Electrolyte Composition, Storage Device, and Battery System

Abstract

To provide an electrolyte composition, a power storage device, and a cell system, capable of expanding a potential window while securing an ionic conductivity.SOLUTION: An electrolyte composition includes ion conductor particles having a garnet type structure including Li, La, Zr, and O, ionic liquid, and electrolyte salt. The electrolyte salt is lithium salt including anions having a sulfonyl imide structure. The ionic liquid includes pyrrolidinium cations. A lithium ion concentration of the ionic liquid in which the electrolyte salt is dissolved is equal to or higher than 1 mol / dm3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrolyte composition, an energy storage device, and a battery system.

Background Art

[0002] An electrolyte composition containing garnet-type structured ion conductor particles containing Li, La, Zr, and O, an ionic liquid, and an electrolyte salt is known (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, there are requirements for expanding the potential window and ensuring ionic conductivity.

[0005] The present invention has been made to meet this requirement, and an object thereof is to provide an electrolyte composition, an energy storage device, and a battery system that can expand the potential window while ensuring ionic conductivity.

Means for Solving the Problems

[0006] To achieve this object, the electrolyte composition of the present invention contains garnet-type structured ion conductor particles containing Li, La, Zr, and O, an ionic liquid, and an electrolyte salt. The electrolyte salt is a lithium salt having a sulfonylimide structure as an anion, the ionic liquid contains a pyrrolidinium cation, and the lithium ion concentration of the ionic liquid in which the electrolyte salt is dissolved is 1 mol / dm 3 or more.

[0007] The energy storage device of the present invention includes a positive electrode layer, an electrolyte layer, and a negative electrode layer in this order, and an electrolyte composition is included in at least one of the positive electrode layer, the electrolyte layer, and the negative electrode layer.

[0008] The battery system of the present invention includes an energy storage device and a charger, and the voltage applied by the charger to the energy storage device is higher than 4.3 V, or the positive electrode potential of the energy storage device during charging is Li / Li + exceeds 4.3 V with respect to the reference.

Effects of the Invention

[0009] The electrolyte composition of the present invention can expand the potential window while ensuring ionic conductivity. The energy storage device and the battery system including the electrolyte composition can increase the energy density and the output density.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of an energy storage device 10 in one embodiment. The energy storage device 10 in the present embodiment is a lithium-ion solid battery in which the power generation element is composed of a solid. That the power generation element is composed of a solid means that the skeleton of the power generation element is composed of a solid, and for example, a form in which a liquid is impregnated in the skeleton is not excluded.

[0012] As shown in FIG. 1, the energy storage device 10 includes a positive electrode layer 11, an electrolyte layer 14, and a negative electrode layer 15 in this order. The positive electrode layer 11, the electrolyte layer 14, and the negative electrode layer 15 are housed in a case (not shown).

[0013] The positive electrode layer 11 is formed by laminating a current collector layer 12 and a composite layer 13. The current collector layer 12 is a conductive member. Examples of the material of the current collector layer 12 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0014] The composite layer 13 contains an active material 19 and an electrolyte composition (described later). The electrolyte composition contains ionic conductor particles 18. In order to reduce the resistance of the composite layer 13, a conductive aid may be included in the composite layer 13. Examples of the conductive aid include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0015] Examples of the active material 19 include metal oxides having a transition metal. Examples of the metal oxide having a transition metal include oxides containing one or more elements selected from Mn, Co, Ni, Fe, Cr, and V and Li. Examples of the metal oxide having a transition metal include LiCoO2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O4, and LiFePO4. Since some transition metal oxides such as inverse spinel type oxides like LiNiVO4 and LiCoPO4, and spinel type oxides like LiNi 0.5 Mn 1.5 O4 exhibit a potential of 4.3 V or more based on metallic lithium, if such a compound is adopted as the active material 19, the energy density of the power storage device 10 can be increased depending on the potential of the negative electrode layer 15.

[0016] For the purpose of suppressing the reaction between the active material 19 and the ionic conductor particles 18, a coating layer can be provided on the surface of the active material 19. The coating layer is Al2O3, ZrO2, LiNbO3, Li4Ti5O 12, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, and Li2MoO4 are exemplified.

[0017] The electrolyte layer 14 is made of an electrolyte composition. The electrolyte composition contains ionic conductor particles 18, an ionic liquid, and an electrolyte salt. The ionic liquid is a compound composed of a cation and an anion and is liquid at normal temperature and pressure. An ionic liquid with a certain salt concentration in which the electrolyte salt is dissolved is an electrolyte solution. Various physical properties and functions of the electrolyte solution are determined by the types of the salt and the ionic liquid and the salt concentration. The salt concentration (lithium ion concentration) of the electrolyte solution is 1 mol / dm 3 or more. This is to ensure the lithium ion conductivity of the electrolyte solution.

[0018] The ionic conductor particles 18 are oxides having a garnet-type structure with lithium ion conductivity. The basic composition of the oxide having a garnet-type structure is Li5La3M2O 12 (M = Nb, Ta). The ionic conductor particles 18 contain Li, La, Zr, and O. The ionic conductor particles 18 are Li7La3Zr2O in which the pentavalent M cation in the basic composition is replaced by a tetravalent cation 12 is exemplified.

[0019] In addition to Li, La, and Zr, the ionic conductor particles 18 can contain at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanoids (excluding La). For example, Li6La3Zr 1.5 W 0.5 O 12 , Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 , Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 , Li 6.25 La3Zr2Ga 0.25 O 12 , Li6.4 La3Zr 1.4 Ta 0.6 O 12 ,Li 6.5 La3Zr 1.75 Te 0.25 O 12 ,Li 6.75 La3Zr 1.75 Nb 0.25 O 12 ,Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 ,Li 6.46 Ga 0.23 La3Zr 1.85 Y 0.15 O 12 ,Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 ,Li 7.05 La 3.00 Zr 1.95 Gd 0.05 O 12 ,Li 6.20 Ba 0.30 La 2.95 Rb 0.05 Zr2O 12 include the following.

[0020] The ion conductor particles 18 preferably contain at least one of Mg and element A (where A is at least one element selected from the group consisting of Ca, Sr, and Ba), and the molar ratio of each element satisfies all of the following (1) to (3), or contain both Mg and element A, and the molar ratio of each element satisfies all of the following (4) to (6). Element A is preferably Sr in order to increase the ionic conductivity of the ion conductor particles 18. (1) 1.33 ≤ Li / (La + A) ≤ 3 (2) 0 ≤ Mg / (La + A) ≤ 0.5 (3) 0 ≤ A / (La + A) ≤ 0.67 (4) 2.0 ≤ Li / (La + A) ≤ 2.5 (5) 0.01 ≤ Mg / (La + A) ≤ 0.14 (6) 0.04 ≦ A / (La + A) ≦ 0.17.

[0021] The median diameter of the equivalent circle diameter of the ion conductor particles 18 appearing in the cross-section of the electrolyte layer 14 is preferably 0.5 - 10 μm. This is to make the surface area of the ion conductor particles 18 an appropriate size and ensure the amount of lithium ion movement between the electrolyte interposed on the surface of the ion conductor particles 18 and the ion conductor particles 18.

[0022] To obtain the median diameter of the ion conductor particles 18, first, an image of the ion conductor particles 18 appearing in the cross-section of the electrolyte layer 14 (a polished surface or a surface obtained by irradiating with a focused ion beam (FIB)) is analyzed by a scanning electron microscope (SEM). The equivalent circle diameter is calculated from the area of each particle of the ion conductor particles 18, and a particle size distribution based on the number is obtained. The median diameter is the equivalent circle diameter at which the cumulative value of the frequency in the particle size distribution is 50%. To ensure accuracy, the image for obtaining the particle size distribution is taken from an area of 400 μm or more of the electrolyte layer 14. 2 or more.

[0023] The electrolyte salt is a lithium salt in which the anion has a sulfonylimide structure. The anion of the electrolyte salt is N(SO2F)2 having a sulfonyl group -S(=O)2-, - , N(SO2CF3)2 - , N(SO2C2F5)2 - etc. are exemplified. The anion is preferably N(SO2F)2 - , N(SO2CF3)2 - . N(SO2F)2 - is abbreviated as [FSI] - : called bis(fluorosulfonyl)imide anion, and N(SO2CF3)2 - is abbreviated as [TFSI] - : may be called bis(trifluoromethanesulfonyl)imide anion.

[0024] The electrolyte salts Li[FSI] and Li[TFSI] are preferred. Li[FSI] and Li[TFSI] have a salt concentration of 1 mol / dm 3This is because the above electrolyte has a small impact on the increase in viscosity and the decrease in ionic conductivity, and further forms a highly stable and low-resistance film (SEI), which can reduce the reductive decomposition of the electrolyte and expand the reductive potential window.

[0025] The cation component of the ionic liquid has a pyrrolidinium cation. The pyrrolidinium cation is a five-membered ring compound represented by, for example, formula (1).

[0026] [Chemical formula] In formula (1), R 1 and R 2 each independently represents an alkyl group having 1 to 10 carbon atoms. The alkyl group may have a substituent. The carbon number of the alkyl group represented by R 1 and R 2 (including substituents) is preferably 1 to 5, more preferably 1 to 4. This is to ensure the ionic conductivity of the electrolyte.

[0027] The substituent is not particularly limited. Examples of the substituent include an alkyl group, a cycloalkyl group, an aryl group, a hydroxyl group, a carboxyl group, a nitro group, a trifluoromethyl group, an amide group, a carbamoyl group, an ester group, a carbonyloxy group, a cyano group, a halogeno group, an alkoxy group, an aryloxy group, a sulfonamide group, etc.

[0028] The anion component of the ionic liquid is not particularly limited. Examples of the anion component include inorganic anions such as BF4 - , N(SO2F)2 - etc., and organic anions such as B(C6H5)4 - , CH3SO3 - , CF3SO3 - , N(SO2CF3)2 - , N(SO2C4F9)2 - etc. It is preferable that the anion component of the ionic liquid is the same sulfonylimide anion as the anion component of the electrolyte salt, because it is easy to control the coordination (interaction) between the lithium ions and the anions contained in the electrolyte.

[0029] Examples of the ionic liquid include N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13-FSI) and N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13-TFSI).

[0030] The water content in the ionic liquid is preferably 200 ppm or less. This is to prevent the potential window of the electrolyte solution from narrowing due to the water content in the ionic liquid. The halogen ion content as an impurity in the ionic liquid is preferably 10 ppm or less. Examples of other impurities contained in the ionic liquid include alkali metal ions and alkaline earth metal ions. The total amount of these impurities is preferably 10 ppm or less. This is to prevent the cycle characteristics of the power storage device 10 containing the electrolyte composition from deteriorating.

[0031] In the electrolyte layer 14 (electrolyte composition), the content (volume %) of the ionic liquid with respect to the total amount of the ionic conductor particles 18 and the ionic liquid is preferably 50 volume % or less (excluding 0 volume %). That is, ionic conductor particles:ionic liquid = (100 - X):X, where 0 < X ≤ 50. This is to reduce the occurrence of bleeding of the ionic liquid while ensuring ionic conductivity by the electrolyte solution intervening between the ionic conductor particles 18.

[0032] The content (volume %) of the ionic liquid is obtained by freezing the electrolyte layer 14 or embedding and solidifying the electrolyte layer 14 in a tetrafunctional epoxy resin or the like, and then analyzing a randomly selected 5000-fold field of view from the cross-section of the electrolyte layer 14 using an SEM equipped with an energy dispersive X-ray spectrometer (EDS). The analysis is performed by identifying the distributions of La, Zr, and S or by image analysis of the contrast of the backscattered electron image to identify the area of the ionic conductor particles 18 and the area of the ionic liquid, and regarding the ratio of the area in the cross-section of the electrolyte layer 14 as the ratio of the volume in the electrolyte layer 14 to obtain the content (volume %) of the ionic liquid.

[0033] The electrolyte layer 14 (electrolyte composition) contains garnet-type structured ion conductor particles 18 containing Li, La, Zr, and O, a lithium salt (electrolyte salt) in which anions have a sulfonylimide structure, and an ionic liquid containing a pyrrolidinium cation. The lithium ion concentration of the electrolyte solution in which the electrolyte salt is dissolved in the ionic liquid is 1 mol / dm 3 or higher. Thereby, while expanding the reduction-side potential window and the oxidation-side potential window of the electrolyte solution contained in the electrolyte layer 14, ionic conductivity can be ensured. It is presumed that this specificity is due to the interaction between the ion conductor particles 18 and the electrolyte solution.

[0034] As the lithium ion concentration of the electrolyte solution exceeds 1 mol / dm 3 and becomes even higher, the ionic conductivity of the electrolyte layer 14 (electrolyte composition) tends to decrease. However, the lithium ion conductivity of the electrolyte composition at 25°C is preferably 4.0×10 -5 S / cm or more. This is to reduce the change in lithium ion concentration that occurs during the operation of the power storage device 10 due to the influence of anions that are more mobile than lithium ions in the electrolyte solution.

[0035] Since the electrolyte composition contains anions derived from the electrolyte solution, the lithium ion conductivity of the electrolyte composition is calculated by multiplying the total ionic conductivity of the electrolyte composition calculated by the AC impedance method by the transport number of lithium ions. The transport number of lithium ions is determined by the AC impedance method and the steady-state DC method.

[0036] The electrolyte layer 14 may contain a binder. The binder binds the ion conductor particles 18. As the binder, one having a wider potential window than the potential window of the electrolyte solution is used. Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer.

[0037] In the electrolyte layer 14 (electrolyte composition), the amount (volume %) of the binder with respect to the combined amount of the ion conductor particles 18 and the ionic liquid is preferably 10 volume % or less (excluding 0 volume %). That is, the combined amount of the ion conductor particles and the ionic liquid: the amount of the binder = (100 - Y):Y, where 0 < Y ≤ 10. This is to ensure the formability of the electrolyte layer 14 by the binder and to reduce the decrease in the ionic conductivity of the electrolyte layer 14. The content (volume %) of the binder can be specified from the area % of the cross-section of the electrolyte layer 14 determined by analysis using SEM-EDS as described above.

[0038] The electrolyte layer 14 may contain a solvent for dissolving the binder. Examples of the solvent include carbonates, acetonitrile, and 1,2-dimethoxyethane. Examples of the carbonate include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinyl ethylene carbonate, and fluoroethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0039] The negative electrode layer 15 has a current collector layer 16 and a composite layer 17 laminated thereon. The current collector layer 16 is a member having conductivity. Examples of the material of the current collector layer 16 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0040] The composite layer 17 contains an active material 20 and an electrolyte composition. The electrolyte composition contains ion conductor particles 18. In order to lower the resistance of the composite layer 17, a conductive aid may be contained in the composite layer 17. Examples of the conductive aid include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag. Examples of the active material 20 include Li, Li-Al alloy, Li4Ti5O 12 , graphite, In, Si, Si-Li alloy, and SiO. Similar to the electrolyte layer 14, the composite layers 13 and 17 may contain a binder and a solvent.

[0041] The energy storage device 10 is manufactured as follows, for example. A solution in which a binder is dissolved in a solvent is mixed with a mixture of an ionic liquid in which an electrolyte salt is dissolved and ionic conductor particles 18 to form a slurry. After tape casting, it is dried to obtain a green sheet (electrolyte sheet) for the electrolyte layer 14.

[0042] An active material 19 is mixed with a mixture of an ionic liquid in which an electrolyte salt is dissolved and ionic conductor particles 18, and further a solution in which a binder is dissolved in a solvent is mixed to form a slurry. After tape casting on the current collector layer 12, it is dried to obtain a green sheet (positive electrode sheet) for the positive electrode layer 11.

[0043] An active material 20 is mixed with a mixture of an ionic liquid in which an electrolyte salt is dissolved and ionic conductor particles 18, and further a solution in which a binder is dissolved in a solvent is mixed to form a slurry. After tape casting on the current collector layer 16, it is dried to obtain a green sheet (negative electrode sheet) for the negative electrode layer 15.

[0044] After cutting the electrolyte sheet, the positive electrode sheet, and the negative electrode sheet into predetermined shapes, they are stacked in the order of the positive electrode sheet, the electrolyte sheet, and the negative electrode sheet, and are pressure-bonded to each other to be integrated. Terminals (not shown) are connected to the current collector layers 12 and 16, and are enclosed in a case (not shown), whereby an energy storage device 10 including a positive electrode layer 11, an electrolyte layer 14, and a negative electrode layer 15 is obtained.

[0045] FIG. 2 is a schematic diagram of the battery system 21. The battery system 21 includes an energy storage device 10 and a charger 22. The battery system 21 can make the voltage applied by the charger 22 to the energy storage device 10 higher than 4.3V, or the positive electrode potential of the energy storage device 10 during charging exceeds 4.3V based on Li / Li + reference. This is because the oxidation-side potential window of the electrolyte layer 14 of the energy storage device 10 is expanded, and the interfacial resistance in the negative electrode layer 15 can be reduced while ensuring the ionic conductivity of the electrolyte layer 14. Thereby, the energy density and the output density of the energy storage device 10 can be increased.

Example

[0046] The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0047] (Preparation of ionic conductor particles) Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr 2.0 O 12 Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed so as to obtain the above composition. Considering the volatilization of Li during firing, Li2CO3 was made about 15 mol% excessive in terms of elements. The weighed raw materials and the organic solvent were put into a nylon pot together with zirconia balls and pulverized and mixed with a ball mill for 15 hours. After drying the slurry taken out of the pot, it was calcined temporarily (at 1100 °C for 10 hours) on a MgO plate. The powder after the temporary calcination, the binder, and the solvent were put into the pot and pulverized and mixed with a ball mill for 15 hours.

[0048] After drying the slurry taken out of the pot, it was put into a mold with a diameter of 12 mm, and a molded body with a thickness of about 1.5 mm was obtained by press molding. A hydrostatic pressure of 1.5 t / cm 2 was further applied to the molded body using a cold isostatic pressing machine (CIP). The molded body was covered with the calcined powder having the same composition as the molded body and fired (at 1100 °C for 4 hours) in a reducing atmosphere to obtain a sintered body. The lithium ion conductivity of the sintered body determined by the AC impedance method was 1.0×10 -3 S / cm. The measurement conditions for the lithium ion conductivity were a temperature of 25 °C, a voltage of 10 mV, and a frequency of 7 MHz - 100 mHz. The sintered body was pulverized in an Ar atmosphere to obtain the ionic conductor particles (hereinafter referred to as "LLZ") in the examples.

[0049] (Preparation of electrolyte) The electrolyte salt LiN(SO2F)2 was compounded with the ionic liquid N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13-FSI, special grade reagent) in the range from 1 mol / dm 3 to 5 mol / dm 3 to obtain various electrolytes.

[0050] The ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (special reagent grade) was mixed with 1 mol / dm of electrolyte salt LiN(SO2F)2. 3 The mixture was combined to obtain an electrolyte solution for the comparative example.

[0051] Example 1 The volume ratio of ionic conductor particles to electrolyte solution was 68:32, and the concentration of salt containing pyrrolidinium cation was 1 mol / dm 3 The electrolyte solution and LLZ were mixed in a mortar in an Ar atmosphere to obtain 0.5 g of an electrolyte composition made of a composite powder. The composite powder was placed in a cylinder made of an insulator with a diameter of 10 mm in an Ar atmosphere, and uniaxially molded under a pressure of 500 MPa to obtain a disk-shaped molded body 31 of the evaluation cell 30 shown in FIG. 3. A stainless steel metal foil 32 was placed on one side of the molded body 31, and a Li metal foil 33 and a Cu metal foil 34 were placed on the other side of the molded body 31. The metal foils 32 and 33 were attached to the molded body 31 by the axial force of a screw to which a tightening torque of 8 N was applied, to obtain an evaluation cell in Example 1.

[0052] Example 2 Salt concentration 2 mol / dm containing pyrrolidinium cation 3 An evaluation cell in Example 2 was obtained in the same manner as in Example 1, except that the above electrolyte solution was compounded with LLZ to obtain a composite powder.

[0053] Example 3 Salt concentration 3 mol / dm containing pyrrolidinium cation 3 An evaluation cell in Example 3 was obtained in the same manner as in Example 1, except that the above electrolyte solution was compounded with LLZ to obtain a composite powder.

[0054] Example 4 Salt concentration 5 mol / dm containing pyrrolidinium cation 3 An evaluation cell in Example 4 was obtained in the same manner as in Example 1, except that the above electrolyte solution was compounded with LLZ to obtain a composite powder.

[0055] Comparative Example 1 An electrolyte solution with a salt concentration of 3 mol / dm containing pyrrolidinium cations 3 was used to obtain a composite powder by compounding it with oxide particles composed of Li 1.5 Al 0.5 Ge 1.5 (PO4)3 (hereinafter referred to as "LAGP"). An evaluation cell in Comparative Example 1 was obtained in the same manner as in Example 1, except for this.

[0056] (Comparative Example 2) An electrolyte solution with a salt concentration of 3 mol / dm containing pyrrolidinium cations 3 was used to obtain a composite powder by compounding it with oxide particles composed of Li3PO4. An evaluation cell in Comparative Example 2 was obtained in the same manner as in Example 1, except for this.

[0057] (Comparative Example 3) An electrolyte solution with a salt concentration of 3 mol / dm containing pyrrolidinium cations 3 was used to obtain a composite powder by compounding it with oxide particles composed of Al2O3. An evaluation cell in Comparative Example 3 was obtained in the same manner as in Example 1, except for this.

[0058] (Comparative Example 4) An electrolyte solution with a salt concentration of 1 mol / dm containing imidazolium cations 3 was used to obtain a composite powder by compounding it with LLZ. An evaluation cell in Comparative Example 4 was obtained in the same manner as in Example 1, except for this.

[0059] (Measurement of ionic conductivity) Using the evaluation cells of Examples 1-4 and Comparative Examples 1-4, the total ionic conductivity of the molded body (electrolyte composition) at 25 °C was measured by the AC impedance method, and the lithium ion conductivity was obtained by multiplying the transport number of lithium ions.

[0060] The transport number was calculated as follows. First, the resistance value R S0 of the evaluation cell was analyzed by AC impedance measurement. The conditions for AC impedance measurement were a temperature of 25 °C, a voltage of 10 mV, and a frequency of 7 MHz - 100 mHz.

[0061] Next, the initial current value I0 immediately after applying a constant voltage V to the evaluation cell was measured, and the initial resistance value R0 of the evaluation cell was calculated according to the following formula A. R0 = V / I0 ··· A The measurement conditions for the initial current value were a voltage of 10 mV, a total time of 6 seconds, and a measurement interval of 0.0002 seconds.

[0062] Resistance value R S0 And the initial resistance value R0 was substituted into the following formula B to calculate the interfacial resistance R INT R INT = R0 - R S0 ··· B Next, the current value I after the evaluation cell reached a steady state by applying a constant voltage V was measured, and the resistance value R P in the steady state of the evaluation cell was calculated according to the following formula C. R P = V / I ··· C The measurement conditions for the current value in the steady state were a voltage of 10 mV, a total time of 10 hours, and a measurement interval of 60 seconds.

[0063] After the evaluation cell reached a steady state, the resistance value R S of the evaluation cell was analyzed by AC impedance measurement under the above conditions. Resistance value R S , resistance value R P and the interfacial resistance R INT were substituted into the following formula D to calculate the transference number t Li t Li = R S / (R P - R INT ) ··· D The lithium ion conductivity at 25 °C of the molded bodies of Examples 1-4 and Comparative Examples 1-4 was 4.0 × 10 -5 S / cm or more.

[0064] (Measurement of oxidation current) For the evaluation cells in the examples and comparative examples, from -0.1 V to 5 V (vs. Li / Li +) The voltage was scanned within the range of (scanning speed: 1 mV / s), and the cyclic voltammetry for detecting the response current was used to evaluate the electrochemical stability of the electrolyte composition. Figure 4 is an example of a cyclic voltammogram (response current of Comparative Example 4). In Figure 4, the reduction current observed from around 0.1 V during the scan in the low potential direction corresponds to the deposition / dissolution reaction of lithium on the metal foil 32 (see Figure 3).

[0065] The oxidation current observed during the scan in the high potential direction was measured, and the ratios of the current values at 4.2 V, 4.5 V, 4.8 V, and 5.0 V to the current value at 4.0 V were calculated with the current value at 4.0 V being set as 1. The determination was made as follows: when the current value at 5.0 V with the current value at 4.0 V being set as 1 was less than 1.5, it was rated as A; when it was 1.5 or more and less than 2.0, it was rated as B; and when it was 2.0 or more, it was rated as C. The results are shown in Table 1.

[0066]

Table 1

[0067] Comparing Example 1 with Comparative Example 5 and Example 3 with Comparative Example 6 in Table 1, it was found that the oxidation current can be reduced by contacting LLZ with the electrolyte solution, that is, the oxidation-side potential window can be expanded compared to the potential window of the electrolyte solution. Further, comparing Example 3 with Comparative Examples 1 - 3, it was found that LLZ can expand the oxidation-side potential window of the electrolyte composition compared to oxide particles other than LLZ.

[0068] Comparing Example 1 and Comparative Example 1, it was found that the combination of pyrrolidinium cation contained in the electrolyte and LLZ is effective in expanding the oxidation-side potential window of the electrolyte composition. Further, comparing Examples 1-4, it was found that the higher the salt concentration of the electrolyte, the more the oxidation-side potential window of the electrolyte composition can be expanded. In particular, when the salt concentration of the electrolyte is 2 mol / dm 3 or more, it was revealed that the electrochemical stability of the electrolyte composition can be made higher.

[0069] The electrolyte compositions in Examples 1-4 were found to have high electrochemical stability in the range of 0.1 V to 5 V (vs. Li / Li + ). Therefore, it can be understood that a power storage device including the electrolyte composition in Examples 1-4 operates if it is a combination of a positive electrode and a negative electrode showing redox reactions in this potential range and the electrolyte composition.

[0070] As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above embodiments at all, and it can be easily inferred that various improvements and modifications are possible without departing from the gist of the present invention.

[0071] In the embodiment, as the power storage device 10, the one including the positive electrode layer 11 provided with the composite layer 13 on one side of the current collector layer 12 and the negative electrode layer 15 provided with the composite layer 17 on one side of the current collector layer 16 has been described. However, it is not necessarily limited to this. For example, it is naturally possible to apply each element in the embodiment to a power storage device including an electrode layer (so-called bipolar electrode) provided with the composite layer 13 and the composite layer 17 on both sides of the current collector layer 12, respectively. If the bipolar electrode and the electrolyte layer 14 are alternately laminated and housed in a case (not shown), a power storage device having a so-called bipolar structure can be obtained.

[0072] In the embodiment, the case where the composite layers 13, 17 and the electrolyte layer 14 all contain the electrolyte composition has been described. However, it is not necessarily limited to this. The power storage device only needs to have at least one of the composite layers 13, 17 and the electrolyte layer 14 containing the electrolyte composition.

[0073] In the embodiment, a power storage device 10 including a lithium ion battery (secondary battery) containing an electrolyte composition and having an electrode layer (a positive electrode layer 11 and a negative electrode layer 15) and an electrolyte layer 14 has been described, but it is not necessarily limited thereto. Other power storage devices include other secondary batteries such as lithium sulfur batteries, lithium oxygen batteries, and lithium air batteries, primary batteries, and electrolytic capacitors.

Explanation of Signs

[0074] 10 Power storage device 11 Positive electrode layer 14 Electrolyte layer (electrolyte composition) 15 Negative electrode layer 18 Ion conductor particles 21 Battery system 22 Charger

Claims

1. An electrolyte composition comprising garnet-type structured ion conductor particles containing Li, La, Zr and O, an ionic liquid, and an electrolyte salt, wherein the electrolyte salt is a lithium salt having a sulfonylimide structure as an anion, the ionic liquid contains a pyrrolidinium cation, The lithium ion concentration of the ionic liquid in which the electrolyte salt is dissolved is 1 mol / dm ３ or more, the content of the ionic liquid relative to the total amount of the ion conductor particles and the ionic liquid is 50% by volume or less.

2. The lithium ion conductivity at 25 °C is 4.0×10 －５ The electrolyte composition according to claim 1, which is 4.0×10

3. comprising a positive electrode layer, an electrolyte layer, and a negative electrode layer in this order, a power storage device in which at least one of the positive electrode layer, the electrolyte layer, and the negative electrode layer contains the electrolyte composition according to Claim 1 or 2.

4. A power storage device according to Claim 3 and a charger. A battery system in which the voltage applied by the charger to the power storage device is higher than 4.3 V, or the positive electrode potential of the power storage device during charging exceeds 4.3 V based on Li / Li ＋ reference.

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