WO2023027008A1 - 固体電解質を用いたリチウムイオン二次電池用支持体、およびそれを用いたリチウムイオン二次電池 - Google Patents
固体電解質を用いたリチウムイオン二次電池用支持体、およびそれを用いたリチウムイオン二次電池 Download PDFInfo
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- WO2023027008A1 WO2023027008A1 PCT/JP2022/031514 JP2022031514W WO2023027008A1 WO 2023027008 A1 WO2023027008 A1 WO 2023027008A1 JP 2022031514 W JP2022031514 W JP 2022031514W WO 2023027008 A1 WO2023027008 A1 WO 2023027008A1
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- support
- solid electrolyte
- electrolyte layer
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- solid
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- 239000007784 solid electrolyte Substances 0.000 title claims abstract description 237
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 52
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 52
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- RNFJDJUURJAICM-UHFFFAOYSA-N 2,2,4,4,6,6-hexaphenoxy-1,3,5-triaza-2$l^{5},4$l^{5},6$l^{5}-triphosphacyclohexa-1,3,5-triene Chemical compound N=1P(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP=1(OC=1C=CC=CC=1)OC1=CC=CC=C1 RNFJDJUURJAICM-UHFFFAOYSA-N 0.000 description 1
- 229920002972 Acrylic fiber Polymers 0.000 description 1
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229920000049 Carbon (fiber) Polymers 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910015014 LiNiCoAlO Inorganic materials 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
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- 230000004523 agglutinating effect Effects 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- 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
-
- 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
-
- 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
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
- H01M10/0562—Solid materials
-
- 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
-
- 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
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
-
- 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
- H01M50/44—Fibrous material
-
- 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
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- 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
Definitions
- the present invention provides a lithium ion secondary battery support contained in a solid electrolyte layer interposed between a positive electrode and a negative electrode of a lithium ion secondary battery, and a lithium ion secondary battery comprising a solid electrolyte layer having this support. Regarding.
- a lithium-ion secondary battery using a liquid electrolyte (hereinafter referred to as "electrolytic solution”) is used.
- electrolytic solution a lithium-ion secondary battery using a liquid electrolyte
- a lithium-ion secondary battery using an electrolytic solution has a structure in which a separator is interposed between a positive electrode and a negative electrode and filled with an electrolytic solution.
- Lithium-ion secondary batteries mainly use organic electrolytes as electrolytes. Since the organic electrolyte solution is a liquid, there is concern about liquid leakage and ignition due to its combustibility. Therefore, in order to improve the safety of the lithium ion secondary battery, a lithium ion secondary battery using a solid electrolyte (hereinafter referred to as an all-solid battery) instead of an electrolytic solution has been developed. All-solid-state batteries, of course, do not leak liquid because the electrolyte is solid, and they are flame-retardant and heat-resistant compared to electrolytes, so they are attracting attention as lithium-ion secondary batteries with excellent safety. It is All-solid-state batteries are highly safe, so small-sized all-solid-state batteries are being mass-produced for wearable devices that come into direct contact with the skin.
- All-solid-state batteries are less prone to characteristic deterioration at high temperatures, eliminating the need for a cooling device. It is an advantageous secondary battery. All-solid-state batteries are expected to be further enlarged for use in electric vehicles, etc., because they are advantageous as secondary batteries with high volumetric energy density.
- the solid electrolyte layer interposed between the positive electrode and the negative electrode of an all-solid-state battery is required to have the function of ionically conducting lithium ions between the positive electrode and the negative electrode and the function of preventing a short circuit between the positive electrode active material and the negative electrode active material. .
- the thickness of the solid electrolyte layer is required to be thin in order to have excellent volumetric energy density and low internal resistance.
- a method of forming a solid electrolyte layer a method of mixing a solid electrolyte and a binder and rolling under heat to form a sheet, or a method of coating a solid electrolyte slurry on an electrode and drying it, etc. are adopted. ing.
- the solid electrolyte layer obtained by rolling under heat to form a sheet may crack during handling. or cracks will occur.
- the solid electrolyte layer is distorted and cracked during drying. Therefore, it is difficult to stably form a thin and uniform solid electrolyte layer. Unless a stable, thin and uniform solid electrolyte layer can be formed, ionic conduction deteriorates and short circuits occur.
- a thin film sheet (hereinafter referred to as a support) contains a solid electrolyte, and a solid electrolyte layer in which the solid electrolyte and the support are integrated is used in an all-solid-state battery.
- a support contains a solid electrolyte, and a solid electrolyte layer in which the solid electrolyte and the support are integrated is used in an all-solid-state battery.
- Various configurations have been proposed for all-solid-state battery supports and lithium-ion secondary battery substrates.
- Patent Literature 1 discloses a technique relating to a solid electrolyte sheet having a plurality of through holes formed by etching a film that serves as a support. It is disclosed that an all-solid-state battery with excellent energy density and output characteristics can be provided by filling the through-holes formed by etching with a solid electrolyte.
- the through-holes are filled with the solid electrolyte, so the solid electrolyte is filled only inside the formed through-holes.
- the film portion which is an insulator, remains in areas other than the through-holes, and an interface between the positive electrode or the negative electrode and the film portion that does not allow lithium ions to pass is generated.
- the interfacial resistance between the solid electrolyte sheet and the positive electrode or negative electrode tends to increase, and even an all-solid-state battery using this support has been required to further reduce the resistance of the all-solid-state battery.
- Patent Document 2 discloses a technique related to a nonwoven fabric which is a solid electrolyte sheet containing a solid electrolyte on the surface and inside of the nonwoven fabric, wherein the weight per square meter of the nonwoven fabric used is 8 g or less and the thickness is 10 to 25 ⁇ m.
- the solid electrolyte layer formed by using the nonwoven fabric described in Patent Document 2 as a support can hold the solid electrolyte necessary for ionic conduction between the positive electrode and the negative electrode while maintaining self-supporting properties, thereby producing a battery that suppresses an increase in impedance. can do.
- Patent Document 3 discloses a technique related to a solid electrolyte sheet having a porosity of 60% or more and 95% or less and a thickness of 5 ⁇ m or more and less than 20 ⁇ m, in which a heat-resistant support is filled with a solid electrolyte. It is disclosed that this solid electrolyte sheet is thin but has self-supporting properties and is excellent in heat resistance, so that it can prevent a short circuit even if it is pressed at a high temperature. In addition, since this solid electrolyte sheet can be pressed at a high temperature, it contributes to the reduction of the interfacial resistance between the solid electrolytes, and the output of the battery can be increased.
- the support of Patent Document 3 contains heat-resistant fibers such as aramid fibers and Al 2 O 3 that are less deformed by heat. It contains a large amount of binder fibers with a large vol. If the thermal dimensional change of the support is large, the support will shrink when the solid electrolyte slurry is applied to the support and the solvent is dried, resulting in irregularities on the surface of the resulting solid electrolyte layer. When a solid electrolyte layer having an uneven surface is superimposed on a positive electrode or a negative electrode, adhesion at the interface deteriorates and the internal resistance of the all-solid-state battery increases.
- heat-resistant fibers such as aramid fibers and Al 2 O 3 that are less deformed by heat. It contains a large amount of binder fibers with a large vol. If the thermal dimensional change of the support is large, the support will shrink when the solid electrolyte slurry is applied to the support and the solvent is dried, resulting in irregularities on the surface of the resulting solid electrolyte
- Patent Document 4 discloses a technology related to a nonwoven fabric base material for a lithium secondary battery separator, which is characterized by containing drawn polyester fibers and, as binder fibers, undrawn polyester fibers and wet heat adhesive fibers. . It is disclosed that by containing drawn polyester fibers, it is possible to provide a nonwoven fabric base material having excellent heat resistance, the drawn polyester fibers forming a skeleton, and excellent thermal dimensional stability. In addition, the unstretched polyester fiber is softened or melted by heat and pressure treatment such as calendering, and strongly adheres to other fibers. The wet heat adhesive fibers are disclosed as flowing or easily deformed in a wet state to exhibit an adhesive function. It is disclosed that by including these binders in the non-woven fabric substrate, it is possible to provide a non-woven fabric substrate for lithium secondary battery separators with high tensile strength and high productivity.
- Patent Document 5 describes a wet-laid nonwoven fabric containing fibrillated heat-resistant fibers having a softening point, melting point, and thermal decomposition temperature of 250°C or higher and 700°C or lower, and a dimensional change rate when heat-treated at 250°C for 50 hours.
- a technique relating to a separator for an electrochemical device is disclosed, which is characterized by a -3% to +1%.
- Patent Literature 6 discloses a technology relating to a base material for a lithium ion secondary battery separator, which is characterized by having a heat shrinkage rate of 2.0% or less at 150°C.
- the separator base material described in Patent Document 6 is used as a lithium ion battery separator by providing a coating layer containing inorganic particles on the separator base material. It is disclosed that the base material for a separator described in Patent Document 6 has a heat shrinkage rate of 2.0% or less, so that even when the separator is heated and dried during battery assembly, unevenness is less likely to occur on the separator. .
- the coating layer curls toward the thinner side. It is disclosed that the problem can be solved.
- the present invention has been made in view of the above problems.
- the object is to contribute to the reduction of interfacial resistance with a layer.
- Another object of the present invention is to obtain a solid electrolyte layer having a low internal resistance by sufficiently forming path lines of lithium ions inside the solid electrolyte layer.
- the path line of lithium ions is maintained and the resistance of the solid electrolyte layer is reduced.
- a support according to the present invention has been made for the purpose of solving the above problems, and has, for example, the following configuration. That is, the support contained in the solid electrolyte layer of the lithium ion secondary battery has a thermal dimensional change rate of ⁇ 10 to 5% in the longitudinal direction and the lateral direction of the support, and an air permeability of 1 to 50 L/cm 2 . /min. , paper or non-woven fabric having a bending resistance in the machine direction and the transverse direction after heat treatment in the range of 5 to 250 mN, respectively. Moreover, the lithium ion secondary battery of the present invention is characterized by comprising a solid electrolyte layer having the support of the above invention.
- the interfacial resistance between the positive electrode or the negative electrode and the solid electrolyte layer can be reduced by improving the thermal dimensional stability of the support. Further, by improving the permeability of the solid electrolyte into the inside of the support, it is possible to obtain a support that reduces the internal resistance of the solid electrolyte layer. Furthermore, by optimizing the bending resistance of the support after heat treatment, deformation of the support inside the solid electrolyte layer is suppressed, and by maintaining the lithium ion path lines formed inside the solid electrolyte layer, solid A support that can contribute to the reduction of the internal resistance of the electrolyte layer can be obtained. Moreover, the use of the support of the present invention in a lithium ion secondary battery can contribute to the reduction of the internal resistance of the battery.
- a support in a lithium-ion secondary battery configured as an all-solid-state battery, a support is configured which is used to form a solid electrolyte layer existing between a positive electrode and a negative electrode.
- the support of the present invention is a support contained in a solid electrolyte layer of a lithium ion secondary battery, and has a thermal dimensional change rate of -10 to 5% in the longitudinal direction and the lateral direction of the support, and an air permeability of 1. ⁇ 50 L/cm 2 /min. , paper or non-woven fabric having a bending resistance in the machine direction and the transverse direction after heat treatment in the range of 5 to 250 mN, respectively.
- the solid electrolyte layer that exists between the positive and negative electrodes is required to conduct lithium ions between the positive and negative electrodes during charging and discharging. For this purpose, it is necessary to form a lithium ion path line between the positive electrode-solid electrolyte layer, inside the solid electrolyte layer, and between the solid electrolyte layer-negative electrode. That is, if the interfacial resistance between the positive electrode-solid electrolyte layer and between the solid electrolyte layer-negative electrode can be reduced, and the internal resistance of the solid electrolyte layer can be reduced, the internal resistance of the all-solid-state battery can be lowered.
- the inventors of the present invention have found that one of the factors that hinder further reduction of the interfacial resistance between the solid electrolyte layer and the positive electrode or negative electrode in conventional supports is that unevenness occurring on the surface of the solid electrolyte layer causes It was found that the interfacial adhesion between the layer and the positive or negative electrode deteriorated.
- the unevenness of the surface of the solid electrolyte layer is caused by dimensional change of the support due to the heat during drying when the solid electrolyte slurry is applied to the support and dried.
- the positive electrode, the solid electrolyte layer, and the negative electrode can be superimposed and pressurized to increase the pressure when they are integrated.
- the body is deformed, and the path lines of lithium ions formed inside the solid electrolyte layer are cut, resulting in an increase in the internal resistance of the solid electrolyte layer.
- highly heat-resistant fibers can be used in order to increase the thermal dimensional stability of the support. As a result, the permeability of the solid electrolyte has deteriorated.
- the vertical and horizontal dimensions of the support may change.
- This thermal dimensional change is a phenomenon that occurs even when only the support is dried, and the fibers constituting the support are deformed by heating above their melting point or softening point.
- the support may have thick or thin portions, resulting in irregularities on the surface of the support.
- the support coated with the solid electrolyte slurry changes its dimensions by heating before the solvent contained in the solid electrolyte slurry is completely dried, so that the surface of the obtained solid electrolyte layer becomes uneven and the strength is reduced. occur.
- the adhesion at the interface between the positive electrode or negative electrode and the solid electrolyte layer deteriorates.
- the present inventors have found that the interfacial resistance between the solid electrolyte layer and the positive or negative electrode can be further reduced by reducing thermal dimensional change of the support and suppressing deformation. If the interfacial resistance between the solid electrolyte layer and the positive or negative electrode can be reduced, the internal resistance of the all-solid-state battery can be further reduced.
- the support of the present invention preferably has a thermal dimensional change rate in the longitudinal direction and the lateral direction of -10 to 5%. Furthermore, from the viewpoint of suppressing irregularities on the surface of the solid electrolyte layer, it is more preferable that the thermal dimensional change rate of the support in the vertical and horizontal directions is in the range of ⁇ 8 to 3%.
- the thermal dimensional change rate in the present invention refers to the thermal dimensional change rate before and after heating at 200° C. for 1 hour. Heating at 200° C. for 1 hour is a thermal condition capable of sufficiently drying the solvent used in the solid electrolyte slurry. That is, if the thermal dimensional change rate in the vertical direction and the horizontal direction of the support before and after heating at 200° C.
- the thermal dimensional change rate when there is a - (minus) indication, it indicates shrinkage, and when there is no indication, it indicates expansion.
- either the longitudinal or lateral thermal dimensional change rate of the support is more than 5% (expansion of more than 5%), it means that the support cannot maintain its shape, such as being melted by heat. show.
- the adhesiveness at the points of contact between the fibers constituting the support is lowered, which may lead to a decrease in the strength of the support. That is, practically, it is preferable that the thermal dimensional change rate of the support in the vertical direction and the horizontal direction is 5% or less.
- the inventors of the present invention have found that in order to form a lithium ion path line between the positive electrode and the negative electrode, it is important to form a solid electrolyte layer having a continuous connection from the surface of the support to the inside by the solid electrolyte. In other words, it was found that it is important not only to uniformly form the solid electrolyte on the surface of the support, but also to sufficiently fill the inside of the support with the solid electrolyte.
- By increasing the permeability of the solid electrolyte into the support lithium ion path lines are formed inside the solid electrolyte layer, and a solid electrolyte layer with low internal resistance can be formed.
- air permeability is used as an index for measuring the permeability of the solid electrolyte into the inside of the support.
- the air permeability indicates the amount of air flowing per unit area and unit time under a constant differential pressure, and the higher the air permeability, the more air is flowing. That is, the higher the permeability of the support, the higher the gas permeability of the support. It is considered that if the air permeability of the support is high, the permeability of the solid electrolyte into the inside of the support is also high. That is, a support with high air permeability can be filled with a sufficient amount of solid electrolyte inside the support.
- the support of the present invention has an air permeability of 1 to 50 L/cm 2 /min. is in the range of Furthermore, from the viewpoint of solid electrolyte permeability and uniform solid electrolyte layer formation, the air permeability is 2 to 40 L/cm 2 /min. is more preferable.
- a support having air permeability within the above range is excellent in solid electrolyte permeability, has moderate overlapping of fibers in the thickness direction, and when the solid electrolyte is permeated into the support, penetration into the interior is not hindered. . Therefore, not only can the solid electrolyte be formed on the surface of the support, but also the solid electrolyte can permeate the inside of the support. As a result, an all-solid-state battery using this support can have a low internal resistance.
- Air permeability is 1 L/cm 2 /min. If it is less than that, the solid electrolyte may not uniformly permeate the inside of the support. It is considered that it is based on the following reasons. When the solid electrolyte permeates the support, the air permeability is 1 L/cm 2 /min.
- the term "less than” means that the number of fibers constituting the support is large and dense, and resistance occurs when the solid electrolyte penetrates into the support. As a result, the solid electrolyte remains on the surface of the support, making it difficult for the solid electrolyte to permeate uniformly into the interior of the support.
- air permeability is 50 L/cm 2 /min.
- Air permeability is 50 L/cm 2 /min. is too rough to retain and reinforce the solid electrolyte, and even if the solid electrolyte is permeated, the solid electrolyte does not stay on the support. As a result, the solid electrolyte layer cannot be formed, or the distortion of the solid electrolyte layer that occurs during drying cannot be suppressed, which may lead to the generation of cracks. In other words, the support cannot hold and reinforce the solid electrolyte, and a thin and uniform solid electrolyte layer cannot be obtained, which is not preferable.
- a solid electrolyte layer using a conventional support has a lithium ion path line inside the solid electrolyte layer that is formed in advance due to deformation of the support when the positive electrode, solid electrolyte layer, and negative electrode are integrated under pressure. was cut off, and the internal resistance was high.
- the solid electrolyte layer formed by impregnating the support with the solid electrolyte slurry and drying it is pressurized in order to be integrated with the positive electrode and the negative electrode. That is, stress is applied in the plane direction of the solid electrolyte layer.
- the bending resistance of the support after heat treatment was used as an index of resistance to uneven force in the surface direction after forming the solid electrolyte layer.
- the heat treatment referred to here means heating at 200° C. for 1 hour, and is a heat condition capable of sufficiently drying the solvent used in the solid electrolyte slurry.
- the bending resistance in the present invention is obtained from the maximum pressure when a test piece is placed on a sample table with a slit width of 6.5 mm and the blade is lowered 8 mm from the surface of the sample table. In other words, the higher the maximum pressure, the more difficult it is for the support to deform.
- the support of the present invention has a bending resistance in the vertical direction and the horizontal direction after heat treatment controlled within the range of 5 to 250 mN. Furthermore, from the viewpoint of suppressing an increase in internal resistance due to pressure integration of the positive electrode, the solid electrolyte layer, and the negative electrode, it is better if the bending resistance in the vertical direction and the horizontal direction after heat treatment is in the range of 10 to 230 mN. preferable.
- a support having a bending resistance after heat treatment within the above range can withstand uneven stress applied to the solid electrolyte layer and can suppress deformation of the support. Then, the positive electrode, the solid electrolyte layer, and the negative electrode can be pressurized and integrated while maintaining the path line of the lithium ions inside the preliminarily formed solid electrolyte layer, and an increase in internal resistance can be suppressed. As a result, by using this support, the internal resistance of the all-solid-state battery can be lowered.
- the support included in the solid electrolyte layer is difficult to deform, that is, too hard.
- a change in the structure of the support may occur, such as the support breaking. If the structure of the support is changed, the solid electrolyte layer is also deformed, causing cracks, leading to breakage of lithium ion path lines and an increase in internal resistance.
- the support of the present invention is composed of paper or non-woven fabric.
- Paper is a product made by agglutinating plant fibers and other fibers.
- non-woven fabrics are made by mechanically, chemically, thermally, or combining various types of fiber webs, such as natural, regenerated, and synthetic fibers, without using a weaving machine, and using adhesives or the fusing power of the fibers themselves.
- a sheet material made by bonding fibers together In other words, since paper or non-woven fabric has a configuration in which fibers are randomly arranged, a support made of paper or non-woven fabric has voids of various sizes and through-holes of various sizes inside. I have countless.
- a support made of paper or non-woven fabric can form a solid electrolyte layer on the surface of the support and fill the interior of the support with a solid electrolyte. Therefore, a solid electrolyte layer prepared using paper or a non-woven fabric as a support is filled with the solid electrolyte not only on the surface of the support but also inside the support, and can form a good lithium ion pathway.
- the internal resistance of the solid electrolyte layer can be reduced, and the interfacial resistance between the solid electrolyte layer and the positive or negative electrode can be lowered. As a result, the internal resistance of the all-solid-state battery can be reduced.
- the thickness of the support of the present invention is preferably in the range of 5 to 40 ⁇ m. More preferably, it is in the range of 8-30 ⁇ m. If the thickness is less than 5 ⁇ m, the thickness of the solid electrolyte layer becomes thin, making it difficult to prevent a short circuit between the positive electrode and the negative electrode. Further, in order to widen the distance between the electrodes for the purpose of preventing a short circuit, a thick solid electrolyte layer can be formed on the surface of the support, but a layer of only the solid electrolyte is generated. In other words, the portion without the support may not be able to suppress the strain of the solid electrolyte layer that occurs during drying, which may lead to the generation of cracks. On the other hand, if the thickness exceeds 40 ⁇ m, the thickness of the solid electrolyte layer becomes too thick, which does not contribute to miniaturization of the all-solid-state battery.
- the density of the support is preferably in the range of 0.15-0.50 g/cm 3 . More preferably, it ranges from 0.17 to 0.48 g/cm 3 . If the density is less than 0.15 g/cm 3 , the number of fibers constituting the support is reduced and the voids in the support are increased. Therefore, the solid electrolyte does not stay on the support, and it becomes difficult to uniformly hold and reinforce the solid electrolyte. On the other hand, if the density exceeds 0.50 g/cm 3 , the penetration of the solid electrolyte into the inside of the support deteriorates, and the inside of the support may not be sufficiently filled with the solid electrolyte. Therefore, the internal resistance of the all-solid-state battery becomes high.
- the support according to the present invention preferably has a maximum penetration area of 0.001 to 0.3 mm 2 . Since the support according to the present invention is made of paper or non-woven fabric, the support has a structure in which fibers are laminated. As a result, there are portions in which fibers do not exist, that is, through portions, in the thickness direction of the support. When the solid electrolyte permeates from the front surface to the back surface of the support, it passes through the through portion of the support.
- the maximum penetration area in the present invention indicates the area of the largest penetration part of the support. In other words, the area of the innumerable penetrating portions of the support is equal to or less than the maximum penetrating area.
- a support having a maximum penetration area in the range of 0.001 to 0.3 mm 2 has excellent penetration of the solid electrolyte in the thickness direction of the support, and retains and reinforces the solid electrolyte. can form a solid electrolyte layer. If the maximum through-hole area is less than 0.001 mm 2 , the penetration of the solid electrolyte into the support in the thickness direction deteriorates, making it impossible to form a uniform solid electrolyte layer. Further, when the maximum through-hole area exceeds 0.3 mm 2 , since the through-hole is large, there are places where the solid electrolyte cannot be held on the support. As a result, cracks occur and a uniform solid electrolyte layer cannot be formed, resulting in a solid electrolyte layer with high internal resistance.
- the support according to the present invention preferably has a tensile strength of 1.0 N/15 mm or more. If the tensile strength is less than 1.0 N/15 mm, breakage is likely to occur during filling of the solid electrolyte.
- the support contains fibers having adhesive strength.
- Fibers having adhesive strength include beaten cellulose fibers, beaten polyamide fibers, synthetic resin binders, and the like.
- the adhesive force of beaten cellulose fibers includes physical bonding due to entanglement between cellulose fibers and chemical bonding due to hydrogen bonding of hydroxyl groups of cellulose.
- the adhesive strength of the beaten polyamide fibers is due to physical bonding due to entanglement of the polyamide fibers. Bonding by any fiber is preferable because it contributes to maintaining the shape of the support and developing tensile strength.
- Synthetic resin binder fibers include those that maintain the fibrous state in the state of constituting the support, and those that cannot maintain the fibrous state and become, for example, in the form of a film.
- the synthetic resin binder fibers that maintain the fiber shape in the state of constituting the support exhibit adhesive strength by thermally bonding the fiber entanglement points. Therefore, the synthetic resin binder fiber that maintains the fibrous state as a constituent material of the support can reduce breakage when forming the solid electrolyte layer, and adheres only the fiber contact points, so that the solid electrolyte penetrates into the support. difficult to inhibit.
- synthetic resin binder fibers, which cannot maintain their fibrous state in the state of forming the support are converted into a film by heat during the process of manufacturing the support.
- the resin melts due to the application of the pressure, and the fibers are fused at the entanglement points. That is, when a binder that is not in a fibrous state is used in the state of constituting the support, the binder component forms a large number of film layers in the interstices between the fibers of the support, blocking the voids when the binder function is exhibited. As a result, the permeation of the solid electrolyte into the inside of the support may be inhibited, which is not preferable.
- the material that can be used as the adhesive fiber is particularly limited as long as it does not repel the solid electrolyte slurry, does not physically or chemically adversely affect the solid electrolyte, and has insulating properties.
- Examples include beaten cellulose fibers, beaten polyamide fibers, polyamide binder fibers, polyester binder fibers, and the like.
- one or more types of fibers selected from these fibers can be used.
- the fiber does not give the fiber an insulating property, and examples thereof include organic fibers such as cellulose fibers, polyamide fibers and polyester fibers, and inorganic fibers such as glass fibers and alumina fibers.
- organic fibers such as cellulose fibers, polyamide fibers and polyester fibers
- inorganic fibers such as glass fibers and alumina fibers.
- one or more types of fibers selected from these fibers can be used. By using these fibers, it is possible to obtain a support that suppresses thermal dimensional change of the support, has excellent solid electrolyte filling properties and heat resistance, and has a suitable bending resistance after heat treatment.
- the thermal dimensional change rate of the support in the range of ⁇ 10 to 5% in the longitudinal direction and the transverse direction, for example, 20 to 100% by mass of fibers having a thermal fiber length change rate of ⁇ 8 to 1%
- the method is not limited to such methods as containing the metal and heat-treating the sheet at a temperature exceeding 200°C.
- fibers with a fiber length of 0.5 to 5 mm are used, and the basis weight is 1 to 1. Examples include, but are not limited to, a range of 12 g/m 2 and heat treatment of the sheet at over 200°C.
- the fibers constituting the support of the present invention preferably have an average fiber diameter of 1 to 20 ⁇ m.
- an average fiber diameter of 1 to 20 ⁇ m pores of various sizes can be uniformly distributed throughout the paper or nonwoven fabric.
- the method for manufacturing the support is not particularly limited, and it can be manufactured by a dry method or a wet method, but preferably a wet method in which fibers dispersed in water are deposited on a wire, dehydrated and dried to form a paper. is preferable from the viewpoint of homogeneity such as formation of the support.
- paper or wet-laid nonwoven fabric formed using a papermaking method is employed as a method for manufacturing a support.
- the papermaking form of the support is not particularly limited as long as it satisfies the thermal dimensional change rate, air permeability, bending resistance after heat treatment, thickness, and density.
- a paper-making method can be employed, and a plurality of layers formed by these paper-making methods may be combined. Additives such as a dispersant, an antifoaming agent, and a paper strength enhancer may be added during papermaking. may be subjected to post-processing.
- Method for producing support and all-solid-state battery and method for measuring properties The method for producing the support and the all-solid-state battery of the present embodiment and the method for measuring characteristics were performed under the following conditions and methods.
- CSF value CSF according to "JIS P8121-2 'Pulp-Freeness Test Method-Part 2: Canadian Standard Freeness Method' (ISO5267-2 'Pulps-Determination of drainage-Part2: 'Canadian Standard' freeness method')" values were measured.
- polyester fiber and polyester binder fiber Since the polyester fiber and polyester binder fiber are optically transparent, the fiber cannot be accurately recognized by image, and thus the fiber length cannot be accurately measured by the automatic optical analysis method described above. Therefore, the fiber lengths of polyester fibers and polyester binder fibers were measured by the following method. A preparation was prepared in which the fibers were randomly dispersed. The fiber length of the fibers on the preparation was measured using a direct scale.
- Thermal fiber length change rate [(L2-L1)/L1] x 100
- L1 Average fiber length before heating at 200°C for 1 hour
- L2 Average fiber length after heating at 200°C for 1 hour
- ⁇ thickness ⁇ The thickness of one support is measured at even intervals using a dial thickness gauge G type (measurement reaction force 2 N, probe: ⁇ 10 mm), and the average value of the measured points is the thickness of the support ( ⁇ m ).
- Basis Weight The basis weight of the absolute dry support was measured by the method specified in "JIS C 2300-2 'Cellulose paper for electrical use-Part 2: Test method' 6 Basis weight".
- Density (g/cm 3 ) W/T W: basis weight (g/m 2 ), T: thickness ( ⁇ m)
- Thermal dimensional change rate [(L2-L1)/L1] ⁇ 100 L1: length before heating at 200°C for 1 hour, L2: length after heating at 200°C for 1 hour
- LiNiCoAlO 2 ternary powder as a positive electrode active material, Li 2 SP 2 S 5 amorphous powder as a sulfide solid electrolyte, and carbon fiber as a conductive aid were mixed.
- This mixed powder was mixed with a dehydrated xylene solution in which SBR (styrene-butadiene rubber) was dissolved as a binder to prepare a positive electrode coating liquid.
- a positive electrode structure was obtained by applying a positive electrode coating liquid to an aluminum foil current collector, which is a positive electrode current collector, drying, and further rolling.
- Negative electrode structure Graphite as a negative electrode active material, Li 2 SP 2 S 5 amorphous powder as a sulfide-based solid electrolyte, PVdF (polyvinylidene fluoride) as a binder, and NMP (N-methyl-2-pyrrolidone) as a solvent. ) were used and mixed to prepare a negative electrode coating liquid.
- a negative electrode structure was obtained by applying a negative electrode coating liquid to a copper foil current collector, which is a negative electrode current collector, drying, and further rolling.
- Solid electrolyte layer Li 2 SP 2 S 5 amorphous powder as a sulfide-based solid electrolyte, SBR as a binder, and xylene as a solvent were mixed together to prepare a solid electrolyte coating solution.
- a solid electrolyte coating solution was applied to the supports of Examples, Comparative Examples, Conventional Examples, and Reference Examples shown below and dried to obtain solid electrolyte layers.
- a negative electrode structure with a size of 88 mm ⁇ 58 mm, a solid electrolyte layer with a size of 92 mm ⁇ 62 mm, and a positive electrode structure with a size of 87 mm ⁇ 57 mm are laminated, dry laminated, and laminated to form a single cell of an all-solid-state battery. got The obtained single cell was placed in an aluminum laminate film to which a terminal was attached, degassed, heat-sealed, and packed.
- the all-solid-state battery was charged to 4.0 V at a current density of 0.1 C in an environment of 25° C., and the impedance in the frequency range of 0.1 Hz to 1 MHz was measured using an LCZ meter.
- the circular arc portion of the obtained Cole-Cole plot was fitted to the shape of a semicircle with the x-axis as the base, and the numerical value at the intersection of the right end of the semicircle and the x-axis was taken as the resistance value.
- the all-solid-state battery was charged to 4.0 V at a current density of 0.1 C in an environment of 25 ° C., then discharged to 2.5 V at a current density of 0.1 C, and the discharge capacity at that time was measured. .
- Example 1 Cellulose fibers with a freeness of 650 ml, a heat fiber length change rate of 0%, and a fiber length of 1.5 mm are used to make cylinder paper, and have a thickness of 15 ⁇ m, a basis weight of 2.4 g/m 2 , and a density of 0.16 g/cm 3 . support was obtained.
- the properties of the support of Example 1 are summarized in Table 2.
- Example 2 Polyamide fibers with a freeness of 200 ml, a heat fiber length change rate of 0%, and a fiber length of 1.2 mm are used to make short mesh paper, and have a thickness of 15 ⁇ m, a basis weight of 2.9 g/m 2 , and a density of 0.19 g/cm 3 . support was obtained.
- the properties of the support of Example 2 are summarized in Table 2.
- Example 3 Using a raw material obtained by mixing 50% by mass of polyester fiber with a thermal fiber length change rate of ⁇ 1% and a fiber length of 3 mm and 50% by mass of a polyester binder fiber with a thermal fiber length change rate of ⁇ 18% and a fiber length of 3 mm, a short net Paper was made to obtain a support having a thickness of 20 ⁇ m, a basis weight of 9.8 g/m 2 and a density of 0.49 g/cm 3 .
- Table 2 The properties of the support of Example 3 are summarized in Table 2.
- Example 4 Using a raw material obtained by mixing 50% by mass of polyester fiber with a thermal fiber length change rate of ⁇ 1% and a fiber length of 3 mm and 50% by mass of a polyester binder fiber with a thermal fiber length change rate of ⁇ 18% and a fiber length of 3 mm, a circular net Paper was made. The obtained nonwoven fabric was heat-treated to obtain a support having a thickness of 20 ⁇ m, a basis weight of 9.4 g/m 2 and a density of 0.47 g/cm 3 . The properties of the support of Example 4 are summarized in Table 2.
- Example 5 Using a raw material obtained by mixing 20% by mass of polyester fiber with a thermal fiber length change rate of ⁇ 1% and a fiber length of 3 mm and 80% by mass of a polyester binder fiber with a thermal fiber length change rate of ⁇ 18% and a fiber length of 3 mm, a short net Paper was made to obtain a support having a thickness of 15 ⁇ m, a basis weight of 5.0 g/m 2 and a density of 0.33 g/cm 3 .
- the properties of the support of Example 5 are summarized in Table 2.
- Example 6 Using a raw material obtained by mixing 20% by mass of polyamide fiber with a thermal fiber length change rate of ⁇ 5% and a fiber length of 3 mm and 80% by mass of a polyamide binder fiber with a thermal fiber length change rate of ⁇ 11% and a fiber length of 3 mm, a short net Paper was made to obtain a support having a thickness of 38 ⁇ m, a basis weight of 9.1 g/m 2 and a density of 0.24 g/cm 3 .
- Table 2 The properties of the support of Example 6 are summarized in Table 2.
- Example 7 A raw material obtained by mixing 50% by mass of cellulose fibers with a freeness of 400 ml, a thermal fiber length change rate of 0%, and a fiber length of 1.1 mm, and 50% by mass of a polyester binder fiber with a thermal fiber length change rate of ⁇ 18% and a fiber length of 3 mm. Cylinder paper was made using The obtained nonwoven fabric was heat-treated to obtain a support having a thickness of 20 ⁇ m, a basis weight of 7.0 g/m 2 and a density of 0.35 g/cm 3 . The properties of the support of Example 7 are summarized in Table 2.
- Example 8 Using a raw material obtained by mixing 50% by mass of polyester fiber with a thermal fiber length change rate of ⁇ 1% and a fiber length of 3 mm and 50% by mass of a polyester binder fiber with a thermal fiber length change rate of ⁇ 18% and a fiber length of 3 mm, a circular net Paper was made. The obtained nonwoven fabric was heat-treated to obtain a support having a thickness of 9 ⁇ m, a basis weight of 2.7 g/m 2 and a density of 0.30 g/cm 3 . The properties of the support of Example 8 are summarized in Table 2.
- Example 9 Cellulose fibers having a freeness of 200 ml, a heat fiber length change rate of 0%, and a fiber length of 0.6 mm are used to make short mesh paper, which has a thickness of 9 ⁇ m, a basis weight of 1.7 g/m 2 , and a density of 0.19 g/cm 3 . support was obtained.
- the properties of the support of Example 9 are summarized in Table 2.
- Example 10 Polyamide fibers having a freeness of 0 ml, a heat fiber length change rate of 0%, and a fiber length of 0.8 mm are fourdrined to a thickness of 6 ⁇ m, a basis weight of 2.5 g/m 2 , and a density of 0.42 g/cm 3 . support was obtained.
- the properties of the support of Example 10 are summarized in Table 2.
- Example 11 Using a raw material obtained by mixing 50% by mass of polyester fiber with a thermal fiber length change rate of ⁇ 1% and a fiber length of 5 mm and 50% by mass of a polyester binder fiber with a thermal fiber length change rate of ⁇ 18% and a fiber length of 5 mm, a short net Paper was made to obtain a support having a thickness of 28 ⁇ m, a basis weight of 11.9 g/m 2 and a density of 0.43 g/cm 3 .
- the properties of the support of Example 11 are summarized in Table 2.
- Example 12 A raw material obtained by mixing 50% by mass of cellulose fiber with a freeness of 100 ml, a thermal fiber length change rate of 0%, and a fiber length of 1.1 mm and a polyester binder fiber of 50% by mass with a thermal fiber length change rate of ⁇ 18% and a fiber length of 3 mm.
- the properties of the support of Example 12 are summarized in Table 2.
- Comparative Example 1 Cellulose fibers with a freeness of 750 ml, a heat fiber length change rate of 0%, and a fiber length of 1.5 mm are used to make cylinder paper, and have a thickness of 23 ⁇ m, a basis weight of 3.0 g/m 2 , and a density of 0.13 g/cm 3 . support was obtained.
- the properties of the support of Comparative Example 1 are summarized in Table 2.
- Comparative Example 2 Polyamide fibers with a freeness of 0 ml, a heat fiber length change rate of 0%, and a fiber length of 0.8 mm are used to make a short mesh paper, which has a thickness of 4 ⁇ m, a basis weight of 1.8 g/m 2 , and a density of 0.46 g/cm 3 . support was obtained.
- the properties of the support of Comparative Example 2 are summarized in Table 2.
- Comparative Example 3 Using a raw material obtained by mixing 80% by mass of polyester fiber with a thermal fiber length change rate of ⁇ 1% and a fiber length of 3 mm and 20% by mass of a polyethylene binder fiber with a fiber length of 3 mm and a thermal fiber length change rate of unmeasurable, a short net paper was made. A support having a thickness of 15 ⁇ m, a basis weight of 5.0 g/m 2 and a density of 0.33 g/cm 3 was obtained. The properties of the support of Comparative Example 3 are summarized in Table 2.
- Comparative Example 4 Cellulose fibers having a freeness of 100 ml, a heat fiber length change rate of 0%, and a fiber length of 0.4 mm are used to make short mesh paper, which has a thickness of 5 ⁇ m, a basis weight of 0.9 g/m 2 , and a density of 0.18 g/cm 3 . support was obtained.
- the properties of the support of Comparative Example 4 are summarized in Table 2.
- Patent Document 3 A support having a thickness of 19 ⁇ m, a basis weight of 3.7 g/m 2 and a density of 0.19 g/cm 3 was obtained. Table 2 summarizes the properties of the support of Conventional Example 1.
- a support was produced by a method similar to that described in Example 2 of Patent Document 1, and a support of Conventional Example 2 was obtained.
- a polyimide film was etched to form holes of 200 ⁇ m square to obtain a support having a thickness of 30 ⁇ m, a basis weight of 8.8 g/m 2 and a density of 0.29 g/cm 3 .
- Table 2 summarizes the properties of the support of Conventional Example 2.
- Patent Document A having a thickness of 10 ⁇ m, a basis weight of 3.0 g/m 2 and a density of 0.30 g/cm 3 was obtained. Table 2 summarizes the properties of the support of Conventional Example 3.
- Examples 1 to 12 Comparative Examples 1 to 4, Conventional Examples 1 to 3, and Reference Examples 1 to 3 of Examples 1 to 12, nonwoven fabric substrates, and blended fibers for separators for electrochemical devices
- Table 1 shows the names and blending ratios.
- Table 2 shows the characteristics of each support, nonwoven fabric base material, separator for electrochemical elements, self-supporting solid electrolyte layer, and battery characteristics of each of the examples, comparative examples, conventional examples, and reference examples described above. Evaluation results are shown.
- the solid electrolyte layer using the support of each example includes the solid electrolyte layer using the support of Comparative Example 1, Comparative Example 3, and Conventional Example 3, and the solid electrolyte layer using the separator substrate of Reference Example 1.
- a self-supporting solid electrolyte layer could be formed.
- the all-solid-state battery using the support of each example is the all-solid-state battery using the support of Comparative Example 2, Comparative Example 4, Conventional Example 1, Conventional Example 2, and Reference Example 3, and the separator of Reference Example 1.
- the resistance was low and the discharge capacity was high.
- the support of each example has a lower air permeability, a higher density, and a smaller maximum penetration area than the support of Comparative Example 1.
- the air permeability of the support of Comparative Example 1 was 51.0 L/cm 2 /min. , the density is as low as 0.13 g/cm 3 , and the maximum penetration area is as large as 0.316 mm 2 . Therefore, when the solid electrolyte coating liquid is applied to the support of Comparative Example 1 and dried, the support of Comparative Example 1 cannot retain or reinforce the solid electrolyte, and the solid electrolyte remains uniformly on the support. presumably could not. Therefore, a uniform solid electrolyte layer could not be formed. As a result, an all solid state battery could not be produced using the support of Comparative Example 1.
- the air permeability is 50 L/cm 2 /min.
- a density of less than 0.15 g/cm 3 and a maximum penetration area of more than 0.3 mm 2 are found to be unfavorable.
- the support of Comparative Example 2 is thinner than the support of each example. Therefore, a short circuit occurred in the all-solid-state battery using the support of Comparative Example 2. This is probably because the support of Comparative Example 2 was as thin as 4 ⁇ m and could not prevent a short circuit between the positive electrode and the negative electrode. Various battery evaluations of the all-solid-state battery using the support of Comparative Example 2 could not be performed because a short circuit occurred. From the comparison between each example and comparative example 2, it can be seen that the thickness of the support is preferably less than 5 ⁇ m.
- the support of Comparative Example 3 had a thermal dimensional change rate of 5.6% in the vertical direction and a thermal dimensional change rate of 5.1% in the lateral direction compared to the supports of each example. .
- the solid electrolyte coating liquid was applied to the support, and the polyethylene binder contained in the support was thermally changed during drying, and the shape of the support could not be maintained and expanded. it is conceivable that. Therefore, a uniform solid electrolyte layer could not be obtained.
- the thermal dimensional change rate of the support in the longitudinal direction and in the transverse direction is preferably more than 5%.
- the all-solid-state battery using the support of Comparative Example 4 has higher resistance and lower discharge capacity than the all-solid-state batteries using the support of each example.
- the support of Comparative Example 4 has a lateral bending resistance of 4 mN, which is weaker than the support of each example. Since the support of Comparative Example 4 has a low bending resistance in the lateral direction, when the positive electrode, the solid electrolyte layer, and the negative electrode are integrated under pressure after the formation of the solid electrolyte layer, the formed path line of lithium ions is not visible. presumed to have been disconnected. Since the solid electrolyte layer, the positive electrode, and the negative electrode are not perfectly flat, when they are superimposed and pressurized, different stresses are applied to each of them.
- the all-solid-state battery using the support of Conventional Example 1 has a higher resistance and a lower discharge capacity than the all-solid-state batteries using the support of each example.
- the support of Conventional Example 1 had a longitudinal thermal dimensional change rate of -11.0% and a transverse thermal dimensional change rate of -10.7% compared to the supports of the respective examples. has contracted. Therefore, it is considered that the support of Conventional Example 1 shrunk greatly when the solid electrolyte coating liquid was applied to the support and dried.
- the thermal dimensional change rates in the vertical and horizontal directions are preferably less than -10.0%.
- the support of Conventional Example 2 is a support in which through-holes are formed in a film, unlike the support of paper or non-woven fabric in each example.
- the solid electrolyte can be filled in the through-holes of the support of Conventional Example 2, but the solid electrolyte can be filled only inside the formed through-holes.
- the interface between the film, which is an insulator, and the positive electrode or negative electrode exists at the interface between the positive electrode or negative electrode and the solid electrolyte layer.
- the support of Conventional Example 2 has a higher resistance of the all-solid-state battery than the support of each example. From the comparison between each example and conventional example 2, it can be seen that paper or non-woven fabric is suitable as a support for reducing the resistance of the all-solid-state battery.
- the support of each example has a higher tensile strength than the support of Conventional Example 3.
- the support of Conventional Example 3 was torn when the solid electrolyte coating solution was applied and excess coating solution was removed. This is probably because the support of Conventional Example 3 has a weak tensile strength of 0.7 N/15 mm. Since the solid electrolyte layer could not be formed on the support of Conventional Example 3, production and evaluation of an all-solid-state battery were not performed.
- a comparison between each example and Conventional Example 3 shows that a tensile strength of less than 1.0 N/15 mm is not preferable in order to suppress breakage of the support during production of the solid electrolyte layer.
- Reference Example 1 shows the case where the base material for a lithium ion secondary battery separator having a low heat shrinkage rate described in Patent Document 6 is used as a support for an all solid state battery.
- the separator base material of Reference Example 1 has an air permeability of 0.7 L/cm 2 /min. , the density is as high as 0.63 g/cm 3 , and the maximum penetration area is as small as 0.0008 mm 2 . Therefore, when the solid electrolyte coating liquid was applied to the separator base material of Reference Example 1, the solid electrolyte coating liquid did not permeate into the support and remained on the support surface.
- the solid electrolyte coating solution was dried while remaining on the surface of the support, and a solid electrolyte layer was formed on the surface of the support. Since the solid electrolyte layer formed on the surface of the support was dried without the support, the solid electrolyte was not reinforced, and cracks were generated. I lost my independence. Although cracks occurred in the solid electrolyte layer using the separator base material of Reference Example 1, an all-solid-state battery could be produced by laminating the positive electrode and the negative electrode. The all-solid-state battery using the separator base material of Reference Example 1 had a very high resistance compared to the all-solid-state battery using the support of each example, and the battery could not be discharged.
- the air permeability of the support was 1 L/cm 2 /min. less than 0.50 g/cm 3 density and less than 0.001 mm 2 maximum penetration area.
- Reference Example 2 shows the case where the highly heat-resistant electrochemical device separator described in Patent Document 5 is used as a support for an all-solid-state battery.
- the electrochemical device separator of Reference Example 2 had an air permeability of 0.6 L/cm 2 /min. , and the maximum penetration area is as small as 0.0003 mm 2 .
- the solid electrolyte layer using the electrochemical device separator of Reference Example 2 had cracks as in Reference Example 1, but an all-solid battery could be produced by laminating the positive electrode and the negative electrode.
- the all-solid-state battery using the separator base material of Reference Example 2 has a higher resistance than the all-solid-state battery using the support of each example and the all-solid-state battery using the separator base material of Reference Example 1. It was too high and the battery could not be discharged. This is because the bending resistance in the vertical direction after heat treatment is as high as 252 mN, that is, it is too hard. thought to have occurred. It is thought that the crack generation cut the lithium ion pass line and caused an increase in resistance. That is, from a comparison of each example with reference examples 1 and 2, it is found that bending resistances in the longitudinal direction and in the transverse direction of more than 250 mN are not preferable.
- the support of Reference Example 3 had lower air permeability than that of Example 5. As a result, the all-solid-state battery using the support of Reference Example 3 has a higher resistance and a lower discharge capacity than the all-solid-state batteries using the support of each example.
- the support of Reference Example 3 is a support containing 20% by mass of polyvinyl alcohol fiber in addition to polyester fiber and polyester binder fiber. Polyvinyl alcohol fibers are effective fibers for improving tensile strength. Polyvinyl alcohol fibers can reinforce the fiber contact points and improve the tensile strength of the support by changing shape due to wet heat.
- the polyvinyl alcohol fibers are not in a fibrous state when forming the support, but instead form a large number of film layers inside the support, closing the interstices between the fibers. As a result, it is thought that the air permeability is lowered and the permeation of the solid electrolyte coating solution into the inside of the support is inhibited. In other words, from the comparison between Example 5 and Reference Example 3, it is understood that the blending of a binder that cannot retain the fibrous state is not preferable.
- the thermal dimensional change rate of the support in the longitudinal direction and the lateral direction is -10 to 5%, respectively, and the air permeability is 1 to 50 L/cm 2 /min.
- the air permeability is 1 to 50 L/cm 2 /min.
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Abstract
Description
しかしながら、特許文献1の固体電解質シートを作製する場合、固体電解質を貫通孔に充填するため、固体電解質は、形成された貫通孔の内部にのみ充填される。そのため、貫通孔以外は絶縁物であるフィルム部が残存しているため、正極もしくは負極と、フィルム部とによる、リチウムイオンを通せない界面が生じてしまう。
つまり、固体電解質シートと、正極もしくは負極との界面抵抗は高くなりやすく、この支持体を用いた全固体電池であっても、更なる全固体電池の低抵抗化が求められていた。
特許文献2に記載の不織布を支持体として形成した固体電解質層は、自立性を有しながら、正極-負極間のイオン伝導に必要な固体電解質を保持でき、インピーダンスの上昇を抑えた電池を作製することができる。
延伸ポリエステル繊維を含有することで、耐熱性に優れ、延伸ポリエステル繊維が骨格を形成し、熱寸法安定性に優れた不織布基材を提供できると開示されている。
また、未延伸ポリエステル繊維は、カレンダー等の熱圧処理により、軟化又は溶融し、その他繊維と強固に接着する。湿熱接着性繊維は、湿潤状態において、流動又は容易に変形して、接着機能を発現する、と開示されている。不織布基材に、これらバインダーを含有することで、引張強度が高く、生産性の高いリチウム二次電池セパレータ用不織布基材を提供できると開示されている。
加えて、不織布基材に含まれる湿熱接着性繊維は、上述の通り、接着機能発現に際し、流動又は変形を経るため、この不織布基材の中の湿熱接着性繊維は繊維状態を保持できておらず、繊維間隙を封鎖してしまう場合があった。更に、繊維形状を保持できないバインダー繊維を多く含むと、密度が高くなってしまう。その結果、固体電解質の不織布基材内部への浸透が不十分となり、固体電解質を不織布基材内部に均一に充填することが困難なため、電池の内部抵抗が高くなってしまっていた。
特許文献6に記載のセパレータ用基材は、熱収縮率が2.0%以下であることによって、電池組立時にセパレータが加熱乾燥された場合でも、セパレータに凹凸が発生しにくいと開示されている。更に、セパレータ用基材の両面に塗工層を有したセパレータの場合には、電池組立時の加熱乾燥時に、セパレータに凹凸が発生する問題に加え、塗工層の厚みが薄い方にカールする課題も解決できると開示されている。
即ち、リチウムイオン二次電池の固体電解質層に含まれる支持体であって、支持体の縦方向および横方向の熱寸法変化率がそれぞれ-10~5%、通気度が1~50L/cm2/min.、熱処理後の縦方向および横方向の剛軟度がそれぞれ5~250mNの範囲の紙もしくは不織布であることを特徴とする。
また、本発明のリチウムイオン二次電池は、上記発明の支持体を有した固体電解質層を備えていることを特徴とする。
また、本発明の支持体をリチウムイオン二次電池に用いることで、電池の内部抵抗低減に寄与できる。
本発明の支持体は、リチウムイオン二次電池の固体電解質層に含まれる支持体であって、支持体の縦方向および横方向の熱寸法変化率がそれぞれ-10~5%、通気度が1~50L/cm2/min.、熱処理後の縦方向および横方向の剛軟度がそれぞれ5~250mNの範囲の紙もしくは不織布である。
一方、支持体の熱寸法安定性を高めるために、耐熱性の高い繊維を使用することもできるが、取り扱い性に優れるシートを形成させるためには、熱寸法変化の大きいバインダー繊維を多く含有する必要があり、その結果、固体電解質の浸透性が悪化してしまった。
本発明における熱寸法変化率は200℃、1時間加熱前後の熱寸法変化率を指す。200℃、1時間の加熱は、固体電解質スラリーに用いられる溶媒を十分に乾燥できる熱条件である。つまり、200℃、1時間加熱前後の、支持体の縦方向および横方向の熱寸法変化率がそれぞれ-10~5%の範囲であれば、得られる固体電解質層表面の凹凸の発生を抑制することができる。
そして、正極もしくは負極と、固体電解質層とを一体化させる際の界面の密着性を良好にでき、正極もしくは負極と、固体電解質層との界面抵抗を低くすることができる。
なお、熱寸法変化率において-(マイナス)表示がある場合は収縮を示し、表示がない場合は膨張を示す。
なお、支持体の縦方向および横方向の熱寸法変化率のいずれかが5%超(5%超の膨張)の場合は、支持体が熱によって融解した等、形状を維持できていないことを示す。また、支持体を構成する繊維同士の接点での接着性が低下し、支持体の強度低下を招くこともある。つまり、現実的には、支持体の縦方向および横方向の熱寸法変化率はそれぞれ5%以下であることが好ましい。
従来の支持体は、支持体内部に空隙は存在するものの、支持体表面の開口部が小さい等の場合があり、固体電解質を支持体表面から支持体の内部に十分に浸透できなかったと考えられる。その結果、支持体の内部に固体電解質によるリチウムイオンのパスラインを形成できず、固体電解質層の内部抵抗が高くなってしまっていた。
上記範囲の通気度を有する支持体は、固体電解質の浸透性に優れ、厚さ方向に繊維の重なりが適度にあって、固体電解質を支持体に浸透させた場合、内部への浸透が阻害されない。そのため、固体電解質を支持体表面に形成させることはもちろん、固体電解質を支持体の内部に浸透させることができる。その結果、この支持体を用いた全固体電池は、内部抵抗を低くすることができる。
固体電解質を支持体に浸透する場合、通気度が1L/cm2/min.未満というのは、支持体を構成する繊維本数が多く、緻密であり、支持体内部へ固体電解質を浸透する際抵抗となってしまう。その結果、支持体表面に固体電解質が留まり、固体電解質の支持体内部への均一な浸透が困難になる。
従来の支持体を用いた固体電解質層は、正極、固体電解質層、負極を加圧一体化する際に、支持体が変形することにより、予め形成された固体電解質層内部のリチウムイオンのパスラインが切断されてしまい、内部抵抗が高くなっていた。
支持体に、固体電解質スラリーを浸透させ、乾燥することで形成された固体電解質層は、正極、負極と一体化するために、加圧が成される。つまり、固体電解質層の面方向に対して、応力が加えられる。この応力は、固体電解質層、正極、負極が完全な平面ではないため、固体電解質層の面に対して完全に均一なものではない。つまり、加圧一体化する際には、固体電解質層の面に対して、力の強い箇所と、弱い箇所とが生じてしまう。本発明の発明者らは、その結果、固体電解質層内部の支持体が力に応じて変形してしまい、固体電解質層にクラックが生じ、固体電解質層内部に形成されたリチウムイオンパスラインが切断されてしまうことを見出した。
紙は、植物繊維、その他の繊維を膠着させて製造したものを指す。また、不織布は、織機を使わずに、天然、再生、合成繊維など各種の繊維ウェブを機械的、化学的、熱的、またはそれらの組合せによって処理し、接着剤又は繊維自体の融着力によって構成繊維を互いに接合して作ったシート状材料を指す。
つまり、紙もしくは不織布は、繊維がランダムに配置された構成であるので、紙もしくは不織布で構成された支持体は、その内部に、様々な大きさの空隙や、様々な大きさの貫通孔を無数有している。そのため、固体電解質は、支持体表面に留まるもの、支持体内部に浸透し留まるもの、浸透する表面側から貫通孔を通り抜け、裏面側まで浸透するものが存在し、それぞれが連続している。つまり、紙もしくは不織布で構成された支持体は、支持体の表面に固体電解質層を形成させることができ、かつ支持体内部に固体電解質を充填することができる。
そのため、紙もしくは不織布を支持体として作製した固体電解質層は、固体電解質が支持体の表面はもちろん、支持体内部にも充填されており、良好なリチウムイオンパスラインを形成できる。その結果、固体電解質層の内部抵抗の低減とともに、固体電解質層と、正極もしくは負極との界面抵抗を低くできる。結果として、全固体電池の内部抵抗の低減につなげることができる。
厚さが5μm未満の場合、固体電解質層の厚さが薄い固体電解質層となってしまうため、正極-負極間の短絡を防止することが困難となる。また、短絡防止を目的に極間距離を広げるため、支持体表面に厚く固体電解質層を形成することもできるが、固体電解質のみの層が生じる。つまり、支持体のない部分は、乾燥時に生じる固体電解質層のひずみを抑制できなかったりして、クラックの発生につながる場合がある。一方、厚さが40μm超の場合、固体電解質層の厚さが厚くなってしまい、全固体電池の小型化に寄与しない。
密度が0.15g/cm3未満の場合、支持体を構成する繊維本数が少なくなり、支持体中の空隙が多くなる。そのため、固体電解質が支持体に留まらず、固体電解質を均一に保持、補強することが困難となる。一方、密度が0.50g/cm3超の場合、固体電解質の支持体内部への浸透性が悪化し、固体電解質を支持体内部に十分充填できない場合がある。そのため、全固体電池の内部抵抗が高くなってしまう。
本発明に係る支持体は、紙もしくは不織布から構成されるため、支持体は繊維が積層した構造を有している。その結果、支持体の厚さ方向には、繊維が存在しない部分、つまり貫通部が存在する。固体電解質は、支持体の表面から裏面に浸透する際には、支持体の貫通部を通り抜ける。
本発明における最大貫通面積は、支持体が有する最も大きな貫通部の面積を示す。つまり、支持体が有する無数の貫通部の面積は、最大貫通面積以下である。最大貫通面積が、0.001~0.3mm2の範囲の支持体は、支持体の厚さ方向への固体電解質の浸透性に優れ、かつ固体電解質の保持、補強が成されるため、均一に固体電解質層を形成できる。
最大貫通面積が0.001mm2未満の場合、支持体への固体電解質の厚さ方向への浸透性が悪化し、均一に固体電解質層が形成できなくなる。また、最大貫通面積が0.3mm2超の場合、貫通部が大きいため、支持体上に固体電解質を保持できない箇所が生じてしまう。その結果、クラックの発生や均一な固体電解質層が形成できなくなり、内部抵抗の高い固体電解質層になってしまう。
叩解したセルロース繊維の接着力は、セルロース繊維同士の交絡による物理結合と、セルロースが有する水酸基の水素結合による化学結合とがある。また、叩解したポリアミド繊維の接着力は、ポリアミド繊維同士の交絡による物理結合がある。いずれの繊維による結合も、支持体の形態維持や、引張強さの発現に寄与するので好ましい。
支持体を構成する状態で、繊維形状を保持している合成樹脂バインダー繊維は、繊維交絡点を熱接着することによって、接着力を発現する。そのため、支持体の構成材料として繊維状態を保持した合成樹脂バインダー繊維は、固体電解質層を形成する際の破断を低減でき、かつ繊維接点のみを接着するため、固体電解質の支持体内部への浸透を阻害しにくい。
一方、支持体を構成する状態で繊維状態を保持できない合成樹脂バインダー繊維は、支持体製造工程で、繊維が熱で膜状に変化し、繊維を構成する樹脂の融点、または軟化点近傍の熱がかかることで樹脂が溶融し、繊維の交絡点で融着する。つまり、支持体を構成する状態において、繊維状態ではないバインダーを用いた場合、バインダー機能発現にあたり、バインダー成分が支持体の繊維間隙にフィルム層を多数形成する等、空隙を封鎖してしまう。その結果、固体電解質の支持体内部への浸透を阻害してしまう場合があり、好ましくない。
その結果、固体電解質の浸透性、熱処理後の剛軟度に優れ、かつ均一な厚さの支持体を形成することができる。
本発明を実施するための形態では、支持体の製造方法として、抄紙法を用いて形成した紙もしくは湿式不織布を採用した。支持体の抄紙形式は、熱寸法変化率や通気度、熱処理後の剛軟度、厚さ、密度を満足することができれば、特に限定はなく、長網抄紙や短網抄紙、円網抄紙といった抄紙形式が採用でき、またこれらの抄紙法によって形成された層を複数合わせたものであってもよい。また、抄紙に際しては、分散剤や消泡剤、紙力増強剤等の添加剤を加えてもよく、紙層形成後に紙力増強加工、親液加工、カレンダー加工、熱カレンダー加工、エンボス加工等の後加工を施してもよい。
本実施の形態の支持体および全固体電池の作製方法および特性の測定方法は、以下の条件および方法で行った。
「JIS P8121-2『パルプ-ろ水度試験法-第2部:カナダ標準ろ水度法』(ISO5267-2『Pulps-Determination of drainability-Part2:“Canadian Standard”freeness method』)」に従って、CSF値を測定した。
〔繊維の繊維長〕
「JIS P 8226-2『パルプ-光学的自動分析法による繊維長測定方法-第2部:非偏光法』」(ISO16065-2『Pulps-Determination of Fibre length by automated optical analysis-Part2:Unpolarized light method』)に記載された装置、ここではFiber Tester PLUS(Lorentzen&Wettre製)を用いて測定し、長さ荷重平均繊維長を繊維の繊維長とした。
ポリエステル繊維、ポリエステルバインダー繊維は、光学的に透明なため、繊維を正確に画像で認識できないため、上記の光学的自動分析法による繊維長測定を正確に行うことができなかった。そのため、ポリエステル繊維およびポリエステルバインダー繊維について、下記方法にて繊維長を測定した。
無作為に繊維を分散させたプレパラートを作製した。プレパラート上の繊維の繊維長を、直接スケールを用いて測定した。
200℃×1時間の加熱前後の平均繊維長を測定した。そして。下記の式により、熱繊維長変化率を算出した。
熱繊維長変化率(%)=[(L2-L1)/L1]×100
L1:200℃×1時間加熱前の平均繊維長
L2:200℃×1時間加熱後の平均繊維長
支持体1枚の厚さを、ダイヤルシックネスゲージGタイプ(測定反力2N、測定子:φ10mm)を用いて均等な間隔で測定し、さらに測定箇所の平均値を、支持体の厚さ(μm)とした。
「JIS C 2300-2 『電気用セルロース紙-第2部:試験方法』 6 坪量」に規定された方法で、絶乾状態の支持体の坪量を測定した。
以下の式を用いて、支持体の密度を計算した。
密度(g/cm3)=W/T
W:坪量(g/m2)、T:厚さ(μm)
以下の式を用いて、支持体の空隙率を計算した。なお、支持体を構成する材料を複数混用している場合には、混用率に比例した計算を行って構成繊維の平均比重を求めてから、算出した。
空隙率(%)=(1-(D/S))×100
D:支持体密度(g/cm3)、S:構成繊維の比重(g/cm3)
「JIS L 1096 『織物及び編物の生地試験方法』通気性 A法(フラジール形式)」に規定された方法で、支持体の通気度を測定した。
5mm×5mmの範囲から、任意の貫通部を100個抽出した。抽出した貫通部を多角形として近似し、その多角形の面積を算出して貫通面積とした。測定した100個の貫通面積のうち最も大きい面積を最大貫通面積とした。
支持体を100mm×100mmに切り出した試験片の、縦方向および横方向の長さを測定した。次に、支持体の試験片を200℃で1時間加熱して、加熱後の試験片の各長さを測定した。下記の式により、縦方向および横方向のそれぞれの熱寸法変化率を算出した。
熱寸法変化率(%)=[(L2-L1)/L1]×100
L1:200℃×1時間加熱前の長さ、L2:200℃×1時間加熱後の長さ
200℃で1時間加熱したサンプルを200×200mmに切り出した。得られた試験片を「JIS L 1096『織物及び編物の生地試験方法』 8.21.5 剛軟度 E法(ハンドルオメーター法)」に規定された方法で、熱処理後の縦方向および横方向それぞれの剛軟度を測定した。
「JIS P 8113 『紙及び板紙-引張特性の試験方法-第2部:定速伸張法』」(ISO1924-2『Paper and board-Determination
of tensile properties-Part2:Constant rate of elongati on method』)に規定された方法で、試験幅15mmで、支持体の縦方向(製造方向)の最大引張荷重を測定し、支持体の引張強さとした。
以下に示す各実施例、比較例、従来例、参考例の支持体を用いて、全固体電池を作製した。
具体的な作製方法は、以下の通りである。
正極活物質としてLiNiCoAlO2三元系粉末を、硫化物系固体電解質としてLi2S-P2S5非晶質粉末を、導電助剤として炭素繊維を、それぞれ用いて混合した。この混合粉末に、結着剤としてSBR(スチレンブタジエンゴム)が溶解した脱水キシレン溶液を混合し、正極塗工液を作製した。正極集電体であるアルミ箔集電体に、正極塗工液を塗工、乾燥し、更に圧延することで、正極構造体を得た。
負極活物質として黒鉛を、硫化物系固体電解質としてLi2S-P2S5非晶質粉末を、結着剤としてPVdF(ポリフッ化ビニリデン)を、溶媒としてNMP(N-メチル-2-ピロリドン)を、それぞれ用いて混合し、負極塗工液を作製した。負極集電体である銅箔集電体に、負極塗工液を塗工、乾燥し、更に圧延することで、負極構造体を得た。
硫化物系固体電解質としてLi2S-P2S5非晶質粉末を、結着剤としてSBRを、溶媒としてキシレンを、それぞれ用いて混合し、固体電解質塗工液を作製した。
以下に示す、実施例、比較例、各従来例、参考例の支持体に、固体電解質塗工液を塗工して、乾燥し、固体電解質層を得た。
作製したそれぞれの固体電解質層について、自立性の評価を行った。
作製した大きさ92mm×62mmの固体電解質層を、水平に持ち上げことができるか評価した。固体電解質層を、形状を保持したまま水平に持ち上げることができた場合を〇として、水平に持ち上げた際に状態が保持されていなかった場合を×とした。
大きさ88mm×58mmの負極構造体、大きさ92mm×62mmの固体電解質層、大きさ87mm×57mmの正極構造体を積層し、ドライラミネート加工を行い、貼り合わせることにより、全固体電池の単セルを得た。
得られた単セルを、端子を取り付けたアルミニウムラミネートフィルムに入れ、脱気、ヒートシールを行いパックした。
作製した全固体電池の具体的な性能評価は、以下の条件および方法で行った。
全固体電池に対して、25℃の環境下で0.1Cの電流密度で4.0Vまで充電を行い、LCZメーターを用いて、周波数0.1Hz~1MHzの範囲のインピーダンスを測定した。得られたコールコールプロットの円弧部分を、x軸を底辺とした半円の形にフィッティングし、半円の右端とx軸とが交わる部分の数値を抵抗値とした。
全固体電池に対して、25℃の環境下で0.1Cの電流密度で4.0Vまで充電を行い、その後0.1Cの電流密度で2.5Vまで放電し、その時の放電容量を測定した。
濾水度650ml、熱繊維長変化率0%、繊維長1.5mmのセルロース繊維を用いて、円網抄紙し、厚さ15μm、坪量2.4g/m2、密度0.16g/cm3の支持体を得た。実施例1の支持体の特性を表2にまとめた。
濾水度200ml、熱繊維長変化率0%、繊維長1.2mmのポリアミド繊維を用いて、短網抄紙し、厚さ15μm、坪量2.9g/m2、密度0.19g/cm3の支持体を得た。実施例2の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維50質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維50質量%とを混合した原料を用いて、短網抄紙し、厚さ20μm、坪量9.8g/m2、密度0.49g/cm3の支持体を得た。実施例3の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維50質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維50質量%とを混合した原料を用いて、円網抄紙した。得られた不織布に熱処理を行い、厚さ20μm、坪量9.4g/m2、密度0.47g/cm3の支持体を得た。実施例4の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維20質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維80質量%とを混合した原料を用いて、短網抄紙し、厚さ15μm、坪量5.0g/m2、密度0.33g/cm3の支持体を得た。実施例5の支持体の特性を表2にまとめた。
熱繊維長変化率-5%、繊維長3mmのポリアミド繊維20質量%と、熱繊維長変化率-11%、繊維長3mmのポリアミドバインダー繊維80質量%とを混合した原料を用いて、短網抄紙し、厚さ38μm、坪量9.1g/m2、密度0.24g/cm3の支持体を得た。実施例6の支持体の特性を表2にまとめた。
濾水度400ml、熱繊維長変化率0%、繊維長1.1mmのセルロース繊維50質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維50質量%とを混合した原料を用いて、円網抄紙した。得られた不織布に熱処理を行い、厚さ20μm、坪量7.0g/m2、密度0.35g/cm3の支持体を得た。実施例7の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維50質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維50質量%とを混合した原料を用いて、円網抄紙した。得られた不織布に熱処理を行い、厚さ9μm、坪量2.7g/m2、密度0.30g/cm3の支持体を得た。実施例8の支持体の特性を表2にまとめた。
濾水度200ml、熱繊維長変化率0%、繊維長0.6mmのセルロース繊維を用いて、短網抄紙し、厚さ9μm、坪量1.7g/m2、密度0.19g/cm3の支持体を得た。実施例9の支持体の特性を表2にまとめた。
濾水度0ml、熱繊維長変化率0%、繊維長0.8mmのポリアミド繊維を用いて、長網抄紙し、厚さ6μm、坪量2.5g/m2、密度0.42g/cm3の支持体を得た。
実施例10の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長5mmのポリエステル繊維50質量%と、熱繊維長変化率-18%、繊維長5mmのポリエステルバインダー繊維50質量%とを混合した原料を用いて、短網抄紙し、厚さ28μm、坪量11.9g/m2、密度0.43g/cm3の支持体を得た。実施例11の支持体の特性を表2にまとめた。
濾水度100ml、熱繊維長変化率0%、繊維長1.1mmのセルロース繊維50質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維50質量%を混合した原料を用いて、短網抄紙し、厚さ25μm、坪量11.0g/m2、密度0.44g/cm3の支持体を得た。実施例12の支持体の特性を表2にまとめた。
濾水度750ml、熱繊維長変化率0%、繊維長1.5mmのセルロース繊維を用いて、円網抄紙し、厚さ23μm、坪量3.0g/m2、密度0.13g/cm3の支持体を得た。比較例1の支持体の特性を表2にまとめた。
濾水度0ml、熱繊維長変化率0%、繊維長0.8mmのポリアミド繊維を用いて、短網抄紙し、厚さ4μm、坪量1.8g/m2、密度0.46g/cm3の支持体を得た。
比較例2の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維80質量%と、熱繊維長変化率測定不能、繊維長3mmのポリエチレンバインダー繊維20質量%とを混合した原料を用いて、短網抄紙し、厚さ15μm、坪量5.0g/m2、密度0.33g/cm3の支持体を得た。比較例3の支持体の特性を表2にまとめた。
濾水度100ml、熱繊維長変化率0%、繊維長0.4mmのセルロース繊維を用いて、短網抄紙し、厚さ5μm、坪量0.9g/m2、密度0.18g/cm3の支持体を得た。比較例4の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維15質量%と熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維85質量%とを混合した原料を用いて、特許文献3の実施例1に記載の支持体を参考に、円網抄紙し、厚さ19μm、坪量3.7g/m2、密度0.19g/cm3の支持体を得た。従来例1の支持体の特性を表2にまとめた。
特許文献1の実施例2に記載の方法と同様の方法で製造した支持体を作製し、従来例2の支持体を得た。従来例2では、ポリイミドフィルムをエッチング処理して、200μm角の穴を形成して、厚さ30μm、坪量8.8g/m2、密度0.29g/cm3の支持体を得た。従来例2の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維85質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維15質量%とを混合した原料を用いて、特許文献2の実施例1に記載の支持体の製造方法を参考に、円網抄紙し、厚さ10μm、坪量3.0g/m2、密度0.30g/cm3の支持体を得た。従来例3の支持体の特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維70質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維30質量%とを混合した原料を用いて、特許文献6の不織布基材1の製造方法を参考に、円網抄紙し、熱カレンダー処理、熱処理を行い、厚さ13μm、坪量8.2g/m2、密度0.63g/cm3の不織布基材を得た。参考例1の不織布基材の特性を表2にまとめた。
濾水度0ml、熱繊維長変化率0%、繊維長0.7mmのポリアミド繊維20質量%と、熱繊維長変化率-10%、繊維長3mmのアクリル繊維20質量%と、熱繊維長変化率0%、繊維長5mmのポリアミド繊維50質量%と、濾水度0ml、熱繊維長変化率0%、繊維長0.2mmのセルロース繊維10質量%とを混合した原料を用いて、特許文献5の電気化学素子用セパレータ1の製造方法を参考に、円網抄紙し、厚さ25μm、坪量12.2g/m2、密度0.48g/cm3の電気化学素子用セパレータを得た。参考例2の電気化学素子用セパレータの特性を表2にまとめた。
熱繊維長変化率-1%、繊維長3mmのポリエステル繊維40質量%と、熱繊維長変化率-18%、繊維長3mmのポリエステルバインダー繊維40質量%と、熱繊維長変化率測定不能、繊維長3mmのポリビニルアルコール繊維20質量%を混合した原料を用いて、短網抄紙し、厚さ15μm、坪量5.0g/m2、密度0.33g/cm3の支持体を得た。参考例3の支持体の特性を表2にまとめた。
比較例1の支持体の通気度は51.0L/cm2/min.と高く、密度が0.13g/cm3と低く、かつ最大貫通面積が0.316mm2と大きい。そのため、比較例1の支持体に固体電解質塗工液を塗工、乾燥した際に、比較例1の支持体が固体電解質を保持、補強できず、固体電解質が支持体に均一に留まることができなかったと考えられる。そのため、均一な固体電解質層を形成することができなかった。その結果、比較例1の支持体を用いて全固体電池を作製することができなかった。
各実施例と比較例1との比較から、通気度50L/cm2/min.超、密度0.15g/cm3未満、最大貫通面積0.3mm2超が好ましくないと分かる。
比較例4の支持体は横方向の剛軟度が弱いため、固体電解質層を形成した後、正極、固体電解質層、負極を加圧一体化した際に、形成されたリチウムイオンのパスラインが切断されたと考えられる。固体電解質層、正極、負極は、完全な平面ではないため、これらを重ね合わせ、加圧すると、それぞれに対して、力の強弱のある応力が加えられる。その結果、強い応力が支持体に局所的に加えられると、支持体の一部が変形してしまい、それに追随して、形成されたリチウムイオンパスラインが切断されたと考えられる。
つまり、各実施例と比較例4との比較から、縦方向および横方向の剛軟度はそれぞれ5mN未満が好ましくないと分かる。
従来例1の支持体は、各実施例の支持体と比較して、縦方向の熱寸法変化率が-11.0%、横方向の熱寸法変化率が-10.7%と、支持体が収縮した。そのため、従来例1の支持体は、支持体に固体電解質塗工液を塗工し、乾燥した際に、支持体が大きく収縮したと考えられる。その結果、得られた固体電解質層表面には大きな凹凸が生じ、正極、固体電解質層、負極を加圧一体化する際に、正極もしくは負極と、固体電解質層との界面の密着性が悪化し、界面抵抗が高くなった影響であると考えられる。
つまり、各実施例と従来例1との比較から、縦方向および横方向の熱寸法変化率はそれぞれ-10.0%未満が好ましくないと分かる。
各実施例と従来例2との比較から、全固体電池の抵抗を低減するためには、支持体として、紙もしくは不織布が適していることが分かる。
従来例3の支持体は、固体電解質塗工液を塗工し、余分な塗工液を除去する際に、破れが生じた。これは、従来例3の支持体の引張強さが0.7N/15mmと弱いことが原因と考えられる。従来例3の支持体は、固体電解質層の形成ができなかったため、全固体電池の作製、評価は行っていない。
各実施例と、従来例3との比較から、固体電解質層製造時の支持体の破断を抑制するためには、引張強さは1.0N/15mm未満が好ましくないと分かる。
参考例1のセパレータ用基材は、各実施例と比較して、通気度が0.7L/cm2/min.と低く、密度が0.63g/cm3と高く、更に最大貫通面積が0.0008mm2と小さい。そのため、固体電解質塗工液を参考例1のセパレータ用基材に塗工した際に、固体電解質塗工液が支持体内部に浸透せず、支持体表面に留まっていた。そのため、固体電解質塗工液が支持体表面上に留まった状態で乾燥され、支持体表面上に固体電解質層が形成されていた。そして、支持体表面に形成された固体電解質層は支持体がない状態で乾燥されたことから、固体電解質が補強されなかったため、クラックが生じ、固体電解質層を持ち上げた際に、割れが生じてしまい、自立性が無かった。
参考例1のセパレータ用基材を用いた固体電解質層は、クラックが生じたものの、正極、負極と重ね合わせることで全固体電池を作製することができた。
参考例1のセパレータ用基材を使用した全固体電池は、各実施例の支持体を用いた全固体電池と比較して、抵抗が非常に高く、電池の放電ができなかった。これは、密度が0.63g/cm3と高く、最大貫通面積が0.0008mm2と小さく、かつ通気度が0.7L/cm2/min.と低かったことが原因と考えられる。
各実施例と参考例1との比較から、支持体の通気度は1L/cm2/min.未満、密度は0.50g/cm3超、最大貫通面積が0.001mm2未満が好ましくないと分かる。
参考例2の電気化学素子用セパレータは、各実施例と比較して、通気度が0.6L/cm2/min.と低く、最大貫通面積が0.0003mm2と小さい。その結果、参考例1と同様の理由によって、クラックが生じ、均一な固体電解質層を形成できず、自立性のある固体電解質層を形成できなかった。
参考例2の電気化学素子用セパレータを用いた固体電解質層は、参考例1と同様に、クラックが生じたものの、正極、負極と重ね合わせることで全固体電池を作製することができた。
参考例2のセパレータ用基材を使用した全固体電池は、各実施例の支持体を用いた全固体電池および参考例1のセパレータ用基材を用いた全固体電池と比較して、抵抗が高く、電池の放電ができなかった。これは、熱処理後の縦方向の剛軟度が252mNと強く、つまり硬すぎるため、正極、固体電解質層、負極と加圧一体化する際に、支持体が折れ、固体電解質層内部にクラックが生じたと考えられる。クラック発生によって、リチウムイオンパスラインが切断され、抵抗の上昇が生じたと考えられる。
つまり、各実施例と参考例1、参考例2との比較から、縦方向および横方向の剛軟度はそれぞれ250mN超が好ましくないと分かる。
参考例3の支持体は、ポリエステル繊維、ポリエステルバインダー繊維に加えて、ポリビニルアルコール繊維を20質量%配合した支持体である。ポリビニルアルコール繊維は、引張強さを向上させるには効果的な繊維である。ポリビニルアルコール繊維は、湿熱による形状変化によって、繊維接点を補強し、支持体の引張強さを向上させることができる。しかしながら、ポリビニルアルコール繊維は、支持体を構成する状態において、繊維状態ではなく、支持体内部にフィルム層を多数形成してしまい、繊維間隙を封鎖してしまっていると考えられる。その結果、通気度が低くなり、固体電解質塗工液の支持体内部への浸透を阻害してしまっていると考えられる。
つまり、実施例5と参考例3との比較から、繊維状態を保持できないバインダーの配合は好ましくないと分かる。
Claims (3)
- リチウムイオン二次電池の固体電解質層に含まれる支持体であって、
支持体の縦方向および横方向の熱寸法変化率がそれぞれ-10~5%、通気度が1~50L/cm2/min.、熱処理後の縦方向および横方向の剛軟度がそれぞれ5~250mNの範囲の紙もしくは不織布である
ことを特徴とするリチウムイオン二次電池用支持体。 - 前記支持体は、厚さが5~40μm、密度が0.15~0.50g/cm3の範囲であ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用支持体。
- 請求項1または請求項2に記載のリチウムイオン二次電池用支持体を有した固体電解質層を備えたリチウムイオン二次電池。
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