Composite diaphragm for lithium battery and battery cell

Abstract

The utility model relates to the technical field of power batteries, in particular to a composite diaphragm for a lithium battery, the lithium battery comprises a first pole piece and a second pole piece, the composite diaphragm is arranged between the first pole piece and the second pole piece, and the composite diaphragm for the lithium battery comprises a base diaphragm layer, a first lithium supplementing structure and a second lithium supplementing structure, the first lithium supplementing structure is arranged on the first side of the base film layer and located between the base film layer and the first pole piece, the second lithium supplementing structure is arranged on the second side of the base film layer and located between the base film layer and the second pole piece, and the first lithium supplementing structure comprises a ceramic layer, a first lithium supplementing layer and a conductive layer which are sequentially stacked from the base film layer to the first pole piece; and the second lithium supplementing structure comprises a ceramic layer, a second lithium supplementing layer and a conductive layer which are sequentially stacked from the base membrane layer to the second pole piece. The composite diaphragm for the lithium battery can realize accurate lithium supplementing, improve the first coulombic efficiency and improve the energy density of the battery.

Description

Technical Field

[0001] The utility model relates to the technical field of power batteries, and specifically provides a composite diaphragm and a battery core for a lithium battery. Background Art

[0002] Lithium-ion batteries, with their high energy density, excellent power performance, and long cycle life, have seen increasing adoption in electric vehicles in recent years. To continuously increase the driving range of electric vehicles, users are demanding higher energy density from lithium-ion batteries. To improve battery energy density, the industry generally prioritizes selecting high-capacity positive and negative electrode materials, reducing the content of inactive substances in the formulation, such as ultra-thin foils, ultra-thin separators, and ultra-thin housings, and employing extreme battery structural design, such as improving space utilization. However, after years of development, these approaches have essentially reached their limits in terms of increasing battery energy density, necessitating the exploration of new methods and approaches.

[0003] There is a phenomenon in batteries, that is, during the first charge and discharge process, the organic electrolyte will combine with the lithium ions migrating from the positive electrode on the surface of the negative electrode material to form an electronically insulating, lithium-ion conductive electrolyte film (SEI film), resulting in low efficiency of the battery's first charge and discharge. Currently, the first efficiency of ternary batteries is generally 80% to 88%. If silicon material is used for the negative electrode, the efficiency is even lower, about 70% to 85%. In the battery, all lithium ions are provided by the positive electrode material. The formation of the SEI film consumes the active lithium in the battery, resulting in a waste of positive electrode materials. Therefore, if lithium can be replenished during the first charge of the battery, the first coulomb efficiency can be improved, and the loss of active lithium in the positive electrode material itself can be reduced, the energy density of the battery can be effectively improved.

[0004] Therefore, this field needs a new technical solution to solve the above problems. Utility Model Content

[0005] The utility model aims to solve the above technical problems and provide a new composite diaphragm and battery cell for lithium batteries that can achieve accurate lithium replenishment, improve the initial coulombic efficiency, and increase the battery energy density.

[0006] The utility model provides a composite diaphragm for a lithium battery, wherein the lithium battery comprises a first pole piece and a second pole piece, and the composite diaphragm is arranged between the first pole piece and the second pole piece. The utility model is characterized in that the composite diaphragm for the lithium battery comprises:

[0007] A base film layer, the base film layer having a first side and a second side disposed opposite to each other;

[0008] A first lithium replenishing structure is provided on a first side of the base membrane layer and located between the base membrane layer and the first pole piece;

[0009] A second lithium replenishing structure is provided on the second side of the base membrane layer and is located between the base membrane layer and the second pole piece;

[0010] Among them, the first lithium replenishing structure includes a ceramic layer, a first lithium replenishing layer and a conductive layer stacked in sequence from the base membrane layer to the first pole piece, and the second lithium replenishing structure includes a ceramic layer, a second lithium replenishing layer and a conductive layer stacked in sequence from the base membrane layer to the second pole piece.

[0011] When the above-mentioned technical solution is adopted, lithium replenishing structures are respectively provided on both sides of the base film layer of the composite diaphragm for lithium batteries of the utility model, that is, lithium replenishing structures are provided at positions of the base film layer close to the first pole piece and the second pole piece, so that the battery can replenish lithium for the first pole piece and the second pole piece at the same time during the charging and discharging process, which can improve the initial coulombic efficiency and thus improve the energy density of the battery; arranging a multi-layer functional layer on the surface of the base film layer can improve the electrolyte wettability and liquid retention performance of the diaphragm, which has a significant effect on improving battery performance.

[0012] In the preferred technical solution of the composite separator for lithium batteries, the first lithium replenishing layer includes a first lithium replenishing additive, a conductive agent and a binder, and the second lithium replenishing layer includes a second lithium replenishing additive, a conductive agent and a binder. The first lithium replenishing additive and the second lithium replenishing additive are made of different materials.

[0013] When the above technical solution is adopted, the first lithium replenishing layer and the second lithium replenishing layer respectively include a first lithium replenishing additive and a second lithium replenishing additive. The first lithium replenishing additive and the second lithium replenishing additive use different materials. The lithium replenishing additive corresponding to the first pole piece is the first pole lithium replenishing additive, and the lithium replenishing additive corresponding to the second pole piece is the second pole lithium replenishing additive. This can achieve precise control of the amount of lithium replenishment in the battery, thereby compensating for the loss of active lithium caused by the formation of the SEI film on the surface of the negative electrode and avoiding waste of positive electrode active materials.

[0014] In the preferred technical solution of the above-mentioned composite separator for lithium batteries, the material of the first lithium supplement additive includes at least one of the following: Li3N, Li2O, Li2O2, Li2S, LiF, Li2CO3, Li2C2O4, Li5FeO4, Li6CoO4, Li2NiO2, Li2MoO3 and Li2CuO2.

[0015] When the above technical solution is adopted, positive electrode lithium replenishment additives are used on the positive electrode side to achieve precise lithium replenishment of the positive electrode plate.

[0016] In the preferred technical solution of the composite separator for lithium batteries, the material of the second lithium supplement additive includes at least one of the following: metallic lithium, lithium silicide, and SLMP.

[0017] When the above technical solution is adopted, the negative electrode lithium replenishment additive is used on the negative electrode side, which can achieve precise lithium replenishment of the negative electrode plate, and can make up for the loss of active lithium caused by the formation of SEI film on the negative electrode surface, avoid the waste of positive electrode active materials, improve the first coulomb efficiency, and improve the battery energy density.

[0018] In the preferred technical solution of the composite separator for lithium batteries, the thickness of the base film layer is 5um to 15um, and the thickness of the ceramic layer is set to 1um to 3um.

[0019] When the above technical solution is adopted, a ceramic layer is provided on the surface of the base membrane layer, which retains the temperature resistance of the composite diaphragm and can avoid thermal runaway problems caused by internal short circuit of the battery due to shrinkage of the composite diaphragm at high temperatures.

[0020] In the preferred technical solution of the composite separator for lithium batteries, the thickness of the first lithium replenishing layer is set to 1 um to 10 um, and the thickness of the second lithium replenishing layer is set to 1 um to 10 um.

[0021] When the above technical solution is adopted, the thickness of the first lithium replenishing layer and the second lithium replenishing layer can be set to be different. By adjusting the material formula or thickness of the first lithium replenishing layer and the second lithium replenishing layer, the precise control of the lithium replenishment amount of the battery can be achieved.

[0022] In the preferred technical solution of the composite separator for lithium batteries, the thickness of the conductive layer is set to be no greater than 2 μm.

[0023] When adopting the above technical solution, the provision of a conductive layer can reduce the contact resistance between the lithium replenishment structure layer and the electrode surface, improve the efficiency of lithium replenishment of the composite diaphragm and the interface uniformity. In addition, the conductive layer evenly covers the surface of the lithium replenishment layer, which plays a stabilizing and protective role on the lithium replenishment additive.

[0024] In the preferred technical solution of the composite diaphragm for lithium batteries, the conductive layer, the first lithium replenishing layer, the ceramic layer, the base film layer, the ceramic layer, the second lithium replenishing layer and the conductive layer are stacked in sequence between the first pole piece and the second pole piece.

[0025] When adopting the above technical solution, between the first electrode and the second electrode are a conductive layer, a first lithium replenishing layer, a ceramic layer, a base film layer, a ceramic layer, a second lithium replenishing layer and a conductive layer stacked in sequence. Such a symmetrical arrangement not only has a good lithium replenishing effect, but also has a simple production process and low manufacturing cost, which is conducive to large-scale production.

[0026] In the preferred technical solution of the composite separator for lithium batteries, the conductive layer includes a conductive agent and a binder, and the material of the conductive agent includes at least one of the following: conductive carbon black, carbon nanotubes, graphene, conductive graphite, Ketjen black and acetylene black;

[0027] The material of the binder includes at least one of the following: polytetrafluoroethylene, polyvinylidene fluoride, acrylic acid, polyethylene oxide, carboxymethyl cellulose sodium, styrene-butadiene rubber, hydroxypropyl methylcellulose, carboxystyrene-butadiene latex and polyvinyl alcohol.

[0028] When adopting the above technical solution, the conductive layer includes a conductive agent and a binder. At the same time, the conductive agent and binder in the conductive layer are made of the same materials as those used in the lithium replenishment layer. This can not only reduce the contact resistance between the lithium replenishment layer and the electrode surface, improve the efficiency of composite diaphragm lithium replenishment and interface uniformity, but also reduce production costs.

[0029] In a second aspect, the present invention provides a battery cell, comprising the composite diaphragm for lithium batteries described in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0031] Figure 1 It is a schematic structural diagram of the composite diaphragm used for lithium batteries of the utility model.

[0032] Reference numerals:

[0033] 1. Basement membrane layer;

[0034] 2. First lithium replenishing structure; 21. Ceramic layer; 22. First lithium replenishing layer; 23. Conductive layer;

[0035] 3. Second lithium replenishing structure; 31. Ceramic layer; 32. Second lithium replenishing layer; 33. Conductive layer. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0037] It should be noted that in the description of this utility model, terms such as "upper," "lower," "left," "right," "front," "back," "inner," and "outer" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or component described must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this utility model. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] Furthermore, it should be noted that, in the description of this utility model, unless otherwise expressly specified or limited, the terms "connect," "dispose," and "install" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections, direct connections, or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of these terms in this utility model based on the specific circumstances.

[0039] like Figure 1 As shown, in the first aspect, the present invention is a composite diaphragm for a lithium battery, the lithium battery includes a first pole piece (not shown in the figure) and a second pole piece (not shown in the figure), the composite diaphragm is arranged between the first pole piece and the second pole piece, the composite diaphragm for the lithium battery includes a base film layer 1, a first lithium replenishing structure 2 and a second lithium replenishing structure 3, the base film layer 1 is configured to isolate the first pole piece and the second pole piece, the base film layer 1 has a first side and a second side relatively arranged, the first lithium replenishing structure 2 is arranged on the first side of the base film layer 1 and is located between the base film layer 1 and the first pole piece, the second lithium replenishing structure 3 is arranged on the second side of the base film layer 1 and is located between the base film layer 1 and the second pole piece, the first lithium replenishing structure 2 includes a ceramic layer 21, a first lithium replenishing layer 22 and a conductive layer 23 stacked in sequence from the base film layer 1 to the first pole piece, and the second lithium replenishing structure 3 includes a ceramic layer 31, a second lithium replenishing layer 32 and a conductive layer 33 stacked in sequence from the base film layer 1 to the second pole piece.

[0040] The base film layer 1 of the composite diaphragm for lithium batteries of the utility model is provided with lithium replenishing structures on both sides, that is, the base film layer 1 is provided with lithium replenishing structures at positions close to the first pole piece and the second pole piece, so that the battery can replenish lithium for the first pole piece and the second pole piece at the same time during the charge and discharge process, thereby improving the initial coulomb efficiency and thus improving the energy density of the battery. In this embodiment, the energy density of the conventional graphite system is increased by about 5% to 10%, and the energy density of the silicon system is increased by about 10% to 20%; a multi-layer functional layer is provided on the surface of the base film layer 1, which can improve the electrolyte wettability and liquid retention performance of the diaphragm, and has a significant effect on improving the battery performance.

[0041] like Figure 1As shown, in this embodiment, the first electrode sheet and the second electrode sheet are the positive electrode sheet and the negative electrode sheet, and the first lithium replenishing structure 2 and the second lithium replenishing structure 3 are the positive electrode lithium replenishing structure and the negative electrode lithium replenishing structure. The first lithium replenishing layer 22 and the second lithium replenishing layer 32 are the positive electrode lithium replenishing layer and the negative electrode lithium replenishing layer. Preferably, the first electrode sheet is the positive electrode sheet, the second electrode sheet is the negative electrode sheet, the first lithium replenishing structure 2 is the positive electrode lithium replenishing structure, the second lithium replenishing structure 3 is the negative electrode lithium replenishing structure, the first lithium replenishing layer 22 is the positive electrode lithium replenishing layer, and the second lithium replenishing layer 32 is the negative electrode lithium replenishing layer.

[0042] The first lithium replenishing layer 22 includes a first lithium replenishing additive, a conductive agent, and a binder, while the second lithium replenishing layer 32 includes a second lithium replenishing additive, a conductive agent, and a binder. The first and second lithium replenishing additives are made of different materials. In this embodiment, the first lithium replenishing additive is a positive electrode replenishing additive, and the second lithium replenishing additive is a negative electrode replenishing additive. The positive electrode replenishing additive is used on one side of the positive electrode sheet, while the negative electrode replenishing additive is used on the other side of the negative electrode sheet. This allows for precise control of the amount of lithium replenished in the battery, thereby compensating for the loss of active lithium caused by the formation of the SEI film on the negative electrode surface and avoiding waste of positive electrode active material.

[0043] like Figure 1 As shown, the thickness of the first lithium replenishing layer 22 is set to 1um to 10um, preferably 1um, 2um, 3um, 4um, 5um, 6um, 7um, 8um, 9um, 10um, and the thickness of the second lithium replenishing layer 32 is set to 1um to 10um, preferably 1um, 2um, 3um, 4um, 5um, 6um, 7um, 8um, 9um, 10um. In this embodiment, the thickness of the first lithium replenishing layer 22 and the second lithium replenishing layer 32 can be set to be the same or different. In a preferred embodiment of the present utility model, the formula and thickness can be precisely designed and controlled according to the pre-lithium amount of the battery during actual production. By adjusting the formula or thickness of the lithium replenishing layer on the surface of the composite diaphragm, precise control of the lithium replenishment amount of the battery can be achieved.

[0044] The positive electrode lithium replenishment additive uses at least one of the high-capacity lithium-rich materials Li3N, Li2O, Li2O2, Li2S, LiF, Li2CO3, Li2C2O4, Li5FeO4, Li6CoO4, Li2NiO2, Li2MoO3, and Li2CuO2. The negative electrode lithium replenishment additive uses at least one of metallic lithium, lithium silicide, and SLMP. The formula of the positive electrode lithium replenishment layer slurry is as follows: the positive electrode lithium replenishment additive accounts for 75%-90%, the conductive agent accounts for 5%-10%, the binder accounts for 5%-15%, and the slurry solids content is 40%-60%. The formula of the negative electrode lithium replenishment layer slurry is as follows: the negative electrode lithium replenishment additive accounts for 75%-90%, the conductive agent accounts for 5%-10%, the binder accounts for 5%-15%, and the slurry solids content is 40%-60%.

[0045] The conductive agent for the positive and negative lithium-replenishing layers is at least one of conductive carbon black, carbon nanotubes, graphene, conductive graphite, Ketjen black, and acetylene black. The binder for the positive and negative lithium-replenishing layers is at least one of polytetrafluoroethylene, polyvinylidene fluoride, acrylic acid, polyethylene oxide, sodium carboxymethylcellulose, styrene-butadiene rubber, hydroxypropyl methylcellulose, carboxystyrene-butadiene latex, and polyvinyl alcohol. The solvent includes at least one of N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, acetonitrile, and ethanol.

[0046] like Figure 1 As shown, between the first pole piece and the second pole piece are a conductive layer 23, a first lithium replenishing layer 22, a ceramic layer 21, a base film layer 1, a ceramic layer 31, a second lithium replenishing layer 32 and a conductive layer 33 stacked in sequence, that is, the positive electrode lithium replenishing structure and the negative electrode lithium replenishing structure are symmetrically arranged along the base film layer 1, which not only has a good lithium replenishing effect, but also has a simple production process and low manufacturing cost, which is conducive to large-scale production. The base membrane layer 1 is located between the positive electrode lithium replenishing structure and the negative electrode lithium replenishing structure. The thickness of the base membrane layer 1 is 5um to 15um, preferably 5um, 6um, 7um, 8um, 9um, 10um, 11um, 12um, 13um, 14um, 15um. The material of the base membrane layer 1 is 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 based film, a polytetrafluoroethylene non-woven base film, a polyvinyl chloride film and a polyvinyl chloride non-woven base film.

[0047] The thickness of the ceramic layers 21 and 31 is set to 1 μm to 3 μm, preferably 1 μm, 2 μm, and 3 μm. The ceramic layers 21 and 31 include ceramic powder and a binder. The ceramic powder is at least one of aluminum oxide, zirconium oxide, boehmite, magnesium hydroxide, barium sulfate, silicon oxide, aluminum nitride, magnesium oxide, and titanium dioxide. The binder is at least one of polytetrafluoroethylene, polyvinylidene fluoride, acrylic acid, polyethylene oxide, sodium carboxymethylcellulose, styrene-butadiene rubber, hydroxypropyl methylcellulose, carboxystyrene-butadiene latex, and polyvinyl alcohol. The solvent includes any one or a combination of at least two of N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, acetonitrile, and ethanol. The ceramic layers 21 and 31 are arranged on the surface of the base film layer 1 to retain the heat resistance of the composite diaphragm and avoid thermal runaway caused by internal short circuits in the battery due to shrinkage of the composite diaphragm at high temperatures. The formula of the slurry for the ceramic layers 21 and 31 is as follows: ceramic powder accounts for 75% to 90%, binder accounts for 10% to 25%, and the solid content of the slurry is 30% to 50%.

[0048] like Figure 1 As shown, the thickness of the conductive layers 23 and 33 is set to ≤ 2um, preferably 1um, 1.1um, 1.2um, 1.3um, 1.4um, 1.5um, 1.6um, 1.7um, 1.8um, 1.9um, and 2um. The conductive layers 23 and 33 include a conductive agent and a binder. The surfaces of the positive and negative lithium replenishing layers are provided with conductive layers 23 and 33, which effectively reduce the contact resistance between the positive and negative lithium replenishing layers and the positive and negative electrode sheets, improve the lithium replenishment efficiency and interface uniformity of the diaphragm lithium replenishment process, and the conductive coating is evenly covered on the surface of the lithium replenishing layer, stabilizing and protecting the lithium replenishing agent. The conductive agent of the conductive layers 23 and 33 is at least one of conductive carbon black, carbon nanotubes, graphene, conductive graphite, Ketjen black, and acetylene black. The binder for conductive layers 23 and 33 is at least one of polytetrafluoroethylene, polyvinylidene fluoride, acrylic acid, polyethylene oxide, sodium carboxymethylcellulose, styrene-butadiene rubber, hydroxypropyl methylcellulose, carboxystyrene-butadiene latex, and polyvinyl alcohol. The solvent for conductive layers 23 and 33 is at least one of N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, acetonitrile, and ethanol. The slurry for conductive layers 23 and 33 has a formula of 85%-95% conductive agent, 5%-15% binder, and a solids content of 10%-30%.

[0049] The preparation method of the composite diaphragm of the present invention is: first, ceramic powder, binder, and solvent are added together into a stirring device and dispersed evenly to obtain a ceramic slurry with a solid content of 30 to 50%, and then the ceramic slurry is applied to the front and back surfaces of the base film layer 1 by gravure, spraying, or dipping. After drying, a diaphragm containing a ceramic coating is obtained, and the thickness of the ceramic layers 21 and 31 after drying is 1um to 3um.

[0050] Then, the positive electrode lithium replenishing additive, conductive agent, binder, and solvent are added to a stirring device and dispersed evenly to obtain a functional layer slurry A with a solid content of 40-60%. At the same time, the negative electrode lithium replenishing additive, conductive agent, binder, and solvent are added to a stirring device and dispersed evenly to obtain a functional layer slurry B with a solid content of 40-60%. Then, the functional layer slurries A and B are correspondingly applied to the A and B surfaces of the diaphragm containing ceramic layers 21 and 31 using one of the methods such as gravure, spraying, or dip coating. After drying, a diaphragm containing a positive electrode lithium replenishing layer and a negative electrode lithium replenishing layer is obtained. The thickness of the first lithium replenishing layer 22 and the second lithium replenishing layer 32 is 1um to 10um.

[0051] Finally, the conductive agent, binder, and solvent are added to a stirring device and dispersed evenly to obtain a conductive slurry with a solid content of 10 to 30%. The conductive slurry is then applied to the front and back surfaces of the diaphragm containing the first lithium replenishing layer 22 and the second lithium replenishing layer 32 using one of the methods such as gravure, spraying, or dip coating. After drying, a composite diaphragm containing conductive layers 23 and 33 is obtained. The thickness of the conductive layers 23 and 33 after drying is ≤2 μm.

[0052] In the second aspect, the battery cell of the present invention includes the composite diaphragm for a lithium battery of the first aspect. The battery cell of this technical solution includes the composite diaphragm for a lithium battery of any technical solution of the present invention, and thus has all the technical effects of the composite diaphragm for a lithium battery of any technical solution of the present invention.

[0053] It should be noted that the above preferred embodiments are only used to illustrate the principles of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the principles of the present invention, those skilled in the art may adjust the above configuration so that the present invention can be applied to more specific application scenarios.

[0054] Of course, the above-mentioned replaceable implementations, as well as the replaceable implementations and the preferred implementations, can be used in a cross-functional manner to combine new implementations to suit more specific application scenarios.

[0055] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A composite diaphragm for a lithium battery, wherein the lithium battery comprises a first pole piece and a second pole piece, wherein the composite diaphragm is disposed between the first pole piece and the second pole piece, wherein: The composite diaphragm for lithium battery comprises: A base film layer, the base film layer having a first side and a second side disposed opposite to each other; A first lithium replenishing structure is provided on a first side of the base membrane layer and located between the base membrane layer and the first pole piece; A second lithium replenishing structure is provided on the second side of the base membrane layer and is located between the base membrane layer and the second pole piece; Among them, the first lithium replenishing structure includes a ceramic layer, a first lithium replenishing layer and a conductive layer stacked in sequence from the base membrane layer to the first pole piece, and the second lithium replenishing structure includes a ceramic layer, a second lithium replenishing layer and a conductive layer stacked in sequence from the base membrane layer to the second pole piece.

2. The composite separator for lithium batteries according to claim 1, characterized in that The thickness of the base film layer is 5um to 15um, and the thickness of the ceramic layer is set to 1um to 3um.

3. The composite separator for lithium batteries according to claim 1, characterized in that: The thickness of the first lithium replenishing layer is set to 1um to 10um, and the thickness of the second lithium replenishing layer is set to 1um to 10um.

4. The composite separator for lithium batteries according to claim 1, characterized in that The thickness of the conductive layer is set to be no greater than 2 μm.

5. The composite separator for lithium batteries according to claim 1, characterized in that: Between the first pole piece and the second pole piece are the conductive layer, the first lithium replenishing layer, the ceramic layer, the base film layer, the ceramic layer, the second lithium replenishing layer and the conductive layer stacked in sequence.

6. A battery cell, characterized in that: A composite separator for a lithium battery comprising the composite separator according to any one of claims 1 to 5.

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