Lithium metal secondary batteries

Abstract

The present invention provides a lithium metal secondary battery having an electrolyte layer and an intermediate layer between the positive electrode and the negative electrode current collector; the intermediate layer includes a stretchable three-dimensional structure; the stretchable three-dimensional structure includes an ionic liquid.

Description

Technical Field

[0001] This invention relates to a lithium metal secondary battery. Background Technology

[0002] To mitigate the negative impacts on the global environment and further advance vehicle emission regulations, as well as to reduce CO2 emissions from the perspective of climate-related disasters, there is a growing interest in electric vehicles. As an example of a secondary battery used in electric vehicles, a high-energy-density lithium metal secondary battery was investigated.

[0003] As a lithium metal secondary battery, for example, one known lithium metal secondary battery includes a negative electrode having a negative electrode current collector, a positive electrode, and a solid electrolyte layer. Furthermore, as a negative electrode structure of a lithium metal secondary battery, there are structures where lithium metal is bonded to the negative electrode current collector; and structures referred to as anode-free structures, where lithium metal is not bonded to the negative electrode current collector, but is directly deposited on the negative electrode current collector.

[0004] However, during the charging of lithium metal rechargeable batteries, lithium metal segregates on the negative electrode current collector, leading to the growth of lithium metal dendrites. As a result, a short circuit occurs between the positive and negative electrodes, thus reducing the durability of the lithium metal rechargeable battery.

[0005] Therefore, a lithium metal secondary battery is known to have a porous layer containing resin between the negative electrode current collector and the solid electrolyte layer (see Patent Document 1).

[0006] [Previous Technical Documents]

[0007] (Patent Documents)

[0008] Patent Document 1: Japanese Patent No. 6838521 Summary of the Invention

[0009] [The problem the invention aims to solve]

[0010] However, lithium metal precipitates between the solid electrolyte layer and the porous layer (see reference). Figure 5 This leads to a decrease in the capacity retention of lithium metal secondary batteries, resulting in insufficient durability. Furthermore, Figure 5 The solid electrolyte layer, lithium metal layer, porous layer, and negative electrode current collector are shown from the top.

[0011] The purpose of this invention is to provide a lithium metal secondary battery that can improve durability.

[0012] [Technical means to solve the problem]

[0013] One aspect of the present invention provides a lithium metal secondary battery having an electrolyte layer and an intermediate layer between a positive electrode and a negative electrode current collector; the intermediate layer includes a stretchable three-dimensional structure; the stretchable three-dimensional structure contains an ionic liquid.

[0014] Optionally, the lithium metal secondary battery has the electrolyte layer between the positive electrode and the intermediate layer.

[0015] Optionally, the aforementioned electrolyte layer is a solid electrolyte layer.

[0016] Optionally, the aforementioned stretchable three-dimensional structure is a polymeric gel electrolyte.

[0017] Optionally, the aforementioned polymeric gel electrolyte includes a fluoropolymer.

[0018] Optionally, the aforementioned stretchable three-dimensional structure is manufactured by compressing a composition containing the aforementioned fluororesin under a surface pressure of 0.5 MPa or higher, and then impregnating it with a liquid containing the aforementioned ionic liquid.

[0019] Optionally, the aforementioned intermediate layer also contains lithium metal.

[0020] Optionally, the aforementioned stretchable three-dimensional structure of the aforementioned intermediate layer is integrated with at least a portion of the aforementioned lithium metal, and the fluorine content is 2.0 at% or more.

[0021] (The effect of the invention)

[0022] According to the present invention, a lithium metal secondary battery with improved durability can be provided. Attached Figure Description

[0023] Figure 1 This is a perspective view illustrating an example of a lithium metal secondary battery according to this embodiment.

[0024] Figure 2 This is a diagram illustrating an example of a method for manufacturing scalable three-dimensional structures.

[0025] Figure 3 It is a drawing of the opposite Figure 1 A diagram showing the elongation of the three-dimensional structure of a lithium metal secondary battery during charging.

[0026] Figure 4 This is a diagram illustrating the results of cross-sectional SEM (scanning electron microscope) images and SEM-EDM fluorine mapping of the lithium metal secondary battery of Example 7 when it is fully charged in the tenth cycle.

[0027] Figure 5 It is a SEM image depicting the state of lithium metal precipitation between the solid electrolyte layer and the porous layer during the charging of a lithium metal secondary battery. Detailed Implementation

[0028] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0029] Figure 1 An example of a lithium metal secondary battery according to this embodiment is illustrated.

[0030] The lithium metal secondary battery 10 has a solid electrolyte layer 13 between a positive electrode 11 and a negative electrode current collector 12, and an intermediate layer 14 between the negative electrode current collector 12 and the solid electrolyte layer 13. The positive electrode 11 has a positive electrode current collector 11a and a positive electrode composite material layer 11b. The intermediate layer 14 includes a stretchable three-dimensional structure and lithium metal; the stretchable three-dimensional structure includes an ionic liquid.

[0031] When the lithium metal secondary battery 10 is charged, lithium metal is deposited within the three-dimensional structure constituting the intermediate layer 14, and the three-dimensional structure elongates. Conversely, when the lithium metal secondary battery 10 is discharged, lithium ions dissolve from the three-dimensional structure constituting the intermediate layer 14, and the three-dimensional structure contracts. Therefore, in its initial state, the intermediate layer 14 of the lithium metal secondary battery 10 may not contain lithium metal. In this case, the lithium metal secondary battery 10 is charged before use. As a result, lithium metal is uniformly deposited within the three-dimensional structure constituting the intermediate layer 14.

[0032] There are no particular limitations on ionic liquids, but examples include 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium=bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, and N-methyl-N-propylpyrrolidineonium bis(fluorosulfonyl)imide.

[0033] Because the stretchable three-dimensional structure pre-contains an ionic liquid, the internal space of the intermediate layer 14 will not be completely crushed even during compression molding as described later in the manufacturing process. In this case, the intermediate layer 14 is preferably a polymeric gel electrolyte. Thus, when the lithium metal secondary battery 10 is charged, at least a portion of the deposited lithium metal becomes integrated with the three-dimensional structure.

[0034] The polymeric gel electrolyte preferably contains a fluoropolymer. This allows for easier integration of at least a portion of the deposited lithium metal with the three-dimensional structure through electrostatic interactions between the F and Li components of the fluoropolymer.

[0035] As a fluoropolymer, there are no particular limitations; examples include polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer.

[0036] When at least a portion of the deposited lithium metal is integrated with the three-dimensional structure, the fluorine content in the intermediate layer 14 is preferably 2.0 at% or more, more preferably 5.0 at% or more. If the fluorine content in the intermediate layer 14 is 2.0 at% or more, the durability of the lithium metal secondary battery 10 will be improved.

[0037] Polymer gel electrolytes can contain resins other than fluoropolymers.

[0038] Resins other than fluoropolymers include, for example, polyesters, polyamides, polyolefins, epoxy resins, acrylic resins, polyurethanes, silicone resins, phenolic resins, and modified versions of these resins; two or more of these resins may be used simultaneously. Furthermore, resins other than fluoropolymers may be copolymers of these resins or modified versions of these copolymers.

[0039] There are no particular limitations on the manufacturing method of the stretchable three-dimensional structure; for example, the following method can be used. First, a composition containing fluororesin 21 is disposed in the solid electrolyte layer 13 (see reference). Figure 2 (a)), and then compression molding (see Figure 2 (b)). Next, when the liquid containing ionic liquid 22 is impregnated in the compression-molded composition (see reference...). Figure 2 (c) Fluoropolymer 21 expands to obtain a stretchable three-dimensional structure 20.

[0040] The stretchable three-dimensional structure 20 contains an ionic liquid 22 within the three-dimensional network structure of the fluororesin 21. Therefore, when the lithium metal secondary battery 10 is charged, lithium metal is deposited within the three-dimensional structure 20 and simultaneously exchanges with the held ionic liquid 22, thereby causing the three-dimensional structure 20 to stretch (see reference). Figure 3 ).

[0041] The surface pressure during compression molding is preferably 0.2 MPa or more, and more preferably 5 MPa or less. If the surface pressure during compression molding is 0.5 MPa or more, the initial compression ratio of the fluororesin 21 in the thickness direction becomes 20% or more and 40% or less, thus improving the durability of the lithium metal secondary battery 10.

[0042] The content of fluororesin 21 in the composition is preferably 4% by mass or more and 12% by mass or less. If the content of fluororesin 21 in the composition is 4% by mass or more, it can expand and contract with the deposition of lithium metal, thus improving the durability of the lithium metal secondary battery 10. If it is 12% by mass or less, the fluororesin 21 will not react with the lithium metal or the solid electrolyte contained in the solid electrolyte layer 13 and will not deteriorate, thus improving the durability of the lithium metal secondary battery 10.

[0043] The molecular weight of fluoropolymer 21 is not particularly limited, for example, it can be above 50,000 and below 1 million.

[0044] Compositions containing fluororesin 21 may also contain ionic liquids, lithium salts, additives, etc.

[0045] Liquids containing ionic liquid 22 may also contain lithium salts, etc.

[0046] There are no particular limitations on lithium salts, but examples include lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide [LiN(SO2F)2], lithium bis(trifluoromethanesulfonyl)imide [LiN(CF3SO2)2], lithium tetrafluoroaluminate (LiAlF4), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium nitrate (LiNO3).

[0047] There are no particular limitations on additives, but examples include vinylene carbonate, fluoroethylene carbonate, poly(ethylene glycol) methyl ether thiol, cesium hexafluorophosphate (CsPF6), and bis(trifluoromethanesulfonyl)imide cesium (Cs-TFSI).

[0048] The ionic liquid contained in the composition may be the same as or different from the ionic liquid 22 contained in the liquid. Similarly, the electrolyte contained in the composition may be the same as or different from the electrolyte contained in the liquid.

[0049] The thickness of the intermediate layer 14 is not particularly limited, for example, it is above 0.1 μm and below 20 μm.

[0050] There are no particular limitations on the negative electrode current collector 12, such as copper foil.

[0051] The thickness of the negative current collector 12 is not particularly limited, for example, it is more than 1 μm and less than 50 μm.

[0052] There are no particular limitations on the positive current collector 11a, such as aluminum foil.

[0053] The thickness of the positive current collector 11a is not particularly limited, for example, it is more than 5μm and less than 50μm.

[0054] The positive electrode composite material layer 11b contains positive electrode active material and may also contain other components.

[0055] As a positive electrode active material, it is only necessary to be able to store and release lithium ions; there are no particular limitations. Examples include lithium composite oxides.

[0056] There are no particular limitations on lithium composite oxides; examples include LiCoO2 and Li(Ni)2.5 / 10 Co 2 / 10 Mn 3 / 10 O2, Li(Ni) 6 / 10 Co 2 / 10 Mn 2 / 10 O2, Li(Ni) 8 / 10 Co 1 / 10 Mn 1 / 10 O2, Li(Ni) 0.8 Co 0.15 Al 0.05 O2, Li(Ni) 1 / 6 Co 4 / 6 Mn 1 / 6 O2, Li(Ni) 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiCoO4, LiMn2O4, LiNiO2, LiFePO4, etc., two or more can be used simultaneously.

[0057] The content of positive electrode active material in the positive electrode composite layer 11b is not particularly limited, for example, it is more than 60% by mass and less than 99% by mass.

[0058] Other components include, for example, solid electrolytes, conductive additives, and adhesives.

[0059] The thickness of the positive electrode composite layer 11b is not particularly limited, for example, it is more than 5 μm and less than 50 μm.

[0060] The solid electrolyte constituting the solid electrolyte layer 13 can be any electrolyte with lithium-ion conductivity and is not particularly limited. Examples include oxide electrolytes and sulfide electrolytes. Among them, sulfide electrolytes are preferred because they are reactive with lithium metal, thus enhancing the effect of the protective layer 12c.

[0061] The thickness of the solid electrolyte layer 13 is not particularly limited, for example, it is more than 10 μm and less than 500 μm.

[0062] The lithium metal secondary battery 10 is a stack of a positive electrode 11, a negative electrode current collector 12, a solid electrolyte layer 13, and an intermediate layer 14. The pressure maintaining the stack is preferably 0.2 MPa or more and 5 MPa or less during charging and discharging. If the pressure is 0.2 MPa or more, the contact resistance decreases, thereby increasing the output of the lithium metal secondary battery 10. If it is 5 MPa or less, the stretchable three-dimensional structure containing ionic liquid constituting the intermediate layer 14 becomes difficult to be squeezed to the outside of the stack, reducing resistance during charging and discharging and improving the durability of the lithium metal secondary battery 10. Therefore, the surface pressure constraining the stack during the manufacture of the lithium metal secondary battery 10 is preferably 0.5 MPa or more and 3 MPa or less.

[0063] Furthermore, the stacking order of the solid electrolyte layer 13 and the intermediate layer 14 can be reversed.

[0064] Furthermore, the lithium metal secondary battery 10 may have an electrolyte layer other than the solid electrolyte layer 13.

[0065] There are no particular limitations on the electrolyte layer other than the solid electrolyte layer 13. Examples include a membrane impregnated with electrolyte, a gel electrolyte layer, etc.

[0066] [Septum]

[0067] There are no particular limitations on the diaphragm; porous resin sheets (films, non-woven fabrics, etc.) can be used.

[0068] Examples of resins that make up porous resin sheets include polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide.

[0069] Electrolyte

[0070] As an electrolyte, a solution in which the electrolyte is dissolved in a non-aqueous solvent can be used.

[0071] There are no particular limitations on the concentration of electrolyte in the electrolyte solution, for example, it can be above 0.1 mol / L and below 10 mol / L.

[0072] An additive containing at least one compound selected from vinylene carbonate, ethylene fluorocarbonate, and propane sulpholactone can be added to the electrolyte. This allows for the addition of a compound with reductive properties that readily forms an SEI (solid electrolyte interface) film. Consequently, the added compound is preferentially decomposed in the electrolyte and forms an SEI film on the negative electrode, thus improving the durability of the electrolyte.

[0073] (Non-aqueous solvent)

[0074] As a non-aqueous solvent, there are no particular limitations; non-protic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used.

[0075] Specific examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile (AN), propionitrile, nitromethane, N,N-dimethylformamide (DMF), dimethyl sulfoxide, sulfolane, γ-butyrolactone, etc.

[0076] (electrolytes)

[0077] As an electrolyte, there are no particular limitations; examples include LiPF6, LiBF4, LiClO4, LiN(SO2CF3), LiN(SO2C2F5)2, LiCF3SO3, LiC4F9SO3, LiC(SO2CF3)3, LiF, LiCl, LiI, Li2S, Li3N, Li3P, and Li 10 GeP2S 12 (LGPS), Li3PS4, Li6PS5Cl, Li7P2S8I, Li x PO y N z (x=2y+3z-5, LiPON), Li7La3Zr2O 12 (LLZO), Li 3x La 2 / 3-x TiO3(LLTO), Li 1+x Al x Ti 2-x (PO4)3 (0≤x≤1, LATP), Li 1.5 Al 0.5 Ge 1.5 (PO4)3(LAGP), (Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 Li 1+x+y Al x (Ti, Ge) 2-x SiyP 3-y O 12 Li 4-2x Zn x GeO4 (LISICON) and other compounds can be used simultaneously, and two or more can be used at the same time. Among them, LiPF6, LiBF4, or both of these are preferred.

[0078] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and the above embodiments can be appropriately modified within the scope of the spirit of the present invention.

[0079] [Example]

[0080] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0081] <Preparation of the positive electrode>

[0082] Li(Ni) will be used as the positive electrode active material 0.6 Co 0.2 Mn 0.2O2, thio-LISICON (Li) as a solid electrolyte 3.25 Ge 0.25 P 0.75 S4), acetylene black as a conductive additive, styrene-butadiene rubber (SBR) as a binder, and butyl butyrate as a solvent were added to a rotary mixer and stirred at 2000 rpm for 3 minutes, followed by a 1-minute degassing treatment to prepare a coating solution for the positive electrode composite layer. At this point, the mass ratio of the positive electrode active material, solid electrolyte, conductive additive, and binder was 75:22:3:3.

[0083] The positive electrode composite material was cast onto the aluminum foil serving as the positive electrode current collector using a coating liquid. After heating to 60°C to remove the solvent, it was rolled to form a composite material with a density of 3.1 g / cc and a basis weight of 26 mg / cm³. 2 The positive electrode is obtained by forming a positive electrode composite material layer.

[0084] <Preparation of Solid Electrolyte Layer>

[0085] Thio-LISICON (Li) as a solid electrolyte was formed using a 10mm diameter zirconium tube at a molding pressure of 150MPa. 3.25 Ge 0.25 P 0.75 S4) Pressing and molding to obtain a solid electrolyte layer with a diameter of 10 mm.

[0086] <Preparation of Cathode-Solid Electrolyte Layer Stack>

[0087] With a positive electrode and a solid electrolyte layer of 10 mm in diameter sandwiched between them, a positive electrode-solid electrolyte layer laminate is formed by pressing with a molding pressure of 1000 MPa.

[0088] (Example 1)

[0089] <Preparation of cathode-solid electrolyte layer-intermediate layer laminate>

[0090] 0.3 parts by weight of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP W#8500 (manufactured by Kureha)) was dissolved in 99.7 parts by weight of dimethyl carbonate (DMC) to obtain a coating solution.

[0091] The coating solution was applied to the solid electrolyte layer of the positive electrode-solid electrolyte layer laminate and dried at 60°C. Then, it was uniaxially pressed under a surface pressure of 500 MPa to form a compressed layer. Next, a mixture of 30.6 parts by mass of lithium bis(fluorosulfonyl)imide (LiFSI) as the lithium salt and 69.4 parts by mass of 1-ethyl-3-methylimidazolium=bis(trifluoromethanesulfonyl)imide (EMI-FSI) as the ionic liquid was impregnated in the compressed layer and then dried at 60°C to form a polymeric gel electrolyte layer (intermediate layer), thus obtaining the positive electrode-solid electrolyte layer-intermediate layer laminate.

[0092] <Preparation of Lithium Metal Secondary Batteries>

[0093] A lithium metal secondary battery is obtained by constraining a positive electrode-solid electrolyte layer-intermediate layer laminate and a copper foil serving as a negative electrode current collector under a surface pressure of 3 MPa, thereby bonding the interface between the intermediate layer and the negative electrode current collector.

[0094] (Example 2)

[0095] <Preparation of cathode-solid electrolyte layer-intermediate layer laminate>

[0096] The surface pressure during uniaxial pressing was changed to 200 MPa. When impregnating the compression layer, except for using a mixture of 22.7 parts by mass of LiFSI and 77.3 parts by mass of EMI-FSI, the positive electrode-solid electrolyte layer-intermediate layer laminate was obtained in the same manner as in Example 1.

[0097] <Preparation of Lithium Metal Secondary Batteries>

[0098] Except for using the obtained positive electrode-solid electrolyte layer-intermediate layer stack, the lithium metal secondary battery was obtained in the same manner as in Example 1.

[0099] (Example 3)

[0100] <Preparation of cathode-solid electrolyte layer-intermediate layer laminate>

[0101] Except for changing the surface pressure during uniaxial pressing to 50 MPa and using a mixture of 12.8 parts by mass of LiFSI and 87.2 parts by mass of EMI-FSI when impregnating the compression layer, the positive electrode-solid electrolyte layer-intermediate layer laminate was obtained in the same manner as in Example 1.

[0102] <Preparation of Lithium Metal Secondary Batteries>

[0103] Except for using the obtained positive electrode-solid electrolyte layer-intermediate layer stack, the lithium metal secondary battery was obtained in the same manner as in Example 1.

[0104] (Example 4)

[0105] <Preparation of cathode-solid electrolyte layer-intermediate layer laminate>

[0106] After dissolving 2.0 parts by weight of PVDF-HFP(8500) in 69.5 parts by weight of DMC, a mixture of 3.6 parts by weight of LiFSI and 24.9 parts by weight of EMI-FSI was added to obtain the coating solution.

[0107] The coating solution was applied to the solid electrolyte layer of the positive electrode-solid electrolyte layer laminate and dried at 60°C. Then, it was uniaxially pressed at a surface pressure of 300 MPa to form a compressed layer. Next, a mixture of 12.8 parts by mass of LiFSI and 87.2 parts by mass of EMI-FSI was impregnated into the compressed layer and dried at 60°C to form a polymer gel electrolyte layer (intermediate layer), thus obtaining the positive electrode-solid electrolyte layer-intermediate layer laminate.

[0108] <Preparation of Lithium Metal Secondary Batteries>

[0109] Except for using the obtained positive electrode-solid electrolyte layer-intermediate layer stack, the lithium metal secondary battery was obtained in the same manner as in Example 1.

[0110] (Example 5)

[0111] <Preparation of cathode-solid electrolyte layer-intermediate layer laminate>

[0112] Except for changing the surface pressure during uniaxial pressing to 100 MPa, the positive electrode-solid electrolyte layer-intermediate layer laminate was obtained in the same manner as in Example 4.

[0113] <Preparation of Lithium Metal Secondary Batteries>

[0114] Except for using the obtained positive electrode-solid electrolyte layer-intermediate layer stack, the lithium metal secondary battery was obtained in the same manner as in Example 1.

[0115] (Example 6)

[0116] <Preparation of cathode-solid electrolyte layer-intermediate layer laminate>

[0117] Except for changing the surface pressure during uniaxial pressing to 5 MPa, the positive electrode-solid electrolyte layer-intermediate layer laminate was obtained in the same manner as in Example 4.

[0118] <Preparation of Lithium Metal Secondary Batteries>

[0119] Except for using the obtained positive electrode-solid electrolyte layer-intermediate layer stack, the lithium metal secondary battery was obtained in the same manner as in Example 1.

[0120] (Example 7)

[0121] <Preparation of Solid Electrolyte Layer-Intermediate Layer-Negative Electrolyte Current Collector Laminate>

[0122] After dissolving 2.0 parts by weight of PVDF-HFP W#8500 (manufactured by Kureha) in 69.5 parts by weight of DMC, a mixture of 3.6 parts by weight of LiFSI and 24.9 parts by weight of EMI-FSI was added to obtain the coating solution.

[0123] The coating solution was applied to the copper foil serving as the negative electrode current collector and dried at room temperature. Then, it was uniaxially pressed between the copper foil and the solid electrolyte layer under a surface pressure of 30 MPa to form a compression layer. Next, a mixture of 12.8 parts by weight of LiFSI and 87.2 parts by weight of EMI-FSI was impregnated into the compression layer and dried at 60°C to form a polymer gel electrolyte layer (intermediate layer), resulting in a solid electrolyte layer-intermediate layer-negative electrode current collector laminate.

[0124] <Preparation of Lithium Metal Secondary Batteries>

[0125] By clamping a stack of positive electrode and solid electrolyte layer-intermediate layer-negative electrode current collector layer, and constraining it with a surface pressure of 3MPa, the interface between the positive electrode composite material layer and the solid electrolyte layer is bonded, thus obtaining a lithium metal secondary battery.

[0126] (Example 8)

[0127] <Preparation of Solid Electrolyte Layer-Intermediate Layer-Negative Electrolyte Current Collector Laminate>

[0128] After dissolving 2.0 parts by weight of PVDF-HFP W#8500 (manufactured by Kureha) in 69.5 parts by weight of DMC, a mixture of 3.6 parts by weight of LiFSI and 24.9 parts by weight of EMI-FSI was added to obtain the coating solution.

[0129] The coating solution is applied to the copper foil that serves as the negative electrode current collector and dried at room temperature. Then, it is uniaxially pressed between the copper foil and the solid electrolyte layer at a surface pressure of 70 MPa to form a polymer gel electrolyte layer (intermediate layer), resulting in a solid electrolyte layer-intermediate layer-negative electrode current collector laminate.

[0130] <Preparation of Lithium Metal Secondary Batteries>

[0131] Except for using the obtained solid electrolyte layer-intermediate layer-negative electrode current collector stack, the lithium metal secondary battery was obtained in the same manner as in Example 7.

[0132] (Comparative Example 1)

[0133] <Preparation of Solid Electrolyte Layer-Intermediate Layer Laminate>

[0134] The coating solution was obtained by dissolving 0.3 parts by mass of PVDF-HFP(8500) in 99.7 parts by mass of DMC.

[0135] After the coating liquid is applied to the solid electrolyte layer, it is dried at 60°C to form an uncompressible layer (intermediate layer), thus obtaining a solid electrolyte layer-intermediate layer laminate.

[0136] <Preparation of Lithium Metal Secondary Batteries>

[0137] Except for using the obtained solid electrolyte layer-intermediate layer stack, the lithium metal secondary battery was obtained in the same manner as in Example 1.

[0138] (Comparative Example 2)

[0139] <Preparation of Solid Electrolyte Layer-Intermediate Layer Laminate>

[0140] 0.3 parts by mass of PVDF-HFP(8500) were dissolved in 99.7 parts by mass of DMC to obtain the coating solution.

[0141] The coating liquid is applied to the solid electrolyte layer and dried at room temperature. Then, it is uniaxially pressed under a surface pressure of 0.01 MPa to form a compression layer (intermediate layer), resulting in a solid electrolyte layer-intermediate layer laminate.

[0142] <Preparation of Lithium Metal Secondary Batteries>

[0143] Except for using the obtained solid electrolyte layer-intermediate layer stack, the lithium metal secondary battery was obtained in the same manner as in Example 1.

[0144] [Initial Performance]

[0145] Three cycles of constant current (CC)-constant voltage (CV) charging and CC discharging were performed on an all-solid-state lithium metal secondary battery, and the 1 / 10C charging capacity and 1 / 10C discharging capacity of the first cycle were calculated. Furthermore, the charge / discharge efficiency was calculated using the formula (discharge capacity) / (charge capacity) × 100.

[0146] In the third cycle, after performing CC-CV charging in the same way as in the first and second cycles, constant current discharge was performed in a 60°C constant temperature bath at 50% SOC. The voltage value was measured after 10 seconds, and the DC resistance value (DCR) was calculated based on the slope of the current value and the voltage value after 10 seconds.

[0147] [Durability]

[0148] Ten charge-discharge cycles were performed in the same manner as described above, and the charge-discharge efficiency was calculated using the formula (discharge capacity of 1 / 10C in the tenth cycle) / (charge capacity of 1 / 10C in the tenth cycle) × 100. Additionally, the capacity retention rate was calculated using the formula (discharge capacity of the tenth cycle) / (discharge capacity) × 100.

[0149] [Fluorine content in the lithium-containing intermediate layer]

[0150] The fluorine content in the lithium-containing intermediate layer was determined based on the cross-sectional SEM image of the fully charged layer during the tenth cycle and the fluorine mapping of the SEM-SXES.

[0151] Figure 4 Cross-sectional SEM images and fluorine mapping results of the lithium metal battery of Example 7 at full charge during the tenth cycle are shown.

[0152] Depend on Figure 4 It is evident that fluorine is distributed throughout the entire intermediate layer 14, primarily at the interface with the negative electrode current collector 12 and the interface with the solid electrolyte layer 13. This indicates that lithium metal is deposited within the three-dimensional structure constituting the intermediate layer 14, and at least a portion of the deposited lithium metal is integrated with the three-dimensional structure. Furthermore, the porous state of the lithium metal was not confirmed.

[0153] Table 1 presents the evaluation results of the initial performance, durability, and fluorine content in the lithium metal intermediate layer of the lithium metal secondary battery.

[0154] [Table 1]

[0155]

[0156] As shown in Table 1, the lithium metal secondary batteries in Examples 1 to 8 have high durability.

[0157] In contrast, the intermediate layer of the lithium metal secondary batteries in Comparative Examples 1 and 2 is not a stretchable three-dimensional structure and does not contain ionic liquid, thus resulting in lower durability.

[0158] (Example 9)

[0159] <Preparation of the positive electrode>

[0160] The conductive additive was mixed with polyvinylidene fluoride (PVDF) as a binder, and dispersed using a rotary mixer. Then, Li1Ni was mixed in as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) was mixed using a planetary mixer. Then, N-methyl-N-pyrrolidone (NMP) was added to prepare a slurry for the positive electrode composite layer. This slurry was coated onto an Al current collector, dried, and then pressed using a roller press and dried under vacuum at 120°C to prepare the positive electrode plate. The electrode plate was stamped to a size of 30mm × 40mm for use as the positive electrode. The thickness of the positive electrode was 70μm.

[0161] <Preparation of the negative electrode>

[0162] A 20μm thick LiCu foil was stamped to a size of 32mm × 42mm and used as a negative electrode.

[0163] <Preparation of the positive electrode-separator-intermediate layer-negative electrode laminate>

[0164] After dissolving 3.0 parts by weight of PVDF-HFP W#8500 (manufactured by Kureha) in 68.5 parts by weight of DMC, a mixture of 4.4 parts by weight of LiFSI and 24.1 parts by weight of MPPy-FSI was added to obtain the coating solution.

[0165] The coating solution is applied to the separator, dried at 80°C, and then sandwiched between the positive and negative electrodes. It is then uniaxially pressed and molded with a surface pressure of 0.2 MPa to form a polymer gel electrolyte layer (intermediate layer), resulting in a positive electrode-separator-intermediate layer-negative electrode laminate.

[0166] <Preparation of Lithium Metal Secondary Batteries>

[0167] A positive electrode-separator-intermediate layer-negative electrode laminate is introduced into a bag-shaped container made of aluminum laminate (manufactured by Dai Nippon Printing). Then, a 5 mol / L LiFSI EC:DMC (volume ratio 3:7) solution as electrolyte is injected into the separator to produce a lithium metal secondary battery.

[0168] <Charge and Discharge Test>

[0169] Charge-discharge tests were conducted on the lithium metal secondary battery. In the first charge-discharge test, the battery was charged at a rate of 0.2C to 4.3V and discharged at 0.2C to 2.65V. Then, it was charged at 0.3C to 4.3V and discharged at 0.3C to 2.65V.

[0170] As a result, the initial battery capacity was 48.0 mAh. With the discharge current at 0.3C set to 100, the capacity retention rate after endurance was calculated using the formula (battery capacity after 5 zero-cycles) / (initial battery capacity) × 100, and the result was 90%.

[0171] (Comparative Example 3)

[0172] <Preparation of Lithium Metal Secondary Batteries>

[0173] Except for injecting electrolyte into the separator after inserting the secondary battery into a bag-shaped container made of aluminum laminate (manufactured by Dai Nippon Printing), which is then heat-sealed into a bag shape, the lithium metal secondary battery is manufactured in the same manner as in Example 9.

[0174] <Charge and Discharge Test>

[0175] The charge-discharge test was conducted in the same manner as in Example 9, and the initial battery capacity was 48.2 mAh. Furthermore, the capacity retention rate after durability testing was calculated to be 25% in the same manner as in Example 9.

[0176] Figure Labels

[0177] 10 Lithium metal secondary batteries

[0178] 11 Positive electrode

[0179] 11a Positive Current Collector

[0180] 11b Positive electrode composite layer

[0181] 12 Negative current collector

[0182] 13 Solid electrolyte layer

[0183] 14 Intermediate Layer

Claims

1. A lithium metal secondary battery, comprising an electrolyte layer and an intermediate layer between a positive electrode and a negative electrode current collector, and the electrolyte layer between the positive electrode and the intermediate layer; the intermediate layer comprising a scalable three-dimensional structure that, when the lithium metal secondary battery is charged, internally deposits lithium metal while elongating, and, when the lithium metal secondary battery is discharged, internally dissolves lithium ions while contracting; the scalable three-dimensional structure being a polymer gel electrolyte containing an ionic liquid and a fluorine resin; the fluorine resin being a polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer; the electrolyte layer being a solid electrolyte layer; the scalable three-dimensional structure being manufactured by compression molding a composition containing the fluorine resin, and then impregnating a liquid containing the ionic liquid; the intermediate layer further containing lithium metal; the scalable three-dimensional structure of the intermediate layer being integrated with at least part of the lithium metal, and the content of fluorine elements being 2.0 at% or more.

2. The lithium metal secondary battery according to claim 1, wherein the fluorine resin is a polyvinylidene fluoride-hexafluoropropylene copolymer.

3. The lithium metal secondary battery according to claim 1 or 2, wherein the ionic liquid is a phosphonium ionic liquid.

4. The lithium metal secondary battery according to any one of claims 1 to 3, wherein the intermediate layer further contains a lithium metal oxide.

2. The lithium metal secondary battery of claim 1, wherein, 5. The lithium metal secondary battery according to any one of claims 1 to 4, wherein the intermediate layer further contains a lithium metal alloy.

3. The lithium metal secondary battery of claim 1, wherein, 6. The lithium metal secondary battery according to any one of claims 1 to 5, wherein the intermediate layer further contains a lithium metal compound.

4. The lithium metal secondary battery of claim 1, wherein, 7. The lithium metal secondary battery according to any one of claims 1 to 6, wherein the intermediate layer further contains a lithium metal compound and a lithium metal alloy.

5. The lithium metal secondary battery of claim 4, wherein, 8. The lithium metal secondary battery according to any one of claims 1 to 7, wherein the intermediate layer further contains a lithium metal compound and a lithium metal oxide.

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