Solid-state lithium-ion battery

Abstract

The application provides a solid-state lithium ion secondary battery and a preparation method thereof. A positive electrode and a solid-state electrolyte layer are co-fired to form a multilayer ceramic structure, and then the multilayer ceramic structure is combined with a metal lithium negative electrode and a polymer solid-state electrolyte film to form a battery unit. A plurality of battery units are assembled into an internal series electric core through an isostatic pressing process. The preparation method of the application expands the application range of the multilayer ceramic technology in the solid-state lithium ion battery, and has a good industrialization prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a solid-state lithium ion battery, in particular to a full solid-state lithium ion battery. BACKGROUND

[0002] Multi-layer ceramic battery (MLCB) is often referred to as the battery version of multi-layer ceramic capacitor (MLCC), and the multi-layer ceramic battery usually has a structure formed by alternately stacking thin film electrodes and solid-state electrolyte layers. In the prior art, the multi-layer ceramic battery is usually co-sintered with the positive electrode, the solid-state electrolyte layer and the negative electrode, but the sintering process between the negative electrode material and the positive electrode material is quite different, such as graphite usually needs a reducing atmosphere, and the positive electrode needs an oxidizing atmosphere. Therefore, the co-sintering process of the multi-layer ceramic greatly limits the selection range of the positive and negative electrode materials. At the same time, the performance of the existing multi-layer ceramic formed by hot pressing and the like needs to be improved, and cannot fully meet the performance requirements of the solid-state battery. SUMMARY

[0003] In order to solve the above problems, the present application provides a high-voltage multi-layer ceramic battery capable of matching a metal lithium negative electrode, which has at least two or more battery units including a positive electrode, a negative electrode and a solid-state electrolyte layer; the positive electrode and the solid-state electrolyte layer form a multi-layer ceramic structure, and the multi-layer ceramic structure is an integrated structure.

[0004] A polymer layer is arranged between the solid-state electrolyte layer and the negative electrode; the negative electrode comprises metal lithium; and two adjacent battery units are electrically connected in series.

[0005] Preferably, the porosity of the multi-layer ceramic structure is <10%; and more preferably, the porosity of the multi-layer ceramic structure is <5%.

[0006] Preferably, the positive electrode comprises a positive electrode active material layer and a positive electrode current collector, the positive electrode current collector is arranged on the side of the positive electrode active material layer away from the solid-state electrolyte layer, and at least one positive electrode current collector is electrically connected to the adjacent negative electrode in the solid-state lithium ion secondary battery.

[0007] Preferably, the negative electrode comprises a negative electrode current collector, the negative electrode current collector is arranged between the positive electrode active material layer of the adjacent battery unit and the negative electrode or arranged on the outermost side of the solid-state lithium ion secondary battery.

[0008] Preferably, a composite current collector layer is further arranged between the positive electrode and the negative electrode, the composite current collector comprises a protective layer and positive electrode current collectors and negative electrode current collectors arranged on both sides of the protective layer, and the positive electrode current collectors and the negative electrode current collectors are electrically connected.

[0009] Preferably, the polymer layer comprises a polymer solid-state electrolyte and a lithium salt.

[0010] Preferably, the solid-state electrolyte layer comprises an oxide solid-state electrolyte.

[0011] Preferably, the metal lithium negative electrode comprises one or more of lithium foil, lithium sheet, lithium-indium alloy.

[0012] The second application of the application also provides a preparation method of the solid-state lithium ion secondary battery as described above, comprising the following steps:

[0013] S1. Preparing a multi-layer ceramic structure comprising a positive electrode active material layer and a solid-state electrolyte layer;

[0014] S2. Forming a battery cell by compounding the multi-layer ceramic structure prepared in step S1, a polymer layer and a metal lithium negative electrode; and / or forming a battery cell by combining a pre-made sheet composed of a polymer layer and a metal lithium negative electrode with the multi-layer ceramic structure prepared in step S1;

[0015] S3. Stacking two or more battery cells prepared in step S2 to obtain a solid-state lithium ion secondary battery, wherein the positive electrode and the negative electrode of adjacent two battery cells are connected.

[0016] Preferably, in step S1, the positive electrode active material layer and the solid-state electrolyte layer are compounded to form a composite structure; and the composite structure is co-sintered in an inert atmosphere to obtain the multi-layer ceramic structure.

[0017] The co-sintering temperature is 600-1400℃; preferably, 800-1100℃.

[0018] Preferably, in step S1, a positive electrode current collector is further provided on the side of the obtained multi-layer ceramic structure away from the solid-state electrolyte layer.

[0019] Preferably, in step S2, a negative electrode current collector and a protective layer are provided on the side of the metal lithium negative electrode away from the polymer layer, and the negative electrode current collector is arranged between the protective layer and the metal lithium negative electrode.

[0020] Preferably, in step S3, the protective layer is located between the positive electrode and the negative electrode of adjacent two battery cells.

[0021] Preferably, in step S3, the solid-state lithium ion secondary battery is prepared by isostatic pressing process.

[0022] Further preferably, in step S3, the stacked battery cells are processed by isostatic pressing process to obtain the solid-state lithium ion secondary battery.

[0023] The isostatic pressing process temperature is 80-140℃, and the pressure is 80-140MPa.

[0024] Preferably, the protective layer surface is provided with conductive glue.

[0025] The application does not have special requirements for the type of conductive glue, and any known type of conductive glue can be used in the application without deviating from the inventive concept of the application. For example, epoxy resin, acrylate resin, polyurethane, etc.

[0026] Preferably, in step S3, the solid-state lithium ion secondary battery is prepared by an isostatic pressing process.

[0027] Further preferably, in step S3, the stacked battery cells are processed by an isostatic pressing process to obtain a solid-state lithium ion secondary battery.

[0028] The isostatic pressing process temperature is 80-140℃, and the pressure is 80-140MPa.

[0029] The application has the following technical effects:

[0030] 1. The application separately co-fires the positive electrode and the solid-state electrolyte layer, and then composites with the negative metal lithium negative electrode. This preparation process enables the multi-layer ceramic battery involved to match the metal lithium negative electrode, avoids the problem that the co-firing conditions of the positive electrode and the solid-state electrolyte must be compatible with the negative electrode material, enables the battery to have higher energy density, and improves the application range of the multi-layer ceramic battery.

[0031] 2. The application provides a polymer layer between the metal lithium negative electrode and the solid-state electrolyte, which on the one hand realizes good interface contact between the metal lithium and the solid-state electrolyte layer through the polymer layer, and on the other hand, the polymer layer can avoid the reaction of part of the solid-state electrolyte with the metal lithium, and plays a role in protecting the metal lithium; on the other hand, the good film-forming performance of the polymer layer plays a supporting role for the metal lithium negative electrode, reducing the manufacturing difficulty of the entire battery.

[0032] 3. The application solves the problem of hard oxide solid-state electrolyte particles and the interface between the co-fired positive electrode and the solid-state electrolyte layer and the electrode through the co-firing process.

[0033] 4. The application gives the binding force between the composite current collector and the pole piece when stacking the solid-state lithium ion secondary battery cell internally connected by the isostatic pressing process, enabling better binding force between the multi-layer ceramic structure and the current collector and between the battery cells during the preparation of the cell, enabling the internally connected cell to be used normally, and avoiding the cracking problem during the cycle process. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The battery structure diagram manufactured for the embodiment of the application;

[0035] 1 - positive electrode current collector 2 - positive electrode 3 - solid electrolyte layer 4 - polymer layer 5 - negative electrode 6 - negative electrode current collector 7 - protective layer. DETAILED DESCRIPTION

[0036] Reference will now be made in detail to the embodiments of the application, one or more examples of which are set forth below. Each example is provided as an explanation and not as a limitation of the application. Indeed, it will be apparent to one of ordinary skill in the art that numerous modifications and variations of the present application are possible in light of the above teachings. For example, features described or illustrated as part of one embodiment can be used with another embodiment to yield a still further embodiment.

[0037] It is therefore intended that the application cover all such modifications and variations of this application as come within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are obvious from the following detailed description of the application, which is to be interpreted in accordance with the principles of patent law, including 35 U.S.C. §§ 102, 103 and 112. It should be understood that the summary of the application is intended only to provide a brief overview of some embodiments of the application and that its scope is to be interpreted broadly as is set out in the claims that follow this detailed description.

[0038] In the present application, the technical features described in an open way include both the closed technical solution consisting of the listed features and the open technical solution containing the listed features.

[0039] In the present application, when referring to a numerical interval, unless otherwise specified, the numerical interval is considered to be continuous and includes the minimum and maximum values of the range and every value between the minimum and maximum values. Further, when the range refers to integers, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood as including any and all sub-ranges subsumed therein.

[0040] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0041] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0042] If not specified otherwise, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0043] If not specified otherwise, the terms "comprising" and "including" as used in the present application are open-ended and also include closed-ended. For example, the terms "comprising" and "including" can mean that other components not listed can also be included or can mean that only the listed components are included.

[0044] If not specified otherwise, the term "or" in the present application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions fulfill the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0045] The first aspect of the present application provides a multilayer ceramic battery capable of matching a metal lithium negative electrode, having at least two or more battery units comprising a positive electrode, a negative electrode and a solid-state electrolyte layer; the positive electrode and the solid-state electrolyte layer form the multilayer ceramic structure, and the multilayer ceramic structure is a unitary structure.

[0046] A polymer layer is provided between the solid-state electrolyte layer and the negative electrode; the negative electrode comprises metal lithium; and two adjacent battery units are electrically connected in series.

[0047] Preferably, the porosity of the multilayer ceramic structure is <10%; further preferably, the porosity of the multilayer ceramic structure is <5%.

[0048] In the present application, the multilayer ceramic is sintered directly from the positive electrode and the solid-state electrolyte. In the existing solid-state lithium ion battery, due to the high hardness of the positive electrode and the solid-state electrolyte material, the interface impedance between the positive electrode and the solid-state electrolyte is a major obstacle to the industrial application of the solid-state lithium ion battery. Mixing the positive electrode material powder and the solid-state electrolyte and then hot pressing and sintering to form a high-density composite electrode, compared with the traditional coating and rolling composite process, hot pressing and sintering forms stronger physical and chemical combination between the positive electrode material and the solid-state electrolyte, effectively reduces the interface impedance and improves the kinetics. Although the existing co-sintering of solid-state electrolyte and positive and negative electrode materials can solve the interface problem between the positive electrode and the solid-state electrolyte, the sintering process cannot match the metal lithium negative electrode, which limits the application of the multilayer ceramic technology in the solid-state battery.

[0049] The present application co-sinters the solid-state electrolyte and the positive electrode material first, forms a positive electrode-solid-state electrolyte multilayer ceramic structure, and then composites with the metal lithium negative electrode, realizing the matching of the multilayer ceramic lithium ion solid-state battery and the metal lithium negative electrode while solving the interface problem of the multilayer ceramic structure.

[0050] Preferably, the positive electrode comprises a positive electrode active material layer and a positive electrode current collector, the positive electrode current collector is arranged on the side of the positive electrode active material layer away from the solid-state electrolyte layer, and in the solid-state lithium ion secondary battery, at least one positive electrode current collector is electrically connected with the adjacent negative electrode.

[0051] The present application realizes the series structure inside the battery cell by using the lithium ion solid-state battery, and improves the voltage inside the battery cell.

[0052] Preferably, the negative electrode comprises a negative electrode current collector, the negative electrode current collector is arranged between the positive electrode active material layer of the adjacent battery cell and the negative electrode or is arranged on the outermost side of the solid-state lithium ion secondary battery.

[0053] Preferably, a composite current collector layer is further arranged between the positive electrode and the negative electrode, the composite current collector layer comprises a protective layer and a positive electrode current collector and a negative electrode current collector arranged on both sides of the protective layer, and the positive electrode current collector and the negative electrode current collector are electrically connected.

[0054] It can be understood that the positive electrode and the negative electrode are the positive electrode and the negative electrode of the adjacent battery cell.

[0055] That is, the composite current collector layer is arranged between the positive electrode and the negative electrode of the adjacent battery cell.

[0056] The positive / negative current collector in the lithium ion battery serves as a carrier of the positive / negative active material, and at the same time, forms an electronic path and conducts current. The composite current collector is a new technology developed in recent years. The composite current collector can adopt a "metal-polymer material-metal" sandwich structure, with a polymer insulating resin material as the "sandwich" layer, and the upper and lower surfaces are deposited with metal as the positive / negative current collector. The composite current collector has obvious advantages compared with the traditional metal foil current collector. For example, the traditional current collector cannot be thinned indefinitely because a certain mechanical strength needs to be ensured. If the current collector is too thin, it is easy to deform and break during the battery cycle. The composite current collector uses part of the organic material to replace the metal foil material, further reduces the amount of metal used, and can prepare a lighter product while ensuring safety.

[0057] In the composite current collector, the protective layer can be a polymer layer. The material of the protective layer is not particularly required in the present application, which is only an illustrative example, not a limitation of the protection scope, and the material of the polymer layer includes one or more of polyethylene terephthalate, polypropylene, polyethylene, polystyrene, polyvinyl chloride, polyamide, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, and polyphenyl ether.

[0058] Since the protective layer is a polymer layer, when the lithium ion battery is short-circuited, the protective layer can block the contact between the burrs generated by the current collector, avoiding the failure of the lithium ion battery.

[0059] The thickness of the protective layer is not particularly required in the present application. In the case of meeting the use requirements, the conventional adjustment of the thickness should be considered within the protection scope of the present application, which is only an illustrative example, not a limitation of the protection scope, and the thickness of the protective layer can be 3 μm to 12 μm. The protective layer with the above thickness is beneficial to the preparation of the protective layer, can also play a bearing role, and can avoid affecting the volume energy density of the lithium ion battery due to the excessive thickness. Specifically, the thickness of the protective layer can be, but is not limited to, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm, etc. In an embodiment, the thickness of the protective layer can be 4 μm to 10 μm. In another embodiment, the thickness of the protective layer can be 5 μm to 11 μm. In yet another embodiment, the thickness of the protective layer can be 6 μm to 9 μm.

[0060] Preferably, the protective layer has a conductive material.

[0061] By adding the conductive material in the protective layer, the electrical connection between the positive current collector and the negative current collector is realized. The application does not have special requirements for the type and addition amount of the conductive material. Materials known to have conductive properties and capable of being used in composite current collectors can be used in the application. Only as an illustrative example, without limiting the scope of protection, the conductive material can be at least one of carbon nanotubes, graphene, conductive graphite, carbon black, carbon fibers, graphite, conductive ceramic powder, and composite conductive material. It can also be at least one of aluminum, copper, nickel, copper, cobalt, tungsten, tin, lead, iron, silver, gold, platinum or an alloy thereof.

[0062] The addition amount of the conductive material can be 0.1-50wt% of the whole protective layer.

[0063] The application does not have special requirements for the structure and material of the positive current collector and the negative current collector. Any known positive current collector and negative current collector can be used in the application without deviating from the inventive concept of the application. Only as an illustrative example, without limiting the scope of protection, the positive current collector and the negative current collector can be selected from one or more of copper, aluminum, nickel, and stainless steel. Preferably, the positive current collector is aluminum and the negative current collector is copper.

[0064] It can be understood that the positive current collector and the negative current collector can be formed by any one of physical vapor deposition, chemical vapor deposition, electroplating, electroless plating, etc. Specifically, physical vapor deposition can include but is not limited to vacuum evaporation, magnetron sputtering, ion plating, etc., chemical vapor deposition can include but is not limited to plasma enhanced chemical vapor deposition, thermal chemical vapor deposition, high-temperature chemical vapor deposition, medium-temperature chemical vapor deposition, etc. Using the above methods can more easily control the thickness of the positive current collector or the negative current collector, and reduce the preparation difficulty. As a preferred embodiment, the positive current collector or the negative current collector can be formed on the surface of the protective layer by electroplating or electroless plating. The temperature of electroplating or electroless plating is relatively low, which can ensure the performance stability of the protective layer during preparation.

[0065] Preferably, the positive current collector is on the surface of the positive electrode.

[0066] Preferably, the negative current collector is deposited on the surface of the negative electrode.

[0067] Preferably, the protective layer is provided with a conductive structure, the conductive structure penetrates the protective layer, so that the positive current collector and the negative current collector are electrically connected.

[0068] The present application does not have a specific requirement for the specific shape of the conductive structure, any known conductive structure can be used in the present application without departing from the inventive concept of the present application, only as an illustrative example, and not as a limitation on the scope of protection, the conductive structure can be at least one of a conductive column, a conductive wire, a conductive mesh, a conductive sheet, a conductive rod.

[0069] As an embodiment, the polymer layer comprises a polymer solid-state electrolyte and a lithium salt;

[0070] Preferably, the polymer is selected from polyethylene glycol, polyethylene oxide (PEO), poly(p-phenylene oxide) (PPO), poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyvinyl chloride (PVC), and combinations thereof. In one variant, the one or more polymer materials can have an ionic conductivity equal to about 10 -4 S / cm.

[0071] Preferably, the lithium salt is selected from lithium hexafluorophosphate (LiPF6); lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium difluoro oxalato borate (LiBF2(C2O4)) (LiODFB), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalato)borate (LiB(C2O4)2) (LiBOB), lithium tetrafluoro oxalato phosphate (LiPF4(C2O4)) (LiFOP), lithium nitrate (LiNO3), lithium hexafluoroarsenate (LiAsF6), lithium triflate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (LiN(CF3SO2)2), lithium bisfluorosulfonylimide (LiN(FSO2)2) (LiFSI), and combinations thereof. In certain variants, the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (LiN(CF3SO2)2), lithium bisfluorosulfonylimide (LiN(FSO2)2) (LiFSI), lithium fluoroalkylphosphonate (LiFAP), lithium phosphate (Li3PO4), and combinations thereof.

[0072] Preferably, the solid-state electrolyte layer comprises an oxide solid-state electrolyte;

[0073] As an embodiment, the oxide solid-state electrolyte comprises one or more of garnet ceramics, LISICON-type oxides, NASICON-type oxides, and perovskite-type ceramics. For example, the one or more garnet ceramics can be selected from a group comprising Li 6.5 La3Zr1.75 Te 0.25 O 12 , Li7La3Zr2O 12 , Li 6.2 Ga 0.3 La 2.95 Rb 0.05 Zr2O 12 , Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 , Li 6.25 Al 0.25 La3Zr2O 12 , Li 6.75 La3Zr 1.75 Nb 0.25 O 12 , Li 6.75 La3Zr 1.75 Nb 0.25 O 12 and combinations thereof. One or more LISICON-type oxides can be selected from the group including Li 14 Zn(GeO4)4, Li 3+x (P 1-x Si x )O4(where 0 < x < 1), Li 3+x Ge x V 1-x O4(where 0 < x < 1), and combinations thereof. One or more NASICON-type oxides can be defined by LiMM'(PO4)3, where M and M' are independently selected from Al, Ge, Ti, Sn, Hf, Zr, and La. For example, in certain variations, one or more NASICON-type oxides can be selected from the group including Li 1+x AlxGe 2-x (PO4)3(LAGP) (where 0 < x < 2), Li 1+x Al x Ti 2-x (PO4)3(LATP) (where 0 < x < 2), Li 1+x Y x Zr 2-x (PO4)3(LYZP) (where 0 < x < 2), Li 1.3 Al 0.3 Ti 1.7Li2TiO3, Li2SrTiO3, Li2ZrTiO3, Li2TaTiO3, Li2NbTiO3, Li2HfTiO3, Li2SnTiO3, Li2GeTiO3, Li2AlTiO3, Li2SiTiO3, Li2B 3.3 La 0.53 TiO3, LiSr 1.65 Zr 1.3 Ta 1.7 O9, Li 2x-y Sr 1-x Ta y Zr 1-y O3 (where x = 0.75y and 0.60 < y < 0.75), Li 3 / 8 Sr 7 / 16 Nb 3 / 4 Zr 1 / 4 O3, Li 3x La (2 / 3-x) TiO3 (where 0 < x < 0.25), and combinations thereof. In one variation, one or more oxide-based materials can have an ionic conductivity greater than or equal to about 10 -5 S / cm to less than or equal to about 10 -1 S / cm.

[0074] Preferably, the oxide solid state electrolyte is capable of reacting with metallic lithium under electrochemical conditions.

[0075] It is understood that the oxide solid state electrolyte layer of the present application can be a multi-layer structure, such as a first oxide solid state electrolyte layer and a second oxide solid state electrolyte layer,

[0076] The cathode is formed of a plurality of cathode active particles comprising one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof. In some embodiments, the cathode electroactive material layer further includes an electrolyte, such as a plurality of electrolyte particles. The cathode active material layer has a thickness greater than or equal to about 1 pm to less than or equal to about 1,000 pm.

[0077] It is understood that the present application does not have a particular requirement for the cathode active material, and any known cathode active material can be used in the present application without departing from the inventive concept of the present application, and the cathode active material is one of a layered oxide cathode, a spinel cathode, and a polyanion cathode, by way of illustrative example only and not by way of limitation. For example, a layered oxide (e.g., a rock-salt layered oxide) comprises one or more lithium-based cathode electroactive materials selected from the group consisting of LiCoO2 (LCO), LiNi x Mn y Co1-x-y O2(wherein 0≤x≤1 and 0≤y≤1), LiNi 1-x-y Co x Al y O2(wherein 0≤x≤1 and 0≤y≤1), LiNi x Mn 1-x O2(wherein 0≤x≤1), and Li 1+x MO2(wherein M is one of Mn, Ni, Co and Al and 0≤x≤1). The spinel cathode comprises one or more lithium-based cathode electroactive materials selected from the group consisting of LiMn2O4(LMO) and LiNi x Mn 1.5 O4. The olivine-type material comprises one or more lithium-based cathode electroactive materials LiMPO4(wherein M is at least one of Fe, Ni, Co and Mn). The polyanionic cation comprises, for example, a phosphate such as LiV2(PO4)3 and / or a silicate such as LiFeSiO4.

[0078] It can be appreciated that the cathode active material can be selected from a mixture of several of the above.

[0079] Preferably, the metallic lithium anode comprises one or several of lithium foil, lithium sheet, lithium-indium alloy.

[0080] The second application of the present application also provides a method for preparing a solid-state lithium ion secondary battery, comprising the following steps:

[0081] S1. Preparing a multi-layer ceramic structure comprising a cathode active material layer, a solid-state electrolyte layer;

[0082] S2. Compounding the multi-layer ceramic structure prepared in step S1, a polymer layer, a metallic lithium anode to form a battery cell; and / or, forming a battery cell with a pre-made sheet consisting of a polymer layer, a metallic lithium anode and the multi-layer ceramic structure prepared in step S1;

[0083] S3. Stacking two or more battery cells prepared in step S2 to obtain a solid-state lithium ion secondary battery, wherein the cathode and anode of adjacent two battery cells are electrically connected.

[0084] Preferably, in step S1, the cathode active material layer and the solid-state electrolyte layer are compounded to form a composite structure; and the composite structure is co-sintered under an inert atmosphere to obtain the multi-layer ceramic structure.

[0085] Co-sintering essentially refers to the process of mixing two or more materials and co-sintering them at a certain temperature. During the co-sintering process of the solid-state electrolyte and the cathode active material, it is beneficial to form a dense interface and improve the performance of the battery.

[0086] The co-sintering process is not particularly limited in the present application, and any known co-sintering method can be used in the present application without departing from the concept of the present application. By way of illustration and not limitation, the co-sintering process can include one of microwave-induced carbon thermal shock fast sintering, pressureless sintering, hot-press sintering, and spark plasma sintering (SPS).

[0087] Preferably, the co-sintering temperature is 600-1400℃ in the present application; more preferably, 800-1100℃.

[0088] As an embodiment, the sintering can be multi-stage sintering, such as increasing the temperature to 600℃ at a certain heating rate, holding for 3h, then heating to 800℃ at a certain heating rate, and holding for 4h. The sintering process is not particularly limited in the present application, and any conventional adjustment of the sintering process should be considered within the protection scope of the present application without departing from the concept of the present application.

[0089] Preferably, the positive electrode active material layer comprises a positive electrode active material and a second solid-state electrolyte.

[0090] Preferably, the second solid-state electrolyte accounts for 5-50wt% of the positive electrode active material layer.

[0091] Since the solid-state lithium ion battery does not contain electrolyte, the lithium ion transmission capacity of the positive electrode active material layer formed by the positive electrode and the second solid-state electrolyte is mainly provided by the second solid-state electrolyte.

[0092] Preferably, the second solid-state electrolyte is also an oxide solid-state electrolyte, which can be the same or different from the solid-state electrolyte in the solid-state electrolyte layer.

[0093] It can be understood that, during the co-sintering process, the solid-state electrolyte and the positive electrode active material layer are rapidly densified to form a ceramic structure with a porosity of <10% or even <5%.

[0094] It can be understood that the porosity of the composite material is the percentage of the void volume in the composite material to the total volume of the composite material, and the porosity represents the densification degree of the ceramic structure.

[0095] Preferably, the method for compounding the positive electrode active material layer and the solid-state electrolyte layer is one of coating, spraying, or laminating the positive electrode active material layer and the solid-state electrolyte layer.

[0096] Preferably, after the green body is obtained by compounding the solid-state electrolyte layer and the positive electrode active material layer, the green body is placed in an isostatic pressing device for cold isostatic pressing treatment.

[0097] As an embodiment, the isostatic pressing treatment is cold isostatic pressing.

[0098] Preferably, in the step S1, a positive current collector is arranged on the side of the obtained multilayer ceramic structure away from the solid electrolyte layer.

[0099] It can be understood that the method of arranging the current collector is not particularly limited in the present application, and the positive current collector can be directly combined with the multilayer ceramic structure, or a metal film can be plated on the surface of the multilayer ceramic structure by a magnetron sputtering method without departing from the concept of the present application.

[0100] Preferably, in the step S2, a negative current collector and a protective layer are arranged on the side of the metal lithium negative electrode away from the polymer layer, and the negative current collector is arranged between the protective layer and the metal lithium negative electrode.

[0101] Preferably, in the step S3, the protective layer is located between the positive electrode and the negative electrode of the adjacent two battery cells.

[0102] It can be understood that the protective layer and the positive current collector and the negative current collector form a composite current collector structure, which not only reduces the thickness of the foil, but also has higher safety performance.

[0103] Preferably, in the step S3, the protective layer is located between the positive electrode and the negative electrode of the adjacent two battery cells.

[0104] Preferably, in the step S3, the solid-state lithium ion secondary battery is prepared by an isostatic pressing process.

[0105] Further preferably, in the step S3, the stacked battery cells are processed by an isostatic pressing process to obtain the solid-state lithium ion secondary battery.

[0106] The isostatic pressing process has a temperature of 80-140℃ and a pressure of 80-140MPa.

[0107] Preferably, the surface of the protective layer is provided with conductive adhesive.

[0108] The present application does not have special requirements for the type of conductive adhesive, and any known type of conductive adhesive can be used in the present application without departing from the concept of the present application. For example, epoxy resin, acrylate resin, polyurethane and other types of conductive adhesive.

[0109] Isostatic pressing is a method of applying equal pressure to an object through a pressurization system to reduce the distance between molecules without changing the external shape, thereby improving the physical properties of the material. This method is usually carried out in a closed container filled with a liquid medium, and the liquid medium is pressed into the container by a high-pressure pump to apply pressure to the object in the container.

[0110] The present application improves the adhesion between the structures in the battery cell during the pressing process by the hot isostatic pressing process.

[0111] The present application will be further described below with reference to specific embodiments and comparative examples.

[0112] Example 1

[0113] Preparation of multilayer ceramic structures:

[0114] Raw material preparation and mixing: Lithium cobalt oxide powder with an average particle size of 10 μm and LLZO powder with a particle size of 500 nm were added to a ball mill jar at a mass ratio of 97:3; an appropriate amount of isopropyl ketone was added as a grinding aid, and the mixture was ball milled at 500 rpm for 24 hours to ensure uniform dispersion of the powder; after ball milling, the mixture was dried in an oven at 80°C for 6 hours.

[0115] Powder molding: The dried powder is ground and sieved to remove lumps; the uniform powder is loaded into a mold and hydraulically molded under a pressure of 20 MPa to obtain a green blank of the positive electrode active material layer.

[0116] Electrolyte spraying and cold isostatic pressing: A 10 μm thick layer of LLZO electrolyte powder with a particle size of 500 nm is sprayed onto the surface of the positive electrode active material green body. The sprayed green body is then placed in a cold isostatic pressing apparatus and subjected to a pressure of 200 MPa to improve the density of the green body. The processing time is approximately 10 minutes. After cold isostatic pressing, the relative density of the green body can reach 56%. This step helps to increase the uniformity of shrinkage during subsequent sintering.

[0117] Sintering: The cold isostatically pressed green body was placed in a tube sintering furnace and evacuated to a vacuum level of 6 × 10⁻⁴ Pa. The temperature was increased to 600 °C at a rate of 3 °C / min and held for 6 hours to remove residual impurities, followed by the introduction of high-purity argon gas. Then, the temperature was increased to 900 °C at a rate of 2 °C / min and held for 4 hours to promote sintering and densification. Finally, the material was cooled to room temperature using a programmed cooling method to obtain a co-sintered multilayer ceramic structure; the porosity of the multilayer ceramic structure was 6%.

[0118] Current collector coating: On the side of the prepared ceramic sheet that is not coated with LLZO electrolyte powder, a 10μm thick metal Al film is deposited by magnetron sputtering under Ar gas protection, which serves as the current collector of the composite electrode.

[0119] Preparation of negative electrode

[0120] A polymer solid electrolyte layer is sprayed onto the surface of a lithium metal foil. The thickness of the polymer solid electrolyte layer is 20 μm. The polymer solid electrolyte is PEO, and the lithium salt is LiPF6 with a concentration of 15 wt%.

[0121] Series high-voltage battery assembly:

[0122] The positive electrode and negative electrode prepared above are compounded with a composite current collector to obtain a battery unit, the composite current collector comprising a protective layer and a negative current collector on one side of the protective layer, the side of the protective layer close to the positive electrode is coated with conductive glue, and four battery units are stacked in sequence, and warm isostatic pressing is performed at 120°C and 100MPa for 30 minutes to ensure close contact between the layers. The number of stacks is 4 layers.

[0123] Example 2

[0124] Preparation of a multilayer ceramic structure:

[0125] Preparation and mixing of raw materials: NCM532 powder with an average particle size of 8μm and LLTO powder with a particle size of 400nm are added to a ball mill tank in a mass ratio of 97:3; an appropriate amount of isopropyl alcohol is added as a grinding aid, and ball milling is performed at a speed of 500rpm for 24 hours to ensure uniform dispersion of the powder; after ball milling, the powder is dried in an oven at 80°C for 6 hours.

[0126] Powder forming: the dried powder is ground and sieved to remove lumps; the uniform powder is loaded into a mold and hydraulically formed under a pressure of 20MPa to obtain a green body of the positive active material layer.

[0127] Spraying of electrolyte and cold isostatic pressing: a layer of 10μm thick LLZO electrolyte powder is sprayed on the surface of the green body of the positive active material layer, wherein the particle size of the LLTO electrolyte powder is 400nm; the sprayed green body is placed in a cold isostatic pressing device and cold isostatic pressed at a pressure of 180MPa to improve the density of the green body. The processing time is about 10 minutes, and the relative density of the green body after cold isostatic pressing can reach 53%.

[0128] Sintering: the green body after cold isostatic pressing is placed in a tube sintering furnace, and vacuum is extracted to a vacuum degree of 6×10^-4Pa. The temperature is raised to 600°C at a rate of 3°C / min, and held for 6 hours to remove residual impurities, and then high-purity argon gas is introduced. Then heat to 850°C at a rate of 2°C / min, and hold for 4 hours to promote sintering and structure densification. Finally, the temperature is cooled to room temperature by programmed cooling to obtain a multilayer ceramic structure with co-sintering; the porosity of the multilayer ceramic structure is 8%.

[0129] Preparation of a negative electrode

[0130] A polymer solid electrolyte layer is sprayed on the surface of the metal lithium foil, the thickness of the polymer solid electrolyte layer is 20μm, wherein the polymer solid electrolyte is PEO, and the lithium salt is Li PF6 with a concentration of 15wt%;

[0131] Assembly of series high-voltage battery:

[0132] Assembly of series high-voltage battery:The positive electrode, the negative electrode and the composite current collector are stacked in the same way to form a battery cell. The PET layer in the composite current collector is provided with an aluminum foil on the side close to the positive electrode and a copper foil on the side close to the negative electrode. The stacked battery cell is subjected to warm isostatic pressing at 120℃ and 100MPa for 30 minutes to ensure close contact between the layers. The stacking number is 4 layers.

[0133] Cycle performance test:

[0134] 1. 0.1C constant current constant voltage charging to 4.2V at 45℃, cutoff current 0.05C, standing for 20min;

[0135] 2. 0.1C constant current discharging to 2.75V at 45℃, standing for 20min;

[0136] 3. Repeat steps 1-2 until the capacity retention rate is 80%, and record the cycle number.

[0137] After testing, the cycle of example 1 is 216cycs, and the cycle of example 2 is 145cycs. It can be seen that, by the multilayer ceramic co-firing technology and the composite current collector, the application realizes the internal series connection of the multilayer ceramic solid-state lithium ion battery, and matches the metal lithium negative electrode, improves the energy density of the battery, and widens the application range of the multilayer ceramic technology; at the same time, the preparation method of the application composites the multilayer ceramic, the current collector and the metal lithium negative electrode by the isostatic pressing process, and obtains a stable internal series high-voltage cell.

[0138] And by comparing example 1 and example 2, the application has better cycle performance by spraying the current collector on the surface of the positive electrode and then compositing the multilayer ceramic and the composite current collector by the isostatic pressing method, compared with example 2.

Claims

1. A method for preparing a solid-state lithium-ion secondary battery, characterized in that, The preparation method includes the following steps: S1. The positive electrode active material layer is combined with the solid electrolyte layer to form a composite structure; the composite structure is co-sintered in an inert atmosphere to obtain a multilayer ceramic structure; a positive electrode current collector is provided on the side of the multilayer ceramic structure away from the solid electrolyte layer. S2. The multilayer ceramic structure, polymer layer, and lithium metal anode prepared in step S1 are combined to form a battery cell; and / or, a preform composed of polymer layer and lithium metal anode is combined with the multilayer ceramic structure prepared in step S1 to form a battery cell; The lithium metal anode is provided with an anode current collector and a protective layer on the side away from the polymer layer, and the anode current collector is disposed between the protective layer and the lithium metal anode; The protective layer is coated with conductive adhesive on the side closest to the positive electrode; S3. Stack the battery cells obtained in two or more steps S2 and press them at an isostatic pressure to obtain a battery cell, wherein the positive and negative electrodes of two adjacent battery cells are connected. The solid-state lithium-ion secondary battery has at least two or more battery cells comprising the positive electrode, the lithium metal negative electrode, the polymer layer and the solid electrolyte layer; The positive electrode and the solid electrolyte layer form the multilayer ceramic structure, which is an integral structure. The polymer layer is disposed between the solid electrolyte layer and the lithium metal anode; The protective layer is located between the positive and negative electrodes of two adjacent battery cells, and the protective layer, the positive electrode current collector, and the negative electrode current collector form a composite current collector structure.

2. The preparation method according to claim 1, characterized in that, The porosity of the multilayer ceramic structure is <10%.

3. The preparation method according to claim 2, characterized in that, The porosity of the multilayer ceramic structure is <5%.

4. The preparation method according to claim 1, characterized in that, The positive electrode includes the positive electrode active material layer and the positive electrode current collector. The positive electrode current collector is disposed on the side of the positive electrode active material layer away from the solid electrolyte layer. In the solid lithium-ion secondary battery, at least one of the positive electrode current collectors is electrically connected to the adjacent negative electrode.

5. The preparation method according to claim 1, characterized in that, The polymer layer comprises a polymer solid electrolyte and a lithium salt.

6. The preparation method according to claim 1, characterized in that, The solid electrolyte layer includes an oxide solid electrolyte.

7. The preparation method according to claim 1, characterized in that, The lithium metal anode includes one or more of lithium foil, lithium sheet, and lithium-indium alloy.

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