Solid electrolyte

Abstract

To provide a solid electrolyte capable of improving ion conductivity.SOLUTION: Wherein the molecular crystal includes a sulfolane-based compound and 112233, - hexafluoropropane-1, 3-disulfonimide lithium (LiCFSA) as a lithium salt, and the inorganic filler is SiO2, A normalized surface area WA (1g / gSE) of the inorganic filler is 15 to m2 / gSE, where W (g / gSE) is a mass of the inorganic filler with respect to m2 of the inorganic filler, and A (900m2 / g) is a specific surface area of the inorganic filler.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to solid electrolytes. [Background technology]

[0002] Various technologies have been proposed for batteries such as those disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-214510 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a molecular crystal solid electrolyte containing an electron-donating sulfur-based organic compound and a lithium salt, but the ionic conductivity is still subject to improvement due to high crystallinity and low ionic mobility.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a solid electrolyte capable of improving ionic conductivity. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> A solid electrolyte, the solid electrolyte includes molecular crystals and an inorganic filler; the molecular crystal contains a sulfolane compound and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium (LiCFSA) as a lithium salt; The inorganic filler is SiO2, The mass of the inorganic filler per 1 g of the solid electrolyte is W (g / g SE), and the specific surface area of ​​the inorganic filler is A (m 2 / g), the normalized surface area WA (m 2 / g SE ) is 15 to 900m 2 / g SE That is, a solid electrolyte.

[0007] <2> a molar ratio of the sulfolane-based compound to the lithium salt contained in the molecular crystal is 2.0 or more and 3.1 or less; <1> The solid electrolyte according to claim 1.

[0008] <3> the proportion of the inorganic filler contained in the solid electrolyte is 3.6 vol% to 69.4 vol%; <1> or <2> The solid electrolyte according to claim 1.

[0009] <4> the proportion of the inorganic filler contained in the solid electrolyte is 27.4 vol% to 60.1 vol%; <1> ~ <3> 10. The solid electrolyte according to claim 9, wherein the first and second electrodes are electrically connected to each other.

[0010] <5> <1> ~ <4> A battery comprising the solid electrolyte according to any one of claims 1 to 4. [Effects of the Invention]

[0011] The solid electrolyte of the present disclosure can improve ionic conductivity. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a graph showing the relationship between the normalized surface area WA of the inorganic filler and the ionic conductivity of the solid electrolyte at room temperature (25° C.). DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of solid electrolytes that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the present disclosure, unless otherwise specified, the average particle size of particles is the median diameter (D50) value, which is the particle size at 50% of the cumulative value in the volume-based particle size distribution measured by laser diffraction / scattering particle size distribution measurement.

[0014] 1.Solid electrolyte In the present disclosure, a solid electrolyte is provided, the solid electrolyte includes molecular crystals and an inorganic filler; the molecular crystal contains a sulfolane compound and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium (LiCFSA) as a lithium salt; The inorganic filler is SiO2, The mass of the inorganic filler per 1 g of the solid electrolyte is W (g / g SE ), and the specific surface area of ​​the inorganic filler is A (m 2 / g), the normalized surface area WA (m 2 / g SE ) is 15 to 900m 2 / g SE The present invention provides a solid electrolyte,

[0015] The solid electrolyte of the present disclosure includes molecular crystals and an inorganic filler. The molecular crystal used in the present disclosure has a solid-solid phase transition at around -3°C in addition to a melting point (solid-liquid phase transition). By mixing molecular crystals with inorganic fillers, the solid-solid phase transition temperature of the molecular crystals is shifted to a lower temperature, and the ionic mobility of the molecular crystals is increased. The solid electrolyte of the present disclosure may be used in a battery.

[0016] The molecular crystal contains a sulfolane compound and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium (LiCFSA) as a lithium salt. The sulfolane-based compound may be sulfolane (SL) or a derivative of sulfolane. The molar ratio of the sulfolane compound to the lithium salt contained in the molecular crystal may be 2.0 or more and 3.1 or less, or 2.9 or more and 3.0 or less.

[0017] The inorganic filler is SiO2. The proportion of the inorganic filler contained in the solid electrolyte may be 3.6 vol% to 69.4 vol%, may be 7.0 vol% or more, may be 13.1 vol% or more, may be 27.4 vol% or more, may be 60.1 vol% or less, may be 53.1 vol% or less, or may be 43.0 vol% or less. The specific surface area of ​​the inorganic filler is not particularly limited, but is preferably 300 to 700 m 2 / g. In the present disclosure, the specific surface area means the BET specific surface area.

[0018] The mass of inorganic filler per 1 g of solid electrolyte is W (g / g SE ), and the specific surface area of ​​the inorganic filler is A (m 2 / g), the normalized surface area WA (m 2 / g SE ) is 15 to 900m 2 / g SE is. Normalized surface area WA (m 2 / g SE ) = mass W (g / g) of inorganic filler per 1 g of solid electrolyte SE ) × specific surface area A of inorganic filler (m 2 / g) In the present disclosure, the normalized surface area WA (m 2 / g SE ) is 15 to 900m 2 / g SEThe ionic conductivity of the solid electrolyte is improved when the normalized surface area WA of the inorganic filler is 900m 2 / g SE It is presumed that above this value, the inorganic filler causes the molecular crystals (ion-conducting parts) to percolate and break down, resulting in a decrease in the conductivity of the solid electrolyte.

[0019] 2.Battery The battery of the present disclosure may include the solid electrolyte of the present disclosure. The battery of the present disclosure comprises a positive electrode, an electrolyte layer, and a negative electrode in this order. The battery of the present disclosure may include a positive electrode current collector, a positive electrode layer, an electrolyte layer, a negative electrode layer, and a negative electrode current collector, in this order. The battery of the present disclosure may contain the solid electrolyte of the present disclosure in at least one layer selected from the group consisting of a positive electrode layer, an electrolyte layer, and a negative electrode layer.

[0020] [Positive electrode] The positive electrode includes a positive electrode layer and, if necessary, a positive electrode current collector. The positive electrode layer contains a positive electrode active material, and may contain a solid electrolyte, a conductive material, a binder, a thickener, and the like, as necessary. The positive electrode layer may be formed by applying a positive electrode slurry to at least one surface of a support such as a positive electrode current collector and drying the applied slurry. The positive electrode slurry contains a positive electrode active material and a solvent, and may also contain a solid electrolyte, a conductive material, a binder, a thickener, a solvent, and the like, as necessary. The method for applying the positive electrode slurry is not particularly limited, and examples thereof include a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a gravure coating method, and a screen printing method. The support can be appropriately selected from those having self-supporting properties and is not particularly limited, and examples thereof include metal foils such as Cu and Al foils.

[0021] The positive electrode active material may be, for example, an oxide active material. 0.8 Co 0.15 Al0.05 O2, LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMn2O4, Li(Ni 0.5 Mn 1.5 )O4, LiFePO4, LiMnPO4, LiNiPO4, LiCuPO4, etc. The positive electrode active material may be positive electrode active material particles. The average particle size of the positive electrode active material particles is not particularly limited and may be 1 nm to 100 μm. The content of the positive electrode active material in the positive electrode layer is not particularly limited, and may be 50.00 to 99.00 mass %.

[0022] At least a portion of the surface of the positive electrode active material may be coated with a lithium ion conductive compound. The lithium ion conductive compound may cover at least a part of the surface of the positive electrode active material, or may cover the entire surface of the positive electrode active material. Examples of lithium ion conductive compounds include B2O3, Li2B4O7, LiBPO4, Li3PO4, LiPO3, and LiNbO3. The thickness of the lithium ion conductive compound coating is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the lithium ion conductive compound is, for example, 100 nm or less, and may be 20 nm or less. The coverage of the lithium ion conductive compound coating the positive electrode active material is, for example, 70% or more, and may be 90% or more, or even 100%. The method for coating the lithium ion conductive compound is not particularly limited, and any conventionally known method may be used as appropriate.

[0023] The solid electrolyte used in the positive electrode layer may be the solid electrolyte of the present disclosure, and other solid electrolytes than the solid electrolyte of the present disclosure contained in the electrolyte layer described below may also be used. The content of the solid electrolyte in the positive electrode layer is not particularly limited.

[0024] Examples of conductive materials include carbon materials, metal particles, conductive polymers, etc. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). The content of the conductive material in the positive electrode layer is not particularly limited.

[0025] Examples of binders include acrylonitrile butadiene rubber (ABR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and styrene-butadiene rubber (SBR). The content of the binder in the positive electrode layer is not particularly limited.

[0026] Examples of thickeners include polysaccharides such as carboxymethyl cellulose (CMC) and methyl cellulose.

[0027] Examples of the solvent include an aqueous solvent and an organic solvent. The aqueous solvent refers to water or a mixed solvent containing water and a polar organic solvent. For example, an appropriate solvent can be selected depending on the types of the positive electrode active material, binder, etc. As the aqueous solvent, water is preferably used because of its ease of handling. Examples of polar organic solvents that can be used in the mixed solvent include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, and ethers such as tetrahydrofuran. Examples of the organic solvent include 1,2,3,4-tetrahydronaphthalene, n-heptane, butyl butyrate, diisobutyl ketone, and N-methyl-2-pyrrolidone (NMP).

[0028] Examples of materials for the positive electrode current collector include metals such as aluminum, copper, SUS, and nickel. The thickness of the positive electrode current collector is, for example, 0.1 μm or more and 100 μm or less. The positive electrode current collector may be in the form of a sheet or the like. The positive electrode current collector may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer disposed on its surface.

[0029] [Negative electrode] The negative electrode includes a negative electrode layer and, if necessary, a negative electrode current collector.

[0030] The negative electrode layer contains a negative electrode active material and may optionally contain at least one of a solid electrolyte, a conductive material, and a binder. The negative electrode layer may contain, as the negative electrode active material, for example, a lithium-based active material, a carbon-based active material, an oxide-based active material, an Si-based active material, or the like. Examples of lithium-based active materials include metallic lithium and lithium alloys, etc. Examples of metal elements contained in lithium alloys other than lithium include Mg, Ag, In, Sn, Si, Ga, Au, and Pt. Examples of carbon-based active materials include graphite, hard carbon, and soft carbon. An example of the oxide-based active material is lithium titanate. Examples of Si-based active materials include simple Si, Si alloys, and silicon oxide. The negative electrode active material may be in the form of particles, for example. The average particle size of the negative electrode active material particles is not particularly limited and may be 1 nm to 100 μm. The solid electrolyte used in the negative electrode layer may be the solid electrolyte of the present disclosure, and other solid electrolytes than the solid electrolyte of the present disclosure contained in the electrolyte layer described below may also be used. Examples of the conductive material and binder used in the negative electrode layer include the same conductive materials and binders as those exemplified as may be contained in the positive electrode layer. The thickness of the negative electrode layer may be 0.1 μm or more and 100 μm or less.

[0031] Examples of materials for the negative electrode current collector include SUS, aluminum, copper, nickel, iron, titanium, and carbon. Examples of the shape of the negative electrode current collector include foil and plate. The planar shape of the negative electrode current collector is not particularly limited, and examples include a circle, an ellipse, a rectangle, and any polygonal shape. The thickness of the negative electrode current collector varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm, or in the range of 5 μm to 20 μm. The negative electrode current collector may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer disposed on its surface.

[0032] [Electrolyte layer] The electrolyte layer includes at least an electrolyte. The electrolyte may be an electrolytic solution or a solid electrolyte. The solid electrolyte contained in the electrolyte layer may be the solid electrolyte of the present disclosure, or may be a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, or the like.

[0033] Examples of sulfide solid electrolytes include solid electrolytes containing Li, M (where M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen element. Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, LiX-Li2S-SiS2, LiX-Li2S-P2S5, LiX-Li2O-Li2S-P2S5, LiX-Li2S-P2O5, LiX-Li3PO4-P2S5, and Li3PS4. The term "Li2S-P2S5" above refers to a material obtained using a raw material composition containing Li2S and P2S5, and the same applies to other terms. Furthermore, the "X" in the LiX represents a halogen element. Examples of halogen elements include F, Cl, Br, and I. The raw material composition containing LiX may contain one or more types of LiX. When two or more types of LiX are contained, the mixing ratio of the two or more types is not particularly limited. The molar ratio of each element in the sulfide solid electrolyte can be controlled by adjusting the content of each element in the raw materials. The molar ratio and composition of each element in the sulfide solid electrolyte can be measured, for example, by ICP atomic emission spectrometry.

[0034] Examples of oxide solid electrolytes include substances having a garnet-type crystal structure containing Li, La, A (A is at least one of Zr, Nb, Ta, and Al), and O. Examples of oxide solid electrolytes include Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4, and Li 3+x PO 4-x N x (1≦x≦3) etc. may also be used.

[0035] The halide solid electrolyte may be, for example, a solid electrolyte containing Li, M, and X (M represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br).

[0036] The solid electrolyte may be in the form of particles from the viewpoint of ease of handling. The average particle size (D50) of the solid electrolyte particles is not particularly limited and may be from 1 nm to 100 μm.

[0037] The solid electrolyte may be used alone or in combination of two or more. When two or more solid electrolytes are used, the two or more solid electrolytes may be mixed, or two or more solid electrolyte layers may be formed to form a multilayer structure. The proportion of the solid electrolyte in the electrolyte layer is not particularly limited, but is, for example, 50% by mass or more, and may be in the range of 60% by mass to 100% by mass, 70% by mass to 100% by mass, or even 100% by mass. The solid electrolyte may contain less than 10% by mass of electrolytic solution relative to the total amount of electrolyte. The solid electrolyte may also be a composite solid electrolyte containing an inorganic solid electrolyte and a polymer electrolyte. When the electrolyte layer is a solid electrolyte layer, the solid electrolyte layer contains a solid electrolyte and, if necessary, a binder and the like. Examples of the binder include the binders that can be contained in the positive electrode layer described above. When the solid electrolyte layer contains a binder, the content of the binder may be 0% by mass to 10% by mass with respect to the total amount of the solid electrolyte layer. The thickness of the solid electrolyte layer is not particularly limited, but may be, for example, 1 μm or more, or from the viewpoint of reducing the resistance of the battery, 100 μm or less.

[0038] The type of battery is not particularly limited, but examples thereof include a lithium ion battery. The battery may be a primary battery or a secondary battery. The battery may also be a solid-state battery. In the present disclosure, a solid-state battery refers to a battery containing a solid electrolyte. The solid-state battery may be a semi-solid battery, which is a solid battery containing a solid electrolyte and a liquid-based material, or an all-solid-state battery, which is a solid battery containing no liquid-based material. The shape of the battery is not particularly limited, and may be, for example, a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminate type. Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery may be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), and as a power source for electrical appliances such as information processing devices. [Example]

[0039] (Examples 1 to 30, Comparative Examples 1 to 10) [Preparation of inorganic filler] Four types of inorganic fillers 1 to 4 shown in Table 1 were prepared. In Examples 1 to 30 and Comparative Examples 2, 4 to 10, one of inorganic fillers 1 to 4 was used, as shown in Tables 2 and 3. In Comparative Examples 1 and 3, no inorganic filler was used.

[0040] [Table 1]

[0041] [Molecular Crystal Synthesis] All experiments were carried out in a glove box or similar environment without exposure to air, under an Ar atmosphere with a dew point of -80°C or below and an oxygen concentration of <3 ppm. In each example and comparative example, sulfolane (SL) was heated to 60°C to form a melt, and LiCFSA was added as a lithium salt in the amounts shown in Tables 2 and 3. The melt was stirred while heating to dissolve the lithium salt. After dissolution, the melt was stirred for 2 hours, and then cooled to room temperature to synthesize molecular crystals. In Examples 1 to 11, 20 to 30 and Comparative Examples 1, 2, and 5 to 10, molecular crystals were obtained in which the molar ratio of SL to LiCFSA contained in the molecular crystals was 3 (SL:LiCSFA=3:1). In Examples 12 to 19 and Comparative Examples 3 and 4, molecular crystals were obtained in which the molar ratio of SL to LiCFSA contained in the molecular crystals was 2.9 (SL:LiCSFA=2.9:1).

[0042] [Solid electrolyte preparation] In Examples 1 to 30 and Comparative Examples 2, 4 to 10, the synthesized molecular crystals and inorganic fillers 1 to 4 shown in Table 1, those shown in Tables 2 and 3, were weighed out in amounts such that the volume ratio in the solid electrolyte was as shown in Tables 2 and 3, and composites of the SL / LiCSFA molecular crystals in a molten state and the inorganic filler were formed. The obtained composites were evaluated as solid electrolytes. The normalized surface area WA (m 2 / g SE The results are shown in Tables 2 and 3. In Comparative Example 1, a molecular crystal in which the molar ratio of SL to LiCFSA contained in the molecular crystal was 3 (SL:LiCSFA=3:1) was evaluated as a solid electrolyte. In Comparative Example 3, a molecular crystal in which the molar ratio of SL to LiCFSA contained in the molecular crystal was 2.9 (SL:LiCSFA=2.9:1) was evaluated as a solid electrolyte.

[0043] [Ionic conductivity measurement] In each example and each comparative example, the diameter was 11.28 mm (1 cm 2 50 mg of solid electrolyte was placed in a cylinder of 1 / 4" diameter and press-molded to obtain a solid electrolyte layer. Carbon-coated aluminum foil was placed on both sides of the solid electrolyte layer for current collection, producing an evaluation cell. AC impedance measurements were performed on the evaluation cell under measurement conditions of a temperature of 25°C, an amplitude of 10 mV, and a frequency of 1 MHz to 10 mHz. This allowed the resistance value of the solid electrolyte associated with ionic conduction to be determined, and the ionic conductivity of the solid electrolyte was calculated from the cell shape. The results are shown in Tables 2 and 3.

[0044] [Table 2]

[0045] [Table 3]

[0046] FIG. 1 is a graph showing the relationship between the normalized surface area WA of the inorganic filler and the ionic conductivity of the solid electrolyte at room temperature (25° C.). As shown in Table 2, it is clear that Examples 1 to 11 have improved ionic conductivities compared to Comparative Examples 1 and 2. As shown in Table 2, it is clear that Examples 12 to 19 have improved ionic conductivities compared to Comparative Examples 3 and 4. As shown in Table 3, it is clear that Examples 20 to 22 have improved ionic conductivities compared to Comparative Examples 5 and 6. As shown in Table 3, it is clear that Examples 23 to 25 have improved ionic conductivities compared to Comparative Examples 7 and 8. As shown in Table 3, it is clear that Examples 26 to 30 have improved ionic conductivities compared to Comparative Examples 9 to 10. As shown in FIG. 1 and Tables 2 to 3, it is clear that Examples 1 to 30 have improved ionic conductivities compared to Comparative Examples 1 to 10. From the above, the normalized surface area WA (m 2 / g SE ) is 15 to 900m 2 / g SE It has been demonstrated that a solid electrolyte that satisfies the above condition can improve ionic conductivity compared to a solid electrolyte that does not satisfy the above condition.

Claims

1. A solid electrolyte, the solid electrolyte includes molecular crystals and an inorganic filler; The molecular crystal contains a sulfolane compound and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium (LiCFSA) as a lithium salt, The inorganic filler is SiO ２ and The mass of the inorganic filler per 1 g of the solid electrolyte is W (g / g ＳＥ ), and the specific surface area of ​​the inorganic filler is A (m ２ / g), the normalized surface area WA (m ２ / g ＳＥ ) is 15 to 900m ２ / g ＳＥ That is, a solid electrolyte.

2. 2. The solid electrolyte according to claim 1, wherein a molar ratio of the sulfolane-based compound to the lithium salt contained in the molecular crystal is 2.0 or more and 3.1 or less.

3. 2. The solid electrolyte according to claim 1, wherein the proportion of the inorganic filler contained in the solid electrolyte is 3.6 vol % to 69.4 vol %.

4. 2. The solid electrolyte according to claim 1, wherein the proportion of the inorganic filler contained in the solid electrolyte is 27.4 vol % to 60.1 vol %.

5. A battery comprising the solid electrolyte of claim 1.

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