セパレーター厚さをD、セパレーターの辺長さをLとするときX=D/Lである)
を満たす形状となるように前記耐熱絶縁層付セパレーターを乾燥させることを特徴とする請求項1に記載のリチウムイオン二次電池の製造方法。 - 前記乾燥工程は、乾燥前水分量w1、乾燥後水分量w2としたときの水分量比Wと乾燥時間Tから、水分減少速度を((1-W)/T)と定義して、
((1-W)/T)≦1.2 (ただし、T=0.5hr)
を満たすように水分量を減少させることを特徴とする請求項1または2に記載のリチウムイオン二次電池の製造方法。 - 前記乾燥工程は、前記所定の範囲で残す水分量として、
乾燥前水分量w1、乾燥後水分量w2としたとき、水分量比W=w1/w2が、
0.4≦W<1
となるように前記耐熱絶縁層付セパレーターを乾燥させることを特徴とする請求項1~3のいずれか一つに記載のリチウムイオン二次電池の製造方法。 - 前記二次電池は、
定格容量に対する電池面積の比が5cm2/Ah以上で、かつ前記定格容量が3Ah以上であることを特徴とする請求項1~4のいずれか一つに記載のリチウムイオン二次電池の製造方法。
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