JP2016139461A - Solid electrolyte for electrochemical element and all-solid battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte for an electrochemical element, having chemically and structurally high stability and capable of achieving both higher output and higher heat resistance of a battery.SOLUTION: A solid electrolyte for an electrochemical element includes an ion conducting plastic crystal that is a complex of a plastic crystal containing a quaternary phosphonium cation and an ionic salt, a counter anion of the quaternary phosphonium cation being hexafluorophosphate, tetrafluoroborate or thiocyanate, and the ionic salt being a lithium salt, sodium salt, magnesium salt or aluminum salt.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solid electrolyte for an electrochemical device and an all-solid battery using the same.

  All-solid-state batteries (all-solid-state secondary batteries) using a non-flammable or flame-retardant solid electrolyte can increase the heat resistance of the battery, reduce the module cost required for cooling, and increase the energy density. Is possible. In a secondary battery using an oxide-based electrolyte that is one of solid electrolytes, there is a void between the electrolyte or electrode active material particles, and therefore a method of filling the void with a lithium ion conductive material has been proposed. . For example, Patent Document 1 (Japanese Patent Laid-Open No. 11-7981) discloses a secondary battery composed of a positive electrode, a solid electrolyte, and a negative electrode in which at least one of the active materials of the positive electrode and the negative electrode is dispersed in a polymer gel. There is disclosed a secondary battery that is characterized. According to Patent Document 1, the use of a polymer gel as a dispersion medium for an electrode has an effect of remarkably reducing the contact resistance between the electrode and the solid electrolyte, and is extremely effective for homogenizing the electrode reaction. ing.

  However, fillers made of organic molecules such as gels and polymers have a problem of chemical stability such as decomposition reaction at high temperature. Furthermore, depending on the type of the gel filler, when the battery driving temperature becomes a high temperature of 100 ° C. or higher, there is a problem that the fluidity of the gel increases and the structural strength of the electrode decreases.

  Therefore, plastic crystals have attracted attention as fillers instead of fillers made of organic molecules. The plastic crystal is a substance showing an intermediate phase between a solid state and a liquid state, and exhibits high ionic conductivity while maintaining the solid state. It is known that when an ionic salt such as a lithium salt is added in this state, the ionic conductivity is further improved by several orders of magnitude. By filling the voids inside the electrode layer with the plastic crystal, the lithium ion conduction path inside the electrode is improved and high output can be realized. In addition, plastic crystals have higher chemical stability at high temperatures than fillers made of organic molecules. Patent Document 2 (International Publication No. 2008/081811) discloses an all-solid lithium secondary battery to which a heat-resistant plastic crystal is applied.

JP-A-11-7981 International Publication No. 2008/081811

In the above Patent Document 2, evaluation results of DSC (Differential Scanning Calibration) measurement (phase transition temperature evaluation), conductivity measurement and cyclic voltammetry measurement (electrochemical stability evaluation) of lithium ion conductive plastic crystals are as follows. Have been described. However, although the physical properties of the plastic crystal itself have been evaluated,
No investigation has been made on the improvement in heat resistance and output of an all-solid battery using a plastic crystal.

  In view of the above circumstances, the present invention provides a solid electrolyte for an electrochemical element that can be filled at a low temperature, has high chemical and structural stability, and can achieve both high output and high heat resistance of a battery. The purpose is to provide.

  In order to achieve the above object, the present invention provides a solid electrolyte for an electrochemical device comprising an ion conductive plastic crystal that is a complex of a plastic crystal containing a quaternary phosphonium cation and an ionic salt. provide.

  Further, the present invention includes a positive electrode, a negative electrode, and a separator that partitions the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode, and the separator includes the ion conductive plastic crystal. An all-solid battery is provided.

  According to the present invention, the electrode can be filled at a low temperature, has high chemical and structural stability, and can achieve both high heat resistance of the battery (can be used at room temperature to less than 150 ° C) and high output. A possible solid electrolyte for an electrochemical device can be provided. Moreover, the all-solid-state battery using this solid electrolyte for electrochemical elements can be provided.

It is sectional drawing which shows typically an example of the all-solid-state battery which concerns on this invention. It is the elements on larger scale of the positive mix layer 40 of FIG. It is the elements on larger scale of the negative mix layer 60 of FIG. It is the elements on larger scale of the separator layer 50 of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

<All solid battery>
FIG. 1 is a cross-sectional view schematically showing an example of an all-solid battery according to the present invention. As shown in FIG. 1, an all-solid battery (hereinafter also simply referred to as a battery) 100 includes a positive electrode 70 housed in a battery case 30, a negative electrode 80, and a separator layer 50 that partitions the positive electrode 70 and the negative electrode 80. The positive electrode 70 includes the positive electrode current collector 10 and the positive electrode mixture layer 40 provided on the positive electrode current collector 10, and the negative electrode 80 is provided on the negative electrode current collector 20 and the negative electrode current collector 20. And the negative electrode composite material layer 60 thus obtained.

  In the all solid state battery 100 according to the present invention, at least one of the positive electrode 70, the negative electrode 80, and the separator layer 50 includes an ion conductive plastic crystal according to the present invention described later. The present invention is applicable to lithium ion batteries, sodium ion batteries, magnesium ion batteries, aluminum ion batteries, and the like as all solid state batteries. In the following description, the present invention will be described in detail by taking a lithium ion battery as an example of the all-solid battery 100. In the following description, the all solid state battery 100 is also simply referred to as “battery”, the positive electrode 70 and the negative electrode 80 are also simply referred to as “electrode”, and the positive electrode mixture layer 40 and the negative electrode mixture layer are simply referred to as “electrode mixture layer”. Or it is also called “mixture layer”.

<Ion conductive plastic crystal>
The ion conductive plastic crystal according to the present invention (in this embodiment, a lithium ion conductive plastic crystal) is a composite of a plastic crystal containing a quaternary phosphonium cation and an ionic salt. The ion conductive plastic crystal according to the present invention is a substance having a plastic crystal state at a driving temperature of a lithium ion battery (room temperature to less than 150 ° C.) and exhibiting high ion conductivity, and further having a temperature equal to or higher than the driving temperature. It has a melting point and realizes high heat resistance of the lithium ion battery. As the quaternary phosphonium cation constituting the plastic crystal, those represented by the following formula (1) are suitable.

In the formula (1), R _{A to} R _D are each independently a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, or an isobutyl group.

  The quaternary phosphonium cation according to the present invention has a high melting point (150 ° C. or higher) and can increase the heat resistance of the battery. In the conventional liquid battery, the upper limit of battery driving temperature is as low as about 80 ° C. in order to prevent material deterioration and safety deterioration at high temperatures. Like the present invention, if a plastic crystal having a melting point of 100 ° C. or higher is used instead of the electrolyte, the battery driving temperature becomes high, so that it is installed in an engine room of an excavator or a car used in a high temperature environment, etc. Battery applications can be expanded.

  More specifically, as the quaternary phosphonium cation, the following formulas (2) to (4) are preferable.

  The plastic crystal further contains a counter anion of a quaternary phosphonium cation and constitutes an ionic crystal. As the counter anion, the plastic crystal exhibits a plastic crystal state at the use temperature of the lithium ion battery (room temperature to less than 150 ° C.), and the melting point of the plastic crystal is higher than the use temperature of the battery. There is no particular limitation. For example, hexafluorophosphate, tetrafluoroborate, thiocyanate, bisfluorosulfonylamide and bistrifluoromethanesulfonylamide, trifluorosulfonylimide (TFSI-), fluorosulfonylimide (FSI-) and bisperfluoroethylsulfonylimide (BETI- ) And the like can be combined with known anions. In general, an anion having a smaller volume tends to have a higher melting point. In this respect, anions such as hexafluorophosphate, tetrafluoroborate, and thiocyanate are more preferable. The volume of the anion can be calculated by the following formula (8). Whether or not it is a plastic crystal state can be examined by DSC measurement. In the present invention, “room temperature” is 25 ° C.

Volume of anion = (Van der Waals radius of anion) ² × 3.14 Formula (8)

  The chemical formulas of hexafluorophosphate, tetrafluoroborate and thiocyanate are the following formulas (5) to (7), respectively.

  Preferred combinations of the quaternary phosphonium cation and the counter anion include formula (2) and formula (5), formula (2) and formula (6), formula (3) and formula (7), formula (4) and formula (7 ). In addition, the quaternary phosphonium cation and the counter anion need only contain at least one of those described above, and may contain two or more.

  The lithium ion conductive plastic crystal according to the present invention is a composite of the plastic crystal and an ionic salt (lithium salt in the present embodiment). In this embodiment, a lithium salt is used as the ionic salt, but other salts can be selected depending on the ionic conductor moving inside the electrolyte of the electrochemical element. As an ionic salt other than the lithium salt, for example, a sodium salt, a magnesium salt, or an aluminum salt can be used.

  The concentration of the lithium salt added is preferably 0.1 mol% to 20 mol%, more preferably 0.5 mol% to 15 mol%, and particularly preferably 1 to 10 mol%. If it is less than 0.1 mol%, the lithium ion conductivity is low, and the battery output decreases. On the other hand, if it exceeds 20 mol%, the melting point is remarkably lowered by the addition of lithium, and the heat resistance of the battery is lowered. In the present invention, the addition concentration of the lithium salt is calculated by the following formula (9).

Lithium salt addition concentration (mol%) = Lithium salt substance amount (mol) / (Plastic crystal substance quantity (mol) + lithium salt substance amount (mol)) Formula (9)

Specific examples of the lithium _{salt, LiPF 6, LiBF 4, LiClO} 4, LiCF 3 SO 3, LiCF 3 CO 2, LiBOB, LiAsF 6, LiSbF 6 and imide salt such as lithium represented by lithium trifluoromethanesulfonyl imide is there. In the present invention, these salts can be used alone or in combination. Other lithium salts may be used as long as they do not decompose on the positive electrode 70 and the negative electrode 80 of the battery 100 according to this embodiment.

  The ion conductive plastic crystal according to the present invention is a complex of an ionic salt and a plastic crystal, and this complex is mixed in a state where the ionic salt and the plastic crystal are at or near the molecular level. It is a thing of the state. There are no limitations on the method of producing the composite, but for example, a method of mixing an ionic salt and an ion conductive plastic crystal in a mortar, and dissolving and recrystallizing the ionic salt and the ion conductive plastic crystal in an organic solvent There are a method, a method in which an ionic salt and an ion conductive plastic crystal are heated to a temperature equal to or higher than a melting point of the plastic crystal, and the ionic salt is dissolved and cooled and solidified. By configuring such a composite state, high ionic conductivity can be expressed.

  Next, each configuration of the battery will be described. In the present embodiment, a mode in which all of the positive electrode 70, the negative electrode 80, and the separator layer 50 include the lithium ion conductive plastic crystal according to the present invention will be described.

<Positive electrode current collector 10>
The positive electrode current collector 10 is electrically connected to the positive electrode 70. As the positive electrode current collector 10, an aluminum foil having a thickness of 10 to 100 μm, an aluminum perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, a foamed metal plate, or the like is used. In addition to aluminum, materials such as stainless steel and titanium are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

<Negative electrode current collector 20>
The negative electrode current collector 20 is electrically connected to the negative electrode 80. As the negative electrode current collector 20, a copper foil having a thickness of 10 to 100 μm, a copper perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, or the like is used. In addition to copper, materials such as stainless steel, titanium, nickel, or carbon-coated aluminum are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method, and the like.

<Positive electrode mixture layer 40>
FIG. 2 is a partially enlarged view of the positive electrode mixture layer 40 of FIG. As shown in FIG. 2, the positive electrode mixture layer 40 includes a positive electrode active material (hereinafter also simply referred to as “active material”) 41, the lithium ion conductive plastic crystal 42, an optional positive electrode conductive agent 43, and an optional positive electrode conductive agent 43. A binder 44 is included. There is no limitation in the positive electrode conductive agent 43 and the binder 44, and a well-known thing can be used.

  In this embodiment, the lithium ion conductive plastic crystal 42 is filled in the voids inside the electrode (inside the positive electrode mixture layer 40), thereby realizing high output of the battery.

Preferred examples of the positive electrode active material 41 include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2−x M _x O ₂ (however, M = Co, Ni, Fe, Cr, Zn, at least one selected from the group consisting of Ti, x = 0.01 to 0.2), Li ₂ Mn ₃ MO ₈ (where M = Fe, Co , At least one selected from the group consisting of Ni, Cu, Zn), Li _1-x A _x Mn ₂ O ₄ (where A = Mg, B, Al, Fe, Co, Ni, Cr, Zn, Ca) At least one selected from the group consisting of x = 0.01 to 0.1), LiNi _1-x M _x O ₂ (however, at least one selected from the group consisting of M = Co, Fe, Ga) Yes, _{= 0.01~0.2), LiFeO 2, Fe} 2 (SO 4) 3, LiCo 1-x M x O 2 ( provided that at least one selected from the group consisting of M = Ni, Fe, Mn , X = 0.01 to 0.2), LiNi _1-x M _x O ₂ (where M = Mn, Fe, Co, Al, Ga, Ca, Mg, at least one selected from the group consisting of x = 0.01-0.2), Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO _4, LiMnPO _{4 and the} like. As the positive electrode active material 41, the above materials may be contained singly or in combination of two or more. In the positive electrode active material 41, lithium ions are desorbed in the charging process, and lithium ions desorbed from the negative electrode active material in the negative electrode mixture layer 60 described later are inserted in the discharging process.

  The particle diameter of the positive electrode active material 41 is usually adjusted so as to be equal to or less than the thickness of the positive electrode mixture layer 40. When there are coarse particles having a size larger than the thickness of the composite material layer in the powder of the positive electrode active material 41, the coarse particles are previously removed by sieving classification, wind classification, or the like to produce particles having a thickness equal to or less than the thickness of the positive electrode composite material layer 40. It is preferable to do.

  Moreover, since the positive electrode active material 41 is generally an oxide type and has high electric resistance, a positive electrode conductive agent 43 made of carbon powder for supplementing electric conductivity is used. Since both the positive electrode active material 41 and the positive electrode conductive agent 43 are usually powders, a binder can be mixed with the powders, and the powders can be bonded together and simultaneously bonded to the positive electrode current collector 10.

  Preferable examples of the positive electrode conductive agent 43 include acetylene black, carbon black, and carbon materials such as graphite or amorphous carbon. Preferable examples of the positive electrode binder 44 include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polyimide, and a mixture thereof. In particular, an imide-based binder is thermally stable and is suitable as a binder when the battery driving temperature is 100 ° C. or higher. In addition, a binder having a reactive group that crosslinks by heating, ultraviolet irradiation, or the like is also preferably used. As the reactive group, a vinylene group, a hydroxyl group, an epoxy group, an allyl group, a carbonyl group, or a reactive group obtained by substituting a part of the reactive group with a different element is preferable.

  There is no particular limitation on the method for manufacturing the positive electrode 70, but the positive electrode active material 41, lithium salt and plastic crystal as raw materials for the lithium ion conductive plastic crystal 42, the positive electrode conductive agent 43, the positive electrode binder 44, and an organic solvent are mixed. The positive electrode slurry is agitated by a known technique, adhered to the positive electrode current collector 10 by a doctor blade method, dipping method, spray method, screen printing, etc., and then the organic solvent is dried and pressure-molded by a roll press. Thus, the positive electrode 70 can be manufactured. In addition, a plurality of positive electrode mixture layers 40 can be laminated on the positive electrode current collector 10 by performing a plurality of times from application to drying. Alternatively, a positive electrode active material 41, a positive electrode conductive agent 43, and a lithium salt and a plastic crystal, which are raw materials for the lithium ion conductive plastic crystal 42, are stirred by a known technique and molded into a pellet by pressurization. Can also be used as the positive electrode mixture layer 40. In the pellet electrode, a binder can be added according to the structural strength of the pellet.

  The content of the lithium ion conductive plastic crystal 42 contained in the positive electrode mixture layer 40 is preferably 10 to 90% by mass. When the content of the lithium ion conductive plastic crystal 42 is less than 10% by mass, the ion conduction path is reduced and the resistance is increased. On the other hand, when the content of the lithium ion conductive plastic crystal 42 is larger than 90% by mass, the amount of the active material is decreased and the energy density of the battery 100 is decreased. Further, an electron conduction path cannot be formed, and the resistance is increased.

  The positive electrode porosity is preferably in the range of 0.01 to 20%, more preferably 0.01 to 10%, and particularly preferably 0.01 to 1%. As for the lower limit, the lower the resistance, the lower the resistance, but 0.01% is practically sufficient. When the positive electrode porosity is higher than 1%, lithium ion diffusion is inhibited. The electrode porosity can be measured with a mercury porosimeter.

  As the positive electrode active material 41, a pellet may be produced using an active material combined with the lithium ion conductive plastic crystal according to the present invention. As a composite method, known techniques can be used. Specifically, mortar mixing, mechanical milling, a method of adding an active material to lithium ion conductive plastic crystals diluted with an organic solvent and drying, and sputtering. Examples thereof include a method of coating the active material surface with a lithium ion conductive plastic crystal.

<Negative electrode mixture layer 60>
FIG. 3 is a partially enlarged view of the negative electrode mixture layer 60 of FIG. As shown in FIG. 3, the negative electrode mixture layer 60 includes a negative electrode active material 61, a lithium ion conductive plastic crystal 62, a negative electrode conductive agent 63, and an optional binder 64. There is no limitation in the negative electrode conductive agent 63 and the binder 64, A well-known thing can be used.

  Preferred examples of the negative electrode active material 61 include carbon materials capable of reversibly inserting and desorbing lithium ions, silicon-based materials Si, SiO, tin-based materials, lithium titanate (with or without substitution elements), lithium vanadium. Examples of the composite oxide include an alloy of lithium and a metal (for example, tin, aluminum, antimony, etc.). Examples of the carbon material include natural graphite, a composite carbonaceous material in which a film is formed on natural graphite by a dry CVD (Chemical Vapor Deposition) method or a wet spray method, a resin material such as epoxy or phenol, or petroleum or coal. Examples thereof include artificial graphite and non-graphitizable carbon material produced by firing using a pitch-based material as a raw material. As the negative electrode active material 61, the above materials may be contained singly or in combination of two or more.

  The particle size of the negative electrode active material 61 is normally adjusted so as to be equal to or less than the thickness of the negative electrode mixture layer 60. When there are coarse particles having a size larger than the thickness of the composite material layer in the powder of the negative electrode active material 61, the coarse particles are removed in advance by sieving classification, wind classification, etc., and particles having a thickness equal to or less than the thickness of the negative electrode composite material layer 60 are produced. It is preferable to do.

  Preferable examples of the negative electrode conductive agent 63 include carbon materials such as acetylene black, carbon black, graphite, or amorphous carbon. Preferable examples of the negative electrode binder 64 include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polyimide, and a mixture thereof. In particular, an imide-based binder is thermally stable and is suitable as a binder when the battery driving temperature is 100 ° C. or higher. In addition, a binder having a reactive group that crosslinks by heating, ultraviolet irradiation, or the like is also preferably used. As the reactive group, a vinylene group, a hydroxyl group, an epoxy group, an allyl group, a carbonyl group, a reactive group obtained by substituting a part of the reactive group with a different element, and the like are preferable.

  Although there is no particular limitation on the manufacturing method of the negative electrode 80, the negative electrode active material 61, the lithium salt and plastic crystal that are raw materials of the lithium ion conductive plastic crystal 62, the negative electrode conductive agent 63, the negative electrode binder 64, and an organic solvent are mixed. The negative electrode slurry was agitated by a known technique and adhered to the negative electrode current collector 20 by a doctor blade method, a dipping method, a spray method, a screen printing method, etc., and then the organic solvent was dried and pressure-molded by a roll press. The negative electrode 80 can be produced. In addition, a plurality of negative electrode mixture layers 60 can be laminated on the negative electrode current collector 20 by performing a plurality of times from application to drying. Alternatively, a negative electrode active material 61, a negative electrode conductive agent 63, and a lithium salt and a plastic crystal, which are raw materials for the lithium ion conductive plastic crystal 62, are agitated by a known technique and molded into a pellet by pressurization. Can be used as the negative electrode mixture layer 60. In the pellet electrode, a binder can be added according to the structural strength of the pellet.

  As in the case of the positive electrode 70, the content of the lithium ion conductive plastic crystal 62 contained in the negative electrode mixture layer 60 is preferably 10 to 90% by mass. The negative electrode porosity is preferably in the range of 0.01 to 20%, more preferably 0.01 to 10%, and particularly preferably 0.01 to 1%. The technical significance of the above range is the same as that of the positive electrode 70 described above.

  As the negative electrode active material 61, a pellet may be produced using an active material combined with the lithium ion conductive plastic crystal according to the present invention. As a composite method, known techniques can be used. Specifically, mortar mixing, mechanical milling, a method of adding an active material to lithium ion conductive plastic crystals diluted with an organic solvent and drying, and sputtering. Examples thereof include a method of coating the active material surface with a lithium ion conductive plastic crystal.

<Separator layer 50>
FIG. 4 is a partially enlarged view of the separator layer 50 of FIG. As shown in FIG. 4, the separator layer 50 includes a solid electrolyte 51, a lithium ion conductive plastic crystal 52, and an optional binder 53.

The solid electrolyte 51 is not particularly limited as long as it is a solid material that conducts lithium ions, but it is preferable that the solid electrolyte 51 includes a nonflammable inorganic solid electrolyte from the viewpoint of safety. _{Specifically, Li 1.4 Al 0.4 Ti 1.6 (} PO 4) 3, LiAlGe (PO 4) 3, Li 3.4 V 0.6 Si 0.4 O 4 and _Li 2 _P 2 O An oxide glass represented by ₆ or the like, a perovskite oxide represented by Li _0.34 La _0.51 TiO _2.94 or a garnet oxide represented by LiLaZrO ₂ can be used. The oxide conductor may contain lithium halides such as LiCl and LiI. A sulfide-based inorganic solid electrolyte can also be suitably used. Further, it may be a polymer electrolyte sheet. These solid electrolytes can be used alone or in combination of two or more.

  When sufficient mechanical strength is maintained with the lithium ion conductive plastic crystal 52 alone, the separator layer 50 can be formed with the lithium ion conductive plastic crystal 52 alone without using the solid electrolyte 51. As a method for forming a separator layer made of lithium ion conductive plastic crystals, a method of stacking pelletized or sheet-formed lithium conductive plastic crystals, a lithium conductive plastic crystal mixed with a solvent, and an electrode mixture layer A method of applying the solution on the top and distilling off the solvent is suitable.

  Further, a composite of the lithium ion conductive plastic crystal 52 and the binder 53 can be used as the separator layer 50. As the binder, known ones can be used, and specifically, styrene-butadiene rubber, carboxymethyl cellulose and polyvinylidene fluoride (PVDF), polyimide, and a mixture thereof can be used.

  In order to prevent the positive and negative electrodes from being short-circuited, a short-circuit prevention layer can be provided inside the separator layer. Even when the battery is heated above the melting point of the plastic crystal, the presence of the short-circuit blocking layer can suppress the direct contact between the positive and negative electrodes, thereby ensuring the safety of the battery. As a material for the short-circuit prevention layer, a polyolefin polymer sheet made of polyethylene or polypropylene having a thickness of 20 to 100 μm, a two-layer structure in which a polyolefin polymer and a fluorine polymer sheet typified by tetrafluoropolyethylene are welded. Polyamide fiber sheets and glass fiber sheets can be used. Particularly at a high temperature of 100 ° C. or higher, a heat-resistant glass fiber sheet is preferable. A mixture of ceramics and a binder may be formed in a thin layer on the surface of the short-circuit prevention layer so that the short-circuit prevention layer does not shrink when the battery temperature increases. The short-circuit prevention layer can be freely selected according to the lithium ion conductive plastic crystal, and a combination in which the lithium ion plastic crystal can easily penetrate into the short-circuit prevention layer can be suitably used.

<Electrode shape>
The form of the positive and negative electrode mixture layers attached to the current collector foil can be appropriately selected depending on the use and shape of the battery. However, a mixture layer may be present so as to cover the entire surface of the current collector foil. You may leave the site | part (henceforth a blank space) in which the compound-material layer does not exist on the four sides of electric foil. As a method of forming a separator layer made of lithium ion conductive plastic crystals on the electrode mixture layer adhered to the current collector foil, a method of laminating pelletized or sheeted lithium ion conductive plastic crystals, a solvent, A method of applying a lithium conductive plastic crystal mixed with the above to the electrode mixture layer and distilling off the solvent is suitable. As a method for filling the electrode with the lithium ion conductive plastic crystal, a method such as heating, vacuum evacuation, or pressurization may be applied. The lithium ion conductive plastic crystal according to the present invention described above can be reliably melted and filled at 200 ° C.

<Battery shape>
The lithium ion battery 100 may be of a bipolar type in which a plurality of single cells in which the positive electrode mixture layer 40, the separator layer 50, and the negative electrode mixture layer 60 are stacked are stacked. Specifically, the area of the separator layer 50 in contact with the electrode mixture layer is smaller than the blank area of the current collector foil, and larger than the electrode mixture layer, thereby suppressing a liquid short circuit between single cells, A battery configuration having a higher energy density can be obtained. In order to suppress a liquid short circuit accompanying deformation of the separator layer 50 due to heating, pressure, or the like, a sealing structure can be applied to the blank portion. The sealing structure and material are not particularly limited, but an adhesive seal and packing using a high heat-resistant material such as silicone rubber, fluororubber, polyetheretherketone, polytetrafluoroethylene, and a known sealing material can be applied.

  A planar bipolar cell can also be formed by forming a plurality of single cells on an insulating substrate and forming a conductive network between the single cells. A method for forming a single cell on an insulating substrate is not particularly limited, and a known technique can be applied. As a method for forming a conductive network, in addition to screen printing and a method in which a solution in which an electronic conductive material is dispersed in a solvent is applied and then dried, a method of connecting single cells with a conductive metal foil, an electronic conductive tape, or the like Can be applied.

  In order to suppress an increase in resistance due to peeling of the electrode and the separator layer, a heating step may be included at the time of manufacturing the cell. In addition, a heating mechanism can be provided outside the battery, and the ion-conductive plastic crystal can be deformed by heating to improve the bondability between the electrode and the separator layer. A known technique can be applied as the heating mechanism, and specific examples include a method of covering the outside of the battery with a linear / planar heating element, a method of providing a heating bath, and the like. By providing the heating mechanism, the battery is dismantled even when the interfacial bondability between the electrode layer / separator layer decreases when an active material that changes in volume during charge / discharge, such as graphite or a silicon-based active material, is applied. The interface can be repaired without any problems.

  In order to suppress peeling of the electrode mixture layer and the separator layer, a pressurizing mechanism can be introduced into the all solid state battery. As the pressing method, an optimum method can be selected depending on the battery shape. For example, in a laminate pack type or square type battery, a method of setting a fixing plate in the electrode stacking direction and fixing the fixing plate with a screw or the like, or a method using a pressurizing device such as a spring can be applied.

<Battery case 30>
The battery case 30 accommodates the positive electrode current collector 10, the negative electrode current collector 20, the positive electrode mixture layer 40, the separator layer 50, and the negative electrode mixture layer 60. The shape of the battery case 30 is a cylindrical shape, a flat oval shape, a flat oval shape, a square shape, or the like according to the shape of the electrode group composed of the positive electrode mixture layer 40, the separator layer 50, and the negative electrode mixture layer 60. You may choose. The material of the battery case 30 is selected from materials that are corrosion resistant to the nonaqueous electrolyte, such as aluminum, stainless steel, and nickel-plated steel.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to these.

  In this example, a lithium ion battery including the lithium ion conductive plastic crystal according to the present invention in a positive electrode, a negative electrode, and a separator was produced, and electrochemical characteristics (initial discharge capacity) were evaluated. The positive electrode and the negative electrode were used as pellet electrodes.

<Preparation of lithium ion conductive plastic crystal>
A mortar is placed in a glove box in an argon atmosphere using LiPF ₆ as a lithium salt, a quaternary phosphonium cation represented by the formula (2) as a plastic crystal, and a hexafluorophosphate represented by the formula (5). The mixture was mixed, sealed in a heat-resistant container, and heated at a temperature equal to or higher than the melting point of the lithium ion conductive plastic crystal. The mixture was stirred in a liquid state and air-cooled, then opened in a glove box, and the mixture was pulverized in a mortar. The prepared mixture was used as a lithium ion conductive plastic crystal. The addition concentration of the lithium salt was 5 mol%. The composition of the lithium ion conductive plastic crystal and the addition concentration of the lithium salt are shown in Table 1 described later.

<Preparation of positive electrode>
Lithium cobaltate, the above lithium ion conductive plastic crystal and acetylene black were weighed at a ratio of 30:50:20 (mass%) and mixed in a mortar to be uniform. 0.1 g of the mixture was weighed and pressed with a die at a pressure of 1 MPa to produce a positive electrode pellet. All the above operations were performed in a glove box in an argon atmosphere.

<Preparation of separator layer>
0.1 g of the lithium ion conductive plastic crystal was weighed and pressed with a die at a pressure of 1 MPa to produce a pellet. The above operation was performed in a glove box in an argon atmosphere.

<Production of negative electrode>
Lithium titanate, the above lithium ion conductive plastic crystal, and acetylene black were weighed in a ratio of 30:50:20 (mass%) and mixed uniformly in a mortar. 0.1 g of the mixture was weighed and pressed with a die at a pressure of 1 MPa to prepare a negative electrode pellet. All the above operations were performed in a glove box in an argon atmosphere.

<Production of evaluation cell>
In a glove box in an argon atmosphere, a positive electrode pellet, a separator layer, and a negative electrode pellet were laminated inside a stainless steel bipolar cell, and the four corners were fixed and sealed. The cell was installed in a thermostat and heated at 200 ° C. for 1 hour.

<Evaluation of electrochemical characteristics>
The cell was installed in the thermostat set to 100 degreeC, charge / discharge was performed in the voltage range of 4.2-2.5V by the charge / discharge rate 0.01C, and the first time discharge capacity was measured. The charge / discharge current was set to 0.01 C with respect to the LCO design capacity. The measurement results are shown in Table 2 described later.

Except that the lithium salt was LiBF ₄ and the plastic crystal was a crystal containing a quaternary phosphonium cation represented by the formula (2) and a tetrafluoroborate represented by the formula (6), the same as in Example 1. Lithium ion batteries were fabricated and their electrochemical properties were evaluated. The configuration of the lithium ion battery is shown in Table 1 below, and the measurement result of the initial discharge capacity is shown in Table 2 below.

  Except that the lithium salt was LiSCN and the plastic crystal was a crystal containing a quaternary phosphonium cation represented by the formula (3) and a thiocyanate represented by the formula (7), the lithium ion was the same as in Example 1. The battery was fabricated and the electrochemical characteristics were evaluated. The configuration of the lithium ion battery is shown in Table 1 below, and the measurement result of the initial discharge capacity is shown in Table 2 below.

  Except that the lithium salt was LiSCN and the plastic crystal was a crystal containing a quaternary phosphonium cation represented by the formula (4) and a thiocyanate represented by the formula (7), the lithium ion was the same as in Example 1. The battery was fabricated and the electrochemical characteristics were evaluated. The configuration of the lithium ion battery is shown in Table 1 below, and the measurement result of the initial discharge capacity is shown in Table 2 below.

  A lithium ion battery was prepared and electrochemical characteristics were evaluated in the same manner as in Example 4 except that the addition concentration of the lithium salt was 0.05 mol%. The configuration of the lithium ion battery is shown in Table 1 below, and the measurement result of the initial discharge capacity is shown in Table 2 below.

  A lithium ion battery was prepared and electrochemical characteristics were evaluated in the same manner as in Example 4 except that the addition concentration of the lithium salt was 10 mol%. The configuration of the lithium ion battery is shown in Table 1 below, and the measurement result of the initial discharge capacity is shown in Table 2 below.

  In this example, a lithium ion battery using a positive electrode and a negative electrode as coating-type electrodes was produced, and electrochemical characteristics (initial discharge capacity) were evaluated.

<Preparation of positive electrode>
Lithium cobaltate (LiCoO ₂ (hereinafter referred to as “LCO”)) is 90% by mass, acetylene black (hereinafter referred to as “AB”) is 5% by mass, and the imide binder is 5% by mass. Then, an imide binder dissolved in LCO, AB and NMP (N-methylpyrrolidone) having an average particle diameter of 10 μm was mixed in an agate mortar to prepare a slurry. Thereafter, a slurry was coated on a carbon-coated aluminum foil having a thickness of 20 μm punched to a diameter of 20 mmφ so as to have a diameter of 10 mmΦ. The coated electrode was allowed to stand in a drier maintained at a temperature of 80 ° C., and NMP was distilled off to obtain a positive electrode having a positive electrode mixture layer density of about 0.6 cm / cm ³ .

<Production of negative electrode>
Average so that lithium titanate (LiTi ₄ O ₁₂ (hereinafter referred to as “LTO”) has a solid content ratio of 90.6% by mass, AB is 4.7% by mass, and imide binder is 4.7% by mass. A slurry was prepared by mixing an imide binder dissolved in LTO, AB powder and NMP having a particle diameter of 20 μm in an agate mortar, and then punched to a diameter of 20 mmφ on a carbon-coated aluminum foil having a thickness of 20 μm so as to have a diameter of 10 mmΦ. The coated electrode was allowed to stand in a dryer maintained at a temperature of 80 ° C. to distill off NMP, and a negative electrode having a composite layer density of about 0.8 cm / cm ³ was obtained. Obtained.

<Preparation of separator layer>
0.1 g of lithium ion conductive plastic crystal was weighed and pressed with a die to produce pellets with a diameter of 15 mmΦ. The lithium ion conductive plastic crystal is a crystal containing LiPF ₆ as a lithium salt, a quaternary phosphonium cation represented by the formula (2) as a plastic crystal, and a hexafluorophosphate represented by the formula (5). The complex of was used. The addition concentration of the lithium salt was 5 mol%. The above operation was performed in a glove box in an argon atmosphere.

<Production of evaluation cell>
The prepared positive electrode, a glass fiber with a diameter of 15 mmΦ and a separator layer made of lithium ion conductive plastic crystal, a glass fiber with a diameter of 15 mmΦ and a negative electrode were laminated in this order from below, and the four corners of the cell were caulked and sealed. The cell was heated at 200 ° C. for 1 hour to complex the plastic crystal and the lithium salt to obtain a bipolar cell.

<Evaluation of electrochemical characteristics>
The cell was installed in the thermostat set to 100 degreeC, charge / discharge was performed in the voltage range of 4.2-2.5V by the charge / discharge rate 0.01C, and the first time discharge capacity was measured. The charge / discharge current was set to 0.01 C with respect to the LCO design capacity.

[Comparative Example 1]
Preparation of lithium ion battery and evaluation of electrochemical characteristics were conducted in the same manner as in Example 4 except that instead of lithium ion conductive plastic crystal, only plastic crystal was used (not a composite with lithium salt). went. The configuration of the lithium ion battery is shown in Table 1 below, and the measurement result of the initial discharge capacity is shown in Table 2 below.

[Reference example]
The ratio of LCO, lithium ion conductive plastic crystal and AB in the positive electrode was 50: 5: 45 (mass%), and the ratio of lithium titanate, lithium ion conductive plastic crystal and AB in the negative electrode was 50: 5: 45. A lithium ion battery was prepared and the electrochemical characteristics were evaluated in the same manner as in Example 1 except that (mass%) was used. The configuration of the lithium ion battery is shown in Table 1 below, and the measurement result of the initial discharge capacity is shown in Table 2 below. In the present specification, the “reference example” is not known because the lithium ion conductive plastic crystal according to the present invention is used, but the electrode content of the lithium ion conductive plastic crystal is the present invention. It is not in the preferable range.

[Comparative Example 2]
A lithium ion battery was prepared and its electrochemical characteristics were evaluated in the same manner as in Example 7 except that the cell was not heated at 200 ° C. for 1 hour when the evaluation cell was prepared. The configuration of the lithium ion battery is shown in Table 1 below, and the measurement result of the initial discharge capacity is shown in Table 2 below.

As shown in Table 2, all of the lithium ion batteries of Examples 1 to 7 according to the present invention achieve a high initial discharge capacity (95 mAhg ⁻¹ or more) at 100 ° C. This is considered to be the effect that a sufficient ion conduction path is formed in the electrode and the interfacial interface resistance is reduced.

  On the other hand, Comparative Example 1 in which the lithium salt was not combined with the plastic crystal and the reference example in which the content of the lithium ion conductive plastic crystal was not within the preferred range of the present invention had a large initial resistance and could not be charged. . This is presumably because a sufficient ion conduction path was not formed in the electrode. Further, the initial discharge capacity of Comparative Example 2 which was not heated at 200 ° C. showed a very low value. This is presumably because the plastic crystal and the lithium salt were not combined, and a sufficient ion conduction path was not formed in the electrode.

  As described above, according to the present invention, the electrode can be filled at a low temperature, the chemical and structural stability is high, the battery has a high heat resistance (can be used at room temperature to less than 150 ° C.), and has a high output. It has been demonstrated that a solid electrolyte for an electrochemical element capable of satisfying both of the above can be provided and an all-solid battery using the solid electrolyte for an electrochemical element can be provided.

  Note that the above-described embodiments have been specifically described in order to help understanding of the present invention, and the present invention is not limited to having all the configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, a part of the configuration of each embodiment can be deleted, replaced with another configuration, or added with another configuration.

  DESCRIPTION OF SYMBOLS 10 ... Positive electrode collector, 20 ... Negative electrode collector, 30 ... Battery case, 40 ... Positive electrode compound layer, 41 ... Positive electrode active material, 42 ... Lithium ion conductive plastic crystal, 43 ... Positive electrode conductive agent, 44 ... Positive electrode binder, 50 ... separator layer, 51 ... solid electrolyte particles, 52 ... lithium ion conductive plastic crystal, 53 ... electrolyte binder, 60 ... negative electrode composite layer, 61 ... negative electrode active material, 62 ... lithium ion conductive plastic viscosity Crystal 63, negative electrode conductive agent, 64 ... negative electrode binder, 70 ... positive electrode, 80 ... negative electrode, 100 ... all solid state secondary battery.

Claims (10)

  A solid electrolyte for an electrochemical device, comprising an ion conductive plastic crystal that is a complex of a plastic crystal containing a quaternary phosphonium cation and an ionic salt. The solid electrolyte for an electrochemical element according to claim 1, wherein the quaternary phosphonium cation is represented by the following formula (1).

(In Formula (1), R _{A to} R _D are each independently a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, or an isobutyl group.) The solid electrolyte for an electrochemical device according to claim 1, wherein the quaternary phosphonium cation is any one of the following formulas (2) to (4).

  The solid electrolyte for an electrochemical device according to claim 1, wherein the plastic crystal further contains hexafluorophosphate, tetrafluoroborate or thiocyanate as a counter anion of the quaternary phosphonium cation.   2. The solid electrolyte for an electrochemical element according to claim 1, wherein the ionic salt is a lithium salt, a sodium salt, a magnesium salt or an aluminum salt.   The solid electrolyte for an electrochemical element according to claim 1, wherein the addition amount of the ionic salt is 0.1 to 20 mol%. A positive electrode, a negative electrode, and a separator that partitions the positive electrode and the negative electrode,
An all-solid-state battery, wherein at least one of the positive electrode, the negative electrode, and the separator includes the ion-conductive plastic crystal according to any one of claims 1 to 6. The positive electrode and the negative electrode each have a current collector and an electrode mixture layer provided on the current collector,
The electrode mixture layer includes an electrode active material and the ion conductive plastic crystal,
The all-solid-state battery according to claim 7, wherein the content of the ion conductive plastic crystal is 10 to 90% by mass of the electrode mixture layer.   The all-solid-state battery according to claim 7, wherein an electrode porosity of the positive electrode or the negative electrode is 0.01 to 20%.   8. The all solid state battery according to claim 7, wherein the solid state battery is a lithium ion battery, a sodium ion battery, a magnesium ion battery, or an aluminum ion battery.

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