CN117157718A - Solid electrolyte, electrolyte composition, electrolyte sheet, and power storage device - Google Patents

Solid electrolyte, electrolyte composition, electrolyte sheet, and power storage device Download PDF

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Publication number
CN117157718A
CN117157718A CN202280028878.9A CN202280028878A CN117157718A CN 117157718 A CN117157718 A CN 117157718A CN 202280028878 A CN202280028878 A CN 202280028878A CN 117157718 A CN117157718 A CN 117157718A
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China
Prior art keywords
electrolyte
solid electrolyte
powder
oxide
composition
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Inventor
野原直也
米仓宏
松浦广幸
山本洋
上木正聪
近藤彩子
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Niterra Co Ltd
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NGK Spark Plug Co Ltd
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Priority claimed from PCT/JP2022/017305 external-priority patent/WO2022230635A1/en
Publication of CN117157718A publication Critical patent/CN117157718A/en
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

Provided are a solid electrolyte, an electrolyte composition, an electrolyte sheet, and an electric storage device, which can reduce gelation. The solid electrolyte (18) has a garnet structure containing Li, la, zr and O, and in the particles (21) having a particle diameter of 10% or more as a cumulative value of the frequency of the volume-based particle size distribution, the number average value of the enveloping degree defined by the area of the outline (22) of the particles/the area of the envelope (23) is 0.8 or more. The electrolyte composition contains: solid electrolyte, ionic liquid comprising imidazolium cation, lithium salt and solid electrolyte comprising-CH 2 CF 2 -a polymer. The electrolyte sheet is formed from an electrolyte composition. The power storage device includes an electrolyte layer formed of an electrolyte composition.

Description

Solid electrolyte, electrolyte composition, electrolyte sheet, and power storage device
Technical Field
The present invention relates to a solid electrolyte, an electrolyte composition, an electrolyte sheet, and an electric storage device.
Background
A garnet-type structured solid electrolyte containing Li, la, zr, and O is known (patent document 1).
Prior art literature
Patent literature
Patent document 1: japanese patent No. 6682709
Disclosure of Invention
Problems to be solved by the invention
In the prior art, when a solid electrolyte having a garnet structure including Li, la, zr, and O is mixed with an organic compound, the organic compound reacts with the solid electrolyte, and gelation (non-fluidization) may occur. If it becomes in a gel state, fluctuation occurs in the dispersion state of the solid electrolyte.
The present invention has been made to solve the above problems, and an object thereof is to provide: solid electrolyte, electrolyte composition, electrolyte sheet and electric storage device capable of reducing gelation.
Solution for solving the problem
In order to achieve the object, aspect 1 of the present invention is a solid electrolyte in which, in a garnet-structured solid electrolyte containing Li, la, zr, and O, the number average value of envelopments defined by the area of the outline of particles/the area of the envelopment is 0.8 or more in particles having a particle diameter of 10% or more as the cumulative value of the frequency of the volume-based particle size distribution.
The 2 nd aspect is a solid electrolyte having a garnet structure including Li, la, zr, and O, wherein a mixture of N-methylpyrrolidone and the solid electrolyte contains 24.5wt% of the solid electrolyte relative to the mixture, and a liquid obtained by diluting a supernatant of the mixture 10 times with pure water has a hydrogen ion concentration index of pH8 or less.
Mode 3 is an electrolyte composition comprising: solid electrolyte in mode 1 or 2, ionic liquid comprising imidazolium cation, lithium salt and electrolyte comprising-CH 2 CF 2 -a polymer. The electrolyte sheet of the present invention is formed of an electrolyte composition. The electric storage device of the present invention includes an electrolyte layer formed of an electrolyte composition.
Mode 4 contains a garnet-type oxide (solid electrolyte) containing Li, la and Zr, and the cumulative value of the frequency of the particle size distribution on the volume basis of the oxide is 10% and the particle size is 1.4 μm or more.
Mode 5 contains an oxide (solid electrolyte) of garnet-type structure containing Li, la and Zr, the oxide being based on a gas adsorption methodSpecific surface area of 1.4m 2 And/g or less.
Mode 6 is an oxide (solid electrolyte) containing a garnet-type structure containing Li, la and Zr, the oxide having a half-value width of less than 0.30 ° in terms of X-ray diffraction of diffraction lines occurring in the range of 37.5 ° to 38.5 ° in 2θ.
Mode 7 is an electrolyte composition comprising the oxide, the electrolyte salt, the ionic liquid, the binder, and the solvent in any one of modes 4 to 6. The ionic liquid comprises an imidazolium cation and a sulfonimide anion. The solvent is aprotic and aprotic polar solvent, and the binder comprises-CH 2 CF 2 -。
ADVANTAGEOUS EFFECTS OF INVENTION
According to the solid electrolyte of the present invention, since the alkalinity is weak, the interaction between the solid electrolyte and the organic compound is less likely to occur, and gelation can be reduced. According to the electrolyte composition including the solid electrolyte, the electrolyte sheet including the electrolyte composition, and the power storage device, fluctuation in the dispersion state of the solid electrolyte can be reduced.
Drawings
Fig. 1 is a cross-sectional view of an electrical storage device in an embodiment.
Fig. 2 is a cross-sectional view of particles of a solid electrolyte.
Fig. 3 is a schematic diagram of the mixture.
Fig. 4 shows an example of cumulative distribution of oxides.
Fig. 5 is an X-ray diffraction pattern of an oxide.
Fig. 6 shows diffraction lines occurring in the range of 37.5 ° -38.5 ° 2θ.
Detailed Description
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 electric storage device 10 in an embodiment. The power storage device 10 in the present embodiment is a secondary battery formed of a solid battery in which a power generation element is formed of a solid. The power generating element being constituted by a solid means that the skeleton of the power generating element is constituted by a solid, and for example, a form in which the skeleton is impregnated with a liquid is not excluded.
As shown in fig. 1, the power 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).
The positive electrode layer 11 is formed by overlapping the current collecting layer 12 and the composite layer 13. The collector layer 12 is a conductive member. Examples of the material of the current collecting layer 12 are metals selected from Ni, ti, fe, and Al, alloys containing 2 or more elements thereof, stainless steel, and carbon materials.
The composite layer 13 is formed of a positive electrode composite material. The positive electrode composite material is formed of the electrolyte composition, the active material 19, and an optional conductive auxiliary agent. The electrolyte composition comprises a solid electrolyte 18, a polymer and an electrolyte solution. In order to reduce the resistance of the composite layer 13, a conductive auxiliary agent may be contained in the positive electrode composite material forming the composite layer 13. Examples of the conductive auxiliary agent include carbon black, acetylene black, ketjen black, carbon fiber, ni, pt, and Ag.
The active material 19 is exemplified by a metal oxide having a transition metal, a sulfur-based active material, and an organic-based active material. Examples of the metal oxide having a transition metal include metal oxides of Li and 1 or more elements selected from Mn, co, ni, fe, cr and V. Example LiCoO with transition metal Metal oxide 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiMn 2 O 4 、LiNiVO 4 、LiNi 0.5 Mn 1.5 O 4 、LiNi 1/3 Mn 1/3 Co 1/3 O 4 And LiFePO 4 。
For the purpose of suppressing the reaction of the active material 19 with the solid electrolyte 18, a coating layer may be provided on the surface of the active material 19. Example of the coating layer Al 2 O 3 、ZrO 2 、LiNbO 3 、Li 4 Ti 5 O 12 、LiTaO 3 、LiNbO 3 、LiAlO 2 、Li 2 ZrO 3 、Li 2 WO 4 、Li 2 TiO 3 、Li 2 B 4 O 7 、Li 3 PO 4 And Li (lithium) 2 MoO 4 。
Sulfur-based active material example S,TiS 2 、NiS、FeS 2 、Li 2 S、MoS 3 And sulfur-carbon composites. Examples of the organic active material include radical compounds represented by 2, 6-tetramethylpiperidin-4-yl methacrylate, polytetramethylpiperidinoxy vinyl ether, quinone compounds, alkylene oxide compounds, tetracyanoquinodimethane, and phenazine oxide.
The negative electrode layer 15 is formed by overlapping a current collecting layer 16 and a composite layer 17. The collector layer 16 is a conductive member. Examples of the material of the current collector layer 16 are selected from the group consisting of metals of Ni, ti, fe, cu and Si, alloys containing 2 or more of these elements, stainless steel, and carbon materials.
The composite layer 17 is formed of a negative electrode composite material. The negative electrode composite material is formed of an electrolyte composition, an active material 20, and an optional conductive auxiliary agent. The electrolyte composition comprises a solid electrolyte 18, a polymer and an electrolyte solution. In order to reduce the resistance of the composite layer 17, a conductive auxiliary agent may be contained in the negative electrode composite material forming the composite layer 17. Examples of the conductive auxiliary agent include carbon black, acetylene black, ketjen black, carbon fiber, ni, pt, and Ag. The active material 20 is exemplified by Li, li-Al alloy, li 4 Ti 5 O 12 Graphite, in, si-Li alloys, and SiO.
The electrolyte layer 14 is formed of an electrolyte composition. The electrolyte composition comprises a solid electrolyte 18, a polymer and an electrolyte solution. The solid electrolyte 18 is an oxide having lithium ion conductivity and having a garnet structure including Li, la, zr, and O. The basic composition of the garnet-structured oxide is Li 5 La 3 M 2 O 12 (m=nb, ta). The solid electrolyte 18 is exemplified by Li in which 5-valent M cations of basic composition are replaced with 4-valent cations 7 La 3 Zr 2 O 12 。
The solid electrolyte 18 may further contain at least 1 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) in addition to Li, la and Zr. For example, li is as follows 6 La 3 Zr 1.5 W 0.5 O 12 、Li 6.15 La 3 Zr 1.75 Ta 0.25 Al 0.2 O 12 、Li 6.15 La 3 Zr 1.75 Ta 0.25 Ga 0.2 O 12 、Li 6.25 La 3 Zr 2 Ga 0.25 O 12 、L i6.4 La 3 Zr 1.4 Ta 0.6 O 12 、Li 6.5 La 3 Zr 1.75 Te 0.25 O 12 、Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 、Li 6.9 La 3 Zr 1.675 Ta 0.289 Bi 0.036 O 12 、 Li 6.46 Ga 0.23 La 3 Zr 1.85 Y 0.15 O 12 、Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.2 5 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 Zr 2 O 12 。
The solid electrolyte 18 has, for example, a crystal structure of a cubic system (space group Ia-3d (-indicating upper line meaning rotation inversion operation), JCPLDS: 84-1753). The solid electrolyte 18 is particularly suitable to contain Mg and at least one of the elements a (a is at least 1 element selected from the group consisting of Ca, sr, and Ba), and the molar ratio of each element satisfies the following (1) to (3); or comprises both Mg and element A, and the molar ratio of each element satisfies the following (4) to (6). The element a is preferably Sr to improve the ion conductivity of the solid electrolyte 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
Fig. 2 is a cross-sectional view of particles 21 of solid electrolyte 18. The particles 21 are particles having a particle diameter of 10% as a cumulative value of the frequency of the particle size distribution based on the volume of the solid electrolyte 18 in the solid electrolyte 18Hereinafter referred to as "D 10 ") particles of above size. To find D 10 In the present embodiment, an image of the solid electrolyte 18 generated by a Scanning Electron Microscope (SEM) is analyzed on a cross section (a polished surface, a surface obtained by irradiating a beam of ions (FIB), a surface obtained by ion milling) of the electrolyte layer 14, and a circle equivalent diameter is calculated from the area of each particle of the solid electrolyte 18, thereby obtaining a volume-based particle size distribution. D (D) 10 The cumulative value (undersize) for the frequency of particle size distribution becomes 10% of the circle-equivalent diameter. The image in which the particle size distribution was obtained was 400 μm in the cross section of the electrolyte layer 14 2 The above area to ensure accuracy.
Next, D is found in the solid electrolyte 18 represented in the cross section of the measured particle size distribution 10 The number average value of the envelope degree of the particles 21 having the above particle diameters. Envelope is defined as "area/envelope inner area of the outline 22 of the particle 21". The envelope inner area is the area inside the envelope 23 that is in contact with the contour 22. The number average value of the envelope degree is obtained by dividing the value of the envelope degree of the added particles 21 by the number of particles 21 for which the envelope degree is obtained.
Excluding from the calculation of envelope degree that has a value lower than D 10 The reason for the particle size of (1) is that, in the case of image recognition, erroneous detection of substances other than the solid electrolyte 18 is prevented, which is based on the relationship of resolution of an image or the like. 2 nd, in the case where one end of the particle cuts off the particle, the apparent diameter of the particle appearing in the cross section sometimes becomes smaller than the actual particle diameter. The envelope degree of the particles having a small apparent diameter becomes close to 1, and therefore, it is excluded from calculation of the envelope degree that the particles have a value lower than D 10 To ensure accuracy.
The degree of envelope is an index indicating how much the contour 22 of the particle 21 has concave and convex, and the closer the degree of envelope is to 1, the less the concave and convex of the contour 22 of the particle 21 is. The envelope degree may be calculated using, for example, image processing software imageJ. There is a relationship between the envelope degree of the particles 21 and the alkalinity of the solid electrolyte 18 as follows: if the number average value of the envelope degree of the particles 21 is 0.8 or more, the alkalinity of the solid electrolyte 18 is reduced.
The envelope may be obtained by, in addition to the cross-sections of the electrolyte layer 14 and the composite layers 13 and 17, arranging the solid electrolytes 18 (powders) so as to be spaced apart (so as not to be aggregated), and performing image analysis on projections of the particles. When the envelope degree is obtained from the projection of the solid electrolyte 18 (powder), the cross section of the electrolyte layer 14 is 400. Mu.m 2 More than the number of particles present in the range of (2) are subjected to image analysis. Alternatively, the envelope degree may be obtained as follows: the enveloping degree can also be obtained by mixing the binder with the solid electrolyte 18 (powder) and performing sheet molding, or by embedding the solid electrolyte 18 (powder) in a synthetic resin to form a solid, and then analyzing an image of the solid electrolyte 18 shown in a cross section of the solid (a polished surface, a surface obtained by irradiation with FIB, a surface obtained by ion milling).
Fig. 3 is a schematic diagram of a mixture 24 comprising a solid electrolyte 18. Mixture 24 is formed from N-methyl pyrrolidone (N-methyl-2-pyrrolidone) and solid electrolyte 18. The mixture 24 was prepared in such a manner that the ratio of the mass of the solid electrolyte 18 at 25 ℃ to the mass of the mixture 24 became 24.5 wt%. The solid electrolyte 18 contained in the mixture 24 is, for example, randomly extracted from the electrolyte layer 14.
The solid electrolyte of garnet-type structure containing Li, la, zr, and O is generally strongly alkaline. For example, a mixture of N-methylpyrrolidone impregnated with a strongly alkaline solid electrolyte at a ratio of 24.5wt% is stirred and left for 12 hours to obtain a supernatant, and the supernatant is diluted with pure water to obtain a liquid having a hydrogen ion concentration index of pH10 or more at 25 ℃. The hydrogen ion concentration index was measured using pH test paper (TOYO ADVANTEC UNIV (1-11)).
In contrast, with respect to the solid electrolyte 18, after the mixture 24 containing the solid electrolyte 18 was stirred, the mixture 24 was left for 12 hours to obtain a supernatant 25, and the hydrogen ion concentration index at 25 ℃ was pH7 or more and pH8 or less, which was a liquid obtained by diluting the obtained supernatant 10 times with pure water. The alkalinity of the solid electrolyte 18 is reduced.
In addition, a solid electrolyte 18 (oxygenThe compound) is a particle diameter (hereinafter referred to as "D") having a cumulative value of 10% of the frequency of the volume-based particle size distribution 10 ") is 1.4 μm or more. The volume-based particle size distribution of the oxide is measured by a laser diffraction/scattering particle size distribution measuring device (e.g., microtrac MT3300EX II). The sample used for measuring the particle size distribution is, for example, an oxide directly taken out from the electrolyte layer 14. An appropriate amount of a sample was placed in a solvent (0.2 wt% aqueous solution of sodium hexametaphosphate), and the mixture was dispersed for 3 minutes using an ultrasonic disperser (for example, SD-600 manufactured by Nippon refiner manufacturing) and mounted in a measuring apparatus. When the particle size distribution was calculated, the refractive index of the sample was set to 1.81 and the refractive index of the solvent was set to 1.33.
Fig. 4 is an example of cumulative distribution (undersize) of cumulative values of frequencies of particle size distribution of volume basis of oxide. In FIG. 4, the particle diameter D at a particle ratio of 10% is shown 10 . The solid electrolyte 18 (oxide) of garnet-type structure containing Li, la and Zr is strongly alkaline. In particular, the oxide particles having a small particle diameter and a large specific surface area have poor chemical stability and are strongly alkaline. If the ratio of particles having a small particle diameter is decreased, the chemical stability of the oxide increases and the basicity decreases. D of oxides 10 If it is 1.4 μm or more, this tendency becomes remarkable.
The thickness of the oxide-containing electrolyte layer 14 is set to a particle diameter (hereinafter referred to as "D") at which the cumulative value of the frequency of the particle size distribution becomes 100%, for example 100 ") 3 times or more. In order to prevent short-circuiting between the electrodes. Thus, D of oxide 10 Preferably below 5 μm. D of oxides 10 If it is 5 μm or more, D is accompanied with this 100 The electrolyte layer 14 needs to be sufficiently thickened as it becomes larger. As the electrolyte layer 14 becomes thicker, the amount of the active material 19 per unit volume of the power storage device 10 becomes smaller, and the discharge capacity of the power storage device 10 decreases. In order to secure the discharge capacity of the power storage device 10, D of oxide 10 Suitably below 5 μm.
The solid electrolyte 18 (oxide) is a powder having a specific surface area of 1.4m2/g or less by a gas adsorption method. Specific surface area of the oxide is in accordance with JIS Z8830:2013 (ISO 9277:2010), for example by means of a fully automated specific surface area measuring device (Macsorb HM-1208), according to the BET method. The sample used for measuring the specific surface area is, for example, an oxide directly taken out from the electrolyte layer 14. Before the measurement of the specific surface area, the material physically adsorbed on the surface of the oxide was removed by degassing treatment in an inert gas (e.g., he) atmosphere at 200 ℃ for 60 minutes. The adsorption gas used for measuring the specific surface area was a mixed gas (He: n2=7:3), and the amount of the adsorption gas was measured by a flow method. The measurement temperature is normal temperature (15-25 ℃). The parameters are calculated according to a one-point method.
The solid electrolyte 18 (oxide) of garnet structure containing Li, la and Zr is strongly alkaline, but the chemical stability of the particles of the oxide increases and the alkalinity decreases as the specific surface area becomes smaller. Specific surface area of 1.4m 2 This tendency is particularly strong for oxides of/g or less.
Fig. 5 shows an example of a diffraction pattern of the solid electrolyte 18 (oxide) measured by a powder X-ray diffraction apparatus (not shown). The powder X-ray diffraction device is provided with an X-ray source, an optical system, an angular instrument and a detector. For the conditions of X-ray diffraction to obtain diffraction line 26, X-rays: the Kbeta filter is used to remove the CuKalpha ray of the Kbeta ray and the accelerating voltage (tube voltage) of the X-ray source: discharge current (tube current) of 50kV, X-ray source: 300mA, optical system: parallel method, goniometer: horizontal, scan axis: theta-2θ type, detector: scintillation counter, divergent slit: 1.0mm, divergent longitudinal limiting slit: 10mm, scattering slit: open, light receiving slit: open, continuous scan, scan speed: 0.3-0.7 °/min, sampling width: 0.02 deg..
Particles of an oxide (sample) used for X-ray diffraction are pulverized to a suitable particle size so as to be fixed to a sample holder without adopting a specific orientation state. The particle size and scanning speed of the sample were adjusted so that the number of diffraction peaks with the highest intensity became 2000-8000. According to the diffraction line 26 shown in FIG. 5, the oxide has a crystal structure of cubic crystal system (space group Ia-3d (-meaning upper line of rotation inversion operation), JCPDS: 84-1753).
Fig. 6 is a diffraction line 26 that occurs in the range of 37.5 ° -38.5 ° 2θ. The half-value width 31 of the diffraction line 26 in which the oxide appears in this range is less than 0.30 °. Half value width 31 is: the length of a line segment that can be cut by the diffraction peak 27 by a straight line parallel to the base line 29 from the midpoint of the perpendicular line 30 that sags from the apex 28 of the diffraction peak 27 to the base line 29. The base line 29 is a line segment connecting a point on the diffraction line 26 at 37.5 ° 2θ and a point on the diffraction line 26 at 38.5 ° 2θ.
1 particle of the oxide is composed of a plurality of crystallites. Crystallites are the largest aggregate considered to be single crystals. If the size of the crystallites becomes large, the number of crystallites per 1 grain becomes small, and the number of diffraction gratings per 1 crystallite becomes large. With this, the half width 31 becomes smaller. Since the half width 31 is measured from the diffraction peak 22 in the high angle region in which 2θ is 30 ° or more, the detection error of the diffraction grating value becomes small, and the accuracy of the half width 31 value can be improved.
The solid electrolyte 18 (oxide) of garnet structure containing Li, la and Zr is strongly alkaline, but if the number of diffraction gratings per 1 crystallite of the oxide becomes large, the chemical stability of the particles of the oxide increases and the alkalinity decreases. This tendency is particularly strong for oxides having a half-value width 31 of the diffraction line 26 below 0.30, which occurs in the range of 37.5 ° to 38.5 ° 2θ.
An example of a method for producing the solid electrolyte 18 will be described. For example, the method of manufacturing the solid electrolyte 18 includes: a compounding step of compounding raw materials to obtain a compounded material, a firing step of firing the compounded material, and a heat treatment step of heating the obtained synthetic powder.
In the compounding step, a material containing an element constituting the solid electrolyte 18 is compounded to obtain a compounded material. Examples of the material include oxides, composite oxides, hydroxides, carbonates, chlorides, sulfates, nitrates, phosphates, and the like, each of which contains Li, la, zr, mg and a (a is at least 1 element selected from the group consisting of Ca, sr, and Ba). The materials are crushed and mixed to obtain a compound material.
The pre-firing step of pre-firing the compound material is preferably included between the compounding step and the firing step. In this step, the compounded material is fired at, for example, 900 to 1100 ℃ for 2 to 15 hours to obtain a calcined material. By performing the baking step, a garnet-type crystal structure can be easily obtained after the baking step.
The pre-firing step and the firing step preferably include a step of pulverizing and mixing the pre-fired material. In this step, the pre-sintered material is crushed and mixed to obtain a mixed material. By performing the step of pulverizing and mixing the calcined material, a uniform crystal phase can be easily obtained after the sintering step. The pre-sintered material added with the binder may be crushed and mixed. Examples of binders are methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral.
In the firing step, the compound material, the presintered material or the mixed material is molded, and then the molded article is fired, for example, at 1000 to 1250 ℃ for 3 to 36 hours to obtain a sintered body. The sintered body was pulverized under an inert gas atmosphere to obtain a synthetic powder.
In the heat treatment step, the synthetic powder is placed in a furnace into and from which the gas flows, and the synthetic powder is heated in an atmosphere in which the gas flows around the synthetic powder. CO by heat treatment 2 From synthetic powder and atmospheric CO 2 Li reacted and formed on the surface of the synthesized powder 2 CO 3 The solid electrolyte 18 is obtained by changing the structure of the synthetic powder. Examples of temperature and time of heat treatment: the temperature is maintained at 640 ℃ or higher for 10 hours or more and at 670 ℃ or higher for 2 hours or more.
The gas is at least 1 selected from the group consisting of an inert gas and oxygen. The inert gas is not particularly limited as long as it does not chemically react with the synthetic powder. Examples of inert gases include nitrogen, helium, neon, argon, krypton, xenon, and radon. Particularly suitable is at least 1 selected from the group consisting of nitrogen, helium and argon.
The inflow and outflow of the gas may be continuous or intermittent. The flow rate of the gas introduced into the furnace continuously or intermittently and the period of the intermittently introduced gas are determined according to the volume of the furnace and the synthetic powderThe quality is appropriately set. CO of gas introduced into furnace 2 The concentration also depends on the temperature of the heat treatment, but is suitably lower than the CO in the atmosphere 2 The concentration (380 ppm) is, for example, 100ppm by volume or less. The dew point of the gas introduced into the furnace is preferably-40℃or lower, particularly-50 ℃. The reason is that the promotion of CO from the synthetic powder 2 Is separated from the shoe pad. The solid electrolyte 18 after the heat treatment is immediately mixed with an organic compound or the like and flaked, thereby obtaining composite layers 13, 17 and an electrolyte layer 14.
The median diameter of the equivalent diameter of the solid electrolyte 18 present in the cross section of the electrolyte layer 14 (hereinafter referred to as "D 50 ") is preferably 4-10 μm, more preferably 4-6 μm. The reason is that the surface area of the solid electrolyte 18 is appropriately sized, and the migration amount of lithium ions between the electrolyte solution sandwiched between the surface of the solid electrolyte 18 and the solid electrolyte 18 is ensured.
To determine D of the solid electrolyte 18 50 First, SEM-based images of the solid electrolyte 18 present on the cross section (polished surface, FIB-irradiated surface, ion-milled surface) of the electrolyte layer 14 were analyzed, and the equivalent circle diameter was calculated from the area of the solid electrolyte 18 together with the particles, to determine the volume-based particle size distribution. D (D) 50 The cumulative value of the frequency of the particle size distribution is 50% of the circle-equivalent diameter. The image in which the particle size distribution was obtained was 400 μm in the electrolyte layer 14 2 The above area to ensure accuracy.
The electrolyte contained in the electrolyte layer 14 contains an ionic liquid in which an electrolyte salt is dissolved. Ionic liquids are compounds formed from cations and anions, which are liquids at normal temperature and pressure. The ionic liquid constitutes the electrolyte, and thus, the flame retardancy of the electrolyte can be improved. The various physical properties and functions of the electrolyte are determined by the type of electrolyte salt and ionic liquid, and the salt concentration.
The electrolyte salt is a compound for exchanging cations between the positive electrode layer 11 and the negative electrode layer 15. The electrolyte salt is, for example, a lithium salt. Anions of the electrolyte salts exemplify halide ions (I - 、Cl - 、Br - Etc.), SCN - 、BF 4 - 、BF 3 (CF 3 ) - 、BF 3 (C 2 F 5 ) - 、PF 6 - 、ClO 4 - 、SbF 6 - 、N(SO 2 F) 2 - 、N(SO 2 CF 3 ) 2 - 、N(SO 2 C 2 F5) 2 - 、B(C 6 H 5 ) 4 - 、B(O 2 C 2 H 4 ) 2 - 、C(SO 2 F) 3 - 、C(SO 2 CF 3 ) 3 - 、CF 3 COO - 、CF 3 SO 2 O - 、C 6 F 5 SO 2 O - 、B(O 2 C 2 O 2 ) 2 - 、RCOO - (R is C1-C4 alkyl, phenyl or naphthyl) and the like.
The anions of the electrolyte salts preferably have sulfonyl groups-S (=o) 2 -N (SO) 2 F) 2 - 、N(SO 2 CF 3 ) 2 - 、N(SO 2 C 2 F 5 ) 2 - And the like. The reason is that even if the salt concentration of the sulfonimide anion becomes high, the influence of the viscosity increase and the ion conductivity decrease of the electrolyte is small, and a film (SEI) having high stability and low resistance is further formed, so that the reduction decomposition of the electrolyte can be reduced and the reduction side potential window can be expanded. N (SO) 2 F) 2 – Called FSI for short]-: bis (fluorosulfonyl) imide anions, N (SO) 2 CF 3 ) 2 – Called [ TFSI ]]-: bis (trifluoromethanesulfonyl) imide anions.
Ionic liquids are suitable with imidazolium as cationic species. The imidazolium cation is, for example, a compound represented by the formula (1).
In the formula (1), R 1 -R 5 Each of which is a single pieceIndependently represents a hydrogen group or an alkyl group. The alkyl group may have a substituent. R is R 1 -R 5 The carbon number of the alkyl group (containing a substituent) shown is preferably 1 to 10, more preferably 1 to 5, still more preferably 1 to 4. To ensure ionic conductivity of the electrolyte.
The substituent is not particularly limited. Examples of the substituent include alkyl, cycloalkyl, aryl, hydroxy, carboxyl, nitro, trifluoromethyl, amide, carbamoyl, ester, carbonyloxy, cyano, halo, alkoxy, aryloxy, sulfonamide and the like.
The anionic species of the ionic liquid is suitably a sulphonimide. Exemplary Sulfonylimide anions N (SO) 2 F) 2 - 、N(SO 2 CF 3 ) 2 - 、N(SO 2 C 2 F 5 ) 2 - 、N(SO 2 C 4 F 9 ) 2 - Etc. If the anionic substance of the ionic liquid is the same as that of the electrolyte salt, coordination (interaction) between lithium ions and anions contained in the electrolyte solution becomes easy to control, and thus is preferable.
Ionic liquids are exemplified by 1-ethyl-3-methylimidazole bis (fluorosulfonyl) imide salt (EMI-FSI), 1-ethyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt (EMI-TFSI). An ionic liquid (electrolyte solution) containing an imidazolium cation and a sulfonimide anion and having an electrolyte salt dissolved therein is preferable because high ion conductivity can be ensured.
The polymer contained in the electrolyte layer 14 is, for example, a binder that binds the solid electrolyte 18. The polymer contains a polymer comprising-CH 2 CF 2 Vinylidene fluoride polymers. The vinylidene fluoride polymer is preferable because it has high mechanical strength. The vinylidene fluoride polymer may contain only-CH 2 CF 2 There is no particular limitation. Examples of the vinylidene fluoride polymer include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride and a copolymerizable monomer.
Examples of the copolymerizable monomer include halogen-containing monomers (excluding vinylidene fluoride) and non-halogen-based copolymerizable monomers. Examples of the halogen-containing monomer include chlorine-containing monomers such as vinyl chloride; fluoromonomers such as trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. Examples of the non-halogen-based copolymerizable monomer include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, and esters or salts thereof; vinyl monomers such as acrylonitrile, vinyl acetate, and styrene.
1 or more than 2 kinds of copolymerizable monomers are polymerized with vinylidene fluoride to form a copolymer. In particular, a copolymer of vinylidene fluoride and hexafluoropropylene is preferable because the potential window can be enlarged.
The polymer may contain a polymer other than the vinylidene fluoride polymer. The content of the vinylidene fluoride polymer in the polymer is, for example, 80 to 100% by mass. Other polymers are exemplified by fluorinated resins (excluding vinylidene fluoride polymers), polyolefin, rubbery polymers such as styrene butadiene rubber, polyimide, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ether. The fluorinated resin may be a fully fluorinated resin, a partially fluorinated resin, or a fluorinated resin copolymer. The fully fluorinated resin is exemplified by polytetrafluoroethylene. The partially fluorinated resin is exemplified by polytrifluoroethylene and polyvinyl fluoride. Examples of the fluorinated resin copolymer include tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer.
The electrolyte layer 14 may contain a solvent for dissolving the polymer. The electrolyte salt is also dissolved in the solvent. The electrolyte layer 14 is obtained by molding an electrolyte composition containing a solid electrolyte 18, an electrolyte salt, an ionic liquid, a polymer, and a solvent into a sheet shape. At least a part of the solvent contained in the electrolyte composition is gasified by drying under reduced pressure or the like after the sheet formation for obtaining the electrolyte layer 14, and disappears from the electrolyte layer 14. The type and amount of the solvent remaining in the electrolyte layer 14 were determined by gas chromatography mass spectrometry (GC-MS).
The solvent is preferably an aprotic polar solvent, more preferably an aprotic and aprotic polar solvent. The classification of solvents (aprotic ) is according to I.M.Kolthoff, anal.Chem.46, 1992 (1974). In Kolthoff classification, solvents are broadly divided into: both acidic and basic, and capable of donating and accepting protons; and "aprotic" without hydrogen atoms capable of forming hydrogen bonds, the latter being subdivided into: "aprotic" which is strongly basic and readily solvated with cations; and "aprotic" which is weakly basic and not readily solvated with cations. In the aprotic and aprotic polar solvents, protons and hydrogen bonds do not substantially contribute to the reaction, and further the solid electrolyte 18 is easily dispersed.
Examples of the aprotic solvent among the aprotic polar solvents include N, N-dimethylformamide, N-dimethylacetamide, hexamethylphosphoric triamide, dimethylsulfoxide, N-methyl-2-pyrrolidone, pyridine, dioxane, tetrahydrofuran, and ether. Examples of aprotic solvents among aprotic polar solvents include propylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, sulfolane, acetonitrile, acetone, isobutyl methyl ketone, nitromethane, methyl ethyl ketone, and tetramethylsilane.
The electrolyte composition contains 1 or 2 or more of these polar solvents. The water content in the solvent and the ionic liquid is preferably 200ppm or less, more preferably 100ppm or less, particularly 10ppm or less, respectively. The reason is that the reaction of the water contained in the solvent, the ionic liquid, and the solid electrolyte 18 is reduced.
In the electrolyte composition in which the solid electrolyte 18 and the organic compound are mixed, the mechanism for estimating gelation (non-fluidization) by the reaction of the solid electrolyte 18 and the organic compound is as follows. First, a small amount of moisture contained in the electrolyte composition reacts with an alkaline solid electrolyte having garnet structure containing Li, la and Zr to generate LiOH, li on the surface of the solid electrolyte 2 O 3 . Thereby, OH in the system - Increasing, the alkalinity is enhanced.
When hydrogen is bonded to the carbon at the 2-position of the imidazolium cation of the ionic liquid, the ionic conductivity of the electrolyte decreases when protons at the 2-position are released by the base. Protons detached from imidazolium cations with OH - And reacts to produce water. The produced water reacts with the solid electrolyte as previously described to further enhance alkalinity.
Under alkaline conditions, vinylidene fluoride polymers tend to form polyene structures due to the release of HF. The electrolyte composition gels due to the polyeneization of the vinylidene fluoride-based polymer. Further by electrochemical reactions from detached HF, unwanted SEI is formed, and the resistance of SEI rises.
In contrast, since the solid electrolyte 18 having a number average value of the enveloping degree of the particles 21 of 0.8 or more is weak in alkalinity, the reaction between the water contained in the electrolyte composition and the solid electrolyte 18 can be reduced. Since the basicity in the system is not easily enhanced, the proton at the 2-position of the imidazolium cation is not easily detached, and the decrease in ion conductivity of the electrolyte resulting from the detachment of the proton is reduced. In addition, the vinylidene fluoride polymer is less likely to cause polyene formation due to HF detachment, and thus gelation of the electrolyte composition is reduced. Further, electrochemical reactions originating from HF are less likely to be caused, and thus, the resistance of the SEI can be maintained low. In particular, when the solvent contained in the electrolyte composition is an aprotic and aprotic polar solvent, protons and hydrogen bonds do not substantially contribute to the reaction, and thus gelation can be further reduced.
Further, since the solid electrolyte 18 having a hydrogen ion concentration index of pH8 or less, which is a liquid obtained by diluting the supernatant liquid 25 of the mixture 24 by 10 times with pure water, is weak in alkalinity, the reaction between the water contained in the electrolyte composition and the solid electrolyte 18 can be reduced, and gelation can be similarly reduced.
D 10 Since the solid electrolyte 18 (oxide) having a size of 1.4 μm or more is also weak in alkalinity, the reaction between the water contained in the electrolyte composition and the solid electrolyte 18 can be reduced, and gelation can be similarly reduced.
Specific surface area of 1.4m 2 Since the solid electrolyte 18 (oxide) having a concentration of not more than/g is also weak in alkalinity, the reaction between the water contained in the electrolyte composition and the solid electrolyte 18 can be reduced, and gelation can be similarly reduced.
Since the solid electrolyte 18 (oxide) having the half width 31 of the diffraction line 26 in the range of 37.5 ° to 38.5 ° and having a half width 31 of less than 0.30 ° is also weak in alkalinity, the reaction of the moisture contained in the electrolyte composition with the solid electrolyte 18 can be reduced, and gelation can be similarly reduced.
The content (volume%) of the ionic liquid in the electrolyte layer 14 (electrolyte composition) is suitably 50 volume% or less (excluding 0 volume%) with respect to the total amount of the solid electrolyte 18 and the ionic liquid. Namely, a solid electrolyte: ionic liquid= (100-X): x,0<X is less than or equal to 50. The reason is that ionic conductivity is ensured by the ionic liquid sandwiched between the solid electrolytes 18 and 18, and the occurrence of ionic liquid exudation is reduced.
The content (vol%) of the ionic liquid was determined as follows: the electrolyte layer 14 was frozen or the electrolyte layer 14 was embedded in a 4-functional epoxy resin or the like and fixed, and then a view of 5000 times randomly selected from the cross section of the electrolyte layer 14 was taken as a target, and analyzed by SEM equipped with an energy dispersive X-ray spectrometer (EDS), to obtain the product. The analysis was performed as follows: the distribution of La, zr, S is specified, or the contrast of the reflected electron image is image-analyzed, the area of the solid electrolyte 18 and the area of the ionic liquid are specified, and the ratio of the area in the cross section of the electrolyte layer 14 is regarded as the ratio of the volume in the electrolyte layer 14, to obtain the content (volume%) of the ionic liquid.
The lithium ion conductivity of the electrolyte composition is determined according to the kind, salt concentration, and the like of the solid electrolyte 18, the electrolyte salt, and the ionic liquid. The electrolyte composition preferably has a lithium ion conductivity of 4.0X10 at 25 ℃ -5 S/cm or more. To ensure the output density of the power storage device 10 including the electrolyte composition.
The electrolyte composition contains anions derived from the electrolyte solution, and therefore, the lithium ion conductivity of the electrolyte composition is calculated as follows: the total ion conductivity calculated by the ac impedance method of the symmetrical battery cell having the current collector adhered to both sides of the electrolyte composition molded into a sheet shape was multiplied by the migration number of lithium ions. The migration number of lithium ions was determined by an ac impedance method and a steady-state dc method.
The migration number was calculated as follows. First, the resistance value R of the battery cell is measured based on the AC impedance S0 And (5) analyzing. The conditions for ac impedance measurement were: the temperature is 25 ℃, the voltage is 10mV, and the frequency is 7MHz-100mHz.
Next, an initial current value I immediately after the constant voltage V is applied to the battery cell is measured 0 The initial resistance R of the battery cell was calculated according to the following formula A 0 。R 0 ＝V/I 0 ···A
The measurement conditions of the initial current value were set as follows: voltage 10mV, total time 6 seconds, measurement interval 0.0002 seconds.
Will have a resistance value R S0 And an initial resistance value R 0 Substituting into the following formula B to calculate the interface resistance R INT 。R INT ＝R 0 -R S0 ···B
Then, the current value I after the steady state is obtained by applying the constant voltage V to the battery cell is measured, and the resistance value R in the steady state of the battery cell is calculated according to the following formula C P 。R P ＝V/I···C
The measurement conditions of the current value in the steady state were set as follows: the voltage was 10mV, the total time was 10 hours, and the measurement interval was 60 seconds.
After the battery cell is in a stable state, the resistance R of the battery cell is measured from the AC impedance under the above conditions S And (5) analyzing. Will have a resistance value R S Resistance value R P And interface resistance R INT Substituting into the following formula D to calculate the migration number t Li 。t Li ＝R S /(R P -R INT )···D
In the electrolyte layer 14 (electrolyte composition), the amount (volume%) of the binder is suitably 10 volume% or less (excluding 0 volume%) with respect to the amount of the solid electrolyte 18 and the ionic liquid added. That is, the amounts of solid electrolyte and ionic liquid are added: amount of binder= (100-Y): y is more than 0 and less than or equal to 10. The reason is that the formability of the electrolyte layer 14 is ensured by the binder, and the decrease in ion conductivity of the electrolyte layer 14 is reduced. The content (vol%) of the binder can be specified by the area% of the cross section of the electrolyte layer 14 obtained by SEM-EDS analysis, as described above.
The power storage device 10 is manufactured as follows, for example. In the case of mixing the ionic liquid in which the electrolyte salt is dissolved and the solid electrolyte 18, a solution in which the polymer is dissolved in a mixed solvent is prepared into a slurry. The tape was molded and then dried to obtain a green sheet (electrolyte sheet) for the electrolyte layer 14.
The active material 19 is mixed with the solid electrolyte 18 and the ionic liquid in which the electrolyte salt is dissolved, and the solution in which the polymer is dissolved in the solvent is further mixed to prepare a slurry. The current collector layer 12 was formed and dried to obtain a green sheet (positive electrode sheet of electrolyte sheet 1) for the positive electrode layer 11.
The active material 20 is mixed with the solid electrolyte 18 and the ionic liquid in which the electrolyte salt is dissolved, and the solution in which the polymer is dissolved in the solvent is further mixed to prepare a slurry. The current collector layer 16 was formed with a tape and then dried to obtain a green sheet (negative electrode sheet of electrolyte sheet 1) for the negative electrode layer 15.
After the electrolyte sheet, the positive electrode sheet and the negative electrode sheet are cut into prescribed shapes, the positive electrode sheet, the electrolyte sheet and the negative electrode sheet are sequentially overlapped and are pressed and connected with each other to be integrated. Terminals (not shown) are connected to the current collecting layers 12 and 16, respectively, and the terminals are sealed in a case (not shown), thereby obtaining the power storage device 10 including the positive electrode layer 11, the electrolyte layer 14, and the negative electrode layer 15 in this order.
Examples
The present invention will be described in further detail with reference to examples, but the present invention is not limited to the examples.
(preparation of solid electrolyte)
To become Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr 2.0 O 12 In the way (1), li is weighed 2 CO 3 、MgO、La(OH) 3 、SrCO 3 、ZrO 2 . Considering volatilization of Li during firing, li 2 CO 3 The element conversion is set to be about 15mol% excess. The weighed raw materials, ethanol and zirconia balls were put into a nylon pot, and crushed and mixed in a ball mill for 15 hours. The slurry taken out of the tank was dried, and then, the slurry was pre-fired on a MgO-made plate (at 900)At c for 1 hour). The powder after the pre-firing and ethanol were put into a nylon pot, and pulverized and mixed in a ball mill for 15 hours.
The slurry taken out of the pot was dried, and then put into a die having a diameter of 12mm, and a molded article having a thickness of about 1.5mm was obtained by press molding. Applying 1.5t/cm to the further shaped body by means of a Cold Isostatic Press (CIP) 2 Is set in the static pressure of (a). The molded body was covered with a calcined powder having the same composition as the molded body, and the molded body was calcined in a reducing atmosphere (at 1100 ℃ for 4 hours) to obtain a sintered body of a solid electrolyte. The lithium ion conductivity of the sintered body obtained by the AC impedance method was 1.0X10 - 3 S/cm. The measurement conditions of lithium ion conductivity were: the temperature is 25 ℃, the voltage is 10mV, and the frequency is 7MHz-100mHz. The sintered body was pulverized in an Ar atmosphere, applied to a sieve having a mesh opening of 250 μm, and powder of the solid electrolyte passing through the sieve was collected.
100g of the powder passing through the sieve, 536g of ball having a diameter of 4mm and 250mL of the fluorine-based inactive liquid were placed in the pot, and the powder was pulverized in a planetary ball mill (rotation speed 200 rpm) for 6 hours. The slurry taken out of the tank was dried to obtain coarse powder of the solid electrolyte.
50g of the powder passing through the sieve, 536g of a ball having a diameter of 4mm and 100mL of a fluorine-based inactive liquid were placed in the pot in the same manner, and the powder was pulverized in a planetary ball mill (rotational speed 300 rpm) for 4 hours. The slurry taken out of the tank was dried to obtain a fine powder of the solid electrolyte.
(heat treatment of coarse powder and micropowder)
Is stored in a tube furnace (volume 1875 cm) with nitrogen gas (flow rate: 10L/min) introduced from one end of the tube furnace and exhaust gas from the other end of the furnace 3 ) The coarse powder (40 g or less) of the solid electrolyte of (C) was heated at 670℃for 2 hours. Immediately after the temperature in the furnace was set to 50 ℃, the heat-treated coarse powder was taken out of the furnace and stored in a closed container to prevent atmospheric exposure. The fine powder of the solid electrolyte was also subjected to heat treatment under the same conditions, and stored in a sealed container.
(calculation of envelope degree)
Heat-treated coarse powder, heat-treated micropowder, and non-heat-treated micropowderAfter the heat-treated coarse powders were each sparsely bonded and fixed to a carbon tape provided with a bonding layer, SEM images of the powders were obtained. From the image analysis, the equivalent diameter of the circle is calculated from the area (projection) of the solid electrolyte together with the particles, the volume-based particle size distribution is obtained, and D is calculated 10 。
Next, D was found to be present in the solid electrolyte in which the particle size distribution was measured by using imageJ 1.52v 10 The number average value of the envelope degree of the particles having the above particle diameters. The number average of the enveloping degrees of the heat-treated coarse powder (hereinafter referred to as "powder a"), the heat-treated fine powder (hereinafter referred to as "powder B") and the non-heat-treated coarse powder (hereinafter referred to as "powder C") was 0.93, 0.80 and 0.75 in this order.
(measurement of Hydrogen ion concentration index)
A mixture was prepared by immersing powder A, powder B and powder C in N-methyl-2-pyrrolidone, respectively, and stirring the resulting mixture, and the mixture was left to stand in a room at 25℃for 12 hours. The ratio of each powder to the mixture was 24.5wt%. The hydrogen ion concentration index of the liquid obtained by diluting the supernatant of the mixture after the standing with pure water 10 times was measured by pH test paper (TOYO ADVANTEC UNIV (1-11)). The hydrogen ion concentration index measured from the mixture containing powder a, powder B, and powder C was pH7-8, and pH10, respectively. The reason why the hydrogen ion concentration index of the powders a and B has a magnitude of pH7 to 8 is that the change in color of the pH test paper is judged visually.
(determination of particle size distribution)
The particle size distribution of powder a, powder B, and powder C was measured by a laser diffraction/scattering particle size distribution measuring apparatus (Microtrac MT3300EX II). A sample for measuring the particle size distribution was placed in a solvent (0.2 wt% aqueous solution of sodium hexametaphosphate), dispersing for 3 minutes with an ultrasonic disperser (SD-600 manufactured by Japanese Kogyo Co., ltd.) and mounting on a measuring apparatus. The refractive index of the sample was set to 1.81, and D was calculated by setting the refractive index of the solvent to 1.33 10 、D 50 、D 90 、D 100 。D 50 、D 90 The cumulative value (undersize) of the frequency of the particle size distribution is 50% and 90% of the particle size. Powder A, powder B,D of powder C 10 Sequentially 3.6 μm, 1.4 μm, and 0.5 μm.
(measurement of specific surface area)
Using a fully automatic specific surface area measuring device (HM-1208), a BET flow 1 point method (He: N) 2 =7: 3) The specific surface areas of powder a, powder B, and powder C were measured. The sample having the specific surface area was subjected to degassing treatment at 200℃for 60 minutes in an inert atmosphere before measurement. The specific surface area of powder A, powder B and powder C is 0.4m in sequence 2 /g、1.4m 2 /g、1.6m 2 /g。
(X-ray diffraction)
Using a powder X-ray diffraction device, X-rays: cukα line, tube voltage: 50kV, tube current: 300mA, optical system: parallel method, goniometer: horizontal, scan axis: theta-2θ type, detector: scintillation counter, divergent slit: 1.0mm, divergent longitudinal limiting slit: 10mm, scattering slit: open, light receiving slit: open, continuous scan, scan speed: 0.3-0.7 °/min, sampling width: under the condition of 0.02 ℃, diffraction patterns of powder A, powder B and powder C are respectively obtained. The scanning speed is adjusted to be in the range of 0.3 to 0.7 DEG/min so that the count value of the diffraction peak with the highest intensity becomes 2000 to 8000. From the obtained diffraction pattern, the half-value width of the diffraction line appearing in the range of 37.5 ° to 38.5 ° in 2θ was determined. The half-value widths of powder a, powder B, and powder C are 0.26 °, 0.29 °, and 0.31 ° in order.
(preparation of electrolyte)
Lithium salt LiN (SO) in ionic liquid 1-ethyl-3-methylimidazole bis (fluorosulfonyl) imide salt (EMI-FSI) 2 F) 2 Compounding 3mol/dm 3 And obtaining electrolyte.
Example 1
To become a solid electrolyte: electrolyte=61: 39 (volume ratio) powder a and an electrolyte were mixed in a mortar in an Ar atmosphere to obtain a composite powder. 18g of composite powder, 0.864g of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and 7.776g of dimethyl carbonate (DMC) were mixed in an Ar atmosphere to obtain a slurry in example 1.
Example 2
The slurry of example 2 was obtained in the same manner as in example 1, except that the powder a was replaced with the powder B.
Comparative example 1
A slurry of comparative example 1 was obtained in the same manner as in example 1 except that the powder a was replaced with the powder C.
Comparative example 2
A slurry of comparative example 2 was obtained in the same manner as in comparative example 1, except that dimethyl carbonate was replaced with Propylene Carbonate (PC).
Example 3
To become a solid electrolyte: electrolyte=61: 39 (volume ratio) powder a and an electrolyte were mixed in a mortar in an Ar atmosphere to obtain a composite powder. 18g of composite powder, 0.864g of vinylidene fluoride (PVDF) and 7.776g of Propylene Carbonate (PC) were mixed in an Ar atmosphere to obtain a slurry in example 3.
Example 4
The slurry of example 4 was obtained in the same manner as in example 3, except that propylene carbonate was replaced with dimethyl carbonate (DMC).
Example 5
The slurry of example 5 was obtained in the same manner as in example 3, except that the powder a was replaced with the powder B.
Example 6
A slurry in example 6 was obtained in the same manner as in example 5, except that propylene carbonate was replaced with dimethyl carbonate.
Comparative example 3
A slurry of comparative example 3 was obtained in the same manner as in example 3 except that the powder a was replaced with the powder C.
Comparative example 4
A slurry of comparative example 4 was obtained in the same manner as in comparative example 3, except that propylene carbonate was replaced with dimethyl carbonate.
Comparative example 5
A slurry in comparative example 5 was obtained in the same manner as in example 3 except that propylene carbonate was replaced with N-methyl-2-pyrrolidone (NMP).
(test methods and results)
The slurries of examples and comparative examples were placed in a beaker, respectively, and placed in a container of an Ar atmosphere at 25℃for 12 hours. After 12 hours, it was visually confirmed whether the slurry gelled (did not flow). The results are shown in tables 1 and 2. At least a part of the slurry was gelled and the slurry was not gelled at all were designated as-.
TABLE 1
TABLE 2
As shown in tables 1 and 2, the slurries in examples 1 to 6 were not gelled at all, but the slurries in comparative examples 1 to 5 were gelled. The slurries in comparative examples 1-5 were colored brown.
The slurries of examples 1 to 6 and comparative examples 1 to 4 contained DMC and PC which are aprotic and aprotic polar solvents. If examples 1 to 4 and comparative examples 1 to 4, in which PC or DMC was contained in the comparative slurry, were compared, the slurries of examples 1 to 6, in which oxide (solid electrolyte) having an envelope degree of 0.80 or more was contained, did not cause gelation, and the slurries of comparative examples 1 to 4, in which oxide having an envelope degree of 0.75 was contained, were gelled. The discoloration and gelation of the slurry are presumed to be caused by the polyeneization of vinylidene fluoride based on the detachment of HF. It is presumed that the slurry containing the oxide having an envelope degree of 0.80 or more does not easily cause interaction of constituent components of the slurry, and therefore, gelation does not occur.
The slurries of examples 1 to 6 containing the oxide at pH7 (solid electrolyte) did not cause gelation, and the slurries of comparative examples 1 to 4 containing the oxide at pH10 did gel. It is presumed that the slurry containing the oxide of pH7 is unlikely to cause interaction of constituent components of the slurry, and therefore, gelation is not caused.
Comprises D 10 1.4 muThe slurries of examples 3 to 6 of oxides (solid electrolytes) having m or more did not cause gelation, and contained D 10 The slurries of comparative examples 3 and 4, which were 0.5 μm oxides, gelled. Presumption D 10 The oxides having a size of 1.4 μm or more are weak in alkalinity and are unlikely to cause interaction between the constituent components of the slurry, and therefore do not cause gelation.
Comprises a specific surface area of 1.4m 2 The slurries of examples 3 to 6, which were composed of oxides (solid electrolytes) of not more than/g, did not cause gelation and contained a specific surface area of 1.6m 2 The slurries of comparative examples 3 and 4 per gram of oxide gelled. The specific surface area was presumed to be 1.4m 2 The oxide having an alkali value of/g or less is less likely to cause interaction between the constituent components of the slurry, and therefore does not cause gelation.
The slurries of examples 3 to 6 containing the oxide having a half-value width of less than 0.30 ° (solid electrolyte) did not cause gelation, and the slurries of comparative examples 3 and 4 containing the oxide having a half-value width of 0.31 ° gelled. It is presumed that the oxide having a half-value width of less than 0.30 ° is weak in alkalinity and is unlikely to cause interaction of constituent components of the slurry, and thus does not cause gelation.
The slurry of comparative example 5 contained NMP as the aprotic polar solvent. If comparative examples 3 and 4 and comparative example 5, the slurries of examples 3 and 4 containing aprotic and aprotic polar solvents (PC, DMC) did not cause gelation, and the slurry of comparative example 5 containing aprotic polar solvent (NMP) gelled. It is presumed that the aprotic and aprotic polar solvents are less basic than the aprotic polar solvents, and therefore, the interaction of the constituent components of the slurry is less likely to occur, and gelation is not caused.
In the case where PVDF was replaced with PVDF in the slurries of examples 3, 5 and comparative example 5, the same results as those of examples 3, 5 and comparative example 5 were obtained and are clarified by the results of examples 1, 2, 4, 6 and comparative examples 1 to 4.
According to this example, it is shown that: an oxide (solid electrolyte) having a garnet structure containing Li, la and Zr and having D 10 Envelope of the above particle sizeAn oxide having a number average value of the degree of 0.8 or more can reduce gelation. The following is indicated: the electrolyte composition containing the solid electrolyte, the ionic liquid containing imidazolium cations, the lithium salt, and the vinylidene fluoride polymer can also reduce gelation. The electrolyte sheet and the power storage device including the electrolyte composition can reduce fluctuation in the dispersion state of constituent components, and therefore, can reduce fluctuation in performance.
The following is indicated: an oxide (solid electrolyte) having a garnet structure containing Li, la and Zr, and an oxide having a hydrogen ion concentration index of pH8 or less in the supernatant of the mixture can reduce gelation. The following is indicated: the electrolyte composition containing the solid electrolyte, the ionic liquid containing imidazolium cations, the lithium salt, and the vinylidene fluoride polymer can also reduce gelation. The electrolyte sheet and the power storage device including the electrolyte composition can reduce fluctuation in the dispersion state of constituent components, and therefore, can reduce fluctuation in performance.
The following is indicated: contains an oxide (solid electrolyte) of garnet structure containing Li, la and Zr, and D 10 An electrolyte composition of an oxide of 1.4 μm or more, an ionic liquid containing an imidazolium cation and a sulfonimide anion, an electrolyte salt, a binder containing a vinylidene fluoride polymer, and an aprotic and aprotic polar solvent can reduce gelation. The electrolyte sheet and the secondary battery comprising the electrolyte composition can reduce fluctuation in the dispersion state of constituent components, and therefore, can reduce fluctuation in performance.
The following is indicated: contains an oxide (solid electrolyte) having a garnet structure containing Li, la and Zr, and has a specific surface area of 1.4m by a gas adsorption method 2 The electrolyte composition of the oxide, the ionic liquid containing imidazolium cation and sulfonimide anion, the electrolyte salt, the binder containing vinylidene fluoride polymer, and the aprotic and aprotic polar solvent can reduce gelation. The electrolyte sheet and the secondary battery comprising the electrolyte composition can reduce fluctuation in the dispersion state of constituent components, and therefore, can reduce fluctuation in performance.
The following is indicated: an electrolyte composition containing an oxide (solid electrolyte) of garnet-type structure containing Li, la and Zr, and having a half-value width of diffraction lines occurring in the range of 37.5 ° to 38.5 ° according to X-ray diffraction, of less than 0.30 °, an ionic liquid containing an imidazolium cation and a sulfonimide anion, an electrolyte salt, a binder containing a vinylidene fluoride-based polymer, and an aprotic and aprotic polar solvent can reduce gelation. The electrolyte sheet and the secondary battery comprising the electrolyte composition can reduce fluctuation in the dispersion state of constituent components, and therefore, can reduce fluctuation in performance.
The present invention has been described above based on the embodiments, but the present invention is not limited to the embodiments described above, and it can be easily estimated that various modifications and variations can be made without departing from the gist of the present invention.
In the embodiment, the power storage device 10 has been described as including the positive electrode layer 11 having the composite layer 13 provided on one side of the current collecting layer 12, and the negative electrode layer 15 having the composite layer 17 provided on one side of the current collecting layer 16, but the present invention is not limited thereto. For example, it is needless to say that each element in the embodiment may be applied to a secondary battery including electrode layers (so-called bipolar electrodes) each having a composite layer 13 and a composite layer 17 on both surfaces of a current collector 12. If bipolar electrodes and electrolyte layers 14 are alternately stacked and housed in a case (not shown), a secondary battery of a so-called bipolar structure is obtained.
In the embodiment, the case where the composite layers 13, 17 and the electrolyte layer 14 all contain the electrolyte composition has been described, but this is not necessarily the case. The secondary battery may be one in which at least 1 of the composite layers 13, 17 and the electrolyte layer 14 contains an electrolyte composition.
In the embodiment, the lithium ion battery (secondary battery) including the electrolyte composition is exemplified, and the power storage device 10 including the electrode layers (the positive electrode layer 11 and the negative electrode layer 15) and the electrolyte layer 14 is described, but not necessarily limited thereto. Examples of the other secondary battery include a lithium sulfur battery, a lithium oxygen battery, and a lithium air battery.
Description of the reference numerals
10. Power storage device
13. Composite layer
14. Electrolyte layer (electrolyte sheet)
17. Composite layer
18. Solid electrolyte
21. Particles
22. Contour profile
23. Envelope line
24. Mixture of
25. Supernatant fluid

Claims (5)

1. A solid electrolyte of garnet structure containing Li, la, zr and O,
in the solid electrolyte, the number average value of envelope degree defined by the area of the outline of particles/the area of the envelope is 0.8 or more in the particles having a particle diameter of 10% or more as the cumulative value of the frequency of the volume-based particle size distribution.
2. The solid electrolyte according to claim 1, wherein,
the mixture formed by N-methylpyrrolidone and the solid electrolyte contains 24.5wt% of the solid electrolyte relative to the mixture,
the hydrogen ion concentration index of the liquid obtained by diluting the supernatant of the mixture 10 times with pure water is pH8 or less.
3. An electrolyte composition comprising: the solid electrolyte of claim 1 or 2, an ionic liquid comprising an imidazolium cation, a lithium salt and a solid electrolyte comprising-CH 2 CF 2 -a polymer.
4. An electrolyte sheet formed from the electrolyte composition of claim 3.
5. An electric storage device comprising an electrolyte layer formed from the electrolyte composition of claim 3.
CN202280028878.9A 2021-04-30 2022-04-07 Solid electrolyte, electrolyte composition, electrolyte sheet, and power storage device Pending CN117157718A (en)

Applications Claiming Priority (7)

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JP2021-077400 2021-04-30
JP2021-077418 2021-04-30
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