Composite lithium supplementing diaphragm, lithium ion battery and electric device

Abstract

The utility model discloses a composite lithium supplementing diaphragm, a lithium ion battery and an electric device, the composite lithium supplementing diaphragm comprises a first diaphragm layer, a second diaphragm layer and a third diaphragm layer, the first diaphragm layer comprises a first base membrane and a first ion conducting water-resisting layer arranged on one side of the first base membrane; the second diaphragm layer comprises a second base membrane and a second conductive ion water-resisting layer arranged on one side of the second base membrane; the lithium supplementing layer is arranged between the first diaphragm layer and the second diaphragm layer, and the lithium supplementing layer is close to the first base membrane and the second base membrane and is far away from the first ion conducting water-resisting layer and the second ion conducting water-resisting layer. The lithium supplement agent in the composite lithium supplement diaphragm is not easy to fall off and inactivate, the utilization rate of lithium is high, the lithium supplement effect is good, the energy density of the battery can be effectively improved, and the cycle storage life of the battery can be effectively prolonged.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, specifically to a composite lithium-replenishing separator, a lithium-ion battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries are highly efficient energy storage devices widely used in various fields, such as mobile phones, laptops, portable tools, automobiles, and home energy storage. During the first charge, a SEI film forms on the graphite surface of a lithium-ion battery. This process consumes a large number of active lithium ions from the positive electrode, leading to irreversible capacity loss and reducing the battery's energy density. Compensating for the loss of active lithium is the most direct way to improve battery energy density and cycle life. However, traditional lithium replenishment methods suffer from problems such as easy shedding and deactivation of the lithium replenishing agent, and low lithium utilization, which are detrimental to improving battery energy density and cycle life. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one objective of this invention is to provide a composite lithium-replenishing separator, in which the lithium-replenishing agent is not easily detached or deactivated, resulting in high lithium utilization and good lithium replenishment effect, effectively improving the battery's energy density and cycle life.

[0004] Specifically, the first aspect of this utility model provides a composite lithium-supplementing separator, comprising:

[0005] The first membrane layer includes a first base membrane and a first ion-conducting water-barrier layer disposed on one side of the first base membrane;

[0006] The second membrane layer includes a second base membrane and a second ion-conducting water-barrier layer disposed on one side of the second base membrane;

[0007] A lithium replenishment layer is disposed between the first membrane layer and the second membrane layer. The lithium replenishment layer is close to the first base membrane and the second base membrane, and far away from the first ion-conducting water barrier layer and the second ion-conducting water barrier layer.

[0008] The lithium replenishing layer of this invention is located in the middle of the composite lithium replenishing membrane, while the ion-conducting water-barrier layer is located on the outermost side of the composite lithium replenishing membrane. This layer protects the lithium replenishing layer and effectively inhibits the reaction between moisture in the environment and the lithium replenishing agent while ensuring smooth lithium ion transport, thus preventing the lithium replenishing agent from becoming deactivated. At the same time, it prevents the lithium replenishing layer from directly contacting the electrolyte and the external environment, effectively reducing the risk of lithium replenishing layer detachment, improving the utilization rate of lithium in the lithium replenishing agent, and improving the energy density and cycle life of the battery.

[0009] According to some embodiments of this utility model, the thickness ratio of the first ion-conducting water barrier layer to the lithium replenishment layer is 1:(1-7); the thickness ratio of the second ion-conducting water barrier layer to the lithium replenishment layer is 1:(1-7). Optimizing the thickness ratio of the ion-conducting water barrier layer and the lithium replenishment layer is beneficial to improving the utilization rate of lithium in the lithium replenishment agent and improving the energy density and cycle storage life of the battery.

[0010] According to some embodiments of the present invention, the thickness ratio of the first ion-conducting water-barrier layer to the lithium replenishment layer is 1:(2-4); the thickness ratio of the second ion-conducting water-barrier layer to the lithium replenishment layer is 1:(2-4).

[0011] According to some embodiments of this invention, the thicknesses of both the first ion-conducting water-barrier layer and the second ion-conducting water-barrier layer are 0.5 μm-10 μm. The resulting composite lithium-replenishing membrane can effectively replenish lithium while also enabling smooth lithium ion transport.

[0012] According to some embodiments of this utility model, both the first ion-conducting water-barrier layer and the second ion-conducting water-barrier layer are physical mixtures of chloride solid electrolyte and binder; the chloride solid electrolyte is Li₂ZrCl₆; the binder is polyvinylidene fluoride, vinylidene fluoride-hexachloropropylene polymer, styrene-butadiene rubber, polypropylene, sodium carboxymethyl cellulose, polyacrylic acid, or polymethyl methacrylate. The resulting ion-conducting water-barrier layer can inhibit the reaction between moisture in the environment and the lithium supplement, while not affecting lithium ion transport.

[0013] According to some embodiments of this invention, the thickness of the lithium replenishment layer is 0.5 μm-30 μm. The resulting composite lithium replenishment separator can effectively replenish lithium, improving the battery's energy density and cycle life.

[0014] According to some embodiments of this utility model, the lithium replenishing layer is a physical mixture of a positive electrode lithium replenishing agent, a conductive agent, and a binder; the positive electrode lithium replenishing agent is Li2NiO2, Li2CuO2, Li6CoO4, Li5FeO4, Li6MnO4, Li2MoO3, Li3N, Li2O, Li2O2, LiOH, Li2CO3, or Li2S; the conductive agent is carbon nanotubes, Ketjen black, carbon black, graphene, or carbon nanotubes; the binder is polyvinylidene fluoride, vinylidene fluoride-hexachloropropylene polymer, styrene-butadiene rubber, polypropylene, sodium carboxymethyl cellulose, polyacrylic acid, or polymethyl methacrylate. The lithium replenishing layer formed thereby has a weaker activity than active lithium, and the requirements for the dew point temperature of the preparation environment are not particularly stringent, and can be consistent with the control of existing separator manufacturing plants.

[0015] According to some embodiments of this utility model, the first separator layer further includes a first conductive layer, which is disposed on the side of the first base film near the lithium replenishment layer; the second separator layer further includes a second conductive layer, which is disposed on the side of the second base film near the lithium replenishment layer. The conductive layer is disposed between the base film and the lithium replenishment layer, preventing the lithium replenishment layer from directly contacting the base film and reducing the risk of micropore blockage in the base film. Furthermore, leading out the conductive layer using a lithium replenishment tab can effectively control the amount and timing of lithium replenishment, increasing battery capacity and lifespan while effectively reducing the risk of lithium plating.

[0016] According to some embodiments of this invention, the thicknesses of the first conductive layer and the second conductive layer are each 1 μm-20 μm. Optimizing the thickness of the conductive layer is beneficial for improving conductivity and effectively controlling the amount and timing of lithium replenishment.

[0017] According to some embodiments of this invention, the thicknesses of the first base film and the second base film are each 3μm-50μm. Optimizing the thickness of the base film is beneficial for improving the energy density of the battery.

[0018] The second aspect of this invention provides a lithium-ion battery, including the composite lithium-replenishing separator of the first aspect of this invention. Due to the use of the aforementioned composite lithium-replenishing separator, the lithium-ion battery of this invention has improved energy density and cycle life.

[0019] A third aspect of this invention provides an electrical device comprising a lithium-ion battery as described in the second aspect of this invention. Because it uses the aforementioned lithium-ion battery, the electrical device of this invention possesses all the advantages of the lithium-ion battery, which will not be elaborated further here.

[0020] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] The above and / or additional aspects and advantages of this utility model will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0022] Figure 1 This is a schematic diagram of the structure of the composite lithium-replenishing separator according to some embodiments of this utility model.

[0023] Figure 2 This is a structural schematic diagram of the composite lithium-replenishing separator in some other embodiments of the present invention.

[0024] Figure label:

[0025] 100. Composite lithium replenishment membrane; 110. First membrane layer; 111. First base membrane; 112. First ion-conducting water-barrier layer; 113. First conductive layer; 120. Second membrane layer; 121. Second base membrane; 122. Second ion-conducting water-barrier layer; 123. Second conductive layer; 130. Lithium replenishment layer. Detailed Implementation

[0026] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this utility model, and should not be construed as limiting this utility model.

[0027] Lithium-ion batteries are highly efficient energy storage devices widely used in various fields, such as mobile phones, laptops, portable tools, automobiles, and home energy storage. Graphite is currently the most commonly used anode material. Taking it as an example, during the first charge of a lithium-ion battery, an SEI film forms on the graphite surface. This process consumes a large number of active lithium ions from the cathode, leading to irreversible capacity loss and reducing the battery's energy density. In particular, with the increasing demand for higher energy density, high-capacity materials such as silicon-carbon are gradually being used in anode materials. These materials have even lower initial coulombic efficiency, resulting in irreversible capacity loss exceeding 20% ​​during the first charge. Furthermore, active lithium is continuously consumed during battery cycling and storage. Therefore, compensating for active lithium loss is the most direct way to improve battery energy density and cycle life. However, traditional lithium replenishment methods suffer from problems such as easy shedding and deactivation of the replenishing agent, and low lithium utilization, which are detrimental to improving battery energy density and cycle life.

[0028] To address the above issues, this invention provides a composite lithium replenishment membrane, wherein the lithium replenishment layer is located in the middle of the composite lithium replenishment membrane, and the ion-conducting water-barrier layer is located on the outermost side of the composite lithium replenishment membrane, which plays a role in protecting the lithium replenishment layer. It can effectively inhibit the reaction between moisture in the environment and the lithium replenishment agent while ensuring smooth lithium ion transport, thus preventing the lithium replenishment agent from deactivating. At the same time, it prevents the lithium replenishment layer from directly contacting the electrolyte and the external environment, effectively reducing the risk of lithium replenishment layer detachment, improving the utilization rate of lithium in the lithium replenishment agent, and improving the energy density and cycle life of the battery.

[0029] Specifically, such as Figure 1As shown, the first aspect of this utility model provides a composite lithium replenishing membrane 100, comprising: a first membrane layer 110, the first membrane layer 110 including a first base membrane 111 and a first ion-conducting water-barrier layer 112 disposed on one side of the first base membrane 111; a second membrane layer 120, the second membrane layer 120 including a second base membrane 121 and a second ion-conducting water-barrier layer 122 disposed on one side of the second base membrane 121; and a lithium replenishing layer 130 disposed between the first membrane layer 110 and the second membrane layer 120, the lithium replenishing layer 130 being close to the first base membrane 111 and the second base membrane 121, and far away from the first ion-conducting water-barrier layer 112 and the second ion-conducting water-barrier layer 122.

[0030] The composite lithium-filling separator 100 has a sandwich structure and is an integral piece. There are no special requirements for the direction of the separator during battery assembly, and the assembly process is completely consistent with the current process. The composite lithium-filling separator 100 can also have a symmetrical structure.

[0031] In some embodiments, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 can be 1:(1-7). The thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 can also be 1:(1-7). Optimizing the thickness ratio of the ion-conducting water barrier layer and the lithium replenishment layer 130 is beneficial to improving the utilization rate of lithium in the lithium replenishment agent and improving the energy density and cycle life of the battery.

[0032] In some specific embodiments, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6 or 1:7.

[0033] In some specific embodiments, the thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6 or 1:7.

[0034] In some embodiments, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 is 1:(2-4). The thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 is also 1:(2-4). A thickness ratio of the ion-conducting water barrier layer to the lithium replenishment layer 130 within this range is more conducive to improving the utilization rate of lithium in the lithium replenishment agent, thereby improving the energy density and cycle life of the battery.

[0035] In some embodiments, the thickness of both the first ion-conducting water-barrier layer 112 and the second ion-conducting water-barrier layer 122 can be 0.5 μm-10 μm. The ion-conducting water-barrier layer contains a large number of ion conductors (i.e., chloride solid electrolyte, which conducts lithium ions through the gaps or channels in the crystal lattice), enabling smooth lithium ion transport; at the same time, the ion-conducting water-barrier layer also has a water-barrier function. Optimizing the thickness of the ion-conducting water-barrier layer is beneficial to improving the water-barrier performance. The resulting composite lithium-replenishing membrane 100 can effectively replenish lithium and enable smooth lithium ion transport.

[0036] In some specific embodiments, the thickness of the first ion-conducting water-barrier layer 112 and the second ion-conducting water-barrier layer 122 can be 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, or 10μm. Preferably, the thickness of the first ion-conducting water-barrier layer 112 and the second ion-conducting water-barrier layer 122 is 2μm-5μm.

[0037] In some embodiments, both the first ion-conducting water-barrier layer 112 and the second ion-conducting water-barrier layer 122 are physical mixtures of a chloride solid electrolyte and a binder. The chloride solid electrolyte may be Li₂ZrCl₆. The binder may be polyvinylidene fluoride, vinylidene fluoride-hexachloropropylene polymer, styrene-butadiene rubber, polypropylene, sodium carboxymethyl cellulose, polyacrylic acid, or polymethyl methacrylate. The resulting ion-conducting water-barrier layer can inhibit the reaction between moisture in the environment and the lithium supplement, while not affecting lithium ion transport.

[0038] In some specific embodiments, the mass percentage of the chloride solid electrolyte in the first ion-conducting water barrier layer 112 and the second ion-conducting water barrier layer 122 can be 65%-98%, for example 65%, 70%, 75%, 80%, 85%, 90%, 95% or 98%.

[0039] In some embodiments, the thickness of the lithium replenishment layer 130 can be 0.5 μm-30 μm. The resulting composite lithium replenishment separator 100 can effectively replenish lithium, improving the energy density and cycle life of the battery.

[0040] In some specific embodiments, the thickness of the lithium replenishment layer 130 can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 15μm, 20μm, 25μm, or 30μm. Preferably, the thickness of the lithium replenishment layer 130 is 3μm-10μm.

[0041] In some embodiments, the lithium replenishment layer 130 is a physical mixture of a positive electrode lithium replenishing agent, a conductive agent, and a binder. The positive electrode lithium replenishing agent is Li₂NiO₂, Li₂CuO₂, Li₆CoO₄, Li₅FeO₄, Li₆MnO₄, Li₂MoO₃, Li₃N, Li₂O, Li₂O₂, LiOH, Li₂CO₃, or Li₂S. The conductive agent is carbon nanotubes, Ketjen black, carbon black, graphene, or carbon nanotubes. The binder is polyvinylidene fluoride, vinylidene fluoride-hexachloropropylene polymer, styrene-butadiene rubber, polypropylene, sodium carboxymethyl cellulose, polyacrylic acid, or polymethyl methacrylate. The lithium replenishment layer 130 formed thus has a lower activity than active lithium, and the dew point temperature requirements of the preparation environment are not particularly stringent; consistency with existing separator manufacturing plant control is sufficient. The lithium replenishment layer 130 itself has a porous structure, does not affect lithium-ion transport, and can be wound up for large-scale use.

[0042] In some specific embodiments, the D50 particle size of the positive electrode lithium supplement can be 0.01 μm-10 μm, for example 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, preferably 0.05 μm-3 μm. The D50 particle size refers to the particle size corresponding to a cumulative particle size distribution percentage of 50% in a sample, also known as the median diameter or median particle size.

[0043] In some specific embodiments, the positive electrode lithium replenishing agent accounts for 60%-95% of the mass of the lithium replenishing layer 130, for example 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, preferably 80%-90%. The conductive agent accounts for 3%-20% of the mass of the lithium replenishing layer 130, for example 3%, 5%, 10%, 15%, or 20%. The binder accounts for 2%-20% of the mass of the lithium replenishing layer 130, for example 2%, 5%, 10%, 15%, or 20%.

[0044] In some embodiments, such as Figure 2 As shown, the first separator layer 110 further includes a first conductive layer 113, which is disposed on the side of the first base film 111 near the lithium replenishment layer 130. The second separator layer 120 further includes a second conductive layer 123, which is disposed on the side of the second base film 121 near the lithium replenishment layer 130. The conductive layer is disposed between the base film and the lithium replenishment layer 130, preventing the lithium replenishment layer 130 from directly contacting the base film and reducing the risk of micropore blockage in the base film. In addition, leading out the conductive layer with a lithium replenishment tab can effectively control the amount and timing of lithium replenishment, increasing battery capacity and lifespan while effectively reducing the risk of lithium plating.

[0045] In some embodiments, the thickness of the first conductive layer 113 and the second conductive layer 123 can each be 1 μm-20 μm. Optimizing the thickness of the conductive layers is beneficial for improving conductivity and effectively controlling the amount and timing of lithium replenishment.

[0046] In some specific embodiments, the thicknesses of the first conductive layer 113 and the second conductive layer 123 can each be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 15 μm, or 20 μm. Preferably, the thicknesses of the first conductive layer 113 and the second conductive layer 123 are each 2 μm to 10 μm.

[0047] In some specific embodiments, the first conductive layer 113 and the second conductive layer 123 are each a physical mixture of a conductive material and a binder. The conductive material can be a carbon material, a conductive oxide, or a conductive polymer. The carbon material can be carbon nanotubes, Ketjen black, carbon black, graphene, or graphite. The conductive oxide can be In₂O₃, ZnO, or SnO₂. The conductive polymer can be polyacetylene, polythiophene, polypyrrole, or polyaniline. The mass percentage of the conductive material in the conductive layer can be 60%-100%, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, preferably 80%-95%.

[0048] In some embodiments, the thickness of the first base film 111 and the second base film 121 can each be 3 μm-50 μm. Optimizing the thickness of the base film is beneficial to improving the energy density of the battery.

[0049] In some specific embodiments, the thicknesses of the first base film 111 and the second base film 121 can each be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, or 50μm. Preferably, the thicknesses of the first base film 111 and the second base film 121 can each be 4μm-10μm.

[0050] In some specific embodiments, the first base film 111 and the second base film 121 are each a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, an aramid film, a polyacrylonitrile film, a polyimide film, a polyamide film, a polyester film, or a natural fiber film. The porosity of the first base film 111 and the second base film 121 is each 10%-65%, for example 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or 65%, preferably 30%-55%.

[0051] The composite lithium-supplementing separator 100 of this invention can be prepared by a method including the following steps:

[0052] Chloride solid electrolyte, binder and solvent are mixed to obtain ion-conducting water-barrier slurry;

[0053] The ion-conducting water-barrier slurry is coated on one side of the first base membrane 111 and dried to form the first ion-conducting water-barrier layer 112, thus obtaining the first membrane layer 110.

[0054] The ion-conducting water-barrier slurry is coated on one side of the second base membrane 121 and dried to form the second ion-conducting water-barrier layer 122, thus obtaining the second membrane layer 120.

[0055] The positive electrode lithium replenishing agent, conductive agent, binder and solvent are mixed to obtain the lithium replenishing layer slurry;

[0056] The lithium replenishing layer slurry is coated on the first base film 111 of the first separator layer 110 to form a lithium replenishing layer 130. Before the solvent dries, the second base film 121 of the second separator layer 120 is attached to the lithium replenishing layer 130, and then dried and rolled to obtain a composite lithium replenishing separator 100.

[0057] In this article, "solvent not dry" means that the solvent in the slurry has not completely evaporated or been completely removed.

[0058] In some embodiments, the chloride solid electrolyte, binder and solvent are mixed and then milled.

[0059] In some embodiments, the method further includes: mixing a conductive material, an adhesive, and a solvent to obtain a conductive layer slurry; coating the conductive layer slurry and the ion-conducting water-barrier layer slurry onto both sides of a first base film 111, and drying them to form a first conductive layer 113 and a first ion-conducting water-barrier layer 112, thereby obtaining a first separator layer 110; coating the conductive layer slurry and the ion-conducting water-barrier layer slurry onto both sides of a second base film 121, and drying them to form a second conductive layer 123 and a second ion-conducting water-barrier layer 122, thereby obtaining a second separator layer 120; coating the lithium replenishment layer slurry onto the first conductive layer 113 of the first separator layer 110 to form a lithium replenishment layer 130; and before the solvent dries, attaching the second conductive layer 123 of the second separator layer 120 to the lithium replenishment layer 130, and drying it to obtain a composite lithium replenishment separator 100.

[0060] In some embodiments, the solvent includes one or more of the following: n-hexane, cyclohexane, benzene, toluene, ethyl acetate, N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, diethyl ether, acetone, N-methylpyrrolidone, ethylene carbonate, dimethyl carbonate, fluorohexane, fluorocyclohexane, fluoroethylene carbonate, and propylene carbonate.

[0061] In some embodiments, coating includes spraying or roller coating.

[0062] The second aspect of this invention provides a lithium-ion battery, including the composite lithium-replenishing separator 100 of the first aspect of this invention. Due to the use of the composite lithium-replenishing separator 100, the lithium-ion battery of this invention has improved energy density and cycle life.

[0063] In some embodiments, the lithium-ion battery includes a composite lithium replenishing membrane 100 and a lithium replenishing tab; the lithium replenishing tab is connected to a first conductive layer 113 and a second conductive layer 123 of the composite lithium replenishing membrane 100. In the case where the composite lithium replenishing membrane 100 does not include the first conductive layer 113 and the second conductive layer 123, the lithium replenishing tab may be connected to a lithium replenishing layer 130 of the composite lithium replenishing membrane 100.

[0064] In some specific embodiments, the lithium-ion battery includes a positive electrode, a negative electrode, a composite lithium replenishing membrane 100 spaced between the positive and negative electrode, an electrolyte, and a casing. It also includes a positive electrode tab, a negative electrode tab, and a lithium replenishing tab. One end of the positive and negative electrode tabs is connected to the positive and negative electrode, respectively, and the other end of each tab extends out of the casing. One end of the lithium replenishing tab is connected to the first conductive layer 113 and the second conductive layer 123 in the composite lithium replenishing membrane 100, and the other end extends out of the casing.

[0065] The activation method for lithium replenishment includes connecting the lithium replenishment tab and the negative electrode tab to the positive and negative terminals of the charging cabinet, respectively, charging with a small current (e.g., 0.02C), and setting a protection voltage (e.g., 4.3V). During charging, lithium ions can be extracted from the lithium replenishment layer 130 in the composite lithium replenishment separator 100 and penetrate through the separator and electrolyte to embed into the negative electrode active material, thus achieving lithium replenishment. The amount of lithium replenishment can be controlled by controlling the charging time. The lithium replenishment process can be performed multiple times. Selectable timings include lithium replenishment before battery capacity grading to replenish the active lithium ions consumed during the initial formation of the SEI film; and lithium replenishment during cycling to replenish the active lithium ions continuously lost during cycling. Controlling the amount of lithium replenishment each time is beneficial for more uniform lithium intercalation in the negative electrode and can avoid the risk of lithium plating.

[0066] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0067] Example 1

[0068] (1) Preparation of composite lithium-supplemented separator 100

[0069] First, an ion-conducting water-barrier slurry is prepared. Specifically, Li2ZrCl6 and polyvinylidene fluoride (PVDF) are stirred with N-methylpyrrolidone (NMP) solvent at a mass ratio of 8:2 for 1 hour. The resulting dispersion is then put into a nano-mill and milled for 3 hours to obtain a slurry for later use.

[0070] Then, a conductive layer slurry is prepared. Specifically, carbon nanotubes and PVDF are stirred with NMP solvent at a mass ratio of 9:1 for 2 hours to obtain the conductive layer slurry for later use.

[0071] Subsequently, the ion-conducting water-barrier layer slurry and the conductive layer slurry are uniformly coated on opposite sides of an 8μm thick polypropylene (PP) base film and dried to form the first membrane layer 110 and the second membrane layer 120. The thickness of the first ion-conducting water-barrier layer 112, the first conductive layer 113, the second ion-conducting water-barrier layer 122, and the second conductive layer 123 is 2μm.

[0072] Next, the lithium replenishment layer 130 slurry is prepared. Specifically, Li5FeO4, carbon nanotubes, and PVDF are stirred with NMP solvent at a mass ratio of 8:1:1 for 2 hours to obtain the lithium replenishment layer slurry for later use.

[0073] Finally, the lithium replenishment layer slurry is applied to the first conductive layer 113 of the first separator layer 110 to form the lithium replenishment layer 130. Before the solvent dries, the second conductive layer 123 of the second separator layer 120 is quickly attached, and then dried and rolled. The lithium replenishment layer 130 has a thickness of 6 μm, the thickness ratio of the first ion-conducting water-barrier layer 112 to the lithium replenishment layer 130 is 1:3, and the thickness ratio of the second ion-conducting water-barrier layer 122 to the lithium replenishment layer 130 is 1:3. The final composite lithium replenishment separator 100 has a thickness of 30 μm.

[0074] (2) Preparation of lithium-ion pouch batteries

[0075] First, lithium iron phosphate (LFP) cathode sheets are prepared. Specifically, LFP, conductive carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 100:3:2. NMP is added, and the mixture is stirred under vacuum until a homogeneous cathode slurry is formed. The cathode slurry is then uniformly coated onto aluminum foil as the cathode current collector. After drying, cold pressing, cutting, and slitting, the cathode sheet is obtained. The areal density of the LFP cathode sheet is 400 g / m³. 2 .

[0076] Then, the graphite negative electrode sheet is prepared. Specifically, the negative electrode active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber, and thickener CMC are thoroughly mixed in an appropriate amount of deionized water solvent at a mass ratio of 100:3:2:1 to form a uniform slurry. The slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying, it is cold-pressed, cut, and slit to obtain the negative electrode sheet. The areal density of the graphite negative electrode sheet is 188 g / m³. 2 .

[0077] Next, an electrolyte was prepared, specifically a carbonate-based electrolyte (the solute was 1 mol / L LiPF6, and the volume ratio of solvent EC (ethylene carbonate):DMC (dimethyl carbonate):DEC (diethyl carbonate) was 1:1:1).

[0078] Finally, the surface density is 400 g / m³. 2 Lithium iron phosphate cathode sheet, composite lithium-supplementing separator 100, areal density 188 g / m³ 2 Graphite negative electrode sheets are stacked sequentially to form a pouch battery. The positive electrode sheet, the first conductive layer 113 and the second conductive layer 123 of the composite lithium-filling separator 100, and the negative electrode sheet are respectively connected to one end of the positive electrode tab, the lithium-filling tab, and the negative electrode tab. 1C = 750mAh. The lithium-filling activation current is 0.02C, and a one-time lithium-filling is performed before capacity grading, with a lithium-filling time of 6.9 hours.

[0079] Example 2

[0080] The method described in Example 1 was followed, except that carbon nanotubes were replaced with polyaniline in the preparation of the conductive layer slurry.

[0081] Example 3

[0082] The method described in Example 1 was followed, except that lithium replenishment activation was performed three times: before battery capacity testing, after 300 cycles, and after 600 cycles. Each lithium replenishment session lasted 2.3 hours.

[0083] Example 4

[0084] The method described in Example 3 is followed, except that the thickness of the lithium replenishment layer 130 is 4 μm, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 is 1:2, and the thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 is 1:2.

[0085] Example 5

[0086] The method described in Example 3 is followed, except that the thickness of the lithium replenishment layer 130 is 8 μm, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 is 1:4, and the thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 is 1:4.

[0087] Example 6

[0088] The method described in Example 3 is followed, except that the thickness of the lithium replenishment layer 130 is 4 μm, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 is 1:1, and the thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 is 1:1.

[0089] Example 7

[0090] The method described in Example 3 is followed, except that the thickness of the lithium replenishment layer 130 is 14 μm, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 is 1:7, and the thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 is 1:7.

[0091] Example 8

[0092] The method described in Example 3 is followed, except that the thickness of the lithium replenishment layer 130 is 4 μm, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 is 1:0.5, and the thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 is 1:0.5.

[0093] Example 9

[0094] The method described in Example 3 is followed, except that the thickness of the first ion-conducting water barrier layer 112 and the second ion-conducting water barrier layer 122 is 0.5 μm, the thickness of the lithium replenishment layer 130 is 4 μm, the thickness ratio of the first ion-conducting water barrier layer 112 to the lithium replenishment layer 130 is 1:8, and the thickness ratio of the second ion-conducting water barrier layer 122 to the lithium replenishment layer 130 is 1:8.

[0095] Example 10

[0096] The method described in Example 3 is followed, except that the thickness of the first ion-conducting water barrier layer 112 and the second ion-conducting water barrier layer 122 is 10 μm, and the thickness of the lithium replenishment layer 130 is 30 μm.

[0097] Example 11

[0098] The method described in Example 3 is followed, except that the thickness of the first conductive layer 113 and the second conductive layer 123 is 10 μm.

[0099] Example 12

[0100] The method described in Example 3 is followed, except that the thickness of the first conductive layer 113 and the second conductive layer 123 is 20 μm.

[0101] Example 13

[0102] The method described in Example 3 is followed, except that the thickness of the first conductive layer 113 and the second conductive layer 123 is 0.5 μm.

[0103] Example 14

[0104] The method described in Example 3 is followed, except that the first conductive layer 113 and the second conductive layer 123 are not formed in the preparation steps of the composite lithium-replenishing separator 100. The lithium-replenishing layer 130 slurry is applied to the base film of the first separator layer 110. Before the solvent dries, the base film of the second separator layer 120 is quickly attached and then dried. The positive electrode, the lithium-replenishing layer 130 in the composite lithium-replenishing separator 100, and the negative electrode are respectively connected to one end of the positive electrode tab, the lithium-replenishing tab, and the negative electrode tab.

[0105] Comparative Example 1

[0106] The method described in Example 3 is followed, except that no ion-conducting water-barrier layer is formed in the preparation step of the composite lithium-replenishing membrane 100.

[0107] Comparative Example 2

[0108] The method described in Example 3 is followed, except that no ion-conducting water-barrier layer is formed in the preparation step of the composite lithium-replenishing membrane 100, and the lithium replenishing agent is a 2μm thick lithium strip sandwiched between the first membrane layer 110 and the second membrane layer 120. The composite lithium-replenishing membrane is formed by rolling. The lithium capacity provided by the lithium strip is consistent with the Li capacity provided by Li5FeO4 in Example 1.

[0109] Comparative Example 3

[0110] Compared to Example 1, the separator used in the battery fabrication is a 16μm thick PP separator, and lithium replenishment activation is not required.

[0111] The battery performance of the above embodiments and comparative examples was tested, and the specific test items, methods, and test results are analyzed as follows.

[0112] Each group of batteries underwent formation, lithium replenishment activation (except for Comparative Example 3), capacity testing, and cycle testing in sequence.

[0113] (1) Battery formation method:

[0114] Charge at 0.05C for 2 hours; let stand for 10 minutes; then charge at 0.2C to 3.8V, and stop at 0.05C.

[0115] (2) Methods to activate lithium replenishment effect:

[0116] Connect the lithium replenishing tab and the negative electrode tab to the positive and negative terminals of the charging cabinet respectively, charge with a small current of 0.02C, and set the protection voltage to 4.3V to activate the lithium replenishment effect.

[0117] (3) Battery capacity testing method:

[0118] Discharge to 2V at a constant current of 0.33C, then charge to 3.8V at a constant current and constant voltage of 0.33C, with a cutoff at 0.05C. Allow a 10-minute rest between charging and discharging. Repeat this cycle three times, and finally discharge to 2V at a constant current of 0.1C. Record the capacity at 0.1C to obtain the capacity of each battery group, which is used to calculate the lithium utilization rate.

[0119] Lithium utilization rate is an important method for evaluating the lithium replenishment effect of composite lithium replenishment membranes. The lithium utilization rates of Examples 1-14 and Comparative Examples 1-2 were calculated, and the results are shown in Table 1 below. The lithium utilization rate calculation method for Examples 1-2 is: ((capacity of each battery group - capacity of Comparative Example 3) + capacity of pre-stored lithium) / 105 * 100%. The capacity of pre-stored lithium was obtained by analyzing the 0.1C discharge curve using the dV / dQ method. The lithium utilization rate calculation method for Examples 3-14 and Comparative Examples 1-2 is: ((capacity of each group - capacity of Comparative Example 3) + (capacity after 300 cycles and lithium replenishment activation - capacity after 300 cycles and before lithium replenishment activation) + (capacity after 600 cycles and lithium replenishment activation - capacity after 600 cycles and before lithium replenishment activation)) / 105 * 100%;

[0120] The capacity after 300 cycles and before re-lithiation activation was tested using the following method:

[0121] 1. After the battery has cycled 300 times at 60℃, remove the battery and let it stand at room temperature (25℃) for 12 hours.

[0122] 2. Charge at a constant current and constant voltage of 0.33C to 3.8V, then cut off at 0.05C;

[0123] 3. Let stand for 10 minutes;

[0124] 4. Discharge to 2V at a constant current of 0.33C;

[0125] 5. Let stand for 10 minutes;

[0126] 6. Repeat steps 2-5 twice;

[0127] 7. Charge at a constant current and constant voltage of 0.33C to 3.8V, then cut off at 0.05C;

[0128] 8. Let stand for 10 minutes;

[0129] 9. Discharge to 2V at a constant current of 0.1C;

[0130] 10. Read the discharge capacity from step 9, which is the capacity after 300 cycles and before lithium replenishment activation, i.e., the capacity after 300 cycles.

[0131] The capacity after 300 cycles and subsequent lithium replenishment activation was tested using the following method:

[0132] After testing the capacity for 300 cycles at room temperature using the method described above (i.e., the capacity after 300 cycles and before lithium replenishment activation), replenish lithium for the corresponding time according to the activation and lithium replenishment method in Example 3, and then test again using the method described above, the capacity after 300 cycles and lithium replenishment activation can be obtained.

[0133] The capacity after 600 cycles and before re-lithiation activation was tested using the following method:

[0134] After 300 cycles and subsequent lithium replenishment activation, the battery is cycled again at 60°C for another 600 cycles. The battery is then removed and left to stand at room temperature (25°C) for 12 hours. Steps 2-9 are the same as described above. The discharge capacity measured in step 9 is the capacity after 600 cycles and before lithium replenishment activation, which is also the capacity after 600 cycles.

[0135] The capacity after 600 cycles and subsequent lithium replenishment activation was tested using the following method:

[0136] After testing the capacity for 600 cycles at room temperature using the method described above (i.e., the capacity after 600 cycles and before lithium replenishment activation), replenish lithium for the corresponding time according to the activation and lithium replenishment method in Example 3, and then test again using the method described above, the capacity after 600 cycles and lithium replenishment activation can be obtained.

[0137] (4) Cyclic testing: The test temperature was 60℃. The battery was charged at a constant current and constant voltage of 0.5C to 3.8V, cut off at 0.05C, and discharged at a constant current of 0.5C, with a 10-minute rest between charge and discharge cycles. Cycling continued until the capacity retention rate reached 80%, and the number of cycles was recorded. Examples 1 and 2 underwent cyclic testing directly after the capacity test. Examples 3-14 and Comparative Examples 1-2 added the following steps to the cyclic testing process: after 300 and 600 cycles, lithium replenishment activation was performed at room temperature (activation method as described above). The test results are shown in Table 1 below.

[0138] Table 1

[0139] Lithium utilization rate / % Loop count Example 1 84.9 1294 Example 2 82.8 1258 Example 3 89.1 1587 Example 4 89.5 1614 Example 5 88.7 1560 Example 6 87.5 1415 Example 7 86.9 1433 Example 8 86.0 1370 Example 9 85.1 1308 Example 10 88.6 1552 Example 11 89.4 1607 Example 12 88.5 1545 Example 13 85.2 1375 Example 14 84.5 1326 Comparative Example 1 73.6 1141 Comparative Example 2 68.1 960 Comparative Example 3 / 793

[0140] Analysis of experimental results:

[0141] Comparing Example 3 and Comparative Example 1, it can be seen that when the composite membrane loses its ion-conducting water-barrier layer, the lithium replenishing agent will react with some of the moisture in the air, and part of the lithium replenishing agent will lose its activity, thus reducing the utilization rate of lithium.

[0142] Comparing Comparative Example 1 and Comparative Example 2, it can be seen that when the lithium replenishing agent in the composite lithium replenishing membrane is active lithium, the environmental stability of lithium is worse, it is more easily reacted, and the utilization rate of lithium is greatly reduced.

[0143] Comparing Examples 1-2 and Example 3, it can be seen that the lithium replenishment effect of multiple activations is better than that of single activations. When lithium replenishment is performed with multiple activations, the lithium utilization rate of the lithium replenishing agent is higher and the cycle life is longer.

[0144] Comparing Examples 3 and 4-8, it can be seen that the thickness ratio of the ion-conducting water barrier layer to the lithium replenishment layer affects the lithium utilization rate of the lithium replenishment agent, thereby affecting the cycle life of the battery.

[0145] Comparing Example 3 with Examples 11-13, it can be seen that the thickness of the conductive layer affects the lithium utilization rate of the lithium replenishment agent, thereby affecting the cycle life of the battery.

[0146] Comparing Example 3 and Example 14, it can be seen that the conductive layer can improve the utilization rate of lithium in the lithium replenishment agent and improve the battery cycle life.

[0147] In summary, the lithium replenishment layer of this invention is located in the middle of the composite lithium replenishment membrane, while the ion-conducting water-barrier layer is located on the outermost side of the composite lithium replenishment membrane. This protects the lithium replenishment layer, effectively inhibiting the reaction between moisture in the environment and the lithium replenishment agent while ensuring smooth lithium ion transport, thus preventing the lithium replenishment agent from deactivating. At the same time, it prevents the lithium replenishment layer from directly contacting the electrolyte and the external environment, effectively reducing the risk of lithium replenishment layer detachment, improving the utilization rate of lithium in the lithium replenishment agent, and improving the energy density and cycle life of the battery.

[0148] In addition, the conductive layer is set so that the lithium replenishment layer does not come into direct contact with the base film, reducing the risk of micropore blockage in the base film and improving the battery cycle life.

[0149] The terms "first" and "second" used in this document are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature marked "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0150] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0151] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A composite lithium-supplementing separator, characterized in that, include: The first membrane layer includes a first base membrane and a first ion-conducting water-barrier layer disposed on one side of the first base membrane; The second membrane layer includes a second base membrane and a second ion-conducting water-barrier layer disposed on one side of the second base membrane; A lithium replenishment layer is disposed between the first membrane layer and the second membrane layer. The lithium replenishment layer is close to the first base membrane and the second base membrane, and far away from the first ion-conducting water barrier layer and the second ion-conducting water barrier layer.

2. The composite lithium-supplementing separator according to claim 1, characterized in that, The thickness ratio of the first ion-conducting water barrier layer to the lithium replenishment layer is 1:(1-7); the thickness ratio of the second ion-conducting water barrier layer to the lithium replenishment layer is 1:(1-7).

3. The composite lithium-supplementing separator according to claim 2, characterized in that, The thickness ratio of the first ion-conducting water barrier layer to the lithium replenishment layer is 1:(2-4); the thickness ratio of the second ion-conducting water barrier layer to the lithium replenishment layer is 1:(2-4).

4. The composite lithium-supplementing separator according to any one of claims 1-3, characterized in that, The thickness of both the first ion-conducting water-barrier layer and the second ion-conducting water-barrier layer is 0.5μm-10μm.

5. The composite lithium-supplementing separator according to any one of claims 1-3, characterized in that, Both the first ion-conducting water barrier layer and the second ion-conducting water barrier layer are physical mixtures of chloride solid electrolyte and binder; The chloride solid electrolyte is Li₂ZrCl₆; The adhesive is polyvinylidene fluoride, polyvinylidene fluoride-hexachloropropylene polymer, styrene-butadiene rubber, polypropylene, sodium carboxymethyl cellulose, polyacrylic acid, or polymethyl methacrylate.

6. The composite lithium-supplementing separator according to any one of claims 1-3, characterized in that, The thickness of the lithium replenishment layer is 0.5μm-30μm.

7. The composite lithium-supplementing separator according to any one of claims 1-3, characterized in that, The lithium replenishment layer is a physical mixture of positive electrode lithium replenishment agent, conductive agent and binder; The positive electrode lithium replenishing agent is Li2NiO2, Li2CuO2, Li6CoO4, Li5FeO4, Li6MnO4, Li2MoO3, Li3N, Li2O, Li2O2, LiOH, Li2CO3 or Li2S; The conductive agent is carbon nanotubes, Ketjen black, carbon black, graphene, or carbon nanotubes. The adhesive is polyvinylidene fluoride, polyvinylidene fluoride-hexachloropropylene polymer, styrene-butadiene rubber, polypropylene, sodium carboxymethyl cellulose, polyacrylic acid, or polymethyl methacrylate.

8. The composite lithium-supplementing separator according to any one of claims 1-3, characterized in that, The first membrane layer further includes a first conductive layer, which is disposed on the side of the first base film near the lithium replenishment layer; The second membrane layer further includes a second conductive layer, which is disposed on the side of the second base film near the lithium replenishment layer.

9. The composite lithium-supplementing separator according to claim 8, characterized in that, The thickness of the first conductive layer and the second conductive layer is 1μm-20μm respectively.

10. The composite lithium-supplementing separator according to any one of claims 1-3, characterized in that, The thickness of the first base film and the second base film are each 3μm-50μm.

11. A lithium-ion battery, characterized in that, The composite lithium-filling separator includes any one of claims 1-10.

12. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 11.

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