Solid composite electrolyte

Abstract

The present invention relates to a solid composite electrolyte comprising a) at least one fluoropolymer and b) at least one sulfide-based solid, ionically conductive inorganic particles, wherein a) the fluoropolymer comprises i) at least 50.0 mol % of vinylidene difluoride (mol % is based on the total moles of repeating units); ii) at least one C2-C8 chloro- and / or bromo- and / or iodo-fluoroolefin; and iii) repeating units derived from at least one C2-C8 fluoroolefin, wherein i), ii) and iii) are different from each other; to a slurry for producing the solid composite electrolyte comprising a) at least one fluoroelastomer according to the present invention, b) sulfide-based solid, ionically conductive inorganic particles, and c) at least one non-aqueous solvent; to an electrode comprising the solid composite electrolyte according to the present invention, d) at least one electroactive material, and optionally e) at least one conductive agent; and to a solid battery comprising a positive electrode, a negative electrode, and a membrane, at least one of which comprises the solid composite electrolyte according to the present invention. The present invention also relates to a binder solution for a solid-state battery comprising a) at least one fluoropolymer according to the present invention and c) at least one non-aqueous solvent.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application No. 22189660.8, filed August 10, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a solid composite electrolyte comprising a) at least one fluoropolymer and b) at least one sulfide-based solid, ionically conductive inorganic particles, wherein a) the fluoropolymer comprises i) at least 50.0 mol % of vinylidene difluoride (VDF) (mol % is based on the total moles of repeating units); ii) at least one C2-C8 chloro- and / or bromo- and / or iodo-fluoroolefin; and iii) repeating units derived from at least one C2-C8 fluoroolefin, wherein i), ii) and iii) are different from each other; to a slurry for producing the solid composite electrolyte comprising a) at least one fluoroelastomer according to the present invention, b) sulfide-based solid, ionically conductive inorganic particles, and c) at least one non-aqueous solvent; to an electrode comprising the solid composite electrolyte according to the present invention, d) at least one electroactive material, and optionally e) at least one conductive agent; and to a solid battery comprising a positive electrode, a negative electrode, and a membrane, at least one of which comprises the solid composite electrolyte according to the present invention. The present invention also relates to a binder solution for a solid-state battery comprising a) at least one fluoropolymer according to the present invention and c) at least one non-aqueous solvent. [Background technology]

[0003] Lithium-ion (Li-ion) batteries have held a dominant position in the market of rechargeable energy storage devices for decades due to their many advantages, such as light weight, reasonable energy density, and good cycle life. Nevertheless, better safety and higher energy density have been constantly required with the development of high-power applications such as electric vehicles, hybrid electric vehicles, grid energy storage, etc.

[0004] Solid-state batteries are considered to be the next generation of energy storage devices, in which highly flammable liquid electrolytes are replaced by solid electrolytes that can substantially eliminate the risk of fire and / or explosion. Organic polymers, inorganic materials, and composite materials have been actively researched as solid electrolytes, each with its own advantages and disadvantages. In particular, composite materials, i.e., inorganic solid electrolytes dispersed in polymers, such as those containing sulfide-based particles dispersed in a polymer matrix, are considered to be the most promising solutions on an industrial scale, taking into account the high ionic conductivity of sulfide-based solid electrolytes and the good mechanical properties and easy processability of polymers. However, there are still drawbacks that need to be resolved, such as poor solvent compatibility of sulfide materials, which greatly limits the choice of polymers that can be used to prepare electrolytes; insufficient bonding strength between polymers and sulfide materials; low adhesion of electrodes to current collectors; and rather complicated processes for preparing solid composite electrolytes.

[0005] Fluorinated polymers, such as VDF-based polymers, are widely used as binders in conventional Li-ion batteries. Due to their good oxidation resistance, they are primarily applied in electrode-forming formulations for Li-ion batteries, especially for the positive electrode. Their use as binders for sulfide-based solid electrodes and / or electrolyte layers has also been actively investigated in this field. For example, U.S. Patent No. 10,511,052 B2 (Idemitsu Kosan) discloses fluorinated polymers, such as VDF-hexafluoropropylene (HFP), VDF-tetrafluoroethylene (TFE), VDF-HFP-TFE, and TFE-HFP, as binders for sulfide-based solid electrolytes. Additionally, Japanese Patent No. 5675694 (Kureha and Toyota) describes a method for producing a sulfide-based solid electrolyte-containing electrode and electrolyte layer, which comprises a fluorinated polymer as a binder, in particular a VDF-based copolymer having a VDF content of 40 to 70 mol%, such as VDF-HFP, VDF-chlorotrifluoroethylene (CTFE), or VDF-TFE-HFP, preferably VDF-TFE-HFP.

[0006] In this regard, VDF-based / fluorinated binders exhibit low bonding strength between solid electrolyte particles and / or electroactive materials in the solid electrolyte layer and / or electrode. As a result, a relatively high binder content is applied to the solid electrolyte and electrode, which results in a significant decrease in ionic conductivity. This has been one of the major problems in solid-state battery technology. Another critical issue is that VDF-based / fluorinated binders exhibit low adhesive strength to the current collector, leading to electrode delamination and ultimately battery failure.

[0007] U.S. Patent Application Publication No. 2015 / 096169 A1 (Kureha and Toyota) discloses that cathodes for sulfide-based solid-state batteries formed with slurries containing fluorine-based copolymers with specific amounts of VDF units (40-70 mol%) exhibit good adhesion to current collectors. In particular, U.S. Patent Application Publication No. '169 embodies VDF-TFE-HFP (55 / 25 / 20 in mol%) as a binder that exhibits higher adhesion compared to amino-modified hydrogenated binders.

[0008] WO 2021 / 039950 (Fujifilm) describes an inorganic solid electrolyte-containing composition comprising an inorganic solid electrolyte, a polymer binder, and a dispersion medium, where the polymer binder comprises a fluorine-based copolymer containing a VDF component and 21 to 65 mol% HFP component. The composition exhibits greater than 60% adsorption to the inorganic solid electrolyte and is effective in controlling excessive viscosity increase, re-solidification, or sedimentation of the inorganic particles, enabling the achievement of solid-state batteries with excellent cycling characteristics. In particular, WO 2021 / 039950 proposes the use of specific functional groups, such as carboxylic acid groups, phosphoric acid groups, and hydroxyl groups, in the VDF-HFP copolymer to enhance the adhesive properties of the electrode.

[0009] In particular, CN 113451638 A (Qingtao Kunshan Energy Development Co. Ltd.) describes a sulfide-based solid electrolyte membrane, characterized by comprising a 3D-structured polymer film, the membrane being fabricated by electrospinning the membrane and then infiltrating it with a sulfide material, and a sulfide-based solid electrolyte. The polymer film is either a VDF-based copolymer, designated as VDF-A, or a VDF-based terpolymer, designated as VDF-AB, where A is selected from the group consisting of trifluoroethylene (TrFE), HFP, and methyl methacrylate, and B is selected from the group consisting of CTFE, 1,1-chlorofluoroethylene, and chlorodifluoroethylene. However, CN '638 A only embodies a VDF-TrFE copolymer and does not provide any further insight into the optimal combination of a fluoropolymer of at least three different monomers and a solvent compatible with the sulfide material.

[0010] In this regard, a gel polymer electrolyte composed of a plasticized VDF-HFP-CTFE terpolymer in which an organic carbonate mixture is absorbed as a liquid electrolyte in a conventional lithium-ion battery has been disclosed by Jarvis et al. (Journal of Power Sources 119-121 (2003) 465-468) [The use of novel VDF-HFP-CTFE terpolymers in lithium-ion polymer cells]. The paper also notes that the incorporation of CTFE into VDF-HFP increases the electrolyte absorption capacity, due to its lower melt flow index, while maintaining structural integrity compared to PVDF homopolymer and VDF-HFP copolymer. However, Jarvis et al. did not provide any hints regarding its use as a binder in, for example, sulfide-based solid composite electrolytes for solid-state batteries.

[0011] Therefore, there remains a continuing need in the art for solutions to overcome the shortcomings of sulfide-based solid composite electrolytes. Summary of the Invention

[0012] A first object of the present invention is a solid composite electrolyte comprising at least one fluoropolymer and b) at least one sulfide-based solid, ionically conductive inorganic particle, wherein a) the fluoropolymer comprises i) at least 50.0% by mole (mol %) of vinylidene difluoride (VDF) (mol % is based on the total moles of repeating units), ii) at least one C2-C8 chloro- and / or bromo- and / or iodo-fluoroolefin; and iii) repeating units derived from at least one C2-C8 fluoroolefin, wherein i), ii) and iii) are different from each other.

[0013] A second object of the present invention is a slurry for producing a solid composite electrolyte comprising a) a fluoropolymer, b) sulfide-based solid, ionically conductive inorganic particles, and c) at least one non-aqueous solvent.

[0014] A third object of the invention is an electrode comprising a solid composite electrolyte according to the invention, d) at least one electroactive material and, optionally, e) at least one conductive agent.

[0015] A fourth object of the present invention is a solid-state battery comprising a positive electrode, a negative electrode and a membrane arranged between the positive and negative electrodes, wherein at least one of the positive electrode, the negative electrode and the membrane comprises the solid composite electrolyte according to the present invention, optionally d) at least one electroactive material and / or e) at least one conductive agent.

[0016] A fifth object of the present invention is a binder solution for solid-state batteries comprising a) at least one fluoropolymer according to the invention and c) at least one non-aqueous solvent.

[0017] Surprisingly, it has been found by the inventors that the solid composite electrolyte according to the invention, in particular by using the fluoropolymer according to the invention, can deliver a particularly advantageous combination of properties, such as excellent adhesion of the electrode to the current collector and significantly increased bond strength within the membrane, while maintaining good ionic conductivity. [Brief explanation of the drawings]

[0018] [Figure 1] Cross-section of an AC impedance spectroscopy pressure cell developed within Solvay to measure the ionic conductivity of films. In the pressure cell, the film is pressed between two stainless steel electrodes during impedance measurements. [Figure 2] Figure 1 shows an equivalent circuit for modeling the conductive behavior of solid composite electrolytes, where R1 and R2 represent the bulk and grain boundary resistances, respectively, and Q2 and Q3 represent the grain boundary and electrode contributions, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0019] Ratios, concentrations, amounts, and other numerical data may be expressed in range format herein. It should be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the upper and lower limits of the range, but also all individual numerical values or subranges encompassed within the range, as if each numerical value and subrange were explicitly recited. In the context of the present invention, the term "weight percent" (wt%) refers to the content of a particular component in a mixture, calculated as the ratio between the weight of the component and the total weight of the mixture. As used herein, the concentration of a repeat unit in "percent by mole" (mol%) refers to the concentration relative to the total number of repeat units in the polymer, unless otherwise specified.

[0020] It should be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. Accordingly, various changes and modifications described herein will be apparent to those skilled in the art. Additionally, descriptions of well-known functions and constructions may be omitted for clarity and brevity.

[0021] The present invention provides a) at least one fluoropolymer; b) at least one sulfide-based solid, ionically conductive inorganic particle; A solid composite electrolyte comprising: a) a fluoropolymer, i) at least 50.0 mol % (mol %) vinylidene difluoride (VDF) (mol % is based on the total moles of repeat units); ii) at least one C2-C8 chloro and / or bromo and / or iodofluoroolefin; and iii) at least one C2-C8 fluoroolefin and a repeat unit derived from i), ii) and iii) are different from each other; A solid composite electrolyte is provided.

[0022] In one embodiment, i) vinylidene difluoride comprises at least 60.0 mol % (mol % is based on the total moles of repeat units).

[0023] In another embodiment, i) vinylidene difluoride comprises at least 70.0 mol % (mol % is based on the total moles of repeat units).

[0024] In one embodiment, ii) the C2 to C8 chloro and / or bromo and / or iodofluoroolefins are selected from the group consisting of 1,1-chlorofluoroethylene (CFE), chlorodifluoroethylene (CDFE), bromotrifluoroethylene, chlorotrifluoroethylene (CTFE), 1,2-dichloro-1,2-difluoroethylene, iodotrifluoroethylene, and combinations thereof.

[0025] In certain embodiments, ii) the C2 to C8 chloro and / or bromo and / or iodofluoroolefin is cis-1,2-dichloro-1,2-difluoroethylene or trans-1,2-dichloro-1,2-difluoroethylene, preferably trans-1,2-dichloro-1,2-difluoroethylene.

[0026] In a preferred embodiment, ii) the C2-C8 chloro and / or bromo and / or iodofluoroolefin is CTFE.

[0027] In one embodiment, iii) the C2-C8 fluoroolefin is - C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP); - hydrogen-containing C2-C8 fluoroolefins, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutylene; - Formula CH2=CH-R f (In the formula, R f is a C1-C6 (per)fluoroalkyl group); - Formula CF2=CFOR f (In the formula, R f is a C1-C6 (per)fluoroalkyl group); (per)fluoroalkyl vinyl ether (PAVE); - of the formula CF2=CFOX (wherein X is a C1-C1 carbon atom containing at least one catenary oxygen atom) 12 (per)fluorooxyalkyl vinyl ether (which is (per)fluorooxyalkyl); - expression [ka] (wherein R f3 , R f4 , R f5 , and R f6 are independently selected from fluorine atoms and C1-C6 (per)fluoroalkyl groups optionally containing at least one oxygen atom. (Per)fluorodioxole having - Formula CFX2=CX2OCF2OR” f [In the formula, R” f is selected from linear or branched C1-C6 (per)fluoroalkyl, C5-C6 cyclic (per)fluoroalkyl, and linear or branched C2-C6 (per)fluorooxyalkyl containing 1-3 catenary oxygen atoms, X2 is F or H; preferably R f is -CF2CF3(MOVE1), -CF2CF2OCF3(MOVE2), or -CF3(MOVE3), and X2 is F. is selected from the group consisting of:

[0028] In certain embodiments, iii) the C2-C8 fluoroolefin is vinyl fluoride. (VF), trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), hexafluoroisobutylene, and combinations thereof.

[0029] In a preferred embodiment, iii) the C2-C8 fluoroolefin is HFP.

[0030] In another preferred embodiment, iii) the C2-C8 fluoroolefin is TrFE.

[0031] In one embodiment, the fluoropolymer is - C2 to C8 non-fluorinated olefins, such as ethylene, propylene; and / or - expression [ka] (Wherein R1, R2 and R3 are equal to or different from each other and are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group; R OH is a C1-C5 hydrocarbon moiety containing a hydrogen atom or at least one hydroxyl group) Hydrophilic (meth)acrylic monomers It further comprises repeat units derived from:

[0032] In certain embodiments, the hydrophilic (meth)acrylic monomer is selected from the group consisting of acrylic acid (AA), methacrylic acid (MA), hydroxyethyl (meth)acrylate, 2-hydroxypropyl acrylate, hydroxyethylhexyl (meth)acrylate, butyl acrylate, and the like, and combinations thereof.

[0033] In another particular embodiment, the fluoropolymer comprises repeat units derived from C2 to C8 non-fluorinated olefins and / or hydrophilic (meth)acrylic monomers in an amount of 0.1 to 10.0 mol %, preferably 0.2 to 5.0 mol %, more preferably 0.2 to 2.0 mol % (mol % is based on the total moles of repeat units).

[0034] In a preferred embodiment, the hydrophilic (meth)acrylic monomer is AA.

[0035] In another preferred embodiment, the hydrophilic (meth)acrylic monomer is MA.

[0036] In one particular embodiment, the fluoropolymer is a terpolymer of VDF-CTFE-HFP.

[0037] In another particular embodiment, the fluoropolymer is a terpolymer of VDF-CTFE-TrFE.

[0038] In another particular embodiment, the fluoropolymer is a tetrapolymer of VDF-CTFE-HFP-AA.

[0039] In the present invention, the fluoropolymer may be produced by a suspension or emulsion polymerization process.

[0040] In some embodiments, the fluoropolymer is a fluoroelastomer.

[0041] In the present invention, the term "fluoroelastomer" is intended to denote fluoropolymer resins that serve as building blocks for obtaining true elastomers, which are defined by ASTM Special Technical Bulletin No. 184 as materials that can be stretched to twice their natural length at room temperature and that simultaneously return to within 10% of their original length when released after being held under tension for 5 minutes.

[0042] Generally, fluoroelastomers are amorphous and exhibit a low degree of crystallinity, i.e., have less than 20% by volume of crystalline phase, and have a glass transition temperature (T) below room temperature. g In most cases, the fluoroelastomer advantageously has a T of less than 10°C, preferably less than 5°C, more preferably less than 0°C, and even more preferably less than -5°C. g It has.

[0043] The term "amorphous" is intended herein to mean a polymer having a heat of fusion of less than 5.0 J / g, preferably less than 3.0 J / g, and more preferably less than 2.0 J / g, as measured by differential scanning calorimetry (DSC) at a heating rate of 10°C / min according to ASTM D3418.

[0044] In the present invention, the term "sulfide-based solid, ionically conductive inorganic particles" is not particularly limited as long as it is a solid electrolyte material that contains sulfur atoms in its molecular structure or composition.

[0045] The sulfide-based solid, ionically conductive inorganic particles preferably contain Li, S, and an element from Groups 13-15, such as P, Si, Sn, Ge, Al, As, Sb, or B, to increase Li-ion conductivity.

[0046] The sulfide-based solid, ionically conductive inorganic particles according to the present invention preferably comprise: - Li 10 SnP2S 12 Lithium tin phosphorus sulfide ("LSPS") materials, such as; - Formula (Li2S) x -(P2S5) y (wherein x+y=1 and 0≦x≦1), Li7P3S 11 , Li7PS6, Li4P2S6, Li 9.6 P3S 12 and lithium phosphosulfide ("LPS") materials, such as glasses, crystalline, or glass-ceramics of the type Li3PS4; - Li2CuPS4, Li 1+2x Zn 1-x PS4 (in the formula, 0≦x≦1), Li 3.33 Mg 0.33 P2S6, and Li 4-3x Sc x Doped LPS, such as P2S6 (where 0≦x≦1); - Expression Li x P y S z Lithium Phosphorus Sulfide Oxygen (“LPSO”) materials of formula O, where 0.33≦x≦0.67, 0.07≦y≦0.2, and 0.4≦z≦0.55; - Li 10 SnP2S 12、 Li 10 GeP2S 12 , Li 10 SiP2S 12 and X-containing lithium phosphorus sulfide materials ("LXPS"), where X is Si, Ge, Sn, As, or Al, such as Li2S-P2S5-SnS; - X-containing lithium phosphorus sulfide oxygen ("LXPSO"), where X is Si, Ge, Sn, As, or Al; - Li2SiS3, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Lithium silicon sulfide ("LSS") materials, such as Li2S-SiS2-Al2S3; - Lithium boron sulfide materials, such as Li3BS3 and Li2S-B2S3-LiI; - Li 0.8 Sn 0.8 S2, Li4SnS4, Li 3.833 Sn 0.833 As 0.166 Lithium tin sulfide and lithium arsenide materials, such as S4, Li3AsS4-Li4SnS4, and Ge-substituted Li3AsS4; - Li4PS4Cl 、 Li7P2S8Cl, Li7P2S8I, and the like a PS b X c (wherein X represents at least one halogen element selected from the group consisting of Cl, Br, and I, or a combination thereof; a represents a number from 2.0 to 7.0; b represents a number from 3.5 to 6.0; and c represents a number from 0 to 3.0); and - combinations thereof is selected from the group consisting of:

[0047] In a more preferred embodiment, the sulfide-based solid, ionically conductive inorganic particles have the general formula Li a PS b X c and more particularly, argyrodite-type sulfide materials of the formula Li6PS5X, where X is Cl, Br, or I.

[0048] In another preferred embodiment, the argyrodite-type sulfide material of formula Li6PS5Y is sulfur and / or lithium deficient, e.g., 0 <x<0.5のLi6-x PS 5-x Cl 1+x , or doped with heteroatoms.

[0049] Particularly preferred sulfide-based solid ionically conductive particles are lithium tin phosphosulfide (“LSPS”) materials (e.g., Li 10 SnP2S 12 ) and argyrodite-type sulfide materials (e.g., Li6PS5Cl).

[0050] In one embodiment, b) the amount of sulfide-based solid, ionically conductive inorganic particles is at least 40.0 wt.-%, preferably at least 60.0 wt.-%, more preferably at least 70.0 wt.-%, even more preferably at least 80.0 wt.-%, most preferably at least 90.0 wt.-%, and / or at most 99.8 wt.-%, preferably at most 99.5 wt.-%, more preferably at most 99.0 wt.-%, most preferably at most 98.0 wt.-%, based on the total weight of the solid composite electrolyte.

[0051] In certain embodiments, the amount of b) sulfide-based solid, ionically conductive inorganic particles is 40.0 to 99.8 wt. %, preferably 60.0 to 99.5 wt. %, more preferably 70.0 to 99.0 wt. %, even more preferably 80.0 to 99.0 wt. %, and most preferably 90.0 to 99.0 wt. %, based on the total weight of the solid composite electrolyte.

[0052] In a more specific embodiment, b) the amount of sulfide-based solid, ionically conductive inorganic particles is 95.0 to 99.0 wt %, based on the total weight of the solid composite electrolyte.

[0053] In the present invention, b) the at least one sulfide-based solid, ionically conductive inorganic particle is different from the lithium salts conventionally used as essential components of lithium secondary batteries.

[0054] The term "lithium salt" is intended herein to mean a substance that must be dissolved in a solvent to ensure ionic conduction.

[0055] In lithium secondary batteries, the liquid electrolyte consists primarily of a lithium salt in a non-aqueous organic solvent, where the liquid electrolyte serves as a conductive path for the movement of cations, i.e., Li + Lithium ions (i.e., Li) pass from the cathode to the anode during discharge. + cations) are used as charge carriers. The dissolution of lithium salts is achieved by + By interaction, i.e., Li + Cation dissolution - (counter)ion interactions are crucial. Thus, many simple lithium salts, such as LiCl, LiF, Li2O, etc., are precluded from electrolyte use because their strong cation-anion interactions result in high lattice energies and thus poor solubility in relevant aprotic solvents. Non-limiting examples of lithium salts include, among others, lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonate (LiSbF6), lithium hexafluorotantalate (LiTaF6), lithium tetrachloroaluminate (LiAlCl4), lithium tetrafluoroborate (LiBF4), lithium chloroborate (Li2B 10 Cl 10 ), lithium fluoroborate (Li2B 10 F 10 ), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide Li(FSO2)2N (LiFSI), lithium bis(trifluoromethanesulfonyl)imide Li(SO2CF3)2N (LiTFSI), and mixtures thereof.

[0056] Li + Cation conductivity originates from both total ionic conductivity and cation transference number. Given that the cation transference number in non-aqueous organic solvents is low, e.g., typically less than 0.5, ionic conductivity plays a crucial role in battery performance.

[0057] In short, a liquid electrolyte, in which at least one lithium salt is dissolved in at least one non-aqueous organic solvent, plays a vital role as one of the main components of a conventional lithium secondary battery.

[0058] In this regard, recent advances in the field of batteries involve the use of solid materials as electrolyte materials, and sulfide-based solid ionically conductive inorganic particles are particularly promising materials. In such solid-state batteries, the solid electrolyte replaces the function / role of the liquid electrolyte. Much effort has been made to understand the ion transport mechanism in solid electrolytes, but the Li transport mechanism within the solid electrolyte, i.e., between the electrode and electrolyte interfaces (both the electrode / solid electrolyte interface and the active material / solid electrolyte interface in the electrode), is still unclear. + The cation diffusion behavior, however, still lacks a deep understanding.

[0059] Like liquid electrolytes, solid electrolytes are ionic conductors that deliver ions between two electrodes. However, unlike liquid electrolytes, solid electrolytes require the addition of Li to make them conductive. + The lithium cation in lithium argyrodite Li6PS5X (where X = Cl, Br, or I) is, for example, Li + Li as a pathway for cations + However, the Li in the non-aqueous solvent that constitutes the liquid electrolyte plays a role in the cation diffusion mechanism. + Unlike lithium salts, which dissociate into a cation and the corresponding counteranion, the lithium site in Li6PS5X is thereby +It is understood that the diffusion / transport of cations occurs by forming localized cages where multiple jump processes, i.e., doublet jumps, intracage jumps, and intercage jumps, are possible (Sulfide and oxide inorganic solid electrolytes for All-Solid-State Li Batteries: Nanomaterials 2020, 10, 1606; doi:10.3390 / nano10081606 by Reddy et al.). That is, unlike liquid electrolytes, only one species in solid electrolytes is mobile, and the structure is determined by the mobile species, i.e., Li, which corresponds to the cooperative conduction mechanism. + It has partial site occupancy of cations.

[0060] In view of the above, lithium salts are distinctly different from sulfide-based solid, ionically conductive inorganic particles that contain lithium species within their inorganic structure in that lithium salts need to be dissolved in a solvent to ensure ionic conduction, whereas sulfide-based solid, ionically conductive inorganic particles have intrinsic ionic conductivities of greater than 0.1 mS / cm at room temperature, which are attributed to the sublattice diffusion of mobile lithium species in the inorganic framework.

[0061] In the present invention, the solid composite electrolyte does not contain a lithium salt.

[0062] The solid composite electrolyte of the present invention is characterized by high adhesion properties to current collectors when it is used in fabricating electrodes, such as positive electrodes, of solid state batteries.

[0063] In the present invention, the type of "current collector" depends on whether the electrode provided thereby is a positive electrode or a negative electrode. When the electrode of the present invention is a positive electrode, the current collector typically comprises, and preferably consists of, at least one metal selected from the group consisting of aluminum (Al), nickel (Ni), titanium (Ti), and alloys thereof, preferably Al. When the electrode of the present invention is a negative electrode, the current collector typically comprises, and preferably consists of, at least one metal selected from the group consisting of lithium (Li), sodium (Na), zinc (Zn), magnesium (Mg), copper (Cu), and alloys thereof, preferably Cu.

[0064] A second object of the present invention is a slurry for producing a solid composite electrolyte comprising a) at least one fluoropolymer, b) at least one sulfide-based solid, ionically conductive inorganic particle, and c) at least one non-aqueous solvent.

[0065] Fluoropolymer is as defined in the present invention.

[0066] c) There are no specific restrictions imposed on the non-aqueous solvent, as long as the non-aqueous solvent a) can dissolve the fluoropolymer, and b) is compatible with the sulfide-based solid, ionically conductive inorganic particles, and the solvent does not adversely affect the ionic conductivity of the resulting solid composite electrolyte.

[0067] In one embodiment, c) the non-aqueous solvent is selected from the group consisting of nitrile-containing solvents, ethers, esters, thiols, thioethers, ketones, and tertiary amines.

[0068] In a preferred embodiment, the non-aqueous solvent c) is a nitrile-containing solvent having the general formula R-CN, where R represents an alkyl group. Non-limiting examples of nitrile-containing solvents are acetonitrile, butyronitrile, valeronitrile, isobutylnitrile, etc.

[0069] In another preferred embodiment, the non-aqueous solvent c) is an ether having the general formula R1-O-R2 (wherein R1 and R2 independently represent alkyl groups). Ether solvents include cyclic ethers based on 3-, 5-, or 6-membered rings. Cyclic ethers can be substituted with alkyl groups, can have unsaturation, and can have additional functional elements such as nitrogen or oxygen atoms in the ring. Non-limiting examples of (cyclic) ether solvents are diethyl ether, 1,2-dimethoxy ether, cyclopentyl methyl ether, diethyl ether, dibutyl ether, 1,3-dioxolane, anisole, tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, etc.

[0070] In another preferred embodiment, c) the non-aqueous solvent is an ester having the general formula R-COO-R, where R and R independently represent alkyl groups. Non-limiting examples of ester solvents are butyl butyrate, ethyl benzoate, etc.

[0071] In another preferred embodiment, the non-aqueous solvent c) is a thiol having the general formula R5 = SH or a thioether having the general formula R6-S-R7 (where R5, R6, and R7 are independently alkyl groups). Thioether solvents include cyclic thioethers based on 3-, 5-, or 6-membered rings. Cyclic thioethers can be substituted with alkyl groups, can have unsaturation, and can have additional functional elements such as nitrogen or oxygen atoms in the ring. Non-limiting examples of thiol solvents are ethanethiol, tert-dodecyl mercaptan, thiophenol, tert-butyl mercaptan, octanol thiol, dimethyl sulfide, ethyl methyl sulfide, methyl benzyl sulfide, etc.

[0072] In another preferred embodiment, c) the non-aqueous solvent is a ketone having the general formula R8R9C=O, where R8 and R9 independently represent alkyl groups. Non-limiting examples of ketone solvents are methyl ethyl ketone, methyl isobutyl ketone, di-isobutyl ketone, acetophenone, benzophenone, etc., preferably methyl isobutyl ketone.

[0073] In another preferred embodiment, c) the non-aqueous solvent is R 10 R 11 R 12 N (wherein, R 10 , R 11 and R 12 are independently alkyl groups). The N atom of the tertiary amine can be buried inside a 3-, 5-, or 6-membered ring. Non-limiting examples of tertiary amine solvents are triethylamine, dimethylbutylamine, tributylamine, cyclohexyldimethylamine, N-ethylpiperidine, etc.

[0074] In the present invention, R to R 12 The alkyl group refers to an "alkyl group" comprising a saturated hydrocarbon having one or more carbon atoms, including straight-chain alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, etc., cyclic alkyl groups (or "cycloalkyl" or "alicyclic" or "carbocyclic" groups) such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl, branched-chain alkyl groups such as isopropyl, tert-butyl, sec-butyl, and isobutyl, and alkyl-substituted alkyl groups such as alkyl-substituted cycloalkyl groups and cycloalkyl-substituted alkyl groups as defined above. Additionally, the alkyl group may contain one or more unsaturated functional groups such as ether, carbonyl, carboxyl, hydroxyl, thio, thiol, thioxy, sulfo, nitrile, nitro, nitroso, azo, amido, imido, amino, imino, or halogen.

[0075] In a preferred embodiment, c) the non-aqueous solvent comprises a nitrile-containing solvent such as acetonitrile; an ether such as tetrahydrofuran, 2-methyl-tetrahydrofuran, 2,5-dimethyl-tetrahydrofuran, 1,3-dioxolane, diethyl ether, and 1,2-dimethoxy ether; an ester such as butyl butyrate; and a ketone such as methyl isobutyl ketone.

[0076] In a more preferred embodiment, c) the non-aqueous solvent is an ester such as butyl butyrate.

[0077] In another more preferred embodiment, c) the non-aqueous solvent is a ketone, such as methyl isobutyl ketone.

[0078] In one embodiment, the slurry may further comprise a second solvent, such as, but not limited to, saturated and aromatic hydrocarbons, including linear and branched alkanes (e.g., heptane), cyclic alkanes (e.g., cyclohexane), and aromatic compounds (e.g., xylene and toluene).

[0079] In the present invention, the slurry can be suitably prepared by a process comprising mixing a) a fluoropolymer, b) sulfide-based solid, ionically conductive inorganic particles, and c) a non-aqueous solvent by any method known to those skilled in the art. In a preferred embodiment, the slurry is prepared by a process comprising a) solubilizing a fluoropolymer in c) a non-aqueous solvent, followed by adding c) sulfide-based solid, ionically conductive inorganic particles, and mixing the resulting mixture.

[0080] In the present invention, the amount of a) fluoropolymer in the slurry is such to provide a solid composite electrolyte comprising a) fluoropolymer in an amount in the range of at least 1.0 wt.-%, preferably at least 1.5 wt.-%, more preferably 2.0 wt.-%, and / or at most 20.0 wt.-%, preferably at most 15.0 wt.-%, more preferably at most 10.0 wt.-%, and most preferably at most 5.0 wt.-%, based on the total weight of a) fluoropolymer and b) sulfide-based solid, ionically conductive inorganic particles.

[0081] In certain embodiments, the amount of a) fluoropolymer in the slurry is such to provide a solid composite electrolyte comprising a) fluoropolymer in an amount ranging from 1.0 to 20.0 wt.%, preferably 1.5 to 15.0 wt.%, more preferably 2.0 to 10.0 wt.%, and most preferably 2.0 to 5.0 wt.%, based on the total weight of a) fluoropolymer and b) sulfide-based solid, ionically conductive inorganic particles. Thus, the resulting solid composite electrolyte exhibits good bonding between a) fluoropolymer and b) sulfide-based solid, ionically conductive inorganic particles while maintaining good ionic conductivity.

[0082] The slurry according to the present invention is typically applied onto at least one foil of an inert flexible support by a technique selected from casting, spray coating, rotary spray coating, roll coating, doctor blading, slot-die coating, gravure coating, inkjet printing, spin coating, and screen printing. In one embodiment, the wet film thus obtained typically has a thickness of 10 to 400 μm, preferably 50 to 200 μm. The wet film is then dried at a temperature of 10°C to 200°C, preferably 20°C to 80°C. An additional drying step in an oven under vacuum at a temperature of 20°C to 150°C, preferably 50°C to 80°C, can be appropriately carried out to completely remove the solvent. Those skilled in the art can select the optimal duration and temperature of the drying step depending on the boiling point of the solvent. The dried film thus obtained can be further subjected to an additional compression step, such as calendering, uniaxial or isostatic compression, to reduce the porosity and increase the density of the solid composite electrolyte.

[0083] In another embodiment, the slurry may further comprise d) at least one electroactive material, and optionally e) at least one conductive agent.

[0084] In a preferred embodiment, d) the electroactive material is for the positive electrode.

[0085] In the present invention, the term "positive electrode" is intended to mean in particular the electrode of an electrochemical cell where reduction occurs during discharge, while the term "negative electrode" is intended to mean in particular the electrode of an electrochemical cell where oxidation occurs during discharge.

[0086] In the present invention, the term "electroactive material" is intended to mean a material that is capable of incorporating or inserting lithium ions into its structure and subsequently releasing them therefrom during the charging and discharging stages of the battery.

[0087] When forming a positive electrode for a solid-state battery, the electroactive material for the positive electrode is not particularly limited. It may include a composite metal chalcogenide of the formula LiMQ2 (where M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Q is a chalcogen such as O or S). Among these, it is preferable to use a lithium-based composite metal oxide of the formula LiMO2 (where M is the same as defined above). Preferred examples thereof include LiCoO2, LiNiO2, LiNi x Co 1-x O2 (0 < x < 1), and spinel-structured LiMn2O4 may be mentioned. Another preferred example thereof is a lithium-nickel-manganese-cobalt-based metal oxide of the formula LiNi x Mn y Co z O2 (x + y + z = 1, referred to as NMC), for example LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, and a lithium-nickel-cobalt-aluminum-based metal oxide of the formula LiNi x Co y Al z O2 (x + y + z = 1, referred to as NCA), for example LiNi 0.8 Co 0.15 Al 0.05 O2 may be mentioned.

[0088] As an alternative, when forming a positive electrode for a lithium metal battery, further, the electroactive material of the positive electrode is of the formula M1M2(JO4) f E 1-f(wherein, M1 is lithium which may be partially substituted by another alkali metal representing less than 20% of M1 metal, M2 is a transition metal at a +2 oxidation level selected from Fe, Mn, Ni or a mixture thereof which may be partially substituted by one or more additional metals representing up to 35% of M2 metal at oxidation levels of +1 to +5 including 0, JO4 is any oxyanion where J is any of P, S, V, Si, Nb, Mo or a combination thereof, E is a fluoride, hydroxide or chloride anion, and f is a molar fraction of the JO4 oxyanion generally included in the range of 0.75 to 1) may contain a lithiated or partially lithiated transition metal oxyanion-based electroactive material.

[0089] M1M2(JO4) as defined above f E 1-f The electroactive material is preferably phosphate-based and may have a regular or modified olivine structure.

[0090] More preferably, the electroactive material of the positive electrode has the formula Li 3-x M’ y M” 2-y (JO4)3 (where 0 ≦ x ≦ 3, 0 ≦ y ≦ 2, M’ and M” are the same or different metals, at least one of which is a transition metal, JO4 is preferably PO4 which may be partially substituted by another oxyanion, and J is any of S, V, Si, Nb, Mo or a combination thereof). Even more preferably, the electroactive material is a phosphate-based electroactive material of the formula Li(Fe x Mn 1-x )PO4 (where 0 ≦ x ≦ 1, preferably x = 1), that is, lithium iron phosphate of the formula LiFePO4.

[0091] In a preferred embodiment, the electroactive material of the positive electrode is LiMQ2 (where M is at least one metal selected from Co, Ni, Fe, Mn, Cr and V, and Q is O or S); LiNi x Co 1-x O2 (0 < x < 1); spinel-structured LiMn2O4; the formula LiNix Mn y Co z Lithium-nickel-manganese-cobalt-based metal oxide (NMC) of O2 (x+y+z=1), formula LiNi x Co y Al z O2 (x+y+z=1) is selected from the group consisting of lithium-nickel-cobalt-aluminum-based metal oxides (NCA), lithium-cobalt-based metal oxides (NCO), lithium-nickel-manganese-based metal oxides (LNMO) and LiFePO4.

[0092] In a more preferred embodiment, the electroactive material of the positive electrode is selected from the group consisting of NMC, NCA, NCO, and LNMO.

[0093] In the present invention, the term "conductive agent" is intended to mean a material used to ensure that the electrode has good charge and discharge performance and to provide additional conductivity. Non-limiting examples of conductive agents are carbonaceous materials and metal powders or fibers, such as carbon black, carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCFs), graphite, graphene, graphite fibers, etc. Examples of carbon black include ketjen black and acetylene black. Examples of metal powders or fibers include nickel and aluminum powders or fibers.

[0094] In certain embodiments, the amount of a) fluoropolymer in the slurry is such to provide a solid composite electrolyte comprising a) fluoropolymer in an amount ranging from 1.0 to 20.0 wt.%, preferably 1.5 to 15.0 wt.%, more preferably 2.0 to 10.0 wt.%, and most preferably 2.0 to 5.0 wt.%, based on the total weight of a) fluoropolymer, b) sulfide-based solid ionically conductive inorganic particles, c) electroactive material, and optionally e) at least one conductive agent. Accordingly, the resulting electrode exhibits outstanding adhesion to the current collector.

[0095] A third object of the invention is an electrode comprising a solid composite electrolyte according to the invention, d) at least one electroactive material and, optionally, e) at least one conductive agent.

[0096] In one embodiment, d) the electroactive material is for the positive electrode.

[0097] In one embodiment, the electrode comprises at least one fluoropolymer according to the present invention, at least one electroactive material for the positive electrode, and at least one sulfide-based solid, ionically conductive inorganic particle.

[0098] In a particular embodiment, the positive electrode comprises a VDF-CTFE-HFP terpolymer as the fluoropolymer, Li6PS5Cl as the sulfide-based solid ionically conductive inorganic particles, and LiNi as the electroactive material for the positive electrode. 0.6 Mn 0.2 Co 0.2 O2 and optionally carbon black as a conductive agent.

[0099] In another specific embodiment, the positive electrode comprises a VDF-CTFE-TrFE tarpaulin as the fluoropolymer, Li6PS5Cl as the sulfide-based solid ionically conductive inorganic particles, and LiNi as the electroactive material for the positive electrode. 0.6 Mn 0.2 Co 0.2 O2 and optionally carbon black as a conductive agent.

[0100] In another particular embodiment, the positive electrode comprises VDF-CTFE-HFP-AA as the fluoropolymer, Li6PS5Cl as the sulfide-based solid ionically conductive inorganic particles, and LiNi as the electroactive material for the positive electrode. 0.6 Mn 0.2 Co 0.2 O2 and optionally carbon black as a conductive agent.

[0101] A fourth object of the present invention is a solid-state battery comprising a positive electrode, a negative electrode and a membrane arranged between the positive and negative electrodes, wherein at least one of the positive electrode, the negative electrode and the membrane comprises the solid composite electrolyte according to the present invention, optionally d) at least one electroactive material and / or e) at least one conductive agent.

[0102] In the present invention, the term "membrane" is intended to mean in particular an ion-permeable membrane placed between the positive and negative electrodes, whose function is to block electrons and allow lithium ions to pass through while ensuring physical separation between the electrodes.

[0103] A fifth object of the present invention is a binder solution for solid-state batteries comprising a) at least one fluoropolymer according to the invention and c) at least one non-aqueous solvent.

[0104] The non-aqueous solvent is as defined in the present invention.

[0105] Those skilled in the art can easily select a) an appropriate amount of non-aqueous solvent to achieve uniform dissolution of the fluoropolymer and suitable evaporation thereof, when the binder solution according to the present invention is used to prepare a solid composite electrolyte, which can be used either as a membrane disposed between a positive electrode and a negative electrode, or as an electrode for a solid-state battery.

[0106] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference conflicts with the statements of this application to the extent that a term may be unclear, the statements of this application shall control.

[0107] The present invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and is not intended to limit the scope of the invention. [Example]

[0108] raw materials - LPSCl (Li6PS5Cl), a crystalline sulfide-based solid ionically conductive inorganic particle, commercially available from NEI; - NMC622 (Cellcore® NMC KHX12), commercially available from Umicore; - conductive carbon (C-NERGY™ SUPER C65T), commercially available from Imerys; Butyl butyrate (BB), commercially available from Sigma Aldrich; and - Methyl isobutyl ketone (MIBK), commercially available from Sigma Aldrich Fluoroelastomers.

[0109] Fluoropolymer: - Polymer 1: VDF-CTFE-HFP (80.0 / 10.0 / 10.0 mol%), synthesized in-house at Solvay Specialty Polymers Italy SpA - Polymer 2: VDF-CTFE-HFP (79.0 / 15.0 / 6.0 mol%), synthesized in-house at Solvay Specialty Polymers Italy SpA Polymer 3: VDF-CTF-HFP-AA (78.7 / 9.9 / 9.9 / 0.5 mol%), synthesized in-house at Solvay Specialty Polymers Italy SpA Polymer 4: VDF-CTFE-TrFE (63.5 / 7.5 / 29.0 mol%), commercially available as Solvene® 300 from Solvay Specialty Polymers Italy SpA Polymer 5: VDF-HFP (78.5 / 21.5 mol%), commercially available from Tecnoflon® N935 Solvay Specialty Polymers Italy SpA (T g =-19℃) Polymer 6: VDF-TFE-HFP (at 60.0 / 20.0 / 20.0 mol%), Tecnoflon® T538 commercially available from Solvay Specialty Polymers Italy SpA Polymer 7: VDF-TFE-HFP (at 65.0 / 19.0 / 16.0 mol%), commercially available as Tecnoflon® TN from Solvay Specialty Polymers Italy SpA.

[0110] Synthesis of polymers 1-3 Polymer 1: In a vertical steel autoclave equipped with baffles and a stirrer operating at 550 rpm, 1.3 L of demineralized water was introduced. The temperature was brought to the reaction temperature of 75°C. 4.0 x 10 5 VDF and 3.0 x 10 Pa (absolute) 5 (absolute) of HFP was introduced. A gaseous mixture of VDF-CTFE-HFP in a nominal molar ratio of 80.0 / 10.0 / 10.0 was added to 20.0 × 10 5 The addition was carried out by using a compressor until a pressure of 100 Pa (absolute) was reached.

[0111] The composition of the gaseous mixture present in the autoclave head, as analyzed by gas chromatography, was 72.6 mol% VDF, 14.2 mol% CTFE, and 13.2 mol% HFP before the reaction started. 40.0 cc of an ammonium persulfate ((NH4)2S2O8) solution in ethyl acetate (3 w / w%) and 2.0 mL of pure ethyl acetate were fed into the autoclave.

[0112] The polymerization pressure was maintained constant until the end of the polymerization. When 200.0 g of the mixture had been fed, the feed was stopped, the reactor was cooled to room temperature, and degassed to remove residual materials. The as-produced latex was vented and further degassed with nitrogen for 24 hours. The resulting polymer was isolated by using a standard isolation procedure using aluminum sulfate (Al2(SO4)3), and then dried in a vented oven at 90°C for 24 hours.

[0113] Polymer 2: Polymer 2 was synthesized similarly to polymer 1. After introducing 1.3 L of demineralized water, the temperature was brought to the reaction temperature of 75 °C. 5 VDF and 4.0 x 10 Pa (absolute) 5 (absolute) of HFP was introduced. A gaseous mixture of VDF-CTFE-HFP in a nominal molar ratio of 79.0 / 15.0 / 6.0 was added to 20.0 × 10 5 The addition was carried out by using a compressor until a pressure of 100 Pa (absolute) was reached.

[0114] The composition of the gaseous mixture present in the autoclave head, as analyzed by gas chromatography, was 78.3 mol% VDF, 14.6 mol% CTFE, and 7.1 mol% HFP before the reaction started. 45.0 cc of ammonium persulfate solution in ethyl acetate (3 w / w%) and 3 mL of pure ethyl acetate were fed into the autoclave.

[0115] The polymerization pressure was maintained constant until the end of the polymerization. When 300.0 g of the mixture had been fed, the feed was stopped, the reactor was cooled to room temperature, and then degassed to remove residual materials. The as-produced latex was vented and further degassed with nitrogen for 24 hours. The resulting polymer was then isolated by using a standard isolation procedure using aluminum sulfate and dried in a vented oven at 90°C for 24 hours.

[0116] Polymer 3: In a vertical steel autoclave equipped with baffles and a stirrer operating at 650 rpm, 1.3 L of demineralized water was introduced. The reaction temperature was brought to 80°C. 3.0 x 10 5 VDF and 3.0 x 10 Pa (absolute) 5 (absolute) of HFP was introduced. A gaseous mixture of VDF-CTFE-HFP in a nominal molar ratio of 80.0 / 10.0 / 10.0 was added to 26.0 × 10 5 The mixture was added by using a compressor until a pressure of 1000 kJ / cm² was reached.

[0117] The composition of the gaseous mixture present in the autoclave head, as analyzed by gas chromatography before the start of the reaction, was 72.7 mol% VDF, 12.9 mol% CTFE, and 14.4 mol% HFP. 40.0 mL of ammonium persulfate solution (3 wt. / wt.%) in ethyl acetate and 5.0 mL of acrylic acid solution (2 wt. / wt.%) were fed into the autoclave. 10 mL of ammonium persulfate solution (3 wt. / wt.%) in ethyl acetate and 5.0 mL of acrylic acid solution (2 wt. / wt.%) were fed into the autoclave for every 20.0 g of polymerization. The polymerization pressure was maintained constant until the end of the polymerization.

[0118] When 200.0 g of the gaseous mixture had been fed, the feed was stopped and the reactor was cooled to room temperature. The as-produced latex was discharged and frozen for 48 hours. After thawing, the resulting polymer was washed with demineralized water and dried in a vented oven at 80° C. for 48 hours.

[0119] Preparation of solid composite electrolyte Inventive Examples 1 and 5 (E1 and E5) A solid composite electrolyte of E1, consisting of 95.0 parts by weight (pbw) LPSCI and 5.0 pbw Polymer 1, was prepared in the form of a film as follows.

[0120] A 10.0 wt% polymer solution was prepared by weighing out 1.0 g of Polymer 1 and 9.0 g of BB. Then, 3.705 g of LPSCl, 1.95 g of the 10.0 wt% polymer solution, and 0.345 g of BB were mixed using four glass balls under magnetic stirring at 400 rpm for a minimum of 6 hours. The solids content of the slurry and the casting speed were adjusted to maintain a slurry viscosity of 2.0–10.0 Pa·s throughout the casting process. The resulting slurry was cast onto a flexible support (Kapton® FN) using an automatic film applicator manufactured by Elcometer Ltd. The wet film was dried on a hot plate at 50°C for 1 hour and then placed in an oven at 80°C under vacuum overnight. The sample was stored in a minigrip bag and then placed in a sealed bag. All experiments were performed in an argon-filled glove box.

[0121] The solid composite electrolyte of E5 was prepared similarly to E1, except that MIBK was used as the solvent instead of BB.

[0122] Inventive Examples 2 and 6 (E2 and E6) The solid composite electrolyte E2 was prepared in the same manner as E1, except that polymer 2 was used instead of polymer 1. The solid composite electrolyte E6 was prepared in the same manner as E2, except that MIBK was used as the solvent instead of BB.

[0123] Inventive Examples 3 and 7 (E3 and E7) The solid composite electrolyte E3 was prepared in the same manner as E1, except that polymer 3 was used instead of polymer 1. The solid composite electrolyte E7 was prepared in the same manner as E3, except that MIBK was used as the solvent instead of BB.

[0124] Inventive Example 4 (E4) The solid composite electrolyte of E4 was prepared similarly to E1, except that polymer 4 was used instead of polymer 1.

[0125] Comparative examples 1~2 (CE1~CE2) The solid composite electrolyte of CE1 was prepared in the same manner as E1, except that polymer 5 was used instead of polymer 1. The solid composite electrolyte of CE2 was prepared in the same manner as CE1, except that MIBK was used as the solvent instead of BB.

[0126] Comparative Example 3 (CE3) The solid composite electrolyte of CE3 was prepared similarly to E1, except that polymer 6 was used instead of polymer 1.

[0127] Comparative Example 4 (CE4) The solid composite electrolyte of CE4 was prepared similarly to E1, except that polymer 7 was used instead of polymer 1.

[0128] Measurement of bonding strength in solid composite electrolytes E1-E4, CE1, CE3, and CE4 A dry, free-standing solid composite electrolyte strip was fixed onto a rigid Al plate (2.6 cm × 10 cm) using double-sided tape (25 mm wide; 0.24 mm thick). Using a motorized tension / compression test stand (Mark-10 ESM303) with a flat, rounded tip, a second double-sided tape (1 cm diameter and 0.24 mm thick) fixed to the bottom of the rounded tip was pressed against the second surface of the solid composite electrolyte with a force of 200 N for 1 minute. In a second step, the tip was removed (peeled) from the surface of the solid composite electrolyte at a constant speed of 100 mm / s. As a result, the solid composite electrolyte was damaged (torn), with one part remaining on the rigid Al support and the other part remaining on the tip connected to the test stand. The force required to split the film into two parts is recorded in Table 1 as the average of five independent peel measurements. The peel test was conducted in a dry chamber with a dew point of -40°C.

[0129] Measurement of the ionic conductivity of solid composite electrolytes E1-E4 and CE1 The ionic conductivity of the solid composite electrolytes E1–E4 and CE1 in film form was measured by AC impedance spectroscopy using an in-house developed pressure cell, where the film is pressed between two stainless steel electrodes during the impedance measurement. A cross-sectional view of the pressure cell is shown in Figure 1.

[0130] Impedance spectra were measured at a pressure of 370 MPa and a temperature of 20° C. AC impedance measurements were performed with a potentiostat (VMP-300, BioLogic Science Instruments SAS) in the frequency range of 1000 Hz to 4.7 MHz.

[0131] The Nyquist plot of the solid composite electrolyte showed the typical behavior of a solid electrolyte (inorganic, polymer, or composite) with a semicircular and Warburg-type impedance in the high- and low-frequency regions, respectively. The conductive behavior of the composite electrolyte was modeled according to an equivalent circuit R1(R2 / Q2)Q3 (see Figure 2), where R is the resistance and Q is a constant phase element, where R1 and R2 represent the bulk and grain boundary resistances, respectively, and Q2 and Q3 represent the grain boundary and electrode contributions, respectively.

[0132] The intercept of the semicircle with the real axis at high frequencies is attributed to the bulk resistance (R1), and the intercept with the real axis at lower frequencies is attributed to the total resistance of the film (R1 + R2). This total resistance, R, is conventionally used to calculate the conductivity of solid composite electrolytes. Therefore, the ionic conductivity, σ, was obtained using the formula σ = d / (R × A), where d is the thickness of the film and A is the area of the stainless steel electrode. The SI unit of ionic conductivity is siemens per meter (S / m), where S is ohms. -1 and 1 millisiemens per centimeter (mS / cm) is the decimal point of the SI unit, i.e., 1 mS / cm = 0.1 S / m. The ionic conductivities of the solid composite electrolytes E1-E4, CE1, CE4, and CE5 are recorded in Table 1.

[0133] Preparation of positive electrodes E1 to E7 and CE1 to CE4 Positive electrodes E1-E4, CE1, CE3, and CE4, composed of 74.0 pbw NMC622, 20.0 pbw LPSCl, 2.0 pbw conductive carbon black, and 4.0 pbw fluoropolymer (selected from polymers 1-7), were prepared as follows.

[0134] A 10.0 wt% binder solution was prepared by weighing out 1.0 g of fluoropolymer and 9.0 g of BB. Then, 1.0 g of LPSCl, 0.1 g of conductive carbon, 3.7 g of NMC622, and 2.0 g of the 10.0 wt% binder solution were mixed using four glass balls under magnetic stirring at 400 rpm for a minimum of 6 hours. The as-obtained slurry was cast onto an Al current collector using an automatic film applicator manufactured by Elcometer Ltd. The viscosity of the slurry was adjusted to maintain a viscosity of 2.0–10.0 Pa·s throughout the casting process and 25.0–30.0 mg / cm. 2 The solids content of the slurry and the casting speed were adapted to obtain a dry electrode loading of 1000 kJ / cm². The wet films were dried on a hot plate at 50 °C for 1 h, then placed in an oven at 80 °C under vacuum overnight, stored in minigrip bags, and then placed in sealed bags. The experiments were carried out in an argon-filled glove box.

[0135] Positive electrodes E5 to E7 and CE2 were prepared in the same manner as above, except that MIBK was used as the solvent instead of BB.

[0136] Measurement of the adhesion properties of positive electrodes to Al current collectors (peel tests): E1-E7 and CE1-CE4 The adhesive strength of the positive electrode to the Al current collector was evaluated using a 180° peel test. An electrode strip (2 cm × 10 cm) of the dried electrode was fixed onto a rigid Al plate (2.6 cm × 10 cm) using double-sided tape (25 mm wide; 0.24 mm thick), with the electrode facing downwards and the current collector facing upwards. The Al current collector was peeled from the electrode using a motorized tension / compression test bench (ESM303, manufactured by Mark-10 Corporation) while maintaining a 180° angle and at a constant speed of 300 mm / min. The force required to remove the Al current collector from the electrode was recorded in Table 1 as the average value of three independent strips produced from three independent electrodes using three independent slurries with the same composition. The peel test was conducted in a dry room with a dew point of -40°C.

[0137] As shown in Table 1, all positive electrodes according to the present invention, i.e., E1 to E7, clearly exhibited outstanding adhesion to the Al current collector, distinguishable from those of CE1 to CE4, while maintaining reasonable ionic conductivity. Although E4 exhibited relatively poor adhesion, it exhibited the highest ionic conductivity and excellent cohesive strength. In particular, E3 and E7, which used polymer 3 (VDF-CTFE-HFP-AA), exhibited even better adhesion than E1 and E5, which used polymer 1 (VEF-CTFE-HFP).

[0138] [Table 1]

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