Lithium ion battery

Abstract

The invention discloses a lithium ion battery. The battery is formed by sequentially laminating and assembling a positive pole piece, a buffer layer, a solid electrolyte layer and a negative pole piece, wherein the positive pole piece comprises a first active material and a first solid electrolyte; the buffer layer comprises a second active material and a second solid electrolyte; the first mass ratio of the first solid electrolyte in the total amount of the first active material and the first solid electrolyte is not more than 40%, and the second mass ratio of the second solid electrolyte in the total amount of the second active material and the second solid electrolyte is 50-80%; and the ratio of the second mass ratio to the first mass ratio is greater than 1.6. The buffer layers are arranged in the positive pole piece and the solid electrolyte layer, so that the problem of micro short circuit in the existing battery is avoided, and excellent electrical performance is realized while high energy density of the battery is ensured.

Description

Technical Field

[0001] This application relates to the field of chemical energy technology, and in particular to an ultra-low liquid content solid or solid lithium-ion battery using a buffer layer. Background Technology

[0002] With the rapid development of new energy technologies, ultra-low liquid content solid-state batteries (liquid content <5%) or solid-state batteries have become one of the main directions for future energy development. Currently, ultra-low liquid content solid-state batteries or solid-state batteries are formed by stacking and pressing a positive electrode, a solid electrolyte layer (thickness typically 20-100 μm), and a negative electrode in sequence. During the pressing process (pressure usually >300 MPa), due to the poor mechanical properties of the solid electrolyte membrane and the high hardness of the positive electrode, which cannot guarantee absolute uniformity and flatness, the solid electrolyte layer is easily perforated or pressed into uneven areas during battery pressing. This can lead to micro-short circuits during battery cycling, affecting battery performance. Summary of the Invention

[0003] To address the aforementioned problems, this application discloses a lithium-ion battery. The battery may include an ultra-low liquid content solid-state battery or an all-solid-state lithium-ion battery. The battery includes a buffer layer, which can be placed between the positive electrode and the solid electrolyte layer, ensuring high energy density while solving the micro-short circuit problem and achieving excellent electrical performance.

[0004] This application discloses a lithium-ion battery, which is assembled by stacking a positive electrode, a buffer layer, a solid electrolyte layer, and a negative electrode in that order; wherein, the positive electrode includes a first active material and a first solid electrolyte; the buffer layer includes a second active material and a second solid electrolyte; the first solid electrolyte accounts for no more than 40% of the total mass of the first active material and the first solid electrolyte, the second solid electrolyte accounts for 50%-80% of the total mass of the second active material and the second solid electrolyte, and the ratio of the second mass percentage to the first mass percentage is greater than 1.6.

[0005] According to some embodiments of this application, the solid electrolyte layer includes a third solid electrolyte; the first volume average particle size of the first solid electrolyte does not exceed the second volume average particle size of the second solid electrolyte; and the second volume average particle size does not exceed the third volume average particle size of the third solid electrolyte.

[0006] According to some embodiments of this application, the ratio of the third volume average particle size to the first volume average particle size is greater than 1.2.

[0007] According to some embodiments of this application, the first active material may be the same as or different from the second active material; the first solid electrolyte, the second solid electrolyte, and the third solid electrolyte may be the same as or different from each other.

[0008] According to some embodiments of this application, the fourth volume average particle size of the first active material is not less than the fifth volume average particle size of the second active material.

[0009] According to some embodiments of this application, the thickness of the buffer layer is 5μm-20μm.

[0010] According to some embodiments of this application, the thickness of the buffer layer is not less than 5% of the thickness of the positive electrode sheet and does not exceed 60% of the thickness of the solid electrolyte layer.

[0011] The liquid content in the battery is <5%;

[0012] More preferably, the liquid content is less than 1%;

[0013] More preferably, the liquid content is less than or equal to 0.01%.

[0014] According to some embodiments of this application, the ratio of the fourth volume average particle size of the first active material to the first volume average particle size of the first solid electrolyte is greater than 2.

[0015] According to some embodiments of this application, the ratio of the fifth volume average particle size of the second active material to the second volume average particle size of the second solid electrolyte is greater than 1.2.

[0016] According to some embodiments of this application, the positive electrode further includes a first conductive agent and a first binder, the buffer layer further includes a second conductive agent and a second binder, and the solid electrolyte layer includes a third binder; wherein the first conductive agent and the second conductive agent may be the same or different, and the first binder, the second binder, and the third binder may be the same or different.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0018] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0019] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this application and in its specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The terms "comprising" or "including," as used in this application, mean that an element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms "and / or" or "and / or" as used in this application include any and all combinations of one or more of the associated listed items.

[0020] Currently, problems encountered in battery pressing and molding can be alleviated by thickening the solid electrolyte layer, such as to more than 300μm, or by reducing the loading and particle size of the positive electrode active material in the positive electrode sheet. However, this results in a significant loss of energy density and electrical performance of the battery.

[0021] The battery disclosed in this application can solve related problems while ensuring excellent electrical performance by adding a buffer layer to the positive electrode and the solid electrolyte layer.

[0022] The following describes some preferred embodiments of this application. It should be noted that the following description is for illustrative purposes only and is not intended to limit the scope of protection of this application. The steps involved in this application may be performed precisely in sequence, or various steps may be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from these processes.

[0023] This application discloses a battery, which may include an ultra-low liquid content solid-state battery or an all-solid-state battery. The battery can be assembled by stacking positive electrode, buffer layer, solid electrolyte layer, and negative electrode in that order. The buffer layer is disposed between the positive electrode and the solid electrolyte layer, serving to buffer pressure and compensate conductivity for the solid electrolyte layer.

[0024] Understandably, low-liquid-content solid-state batteries refer to batteries with a liquid content of less than 5%, while all-solid-state batteries refer to batteries that contain virtually no liquid.

[0025] The positive electrode may include a first active material and a first solid electrolyte. As an example, the first active material may include, but is not limited to, layered oxide materials (e.g., lithium cobalt oxide LiCoO2, nickel-cobalt-manganese ternary material LiNi). x Co y Mn 1-x- y O2, nickel-cobalt-aluminum ternary material LiNi x Co y Al 1-x-y O2, etc.), spinel structure materials (e.g., lithium manganese oxide LiMn2O4, high-voltage nickel-manganese spinel LiNi), etc. 0.5 Mn 1.5 The cathode material can be any combination of lithium salts, such as lithium iron phosphate (LiFePO4), olivine-based materials (e.g., elemental sulfur (S), transition metal chalcogenides and their complexes), conversion-type cathode materials (e.g., metal fluorides such as CoF2, FeF3, metal chlorides such as CoCl2), lithium-rich layered oxides (e.g., Li2MnO3·LiMO2, M = Ni, Co, Mn), polyanionic compounds (e.g., phosphates, pyrophosphates, sulfates, silicates, borates and mixed polyanions), etc. In some embodiments, the first cathode material can be a lithium salt, such as lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, etc.

[0026] The first solid electrolyte may include, but is not limited to, polymer solid electrolytes, inorganic solid electrolytes, glassy and glass-ceramic electrolytes, composite solid electrolytes, or any combination thereof. Exemplary polymer solid electrolytes may include polyethylene oxide (PEO), poly(propylene oxide) (PPO), polyolefin polymer electrolytes (e.g., polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), etc.), polyacrylonitrile (PAN) based electrolytes, polymethyl methacrylate (PMMA) based electrolytes, polyvinylpyrrolidone (PVP) based electrolytes, polysiloxane alkyl electrolytes (e.g., polydimethylsiloxane (PDMS), etc.), ionic liquid polymer electrolytes (e.g., poly(ionic liquid), etc.), etc., or any combination thereof. The above polymer solid electrolytes can be used in combination with different types of lithium salts (e.g., LiClO4, LiTFSI, LiBF4, etc.) to achieve good flexibility and high ionic conductivity.

[0027] Exemplary inorganic solid electrolytes may include oxide solid electrolytes, halide solid electrolytes, sulfide solid electrolytes, etc. Among them, oxide solid electrolytes may include, but are not limited to, garnet-type solid electrolytes such as LLZO, LLTO, LBLTO, etc., or element-substituted electrolytes like garnet-type solid electrolytes; NASICON-type solid electrolytes such as LTPA, LAGP, etc., or their element-substituted electrolytes; and Li3xLa... (2 / 3)-x TiO3, Li 0.34 La 0.51 TiO 2.94 Perovskite-type solid electrolytes such as Li3OCl, Li3OBr, etc., or their elemental substitutes, and anti-perovskite-type oxide electrolytes such as Li3OCl, Li3OBr, etc., and Li 14 ZnGe4O 16 The inorganic oxide may include one or more of the following: LISICON-type solid electrolytes such as Li4SiO4, LiGeO4, or their elemental substitutes; borate oxide electrolytes such as Li3BO3, Li2B4O7, or their elemental substitutes; composite oxide electrolytes such as LLZO-LLTO, LATP-LLZO, or Li3PO4 or its N-substitutes. Optionally or preferably, the inorganic oxide may include one or more of LLZO, LLTO, LAGP, LATP, LBSPO, LPO, Li4SiO4, Li2ZnTi3O8, and / or their derivatives. The halide solid electrolyte may have the chemical formula Li... a MX b In this designation, M represents a metallic element or a metalloid, and X represents a halogen. "Metalloid" can refer to elements with metallic-like properties and may include B, Si, Ge, As, Sb, Te, etc. Optionally or preferably, M may include, but is not limited to, Al, Zn, Mg, Ca, Ba, Mn, Zr, Cd, Co, Yb, Y, Cr, In, Ga, Sr, Hf, Ti, Ta, Sn, Nb, Er, Sc, etc., or any combination thereof. In some embodiments, M may be one or more of Y, In, or Zr. For example, the halide solid electrolyte may be a Zr-based halide solid electrolyte, including Li₂ZrCl₆, Li₃Zr₂I₉, Li₂ZrI₆, etc. As another example, the halide solid electrolyte may be an In-based halide solid electrolyte, including Li₃InCl₆, Li₃InBr₆, Li₃InI₆, Li₃In₂Cl₉, etc. For example, halide solid electrolytes can be Y-based halide solid electrolytes, including Li3YCl6, Li3YBr6, Li3YI6, and Li3Y(Cl 1-x Br x6. In the above-mentioned halide solid electrolytes, M and X can each contain two or more elements to form a mixed halide electrolyte. For example, Li₂ZrCl 6-x Br x Li 2+x Zr 1-x In x Cl6, etc. Sulfide solid electrolytes can include, but are not limited to, lithium sulfide series (Li2S-P2S5 systems, such as LGPS, Li7P3S, etc.). 11 The electrolyte may include, but is not limited to, Li3PS4, germanium sulfide series (e.g., LGPS, LSPS), tin sulfide series (e.g., Li4SnS4), lithium boron sulfide series (e.g., Li3BS3), sulfide halide series (e.g., Li6PS5X, Li3InX6, where X = Cl, Br, I), or any combination thereof. Optionally or preferably, the sulfide solid electrolyte may include one or more of Li6PS5Cl, Li2S-P2S5, LGPS, etc.

[0028] Exemplary glassy and glass-ceramic electrolytes may include, but are not limited to, Li₂O-B₂O₃-SiO₂ systems, Li₂S-P₂S₅ systems, LiF-AlF₃ systems, Li₂O-Al₂O₃-TiO₂-P₂O₅ systems, Li₂O-SiO₂-P₂O₅ systems, 70Li₂S·30P₂S₅ glass-ceramic systems, Li₂S-P₂S₅-LiI systems, Li₂S-P₂S₅-P₂S₃ systems, Li₂O-B₂O₃-P₂O₅ systems, Li₂O-Al₂O₃-GeO₂-P₂O₅ systems, and Li₂O-B₂O₃-P₂O₅ systems. 1+x Al x Ti 2-x (PO4)3, Li 10 GeP2S 12 One or more of the following, or any combination of multiple electrolytes: Li3PS4-LiI composite electrolyte, Li2S-P2S5-LiBH4 system, etc.

[0029] Exemplary composite solid electrolytes may include inorganic-polymer composite electrolytes, inorganic-inorganic composite electrolytes, polymer-polymer composite electrolytes, ternary composite electrolytes, and functionalized composite electrolytes. Among them, inorganic-polymer composite electrolytes may include ceramic-filled polymer electrolytes such as PEO-LLZO and PEO-LAGP, polymer-reinforced ceramic electrolytes such as LLZO-PEO and LATP-PEO, and polymer-coated ceramic electrolytes such as LGPS-PEO. Inorganic-inorganic composite electrolytes may include oxide-oxide composite electrolytes such as LLZO-LATP, and sulfide-oxide composite electrolytes such as Li... 10 GeP2S12 -Li3BO3, etc., halide-oxide composite electrolytes such as LiF-Li3YCl6, etc. Polymer-polymer composite electrolytes can include PEO-PVDF composite electrolytes, PEO-PAN composite electrolytes, PEO-PMMA composite electrolytes, etc. Ternary composite electrolytes can include polymer, ceramic, lithium salt ternary polymers such as PEO-LLZO-LiTFSI, polymer, inorganic filler, lithium salt ternary polymers such as PAN-SiO2-LiClO4, copolymer, ceramic, lithium salt ternary polymers such as PVDF-HFP-Al2O3-LiTFSI, etc. Functionalized composite electrolytes can include surface-modified LLZO-PEO composite electrolytes, cross-linked PEO-ceramic composite electrolytes, ionic liquid-enhanced composite electrolytes, etc.

[0030] The aforementioned first solid electrolyte can also be modified, doped, or composited to enhance its physicochemical properties, including improving stability and mechanical strength, and increasing ionic conductivity. For example, a conductive polymer or protective layer can be coated on the surface of the first solid electrolyte, other metal elements such as Al, Mg, and Ca can be doped, two or more first solid electrolytes can be reused, or it can be composited with carbon nanotubes (CNTs) or graphene.

[0031] In some embodiments, the mass percentage of the first solid electrolyte in the total mass of the first active material and the first solid electrolyte (referred to in this application as the first mass percentage, denoted as w1) does not exceed 40%. Optionally or preferably, the first mass percentage does not exceed 34%. Optionally or preferably, the first mass percentage does not exceed 28%. Optionally or preferably, the first mass percentage does not exceed 22%. Optionally or preferably, the first mass percentage does not exceed 18%. Optionally or preferably, the first mass percentage does not exceed 10%. Alternatively, the first mass percentage can be any value within the above range, such as 18%, 28%, etc.

[0032] The buffer layer may include a second active material and a second solid electrolyte. In some embodiments, the second active material may be selected from one or more of the first active materials described above. That is, the second active material may be the same as or different from the first active material. For example, the second active material may be the same as the first active material, both being layered oxide materials such as nickel-cobalt-manganese ternary materials LiNi. x Co y Mn 1-x-yO2. Alternatively, the second active material can be lithium cobalt oxide, while the first active material remains the nickel-cobalt-manganese ternary material described above. Similarly, the second solid electrolyte can also be one or more of the first solid electrolytes as described above. They can also be the same or different. For example, both the first and second solid electrolytes are Li2ZrCl6. Or, the first solid electrolyte is Li2ZrCl6, and the second solid electrolyte is LLTO. This application does not limit the selection of the above components.

[0033] In some embodiments, the mass percentage of the second solid electrolyte in the total mass of the second active material and the second solid electrolyte (referred to in this application as the second mass percentage, denoted as w2) is 50%-80%. Optionally or preferably, the second mass percentage is 55%-75%. Optionally or preferably, the second mass percentage is 60%-70%. Optionally or preferably, the second mass percentage is 62%-68%. Optionally or preferably, the second mass percentage is 64%-66%. Alternatively, the second mass percentage can be any value within the above range, such as 50%, 60%, 70%, 80%, etc.

[0034] In some embodiments, the ratio w2 / w1 of the second mass percentage to the first mass percentage can be greater than 1.6. For example, this ratio w2 / w1 can be 1.7, 1.8, 1.9, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.5, 4.0, 5.0, or more. The ratio w2 / w1 can also be any value within the above range, such as 1.79, 2.14, 2.17, 2.86, 3.33, etc.

[0035] The solid electrolyte layer may include a third solid electrolyte. The third solid electrolyte may be one or more of the first or second solid electrolytes as described above. That is, the first, second, and third solid electrolytes may be the same or different. For example, they may be completely different, mutually identical, or completely the same. As an example, all three may be Li₂ZrCl₆. Alternatively, the first and second solid electrolytes may both be Li₂ZrCl₆, and the third solid electrolyte may be Li₆PS₅Cl. Or, the first solid electrolyte may be Li₂ZrCl₆, the second solid electrolyte may be LLTO, and the third solid electrolyte may be Li₆PS₅Cl. This application does not specifically limit the selection of the above three solid electrolytes.

[0036] The aforementioned active materials (including the first and second active materials) and solid electrolytes (including the first, second, and third solid electrolytes) can be in particulate form and participate in the composition of their respective components (e.g., positive electrode, buffer layer, and solid electrolyte layer). Based on the volume average particle size Dv50, the first volume average particle size (denoted as DE1) of the first solid electrolyte can not exceed the second volume average particle size (denoted as DE2) of the second solid electrolyte, and the third volume average particle size (denoted as DE3) of the third solid electrolyte can not be less than the second volume average particle size of the second solid electrolyte. Furthermore, the fourth volume average particle size (denoted as DC1) of the first active material can not be less than the fifth volume average particle size (denoted as DC2) of the second active material. The relationship between these parameters can be expressed as: DE1 ≤ DE2 ≤ DE3, DC1 ≥ DC2.

[0037] Meanwhile, among the aforementioned parameters, the ratio DC1 / DE1 between the fourth volume average particle size DC1 of the first active material relating to the positive electrode sheet and the first volume average particle size DE1 of the first solid electrolyte can be greater than 2. For example, this ratio DC1 / DE1 can be 2.3, 2.6, 2.9, 3.3, 3.6, or even larger. This ratio DC1 / DE1 can also be any value within the aforementioned numerical range, such as 3.33. The ratio DC2 / DE2 between the fifth volume average particle size DC2 of the second active material relating to the buffer layer and the second volume average particle size DE2 of the second solid electrolyte can be greater than 1.2. For example, this ratio DC2 / DE2 can be 1.3, 1.5, 2.0, 2.5, 3.0, 3.5, or even larger. This ratio DC1 / DE1 can also be any value within the aforementioned numerical range, such as 1.5, 2.0, 3.33, etc. The ratio of the third volume average particle size DE3 of the third solid electrolyte layer to the first average particle size DE1 of the first solid electrolyte layer, DE3 / DE1, can be greater than 1.2. This ratio, DC1 / DE1, can also be any value greater than 1.2, such as 1.67. By selecting the particle size of each component, the mechanical strength and ionic conductivity of the positive electrode, buffer layer, and solid electrolyte layer can be improved / optimized, thereby enhancing the structural stability and electrical performance of the battery.

[0038] In some embodiments, the positive electrode may further include a first conductive agent and a first binder, the buffer layer may further include a second conductive agent and a second binder, and the solid electrolyte layer may further include a third binder. The conductive agent may be one or more selected from metal conductive agents, carbon-based conductive agents, inorganic crystalline conductive agents, polymer conductive agents, etc. Exemplary metal conductive agents may include metal powders (such as aluminum powder, nickel powder, etc.), metal fibers, or metal compound fibers, etc. Exemplary carbon-based conductive agents may include graphene, carbon nanofibers (VGCF), carbon nanotubes (including single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs)), carbon black (such as acetylene black, etc.), amorphous carbon, etc. Exemplary inorganic crystalline conductive agents may include oxide conductive agents such as lithium oxide, aluminum oxide, magnesium oxide, etc., sulfide conductive agents such as lithium sulfide, germanium sulfide, etc., phosphate conductive agents such as lithium phosphate, fluoride conductive agents such as lithium fluoride, etc. Exemplary polymeric conductive agents may include polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyaniline (PANI), polypyrrole (PPY), polythiophene (PT), poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), polyacrylonitrile (PAN), etc. Alternatively, any known or commercially available conductive agent may also be applicable to this application. The first and second conductive agents described above may each be selected from one or more of the foregoing examples. They may be the same or different.

[0039] Any known adhesive, including but not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aromatic polyamide resin, polyamide, polyimide, polyamide-imide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, polyhexafluoropropylene, styrene-butadiene rubber, carboxymethyl cellulose, etc., or any combination thereof, can be used in this application. Copolymers can also be used as adhesives, exemplary of which are copolymers of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, trifluorochloroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, hexadiene, etc. Alternatively, mixtures of two or more materials in the above examples can also be used as adhesives. The first adhesive, second adhesive, and third adhesive can each be selected from one or more of the above examples. The above three can also be the same or different.

[0040] The positive electrode also includes a current collector for collecting and conducting electrons. The positive electrode is obtained by combining and pressing the positive electrode film made from the above materials with the current collector. The current collector can be materials such as aluminum foil, nickel foil, or stainless steel foil.

[0041] The negative electrode can be a metal electrode or an alloy electrode, such as a lithium metal negative electrode or an alloy electrode of metals such as lithium, tin, aluminum, germanium, and indium. The negative electrode can also be a silicon-based negative electrode, a carbon-based negative electrode, a metal oxide negative electrode, or a composite material negative electrode. Alternatively, the negative electrode can be prepared using a solid electrolyte, such as one or more of the aforementioned solid electrolytes combined with an active material, or prepared by mixing it with lithium metal, silicon, graphite, etc. This application does not limit the selection of the negative electrode.

[0042] It should be noted that the examples of the various components constituting the battery described above are for illustrative purposes only and are not intended to limit the scope of protection of the technical solution of this application. Any binder obtained by adjusting / modifying / updating without departing from the inventive concept of this application is within the scope of protection of this application.

[0043] The components of the battery can be presented in layered, film-like, or block-like form, and are finally stacked to form the battery. The thickness of the buffer layer can be 5μm-20μm. Optionally or preferably, the thickness of the buffer layer can be 6μm-18μm. Optionally or preferably, the thickness of the buffer layer can be 8μm-16μm. Optionally or preferably, the thickness of the buffer layer can be 10μm-14μm. Alternatively, the thickness of the buffer layer can be any value within the above range, such as 6.5μm, 10μm, 18μm, etc. Furthermore, the thickness of the buffer layer (denoted as T2) can be not less than 5% of the thickness of the positive electrode (denoted as T1) and not more than 60% of the thickness of the solid electrolyte layer (denoted as T3). That is, 5%T1≤T2≤60%T3. Setting a reasonable buffer layer thickness can avoid the battery from being ineffective due to being too thin, and from having a reduced energy density and electrical performance loss due to being too thick.

[0044] The components of the battery can be prepared using known methods, including but not limited to wet coating, dry pressing, 3D printing, solution casting, thin film deposition, and colloidal electrospinning. The buffer layer can be composite-formed based on the positive electrode or solid electrolyte layer, or it can be formed separately. For example, the raw materials for preparing the buffer layer (including proportionally weighed active materials, solid electrolyte, conductive agent, binder, etc.) can be mixed in a solvent to form a slurry, which is then uniformly coated onto the prepared positive electrode or solid electrolyte layer. After drying, the solvent is removed, and the mixture is compacted to obtain a composite of the buffer layer and the positive electrode or solid electrolyte layer. Alternatively, the above raw materials can be mixed in a mixer until homogeneous, and then pressed using methods such as direct pressing, hot pressing, extrusion, or rolling to obtain a separate buffer layer. This buffer layer is then composite-pressed with the positive electrode, solid electrolyte layer, and negative electrode to obtain the battery.

[0045] The present application will be further described in detail below with reference to embodiments. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection claimed in this application.

[0046] Example 1 - Battery Preparation

[0047] 1) Preparation of the positive electrode sheet:

[0048] Weigh the NCM811 positive electrode, Li2ZrCl6, and VGCF conductive agent in a ratio of 70:28:1.5 and mix them in a small high-speed mixer for 30 minutes. Then add 0.5% PTFE binder and continue high-speed mixing for 10 minutes to mix and pre-fiberize. Take out the mixture and pour it into a differential roller to form a film and thin it to the target thickness. Then, press it with aluminum foil to obtain the positive electrode sheet.

[0049] 2) Preparation of the buffer layer:

[0050] Weigh the NCM811 positive electrode, Li2ZrCl6, and VGCF conductive agent in a ratio of 38:60:1.5 and mix them in a small high-speed mixer for 30 minutes. Then add 0.5% PTFE binder and continue high-speed mixing for 10 minutes to mix and pre-fiberize. Take out the mixture and pour it into a differential roller to form a film and thin it to the target thickness to obtain a buffer layer.

[0051] 3) Preparation of solid electrolyte membrane: Li6PS5Cl and PTFE binder were weighed at a ratio of 99:1 and placed in a small high-speed mixer for shearing and mixing. After uniform mixing, the mixture was taken out and repeatedly ground in a mortar until it reached a dough-like (lumpy) state. The dough-like mixture was then rolled multiple times on a differential roller press at a roller temperature of 80℃ and a speed ratio of 3:1 to obtain a dry-process sulfide electrolyte membrane of the target thickness.

[0052] 4) Preparation of negative electrode sheet: Li sheet and In sheet are composite pressed at a mass ratio of 1:30 to prepare LiIn alloy sheet;

[0053] 5) Battery assembly: Cut the above-mentioned composite positive electrode sheet, buffer layer, electrolyte membrane and negative electrode sheet into pieces according to the 20×20mm battery model, and stack them in the order of negative electrode sheet-solid electrolyte membrane-buffer layer-positive electrode sheet. Then, put them into aluminum-plastic film for vacuum sealing. Finally, put the sealed battery into an isostatic press for pressing at a pressure of 500MPa.

[0054] Example 2 - Battery Preparation

[0055] Example 2 differs from Example 1 in that the thickness of the prepared buffer layer is different.

[0056] Example 3 - Battery Preparation

[0057] The difference between Example 3 and Example 1 and Example 2 is that the thickness of the prepared buffer layer is different.

[0058] Example 4 - Battery Preparation

[0059] Example 4 differs from Example 1 in that the particle size of the solid electrolyte constituting the buffer layer is different.

[0060] Example 5 - Battery Preparation

[0061] Example 5 differs from Example 1 in that the particle size of the solid electrolyte constituting the buffer layer and the particle size of the active material are different.

[0062] Example 6 - Battery Preparation

[0063] The difference between Example 6 and Example 5 lies in the proportion of solid electrolyte in the positive electrode.

[0064] Example 7 - Battery Preparation

[0065] The difference between Example 7 and Example 5 is that the proportion of solid electrolyte in the buffer layer is different.

[0066] Example 8 - Battery Preparation

[0067] The difference between Example 7 and Example 5 is that the proportion of solid electrolyte in the buffer layer is different.

[0068] Comparative Example 1 - Preparation of Battery

[0069] The difference between Comparative Example 1 and Example 1 is that no buffer layer was added.

[0070] Tables 1 and 2 show the relevant parameters of the above embodiments and comparative examples.

[0071] Table 1 Particle size and thickness parameters

[0072]

[0073] Table 2. Mass percentage, mass ratio, and particle size ratio

[0074]

[0075]

[0076] Example 9 - Battery Cycle Performance Test

[0077] Batteries obtained in Examples 1-8 and Comparative Example 1 were connected to the Blue Battery Test Cabinet for charge-discharge testing. The test temperature was 55℃, the voltage range was 2.0-3.65V, the first charge-discharge rate was 0.1C, and from the second cycle onwards, the charge-discharge rate was 0.3C. After 50 cycles, the discharge specific capacity of the 50th cycle was divided by the discharge specific capacity of the 2nd cycle to obtain the cycle capacity retention rate. The test results are summarized in Table 3.

[0078] Example 10 - Energy Density VED Calculation

[0079] Based on the first charge-discharge results of the batteries obtained in Examples 1-8 and Comparative Example 1, the energy value of the first discharge was read as E, and the volume of the single-layer soft-pack battery excluding the aluminum-plastic film encapsulation was measured as V. VED = E / V was calculated. The calculation results are summarized in Table 3.

[0080] Table 3 Energy Density and Cycle Retention Rate

[0081] Example Energy density VED Wh / L Cyclic capacity retention % 1 850.4 89.0 2 843.3 89.6 3 853.7 88.3 4 850.5 89.7 5 850.6 90.4 6 967.0 88.9 7 859.4 90.1 8 832.5 90.8 Comparative Example 1 816.3 80.2

[0082] As shown in Table 3, compared to Comparative Example 1, the batteries in Examples 1-8 improved energy density and cycle capacity retention by adding a buffer layer between the positive electrode and the solid electrolyte layer, with an improvement of nearly 10%, by using a buffer layer. The battery provided in this application uses a buffer layer, which not only ensures high energy density but also achieves excellent electrical performance.

[0083] This application has described the basic concepts. Obviously, for those skilled in the art, the above detailed disclosure is merely illustrative and does not constitute a limitation of this application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are suggested in this application, and therefore such modifications, improvements, and corrections still fall within the spirit and scope of the exemplary embodiments of this application.

[0084] Furthermore, this application uses specific terms to describe its embodiments. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic related to at least one embodiment of this application. Therefore, it should be emphasized and noted that "an embodiment," "one embodiment," or "an alternative embodiment" mentioned twice or more in different locations in this application do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of this application can be appropriately combined.

[0085] Similarly, it should be noted that, in order to simplify the description of this application and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of the embodiments of this application sometimes combines multiple features into one embodiment or its description. However, this disclosure method does not imply that the subject matter of this application requires more features than those mentioned in the claims. In fact, the embodiments have fewer features than all the features of the single embodiments disclosed above.

[0086] Finally, it should be understood that the embodiments described in this application are merely illustrative of the principles of the embodiments of this application. Other modifications may also fall within the scope of this application. Therefore, alternative configurations of the embodiments of this application are considered as examples and not limitations, and are regarded as consistent with the teachings of this application. Accordingly, the embodiments of this application are not limited to the embodiments explicitly described and illustrated in this application.

Claims

1. A lithium-ion battery, characterized in that, The battery is assembled by stacking the positive electrode, buffer layer, solid electrolyte layer, and negative electrode in that order; wherein, The positive electrode includes a first active material and a first solid electrolyte; The buffer layer includes a second active material and a second solid electrolyte; The first solid electrolyte accounts for no more than 40% of the total mass of the first active material and the first solid electrolyte, and the second solid electrolyte accounts for 50%-80% of the total mass of the second active material and the second solid electrolyte, and the ratio of the second mass percentage to the first mass percentage is greater than 1.

6.

2. The battery according to claim 1, characterized in that, The solid electrolyte layer includes a third solid electrolyte; The first volume average particle size of the first solid electrolyte does not exceed the second volume average particle size of the second solid electrolyte; the second volume average particle size does not exceed the third volume average particle size of the third solid electrolyte.

3. The battery according to claim 2, characterized in that, The ratio of the third volume average particle size to the first volume average particle size is greater than 1.

2.

4. The battery according to claim 2, characterized in that, The first active material may be the same as or different from the second active material; the first solid electrolyte, the second solid electrolyte, and the third solid electrolyte may be the same as or different from each other.

5. The battery according to claim 1, characterized in that, The fourth volume average particle size of the first active material is not less than the fifth volume average particle size of the second active material.

6. The battery according to claim 1, characterized in that, The thickness of the buffer layer is 5μm-20μm.

7. The battery according to claim 1, characterized in that, The thickness of the buffer layer is not less than 5% of the thickness of the positive electrode sheet and does not exceed 60% of the thickness of the solid electrolyte layer.

8. The battery according to claim 1, characterized in that, The ratio of the fourth volume average particle size of the first active material to the first volume average particle size of the first solid electrolyte is greater than 2.

9. The battery according to claim 1, characterized in that, The ratio of the fifth volume average particle size of the second active material to the second volume average particle size of the second solid electrolyte is greater than 1.

2.

10. The battery according to claim 1, characterized in that, The positive electrode sheet further includes a first conductive agent and a first binder, the buffer layer further includes a second conductive agent and a second binder, and the solid electrolyte layer includes a third binder; wherein the first conductive agent and the second conductive agent may be the same or different, and the first binder, the second binder, and the third binder may be the same or different.

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