Lithium-carrying film, preparation method and application thereof, lithium-supplementing negative electrode, preparation method of lithium-supplementing negative electrode, lithium ion battery, lithium foil coated with lithium-carrying film, and preparation method and application of lithium foil

Abstract

The invention belongs to the field of lithium ion batteries, and particularly relates to a lithium-loaded film and a preparation method and application thereof, a lithium supplementing negative electrode and a preparation method thereof, a lithium ion battery, a lithium foil coated with the lithium-loaded film and a preparation method and application thereof. Specifically, the lithium-carrying film comprises a base film, a release film arranged on one side of the base film, and a polymer protective layer arranged on one side, deviating from the base film, of the release film. In the preparation process of the lithium-supplementing negative electrode, the lithium foil and the base film of the lithium-carrying film are peeled off and transferred to the surface of the negative electrode piece, meanwhile, a protective layer can be left on the surface of the lithium foil, the steps of supplementing lithium and forming the lithium foil protective layer can be completed at the same time, an additional coating process is not needed, the sequence turning time of the lithium-supplementing negative electrode is prevented from being increased, and the production efficiency is improved. And the activity of the metal lithium can be ensured to the greatest extent.

Description

Technical Field

[0001] The present invention belongs to the field of lithium ion batteries, and specifically relates to a lithium-carrying film and a preparation method and application thereof, a lithium-supplementing negative electrode and a preparation method thereof, a lithium ion battery, a lithium foil covered with a lithium-carrying film and a preparation method and application thereof. Background Art

[0002] At present, the commonly used negative electrode lithium replenishment methods include lithium strip rolling replenishment, inert lithium powder replenishment, vacuum evaporation replenishment, etc. Among them, lithium strip rolling replenishment has attracted widespread attention due to its relatively high safety, easy adjustment of lithium strip thickness, and higher manufacturability such as roll-to-roll production. However, due to the low potential of metallic lithium and its extremely high chemical reactivity with oxygen and water, it is very easy to react in a normal air environment, causing lithium to lose its lithium replenishment activity and even causing safety risks. Therefore, the environmental humidity needs to be strictly controlled during the production of negative electrode rolling replenishment, which increases the manufacturing cost and the difficulty of mass production.

[0003] Patent application CN114583143A describes a negative electrode lithium replenishment lithium belt and its preparation method and application. The thickness of the negative electrode lithium replenishment lithium belt is 3-10μm, and at least one area is provided on the surface of the negative electrode lithium replenishment lithium belt. By setting the area in the negative electrode lithium replenishment lithium belt, the area forms a criss-cross heat diffusion and electrolyte infiltration network, and solves the gas production problem caused by poor or slow wettability of the negative electrode after the lithium belt covers the negative electrode plate, improves the dissolution efficiency of metal lithium in the negative electrode, and effectively improves the lithium replenishment effect of the negative electrode.

[0004] Although patent application CN114583143A can improve the dissolution efficiency of metallic lithium in the negative electrode and improve the lithium replenishment effect of the negative electrode, it cannot solve the safety problem caused by the easy reaction of lithium with water in the air under high humidity. Summary of the invention

[0005] The purpose of the present invention is to provide a lithium-carrying film that can simultaneously complete lithium replenishment and form a lithium foil protective layer during the preparation process of a lithium replenishing negative electrode.

[0006] A first aspect of the present invention provides a lithium-carrying film, comprising a base film, a release film disposed on one side of the base film, and a polymer protective layer disposed on a side of the release film away from the base film.

[0007] In one or more embodiments, the content of the release film in the lithium-carrying film is 0.1-1.5 g / m 2 ; and / or, in the lithium-carrying film, the content of the polymer protective layer is 0.1-1.5g / m 2 .

[0008] In one or more embodiments, the content of the release film in the lithium-carrying film is 0.1-0.4 g / m2 , preferably 0.1-0.2g / m 2 ; and / or, in the lithium-carrying membrane, the content of the polymer protective layer is 0.6-0.9g / m 2 , preferably 0.8-0.9g / m 2 .

[0009] In one or more embodiments, the base film is selected from one or more of PET base film, PVC base film, PP base film, PE base film, and BOPP base film; and / or the polymer protective layer is selected from one or more of polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer and polyvinyl pyrrolidone.

[0010] In one or more embodiments, the release film has one or more of the following features:

[0011] The release film is a silicone oil layer;

[0012] The silicone oil layer comprises a silicone oil main agent, a cross-linking agent and a catalyst;

[0013] The silicone oil main agent is silicone oil and / or modified silicone oil, and the modified silicone oil is preferably selected from one or more of methyl silicone oil, methylphenyl silicone oil and hydroxy silicone oil;

[0014] The cross-linking agent is hydrogen-containing silicone oil, preferably one or two selected from hydroxyl hydrogen-containing silicone oil and methyl hydrogen-containing silicone oil;

[0015] The catalyst is a noble metal catalyst;

[0016] In the silicone oil layer, the mass fraction of the silicone oil main agent is 85-95%;

[0017] In the silicone oil layer, the mass fraction of the crosslinking agent is 2-10%;

[0018] In the silicone oil layer, the mass fraction of the catalyst is 0.1-5%.

[0019] The second invention of the present invention provides a method for preparing the lithium-carrying film according to the first aspect of the present invention, the method comprising the steps of: coating a release film on one side of the base film, and then coating a polymer protective layer on the release film; preferably, the coating weight of the release film is 0.1-1.5 g / m 2 Preferably, the coating weight of the polymer protective layer is 0.1-1.5 g / m 2 .

[0020] The third invention of the present invention provides a method for preparing a lithium-supplemented negative electrode, the method comprising the steps of:

[0021] (1) pressing a lithium ribbon onto one side of the polymer protective layer of the lithium-carrying film described in the first aspect of the present invention to obtain a lithium foil covered with the lithium-carrying film;

[0022] (2) pressing the lithium foil covered with the lithium-carrying film onto the surface of the negative electrode, and removing the base film to obtain a lithium-supplemented negative electrode;

[0023] Preferably, the thickness of the lithium foil is 1-10 μm.

[0024] The fourth aspect of the present invention provides a lithium-supplemented negative electrode prepared using the method described in the third aspect of the present invention.

[0025] A fifth aspect of the present invention provides a lithium-ion battery comprising the lithium-supplementing negative electrode described in the fourth aspect of the present invention.

[0026] The sixth aspect of the present invention provides the use of the lithium-carrying film described in the first aspect of the present invention in the preparation of a waterproof and oxygen-proof lithium-supplementing negative electrode; and / or the use of the lithium-carrying film described in the first aspect of the present invention in increasing the stable storage time of the lithium-supplementing negative electrode in the air.

[0027] In the seventh aspect of the present invention, a lithium foil covered with a lithium-carrying film is provided, wherein the lithium foil covered with a lithium-carrying film comprises the lithium-carrying film and lithium foil described in the first aspect of the present invention, and the lithium foil is adhered to one side of the polymer protective layer of the lithium-carrying film; preferably, the thickness of the lithium foil is 1-10 μm.

[0028] The eighth aspect of the present invention provides a method for preparing the lithium foil covered with the lithium-carrying film as described in the seventh aspect of the present invention, the method comprising the steps of: pressing a lithium tape onto one side of the polymer protective layer of the lithium-carrying film to obtain a lithium foil covered with the lithium-carrying film.

[0029] The ninth aspect of the present invention provides a use of the lithium foil covered with a lithium-carrying film as described in the seventh aspect in preparing a lithium-supplementing negative electrode.

[0030] The present invention has the following beneficial effects:

[0031] During the preparation of the lithium-replenishing negative electrode, the lithium foil and the base film of the lithium-carrying film are peeled off and transferred to the surface of the negative electrode, while a protective layer can be left on the surface of the lithium foil. The steps of lithium replenishment and formation of the lithium foil protective layer can be completed simultaneously without the need for an additional coating process, thus avoiding increasing the conversion time of the lithium-replenishing negative electrode and ensuring the activity of metallic lithium to the greatest extent.

[0032] Compared with rolling lithium foil directly on the pole piece, which usually causes the pole piece to be crushed due to the great ductility of lithium foil, the lithium-carrying film of the present application has high mechanical strength. By using the lithium-carrying film of the present application as an intermediate medium, the problem of the pole piece being easily crushed due to direct rolling of lithium foil can be avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the structure of the lithium-carrying film in any embodiment of the present invention; wherein, 1-polymer protective layer, 2-release film, 3-base film. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0035] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0036] Herein, “comprising”, “including”, “containing” and similar terms encompass the meanings of “consisting essentially of” and “consisting of”. For example, when “A comprises B and C” is disclosed herein, “A consists essentially of B and C” and “A consists of B and C” should be deemed to be disclosed herein.

[0037] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0038] In this document, unless otherwise specified, percentage refers to mass percentage and ratio refers to mass ratio.

[0039] Herein, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all substitutes, improvements and equivalents of the methods and materials described in the present invention can be included in the scope limited by the claims.

[0040] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0041] The present invention provides a lithium-carrying film for negative electrode rolling and replenishing lithium. The rolled lithium-replenishing negative electrode prepared using the lithium-carrying film of the present invention can form a protective layer on the surface of metallic lithium while replenishing lithium, thereby improving the stability of lithium in an air environment.

[0042] The present invention provides a lithium-carrying film, such as Figure 1 As shown, the lithium-carrying film includes a base film 3, a release film 2 arranged on one side of the base film, and a polymer protective layer 1 arranged on the side of the release film away from the base film.

[0043] In the present invention, the base film plays the role of carrying the release film and the polymer protective layer. The base film materials used in the field of packaging and electrochemistry in the art can be used in the present invention. Exemplary base films include, but are not limited to, one or more of PET base films, PVC base films, PP base films, PE base films and BOPP base films. Preferably, the base film is a PET base film.

[0044] The base film can be purchased directly or made by yourself. For example, PET base film can be obtained by heating, melting, extruding and stretching diethyl terephthalate as raw material. When the base film is selected from two or more of the above materials, the raw materials corresponding to each base film are first mixed, and then heated, melted, extruded and stretched to form.

[0045] The release film is directly coated on one side of the base film. Its main function is to reduce the adhesion of the base film surface and achieve a release effect.

[0046] In some embodiments, the content of the release film in the lithium-carrying film is 0.1-1.5 g / m 2 , for example 0.2g / m 2 , 0.3g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 1.3g / m 2 , or in the range of any two values, preferably 0.2-0.7g / m 2 Preferably, the content of the release film is 0.1-0.4 g / m 2 , preferably 0.1-0.2g / m 2 .

[0047] In some embodiments, the release film is a silicone oil layer, which includes a silicone oil main agent, a cross-linking agent and a catalyst.

[0048] In some embodiments, the silicone oil main agent is silicone oil and / or modified silicone oil; preferably, the modified silicone oil is selected from one or more of methyl silicone oil, methylphenyl silicone oil and hydroxy silicone oil. In some embodiments, the silicone oil main agent is hydroxy silicone oil.

[0049] In some embodiments, the crosslinking agent is a hydrogen-containing silicone oil. Preferably, the crosslinking agent is selected from one or both of hydroxyl hydrogen-containing silicone oil and methyl hydrogen-containing silicone oil. In some embodiments, the crosslinking agent is a hydroxyl hydrogen-containing silicone oil.

[0050] In some embodiments, the catalyst is a noble metal catalyst, such as a platinum catalyst.

[0051] In some embodiments, in the silicone oil layer, the mass fraction of the silicone oil main agent is 85-95%, such as 85%, 88%, 90%, 92%, 95%, or a range between any two numerical values.

[0052] In some embodiments, in the silicone oil layer, the mass fraction of the crosslinking agent is 2-10%, such as 3%, 5%, 7%, 9%, or a range between any two values.

[0053] In some embodiments, in the silicone oil layer, the mass fraction of the catalyst is 0.1-5%, such as 0.5%, 1%, 2%, 3%, or a range between any two values.

[0054] The polymer protective layer is waterproof and can remain on the surface of lithium metal to form a protective layer while the lithium foil and the base film of the lithium-carrying membrane are peeled off, thereby reducing the reactivity of metallic lithium with oxygen and water in the air. In addition, the polymer protective layer can dissolve in the electrolyte and is compatible with the electrochemical system of the lithium battery without causing additional side reactions.

[0055] In some embodiments, the content of the polymer protective layer on the base film is 0.1-1.5 g / m 2 , for example 0.2g / m 2 , 0.3g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 1.3g / m 2 , or in the range between any two values, preferably 0.3-0.8g / m 2 Preferably, the content of the polymer protective layer is 0.6-0.9 g / m 2 , preferably 0.8-0.9g / m 2.

[0056] The polymer protective layer is a polymer layer commonly used in the art for protecting the lithium replenishing layer. In some embodiments, the polymer protective layer is selected from one or more of polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer and polyvinyl pyrrolidone. Preferably, the polymer protective layer is polymethyl methacrylate (PMMA).

[0057] The present invention also provides a method for preparing the lithium-carrying film of the present invention. The method comprises the steps of: coating a release film on one side of the base film, and then coating a polymer protective layer on the release film.

[0058] In some embodiments, the coating weight of the release film is 0.1-1.5 g / m 2 , for example 0.2g / m 2 , 0.3g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 1.3g / m 2 , or in the range of any two values, preferably 0.2-0.7g / m 2 Preferably, the coating weight of the release film is 0.1-0.4 g / m 2 , preferably 0.1-0.2g / m 2 .

[0059] In some embodiments, the coating weight of the polymer protective layer is 0.1-1.5 g / m 2 , for example 0.2g / m 2 , 0.3g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 1.3g / m 2 , or in the range of any two values, preferably 0.2-0.7g / m 2 Preferably, the coating weight of the polymer protective layer is 0.6-0.9 g / m 2 , preferably 0.8-0.9g / m 2 .

[0060] The present invention also provides a lithium foil covered with a lithium-carrying film. The lithium foil covered with a lithium-carrying film comprises a lithium-carrying film and a lithium foil, and the lithium foil is attached to one side of the polymer protective layer of the lithium-carrying film. The thickness of the lithium foil is 1-10 μm, for example, 3-7 μm. The preparation method of the lithium foil covered with a lithium-carrying film comprises the steps of: pressing a lithium tape onto one side of the polymer protective layer of the lithium-carrying film to obtain a lithium foil covered with a lithium-carrying film. The lithium foil covered with a lithium-carrying film can be used to prepare a lithium-supplementing negative electrode. Therefore, the present invention also provides a preparation method of a lithium foil covered with a lithium-carrying film. The present invention also provides the use of a lithium foil covered with a lithium-carrying film in the preparation of a lithium-supplementing negative electrode.

[0061] The lithium-carrying film of the present invention is used to prepare a lithium-supplementing negative electrode, which can simultaneously realize the loading of lithium on the negative electrode and the provision of a protective layer on the surface of the lithium. The protective layer can play a role in waterproofing and oxygen-proofing, thereby preventing lithium from chemically reacting with water and oxygen in the air. Therefore, the present invention provides a method for preparing a lithium-supplementing negative electrode. The method comprises the steps of:

[0062] (1) pressing a lithium ribbon onto one side of the polymer protective layer of the lithium-carrying film to obtain a lithium foil covered with the lithium-carrying film;

[0063] (2) Pressing the lithium foil covered with the lithium-carrying film onto the surface of the negative electrode, and removing the base film to obtain a lithium-supplemented negative electrode.

[0064] In some embodiments, the thickness of the lithium foil is 1-10 μm.

[0065] In some embodiments, a lithium ribbon is pressed onto one side of the polymer protective layer of the lithium-carrying membrane by a lithium ribbon calendering device.

[0066] In some embodiments, the lithium foil covered with the lithium-carrying film is pressed onto the surface of the negative electrode by a coating device.

[0067] The present invention provides a lithium-supplementing negative electrode prepared by the method for preparing a lithium-supplementing negative electrode of the present invention. After the base film is torn off in step (2), both the base film and the release film leave the surface of the lithium foil. The lithium-supplementing negative electrode has a three-layer structure of polymer protective layer-lithium-negative electrode. In some embodiments, the lithium-supplementing negative electrode has a three-layer structure of PMMA-metal lithium-negative electrode.

[0068] The present invention also provides a lithium-ion battery comprising the lithium-supplementing negative electrode of the present invention. The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The negative electrode sheet of the lithium-ion battery of the present invention is a lithium-supplementing negative electrode prepared using the method for preparing a lithium-supplementing negative electrode of the present invention. The positive electrode sheet, the negative electrode sheet and the separator are stacked (for example, Z-shaped stacking or winding stacking) according to the design requirements, and then the electrolyte is injected, and the lithium-ion battery is prepared after aging, exhaustion and heat sealing.

[0069] The positive electrode sheet includes a positive electrode collector and a positive electrode material layer formed on the surface of the positive electrode collector. The positive electrode material layer includes a positive electrode material, a conductive agent and a binder. The positive electrode material layer is obtained by coating a positive electrode slurry containing a positive electrode material, a conductive agent, a binder and a solvent on the positive electrode collector, and then rolling, die-cutting and drying. The solvent of the positive electrode slurry can be N-methyl-2-pyrrolidone (NMP). The positive electrode collector can be copper foil, aluminum foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The positive electrode material includes one or more selected from lithium iron phosphate, a binary positive electrode material, a ternary positive electrode material, a quaternary positive electrode material, etc. Preferably, the positive electrode material is lithium iron phosphate. The conductive agent of the positive electrode can be one or more selected from conductive carbon black, carbon fiber, acetylene black, conductive graphite, graphene, carbon nanotubes and carbon microspheres. The binder of the positive electrode can be one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, fluorinated rubber, polyurethane and sodium alginate. In some embodiments, the conductive agent in the positive electrode material layer is carbon black and carbon nanotubes, and the binder is PVDF. The content ratio of each component in the positive electrode material layer can be conventional, for example, the mass fraction of the positive electrode material can be 90%-98%, such as 92%, 94%, 96%, 97%, the mass fraction of the conductive agent can be 1%-5%, such as 1.2%, 1.5%, 2%, 3%, 3.5%, 4%, and the mass fraction of the binder can be 1%-5%, such as 1.5%, 2%, 2.5%, 3%, 4%.

[0070] The negative electrode sheet includes a negative electrode collector and a negative electrode material layer arranged on the surface of the negative electrode collector. The negative electrode collector can be a copper foil. The negative electrode material layer includes a negative electrode material, a conductive agent and a binder. The negative electrode material layer is obtained by coating a negative electrode slurry containing a negative electrode material, a conductive agent, a binder and a solvent onto the negative electrode collector, and then rolling, die cutting and drying. The solvent of the negative electrode slurry can be water. The negative electrode material can be selected from carbon powder, graphite, lithium metal, mesophase carbon balls, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, spinel structured lithiated TiO2-Li4Ti5O 12and Li-Al alloy. The negative electrode conductive agent can be one or more selected from conductive carbon black (SP), acetylene black, carbon nanotubes, carbon nanowires, carbon microspheres, carbon fibers and graphene. The negative electrode binder can be one or more selected from polyvinylidene fluoride, polytetrafluoroethylene, acrylonitrile multipolymer, polyacrylate butyl, polyacrylonitrile and styrene-butadiene rubber (SBR). The negative electrode material layer and the negative electrode slurry can also include a thickener, such as carboxymethyl cellulose (CMC). In some embodiments, the negative electrode material in the negative electrode material layer is graphite, the conductive agent is conductive carbon black, the binder is styrene-butadiene rubber, and the thickener is carboxymethyl cellulose. The mass ratio of each component in the negative electrode material layer can be conventional. For example, the mass fraction of the negative electrode material can be 90%-98%, for example 93%, 95%, 96%, 97%, the mass fraction of the conductive agent can be 0.5%-5%, for example 1%, 1.5%, 2%, the mass fraction of the binder can be 0.5%-5%, for example 1%, 1.5%, 1.8%, 2%, 2.5%, 3%, and the mass fraction of the thickener can be 0-5%, for example 1%, 1.2%, 1.5%, 1.8%, 2%, 3%.

[0071] The diaphragm can be a polymer diaphragm, a ceramic diaphragm or a polymer / ceramic composite diaphragm. The polymer diaphragm includes a single-layer polymer diaphragm and a multi-layer polymer diaphragm. The single-layer polymer diaphragm includes a polyethylene (PE) diaphragm and a polypropylene (PP) diaphragm. The composite polymer diaphragm includes a polyethylene and polystyrene mixed diaphragm.

[0072] The electrolyte can be a non-aqueous electrolyte, comprising an organic solvent and a lithium salt. The organic solvent can be a carbonate solvent commonly used in the art for electrolytes, including but not limited to one or more selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, γ-butyrolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), preferably two or more. Preferably, the carbonate solvent comprises at least one cyclic carbonate and at least one chain carbonate. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate and γ-butyrolactone. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The volume ratio of cyclic carbonate and chain carbonate can be 1:4 to 2:3, such as 2:7, 1:3, 3:7, 1:2. The lithium salt may be a lithium salt commonly used in the art, including but not limited to lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalate borate) (LiBOB), lithium acetate, lithium trifluoroacetate, lithium fluoroalkyl phosphate, lithium hexafluorophosphate (LiPF6), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium perchlorate, lithium hexafluoroarsenate, lithium fluoride, etc. In some embodiments, the lithium salt is LiPF6. The concentration of the lithium salt in the electrolyte may be 0.5-2 mol / L, for example 1 mol / L, 1.2 mol / L, 1.5 mol / L.

[0073] The present invention also provides an application of the lithium-carrying film of the present invention in preparing a lithium-replenishing negative electrode that is waterproof and oxygen-proof. When the lithium-carrying film of the present invention is used to prepare a lithium-replenishing negative electrode, lithium can be coated on the negative electrode and a protective layer can be coated on the surface of the lithium at the same time, without the need for an additional coating process, and the activity of the metallic lithium can be guaranteed to the greatest extent.

[0074] The present invention also provides the use of the lithium-carrying membrane of the present invention in increasing the stable storage time of the lithium-supplemented negative electrode in the air. In some embodiments, the relative humidity of the air is 10-30wt%, for example 20wt%.

[0075] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are calculated by weight.

[0076] Herein, the silicone oil layer comprises: 92 wt % hydroxy silicone oil, 7 wt % hydroxy hydrogen silicone oil and 1 wt % platinum catalyst.

[0077] In this paper, the electrolyte is LiPF6 solution, the solvent is a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC), the volume ratio of DMC, EMC and EC is 20:55:25, and the LiPF6 concentration is 1.2 mol / L.

[0078] Example 1

[0079] (1) Preparation of positive electrode sheets: LiFePO4, PVDF, SP, and CNT were mixed in NMP system in the proportions of 96.8%, 2%, 0.9%, and 0.3% by mass, respectively, to prepare a positive electrode slurry with a solid content of 62 wt%, which was then coated, rolled, slit, and dried to prepare positive electrode sheets.

[0080] (2) Preparation of negative electrode sheets. Graphite, CMC, SBR, and SP were mixed in a deionized water system in a ratio of 95.5%, 1.2%, 1.8%, and 1.5% by mass, respectively, to prepare a negative electrode slurry with a solid content of 55 wt%, which was then coated, rolled, slit, and baked to prepare a negative electrode sheet without lithium supplementation.

[0081] (3) Preparation of lithium-loaded membrane. Using diethyl terephthalate as raw material, the PET base film was obtained after heating to 300°C for melting, extrusion, and stretching. A silicone oil layer was first coated on the PET base film with a coating weight of 0.4 g / m 2 , then coated with PMMA, the coating weight is 0.6g / m 2 .

[0082] (4) Preparation of lithium-replenishing negative electrode by rolling. The metal lithium strip is pressed onto the PMMA of the lithium-carrying film by a lithium strip rolling device to form a lithium foil with a thickness of 5 μm; the lithium foil is then pressed onto the negative electrode surface by a coating device, and the PET base film is torn off to obtain a lithium-replenishing negative electrode. The prepared lithium-replenishing negative electrode has a three-layer structure of PMMA-metal lithium-negative electrode (graphite).

[0083] (5) Lithium-ion battery manufacturing: The lithium-supplemented negative electrode is wound together with the positive electrode and a polyethylene separator to form a bare battery cell, and then subjected to hot pressing, top sealing, liquid injection, standing, formation, secondary sealing, and capacity separation to obtain a finished soft-pack lithium-ion battery.

[0084] Example 2

[0085] The difference from Example 1 is that the mass ratio of the lithium-carrying film silicone oil layer to the PMMA layer is 2:8, and the coating weight of the silicone oil layer is 0.2 g / m 2 ; PMMA coating weight is 0.8g / m 2 .

[0086] Example 3

[0087] The difference from Example 1 is that the mass ratio of the lithium-carrying film silicone oil layer to the PMMA layer is 3:7, and the coating weight of the silicone oil layer is 0.3 g / m 2 ; PMMA coating weight is 0.7g / m 2 .

[0088] Example 4

[0089] The difference from Example 1 is that the mass ratio of the lithium-carrying film silicone oil layer to the PMMA layer is 5:5, and the coating weight of the silicone oil layer is 0.5 g / m 2 ; PMMA coating weight is 0.5g / m 2 .

[0090] Example 5

[0091] The difference from Example 1 is that the mass ratio of the lithium-carrying film silicone oil layer to the PMMA layer is 6:4, and the coating weight of the silicone oil layer is 0.6 g / m 2 ; PMMA coating weight is 0.4g / m 2 .

[0092] Example 6

[0093] The difference from Example 1 is that the mass ratio of the lithium-carrying film silicone oil layer to the PMMA layer is 7:3, and the coating weight of the silicone oil layer is 0.7 g / m 2 ; PMMA coating weight is 0.3g / m 2 .

[0094] Comparative Example 1

[0095] The difference from Example 1 is that only a silicone oil layer is coated on the PET base film of the lithium-carrying film, and the coating mass is 1 g / m 2 .

[0096] Test Case

[0097] The peeling force of the lithium-carrying film prepared above was measured and recorded, and a 180-degree peeling force test was performed using a peeling force testing machine in accordance with the national standard GB / T25256-2010 test standard.

[0098] The lithium-supplemented negative electrodes prepared in Examples 1-6 and Comparative Example 1 were placed in air with a relative humidity of 20 wt %, and the color of the lithium layer on the surface of the negative electrode was observed. The time when it changed from bright white to dark black was recorded, which was the stable storage time.

[0099] The battery was charged to 3.65V at 0.5C constant current and constant voltage, and then cut off at 0.05C. After standing for 5 minutes, it was discharged to 2.5V at 0.5C constant current to measure the initial efficiency of the battery.

[0100] The test results are shown in Table 1 below.

[0101] Table 1

[0102]

[0103]

[0104] It can be seen that after adding the PMMA coating, the stability time of the lithium-supplemented negative electrode in the air with a relative humidity of 20wt% is significantly extended. The addition of PMMA slightly reduces the ionic conductivity and the first efficiency of the battery cell, while the peeling force increases significantly. Taking all factors into consideration, that is, increasing the stability time of the lithium-supplemented negative electrode in the air with a relative humidity of 20wt%, while ensuring a low peeling force and a low first efficiency loss, the optimal mass ratio of the silicone oil layer to the PMMA layer is 4:6.

Claims

1. A lithium-carrying film, characterized in that: The lithium-carrying film comprises a base film, a release film arranged on one side of the base film, and a polymer protective layer arranged on the release film on a side away from the base film.

2. The lithium-carrying film according to claim 1, characterized in that: In the lithium-carrying film, the content of the release film is 0.1-1.5 g / m 2 and / or, In the lithium-carrying film, the content of the polymer protective layer is 0.1-1.5 g / m 2 .

3. The lithium-carrying film according to claim 1, characterized in that: In the lithium-carrying film, the content of the release film is 0.1-0.4 g / m 2 , preferably 0.1-0.2g / m 2 and / or, In the lithium-carrying film, the content of the polymer protective layer is 0.6-0.9 g / m 2 , preferably 0.8-0.9g / m 2 .

4. The lithium-carrying film according to claim 1, characterized in that The base film is selected from one or more of PET base film, PVC base film, PP base film, PE base film, and BOPP base film; and / or the polymer protective layer is selected from one or more of polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer and polyvinyl pyrrolidone.

5. The lithium-carrying film according to claim 1, characterized in that: The release film has one or more of the following features: The release film is a silicone oil layer; The silicone oil layer comprises a silicone oil main agent, a cross-linking agent and a catalyst; The silicone oil main agent is silicone oil and / or modified silicone oil, and the modified silicone oil is preferably selected from one or more of methyl silicone oil, methylphenyl silicone oil and hydroxy silicone oil; The cross-linking agent is hydrogen-containing silicone oil, preferably one or two selected from hydroxyl hydrogen-containing silicone oil and methyl hydrogen-containing silicone oil; The catalyst is a noble metal catalyst; In the silicone oil layer, the mass fraction of the silicone oil main agent is 85-95%; In the silicone oil layer, the mass fraction of the crosslinking agent is 2-10%; In the silicone oil layer, the mass fraction of the catalyst is 0.1-5%.

6. A method for preparing a lithium-carrying film according to any one of claims 1 to 5, characterized in that: The method comprises the steps of: coating a release film on one side of the base film, and then coating a polymer protective layer on the release film; preferably, the coating weight of the release film is 0.1-1.5 g / m 2 Preferably, the coating weight of the polymer protective layer is 0.1-1.5 g / m 2 .

7. A method for preparing a lithium-supplemented negative electrode, characterized in that: The method comprises the steps of: (1) pressing a lithium ribbon onto one side of the polymer protective layer of the lithium-carrying film according to any one of claims 1 to 5 to obtain a lithium foil covered with the lithium-carrying film; (2) pressing the lithium foil covered with the lithium-carrying film onto the surface of the negative electrode, and removing the base film to obtain a lithium-supplemented negative electrode; Preferably, the thickness of the lithium foil is 1-10 μm.

8. A lithium-supplemented negative electrode prepared using the method of claim 7.

9. A lithium ion battery comprising the lithium-supplemented negative electrode according to claim 8.

10. Use of the lithium-carrying membrane according to any one of claims 1 to 5 in preparing a water-proof and oxygen-proof lithium-supplementing negative electrode; and / or use of the lithium-carrying membrane according to any one of claims 1 to 5 in increasing the stable storage time of a lithium-supplementing negative electrode in air.

11. A lithium foil coated with a lithium-carrying film, characterized in that: The lithium foil covered with a lithium-carrying film comprises the lithium-carrying film and lithium foil according to any one of claims 1 to 5, and the lithium foil is attached to one side of the polymer protective layer of the lithium-carrying film; preferably, the thickness of the lithium foil is 1-10 μm.

12. A method for preparing the lithium foil covered with a lithium-carrying film according to claim 11, characterized in that: The method comprises the steps of: pressing a lithium strip onto one side of a polymer protective layer of a lithium-carrying film to obtain a lithium foil covered with the lithium-carrying film.

13. Use of the lithium foil covered with a lithium-carrying film as claimed in claim 11 in preparing a lithium-supplementing negative electrode.

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