Positive pole piece, preparation method thereof and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a positive pole piece, a preparation method thereof and a lithium ion battery. The positive pole piece comprises a positive current collector and a positive active material layer arranged on the surface of at least one side of the positive current collector, and the positive active material layer comprises a lithium-rich manganese-based positive material, a conductive agent and a composite material; the composite material includes a conductive polymer, a binder polymer, and a lithium ion conductor. According to the lithium-rich manganese-based system positive pole piece provided by the invention, a composite network of a conductive polymer-bonding polymer and a lithium ion conductor is constructed, so that the consumption of a conductive agent is reduced, the bonding property of a positive active material layer is ensured, and triple functions of electron conduction, bonding and ion auxiliary transmission are considered; the solid-state battery can be in better contact with a solid-state electrolyte layer, is good in interface contact, and is suitable for a high-capacity and long-circulation solid-state battery scene.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a positive electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the rapid development of electric vehicles, large-scale energy storage, and other fields, higher demands are being placed on the energy density, safety, and cycle life of lithium-ion batteries. Traditional liquid lithium-ion batteries are limited by the flammable and explosive properties of organic electrolytes, posing serious safety hazards, and their energy density is gradually approaching its theoretical limit. All-solid-state lithium batteries, which use non-flammable inorganic solid electrolytes, are considered an ideal solution for next-generation high-safety, high-energy-density energy storage devices.

[0003] In terms of cathode materials, lithium-rich manganese-based materials (xLi2MnO2·(1-x)LiMO2, M=Mn, Ni, Co, etc.) are considered as one of the key cathode materials for achieving high energy density batteries of 500Wh / kg or more due to their extremely high reversible specific capacity (>250mAh / g) and operating voltage (>3.5V), as well as the cost advantage brought by the abundant manganese element.

[0004] However, combining this highly promising lithium-rich manganese-based cathode material with a solid electrolyte to construct an all-solid-state battery faces severe technical challenges. The core issues mainly focus on two aspects: solid-solid interface contact and intrinsic electrochemical performance, which seriously restrict its practical application.

[0005] Unlike liquid electrolytes, which can fully wet electrode particles to form a good liquid-solid interface, the rigid solid-solid point contact in solid-state batteries is an inherent physical characteristic. This leads to a series of interface problems: Poor interface contact and high interface impedance: The lithium-rich manganese-based cathode material particles and solid electrolyte particles are in rigid contact, making it difficult to form a tight, continuous, large-area effective contact interface under the pressure of electrode fabrication and battery assembly. This poor contact results in an obstructed lithium-ion transport path on the cathode side, generating extremely high interface impedance, which severely limits the rate performance and capacity of the battery. Severe interface side reactions: Lithium-rich manganese-based materials, when charged to high voltages (>4.5V vs. Li...),... +When lithium-rich manganese-based materials are used in the Li₂MnO₃ process, their lattice oxygen participates in the reaction, releasing active oxygen. This highly reactive oxygen species undergoes violent chemical side reactions with mainstream solid electrolytes such as sulfides and halides, which have poor oxidation stability, generating a mixed ion / electron conductive interface layer at the interface composed of Li₂S, Li₃PO₄, and phosphorus-sulfur compounds. This interface layer not only further increases the interfacial impedance but also irreversibly consumes active lithium and electrolyte, leading to rapid capacity decay. Poor interfacial mechanical stability: During cycling, lithium-rich manganese-based materials exhibit significant lattice volume changes (especially during the initial Li₂MnO₃ phase activation process). Under solid-solid interface constraints, this volume change induces enormous interfacial stress, leading to contact point detachment, interface cracking, and even the breakage of cathode particles or solid electrolyte particles, causing interruption of ion transport pathways and a sharp deterioration in battery performance.

[0006] The inherent capacity and cycling performance issues of lithium-rich manganese-based materials are not only not alleviated after coupling with solid-state electrolytes, but are actually amplified: low initial coulombic efficiency and rapid capacity decay: During the first charge, lithium-rich manganese-based materials undergo irreversible lattice oxygen evolution and Li₂O removal, resulting in extremely low initial coulombic efficiency (typically below 80%). In solid-state batteries, due to the lack of dissolution and redistribution of interfacial byproducts by liquid electrolytes, these irreversible products permanently clog the narrow solid-solid interface, exacerbating lithium-ion transport obstacles and causing capacity decay in subsequent cycles to be much faster than in liquid batteries. Voltage drop and structural evolution: A continuous voltage drop is commonly observed in materials during cycling, which is related to the migration of transition metal ions and the transformation of the lattice structure from layered to spinel or even rock salt phases. The slow ion transport kinetics and severe interfacial side reactions in solid-state systems may accelerate this harmful structural evolution process, leading to a continuous decline in the operating voltage plateau and a sustained loss of energy density.

[0007] In summary, developing a new technology that can simultaneously solve the poor interfacial contact of lithium-rich manganese-based cathodes / solid electrolytes and synergistically improve their intrinsic capacity and cycle stability has become an urgent need to promote the development of high-energy-density all-solid-state batteries. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a positive electrode sheet, its preparation method, and a lithium-ion battery. The positive electrode sheet provided by this invention, based on a lithium-rich manganese-based system, reduces the amount of conductive agent used by constructing a composite network of conductive polymer, binder polymer, and lithium-ion conductor, ensuring the adhesion of the positive electrode active material layer. Furthermore, it combines the triple functions of "electron conduction + bonding + ion-assisted transport," enabling better contact with the solid electrolyte layer and resulting in excellent interfacial contact, making it suitable for high-capacity and long-cycle solid-state battery applications.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer comprising a lithium-rich manganese-based positive electrode material, a conductive agent and a composite material; the composite material comprising a conductive polymer, a binder polymer and a lithium-ion conductor.

[0011] In the positive electrode sheet provided by this invention, the conductive polymer can assist the transfer of electrons between the particles of the lithium-rich manganese-based positive electrode material, reducing the amount of conductive agent used. At the same time, the binder polymer ensures the adhesion of the active material layer. In conjunction with the lithium-ion conductor, it achieves the triple function of "electron conduction + adhesion + ion-assisted transport", which allows the positive electrode sheet to make better contact with the solid electrolyte layer. The solid-solid interface has good contact and is suitable for high-capacity and long-cycle solid-state battery scenarios.

[0012] Preferably, the positive electrode active material layer comprises 75wt%~90wt% of lithium-rich manganese-based positive electrode material, 1wt%~5wt% of conductive agent and the balance being a composite material.

[0013] For example, the mass percentage of the lithium-rich manganese-based cathode material can be 75wt%, 78wt%, 80wt%, 83wt%, 85wt%, 88wt%, or 90wt%, etc.; the mass percentage of the conductive agent can be 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%, etc.

[0014] In this invention, adjusting the mass ratio of each raw material in the positive electrode active material layer is more conducive to constructing a stable electrode structure and an efficient three-dimensional conductive-ion transport network, suppressing voltage decay, and improving rate performance.

[0015] Preferably, the mass ratio of the conductive polymer, the binder polymer, and the lithium-ion conductor is 1:(0.4~0.7):(0.3~0.6), for example, 1:0.4:0.3, 1:0.4:0.5, 1:0.4:0.6, 1:0.5:0.3, 1:0.5:0.5, 1:0.5:0.6, 1:0.7:0.3, 1:0.7:0.5, or 1:0.7:0.6, etc.

[0016] In the composite material of the present invention, the mass ratio of the conductive polymer, the binder polymer and the lithium-ion conductor is controlled to be 1:(0.4~0.7):(0.3~0.6), which better leverages the "multifunctional synergistic effect" of each component, significantly improves the interfacial stability of the material, enhances the structural integrity of the electrode, improves the material's initial efficiency, rate capability, long cycle life and alleviates voltage decay.

[0017] Preferably, the adhesive polymer includes non-in-situ self-assembly adhesive polymers and / or in-situ self-assembly adhesive polymers, wherein the in-situ self-assembly adhesive polymer includes ferroelectric polymers, wherein the ferroelectric polymer includes any one or a combination of at least two of ferroelectric PVDF, ferroelectric P (VDF-TrFE), ferroelectric P (VDF-TrFE-CTFE), or ferroelectric P (VDF-HFP).

[0018] In this invention, in-situ self-assembly refers to the process by which polymer molecules form an ordered structure at a specific interface or substrate surface driven by intermolecular interaction forces (such as dipole-dipole interactions, hydrogen bonds, etc.); non-in-situ self-assembly refers to the type of adhesive conventionally recognized by those skilled in the art, such as at least one of polyvinylidene fluoride, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose (CMC), polyvinylpyrrolidone (HPC), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), or fluororubber (FKM).

[0019] In this invention, the ferroelectric polymer can be prepared using commercially available products or based on conventional preparation methods.

[0020] By way of example, the present invention provides a process for preparing ferroelectric polymers:

[0021] The precursor polymer is assembled in N,N-dimethylformamide (DMF); the precursor polymer includes at least one of PVDF, P(VDF-TrFE), P(VDF-HFP) or P(VDF-TrFE-CTFE).

[0022] Among them, the vinylidene fluoride-trifluoroethylene copolymer is P(VDF-TrFE), the vinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer is P(VDF-TrFE-CTFE), and the vinylidene fluoride and hexafluoropropylene copolymer is P(VDF-HFP).

[0023] The composite material of this invention uses in-situ self-assembled ferroelectric polymers, which further improves the interfacial contact of lithium-rich manganese-based cathode materials in the cathode sheet, enhances the interfacial effect between lithium-rich manganese-based cathode materials and solid electrolyte layers in solid-state batteries, reduces solid-solid interface contact resistance, and thus exhibits better capacity and high-rate cycle stability.

[0024] It is also understood that the specific material types of the conductive polymer and lithium-ion conductor in this invention are conventional technical solutions. For example, the conductive polymer includes, but is not limited to, polyaniline and / or polythiophene; the lithium-ion conductor includes, but is not limited to, at least one of LiPSCl, LiGePS or LiPS.

[0025] Preferably, the conductive agent includes carbon nanotubes and graphene.

[0026] In the positive electrode of this invention, a composite conductive agent system of carbon nanotubes and graphene is selected, which forms a point-line-surface network structure with the particles of lithium-rich manganese-based positive electrode material. The composite material is dispersed in it, working together to better improve the electron transport effect of the positive electrode.

[0027] Preferably, the mass ratio of carbon nanotubes to graphene is 1:(0.5~2), such as 1:0.5, 1:0.8, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, etc.

[0028] Preferably, the lithium-rich manganese-based cathode material includes a lithium-rich manganese-based core and a coating coating on the surface of the lithium-rich manganese-based core. The lithium-rich manganese-based core includes a lithium-rich manganese-based matrix material and zirconium ions and magnesium ions doped in the lithium-rich manganese-based matrix material. The coating coating includes a LiAlO2-Al2O3 composite coating.

[0029] In the lithium-rich manganese-based cathode material provided by this invention, the doping of zirconium and magnesium ions in the core can regulate the lattice structure of the lithium-rich manganese-based matrix material and increase the bulk transport channels for lithium ions; the composite layer can suppress the side reactions between the lithium-rich manganese-based active material and the electrolyte, and reduce the resistance to lithium ion interface migration; the composite components can coordinate-assisted Li + Diffusion, providing high-conductivity channels; Zr co-doped in the core. 4+ With Mg 2+ The ionic radii of both are compatible with those of the matrix metal ions, which can simultaneously stabilize the crystal structure, suppress lattice distortion during charging and discharging, and increase the bulk phase conduction channels of lithium ions through lattice regulation, thereby improving the bulk phase migration rate.

[0030] Meanwhile, this invention also utilizes the synergistic coating of LiAlO2 and Al2O3, which works together with dopant ions. LiAlO2 improves the interfacial compatibility between the lithium-rich manganese-based active material and the solid electrolyte, reducing interfacial impedance. Al2O3 enhances the structural stability of the coating layer, suppressing side reactions on the surface of the active material and element dissolution. The combination of the two substances in the composite layer reduces the resistance to lithium-ion transport. In addition, the LiAlO2-Al2O3 composite coating can also work together with the lithium-ion conductor in the composite material to further improve the ion transport effect.

[0031] Preferably, the lithium-rich manganese-based matrix material comprises materials with the general chemical formula Li. 1+a [Ni β Coγ Mn 1-β-γ ] 1-a O2, where 0.05≤a≤0.2, 0.1≤β≤0.3, and 0.05≤γ≤0.15.

[0032] For example, 'a' can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2, etc.; 'β' can be 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, or 0.3, etc.; and 'γ' can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, or 0.15, etc.

[0033] Preferably, the zirconium ion doping amount is 0.5% to 2% of the total molar amount of transition metal elements in the lithium-rich manganese-based matrix material, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%.

[0034] Preferably, the amount of magnesium ions doped is 0.3% to 1.5% of the total molar amount of transition metal elements in the lithium-rich manganese-based matrix material, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%.

[0035] Preferably, the molar ratio of LiAlO2 to Al2O3 in the coating is 1:0.8 to 1:1.2, such as 1:0.8, 1:0.9, 1:1, 1:1.1 or 1:1.2.

[0036] Preferably, the mass of the coating is 1wt% to 3wt% of the lithium-rich manganese-based cathode material, for example, 1wt%, 1.3wt%, 1.5wt%, 1.8wt%, 2wt%, 2.3wt%, 2.5wt%, 2.8wt%, or 3wt%.

[0037] It should be noted that this invention does not limit the specific preparation method of lithium-rich manganese-based cathode material. It can realize the doping of zirconium ions and magnesium ions in lithium-rich manganese-based matrix material, and thus realize the method of LiAlO2-Al2O3 co-coating. In principle, this invention is applicable without violating the overall technical concept of this invention.

[0038] By way of example, the present invention provides a method for preparing a lithium-rich manganese-based cathode material, the method comprising the following steps:

[0039] Preparation of Zr-doped 4+ With Mg 2+ The core is then mixed with LiAlO2 and Al2O3 in a solid phase and sintered to obtain the lithium-rich manganese-based active material; the conductive agent, composite components and the lithium-rich manganese-based active material are mixed to obtain the modified lithium-rich manganese-based cathode material of the first aspect.

[0040] Optionally, the sintering is carried out in an air atmosphere.

[0041] Optionally, the sintering temperature is 800℃~950℃, for example, it can be 800℃, 850℃, 900℃ or 950℃.

[0042] Optionally, the sintering time is 8h to 12h, for example, it can be 8h, 9h, 10h, 11h or 12h.

[0043] Optionally, the method for preparing the kernel includes:

[0044] Zr-doped preparation by co-precipitation method 4+ With Mg 2+ The precursor is then mixed with lithium carbonate and sintered in an oxygen-containing atmosphere to obtain the core.

[0045] Zr-doped preparation by co-precipitation method 4+ With Mg 2+ In the precursor process, the nickel source used can be any one or at least a combination of two of nickel nitrate, nickel sulfate, or nickel chloride. Typical but non-limiting combinations include combinations of nickel nitrate and nickel sulfate, nickel nitrate and nickel chloride, nickel sulfate and nickel chloride, or combinations of nickel nitrate, nickel sulfate, and nickel chloride.

[0046] The cobalt source can be any one or a combination of at least two of cobalt nitrate, cobalt sulfate, or cobalt chloride. Typical but non-limiting combinations include combinations of cobalt nitrate and cobalt sulfate, cobalt nitrate and cobalt chloride, cobalt sulfate and cobalt chloride, or cobalt nitrate, cobalt sulfate, and cobalt chloride.

[0047] The manganese source can be any one or a combination of at least two of manganese nitrate, manganese sulfate, or manganese chloride. Typical but non-limiting combinations include combinations of manganese nitrate and manganese sulfate, manganese nitrate and manganese chloride, manganese sulfate and manganese chloride, or combinations of manganese nitrate, manganese sulfate, and manganese chloride.

[0048] The zirconium source can be zirconium nitrate and / or zirconium oxychloride.

[0049] The magnesium source can be magnesium nitrate and / or magnesium acetate.

[0050] Furthermore, this invention does not limit the specific parameters of the coprecipitation method, as long as it can yield a product with the chemical formula Ni. β Co γ Mn 1-β-γ CO3 or Ni β Co γ Mn 1-β-γ The precursor of (OH)2 is sufficient, where 0.1≤β≤0.3 and 0.05≤γ≤0.15.

[0051] It should also be noted that the positive current collector in this invention is selected from metal foil materials and composite current collectors; the metal foil materials include, but are not limited to, aluminum foil or carbon-coated aluminum foil; the composite current collector has a sandwich-like sandwich structure, with the middle polymer layer mainly composed of high-molecular insulating resin and other materials, and metal layers deposited on both sides of the middle polymer layer by electroplating, chemical plating or other methods. Schematally, the high-molecular resin includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, and poly... The metal layer is selected from one or more of the following: amide-imide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trifluorochloroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone and its derivatives, sodium carboxymethyl cellulose, styrene-butadiene rubber, fluorinated rubber, polyvinyl alcohol, or polyvinylidene fluoride. The metal layer is selected from at least one of aluminum, copper, nickel, cobalt, tungsten, tin, lead, iron, silver, or gold.

[0052] In a second aspect, the present invention provides a method for preparing a positive electrode sheet as described in the first aspect, the method comprising the following steps:

[0053] A mixed slurry is obtained by mixing lithium-rich manganese-based cathode material, conductive agent, composite material and solvent, and coating the mixed slurry onto the surface of at least one side of the cathode current collector to obtain the cathode electrode sheet;

[0054] The composite material includes a conductive polymer, a binder polymer, and a lithium-ion conductor.

[0055] This invention does not require a complicated preparation method; the corresponding raw materials are simply mixed according to the formula, and then coated.

[0056] Preferably, when the bonding polymer in the composite material is an in-situ self-assembling bonding polymer, the coated mixed slurry is subjected to in-situ assembly heat treatment to obtain a positive electrode sheet.

[0057] In this invention, the in-situ self-assembly of the binder polymer can be achieved during the preparation of the positive electrode active material layer, thereby obtaining a ferroelectric polymer binder. On the one hand, it can act as a binder to provide a good bonding effect, preventing the positive electrode sheet from pulverizing and falling off under the expansion, contraction, and polarization effects during cycling. On the other hand, the spontaneous polarization field of the ferroelectric polymer can guide lithium ions to be extracted and inserted more orderly, suppressing irreversible phase transitions and side reactions to a certain extent, reducing charge loss in the first cycle, and thus improving the first coulombic efficiency and reversible capacity. In addition, the built-in electric field of the formed ferroelectric polymer can stabilize the lattice position of the transition metal ions and hinder their migration to the lithium layer. This "pinning" effect helps to maintain the original layered structure of the material, thereby effectively slowing down the voltage decay during cycling.

[0058] Preferably, the heat treatment includes performing a first heat treatment and a second heat treatment in sequence, wherein the first heat treatment is performed under normal pressure and the second heat treatment is performed under negative pressure.

[0059] It is understood that the normal pressure in this invention is atmospheric pressure.

[0060] In this invention, heat treatment is performed simultaneously with in-situ assembly, which further enhances the cross-linking effect between binder polymers, allowing for better composite with conductive polymers and lithium-ion conductors, thus achieving a synergistic effect and improving the capacity and cycle performance of solid-state batteries.

[0061] Preferably, the temperature of the first heat treatment is 60°C to 70°C, such as 60°C, 65°C, or 70°C.

[0062] Preferably, the temperature of the second heat treatment is 80~90℃, such as 80℃, 85℃ or 90℃.

[0063] Preferably, the negative pressure value is 0.15 atm to 0.25 atm, for example, 0.15 atm, 0.2 atm or 0.25 atm.

[0064] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode sheet as described in the first aspect or a positive electrode sheet prepared by the preparation method described in the second aspect; the lithium-ion battery comprises a solid-state battery.

[0065] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] In the positive electrode sheet provided by this invention, the conductive polymer can assist the transfer of electrons between the particles of the lithium-rich manganese-based positive electrode material, reducing the amount of conductive agent used. At the same time, the binder polymer ensures the adhesion of the active material layer. In conjunction with the lithium-ion conductor, it achieves the triple function of "electron conduction + adhesion + ion-assisted transport", which allows the positive electrode sheet to make better contact with the solid electrolyte layer. The solid-solid interface has good contact and is suitable for high-capacity and long-cycle solid-state battery scenarios. Detailed Implementation

[0068] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0069] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0070] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0071] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0072] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0073] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0074] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0075] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0076] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0077] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0078] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0079] Example 1

[0080] This embodiment provides a positive electrode sheet, which includes a commercial aluminum foil for a positive current collector and a positive active material layer disposed on one side surface of the aluminum foil. The positive active material layer includes 88 wt% lithium-rich manganese-based positive electrode material, 2 wt% conductive agent and 10 wt% composite material.

[0081] The lithium-rich manganese-based cathode material includes a lithium-rich manganese-based core Li 1.1 [Ni 0.1 Co 0.05 Mn 0.85 ] 0.1O2 and a coating layer covering the surface of the lithium-rich manganese-based core, wherein the lithium-rich manganese-based core comprises a lithium-rich manganese-based matrix material and zirconium and magnesium ions doped in the lithium-rich manganese-based matrix material, wherein the doping amount of zirconium ions and the doping amount of magnesium ions are each 1% of the total molar amount of transition metal elements (nickel, cobalt, and manganese) in the lithium-rich manganese-based matrix material, and the coating layer is a LiAlO2-Al2O3 composite coating, the mass of which is 2 wt% of the lithium-rich manganese-based cathode material;

[0082] The conductive agent is carbon nanotubes and graphene in a mass ratio of 1:1.

[0083] The composite material comprises a conductive polymer polyaniline, a ferroelectric PVDF, and a lithium-ion conductor LiPSCl in a mass ratio of 1:0.5:0.5.

[0084] The method for preparing the positive electrode sheet is as follows:

[0085] A slurry is formed by combining lithium-rich manganese-based cathode material, conductive agent, and composite material (the binder polymer in the composite material is PVDF) under the action of DMF. The slurry is coated onto one side of an aluminum foil and then in-situ self-assembled. In this step, the PVDF in the composite material forms ferroelectric PVDF. Simultaneously with the in-situ self-assembly, a first heat treatment process at 60°C under normal pressure and a second heat treatment process at 0.2 atm and 85°C are performed in sequence. The material is then rolled to form a cathode sheet.

[0086] Example 2

[0087] This embodiment provides a positive electrode sheet, which includes a commercial aluminum foil for a positive current collector and a positive active material layer disposed on one side surface of the aluminum foil. The positive active material layer includes 90 wt% lithium-rich manganese-based positive electrode material, 1 wt% conductive agent and 9 wt% composite material.

[0088] The lithium-rich manganese-based cathode material includes a lithium-rich manganese-based core Li 1.2 [Ni 0.3 Co 0.15 Mn 0.5 ] 0.2 O2 and a coating layer covering the surface of the lithium-rich manganese-based core, wherein the lithium-rich manganese-based core comprises a lithium-rich manganese-based matrix material and zirconium and magnesium ions doped in the lithium-rich manganese-based matrix material, wherein the doping amount of zirconium ions and the doping amount of magnesium ions are each 2% of the total molar amount of transition metal elements (nickel, cobalt, and manganese) in the lithium-rich manganese-based matrix material, and the coating layer is a LiAlO2-Al2O3 composite coating, the mass of which is 3 wt% of the lithium-rich manganese-based cathode material;

[0089] The conductive agent is carbon nanotubes and graphene in a mass ratio of 1:2;

[0090] The composite material comprises a conductive polymer polyaniline, a ferroelectric PVDF, and a lithium-ion conductor LiPSCl in a mass ratio of 1:0.5:0.5.

[0091] The method for preparing the positive electrode sheet is as follows:

[0092] A slurry is formed by combining lithium-rich manganese-based cathode material, conductive agent, and composite material (the binder polymer in the composite material is PVDF) under the action of DMF. The slurry is coated onto one side of an aluminum foil and then in-situ self-assembled. In this step, the PVDF in the composite material forms ferroelectric PVDF. Simultaneously with the in-situ self-assembly, a first heat treatment process at 70°C under normal pressure and a second heat treatment process at 0.25 atm and 90°C are performed in sequence. The material is then rolled to form a cathode sheet.

[0093] Example 3

[0094] This embodiment provides a positive electrode sheet, which includes a commercial aluminum foil for a positive current collector and a positive active material layer disposed on one side surface of the aluminum foil. The positive active material layer includes 75 wt% lithium-rich manganese-based positive electrode material, 4 wt% conductive agent and 21 wt% composite material.

[0095] The lithium-rich manganese-based cathode material includes a lithium-rich manganese-based core Li 1.1 [Ni 0.1 Co 0.05 Mn 0.85 ] 0.1 O2 and a coating layer covering the surface of the lithium-rich manganese-based core, wherein the lithium-rich manganese-based core comprises a lithium-rich manganese-based matrix material and zirconium and magnesium ions doped in the lithium-rich manganese-based matrix material, wherein the doping amount of zirconium ions and the doping amount of magnesium ions are each 0.5% of the total molar amount of transition metal elements (nickel, cobalt, and manganese) in the lithium-rich manganese-based matrix material, and the coating layer is a LiAlO2-Al2O3 composite coating, the mass of which is 1 wt% of the lithium-rich manganese-based cathode material;

[0096] The conductive agent is carbon nanotubes and graphene in a mass ratio of 1:0.5;

[0097] The composite material comprises a conductive polymer polyaniline, a ferroelectric PVDF, and a lithium-ion conductor LiPSCl in a mass ratio of 1:0.5:0.5.

[0098] The method for preparing the positive electrode sheet is as follows:

[0099] A slurry is formed by combining lithium-rich manganese-based cathode material, conductive agent, and composite material (the binder polymer in the composite material is PVDF) under the action of DMF. The slurry is coated onto one side of an aluminum foil and then in-situ self-assembled. In this step, the PVDF in the composite material forms ferroelectric PVDF. Simultaneously with the in-situ self-assembly, a first heat treatment process at 60°C under normal pressure and a second heat treatment process at 0.2 atm and 85°C are performed in sequence. The material is then rolled to form a cathode sheet.

[0100] Example 4

[0101] The difference between this embodiment and Embodiment 1 is that the composite material in this embodiment includes conductive polymer polyaniline, ferroelectric PVDF, and lithium-ion conductor LiPSCl in a mass ratio of 1:0.4:0.3.

[0102] All other conditions remain the same as in Example 1.

[0103] Example 5

[0104] The difference between this embodiment and Embodiment 1 is that the composite material in this embodiment includes conductive polymer polyaniline, ferroelectric PVDF, and lithium-ion conductor LiPSCl in a mass ratio of 1:0.4:0.6.

[0105] All other conditions remain the same as in Example 1.

[0106] Example 6

[0107] The difference between this embodiment and Embodiment 1 is that the composite material in this embodiment includes conductive polymer polyaniline, ferroelectric PVDF, and lithium-ion conductor LiPSCl in a mass ratio of 1:0.7:0.3.

[0108] All other conditions remain the same as in Example 1.

[0109] Example 7

[0110] The difference between this embodiment and Embodiment 1 is that the composite material in this embodiment includes conductive polymer polyaniline, ferroelectric PVDF, and lithium-ion conductor LiPSCl in a mass ratio of 1:0.7:0.6.

[0111] All other conditions remain the same as in Example 1.

[0112] Example 8

[0113] The difference between this embodiment and Embodiment 1 is that the positive electrode active material layer includes 95wt% lithium-rich manganese-based positive electrode material, 2wt% conductive agent and 3wt% composite material.

[0114] All other conditions remain the same as in Example 1.

[0115] Example 9

[0116] The difference between this embodiment and Embodiment 1 is that the positive electrode active material layer includes 70 wt% lithium-rich manganese-based positive electrode material, 2 wt% conductive agent, and 28 wt% composite material.

[0117] All other conditions remain the same as in Example 1.

[0118] Example 10

[0119] The difference between this embodiment and Embodiment 1 is that the composite material in this embodiment includes conductive polymer polyaniline, ferroelectric PVDF, and lithium-ion conductor LiPSCl in a mass ratio of 1:0.2:0.5.

[0120] All other conditions remain the same as in Example 1.

[0121] Example 11

[0122] The difference between this embodiment and Embodiment 1 is that the composite material in this embodiment includes conductive polymer polyaniline, ferroelectric PVDF, and lithium-ion conductor LiPSCl in a mass ratio of 1:0.9:0.5.

[0123] All other conditions remain the same as in Example 1.

[0124] Example 12

[0125] The difference between this embodiment and Embodiment 1 is that the composite material in this embodiment includes conductive polymer polyaniline, ferroelectric PVDF, and lithium-ion conductor LiPSCl in a mass ratio of 1:0.5:0.1.

[0126] All other conditions remain the same as in Example 1.

[0127] Example 13

[0128] The difference between this embodiment and Embodiment 1 is that the composite material in this embodiment includes conductive polymer polyaniline, ferroelectric PVDF, and lithium-ion conductor LiPSCl in a mass ratio of 1:0.5:0.8.

[0129] All other conditions remain the same as in Example 1.

[0130] Example 14

[0131] The difference between this embodiment and Embodiment 1 is that the lithium-rich manganese-based cathode material in this embodiment does not have a coating.

[0132] All other conditions remain the same as in Example 1.

[0133] Example 15

[0134] The difference between this embodiment and Embodiment 1 is that the lithium-rich manganese-based core in this embodiment is not doped with zirconium and magnesium ions.

[0135] All other conditions remain the same as in Example 1.

[0136] Example 16

[0137] The difference between this embodiment and Embodiment 1 is that the adhesive polymer in this embodiment is a non-in-situ self-assembling adhesive polymer, that is, a conventional commercially available PVDF adhesive.

[0138] In the preparation method, N-methylpyrrolidone (NMP) is used as a solvent. After the slurry is coated, it is directly dried and rolled to obtain the positive electrode sheet.

[0139] All other conditions remain the same as in Example 1.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 1 is that the composite material in this comparative example does not contain conductive polymer.

[0142] All other conditions remain the same as in Example 1.

[0143] Comparative Example 2

[0144] The difference between this comparative example and Example 1 is that the composite material in this comparative example does not contain lithium-ion conductors.

[0145] All other conditions remain the same as in Example 1.

[0146] Solid-state battery fabrication and performance testing

[0147] (1) Fabrication of solid-state batteries:

[0148] Positive electrode: The positive electrode of Examples 1-16 and Comparative Examples 1-2, respectively.

[0149] Negative electrode: Lithium metal sheet.

[0150] Solid electrolyte layer: Li6PS5Cl powder was thoroughly ground in an inert atmosphere glove box, and then cold-pressed using a mold to obtain a self-supporting electrolyte membrane.

[0151] A pouch solid-state lithium-ion battery is fabricated by assembling the positive electrode, solid electrolyte layer, and negative electrode using a stacking process under Ar-filled conditions and a pressure of 6.8 MPa.

[0152] (2) Performance testing:

[0153] (a) Discharge specific capacity: The first charge-discharge cycle was completed at a rate of 0.1C within a voltage range of 2.0-4.8V, and the first charge-discharge capacity was recorded.

[0154] (b) Cycling performance: Capacity retention was tested by performing 100 cycles at a current density of 0.33C and a voltage range of 2.0-4.8V.

[0155] The test results are shown in Table 1.

[0156] Table 1

[0157]

[0158] From Table 1, we can obtain:

[0159] The modified lithium-rich manganese-based cathode provided by this invention can exhibit excellent discharge capacity and cycle stability, meeting the high-performance requirements of solid-state batteries.

[0160] Data analysis from Examples 1, 8, and 9 shows that the mass percentage of each substance in the active material layer of the positive electrode has a significant impact on the performance of the positive electrode. By controlling the content of the positive active material to 75wt%~90wt% and the conductive agent to 1wt%~5wt%, the content of the composite material can be controlled, which is more conducive to building a stable electrode structure and an efficient three-dimensional conductive-ion transport network, suppressing voltage decay, and improving the solid-solid interface contact between the positive electrode and the solid electrolyte layer, thereby improving capacity and cycle performance at different rates.

[0161] Data analysis of Examples 1, 4-7, and 10-13 shows that the mass ratio of the conductive polymer, lithium-ion conductor, and binder polymer in the composite material plays an important role in the synergistic effect of the three components. In particular, adjusting the mass ratio of the conductive polymer, binder polymer, and lithium-ion conductor to 1:(0.4~0.7):(0.3~0.6) significantly improves the interfacial stability of the material and enhances the structural integrity of the electrode, thereby improving the capacity and cycle performance of lithium-rich manganese-based materials in solid-state batteries.

[0162] Data analysis of Examples 1, 14, and 15 shows that the LiAlO2-Al2O3 coating and the doping of zirconium and magnesium ions in the lithium-rich manganese-based cathode material of the present invention are more suitable for solid-state battery systems and can work synergistically with conductive agents and composite materials to achieve higher capacity and better cycle performance.

[0163] Data analysis of Examples 1 and 16 shows that when the binder polymer is a ferroelectric polymer that can be self-assembled in situ, it not only ensures a good bonding effect, but also guides the insertion and extraction of lithium ions based on the spontaneous polarization field of the ferroelectric polymer and stabilizes the structure of the lithium-rich manganese-based cathode material, thereby improving the capacity and cycle performance of the lithium-rich manganese-based cathode material in solid-state batteries.

[0164] Data analysis of Examples 1, 1, and 2 shows that, in the positive electrode sheet of the present invention, the synergistic cooperation between the three-component composite material and the lithium-rich manganese-based positive electrode material enables the positive electrode sheet to make better contact with the solid electrolyte layer, resulting in good contact between the solid and solid interfaces, which is suitable for high-capacity and long-cycle solid-state battery scenarios.

[0165] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector. The positive active material layer includes a lithium-rich manganese-based positive electrode material, a conductive agent, and a composite material. The composite material includes a conductive polymer, a binder polymer, and a lithium-ion conductor.

2. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material layer comprises 75wt%~90wt% lithium-rich manganese-based positive electrode material, 1wt%~5wt% conductive agent, and the balance being composite material.

3. The positive electrode sheet according to claim 1, characterized in that, The mass ratio of the conductive polymer, the binder polymer, and the lithium-ion conductor is 1:(0.4~0.7):(0.3~0.6).

4. The positive electrode sheet according to claim 1 or 3, characterized in that, The adhesive polymer includes non-in-situ self-assembly adhesive polymers and / or in-situ self-assembly adhesive polymers, wherein the in-situ self-assembly adhesive polymer includes ferroelectric polymers, wherein the ferroelectric polymer includes any one or a combination of at least two of ferroelectric PVDF, ferroelectric P (VDF-TrFE), ferroelectric P (VDF-TrFE-CTFE), or ferroelectric P (VDF-HFP).

5. The positive electrode sheet according to claim 1, characterized in that, The conductive agent includes carbon nanotubes and graphene; Preferably, the mass ratio of the carbon nanotubes to graphene is 1:(0.5~2).

6. The positive electrode sheet according to claim 1, characterized in that, The lithium-rich manganese-based cathode material includes a lithium-rich manganese-based core and a coating coating on the surface of the lithium-rich manganese-based core. The lithium-rich manganese-based core includes a lithium-rich manganese-based matrix material and zirconium ions and magnesium ions doped in the lithium-rich manganese-based matrix material. The coating coating includes a LiAlO2-Al2O3 composite coating.

7. The positive electrode sheet according to claim 6, characterized in that, The lithium-rich manganese matrix material includes materials with the general chemical formula Li. 1+a [Ni β Co γ Mn 1-β-γ ] 1-a O2, where 0.05≤a≤0.2, 0.1≤β≤0.3, 0.05≤γ≤0.15; Preferably, the zirconium ion doping amount is 0.5% to 2% of the total molar amount of transition metal elements in the lithium-rich manganese-based matrix material; Preferably, the amount of magnesium ions doped is 0.3% to 1.5% of the total molar amount of transition metal elements in the lithium-rich manganese-based matrix material; Preferably, the molar ratio of LiAlO2 to Al2O3 in the coating is 1:0.8 to 1:1.2; Preferably, the mass of the coating is 1 wt% to 3 wt% of the lithium-rich manganese-based cathode material.

8. A method for preparing a positive electrode sheet as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: A mixed slurry is obtained by mixing lithium-rich manganese-based cathode material, conductive agent, composite material and solvent, and coating the mixed slurry onto the surface of at least one side of the cathode current collector to obtain the cathode electrode sheet; The composite material includes a conductive polymer, a binder polymer, and a lithium-ion conductor.

9. The preparation method according to claim 8, characterized in that, When the bonding polymer in the composite material is an in-situ self-assembly bonding polymer, the coated mixed slurry is subjected to in-situ assembly heat treatment to obtain a positive electrode sheet. Preferably, the heat treatment includes performing a first heat treatment and a second heat treatment in sequence, wherein the first heat treatment is performed under normal pressure and the second heat treatment is performed under negative pressure; Preferably, the temperature of the first heat treatment is 60°C to 70°C, and the temperature of the second heat treatment is 80°C to 90°C. Preferably, the negative pressure value is 0.15 atm to 0.25 atm.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode sheet as described in any one of claims 1-7 or a positive electrode sheet prepared by the preparation method as described in any one of claims 8-9; The lithium-ion battery includes a solid-state battery.

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