Functional material for diaphragm, preparation method thereof, diaphragm and lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and particularly relates to a functional material for diaphragm, a preparation method of the functional material, a diaphragm and a lithium ion battery. The core of the functional material for diaphragm comprises a composite inorganic material, and the shell comprises resin; the composite inorganic material comprises M / Li2O composite layered material, the M / Li2O composite layered material is mainly prepared by in-situ reaction of metallic lithium and layered double metal oxide containing M, the surface of the M / Li2O composite layered material has a composite of oxides mainly composed of Li2O and M, and M comprises Co, Fe or Mn. In the preheating process of battery preparation, the shell material in the functional material for diaphragm softens and is bonded with the positive electrode sheet and / or the negative electrode sheet, at the same time, the shell is broken by preheating, the M / Li2O composite layered material in the core is exposed, has good stability and has the effect of supplementing lithium, is transferred to the surface of the positive electrode sheet and / or the negative electrode sheet, and can realize prelithiation of the positive electrode sheet and / or the negative electrode sheet.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a functional material for a separator, a method for preparing the same, a separator, and a lithium-ion battery. Background Technology

[0002] The initial efficiency (AQI) of lithium-ion batteries plays a crucial role in battery performance, serving as an important indicator of actual lithium intercalation and discharge performance. Improving AQI is essential for enhancing overall battery performance. One method to improve AQI is pre-lithiation, which provides an additional lithium source to compensate for lithium loss during the first charge and discharge cycle, mitigating AQI issues and ultimately improving battery capacity and cycle stability. Currently, battery performance can be improved through pre-lithiation treatments of both cathode and anode materials. Cathode pre-lithiation involves adding active lithium to the cathode to compensate for irreversible capacity loss during the first charge and discharge cycle; common methods include additives and over-lithiated cathode materials. Anode pre-lithiation stores a portion of lithium in the anode to compensate for lithium loss due to irreversible capacity loss; main methods include direct lithium metal contact, electrochemical pre-lithiation, addition of lithium-containing active materials, and chemical pre-lithiation.

[0003] However, existing cathode pre-lithiation technologies suffer from poor stability of pre-lithiation agents during synthesis. For example, the lithium source for lithium-rich additives like Li₂CuO₂ / Li₂CoO₂ is typically LiOH and Li₂CO₃. LiOH is unstable in air, while Li₂CO₃ generates gas during battery fabrication, affecting battery performance. Binary lithium compounds like Li₂O₂ require activation at a high voltage of 4.77V for pre-lithiation, which may lead to electrolyte decomposition. Anode pre-lithiation agents, such as lithium metal powder, have high chemical reactivity and are difficult to process. Strong reducing solvents like 1,2-dimethoxyethane (DME) or tetrahydrofuran (THF) are used for anode chemical pre-lithiation with lithium metal and naphthalene (Li-Naph). However, DME and THF are highly flammable, posing potential risks during battery manufacturing.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a functional material for separators. During the preheating process in battery fabrication, the shell material of this functional material softens and adheres to the positive and / or negative electrode. Simultaneously, the shell cracks during preheating, exposing the M / Li₂O composite layered material in the core. This material exhibits lithium replenishment and good stability, and its transfer to the surface of the positive and / or negative electrode enables pre-lithiation of the electrode. This invention solves the problems of poor material stability of pre-lithiation agents in existing technologies, the need for activation at a high voltage of 4.77V leading to electrolyte decomposition, the high chemical reactivity of lithium metal powder resulting in difficult processing, and the high flammability of DME and THF-based chemical pre-lithiation reagents posing potential hazards.

[0006] A second objective of this invention is to provide a method for preparing a functional material for a diaphragm.

[0007] A third objective of this invention is to provide a diaphragm.

[0008] The fourth objective of this invention is to provide a lithium-ion battery.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] This invention first provides a functional material for membranes, which has a core-shell structure. The core of the core-shell structure comprises a composite inorganic material, and the shell comprises a resin. The composite inorganic material comprises an M / Li2O composite layered material, which is mainly prepared by in-situ reaction of lithium metal and a layered bimetallic oxide containing M. The surface of the M / Li2O composite layered material has a composite material whose main components are oxides of Li2O and M, wherein M includes Co, Fe, or Mn.

[0011] Furthermore, the median particle size D of the M / Li2O composite layered material, the softening temperature t of the resin, the thickness d of the shell, the preheating temperature T after the electrode assembly is formed by the diaphragm containing the functional material for the diaphragm and the negative and positive electrodes, and the preheating time m after the electrode assembly is formed by the diaphragm containing the functional material for the diaphragm and the negative and positive electrodes satisfy the following relationships: 0.25≤12t / mT≤0.6, 4.5≤2d / T+3D≤8.

[0012] Furthermore, the median particle size D of the M / Li2O composite layered material is 0.5~1μm.

[0013] Furthermore, the softening temperature t of the resin is 60~80℃.

[0014] Furthermore, the thickness d of the shell is 100~200nm.

[0015] Furthermore, the preheating temperature T after the diaphragm containing the aforementioned functional material for the diaphragm is formed into an electrode assembly with a negative electrode and a positive electrode is 70~90℃.

[0016] Furthermore, the preheating time m after the diaphragm containing the functional material for the diaphragm is made into an electrode assembly with negative and positive electrodes is 20~40 min.

[0017] Furthermore, the layered bimetallic oxide also includes a metallic element Q in addition to M, wherein Q includes Mg, Ni, Zn or Al.

[0018] Furthermore, during the in-situ reaction, the molar ratio of the layered bimetallic oxide to the lithium metal is 0.05 to 1:1.

[0019] Furthermore, the temperature of the in-situ reaction is 185~250℃.

[0020] Furthermore, the in-situ reaction time is 1 to 6 hours.

[0021] Further, the resin includes at least one selected from polyethylene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polystyrene-n-butyl acrylate copolymer, and epoxy resin.

[0022] The present invention also provides a method for preparing the above-mentioned functional material for diaphragms, comprising the following steps: mixing composite inorganic materials with resin and heating.

[0023] Furthermore, the heating temperature is 100~200℃.

[0024] Furthermore, the heating time is 3-4 hours.

[0025] The present invention also provides a diaphragm, the diaphragm comprising a base membrane and a functional coating disposed on at least one surface of the base membrane, the functional coating comprising the above-mentioned functional material for diaphragms.

[0026] Furthermore, the thickness of the functional coating is 2~4μm.

[0027] Furthermore, the functional coating also includes at least one of a thickener, an aqueous binder, a dispersant, and a solid electrolyte material.

[0028] Furthermore, the mass ratio of the functional material for the diaphragm, the thickener, the aqueous binder, the dispersant, and the solid electrolyte material in the functional coating is 88~92:1~2:5~8:0.1~1:0.5~1.5.

[0029] Furthermore, the thickener includes at least one of sodium carboxymethyl cellulose, xanthan gum, starch, and sodium phosphate.

[0030] Furthermore, the water-based adhesive includes at least one of polymethyl methacrylate, polybutyl methacrylate, and styrene-butadiene latex.

[0031] Furthermore, the dispersant includes at least one of sodium polyacrylate, ammonium polyacrylate, and sodium pyrophosphate.

[0032] Furthermore, the solid electrolyte material includes at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium titanium oxide.

[0033] Furthermore, the particle size D50 of the solid electrolyte material is 0.5~1μm.

[0034] Furthermore, the diaphragm is mainly made by coating the base membrane with a slurry containing the functional material for the diaphragm.

[0035] The present invention also provides a lithium-ion battery comprising the above-described separator.

[0036] Furthermore, the lithium-ion battery is mainly formed by stacking the separator, negative electrode and positive electrode into an electrode assembly, and then sequentially undergoing preheating, encapsulation, electrolyte injection, precharging and formation.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The functional material for separators provided by the present invention softens and bonds to the positive and / or negative electrode after preheating during the lithium-ion battery or cell processing process. At the same time, the shell is cracked after preheating, exposing the M / Li2O composite layered material in the core. The M / Li2O composite layered material has a lithium replenishing effect. The M / Li2O composite layered material (as a lithium replenishing agent) can be transferred to the positive and / or negative electrode without the need for pressure, thereby achieving pre-lithiation of the positive and / or negative electrode, thus improving the first efficiency and cycle stability of the battery.

[0039] (2) By controlling the parameters to satisfy the relationship 0.25≤12t / mT≤0.6 and 4.5≤2d / T+3D≤8, the present invention can ensure that the transfer rate Y of the functional coating containing the functional material for the separator is greater than 97%, and the first efficiency of the separator containing the functional material for the separator after being assembled into a battery is greater than 88%. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0041] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" 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, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0042] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0043] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0044] In a first aspect, the present invention provides a transferable functional material for a separator with lithium replenishment function, the functional material for a separator having a core-shell structure, wherein the core of the core-shell structure comprises a composite inorganic material, and the shell of the core-shell structure comprises a resin.

[0045] The composite inorganic material includes an M / Li₂O composite layered material. The M / Li₂O composite layered material is mainly prepared by in-situ reaction of metallic lithium and a layered bimetallic oxide containing M. Furthermore, the surface of the M / Li₂O composite layered material has a composite material whose main components are Li₂O and M oxides, wherein M includes Co, Fe, or Mn.

[0046] It is understandable that layered bimetallic oxides (LDOs) are a class of layered inorganic materials composed of two metallic elements, typically obtained by calcining layered bimetallic hydroxide (LDH) precursors. The interlayers of LDOs contain abundant metal ions, which react with molten Li to synthesize in situ a composite material consisting mainly of Li₂O and M oxides, yielding an M / Li₂O composite layered material.

[0047] The composite material (mainly composed of Li2O and M oxides) on the surface of the M / Li2O composite layered material has lithium replenishment function. The M oxide includes Co3O4, Mn3O4, or Fe3O4.

[0048] The shell acts as an adhesive layer, and its composition consists of materials with adhesive properties, such as resin.

[0049] The functional material for separators provided by this invention softens and bonds to the positive and / or negative electrode sheets after preheating during the lithium-ion battery or cell processing. Simultaneously, the shell cracks during preheating, exposing the M / Li2O composite layered material in the core. The M / Li2O composite layered material has a lithium replenishing effect, and the M / Li2O composite layered material (as a lithium replenishing agent) can be transferred to the positive and / or negative electrode sheets without the need for pressure, thereby achieving pre-lithiation of the positive and / or negative electrode sheets and improving the battery's initial efficiency and cycle stability.

[0050] In some specific embodiments, the median particle size D of the M / Li2O composite layered material, the softening temperature t of the resin, the thickness d of the shell, the preheating temperature T after the electrode assembly is formed by the diaphragm containing the functional material for the diaphragm and the negative and positive electrodes, and the preheating time m after the electrode assembly is formed by the diaphragm containing the functional material for the diaphragm and the negative and positive electrodes satisfy the following relationship: 0.25≤12t / mT≤0.6, and 4.5≤2d / T+3D≤8.

[0051] Among them, the value of 12t / mT includes, but is not limited to, any one of 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6 or any range between any two; the value of 2d / T+3D includes, but is not limited to, any one of 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 or any range between any two.

[0052] By controlling the parameters to satisfy the above relationship, this invention can ensure that the transfer rate Y of the functional coating containing the above-mentioned functional material for separators is ≥97%, and that the first-time efficiency of the separator containing the functional material for separators after being assembled into a battery is >88%. The transfer rate is the ratio of the coverage area of ​​the functional coating on the positive electrode to the area of ​​the positive electrode.

[0053] Specifically, satisfying the above relationships can effectively improve the transfer rate Y of the functional coating, and at the same time, more materials with lithium replenishment function can be transferred to the electrode, which is beneficial to improving the first efficiency of the battery. The particle size of the M / Li2O composite layered material and the thickness of the resin affect the transfer rate Y; if the particle size of the M / Li2O composite layered material is too small and the resin is too thick, insufficient preheating temperature will affect the softening and cracking of the resin, causing the composite to fail to transfer to the electrode, and the lithium replenishment function material cannot play its role, affecting the first efficiency of the battery.

[0054] In some specific embodiments, the median particle size D of the M / Li2O composite layered material is 0.5~1μm, including but not limited to point values ​​or ranges between any one of 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, and 1μm. This is beneficial for improving the transfer rate Y and heat resistance of the functional coating.

[0055] In some specific embodiments, the softening temperature t of the resin is 60~80℃, including but not limited to any one of 60℃, 65℃, 70℃, 75℃, and 80℃, or a range between any two. The softening temperature of the resin determines the melting temperature and the bond strength.

[0056] In some specific embodiments, the thickness d of the shell is 100~200nm, including but not limited to a point value or a range between any two of 100nm, 120nm, 130nm, 150nm, 160nm, 180nm, and 200nm. This allows the shell to soften easily when heated, providing strong adhesion, while also being easily cracked. After transfer, the lithium-replenishing material can be exposed, thereby improving the battery's initial efficiency.

[0057] In some specific embodiments, the preheating temperature T after the separator containing the aforementioned functional material for the separator is used to form the electrode assembly with the negative and positive electrode sheets is 70~90℃, including but not limited to any one of 70℃, 75℃, 80℃, 85℃, and 90℃, or any range between two of them. This softens the shell and facilitates adhesion and transfer.

[0058] In some specific embodiments, the preheating time m after the separator containing the functional material for the separator is used to form the electrode assembly with the negative and positive electrode sheets is 20~40 min, including but not limited to any one of 20 min, 25 min, 30 min, 35 min, and 40 min, or any range between two values. This softens the shell and facilitates adhesion and transfer.

[0059] In some specific embodiments, the layered bimetallic oxide further includes a metal element Q in addition to M, wherein Q includes Mg, Ni, Zn, or Al. That is, the bimetallic elements in the layered bimetallic oxide are M and Q, wherein element M undergoes an in-situ reaction with lithium metal to generate a complex of oxides whose main components are Li2O and M.

[0060] In some specific embodiments, during the in-situ reaction, the molar ratio of the layered bimetallic oxide to the lithium metal is 0.05 to 1:1, including but not limited to any one of the following values ​​or a range between any two: 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, and 1:1. This ensures the amount of lithium replenishment transferred to the electrode, thereby effectively improving the battery's initial efficiency.

[0061] In some specific embodiments, the in-situ reaction is carried out under an inert atmosphere, such as an argon atmosphere or a nitrogen atmosphere, but is not limited thereto.

[0062] In some specific embodiments, the preparation method of the M / Li2O composite layered material specifically includes: mixing and stirring a layered bimetallic oxide containing M with molten lithium metal to carry out an in-situ synthesis reaction.

[0063] In some specific embodiments, the layered bimetallic oxide containing M can be prepared by any preparation method commonly used in the art, such as: directionally growing the metal precursor in a solvent by hydrothermal method, forming a coprecipitate by adjusting the pH, and forming a layered bimetallic oxide after high-temperature calcination.

[0064] In some specific embodiments, the temperature of the in-situ reaction is 185~250℃, including but not limited to any one of 185℃, 190℃, 195℃, 200℃, 210℃, 220℃, 230℃, 240℃, and 250℃, or a range between any two.

[0065] In some specific implementations, the in-situ reaction time is 1 to 6 hours, including but not limited to any one of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours, or any range between two of them.

[0066] In some specific embodiments, the resin includes at least one selected from polyethylene, polyvinyl acetate, ethylene-vinyl acetate copolymer (EVA), polystyrene-n-butyl acrylate copolymer, and epoxy resin.

[0067] Secondly, the present invention provides a method for preparing the above-mentioned functional material for diaphragms, comprising the following steps: mixing composite inorganic materials with resin and heating to a molten state, stirring evenly, and cooling to obtain the functional material for diaphragms.

[0068] The preparation method is simple, easy to implement, and safe, making it suitable for mass production.

[0069] In some specific embodiments, the heating temperature is 100~200℃, including but not limited to any one of 100℃, 120℃, 130℃, 150℃, 160℃, 180℃, 200℃ or any range between two of them.

[0070] In some specific implementations, the heating time is 3 to 4 hours, for example, 3 hours, 3.5 hours or 4 hours.

[0071] The thickness of the shell can be adjusted by controlling the heating temperature and time, as well as the amount of resin added.

[0072] In some specific implementations, the mass ratio of the composite inorganic material to the resin is 1.2 to 3:1, for example, 1.5:1, 2.0:1 or 2.5:1.

[0073] Thirdly, the present invention provides a diaphragm, the diaphragm comprising a base membrane and a functional coating disposed on at least one surface of the base membrane, the functional coating comprising the aforementioned functional material for the diaphragm.

[0074] After preheating during battery fabrication, the functional coating can transfer the M / Li2O composite layered material with lithium replenishment function to the positive and negative electrode surfaces, thereby simultaneously achieving pre-lithiation of the positive and negative electrodes.

[0075] In some specific implementations, batteries using this separator can achieve an initial efficiency (first coulombic efficiency) of over 90% and improve cycle performance by at least 2%.

[0076] In some specific embodiments, the thickness of the functional coating is 2~4μm, including but not limited to a point value or a range between any two of 2μm, 2.2μm, 2.5μm, 2.8μm, 3μm, 3.3μm, 3.5μm, 3.8μm, and 4μm. This coating thickness, after transfer, can meet the thermal safety and electrical performance requirements of the battery.

[0077] In some specific embodiments, the functional coating further includes at least one of a thickener, an aqueous binder, a dispersant, and a solid electrolyte material.

[0078] In some specific embodiments, the mass ratio of the functional material for the diaphragm, the thickener, the aqueous binder, the dispersant, and the solid electrolyte material in the functional coating is 88~92 (e.g., 89, 90, or 91): 1~2 (e.g., 1.2, 1.5, or 1.8): 5~8 (e.g., 5.5, 6, 6.5, 7, or 7.5): 0.1~1 (e.g., 0.3, 0.5, or 0.8): 0.5~1.5 (e.g., 0.7, 1, or 1.3); preferably 90:1.5:7:0.5:1.

[0079] In some specific embodiments, the thickener includes at least one of sodium carboxymethyl cellulose, xanthan gum, starch, and sodium phosphate.

[0080] In some specific embodiments, the water-based adhesive includes at least one of polymethyl methacrylate, polybutyl methacrylate, and styrene-butadiene latex.

[0081] In some specific embodiments, the dispersant includes at least one of sodium polyacrylate, ammonium polyacrylate, and sodium pyrophosphate.

[0082] In some specific embodiments, the solid electrolyte material includes at least one of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium titanium oxide. Adding the above-mentioned solid electrolyte material can improve the ionic conductivity of the membrane.

[0083] In some specific embodiments, the particle size D50 of the solid electrolyte material is 0.5~1μm, for example 0.6μm, 0.7μm, 0.8μm or 0.9μm.

[0084] In some specific embodiments, the diaphragm is mainly made by coating the base membrane with a slurry containing the functional material for the diaphragm.

[0085] In some specific embodiments, the preparation method of the diaphragm includes: uniformly mixing a diaphragm functional material, a thickener, an aqueous binder, a dispersant, a solid electrolyte material, and a solvent (e.g., deionized water) to obtain a slurry, wherein the amount of solvent added is such that the solid content of the slurry is 30% to 40%, preferably 35%. Then, the slurry is coated onto the surface of a PE base film with a thickness of 5 to 12 μm by gravure transfer coating, and then dried to form a diaphragm with a functional coating.

[0086] Fourthly, the present invention provides a lithium-ion battery comprising the above-described separator.

[0087] This lithium-ion battery has advantages such as high initial coulombic efficiency and good cycle performance.

[0088] In some specific embodiments, the lithium-ion battery further includes a negative electrode, a positive electrode, and an electrolyte, but the present invention does not limit this.

[0089] In some specific embodiments, the lithium-ion battery is mainly formed by stacking the separator, negative electrode and positive electrode into an electrode assembly, and then sequentially undergoing preheating, encapsulation, liquid injection, precharging and formation.

[0090] In some specific embodiments, the preparation method of the lithium-ion battery specifically includes: (1) using lithium iron phosphate as the positive electrode active material, mixing lithium iron phosphate, conductive agent (Super P) and PVDF (polyvinylidene fluoride) in a mass ratio of 96.5:1.5:2 to obtain a positive electrode slurry, coating the positive electrode slurry onto carbon-coated aluminum foil to obtain a positive electrode sheet. (2) using artificial graphite as the negative electrode active material, mixing artificial graphite, CMC (carboxymethyl cellulose), conductive agent (Super P) and SBR (styrene-butadiene rubber) in a mass ratio of 95.5:1.5:1.0:2 to obtain a negative electrode slurry, coating the negative electrode slurry onto copper foil, and processing it to obtain a negative electrode sheet. (3) stacking the above-mentioned separator containing functional coating, negative electrode sheet and positive electrode sheet into an electrode assembly in the form of a stack, and then preheating it. (4) using a soft pack form to encapsulate the prepared electrode assembly, and then injecting electrolyte. (5) The cells are pre-charged and formed to obtain lithium-ion batteries.

[0091] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0092] Example 1

[0093] The preparation method of the functional material for the diaphragm provided in this embodiment includes: (1) melting lithium metal foil at 185°C to obtain molten lithium metal; mixing layered bimetallic oxide (Zn-Co oxide, i.e., Zn-Co LDO) with molten lithium metal under an argon atmosphere and stirring evenly to carry out an in-situ reaction, wherein the temperature of the in-situ reaction is 200°C, the time of the in-situ reaction is 2h, the molar ratio of layered bimetallic oxide to lithium metal is 0.5:1, to obtain M / Li2O composite layered material, the surface of which has a composite mainly composed of Li2O and Co3O4, and the median particle size D of which is 0.8μm. (2) mixing the above M / Li2O composite layered material with ethylene-vinyl acetate copolymer (i.e., resin, whose softening temperature t is 70°C) and heating to a molten state, stirring evenly, and cooling to obtain the functional material for the diaphragm; wherein the heating temperature is 150°C and the heating time is 3.5h. The functional material for the diaphragm has a core-shell structure, wherein the core is an M / Li2O composite layered material and the shell is an ethylene-vinyl acetate copolymer with a shell thickness d of 150 nm.

[0094] The method for preparing the diaphragm provided in this embodiment includes: weighing the above-mentioned functional material for diaphragms, thickener (sodium carboxymethyl cellulose), aqueous binder (methyl propylene polypropylene), dispersant (sodium pyrophosphate), and solid electrolyte material (lithium aluminum titanium phosphate with a particle size D50 of 0.8 μm) in a mass ratio of 90:1.5:7:0.5:1, and adding deionized water to mix evenly to obtain a slurry, wherein the amount of solvent added is such that the solid content of the slurry is 35%. Then, the slurry is coated onto the surface of a PE base film with a thickness of 9 μm by gravure transfer coating, and then dried to obtain a diaphragm with a functional coating, wherein the thickness of the functional coating is 3 μm.

[0095] The method for preparing a lithium-ion battery provided in this embodiment includes: (1) using lithium iron phosphate as the positive electrode active material, mixing lithium iron phosphate, conductive agent (Super P) and PVDF (polyvinylidene fluoride) in a mass ratio of 96.5:1.5:2 to obtain a positive electrode slurry, coating the positive electrode slurry onto a carbon-coated aluminum foil, and drying to obtain a positive electrode sheet. (2) using artificial graphite as the negative electrode active material, mixing artificial graphite, CMC (carboxymethyl cellulose), conductive agent (Super P) and SBR (styrene-butadiene rubber) in a mass ratio of 95.5:1.5:1.0:2 to obtain a negative electrode slurry, coating the negative electrode slurry onto a copper foil, and drying to obtain a negative electrode sheet. (3) stacking the above-mentioned separator containing the functional coating, the above-mentioned negative electrode sheet and the above-mentioned positive electrode sheet into an electrode assembly in the form of a stack, and then preheating, wherein the preheating temperature T is 80°C and the preheating time m is 30 min. (4) The prepared electrode assembly is packaged in a soft-pack form and then injected with electrolyte. (5) The cell is pre-charged and formed to obtain a lithium-ion battery.

[0096] Example 2

[0097] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in Example 1, except that in step (1), the molar ratio of layered bimetallic oxide and lithium metal is 0.05:1.

[0098] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0099] Example 3

[0100] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in Example 1, except that in step (1), the molar ratio of layered bimetallic oxide and metallic lithium is 1:1.

[0101] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0102] Example 4

[0103] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in Example 1, except that: in step (1), the median particle size D of the M / Li2O composite layered material is 0.5 μm.

[0104] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0105] Example 5

[0106] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in Example 1, except that: in step (1), the median particle size D of the M / Li2O composite layered material is 1.0 μm.

[0107] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0108] Example 6

[0109] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in embodiment 1, except that the thickness d of the shell is 100 nm in step (2).

[0110] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0111] Example 7

[0112] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in embodiment 1, except that the thickness d of the shell is 200 nm in step (2).

[0113] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0114] Example 8

[0115] The preparation method of the diaphragm functional material provided in this embodiment is basically the same as that in Example 1, except that in step (2), polystyrene-butyl acrylate copolymer resin is used, and its softening temperature t is 60℃.

[0116] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0117] Example 9

[0118] The preparation method of the diaphragm functional material provided in this embodiment is basically the same as that in Example 1, except that in step (2), polyvinyl acetate resin is used, and its softening temperature t is 80℃.

[0119] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0120] Example 10

[0121] The separator obtained in Example 1 was used to prepare a lithium-ion battery according to the method of Example 1, except that the preheating temperature T in step (3) was 70°C.

[0122] Example 11

[0123] The separator obtained in Example 1 was used to prepare a lithium-ion battery according to the method of Example 1, except that the preheating temperature T in step (3) was 90°C.

[0124] Example 12

[0125] The separator obtained in Example 1 was used to prepare a lithium-ion battery according to the method of Example 1, except that the preheating time m in step (3) was 20 min.

[0126] Example 13

[0127] The separator obtained in Example 1 was used to prepare a lithium-ion battery according to the method of Example 1, except that the preheating time m in step (3) was 40 min.

[0128] Example 14

[0129] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in Example 8, except that: in step (2), the thickness d of the shell is 200 nm.

[0130] Using the functional material for diaphragms obtained in this embodiment, a diaphragm is made according to the method and parameters of Example 8.

[0131] The separator prepared in this embodiment is used to prepare a lithium-ion battery according to the method of Example 8, except that in step (3), the preheating temperature T is 90°C and the preheating time m is 40 min.

[0132] Example 15

[0133] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in embodiment 5, except that: in step (2), the thickness d of the shell is 200 nm.

[0134] Using the functional material for diaphragms obtained in this embodiment, a diaphragm is made according to the method and parameters of Example 5.

[0135] Using the separator prepared in this embodiment, a lithium-ion battery is prepared according to the method of Example 5, except that: in step (3), the preheating temperature T is 70°C.

[0136] Example 16

[0137] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in Example 1, except that in step (1), the layered bimetallic oxide is replaced with Ni-Fe LOD, that is, the surface of the M / Li2O composite layered material has a composite with Li2O and Fe3O4 as the main components.

[0138] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0139] Example 17

[0140] The preparation method of the functional material for the diaphragm provided in this embodiment is basically the same as that in Example 1, except that in step (1), the layered bimetallic oxide is replaced with Ni-Mn LDO, that is, the surface of the M / Li2O composite layered material has a composite with Li2O and Mn3O4 as the main components.

[0141] Using the functional material for separators prepared in this embodiment, separators and lithium-ion batteries are manufactured according to the method and parameters of Example 1.

[0142] Comparative Example 1

[0143] The preparation method of the functional material for the diaphragm provided in this comparative example is basically the same as that in Example 1, except that: lithium metal was not added in step (1) (i.e., no in-situ synthesis reaction occurred).

[0144] Using the functional material for separators prepared in this comparative example, separators and lithium-ion batteries were manufactured according to the method and parameters of Example 1.

[0145] Comparative Example 2

[0146] The preparation method of the diaphragm functional material provided in this comparative example is basically the same as that in Example 1, except that the ethylene-vinyl acetate copolymer is replaced with an equal mass of PVDF (polyvinylidene fluoride). That is, the shell material of the diaphragm functional material prepared in this comparative example is PVDF.

[0147] Using the functional material for separators prepared in this comparative example, separators and lithium-ion batteries were manufactured according to the method and parameters of Example 1.

[0148] Comparative Example 3

[0149] The preparation method of the diaphragm provided in this comparative example is basically the same as that in Example 1, except that the functional material of the diaphragm is replaced with an equal mass of PVDF (polyvinylidene fluoride). That is, the diaphragm prepared in this comparative example does not contain M / Li2O composite layered material, and the main material in the functional coating of the diaphragm is PVDF.

[0150] Using the separator prepared in this comparative example, a lithium-ion battery was manufactured according to the method and parameters of Example 1.

[0151] The key parameters in each embodiment and comparative example, as well as the values ​​of 12t / mT and 2d / T+3D, are shown in Table 1.

[0152] Table 1. Comparison of parameters in each embodiment and comparative example

[0153]

[0154] Experimental Example

[0155] The separators and lithium-ion batteries prepared in each embodiment and each comparative example were tested respectively. The test methods are as follows: (1) Test method for bonding strength of functional coating to electrode: The separators with functional coating prepared in each embodiment and each comparative example were stacked and hot-pressed with the positive electrode. The hot-pressing pressure was 1MPa, the hot-pressing temperature was 70℃, and the hot-pressing time was 10s. After hot pressing, they were cut into strips with a width of 15mm and a length of 100mm. The test equipment was a universal tensile testing machine with a test speed of 150mm / min and an effective test width of 15mm. The bonding strength = F / h, where F is the average value of the stable and uniform force during the test, in N; h is the effective bonding width between the separator and the positive electrode, in m; and the bonding strength unit is N / m. (2) Test method for first efficiency: The lithium-ion batteries were charged and discharged using the constant current and constant voltage (CC / CV) method. The voltage, current and capacity data during the charging and discharging process were recorded. The first efficiency was calculated from the first charge and discharge capacity of the battery. (3) Cyclic performance test method: At 25℃ and 45℃, the capacitor was charged at a constant current of 1C to 3.65V, charged at a constant voltage of 0.05C, and discharged at a constant current of 1C to 2.8V. The number of cycles was 1000, and the capacity retention rate was compared. The test results are shown in Table 2.

[0156] Table 2 Performance test results of the separators and lithium-ion batteries in each embodiment and comparative example.

[0157]

[0158] As can be seen from Tables 1 and 2, the addition of functional materials for the separator in each embodiment provides lithium replenishment and good stability, while also achieving pre-lithiation of the positive and negative electrodes, thereby improving the battery's initial efficiency and cycle stability.

[0159] Furthermore, Examples 1-13 satisfy the relationships 0.25≤12t / mT≤0.6 and 4.5≤2d / T+3D≤8, resulting in high initial efficiency and capacity retention. However, Examples 14-15 do not satisfy the relationships 0.25≤12t / mT≤0.6 and 4.5≤2d / T+3D≤8, leading to a decrease in the initial efficiency and capacity retention of the battery.

[0160] In contrast, in Comparative Example 1, the layered bimetallic oxide did not react in situ with lithium metal, meaning that a complex of oxides mainly composed of Li2O and M was not formed on the surface of the layered bimetallic oxide, resulting in a significant decrease in the battery's initial efficiency and capacity retention.

[0161] Comparative Example 2: Because the shell material is PVDF, PVDF has poor adhesion than resin and low transfer rate, the material with lithium replenishment function cannot be transferred to the electrode, resulting in a reduction in lithium replenishment function and a significant decrease in the battery's initial efficiency and capacity retention rate.

[0162] Comparative Example 3 showed a significant decrease in the battery's initial efficiency and capacity retention rate due to the absence of M / Li2O composite layered material in the separator.

[0163] In summary, the functional material and separator provided by this invention soften and bond with the positive and negative electrode plates during the preheating process of battery preparation. At the same time, the shell material of the functional material softens and bonds with the positive and negative electrode plates during preheating. Simultaneously, the shell cracks after preheating, exposing the M / Li2O composite layered material in the core. This material has a lithium replenishment function and good stability. When transferred to the surface of the positive and negative electrode plates, it can simultaneously achieve pre-lithiation of the positive and negative electrode plates, thereby improving the battery's first efficiency and cycle stability.

[0164] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A functional material for a diaphragm, characterized by, The functional material for the separator has a core-shell structure, the core of the core-shell structure comprises a composite inorganic material, and the shell of the core-shell structure comprises a resin; The composite inorganic material comprises an M / Li2O composite layered material, the M / Li2O composite layered material is prepared by in-situ reaction of lithium and a layered double metal oxide containing M, and the surface of the M / Li2O composite layered material has a composite of oxides mainly composed of Li2O and M, wherein M comprises Co, Fe or Mn; The softening temperature t of the resin is 60-80°C; The resin comprises at least one of polyethylene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polystyrene-n-butyl acrylate copolymer and epoxy resin.

2. The functional material for a diaphragm according to claim 1, wherein The median particle size D of the M / Li2O composite layered material, the softening temperature t of the resin, the thickness d of the shell, the preheating temperature T after the separator containing the functional material for the separator is used to make a polar group with a negative electrode sheet and a positive electrode sheet, and the preheating time m after the separator containing the functional material for the separator is used to make a polar group with a negative electrode sheet and a positive electrode sheet satisfy the following relationship: 0.25≤12t / mT≤0.6, 4.5≤2d / T+3D≤8.

3. The functional material for a diaphragm according to claim 2, wherein At least one of the following conditions is met: (1) the median particle size D of the M / Li2O composite layered material is 0.5-1 μm; (2) the thickness d of the shell is 100-200 nm; (3) the preheating temperature T after the separator containing the functional material for the separator is used to make a polar group with a negative electrode sheet and a positive electrode sheet is 70-90°C; (4) the preheating time m after the separator containing the functional material for the separator is used to make a polar group with a negative electrode sheet and a positive electrode sheet is 20-40 min.

4. The functional material for a diaphragm according to claim 1, wherein At least one of the following conditions is met: (1) the layered double metal oxide further comprises a metal element Q in addition to M, wherein Q comprises Mg, Ni, Zn or Al; (2) the molar ratio of the layered double metal oxide to the lithium in the process of the in-situ reaction is 0.05-1:1; (3) the temperature of the in-situ reaction is 185-250°C, and the time of the in-situ reaction is 1-6 h.

5. The method of producing a functional material for a separator according to any one of claims 1 to 4, characterized by, The method comprises the following steps: mixing the composite inorganic material and the resin and heating.

6. The method of claim 5, wherein the functional material for a diaphragm is prepared by the steps of: The temperature of the heating is 100-200°C, and the time of the heating is 3-4 h.

7. A diaphragm characterized by, The separator comprises a base film and a functional coating layer provided on at least one surface of the base film, and the functional coating layer comprises the functional material for the separator according to any one of claims 1-4.

8. The separator of claim 7, wherein At least one of the following conditions is met: (1) the thickness of the functional coating layer is 2-4 μm; (2) the functional coating further comprises at least one of a thickening agent, a water-based adhesive, a dispersing agent and a solid electrolyte material; the mass ratio of the separator functional material, the thickening agent, the water-based adhesive, the dispersing agent and the solid electrolyte material in the functional coating is 88-92: 1-2: 5-8: 0.1-1: 0.5-1.5; the thickening agent comprises at least one of sodium carboxymethyl cellulose, xanthan gum, starch and sodium phosphate; the water-based adhesive comprises at least one of polyacrylate, polybutyl methacrylate and butadiene styrene latex; the dispersing agent comprises at least one of sodium polyacrylate, ammonium polyacrylate and sodium pyrophosphate; the solid electrolyte material comprises at least one of lithium aluminum titanium phosphate, lithium lanthanum zirconium oxide and lithium lanthanum zirconium titanium oxide; the particle size D50 of the solid electrolyte material is 0.5-1 μm; (3) the separator is mainly prepared by coating the slurry containing the separator functional material on the base film.

9. A lithium-ion battery, characterized by The lithium ion battery comprises the separator as claimed in claim 7 or 8. The lithium ion battery is mainly prepared by stacking the separator, a negative electrode sheet and a positive electrode sheet into a pole group, and then sequentially performing preheating, packaging, liquid injection, pre-charging and formation.

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