Functional material for diaphragm, preparation method of functional material, diaphragm and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a functional material for a diaphragm, a preparation method of the functional material, the diaphragm and a lithium ion battery. The core of the functional material for the diaphragm comprises a composite inorganic material, and the shell comprises resin; the composite inorganic material comprises an M / Li2O composite layered material, the M / Li2O composite layered material is mainly prepared from metal lithium and an M-containing layered bimetallic oxide through an in-situ reaction, the surface of the M / Li2O composite layered material is provided with a compound of an oxide mainly comprising 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 the diaphragm is softened and bonded with the positive plate and / or the negative plate, meanwhile, the shell is broken through preheating, and the M / Li2O composite layered material in the core is exposed, has a lithium supplementing effect and is good in stability, and is transferred to the surface of the positive plate and / or the negative plate, so that the lithium supplementing effect is improved. The pre-lithiation of the positive plate and / or the negative plate can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a functional material for a separator, a preparation method thereof, a separator and a lithium ion battery. BACKGROUND

[0002] The initial efficiency of a lithium ion battery plays a key role in battery performance and is an important indicator of the actual lithium intercalation degree and discharge performance. In order to improve the overall performance of the battery, it is crucial to improve the initial efficiency. The method for improving the initial efficiency is pre-lithiation, that is, to provide an additional lithium source to compensate for the loss of lithium during the first charge and discharge process, to reduce the problem of low initial efficiency, and ultimately to improve the battery capacity and cycle stability. Currently, the battery performance can be improved by pre-lithiation of positive electrode materials and negative electrode materials. Positive electrode pre-lithiation adds active lithium to the positive electrode to compensate for the irreversible capacity loss during the first charge and discharge process. Common methods include additives and over-lithiated positive electrode materials. Negative electrode pre-lithiation stores a portion of lithium in the negative electrode to compensate for the loss of lithium caused by irreversible capacity. The main methods include direct contact with lithium metal, electrochemical pre-lithiation, lithium-containing active material addition, and chemical pre-lithiation.

[0003] However, the existing positive electrode pre-lithiation has poor stability of the pre-lithium material in synthesis. For example, the lithium source in the preparation process of the lithium-rich additive Li2CuO2 / Li2CoO2 is usually LiOH and Li2CO3. LiOH is unstable in air, and Li2CO3 generates gas during battery preparation, affecting battery performance. Binary lithium compounds such as Li2O2 need to be activated at a high voltage of 4.77V to perform pre-lithiation, which may cause decomposition of the electrolyte. The negative electrode pre-lithium agent such as metal lithium powder has high chemical reactivity, and the processing operation is difficult. Strongly reducing solvents such as 1,2-dimethoxyethane (DME) or tetrahydrofuran (THF) are used with metal lithium and naphthalene (Li-Naph) for negative electrode chemical pre-lithiation. However, DME and THF, which are chemical pre-lithiation reagents, are highly flammable, which poses a risk during battery manufacturing.

[0004] Therefore, the present application is proposed. SUMMARY

[0005] The first object of the present application is to provide a functional material for a separator, in which a shell material softens and adheres to a positive electrode sheet and / or a negative electrode sheet during a preheating process of battery preparation, and at the same time, the shell is broken by preheating, so that the M / Li2O composite layered material in the core is exposed, has a good stability and a lithium supplement effect, and can realize the prelithiation of the positive electrode sheet and / or the negative electrode sheet when transferred to the surface of the positive electrode sheet and / or the negative electrode sheet. The problems of poor material stability of the prelithiation agent in the prior art, decomposition of electrolyte caused by activation of prelithiation at a high voltage of 4.77V, high chemical reactivity of lithium metal powder leading to high difficulty in processing operation, and high flammability of DME and THF type chemical prelithiation reagents leading to hidden dangers are solved.

[0006] The second object of the present application is to provide a preparation method of a functional material for a separator.

[0007] The third object of the present application is to provide a separator.

[0008] The fourth object of the present application is to provide a lithium ion battery.

[0009] In order to achieve the above objects of the present application, the following technical solutions are adopted: The present application first provides a functional material for a separator, which 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, which is mainly prepared by in-situ reaction of lithium metal and 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 includes Co, Fe or Mn.

[0010] Further, 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 a 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 a 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.

[0011] Further, the median particle size D of the M / Li2O composite layered material is 0.5-1 μm.

[0012] Further, the softening temperature t of the resin is 60-80℃.

[0013] Further, the thickness d of the shell is 100-200 nm.

[0014] Further, the preheating temperature T of the electrode group after the separator containing the functional material for the separator is used with the negative electrode sheet and the positive electrode sheet is 70-90℃.

[0015] Further, the preheating time m of the electrode group after the separator containing the functional material for the separator is used with the negative electrode sheet and the positive electrode sheet is 20-40min.

[0016] Further, the layered double metal oxide further comprises a metal element Q in addition to M, wherein Q comprises Mg, Ni, Zn or Al.

[0017] Further, the molar ratio of the layered double metal oxide and the metal lithium in the in-situ reaction is 0.05-1:1.

[0018] Further, the temperature of the in-situ reaction is 185-250℃.

[0019] Further, the time of the in-situ reaction is 1-6h.

[0020] Further, the resin comprises at least one of polyethylene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polystyrene-n-butyl acrylate copolymer and epoxy resin.

[0021] The application further provides a preparation method of the functional material for the separator, comprising the following steps: mixing and heating the composite inorganic material and the resin.

[0022] Further, the heating temperature is 100-200℃.

[0023] Further, the heating time is 3-4h.

[0024] The application further provides a separator, which comprises a base film and a functional coating layer arranged on at least one surface of the base film, and the functional coating layer comprises the functional material for the separator.

[0025] Further, the thickness of the functional coating layer is 2-4μm.

[0026] Further, the functional coating layer further comprises at least one of thickening agent, water-based adhesive, dispersant and solid electrolyte material.

[0027] Further, the mass ratio of the functional material for the separator, the thickening agent, the water-based adhesive, the dispersant and the solid electrolyte material in the functional coating layer is 88-92:1-2:5-8:0.1-1:0.5-1.5.

[0028] Further, the thickening agent comprises at least one of sodium carboxymethyl cellulose, xanthan gum, starch and sodium phosphate.

[0029] Further, the water-based adhesive comprises at least one of polymethyl acrylate, polybutyl methacrylate and butadiene styrene latex.

[0030] Further, the dispersant comprises at least one of sodium polyacrylate, ammonium polyacrylate and sodium pyrophosphate.

[0031] Further, the solid electrolyte material comprises at least one of lithium aluminum titanium phosphate, lithium lanthanum zirconium oxide and lithium lanthanum zirconium titanium oxide.

[0032] Further, the particle size D50 of the solid electrolyte material is 0.5-1 μm.

[0033] Further, the separator is mainly prepared by coating the slurry containing the functional material for the separator on the base film.

[0034] The application further provides a lithium ion battery comprising the separator.

[0035] Further, the lithium ion battery is mainly prepared by stacking the separator, the negative electrode sheet and the positive electrode sheet into a pole group, and then sequentially undergoing preheating, packaging, liquid injection, pre-charging and formation.

[0036] Compared with the prior art, the application has the following beneficial effects: (1) The functional material for the separator provided by the application can cause the shell material to soften and adhere to the positive electrode sheet and / or the negative electrode sheet after preheating in the processing of the lithium ion battery or the battery cell, and the core M / Li2O composite layered material is exposed after the shell is broken by preheating. The M / Li2O composite layered material has a lithium supplement effect, and the M / Li2O composite layered material (as a lithium supplement agent) can be transferred to the positive electrode sheet and / or the negative electrode sheet without using pressure, thereby realizing the pre-lithiation of the positive electrode sheet and / or the negative electrode sheet, and improving the initial efficiency and cycle stability of the battery.

[0037] (2) The application can ensure that the transfer rate Y of the functional coating containing the functional material for the separator is ≥97% and the initial efficiency of the battery assembled by the separator containing the functional material for the separator is >88% by controlling the parameters to satisfy the relationship 0.25≤12t / mT≤0.6 and 4.5≤2d / T+3D≤8. DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be described clearly and completely in combination with specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased on the market.

[0039] If not specifically stated, in the present application, "first aspect", "second aspect", "third aspect", "fourth aspect" and the like are only used for description purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implying the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth" and the like only serve the purpose of non-exhaustive enumeration and description, and should be understood as not constituting a closed limitation on the quantity.

[0040] If not specifically stated, "including" and "containing" mentioned in the present application mean open-ended, and can also be closed-ended. For example, "including" and "containing" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0041] If not specifically stated, in the present application, "one or more" or "at least one" means any one, any two or any two or more of the listed items. Among them, "several" means any two or more.

[0042] In a first aspect, the present application provides a functional material for diaphragm with lithium supplementing function and transferability, the functional material for diaphragm 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.

[0043] 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. 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.

[0044] It can be understood that the layered double hydroxide (LDO) is a kind of layered inorganic material composed of two metal elements, which is usually prepared by calcining layered double hydroxide (LDH) precursor. The interlayer of the layered double hydroxide contains a large number of metal ions, which reacts with molten Li to in-situ synthesize a composite mainly composed of Li2O and M oxide, thereby obtaining a M / Li2O composite layered material.

[0045] The composite (mainly composed of Li2O and M oxide) on the surface of the M / Li2O composite layered material has a lithium supplement function. The oxide of M includes Co3O4, Mn3O4 or Fe3O4.

[0046] The shell is used as a bonding layer, and the composition is a material having a bonding effect, such as a resin.

[0047] The functional material for the diaphragm provided by the present application can soften the shell material and bond with the positive plate and / or negative plate after preheating in the processing process of lithium ion battery or battery core, and at the same time, the shell is broken after preheating, the M / Li2O composite layered material in the core is exposed, the M / Li2O composite layered material has a lithium supplement function, the M / Li2O composite layered material (as a lithium supplement agent) can be transferred to the positive plate and / or negative plate without using pressure, the prelithiation of the positive plate and / or negative plate is realized, and thus the initial efficiency and cycle stability of the battery are improved.

[0048] 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 pole group is made by using the diaphragm containing the functional material for the diaphragm and the negative plate and the positive plate, and the preheating time m after the pole group is made by using the diaphragm containing the functional material for the diaphragm and the negative plate and the positive plate satisfy the following relationship: 0.25≤12t / mT≤0.6, and 4.5≤2d / T+3D≤8.

[0049] The value of 12t / mT includes but is not limited to any one of the point values of 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6 or a range value between any two of them; the value of 2d / T+3D includes but is not limited to any one of the point values of 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 or a range value between any two of them.

[0050] By controlling the parameters to satisfy the above relationship, the present application can ensure that the transfer rate Y of the functional coating containing the above-mentioned functional material for the diaphragm is ≥97%, and the initial efficiency of the battery assembled by using the diaphragm containing the functional material for the diaphragm is >88%. The transfer rate is the ratio of the coverage area of the functional coating on the positive plate to the area of the positive plate.

[0051] Specifically, satisfying the above relationship can effectively improve the transfer rate Y of the functional coating, and at the same time, more materials with lithium supplement function can be transferred to the pole piece, which is beneficial to the initial 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, the resin is too thick, and the preheating temperature is not enough, it will affect the softening and rupture of the resin, causing the composite to fail to transfer to the pole piece, and the lithium supplement functional material cannot play a role, affecting the initial efficiency of the battery.

[0052] In some specific embodiments, the median particle size D of the M / Li2O composite layered material is 0.5-1 μm, including but not limited to any one of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or a range value between any two of them. This is conducive to improving the transfer rate Y of the functional coating and the heat resistance of the functional coating.

[0053] In some specific embodiments, the softening temperature t of the resin is 60-80°C, including but not limited to any one of 60°C, 65°C, 70°C, 75°C, 80°C, or a range value between any two of them. Among them, the softening temperature of the resin determines the melting temperature and the bonding strength.

[0054] In some specific embodiments, the thickness d of the shell is 100-200 nm, including but not limited to any one of 100 nm, 120 nm, 130 nm, 150 nm, 160 nm, 180 nm, 200 nm, or a range value between any two of them. In this way, the shell is easy to soften under heat and has strong adhesion, and at the same time, it is easy to break, and the material with lithium supplement function can be exposed after transfer, thereby improving the initial efficiency of the battery.

[0055] In some specific embodiments, the preheating temperature T of the pole group after the separator containing the functional material for the separator is used with the negative pole piece and the positive pole piece is 70-90°C, including but not limited to any one of 70°C, 75°C, 80°C, 85°C, 90°C, or a range value between any two of them. In this way, the shell can be softened and play a role in adhesion and transfer.

[0056] In some specific embodiments, the preheating time m of the pole group after the separator containing the functional material for the separator is used with the negative pole piece and the positive pole piece is 20-40 min, including but not limited to any one of 20 min, 25 min, 30 min, 35 min, 40 min, or a range value between any two of them. In this way, the shell can be softened and play a role in adhesion and transfer.

[0057] In some embodiments, the layered double hydroxide further comprises a metal element Q in addition to M, wherein Q comprises Mg, Ni, Zn, or Al. That is, the double metal elements in the layered double hydroxide are M and Q, respectively, wherein the element M reacts in situ with lithium metal to form a composite of oxides mainly composed of Li2O and M.

[0058] In some embodiments, the molar ratio of the layered double hydroxide to the lithium metal during the in-situ reaction is 0.05-1:1, including but not limited to any one of the point values 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, 1:1 or a range value between any two of them. This can ensure the amount of lithium supplement transferred to the pole piece, thereby effectively improving the initial efficiency of the battery.

[0059] In some embodiments, the in-situ reaction is carried out in an inert atmosphere, such as an argon atmosphere or a nitrogen atmosphere, but is not limited thereto.

[0060] In some embodiments, the preparation method of the M / Li2O composite layered material specifically comprises: mixing and stirring the layered double hydroxide containing M with molten lithium metal to carry out in-situ synthesis reaction.

[0061] In some embodiments, the layered double hydroxide containing M can be prepared by any commonly used preparation method in the art, for example: directional growth of metal precursors in a solvent by hydrothermal method, formation of coprecipitate by adjusting pH, and formation of layered double hydroxide after high-temperature calcination.

[0062] In some embodiments, the temperature of the in-situ reaction is 185-250°C, including but not limited to any one of the point values 185°C, 190°C, 195°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or a range value between any two of them.

[0063] In some embodiments, the time of the in-situ reaction is 1-6h, including but not limited to any one of the point values 1h, 2h, 3h, 4h, 5h, 6h or a range value between any two of them.

[0064] In some embodiments, the resin comprises at least one of polyethylene, polyvinyl acetate, ethylene-vinyl acetate copolymer (EVA), polystyrene-n-butyl acrylate copolymer, and epoxy resin.

[0065] In a second aspect, the present application provides a preparation method of the functional material for the diaphragm, comprising the following steps: mixing the composite inorganic material and the resin and heating to a molten state, stirring uniformly, and obtaining the functional material for the diaphragm after cooling.

[0066] The preparation method is simple, easy to implement, safe, and suitable for batch production.

[0067] 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 a range value between any two of them.

[0068] In some specific embodiments, the heating time is 3-4h, such as 3h, 3.5h or 4h.

[0069] By controlling the heating temperature and time, and the amount of resin added, the thickness of the shell can be controlled.

[0070] In some specific embodiments, the mass ratio of the composite inorganic material to the resin is 1.2-3:1, such as 1.5:1, 2.0:1 or 2.5:1.

[0071] In a third aspect, the present application provides a diaphragm, comprising a base film and a functional coating layer arranged on at least one surface of the base film, wherein the functional coating layer comprises the functional material for the diaphragm.

[0072] The functional coating layer can transfer the M / Li2O composite layered material with lithium supplementing effect to the positive and negative electrode surfaces after preheating during the preparation of the battery, thereby realizing the prelithiation effect of the positive and negative electrodes at the same time.

[0073] In some specific embodiments, the battery using the diaphragm has a first efficiency (first coulomb efficiency) of more than 90%, and the cycle performance is improved by at least 2%.

[0074] In some specific embodiments, the thickness of the functional coating layer is 2-4μm, including but not limited to any one of 2μm, 2.2μm, 2.5μm, 2.8μm, 3μm, 3.3μm, 3.5μm, 3.8μm, 4μm, or a range value between any two of them. The coating thickness can meet the thermal safety and electrical performance requirements of the battery after transfer.

[0075] In some specific embodiments, the functional coating layer further comprises at least one of a thickening agent, a water-based adhesive, a dispersing agent, and a solid-state electrolyte material.

[0076] In some embodiments, the mass ratio of the functional material, the thickening agent, the aqueous binder, the dispersant and the solid-state 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.

[0077] In some embodiments, the thickening agent comprises at least one of sodium carboxymethyl cellulose, xanthan gum, starch and sodium phosphate.

[0078] In some embodiments, the aqueous binder comprises at least one of polymethyl acrylate, polybutyl methacrylate and butadiene styrene latex.

[0079] In some embodiments, the dispersant comprises at least one of sodium polyacrylate, ammonium polyacrylate and sodium pyrophosphate.

[0080] In some embodiments, the solid-state electrolyte material comprises at least one of lithium aluminum titanium phosphate, lithium lanthanum zirconium oxide and lithium lanthanum zirconium titanium oxide. The addition of the above-mentioned solid-state electrolyte material can improve the ionic conductivity of the separator.

[0081] In some embodiments, the particle size D50 of the solid-state electrolyte material is 0.5-1 μm, e.g., 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm.

[0082] In some embodiments, the separator is prepared by coating the functional material for the separator on the base film with a slurry.

[0083] In some embodiments, the method for preparing the separator comprises: mixing the functional material for the separator, the thickening agent, the aqueous binder, the dispersant, the solid-state electrolyte material and a solvent (e.g., deionized water) to obtain a slurry, wherein the amount of the solvent added is such that the solid content of the slurry is 30%-40%, preferably 35%. Then the slurry is coated on the surface of a PE base film with a thickness of 5-12 μm by means of gravure transfer coating, and then dried to form a separator with a functional coating.

[0084] In a fourth aspect, the present application provides a lithium ion battery comprising the above-mentioned separator.

[0085] The lithium ion battery has the advantages of high first coulomb efficiency and good cycle performance.

[0086] In some specific embodiments, the lithium ion battery further comprises a negative electrode sheet, a positive electrode sheet and an electrolyte, which are not limited by the present application.

[0087] In some specific embodiments, the lithium ion battery is prepared by sequentially preheating, packaging, injecting electrolyte, pre-charging and formation after the diaphragm, the negative electrode sheet and the positive electrode sheet are stacked into a pole group.

[0088] In some specific embodiments, the preparation method of the lithium ion battery specifically comprises: (1) taking lithium iron phosphate as a positive electrode active material, mixing lithium iron phosphate, a conductive agent (Super P) and PVDF (polyvinylidene fluoride) according to a mass ratio of 96.5:1.5:2 to obtain a positive electrode slurry, and coating the positive electrode slurry on a carbon-coated aluminum foil to obtain a positive electrode sheet; (2) taking artificial graphite as a negative electrode active material, mixing the artificial graphite, CMC (carboxymethyl cellulose), a conductive agent (Super P) and SBR (styrene butadiene rubber) according to a mass ratio of 95.5:1.5:1.0:2 to obtain a negative electrode slurry, coating the negative electrode slurry on a copper foil, and processing to obtain a negative electrode sheet; (3) stacking the diaphragm, the negative electrode sheet and the positive electrode sheet containing the functional coating in the form of a laminated sheet to form a pole group, and then preheating; (4) using a soft package form, packaging the prepared pole group, and then injecting electrolyte; (5) pre-charging and formation on the battery cell to obtain a lithium ion battery.

[0089] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained by purchase.

[0090] Example 1 The preparation method of the functional material for the diaphragm provided in the embodiment comprises: (1) melting lithium metal foil at 185 DEG C to obtain molten metal lithium; mixing and stirring layered double hydroxide (Zn-Co oxide, i.e. Zn-Co LDO) and the molten metal lithium under an argon atmosphere to perform in-situ reaction, wherein the temperature of the in-situ reaction is 200 DEG C, the time of the in-situ reaction is 2h, the molar ratio of the layered double hydroxide and the metal lithium is 0.5:1, and M / Li2O composite layered material is obtained, the surface of the M / Li2O composite layered material has a composite mainly composed of Li2O and Co3O4, and the median particle size D of the M / Li2O composite layered material is 0.8 μm. (2) mixing and heating the M / Li2O composite layered material to a molten state, stirring uniformly, and obtaining the functional material for the diaphragm after cooling, wherein the heating temperature is 150 DEG C, and the heating time is 3.5h. The functional material for the diaphragm has a core-shell structure, wherein the core is the M / Li2O composite layered material, the shell is ethylene-vinyl acetate copolymer, and the thickness d of the shell is 150 nm.

[0091] The preparation method of the diaphragm provided in the embodiment comprises: weighing the functional material for the diaphragm, thickening agent (sodium carboxymethyl cellulose), water-based adhesive (polypropylene methyl propyl ester), dispersing agent (sodium pyrophosphate), and solid electrolyte material (lithium titanium aluminum phosphate, the particle size D50 is 0.8 μm) in a mass ratio of 90:1.5:7:0.5:1, and adding deionized water to mix uniformly to obtain a slurry, wherein the amount of solvent added is to make the solid content of the slurry 35%. Then the slurry is coated on the surface of a PE base film with a thickness of 9 μm by means of gravure transfer coating, and then dried to obtain a diaphragm with a functional coating, wherein the thickness of the functional coating is 3 μm.

[0092] The preparation method of the lithium ion battery provided in the embodiment comprises the following steps: (1) taking lithium iron phosphate as a positive active material, mixing lithium iron phosphate, a conductive agent (Super P) and PVDF (polyvinylidene fluoride) according to a mass ratio of 96.5:1.5:2 to obtain a positive electrode slurry, coating the positive electrode slurry on a carbon-coated aluminum foil, and drying to obtain a positive electrode sheet; (2) taking artificial graphite as a negative active material, mixing the artificial graphite, CMC (carboxymethyl cellulose), a conductive agent (Super P) and SBR (styrene butadiene rubber) according to a mass ratio of 95.5:1.5:1.0:2 to obtain a negative electrode slurry, coating the negative electrode slurry on a copper foil, and drying to obtain a negative electrode sheet; (3) stacking the above-mentioned functional-coating-containing separator, the above-mentioned negative electrode sheet and the above-mentioned positive electrode sheet into a pole group in the form of a stack, and then preheating, wherein the preheating temperature T is 80℃, and the preheating time m is 30 min; (4) packaging the prepared pole group in a soft package form, and then injecting an electrolyte; and (5) pre-charging and forming the battery cell to obtain the lithium ion battery.

[0093] Embodiment 2 The preparation method of the functional material for the separator provided in the embodiment is basically the same as that in Embodiment 1, and the only difference lies in that in step (1), the molar ratio of the layered double metal oxide and the metal lithium is 0.05:1.

[0094] The functional material for the separator prepared in the embodiment is used to prepare a separator and a lithium ion battery according to the method and parameters in Embodiment 1.

[0095] Embodiment 3 The preparation method of the functional material for the separator provided in the embodiment is basically the same as that in Embodiment 1, and the only difference lies in that in step (1), the molar ratio of the layered double metal oxide and the metal lithium is 1:1.

[0096] The functional material for the separator prepared in the embodiment is used to prepare a separator and a lithium ion battery according to the method and parameters in Embodiment 1.

[0097] Embodiment 4 The preparation method of the functional material for the separator provided in the embodiment is basically the same as that in Embodiment 1, and the only difference lies in that in step (1), the median particle size D of the M / Li2O composite layered material is 0.5 μm.

[0098] The functional material for the separator prepared in the embodiment is used to prepare a separator and a lithium ion battery according to the method and parameters in Embodiment 1.

[0099] Embodiment 5 The preparation method of the functional material for the separator provided in the embodiment is basically the same as that in Embodiment 1, and the only difference lies in that in step (1), the median particle size D of the M / Li2O composite layered material is 1.0 μm.

[0100] The functional material for diaphragm prepared in this example is used to prepare diaphragm and lithium ion battery according to the method and parameters of Example 1.

[0101] Example 6 The preparation method of the functional material for diaphragm provided in this example is basically the same as that of Example 1, except that the thickness d of the shell in step (2) is 100 nm.

[0102] The functional material for diaphragm prepared in this example is used to prepare diaphragm and lithium ion battery according to the method and parameters of Example 1.

[0103] Example 7 The preparation method of the functional material for diaphragm provided in this example is basically the same as that of Example 1, except that the thickness d of the shell in step (2) is 200 nm.

[0104] The functional material for diaphragm prepared in this example is used to prepare diaphragm and lithium ion battery according to the method and parameters of Example 1.

[0105] Example 8 The preparation method of the functional material for diaphragm provided in this example is basically the same as that of Example 1, except that the softening temperature t of the polystyrene-n-butyl acrylate copolymer resin used in step (2) is 60℃.

[0106] The functional material for diaphragm prepared in this example is used to prepare diaphragm and lithium ion battery according to the method and parameters of Example 1.

[0107] Example 9 The preparation method of the functional material for diaphragm provided in this example is basically the same as that of Example 1, except that the softening temperature t of the polyvinyl acetate resin used in step (2) is 80℃.

[0108] The functional material for diaphragm prepared in this example is used to prepare diaphragm and lithium ion battery according to the method and parameters of Example 1.

[0109] Example 10 The diaphragm prepared in Example 1 is used to prepare lithium ion battery according to the method of Example 1, except that the preheating temperature T in step (3) is 70℃.

[0110] Example 11 The diaphragm prepared in Example 1 is used to prepare lithium ion battery according to the method of Example 1, except that the preheating temperature T in step (3) is 90℃.

[0111] Example 12 The separator prepared in Example 1 was used to prepare a lithium ion battery according to the method of Example 1, except that in step (3), the preheating time m was 20 min.

[0112] Example 13 The separator prepared in Example 1 was used to prepare a lithium ion battery according to the method of Example 1, except that in step (3), the preheating time m was 40 min.

[0113] Example 14 The method for preparing the functional material for a separator provided in this example is basically the same as that of Example 8, except that in step (2), the thickness d of the shell is 200 nm.

[0114] The functional material for a separator prepared in this example was used to prepare a separator according to the method and parameters of Example 8.

[0115] The separator prepared in this example was used to prepare a lithium ion battery according to the method of Example 8, except that in step (3), the preheating temperature T was 90°C and the preheating time m was 40 min.

[0116] Example 15 The method for preparing the functional material for a separator provided in this example is basically the same as that of Example 5, except that in step (2), the thickness d of the shell is 200 nm.

[0117] The functional material for a separator prepared in this example was used to prepare a separator according to the method and parameters of Example 5.

[0118] The separator prepared in this example was used to prepare a lithium ion battery according to the method of Example 5, except that in step (3), the preheating temperature T was 70°C.

[0119] Example 16 The method for preparing the functional material for a separator provided in this example is basically the same as that of Example 1, except that in step (1), the layered double hydroxide is replaced by Ni-Fe LOD, i.e., the surface of the M / Li2O composite layered material has a composite mainly composed of Li2O and Fe3O4.

[0120] The functional material for a separator prepared in this example was used to prepare a separator and a lithium ion battery according to the method and parameters of Example 1.

[0121] Example 17 The method for preparing the functional material for a separator provided in this example is basically the same as that of Example 1, except that in step (1), the layered double hydroxide is replaced by Ni-Mn LDO, i.e., the surface of the M / Li2O composite layered material has a composite mainly composed of Li2O and Mn3O4.

[0122] The functional material for diaphragm prepared in this example is used to prepare diaphragm and lithium ion battery according to the method and parameters of Example 1.

[0123] Comparative Example 1 The preparation method of the functional material for diaphragm provided in this comparative example is basically the same as that of Example 1, and the only difference is that no lithium metal is added in step (1) (i.e. no in-situ synthesis reaction occurs).

[0124] The functional material for diaphragm prepared in this comparative example is used to prepare diaphragm and lithium ion battery according to the method and parameters of Example 1.

[0125] Comparative Example 2 The preparation method of the functional material for diaphragm provided in this comparative example is basically the same as that of Example 1, and the only difference is that the ethylene-vinyl acetate copolymer is replaced by equal mass of PVDF (polyvinylidene fluoride). That is, the material of the shell of the functional material for diaphragm prepared in this comparative example is PVDF.

[0126] The functional material for diaphragm prepared in this comparative example is used to prepare diaphragm and lithium ion battery according to the method and parameters of Example 1.

[0127] Comparative Example 3 The preparation method of the diaphragm provided in this comparative example is basically the same as that of Example 1, and the only difference is that the functional material for diaphragm is replaced by equal mass of PVDF (polyvinylidene fluoride). That is, there is no M / Li2O composite layered material in the diaphragm prepared in this comparative example, and the main material in the functional coating of the diaphragm is PVDF.

[0128] The diaphragm prepared in this comparative example is used to prepare lithium ion battery according to the method and parameters of Example 1.

[0129] The key parameter comparison in each example and each comparative example, as well as the values of 12t / mT and 2d / T+3D, are shown in Table 1.

[0130] Table 1: Parameter comparison in each example and each comparative example

[0131] Experimental Example The separators prepared in each of the examples and each of the comparative examples and the lithium ion batteries were tested, and the testing methods were as follows: (1) a testing method for the adhesion strength of the functional coating to the pole piece: the separators with the functional coating prepared in each of the examples and each of the comparative examples were laminated and hot-pressed with the positive pole piece, the hot-pressing pressure was 1 MPa, the hot-pressing temperature was 70 DEG C, the hot-pressing time was 10 s, and after hot-pressing, the sample was cut into a sample bar with a width of 15 mm and a length of 100 mm, the testing equipment was a universal testing tensile machine, the testing speed was 150 mm / min, the testing effective width was 15 mm, the adhesion strength was F / h, wherein F was the average value of the stable and uniform force value during the testing, the unit was N; h was the effective adhesion width of the separator and the positive pole piece, the unit was m; the unit of the adhesion strength was N / m. (2) a testing method for the initial efficiency: the lithium ion batteries were charged and discharged by using the constant current and constant voltage (CC / CV) method, the voltage, current and capacity data in the charging and discharging process were recorded, and the initial efficiency was calculated from the first charge and discharge capacity of the battery. (3) a testing method for the cycle performance: the batteries were charged at 1 C constant current to 3.65 V and 0.05 C constant voltage at 25 DEG C and 45 DEG C, and discharged at 1 C constant current to 2.8 V, the cycle number was 1000 times, and the capacity retention rate was compared. The testing results are shown in Table 2.

[0132] Table 2: Performance testing results of the separators and lithium ion batteries of each of the examples and each of the comparative examples

[0133] As can be seen from Table 1 and Table 2, each of the examples has the effect of supplementing lithium due to the addition of the functional material for the separator in the battery separator, has good stability, and realizes the pre-lithiation of the positive pole piece and the negative pole piece, thereby improving the initial efficiency and the cycle stability of the battery.

[0134] Furthermore, Examples 1-13 satisfy the relationship 0.25≤12t / mT≤0.6 and 4.5≤2d / T+3D≤8, and have high initial efficiency and capacity retention rate; and Examples 14-15 do not satisfy the relationship 0.25≤12t / mT≤0.6 and 4.5≤2d / T+3D≤8, resulting in a decrease in the initial efficiency and the capacity retention rate of the battery.

[0135] And Comparative Example 1 does not have in-situ reaction between the layered double metal oxide and lithium, i.e., the composite of the oxide with Li2O and M as the main components is not formed on the surface of the layered double metal oxide, resulting in a significant decrease in the initial efficiency and the capacity retention rate of the battery.

[0136] Comparative Example 2 has PVDF as the material of the shell, and the adhesion of PVDF is poorer than that of the resin, resulting in low transfer rate and inability of the lithium supplementing functional material to transfer to the pole piece, thereby reducing the lithium supplementing function and resulting in a significant decrease in the initial efficiency and the capacity retention rate of the battery.

[0137] The comparative example 3 has no M / Li2O composite layered material in the diaphragm, resulting in a significant decrease in the initial efficiency and capacity retention rate of the battery.

[0138] In summary, the functional material for diaphragm and the diaphragm provided by the present application can soften and adhere to the positive and negative electrode sheets during the preheating process of the battery preparation, and the shell can be broken, and the M / Li2O composite layered material in the core is exposed, which has good stability and lithium supplement effect, and can be transferred to the surface of the positive and negative electrode sheets to realize the pre-lithiation of the positive and negative electrode sheets, thereby improving the initial efficiency and cycle stability of the battery.

[0139] Although the present application has been illustrated and described with reference to specific embodiments, it is realized that the above examples are merely used to illustrate the technical solutions of the present application, and are not intended to limit the present application; it should be understood by those skilled in the art that the technical solutions recorded in the above examples can be modified, or some or all of the technical features can be replaced equivalently without departing from the spirit and scope of the present application; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application; therefore, this means that all these replacements and modifications within the scope of the present application 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 includes a composite inorganic material, and the shell of the core-shell structure includes a resin; The composite inorganic material includes 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 includes Co, Fe or Mn.

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 softening temperature t of the resin is 60-80℃; (3) the thickness d of the shell is 100-200 nm; (4) 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℃; (5) 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 includes a metal element Q in addition to M, wherein Q includes Mg, Ni, Zn or Al; (2) the molar ratio of the layered double metal oxide to the lithium during the in-situ reaction is 0.05-1:1; (3) the temperature of the in-situ reaction is 185-250℃, and the time of the in-situ reaction is 1-6 h.

5. The functional material for a separator according to claim 1, wherein The resin includes at least one of polyethylene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polystyrene-n-butyl acrylate copolymer and epoxy resin.

6. The method of producing a functional material for a separator according to any one of claims 1 to 5, wherein It includes the following steps: mixing the composite inorganic material with the resin and heating.

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

8. A diaphragm characterized by, The separator includes a base film and a functional coating layer provided on at least one surface of the base film, and the functional coating layer includes the functional material for the separator according to any one of claims 1-5.

9. The diaphragm of claim 8, 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.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises the separator as claimed in claim 8 or 9. 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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