Solid electrolyte laminated sheet and solid state battery

Abstract

Provided is a solid electrolyte laminated sheet having a self-supporting property and capable of realizing a solid state battery having high output characteristics. A plurality of supports are used, a solid electrolyte is filled in each support to form a self-supporting sheet, and the self-supporting sheets are superimposed to form a solid electrolyte laminated sheet. Specifically, the solid electrolyte laminated sheet is configured by setting a layer of the solid electrolyte laminated sheet in contact with a positive electrode layer being the outermost layer as a self-supporting sheet in which a solid electrolyte resistant to oxidation is filled, and a layer in contact with a negative electrode layer being the opposite outermost layer as a self-supporting sheet in which a solid electrolyte resistant to reduction is filled.

Claims

1. A solid state battery, comprising: a positive electrode layer containing a positive electrode active material; a negative electrode layer containing a negative electrode active material; and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer comprises a solid electrolyte laminated sheet, and the solid electrolyte laminated sheet comprises: a plurality of supports, wherein the supports are a plurality of self-supporting sheets, and each of the self-supporting sheets is filled with a solid electrolyte, the supports have a porosity of 86% or more and 95% or less, the supports comprise at least one selected from the group consisting of an aramid fiber, an Al.sub.2O.sub.3 and a glass fiber, and the self-supporting sheets constitute a laminate, wherein one outermost layer is a self-supporting sheet in which a solid electrolyte resistant to oxidation is filled and in which is in contact with the positive electrode layer, and the other outermost layer is a self-supporting sheet in which a solid electrolyte resistant to reduction is filled and in which is in contact with the negative electrode layer.

2. The solid electrolyte laminated sheet according to claim 1, wherein the supports have a thickness of 5 μm to 30 μm.

3. The solid electrolyte laminated sheet according to claim 1, wherein the solid electrolyte contains a lithium element.

4. The solid electrolyte laminated sheet according to claim 2, wherein the solid electrolyte contains a lithium element.

5. The solid electrolyte laminated sheet according to claim 1, wherein the solid electrolyte contains at least either phosphorus or sulfur.

6. The solid electrolyte laminated sheet according to claim 2, wherein the solid electrolyte contains at least either phosphorus or sulfur.

7. The solid electrolyte laminated sheet according to claim 4, wherein the solid electrolyte contains at least either phosphorus or sulfur.

Description

EXAMPLES

(1) Next, examples of the disclosure are described, but the disclosure is not limited to these examples.

Example 1

(2) [First Self-supporting Sheet]

(3) (Preparation of Solid Electrolyte (1) Slurry)

(4) 9.7 g of powder of Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) serving as a sulfide-based solid electrolyte were kneaded with 2.75 g of butyl butyrate for 1 minute to obtain a slurry. Further, 3 g of a butyl butyrate solution (binder solution) containing 10% by mass of SBR were added thereto and kneaded. In order to adjust the viscosity, 3 g of butyl butyrate were further added to obtain a solid electrolyte (1) slurry. The obtained solid electrolyte (1) slurry had a solid content of 54.9%.

(5) [Fabrication of First Self-Supporting Sheet]

(6) On a nonwoven fabric (material: polyethylene terephthalate, porosity: 86%, thickness: 19 μm) cut into a 100 mm square and previously fixed onto a steel sheet, coating was performed using a bar coater. After that, the butyl butyrate as the solvent was removed by drying at about 100° C. to obtain a sheet in which the solid electrolyte (1) is filled. By hollowing out a 10 mmφ circular sheet from the obtained sheet and pressing the same using a pressing machine with a pressure of about 3500 kg/cm.sup.2, a 10 mmφ solid electrolyte (1) sheet having a thickness of 25 μm was obtained.

(7) (Self-Supporting Property)

(8) The obtained solid electrolyte (1) sheet was a self-supporting sheet without chipping of the periphery or cracks occurring therein even if pinched with tweezers, and having a strength that enables easy handling or moving operation.

(9) (Ionic Conductivity)

(10) The ionic conductivity of the obtained solid electrolyte (1) sheet was measured. The result was 1×10.sup.−3 mS/cm.

(11) [Second Self-Supporting Sheet]

(12) (Preparation of Solid Electrolyte (2) Slurry)

(13) 9.7 g of powder of Thio-LISICON (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) serving as a sulfide-based solid electrolyte were kneaded with 2.75 g of butyl butyrate for 1 minute to obtain a slurry. Further, 3 g of a butyl butyrate solution (binder solution) containing 10% by mass of SBR were added thereto and kneaded. In order to adjust the viscosity, 3 g of butyl butyrate were further added to obtain a solid electrolyte (2) slurry. The obtained solid electrolyte (2) slurry had a solid content of 54.9%.

(14) [Fabrication of Second Self-supporting Sheet]

(15) On a nonwoven fabric (material: polyethylene terephthalate, porosity: 86%, thickness: 19 μm) cut into a 100 mm square and previously fixed onto a steel sheet, coating was performed using a bar coater. After that, the butyl butyrate as the solvent was removed by drying at about 140° C. to obtain a sheet in which the solid electrolyte (2) is filled. By hollowing out a 10 mmφ circular sheet from the obtained sheet and pressing the same using a pressing machine with a pressure of about 3500 kg/cm.sup.2, a 10 mmφ solid electrolyte (2) sheet having a thickness of 25 μm was obtained.

(16) (Self-supporting Property)

(17) The obtained solid electrolyte (2) sheet was a self-supporting sheet without chipping of the periphery or cracks occurring therein even if pinched with tweezers, and having a strength that enables easy handling or moving operation.

(18) (Ionic Conductivity)

(19) The ionic conductivity of the obtained solid electrolyte (2) sheet was measured. The result was 1×10.sup.−2 mS/cm.

(20) <Solid Electrolyte Sheet Laminate>

(21) By superimposing the first self-supporting sheet and the second self-supporting sheet and pressing the same with a pressure of 3500 kg/cm.sup.2, a solid electrolyte laminated sheet was obtained.

(22) (Ionic Conductivity)

(23) The ionic conductivity of the obtained solid electrolyte laminated sheet was measured. The result was 3×10.sup.−3 mS/cm.

(24) <Solid State Battery>

(25) (Positive Electrode)

(26) Li(NiCoMn)O.sub.2 as a positive electrode active material, Thio-LISICON (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) as a solid electrolyte, acetylene black as a conduction aid, and SBR as a binder were weighed at a mass % ratio of 75:22:3:3. By putting these materials and an appropriate amount of butyl butyrate into a rotation/revolution mixer, stirring them at 2000 rpm for 3 minutes and then performing a defoaming process for 1 minute, a positive electrode coating liquid was prepared.

(27) (Negative Electrode)

(28) Graphite powder as a negative electrode active material, Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) as a solid electrolyte, and SBR as a binder were weighed at a mass % ratio of 65:35:3. By putting these materials and an appropriate amount of butyl butyrate into a rotation/revolution mixer, stirring them at 2000 rpm for 3 minutes and then performing a defoaming process for 1 minute, a negative electrode coating liquid was prepared.

(29) (Solid Electrolyte)

(30) The solid electrolyte laminated sheet obtained above was used as a solid electrolyte.

(31) (Fabrication of Solid State Battery)

(32) By disposing the first self-supporting sheet of the solid electrolyte sheet to contact the negative electrode, disposing the second self-supporting sheet to contact the positive electrode and laminating them, a solid state battery was fabricated.

(33) <Measurement of Resistance Value>

(34) Under an environment of 25° C., charging was performed to 4.2 V at a current density of 0.1 C, discharging was performed to 2.5 V at a current density of 0.1 C, and discharge capacity was measured. Then, a value at the time of measurement at an alternating current frequency of 1 kHz was taken as an impedance (resistance) value.

Examples 2 to 3 and Comparative Examples 1 to 4>

(35) Solid electrolyte sheets were obtained in the same manner as in Example 1 except that the solid electrolytes described in Table 1 were used, and solid state batteries were fabricated. The obtained solid electrolyte sheets and solid state batteries were evaluated in the same manner as in Example 1. The results are shown in Table 1.

(36) TABLE-US-00001 TABLE 1 First Self-Supporting Sheet Discharge (Negative Electrode Second Self-Supporting Sheet Nonwoven Capacity Resistance Side) (Positive Electrode Side) Fabric (mAh/g) (Ω) Example 1 Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) Thio-LISICON PET 145 21 (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) Example 2 Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) Thio-LISICON PE 141 28 (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) Example 3 Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) Thio-LISICON Glass fiber 142 25 (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) Comparative Thio-LISICON Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) PET 50 183 Example 1 (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) Comparative Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) PET 140 62 Example 2 Comparative Li.sub.2S—P.sub.2S.sub.5 (80:20 mol %) Single layer without PET 143 45 Example 3 laminating Comparative Thio-LISICON Single layer without PET 57 168 Example 4 (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) laminating

(37) In Comparative Example 1, the sheets used in Example 1 were disposed in a reverse manner. That is, a sheet susceptible to oxidation was disposed in contact with the positive electrode layer, and a sheet susceptible to reduction was disposed in contact with the negative electrode layer. Reductive decomposition of Thio-LISICON (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) was intense, the discharge capacity reduced, and the resistance increased.

(38) In Comparative Example 2, since two self-supporting sheets in which the same solid electrolyte was filled were superimposed, the resistance was higher than in Example 1.

(39) In Comparative Examples 3 and 4, the self-supporting sheets were not laminated and tests were conducted on a single-layer sheet. Comparative Example 3 had smaller ionic conductivity than Example 1 and therefore had a larger resistance than Example 1. In Comparative Example 4, reductive decomposition of Thio-LISICON (Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4) was intense, the discharge capacity reduced, and the resistance increased.

(40) The disclosure provides a solid electrolyte laminated sheet including a plurality of supports, wherein each of the supports is a self-supporting sheet in which a solid electrolyte is filled, and the self-supporting sheets constitute a laminate, wherein one outermost layer is a self-supporting sheet in which a solid electrolyte resistant to oxidation is filled, and the other outermost layer is a self-supporting sheet in which a solid electrolyte resistant to reduction is filled.

(41) The supports may be a nonwoven fabric.

(42) The supports may be a heat-resistant fiber.

(43) The supports may include at least one selected from the group consisting of an aramid fiber, an Al.sub.2O.sub.3 fiber and a glass fiber.

(44) The supports may have a porosity of 60% to 95% and may have a thickness of 5 μm to 30 μam.

(45) The solid electrolyte may contain a lithium element.

(46) The solid electrolyte may contain at least either phosphorus or sulfur.

(47) Another embodiment of the disclosure provides a solid state battery including a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, wherein the solid electrolyte layer includes the above solid electrolyte laminated sheet.

(48) The solid electrolyte laminated sheet of the disclosure have both oxidation resistance and reduction resistance properties. Accordingly, according to the solid electrolyte laminated sheet of the disclosure, a solid state battery having high output characteristics can be realized.

(49) Further, if the solid electrolyte laminated sheet of the disclosure is formed of supports composed of a heat-resistant fiber, in a manufacturing process or the like of the solid state battery, a short circuit can be suppressed even if pressing is performed at a high temperature exceeding, for example, 200° C. In addition, the solid electrolyte can be sintered by high-temperature pressing, and as a result, interfacial resistance can be reduced and the battery's output can be further improved.