Lithium supplementing separator for lithium ion battery, lithium ion battery, and preparation method

Abstract

The present disclosure provides a lithium supplementing diaphragm for a lithium ion battery, a lithium ion battery, and a preparation method, and belongs to the field of batteries. The lithium supplementing diaphragm comprises a diaphragm base, a pre-lithium layer, a first protective layer, and a second protective layer. The pre-lithium layer is located on one side of the diaphragm base, and the first protective layer is located on the side of the pre-lithium layer away from the diaphragm base. The second protective layer is arranged on the first surface of the diaphragm base. The material of the second protective layer comprises a polymer and an ester compound. The polymer is insoluble in the electrolyte of the lithium ion battery. The ester compound is soluble in the electrolyte of the lithium ion battery. The second protective layer of the lithium supplementing diaphragm of the present disclosure is an organic material layer, and the preparation method does not need to be carried out in a vacuum, thereby being low in cost. The first protective layer and the second protective layer isolate the lithium metal in the pre-lithium layer from water, carbon dioxide, oxygen, nitrogen, and the like in the air during the assembly process, thereby reducing the consumption of lithium in the pre-lithium layer and improving the utilization rate of lithium. The technical problems of the prior art, such as high lithium consumption of the lithium supplementing diaphragm and complex preparation method, are solved.

Description

Technical Field

[0001] The present disclosure relates to the field of batteries, and in particular to a lithium-supplementing diaphragm for a lithium-ion battery and a preparation method thereof, as well as a lithium-ion battery and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have advantages such as high specific energy and long cycle life, and are widely used in electronic products, electric vehicles and other fields. However, existing lithium-ion batteries also have problems such as transition metal dissolution and particle breakage of cathode active materials, which in turn lead to technical problems such as decreased cycle life of battery cells and reduced energy density. In order to alleviate the above technical problems, the existing technology proposes to pre-lithiate the anode or cathode to increase the total amount of active lithium during the cycle, which not only helps to improve the battery energy density, but also can significantly extend the service life of the battery cell. However, the existing anode / cathode pre-lithiation has problems such as cumbersome operation, high risk, low utilization rate of metal lithium, high humidity requirements for storage and use environment, and high cost.

[0003] The primary function of a diaphragm in a lithium-ion battery is to separate the positive and negative electrodes of the battery, preventing short circuits and ensuring that lithium ions can flow normally through the microporous channels during the charge and discharge process to ensure the normal operation of the battery. Although there are reports of placing a lithium-replenishing layer on the diaphragm layer, the lithium in existing lithium-replenishing diaphragms is easily consumed by reactions with water, gas, and other substances in the air during assembly. The high lithium consumption makes existing lithium-replenishing diaphragms for lithium-ion batteries unsuitable for the assembly environment of lithium-ion batteries, limiting their industrial application. There are also reports of placing inorganic materials such as metals and metal compounds on the surface of the lithium-replenishing layer as a protective layer. However, inorganic materials such as metals and metal compounds are relatively expensive, and the construction method requires a vacuum environment, which cannot be continuously produced, resulting in low efficiency and high production costs. Furthermore, the temperature and humidity of the environment must be strictly controlled during storage and use, further increasing manufacturing costs. Moreover, the bonding force between the pre-lithium layer and the diaphragm substrate in existing lithium-replenishing diaphragms is weak, affecting the stability of the lithium-replenishing diaphragms. In addition, the inorganic protective layer in the existing lithium-supplementing diaphragm has a low porosity after the battery is assembled, which affects the ionic conductivity of the battery cell after assembly and further affects the performance of the battery cell.

[0004] Therefore, it is indeed necessary to propose a lithium-supplementing diaphragm for lithium-ion batteries, a lithium-ion battery, and a preparation method to solve or at least alleviate at least one of the above technical problems. Summary of the Invention

[0005] In view of the above technical problems, the present disclosure provides a lithium-replenishing diaphragm for lithium-ion batteries, a lithium-ion battery, and a preparation method to solve or at least alleviate at least one technical problem existing in the above lithium-ion battery lithium-replenishing diaphragm, lithium-ion battery, and preparation method.

[0006] According to a specific embodiment of the present disclosure, in a first aspect, the present disclosure provides a lithium-supplementing diaphragm for a lithium-ion battery, comprising: a diaphragm substrate and a pre-lithium layer, wherein the pre-lithium layer is disposed on one side of the diaphragm substrate, and the lithium-supplementing diaphragm further comprises a first protective layer and a second protective layer.

[0007] The first protective layer is arranged on a side of the pre-lithium layer away from the diaphragm substrate, and is used to protect the pre-lithium layer;

[0008] The two opposite surfaces of the diaphragm substrate are defined as the first surface and the second surface respectively. The second protective layer is arranged on the first surface. The material of the second protective layer includes a polymer and an ester compound. The polymer is insoluble in the electrolyte of the lithium-ion battery; the ester compound is soluble in the electrolyte of the lithium-ion battery.

[0009] Optionally, the lithium-replenishing diaphragm for lithium-ion batteries further includes a third protective layer, which is disposed on the second surface of the diaphragm substrate. The material of the third protective layer includes a polymer and an ester compound. The polymer is insoluble in the electrolyte of the lithium-ion battery; the ester compound is soluble in the electrolyte of the lithium-ion battery.

[0010] Optionally, the mass ratio of the polymer to the ester compound in the second protective layer is 1:4-50:1.

[0011] Optionally, the mass ratio of the polymer to the ester compound in the third protective layer is 1:4-50:1.

[0012] Optionally, both the polymer and the ester compound have a stable electrochemical window in the range of 0-4.5V.

[0013] Optionally, the melting point of the ester compound is greater than or equal to 25°C.

[0014] Optionally, the polymer includes at least one of polyester, polyurethane, polyacrylate, polymethacrylate, polycarbonate, acrylic polymer, and acrylonitrile polymer.

[0015] Optionally, the ester compound includes at least one of ethylene carbonate, propylene carbonate, ethylene sulfate, propylene sulfate, and methylene methanedisulfonate.

[0016] Optionally, the ester compound is soluble in ester and ether solvents.

[0017] Optionally, the material of the pre-lithium layer includes at least one of metallic lithium, lithium silicon alloy, lithium magnesium alloy, lithium copper alloy, lithium silver alloy, lithium beryllium alloy, lithium zinc alloy, lithium cadmium alloy, lithium aluminum alloy, lithium gold alloy and lithium boron alloy.

[0018] Optionally, the material of the first protective layer includes Al2O3, MgO, ZnO2, TiO2, ZrO2, LaO2, CeO2, Y2O3, SixO, SiC, SiNx SiCN x AlN, Mg(OH)2, BaSO4, boehmite or perovskite; or, Li2CO3, Li3N, LiF, Li3PO4, Li4SiO4, Li4Ti5O 12 at least one of LiPON, LiSiON, LLZO, LLZTO, LATP, Li3Fe2(PO4)3, Li3V2(PO4)3, Li3In2(PO4)3, Li3Sc2(PO4)3, Li3Cr2(PO4)3.

[0019] Optionally, the thickness of the first protective layer is 10-1000 nm.

[0020] Optionally, the thickness of the second protective layer is 50-1000 nm.

[0021] Optionally, the thickness of the third protective layer is 50-1000 nm.

[0022] According to the specific embodiment of the present disclosure, in a second aspect, the present disclosure provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator is any one of the lithium supplementing separators for lithium ion batteries as described above.

[0023] According to the specific embodiment of the present disclosure, in a third aspect, the present disclosure provides a preparation method of the lithium supplementing separator for lithium ion batteries as described above, comprising the following steps:

[0024] coating a first slurry on the first surface of the separator substrate, and forming a second protective layer on the first surface of the separator substrate after drying, the first slurry comprising the polymer, the ester compound and an organic solvent for dissolving the polymer and the ester compound;

[0025] depositing a pre-lithium layer on one side of the separator substrate;

[0026] depositing a first protective layer on the surface of the pre-lithium layer away from the separator substrate.

[0027] Optionally, after forming the second protective layer on the first surface of the separator substrate, the method further comprises coating a second slurry on the second surface of the separator substrate, and forming a third protective layer on the second surface of the separator substrate after drying, the second slurry comprising the polymer, the ester compound and an organic solvent for dissolving the polymer and the ester compound.

[0028] Optionally, the first slurry and the second slurry are partially different or completely different in composition.

[0029] Optionally, the solid content of the first slurry is 1%-35%, and the viscosity of the first slurry is 10-3000 cps.

[0030] Optionally, the solid content of the second slurry is 1%-35%, and the viscosity of the second slurry is 10-3000 cps.

[0031] Optionally, in the first slurry, the mass percentage of the polymer is 5%-50%, the mass percentage of the ester compound is 1%-20%, and the mass percentage of the organic solvent is 30%-94%.

[0032] Optionally, in the second slurry, the mass percentage of the polymer is 5%-50%, the mass percentage of the ester compound is 1%-20%, and the mass percentage of the organic solvent is 30%-94%.

[0033] Optionally, the organic solvent includes at least one of cyclohexane, ethyl acetate, butyl acetate, butanone and pyrrolidone.

[0034] Optionally, the preparation method of the first slurry and / or the second slurry includes: adding an ester compound to a polymer in proportion, stirring at a speed of 500-3000 rpm for 10-30 minutes; adding an organic solvent and adjusting the solid content to 1%-35%, the viscosity to 10-3000 cps, and stirring for 5-10 minutes to obtain the first slurry and / or the second slurry.

[0035] Optionally, the first slurry is coated on the first surface of the diaphragm substrate, and / or the second slurry is coated on the second surface of the diaphragm substrate by dipping, roller coating, spraying, scraping or transfer coating, and the drying temperature after coating the first slurry and / or the second slurry is 20-40°C.

[0036] Optionally, the method of depositing the pre-lithium layer on one side of the separator substrate includes at least one of vacuum evaporation, ion plating, radio frequency sputtering, magnetron sputtering or reactive sputtering.

[0037] Optionally, the method of depositing the first protective layer on the surface of the pre-lithium layer away from the diaphragm substrate includes at least one of scraping, roller coating, spraying, chemical vapor deposition, plasma vapor deposition, atomic layer deposition, pulsed laser deposition, vacuum evaporation, ion plating, radio frequency sputtering, magnetron sputtering or reactive sputtering.

[0038] According to a specific embodiment of the present disclosure, in a fourth aspect, the present disclosure provides a method for preparing a lithium ion battery, comprising the following steps:

[0039] Evenly coating the positive electrode active material on the surface of the positive electrode current collector to form a positive electrode sheet;

[0040] Evenly coating the negative electrode active material on the surface of the negative electrode current collector to form a negative electrode sheet;

[0041] A lithium-supplementing diaphragm is prepared by any of the above-mentioned methods for preparing a lithium-supplementing diaphragm;

[0042] The lithium supplement diaphragm is set between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the lithium supplement diaphragm and the negative electrode sheet are placed in a shell. The electrolyte is injected into the shell and the shell is sealed.

[0043] Compared with the prior art, the above solution of the embodiment of the present disclosure has at least the following beneficial effects:

[0044] (1) The lithium-ion battery replenishing diaphragm provided by the present disclosure has an organic protective layer provided on at least one surface of the diaphragm substrate. The organic protective layer includes a polymer and an ester compound. The polymer is insoluble in the electrolyte of the lithium-ion battery, is stable in the electrolyte, does not dissolve or swell, and forms a dense protective layer with the ester compound after film formation to protect the pre-lithium layer. After the battery cell is assembled, it serves as a skeleton to ensure the stability of the battery cell structure. The ester compound is soluble in the electrolyte of the lithium-ion battery. After film formation, it forms a dense protective layer with the polymer to protect the pre-lithium layer. After assembly, it can be dissolved in the electrolyte to form a gap, provide an ion channel, and does not affect the ionic conductivity of the lithium-ion battery replenishing diaphragm after the battery cell is assembled. Therefore, the lithium-ion battery replenishing diaphragm provided by the present disclosure can isolate the lithium metal in the pre-lithium layer from water, carbon dioxide, oxygen, nitrogen, etc. in the air without affecting the ionic conductivity of the lithium-ion battery replenishing diaphragm after the battery cell is assembled, thereby preventing the lithium of the lithium-ion battery replenishing diaphragm from being consumed by water, gas, etc. in the air during the assembly process, thereby affecting the lithium replenishing efficiency. The lithium-ion battery lithium-supplementing separator disclosed herein can adapt to the assembly environment of lithium-ion batteries and reduce the limitations of industrial applications.

[0045] (2) The second protective layer and / or the third protective layer disclosed in the present invention can be continuously produced in an open environment by roller coating, dip coating, transfer coating, etc., without the need for vacuum evaporation through a vacuum coating machine, thereby minimizing the time costs of equipment vacuuming, vacuum breaking, equipment cleaning, etc., and achieving fast production speed, high efficiency, and high yield rate; and the preparation method of the lithium-replenishing diaphragm disclosed in the present invention does not require strict control of the temperature and humidity of the environment, which can further reduce manufacturing costs.

[0046] (3) The second protective layer and / or the third protective layer disclosed in the present invention is an organic coating, which can improve the adhesion of the lithium-replenishing diaphragm to the positive electrode sheet, reduce the internal resistance between the positive electrode sheet and the diaphragm, and improve battery performance; it can also improve the bonding force between the pre-lithium layer and the diaphragm matrix, and increase the stability of the lithium-replenishing diaphragm.

[0047] (4) The second protective layer and the third protective layer disclosed in the present invention are organic protective layers, which are lower in cost than existing protective layers made of inorganic materials such as metals and metal alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate preferred embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained from these drawings without creative labor by those of ordinary skill in the art. In the drawings:

[0049] Figure 1 Structure diagram of the lithium supplementing separator for lithium ion battery in the first embodiment of the present disclosure;

[0050] Figure 2 Structure diagram of the lithium supplementing separator for lithium ion battery in some embodiments of the present disclosure;

[0051] Figure 3 Structure diagram of the lithium supplementing separator for lithium ion battery in some other embodiments of the present disclosure;

[0052] Figure 4 Structure diagram of the lithium supplementing separator for lithium ion battery in some other embodiments of the present disclosure;

[0053] Figure 5 Flow chart of the preparation method of the lithium supplementing separator for lithium ion battery provided in the third embodiment of the present disclosure;

[0054] Figure 6 Flow chart of the preparation method of the lithium supplementing separator for lithium ion battery provided in the third embodiment of the present disclosure;

[0055] Reference signs in the detailed description of the embodiments are as follows:

[0056] Lithium ion battery 100;

[0057] Lithium supplementing separator 10, separator base 1, pre-lithium layer 2, first protective layer 3, second protective layer 4, third protective layer 5, positive electrode sheet 20, negative electrode sheet 30. Detailed description

[0058] In order to make the purpose, technical solutions and advantages of the present disclosure clearer, the present disclosure will be described in further detail below in combination with the drawings. Obviously, the described embodiments are only some embodiments of the present disclosure, but not all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present disclosure.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure.

[0060] It should also be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or device. In the absence of further limitations, an element defined by the phrase "comprising a" does not exclude the presence of other identical elements in the product or device comprising the element.

[0061] In the description of the embodiments of the present disclosure, the orientations or positional relationships indicated by technical terms such as "upper", "lower", and "thickness" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present disclosure.

[0062] In the description of the embodiments of the present disclosure, the term "and / or" is used only to describe the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0063] In the description of the embodiments of the present disclosure, the symbol “-” represents the two endpoint data before and after the “-” and all data between the two endpoints. For example, AB represents all data greater than or equal to A and less than or equal to B.

[0064] References to "embodiments" in this disclosure mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the disclosure. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this disclosure may be combined with other embodiments.

[0065] Most existing lithium replenishment methods for lithium-ion batteries are achieved through anode / cathode pre-lithiation technology. However, existing anode / cathode pre-lithiation has technical problems such as cumbersome operation, high risk, low metal lithium utilization, and high cost.

[0066] After research, the inventors found that pre-lithiation of the diaphragm can also increase the total amount of active lithium during the battery cycle, which not only helps to improve the battery energy density, but also can significantly extend the service life of the battery cell.

[0067] The inventors also discovered through research that, although there are reports of providing a lithium-replenishing layer on the lithium battery separator layer, due to the high activity of lithium metal, the lithium in the lithium-replenishing layer will be consumed by water and gas in the air during the battery assembly process, affecting the efficiency of lithium replenishment. Moreover, the reaction between lithium metal and water is very rapid, releasing a large amount of heat and hydrogen, causing significant safety issues. As a result, existing lithium-ion battery lithium-replenishing separators are unable to adapt to the assembly environment of lithium-ion batteries, limiting their industrial application. There are also reports of providing a metal material as a protective layer on the surface of the lithium-replenishing layer, but the metal material is relatively expensive, and the construction method requires a vacuum environment, which cannot be continuously produced, has low efficiency, and high production costs. Moreover, the existing inorganic protective layer cannot swell / dissolve in the electrolyte after the battery is assembled, which in turn makes the separator porosity low, affecting the ionic conductivity of the battery cell after assembly.

[0068] In order to solve the above technical problems, the present invention provides an organic protective layer on at least one surface of the diaphragm substrate. The material of the organic protective layer includes a polymer and an ester compound. The polymer does not dissolve or swell in the electrolyte of the lithium-ion battery, and the ester compound dissolves in the electrolyte of the lithium-ion battery.

[0069] Specifically, an embodiment of the present disclosure provides a lithium-replenishing diaphragm for a lithium-ion battery, comprising: a diaphragm substrate, a pre-lithium layer, a first protective layer, and a second protective layer. The pre-lithium layer is arranged on one side of the diaphragm substrate, and the first protective layer is arranged on the side of the pre-lithium layer away from the diaphragm substrate to protect the pre-lithium layer; the two opposite surfaces of the diaphragm substrate are respectively defined as the first surface and the second surface, the second protective layer is arranged on the first surface, and the material of the second protective layer includes a polymer and an ester compound, the polymer is insoluble in the electrolyte of the lithium-ion battery; the ester compound is soluble in the electrolyte of the lithium-ion battery.

[0070] In some embodiments, the lithium replenishing diaphragm for lithium-ion batteries further includes a third protective layer, which is disposed on the second surface of the diaphragm substrate. The material of the third protective layer includes the polymer and the ester compound.

[0071] In the technical solution disclosed in the present invention, a second protective layer and / or a third protective layer are provided on the surface of the diaphragm substrate. The second protective layer and / or the third protective layer are both organic protective layers, including polymers and ester compounds. The polymers are insoluble in the electrolyte of the lithium-ion battery, are stable in the electrolyte, do not dissolve or swell, and form a dense protective layer together with the ester compounds after film formation. After assembling the battery cell, it serves as a skeleton to ensure the stability of the battery cell structure. The ester compound dissolves in the electrolyte of the lithium-ion battery, forms a dense protective layer together with the polymer after film formation, and can be dissolved in the electrolyte after assembly to form gaps, provide ion channels, and does not affect the ion conductivity of the battery cell after assembly. Moreover, the second protective layer and / or the third protective layer disclosed in the present invention can be continuously produced in an open environment using roller coating, dip coating, transfer coating, etc., without the need for vacuum evaporation through a vacuum coating machine, minimizing the time cost of equipment vacuuming, breaking vacuum, and equipment cleaning, thereby improving production efficiency; and there is no need to strictly control the temperature and humidity of the environment, which can further reduce manufacturing costs. At the same time, the second and / or third protective layers disclosed herein are organic coatings, which can improve the adhesion of the lithium-replenishing separator to the positive electrode sheet, reducing the internal resistance between the positive electrode sheet and the separator; they can also improve the bonding between the pre-lithium layer and the separator substrate, increasing the stability of the lithium-replenishing separator. Furthermore, the first, second, and / or third protective layers disclosed herein isolate the lithium metal in the pre-lithium layer from water, carbon dioxide, oxygen, nitrogen, and other gases in the air, preventing the lithium from being consumed by water and gases in the air during the assembly of the lithium-replenishing separator, which would affect the lithium-replenishing efficiency.

[0072] Optional embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

[0073] See also Figure 1 The first embodiment of the present disclosure provides a lithium-replenishing separator 10 for a lithium-ion battery (hereinafter referred to as the lithium-replenishing separator 10). The lithium-replenishing separator 10 includes a separator substrate 1, a pre-lithium layer 2, a first protective layer 3, a second protective layer 4, and a third protective layer 5. The first protective layer 3 is disposed on the side of the pre-lithium layer 2 away from the separator substrate 1, the second protective layer 4 is disposed on the surface of the separator substrate 1 away from the pre-lithium layer 2, and the third protective layer 5 is disposed on the surface of the separator substrate 1 close to the pre-lithium layer 2. The second protective layer 4, the separator substrate 1, the third protective layer 5, the pre-lithium layer 2, and the first protective layer 3 are stacked in sequence.

[0074] The separator substrate 1 can be a commonly used separator for lithium ion batteries. The separator substrate 1 can include, but is not limited to, a base film, a base film / ceramic composite separator, a base film / adhesive composite separator, or a base film / ceramic / adhesive composite separator. The base film includes, but is not limited to, at least one of a polyethylene base film, a polyethylene non-woven base film, a polypropylene base film, a polypropylene non-woven base film, a polypropylene / polyethylene / polypropylene composite base film, a polyimide base film, a polyimide non-woven base film, a polytetrafluoroethylene base film, a polytetrafluoroethylene non-woven base film, a polyvinyl chloride base film, and a polyvinyl chloride non-woven base film. The ceramic includes, but is not limited to, at least one of alumina, zirconia, boehmite, magnesium hydroxide, barium sulfate, silicon oxide, aluminum nitride, magnesium oxide, titanium dioxide, yttrium oxide, and cerium oxide. The adhesive includes, but is not limited to, at least one of polytetrafluoroethylene, polyvinylidene fluoride, acrylic acid, polyethylene oxide, carboxymethyl cellulose sodium, styrene butadiene rubber, hydroxypropyl methyl cellulose, carboxy styrene latex, and polyvinyl alcohol. The thickness of the separator substrate 1 is preferably, but not limited to, 5-50 μm. As an example, in some embodiments, the thickness of the separator substrate 1 is 5 μm, 16 μm, 20 μm, 25 μm, 30 μm, 40 μm, or 50 μm, etc.

[0075] The material of the pre-lithium layer 2 can be, but is not limited to, at least one of metallic lithium, lithium-silicon alloy, lithium-magnesium alloy, lithium-copper alloy, lithium-silver alloy, lithium-beryllium alloy, lithium-zinc alloy, lithium-cadmium alloy, lithium-aluminum alloy, lithium-gold alloy, and lithium-boron alloy. The thickness of the pre-lithium layer 2 is preferably, but not limited to, 0.1-10 μm. As an example, in some embodiments, the thickness of the pre-lithium layer 2 is 0.1 μm, 0.5 μm, 1 μm, 5 μm, 8 μm, or 10 μm, etc.

[0076] The first protective layer 3 is used to protect the pre-lithium layer 2, preventing the lithium in the pre-lithium layer 2 from being directly exposed to air, which is consumed by water and gas in the air during the assembly process of the battery cell. The first protective layer 3 is preferably a high ionic conductive material, which can provide protection for the pre-lithium layer 2 while improving the ionic conductivity of the overall lithium supplementing separator, improving the lithium supplementing efficiency and effect during use. In some embodiments, the first protective layer 3 is an inorganic protective layer. The material of the first protective layer 3 includes, but is not limited to, Al2O3, MgO, ZnO2, TiO2, ZrO2, LaO2, CeO2, Y2O3, SixO, SiC, SiN x , SiCN x , AlN, Mg(OH)2, BaSO4, boehmite, or perovskite; or Li2CO3, Li3N, LiF, Li3PO4, Li4SiO4, Li4Ti5O 12, LiPON, LiSiON, LLZO, LLZTO, LATP, Li3Fe2(PO4)3, Li3V2(PO4)3, Li3In2(PO4)3, Li3Sc2(PO4)3, Li3Cr2(PO4)3. The thickness of the third protective layer 5 is preferably, but not limited to, 10-1000 nm. As an example, in some embodiments, the thickness of the third protective layer 5 is 10 nm, 30 nm, 100 nm, 300 nm, 500 nm, 800 nm, or 1000 nm.

[0077] The second protective layer 4 is provided on the lower surface of the diaphragm substrate 1 . The third protective layer 5 is provided on the upper surface of the diaphragm substrate 1 and is located between the diaphragm substrate 1 and the pre-lithium layer 2 .

[0078] The material of the second protective layer 4 and / or the material of the third protective layer 5 both include polymers and ester compounds. If there are too many polymers, the porosity release of the lithium-replenishing membrane 10 will be weak, which will affect the ionic conductivity; if there are too many ester compounds, the stability of the second protective layer 4 and / or the third protective layer 5 will deteriorate, and the protection of the pre-lithium layer 2 will be insufficient. Preferably, the mass ratio of the polymer and the ester compound is 1:4-50:1. More preferably, the mass ratio of the polymer and the ester compound is 1.25:1-5:1. Within this mass ratio range, the second protective layer 4 and / or the third protective layer 5 can better balance the protection of the pre-lithium layer 2 and the ionic conductivity of the lithium-replenishing membrane 10. As an example, in some embodiments, the mass ratio of the polymer and the ester compound is 5:1, 3.3:1, 1.25:1, 1.4:1 or 2.25:1.

[0079] Preferably, the polymer has a stable electrochemical window of 0-4.5V, so as to avoid the polymer participating in the battery reaction during the battery charge and discharge process, thereby preventing the battery stability from being deteriorated.

[0080] The polymer is stable in the electrolyte of lithium-ion batteries, neither dissolving nor swelling. Therefore, after film formation, it forms a dense protective layer on the surface of the diaphragm substrate 1 together with the ester compound, isolating the pre-lithium layer 2 from the air and protecting the diaphragm substrate 1 and the pre-lithium layer 2. Furthermore, after assembly into the battery cell, it can serve as a skeleton, ensuring the stability of the cell structure. The polymer preferably includes, but is not limited to, at least one of polyester, polyurethane, polyacrylate, polymethacrylate, and polycarbonate.

[0081] Preferably, the ester compound has a stable electrochemical window of 0-4.5V to prevent the ester compound from participating in the battery reaction during the battery charge and discharge process, resulting in deterioration of battery stability. In some embodiments, the ester compound has a melting point of ≥25°C and is solid at room temperature.

[0082] The ester compound can be dissolved in the electrolyte of the lithium-ion battery. Therefore, after film formation, it forms a dense protective layer together with the polymer to isolate the pre-lithium layer 2 from the air, protecting the diaphragm matrix 1 and the pre-lithium layer 2; after assembling the battery cell, it dissolves in the electrolyte, thereby allowing the lithium-supplementing diaphragm to form gaps, providing ion channels, and not affecting the ionic conductivity of the lithium-ion battery. Preferably, the ester compound can be dissolved in ester and ether solvents. The ester compound preferably includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (TMC), ethylene sulfate (DTD), propylene sulfate, and methylene methanedisulfonate.

[0083] The polymer and ester compound of the second protective layer 4 and / or the third protective layer 5 work together to protect the pre-lithium layer 2 of the lithium replenishing separator 10 during assembly without affecting the ionic conductivity of the lithium replenishing separator after the battery cell is assembled.

[0084] If the thickness of the second protective layer 4 and / or the third protective layer 5 is too small, for example, less than 50 nm, the protection performance of the pre-lithium layer 2 will be insufficient, and the lithium consumption of the pre-lithium layer 2 will increase; if the thickness of the second protective layer 4 is too large, for example, greater than 1000 nm, the overall thickness of the battery cell will increase, and the volume energy density of the battery cell will be reduced. In some preferred embodiments, the thickness of the second protective layer 4 and / or the third protective layer 5 is 50-1000 nm. In some more preferred embodiments, the thickness of the second protective layer 4 and / or the third protective layer 5 is 200-500 nm. In this embodiment, the thickness of the second protective layer 4 and / or the third protective layer 5 is 200 nm.

[0085] The components of the second protective layer 4 and the third protective layer 5 can be completely identical, partially identical, or completely different. For example, in some embodiments, the components of the second protective layer are polyurethane and ethylene sulfate, and the components of the third protective layer are polyester and ethylene carbonate; in some embodiments, the components of both the second and third protective layers are polyurethane and ethylene sulfate; in other embodiments, the components of the second protective layer are polyurethane and ethylene sulfate, and the components of the third protective layer are polyurethane, polyacrylate, and propylene carbonate.

[0086] It is understood that the present disclosure is not limited to the embodiment in which the organic protective layer is provided on both the upper and lower surfaces of the diaphragm substrate 1. The organic protective layer may also be provided on only one surface of the diaphragm substrate 1. For example, see Figure 2 In some embodiments, the third protective layer 5 is provided only on the upper surface of the diaphragm substrate 1; see Figure 3 In some other embodiments, the second protective layer 4 is provided only on the lower surface of the diaphragm substrate 1 .

[0087] A second embodiment of the present disclosure provides a lithium-ion battery 100. Figure 4Fig. 1 is a schematic diagram of a lithium-ion battery 100, including a lithium supplement diaphragm, a positive electrode sheet 20 and a negative electrode sheet 30, the lithium supplement diaphragm being located between the positive electrode sheet 20 and the negative electrode sheet 30, the lithium supplement diaphragm being any one of the lithium supplement diaphragms 10 for lithium-ion batteries as described in the first embodiment.

[0088] Referring to Figure 5 The third embodiment of the present disclosure provides a preparation method of the lithium supplement diaphragm 10 for lithium-ion batteries as described in any one of the preceding embodiments, including the following steps:

[0089] Step (S1), applying a first slurry on a first surface of the diaphragm substrate 1, and forming a second protective layer 4 on the first surface of the diaphragm substrate 1 after drying, the first slurry including the polymer, the ester compound and the organic solvent, the organic solvent being used to dissolve the polymer and the ester compound;

[0090] Step (S2), depositing a pre-lithium layer 2 on one side of the diaphragm substrate 1;

[0091] Step (S3), depositing a first protective layer 3 on the surface of the pre-lithium layer 2 away from the diaphragm substrate 1.

[0092] The polymer and the ester compound in step (S1) are the same as the polymer and the ester compound in the first embodiment, including all the features described in the first embodiment, which will not be repeated here.

[0093] It can be understood that in some embodiments, after forming the second protective layer 4 on the first surface of the diaphragm substrate 1 in step (S1), a second slurry is further applied on a second surface of the diaphragm substrate 1, and a third protective layer 5 is formed on the second surface of the diaphragm substrate 1 after drying. The second slurry includes the polymer, the ester compound and the organic solvent, and the organic solvent is used to dissolve the polymer and the ester compound.

[0094] In some embodiments, the mass percentage of the polymer in the first slurry and / or the second slurry is 5%-50%, the mass percentage of the ester compound is 1%-20%, and the mass percentage of the organic solvent is 30%-94%.

[0095] In some embodiments, the solid content in the first slurry and / or the second slurry is 1%-35%. In some preferred embodiments, the solid content in the first slurry and / or the second slurry is 10%-15%. The viscosity of the first slurry and / or the second slurry is preferably 10-3000 cps. More preferably, the viscosity of the first slurry and / or the second slurry is 500-1000 cps. Within the above data range, the slurry can match a faster coating speed, and the coating uniformity and stability are better.

[0096] The organic solvent may be, but is not limited to, at least one of cyclohexane, ethyl acetate, butyl acetate, butanone, and pyrrolidone.

[0097] In some embodiments, the preparation method of the first slurry and / or the second slurry includes: adding an ester compound to a polymer in proportion, stirring at a speed of 500-3000 rpm for 10-30 minutes; adding an organic solvent and adjusting the solid content to 1%-35%, the viscosity to 10-3000 cps, and stirring for 5-10 minutes to obtain the first slurry and / or the second slurry.

[0098] The method of coating the first slurry and / or the second slurry on the first surface and / or the second surface of the diaphragm substrate 1 may be, but is not limited to, dipping, roller coating, spraying, blade coating or transfer coating. The coating speed is preferably 0-30 mpm, more preferably 15-30 mpm. The drying temperature after coating the first slurry and / or the second slurry is preferably, but not limited to, 20-40°C. The coating thickness after drying is 50-1000 nm, preferably 200-500 nm. In the present embodiment, the coating thickness after drying is 200 nm. In the present embodiment, the first slurry and the second slurry are respectively coated on the lower surface and the upper surface of the diaphragm substrate 1 by a roller coating process.

[0099] The components of the first slurry and the second slurry may be completely the same, partially the same, or completely different.

[0100] In step (S2), the method of depositing the pre-lithium layer 2 on one side of the diaphragm substrate 1 includes, but is not limited to, at least one of vacuum evaporation, ion plating, radio frequency sputtering, magnetron sputtering, or reactive sputtering. In this embodiment, the pre-lithium layer 2 is deposited on one side of the diaphragm substrate 1 by a vacuum evaporation process.

[0101] In step (S3), the method for depositing the first protective layer 3 on the surface of the pre-lithium layer 2 away from the diaphragm substrate 1 includes but is not limited to at least one of blade coating, roller coating, spray coating, chemical vapor deposition, plasma vapor deposition, atomic layer deposition, pulsed laser deposition, vacuum evaporation, ion plating, radio frequency sputtering, magnetron sputtering or reactive sputtering. In this embodiment, the first protective layer 3 is deposited on the surface of the pre-lithium layer 2 away from the diaphragm substrate 1 by vacuum evaporation technology.

[0102] See also Figure 6 A fourth embodiment of the present disclosure provides a method for preparing a lithium-ion battery, comprising the following steps:

[0103] Evenly coating the positive electrode active material on the surface of the positive electrode current collector to form a positive electrode sheet;

[0104] Evenly coating the negative electrode active material on the surface of the negative electrode current collector to form a negative electrode sheet;

[0105] Prepare a lithium-supplementing diaphragm by using any of the preparation methods for a lithium-supplementing diaphragm described in the third embodiment;

[0106] The lithium supplement diaphragm is set between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the lithium supplement diaphragm and the negative electrode sheet are placed in a shell. The electrolyte is injected into the shell and the shell is sealed.

[0107] The positive electrode collector, positive electrode active material, negative electrode collector, negative electrode active material, shell and electrolyte can be selected from the positive electrode collector, positive electrode active material, negative electrode collector, negative electrode active material, shell and electrolyte commonly used in lithium ion batteries.

[0108] The following describes the preparation process, test methods, and test data of the comparative examples and embodiments:

[0109] Example 1:

[0110] The lithium-ion battery lithium supplementation diaphragm of this embodiment comprises, in sequence: a 200nm second protective layer, a 25μm alumina ceramic coating diaphragm, a 1μm pre-lithium layer, and a 30nm Li2CO3 first protective layer. The preparation method comprises the following steps:

[0111] Step (S1) of applying a first slurry on the lower surface of a 25 μm alumina ceramic coating membrane by a roller coating process, and forming a second protective layer with a thickness of 200 nm on the lower surface of the alumina ceramic coating membrane after drying at 40° C., wherein the components of the first slurry are, by mass percentage, 5% polyurethane: ethylene sulfate: cyclohexane: butyl acetate: 1%: 45%: 49%;

[0112] Step (S2), depositing a pre-lithium layer with a thickness of 1000 nm on the upper surface of the alumina ceramic coating diaphragm by a vacuum evaporation process, wherein the component of the pre-lithium layer is lithium metal;

[0113] Step (S3), depositing a first protective layer with a thickness of 30 nm on the upper surface of the pre-lithium layer by vacuum evaporation technology, wherein the component of the first protective layer is Li2CO3, thereby obtaining a lithium-ion battery lithium supplementing diaphragm.

[0114] Example 2:

[0115] The lithium-ion battery lithium supplementation membrane of this embodiment comprises, in sequence: a 50nm second protective layer, a 16μm PP membrane, a 1000nm third protective layer, a 0.5nm pre-lithium layer, and a 100nm Li2CO3 first protective layer. The preparation method comprises the following steps:

[0116] Step (S1), applying a first slurry on the lower surface of a 16 μm PP membrane by a roller coating process, and forming a second protective layer with a thickness of 50 nm on the lower surface of the 16 μm PP membrane after drying at 40° C., wherein the components of the first slurry are as follows: polyurethane: ethylene sulfate: cyclohexane: butyl acetate (5%:1%:45%:49%) by mass percentage; applying a second slurry on the upper surface of the 16 μm PP membrane by a roller coating process, and forming a third protective layer with a thickness of 1000 nm on the upper surface of the 16 μm PP membrane after drying at 40° C., wherein the components of the second slurry are as follows: polyester: ethylene carbonate: butyl acetate (50%:15%:35%) by mass percentage;

[0117] Step (S2), depositing a pre-lithium layer with a thickness of 0.5 nm on the third protective layer by a vacuum evaporation process, wherein the pre-lithium layer is composed of a lithium-silver alloy;

[0118] Step (S3) is to deposit a first protective layer with a thickness of 100 nm on the upper surface of the pre-lithium layer by vacuum evaporation technology, wherein the component of the first protective layer is Li2CO3, thereby obtaining a lithium-ion battery lithium supplementing diaphragm.

[0119] Example 3:

[0120] The lithium-ion battery lithium supplementation diaphragm of this embodiment comprises, in sequence: a 1000nm second protective layer, a 50μm boehmite ceramic coating diaphragm, a 10μm pre-lithium layer, and a 1000nm Li2CO3 first protective layer. The preparation method comprises the following steps:

[0121] Step (S1): applying a first slurry on the lower surface of a 50 μm boehmite ceramic coating membrane by a roller coating process, and forming a second protective layer with a thickness of 1000 nm on the lower surface of the boehmite ceramic coating membrane after drying at 40° C., wherein the components of the first slurry are, by mass percentage, 25% polyacrylate: propylene carbonate: butanone: 55%;

[0122] Step (S2), depositing a pre-lithium layer with a thickness of 10 μm on the upper surface of the boehmite ceramic coating diaphragm by a vacuum evaporation process, wherein the component of the pre-lithium layer is a lithium-magnesium alloy;

[0123] Step (S3), depositing a first protective layer with a thickness of 1000 nm on the upper surface of the pre-lithium layer by vacuum evaporation technology, wherein the component of the first protective layer is Li2CO3, thereby obtaining a lithium-ion battery lithium supplementing diaphragm.

[0124] Example 4:

[0125] The lithium-ion battery lithium supplementation diaphragm of this embodiment comprises, in sequence: a 500nm second protective layer, a 25μm alumina ceramic coating diaphragm, a 5μm pre-lithium layer, and a 10nm Al2O3 first protective layer. The preparation method comprises the following steps:

[0126] Step (S1): applying a first coating slurry on the lower surface of a 25 μm alumina ceramic coating membrane by a roller coating process, and forming a second protective layer with a thickness of 500 nm on the lower surface of the alumina ceramic coating membrane after drying at 40° C., wherein the components of the first slurry are, by mass percentage, polymethyl methacrylate: propylene sulfate: propylene carbonate: ethyl acetate in a ratio of 35%: 10%: 15%: 40%;

[0127] Step (S2), depositing a pre-lithium layer with a thickness of 10 μm on the upper surface of the boehmite ceramic coating membrane by a vacuum evaporation process, wherein the component of the pre-lithium layer is a lithium-copper alloy;

[0128] Step (S3), depositing a first protective layer with a thickness of 1000 nm on the upper surface of the pre-lithium layer by vacuum evaporation technology, wherein the component of the first protective layer is Li2CO3, thereby obtaining a lithium-ion battery lithium supplementing diaphragm.

[0129] Example 5:

[0130] The lithium-ion battery lithium supplementation diaphragm of this embodiment comprises, in sequence: a 32 μm alumina ceramic coating diaphragm, a 200 nm third protective layer, an 8 μm pre-lithium layer, and a 300 nm Li3N first protective layer. The preparation method comprises the following steps:

[0131] Step (S1): coating the upper surface of a 32 μm alumina ceramic coating membrane with a second slurry by a roller coating process, and forming a 200 nm thick third protective layer on the lower surface of the alumina ceramic coating membrane after drying at 40° C., wherein the components of the second slurry are, by mass percentage, polyurethane: polyacrylate: propylene carbonate: pyrrolidone: butyl acetate in a ratio of 20%: 25%: 20%: 10%: 25%;

[0132] Step (S2), depositing a pre-lithium layer with a thickness of 8 μm on the upper surface of the alumina ceramic coating diaphragm by a vacuum evaporation process, wherein the component of the pre-lithium layer is a lithium-zinc alloy;

[0133] Step (S3) is to deposit a first protective layer with a thickness of 300 nm on the upper surface of the pre-lithium layer by vacuum evaporation technology, wherein the component of the first protective layer is Li3N, thereby obtaining a lithium-ion battery lithium supplementing diaphragm.

[0134] Comparative Example 1:

[0135] The diaphragm in this comparative example does not have any protective layer and is a 25 μm alumina ceramic coating diaphragm.

[0136] Comparative Example 2:

[0137] In this comparative example, the diaphragm does not have an organic protective layer. The diaphragm comprises, in order: a 25 μm alumina ceramic coating diaphragm, a 1 μm pre-lithium layer, and a 30 nm Li2CO3 first protective layer. The preparation method comprises:

[0138] A 1 μm thick pre-lithium layer is deposited on the upper surface of a 25 μm alumina ceramic coating diaphragm by vacuum evaporation, wherein the pre-lithium layer is composed of lithium metal;

[0139] A first protective layer with a thickness of 30 nm is deposited on the upper surface of the pre-lithium layer by vacuum evaporation technology, and the component of the first protective layer is Li2CO3.

[0140] The pre-lithium layer consumption of the lithium-supplementing separators of Examples 1-5 and Comparative Example 2 was tested as follows: Each of the lithium-supplementing separators of Examples 1-5 and Comparative Example 2 was exposed to a -25°C dew point environment for 8 hours. The thickness of the pre-lithium layer on the separator cross section was observed using a scanning electron microscope (SEM) to obtain the pre-lithium layer consumption data. The test data is shown in Table 1.

[0141] The lithium-supplemented separators of Examples 1-5, Comparative Example 2, and the separator of Comparative Example 1 were immersed in a 45°C electrolyte for 24 hours, then removed, washed, and dried. The permeability, porosity, and ionic conductivity of the separators were tested. The test data are shown in Table 1.

[0142] Table 1

[0143]

[0144] As can be seen from Table 1, the lithium consumption of the lithium-replenishing diaphragms in Examples 1-5 is much lower than the lithium consumption of the lithium-replenishing diaphragm in Comparative Example 2, indicating that the present disclosure provides an organic protective layer on at least one surface of the diaphragm substrate, which can better protect the pre-lithium layer, greatly reduce the lithium consumption of the pre-lithium layer, and improve the utilization rate of lithium.

[0145] Table 1 also shows that the permeability and porosity of the lithium-replenishing separators of Examples 1-5 are not much different from those of the separators of Comparative Examples 1 and 2. This is because the ester compound in the organic protective layer of the present disclosure dissolves in the electrolyte after assembly, generating voids. This indicates that the provision of an organic protective layer on at least one surface of the separator substrate of the present disclosure has little effect on the permeability and porosity of the lithium-replenishing separator, which can be essentially ignored. Table 1 also shows that the ionic conductivity of the lithium-replenishing separators of Examples 1-5 is not much different from that of the separators of Comparative Examples 1 and 2. This indicates that the provision of an organic protective layer on at least one surface of the separator substrate of the present disclosure has little effect on the ionic conductivity of the lithium-replenishing separator, which can be essentially ignored. This further demonstrates that the provision of an organic protective layer on at least one surface of the separator substrate of the present disclosure has little effect on the permeability and porosity of the lithium-replenishing separator.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present disclosure, and they should all be included in the scope of the claims and description of the present disclosure. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present disclosure is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A lithium-supplementing diaphragm for a lithium-ion battery, comprising: The diaphragm substrate and the pre-lithium layer, the diaphragm substrate includes a first surface and a second surface opposite to each other, the pre-lithium layer is arranged on the second surface of the diaphragm substrate, characterized in that the lithium supplement diaphragm further includes a first protective layer and a second protective layer, The first protective layer is provided on a side of the pre-lithium layer away from the diaphragm substrate, and is used to protect the pre-lithium layer; the first protective layer is an inorganic protective layer; The second protective layer is arranged on the first surface, and the material of the second protective layer includes a polymer and an ester compound, the polymer is insoluble in the electrolyte of the lithium-ion battery; the ester compound is soluble in the electrolyte of the lithium-ion battery; the polymer includes at least one of polyester, polyurethane, polyacrylate, polymethacrylate, polycarbonate, acrylic polymer, and acrylonitrile polymer; the ester compound includes at least one of ethylene carbonate, propylene carbonate, ethylene sulfate, propylene sulfate, and methylene methanedisulfonate.

2. The lithium-supplementing diaphragm for lithium-ion batteries according to claim 1, characterized in that: The lithium-replenishing diaphragm for a lithium-ion battery also includes a third protective layer, which is arranged on the second surface of the diaphragm substrate. The pre-lithium layer is arranged on the side of the third protective layer away from the diaphragm substrate. The material of the third protective layer includes a polymer and an ester compound, the polymer is insoluble in the electrolyte of the lithium-ion battery; the ester compound is soluble in the electrolyte of the lithium-ion battery; the polymer includes at least one of polyester, polyurethane, polyacrylate, polymethacrylate, polycarbonate, acrylic polymer, and acrylonitrile polymer; the ester compound includes at least one of ethylene carbonate, propylene carbonate, ethylene sulfate, propylene sulfate, and methylene methanedisulfonate.

3. The lithium-supplementing diaphragm for lithium-ion batteries according to claim 2, characterized in that: The mass ratio of the polymer to the ester compound in the second protective layer and / or the third protective layer is 1:4-50:

1.

4. The lithium-supplementing diaphragm for lithium-ion batteries according to claim 1 or 2, characterized in that: The polymer and the ester compound both have a stable electrochemical window in the range of 0-4.5V, and the melting point of the ester compound is greater than or equal to 25°C.

5. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, characterized in that: The separator is a lithium-supplementing separator for a lithium-ion battery according to any one of claims 1 to 4.

6. A method for preparing a lithium-supplementing diaphragm for a lithium-ion battery according to any one of claims 1 to 4, characterized in that: The following steps are involved: Applying a first slurry on the first surface of the diaphragm substrate and drying it to form the second protective layer on the first surface of the diaphragm substrate, wherein the first slurry includes the polymer, the ester compound and an organic solvent, and the organic solvent is used to dissolve the polymer and the ester compound; Depositing the pre-lithium layer on the second surface of the diaphragm substrate; The first protective layer is deposited on a surface of the pre-lithium layer away from the separator substrate.

7. The method for preparing a lithium-supplementing diaphragm for a lithium-ion battery according to claim 6, wherein: After forming the second protective layer on the first surface of the diaphragm substrate and before depositing the pre-lithium layer, the method further includes coating a second slurry on the second surface of the diaphragm substrate and forming a third protective layer on the second surface of the diaphragm substrate after drying, wherein the second slurry includes the polymer, the ester compound and the organic solvent, and the organic solvent is used to dissolve the polymer and the ester compound.

8. The method for preparing a lithium-supplementing diaphragm for a lithium-ion battery according to claim 7, wherein: The components of the first slurry and the second slurry are partially different or completely different.

9. The method for preparing a lithium-supplementing diaphragm for a lithium-ion battery according to any one of claims 7 to 8, characterized in that: The solid content of the first slurry is 1%-35%, and the viscosity of the first slurry is 10-3000 cps; and / or the solid content of the second slurry is 1%-35%, and the viscosity of the second slurry is 10-3000 cps; And / or, in the first slurry and / or the second slurry, the mass percentage of the polymer is 5%-50%, the mass percentage of the ester compound is 1%-20%, and the mass percentage of the organic solvent is 30%-94%.

10. The method for preparing a lithium-supplementing diaphragm for a lithium-ion battery according to any one of claims 6 to 8, characterized in that: The organic solvent includes at least one of cyclohexane, ethyl acetate, butyl acetate, butanone and pyrrolidone.

11. A method for preparing a lithium ion battery, characterized in that: The following steps are involved: Evenly coating the positive electrode active material on the surface of the positive electrode current collector to form a positive electrode sheet; Evenly coating the negative electrode active material on the surface of the negative electrode current collector to form a negative electrode sheet; The lithium-supplementing diaphragm is prepared by the method for preparing the lithium-supplementing diaphragm according to any one of claims 6 to 10; The lithium supplementing diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the lithium supplementing diaphragm and the negative electrode sheet are placed in a shell. After the electrolyte is injected into the shell, the shell is sealed.

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