Lithium supplement diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium supplementing diaphragm and a preparation method thereof and a lithium ion battery, the lithium supplementing diaphragm comprises a porous base membrane and a lithium supplementing layer, the lithium supplementing layer is arranged on the side, facing a positive electrode, of the porous base membrane, the lithium supplementing layer comprises Li-Al alloy powder, the mass percent of Li in the Li-Al alloy powder is 0.3%-15%. According to the lithium supplementing diaphragm, the Li-Al alloy powder serves as the lithium source, the safety is high, the Li-Al alloy powder does not need to be stored and processed in the protective atmosphere, the processing difficulty of the diaphragm is reduced, and the lithium supplementing diaphragm is easier to store.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium supplementing diaphragm and a preparation method thereof, and a lithium ion battery. Background Art

[0002] Under the current national policy of vigorously developing clean and sustainable energy, the development of lithium-ion batteries shows a strong trend. However, the charging and discharging of commercial lithium-ion batteries will generate SEI film on the negative electrode surface, consuming a large amount of active lithium and causing irreversible capacity loss. Especially for positive electrode materials with low energy density such as LiFePO4, it is particularly important to increase the proportion of active lithium.

[0003] In recent years, many universities and enterprises have done a lot of research work on lithium replenishment. The disclosed lithium replenishment technology, such as patent publication number: CN105932206A, discloses a lithium replenishment composite diaphragm. This invention first coats a ceramic layer on the surface of the porous base membrane, and then introduces a lithium-containing layer. However, the lithium source in the lithium-containing layer is metallic lithium powder, which has poor safety. This diaphragm that directly replenishes metallic lithium is not easy to process and preserve. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a lithium-supplementing diaphragm and a preparation method thereof, and a lithium-ion battery. The lithium-supplementing diaphragm uses Li-Al alloy powder as a lithium source, has higher safety, and the Li-Al alloy powder does not need to be stored and processed in a protective atmosphere, thereby reducing the processing difficulty of the diaphragm, and the lithium-supplementing diaphragm is easier to preserve.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a lithium replenishing diaphragm, comprising a porous base membrane and a lithium replenishing layer, wherein the lithium replenishing layer is arranged on a side of the porous base membrane facing the positive electrode, and the lithium replenishing layer comprises Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 0.3%-15%.

[0007] The lithium-supplementing diaphragm provided by the present invention uses Li-Al alloy powder as a lithium source, so it has high safety. The Li-Al alloy powder does not need to be stored and processed in a protective atmosphere, which reduces the processing difficulty of the diaphragm, and the lithium-supplementing diaphragm is easier to store.

[0008] Furthermore, the porous base membrane includes one of a PP porous base membrane and a PE porous base membrane, the porosity of the porous base membrane is 35%-55%, the thickness of the PP porous base membrane is 10-22 μm, and the thickness of the PE porous base membrane is 5-14 μm.

[0009] Furthermore, the thickness of the lithium replenishing layer is 1 to 5 μm.

[0010] Furthermore, the D50 particle size of the Li-Al alloy powder is 0.3-0.6 μm.

[0011] Furthermore, the lithium supplement layer also includes a binder and an additive, and the mass ratio of the Li-Al alloy powder, the binder and the additive is (55-70):6:(0.2-0.5); the binder includes at least one of PVA, CMC, and PVDF; the additive includes at least one of PVP and polyoxyethylene dioleate.

[0012] In a second aspect, the present invention provides a method for preparing the lithium supplementing diaphragm as described in the first aspect, the preparation method comprising the following steps:

[0013] S1, adding the binder, additives and Li-Al alloy powder into water, stirring and mixing to obtain lithium supplement slurry;

[0014] S2. Coating the lithium replenishing slurry on the side of the porous base film facing the positive electrode, and then drying to solidify the lithium replenishing slurry to form the lithium replenishing layer, thereby obtaining the lithium replenishing separator.

[0015] Furthermore, in step S1, the binder and the additive are first added into water for mixing, and then the Li-Al alloy powder is added.

[0016] Furthermore, the mass percentages of the components in the lithium supplement slurry are as follows: Li-Al alloy powder: 55%-70%; binder: 4%-6%; water: 24%-40%; additives: 0.2%-0.5%;

[0017] And / or, in step S1, the stirring and mixing device is IKA@EUROSTAR 200control, and the stirring speed is 800-2500r / s;

[0018] and / or, in step S2, coating the lithium supplement slurry on the side of the porous base film (1) facing the positive electrode to form a coating with a thickness of 1 to 5 μm;

[0019] And / or, the drying temperature is 40-60° C., and the drying time is 40-60 min.

[0020] In a third aspect, the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and an isolation membrane arranged between the positive electrode sheet and the negative electrode sheet, wherein the isolation membrane is the lithium-supplementing membrane described in the first aspect, or the lithium-supplementing membrane prepared by the preparation method described in the second aspect, and the lithium-supplementing layer of the lithium-supplementing membrane is arranged on the side of the porous base membrane facing the positive electrode sheet.

[0021] Furthermore, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material in the positive electrode active material layer includes at least one of LFP, NCM, LCO, and LMO; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material in the negative electrode active material layer includes at least one of artificial graphite, natural graphite, and hard carbon.

[0022] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0023] 1. The lithium-supplementing diaphragm provided by the present invention uses Li-Al alloy powder as a lithium source, so it has higher safety. The Li-Al alloy powder does not need to be stored and processed in a protective atmosphere, which reduces the processing difficulty of the diaphragm, and the lithium-supplementing diaphragm is easier to store.

[0024] 2. After being applied to lithium-ion batteries, the aluminum in the lithium-supplementing diaphragm provided by the present invention will be oxidized to Al2O3, which can be used as a ceramic layer of the diaphragm to enhance its safety performance. There is no need to coat the base film used in the present invention with a ceramic layer, and there is no need to increase the thickness of the diaphragm, thereby reducing the cost of using the diaphragm and improving the energy density of the battery cell.

[0025] 3. Li-Al alloy powder does not need to be stored and processed in a protective atmosphere, which reduces processing difficulty and reduces environmental and equipment costs.

[0026] 4. The preparation method of the lithium-supplementing diaphragm provided by the present invention uses water as a solvent, which is more non-toxic and environmentally friendly, and is simple to operate and does not need to be carried out in a protective atmosphere.

[0027] 5. There is no need to directly add lithium powder to the base film to avoid puncturing or clogging the diaphragm and reduce the risk of battery cell failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1A schematic diagram of the structure of the lithium supplement diaphragm provided by the present invention;

[0030] Figure 2 This is a schematic structural diagram of the lithium-ion battery provided by the present invention.

[0031] Icon: 1-porous base film, 2-lithium replenishing layer, 3-positive electrode current collector, 4-positive electrode active material layer, 5-negative electrode active material layer, 6-negative electrode current collector. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0033] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0034] Figure 1 The schematic diagram of the structure of the lithium supplement diaphragm provided by the present invention is as follows: Figure 1 As shown, in the first aspect, the present invention provides a lithium replenishing diaphragm, the lithium replenishing diaphragm comprising a porous base membrane 1 and a lithium replenishing layer 2, the lithium replenishing layer 2 is arranged on the side of the porous base membrane 1 facing the positive electrode, the lithium replenishing layer 2 comprises Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 0.3%-15%, for example, it can be 0.3%, 1%, 3%, 5%, 7%, 9%, 11%, 13% or 15%.

[0035] The lithium-supplementing diaphragm provided by the present invention uses Li-Al alloy powder as a lithium source, so it has high safety. The Li-Al alloy powder does not need to be stored and processed in a protective atmosphere, which reduces the processing difficulty of the diaphragm, and the lithium-supplementing diaphragm is easier to store.

[0036] In the above-mentioned lithium-replenishing separator, as an optional embodiment, the porous base membrane 1 includes one of a PP (polypropylene) porous base membrane and a PE (polyethylene) porous base membrane, the porosity of the porous base membrane 1 is 35%-55% (for example, it can be 35%, 40%, 45%, 50% or 55%), the thickness of the PP porous base membrane is 10-22μm (for example, it can be 10μm, 15μm, 20μm or 22μm), and the thickness of the PE porous base membrane is 5-14μm (for example, it can be 5μm, 10μm or 14μm).

[0037] In the above lithium replenishing separator, as an optional implementation, the thickness of the lithium replenishing layer 2 is 1 to 5 μm, for example, 1 μm, 2 μm, 3 μm or 5 μm.

[0038] In the above lithium supplement separator, as an optional implementation, the D50 particle size of the Li-Al alloy powder is 0.3-0.6 μm, for example, 0.3 μm, 0.4 μm, 0.5 μm or 0.6 μm.

[0039] In the above-mentioned lithium replenishing separator, as an optional embodiment, the lithium replenishing layer 2 also includes a binder and an additive, and the mass ratio of the Li-Al alloy powder, the binder and the additive is (55-70):6:(0.2-0.5), for example, it can be 55:6:0.2, 60:6:0.2, 65:6:0.2, 70:6:0.2 or 55:6:0.4.

[0040] In the above-mentioned lithium supplement separator, as an optional implementation, the binder includes at least one of PVA (polyvinyl alcohol), CMC (carboxymethyl cellulose), and PVDF (polyvinylidene fluoride).

[0041] In the above lithium supplement separator, as an optional embodiment, the additive includes at least one of PVP (polyvinyl pyrrolidone) and polyoxyethylene dioleate. The additive acts as a thickener and leveling agent to assist in homogenization and coating.

[0042] In a second aspect, the present invention provides a method for preparing the lithium supplementing diaphragm as described in the first aspect, the preparation method comprising the following steps:

[0043] S1, adding the binder, additives and Li-Al alloy powder into water, stirring and mixing to obtain lithium supplement slurry;

[0044] S2, coating the lithium replenishing slurry on the side of the porous base film 1 facing the positive electrode, and then drying to solidify the lithium replenishing slurry to form the lithium replenishing layer 2, thereby obtaining the lithium replenishing separator.

[0045] The preparation method provided by the invention uses water as solvent, is more non-toxic and environmentally friendly, and is simple to operate without the need to be performed in a protective atmosphere.

[0046] In the above-mentioned method for preparing the lithium supplementing separator, as an optional implementation mode, in step S1, the binder and the additive are first added into water for mixing, and then the Li-Al alloy powder is added.

[0047] In the preparation method of the above-mentioned lithium-supplementing diaphragm, as an optional implementation mode, the mass percentages of the components in the lithium-supplementing slurry are as follows: Li-Al alloy powder: 55%-70% (for example, it can be 55%, 60%, 65% or 70%); binder: 4%-6%; water: 24%-40% (for example, it can be 24%, 30%, 35% or 40%); additives: 0.2%-0.5%.

[0048] In the above-mentioned method for preparing the lithium-supplementing separator, as an optional implementation, in step S1, the stirring and mixing device used is IKA@EUROSTAR 200control, and the stirring speed is 800-2500r / s, for example, it can be 800r / s, 1500r / s, 2000r / s or 2500r / s.

[0049] In the above method for preparing the lithium-replenishing separator, as an optional implementation, in step S2, the lithium-replenishing slurry is coated on the side of the porous base membrane (1) facing the positive electrode to form a coating with a thickness of 1 to 5 μm.

[0050] In the above-mentioned method for preparing the lithium-supplementing diaphragm, as an optional embodiment, the drying temperature is 40-60°C (for example, it can be 40°C, 45°C, 50°C, 55°C or 60°C), and the drying time is 40-60min (for example, it can be 40min, 45min, 50min, 55min or 60min).

[0051] Figure 2 The schematic diagram of the structure of the lithium-ion battery provided by the present invention is as follows: Figure 2 As shown, in the third aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator arranged between the positive electrode sheet and the negative electrode sheet, the separator is the lithium-supplementing separator described in the first aspect, or the lithium-supplementing separator prepared by the preparation method described in the second aspect, and the lithium-supplementing layer 2 of the lithium-supplementing separator is arranged on the side of the porous base film 1 facing the positive electrode sheet.

[0052] In the above-mentioned lithium-ion battery, as an optional embodiment, the positive electrode plate includes a positive electrode current collector 3 and a positive electrode active material layer 4, and the positive electrode active material in the positive electrode active material layer 4 includes at least one of LFP (lithium iron phosphate), NCM (nickel cobalt manganese), LCO (lithium cobalt oxide), and LMO (lithium manganese oxide).

[0053] In the above lithium-ion battery, as an optional embodiment, the negative electrode plate includes a negative electrode current collector 6 and a negative electrode active material layer 5, and the negative electrode active material in the negative electrode active material layer 5 includes at least one of artificial graphite, natural graphite, and hard carbon.

[0054] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0055] In the following examples and comparative examples:

[0056] Li-Al alloy powder was purchased from Sigma-Aldrich Trading Co., Ltd. under the brand name Aldrich.

[0057] Example 1

[0058] The present embodiment provides a lithium replenishing diaphragm, which includes a PP porous base membrane and a lithium replenishing layer, wherein the lithium replenishing layer is arranged on the side of the PP porous base membrane facing the positive electrode, and the lithium replenishing layer includes Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 3%, the D50 particle size of the Li-Al alloy powder is 0.5μm, the porosity of the PP porous base membrane is 40%, and the thickness of the PP porous base membrane is 16μm.

[0059] The preparation method of the lithium supplementing diaphragm comprises the following steps:

[0060] S1. PVA and PVP were added into water and stirred evenly using a stirring device IKA@EUROSTAR 200control at a stirring speed of 1000 r / s for 30 min. Then, Li-Al alloy powder was added and stirred at a stirring speed of 2000 r / s for 2 h to obtain a lithium supplement slurry. The mass percentage of each component in the lithium supplement slurry was as follows: Li-Al alloy powder: 55%; PVA: 6%; solvent water: 38.8%; PVP: 0.2%;

[0061] S2. Use a scraper to coat the lithium supplement slurry on the side of the PP porous base film facing the positive electrode to form a coating with a thickness of 2 μm, and then place the coated porous base film in a 60° C. vacuum oven for 60 minutes to cure, thereby obtaining the lithium supplement separator.

[0062] This embodiment also provides a soft-pack lithium-ion battery, the soft-pack lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator arranged between the positive electrode sheet and the negative electrode sheet, the separator being the lithium-supplementing separator in this embodiment, and the method for preparing the soft-pack lithium-ion battery comprising the following steps:

[0063] Positive electrode sheet: The positive electrode material LiFePO4, the conductive agent CNTs, the binder PVDF, and the solvent NMP are stirred and dispersed evenly to obtain a positive electrode slurry, which is then coated on an aluminum foil, and then rolled and cut to obtain a positive electrode sheet;

[0064] Negative electrode sheet: The negative electrode material artificial graphite, conductive agent SP, binder SBR, thickener CMC and water are stirred and dispersed evenly to obtain negative electrode slurry, which is then coated on copper foil, and then rolled and cut to obtain negative electrode sheet;

[0065] Electrolyte: Prepared by dissolving 1M LiPF6 in a solvent with a volume ratio of EC:DEC:EMC=1:1:1;

[0066] Separator: Use the lithium-supplement separator in this embodiment, and place the lithium-supplement layer of the lithium-supplement separator toward the positive electrode;

[0067] The positive electrode sheet, negative electrode sheet, electrolyte and isolation membrane prepared above were used to prepare a soft-pack lithium-ion battery with a capacity of 5.3 Ah.

[0068] Example 2

[0069] The present embodiment provides a lithium-supplementing diaphragm, which includes a PP porous base membrane and a lithium-supplementing layer, wherein the lithium-supplementing layer is arranged on the side of the PP porous base membrane facing the positive electrode, and the lithium-supplementing layer includes Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 5%, the D50 particle size of the Li-Al alloy powder is 0.5 μm, the porosity of the PP porous base membrane is 40%, and the thickness of the PP porous base membrane is 16 μm.

[0070] The preparation method of the lithium supplementing diaphragm comprises the following steps:

[0071] S1. Add PVDF and PVP into water and stir them evenly using a stirring device IKA@EUROSTAR 200control at a stirring speed of 1000 r / s for 30 min. Then add Li-Al alloy powder and stir at a stirring speed of 2000 r / s for 2 h to obtain lithium replenishment slurry, wherein the mass percentage of each component in the lithium replenishment slurry is as follows: Li-Al alloy powder: 60%; PVDF: 6%; solvent water: 33.8%; PVP: 0.2%;

[0072] S2. Use a scraper to coat the lithium supplement slurry on the side of the PP porous base film facing the positive electrode to form a coating with a thickness of 2 μm, and then place the coated porous base film in a 60° C. vacuum oven for 60 minutes to cure, thereby obtaining the lithium supplement separator.

[0073] The soft-pack lithium-ion battery provided in this embodiment is substantially the same as that in Embodiment 1, except that the isolation membrane uses the lithium-supplementing membrane in this embodiment.

[0074] Example 3

[0075] The present embodiment provides a lithium replenishing diaphragm, which includes a PP porous base membrane and a lithium replenishing layer, wherein the lithium replenishing layer is arranged on the side of the PP porous base membrane facing the positive electrode, and the lithium replenishing layer includes Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 7%, the D50 particle size of the Li-Al alloy powder is 0.4μm, the porosity of the PP porous base membrane is 40%, and the thickness of the PP porous base membrane is 16μm.

[0076] The preparation method of the lithium supplementing diaphragm comprises the following steps:

[0077] S1. PVA and PVP were added into water and stirred evenly using a stirring device IKA@EUROSTAR 200control at a stirring speed of 1000 r / s for 30 min. Then, Li-Al alloy powder was added and stirred at a stirring speed of 2000 r / s for 2 h to obtain a lithium supplement slurry, wherein the mass percentage of each component in the lithium supplement slurry is as follows: Li-Al alloy powder: 65%; PVA: 6%; solvent water: 28.8%; PVP: 0.2%;

[0078] S2. Use a scraper to coat the lithium supplement slurry on the side of the PP porous base film facing the positive electrode to form a coating with a thickness of 2 μm, and then place the coated porous base film in a 60° C. vacuum oven for 60 minutes to cure, thereby obtaining the lithium supplement separator.

[0079] The soft-pack lithium-ion battery provided in this embodiment is substantially the same as that in Embodiment 1, except that the isolation membrane uses the lithium-supplementing membrane in this embodiment.

[0080] Example 4

[0081] The present embodiment provides a lithium replenishing diaphragm, which includes a PP porous base membrane and a lithium replenishing layer, wherein the lithium replenishing layer is arranged on the side of the PP porous base membrane facing the positive electrode, and the lithium replenishing layer includes Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 10%, the D50 particle size of the Li-Al alloy powder is 0.3μm, the porosity of the PP porous base membrane is 40%, and the thickness of the PP porous base membrane is 16μm.

[0082] The preparation method of the lithium supplementing diaphragm comprises the following steps:

[0083] S1. PVA and PVP were added into water and stirred evenly using a stirring device IKA@EUROSTAR 200control at a stirring speed of 1000 r / s for 30 min. Then, Li-Al alloy powder was added and stirred at a stirring speed of 2000 r / s for 2 h to obtain a lithium supplement slurry. The mass percentage of each component in the lithium supplement slurry was as follows: Li-Al alloy powder: 70%; PVA: 6%; solvent water: 23.8%; PVP: 0.2%;

[0084] S2. Use a scraper to coat the lithium supplement slurry on the side of the PP porous base film facing the positive electrode to form a coating with a thickness of 2 μm, and then place the coated porous base film in a 60° C. vacuum oven for 60 minutes to cure, thereby obtaining the lithium supplement separator.

[0085] The soft-pack lithium-ion battery provided in this embodiment is substantially the same as that in Embodiment 1, except that the isolation membrane uses the lithium-supplementing membrane in this embodiment.

[0086] Example 5

[0087] The present embodiment provides a lithium replenishing diaphragm, which includes a PP porous base membrane and a lithium replenishing layer, wherein the lithium replenishing layer is arranged on the side of the PP porous base membrane facing the positive electrode, and the lithium replenishing layer includes Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 12%, the D50 particle size of the Li-Al alloy powder is 0.3μm, the porosity of the PP porous base membrane is 45%, and the thickness of the PP porous base membrane is 16μm.

[0088] The preparation method of the lithium supplementing diaphragm comprises the following steps:

[0089] S1. PVA and PVP were added into water and stirred evenly using a stirring device IKA@EUROSTAR 200control at a stirring speed of 1000 r / s for 30 min. Then, Li-Al alloy powder was added and stirred at a stirring speed of 2000 r / s for 2 h to obtain a lithium supplement slurry. The mass percentage of each component in the lithium supplement slurry was as follows: Li-Al alloy powder: 55%; PVA: 6%; solvent water: 38.8%; PVP: 0.2%;

[0090] S2. Use a scraper to coat the lithium supplement slurry on the side of the PP porous base film facing the positive electrode to form a coating with a thickness of 2 μm, and then place the coated porous base film in a 60° C. vacuum oven for 60 minutes to cure, thereby obtaining the lithium supplement separator.

[0091] The soft-pack lithium-ion battery provided in this embodiment is substantially the same as that in Embodiment 1, except that the isolation membrane uses the lithium-supplementing membrane in this embodiment.

[0092] Example 6

[0093] The present embodiment provides a lithium replenishing diaphragm, which includes a PP porous base membrane and a lithium replenishing layer, wherein the lithium replenishing layer is arranged on the side of the PP porous base membrane facing the positive electrode, and the lithium replenishing layer includes Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 15%, the D50 particle size of the Li-Al alloy powder is 0.3μm, the porosity of the PP porous base membrane is 50%, and the thickness of the PP porous base membrane is 16μm.

[0094] The preparation method of the lithium supplementing diaphragm comprises the following steps:

[0095] S1. PVA and PVP were added into water and stirred evenly using a stirring device IKA@EUROSTAR 200control at a stirring speed of 1000 r / s for 30 min. Then, Li-Al alloy powder was added and stirred at a stirring speed of 2000 r / s for 2 h to obtain a lithium supplement slurry. The mass percentage of each component in the lithium supplement slurry was as follows: Li-Al alloy powder: 55%; PVA: 6%; solvent water: 38.8%; PVP: 0.2%;

[0096] S2. Use a scraper to coat the lithium supplement slurry on the side of the PP porous base film facing the positive electrode to form a coating with a thickness of 2 μm, and then place the coated porous base film in a 60° C. vacuum oven for 60 minutes to cure, thereby obtaining the lithium supplement separator.

[0097] The soft-pack lithium-ion battery provided in this embodiment is substantially the same as that in Embodiment 1, except that the isolation membrane uses the lithium-supplementing membrane in this embodiment.

[0098] Comparative Example 1

[0099] The diaphragm provided in this comparative example is as follows:

[0100] The diaphragm described in this comparative example uses a PP porous base film with a thickness of 16 μm and a porosity of 40%. A coating layer is provided on the side of the PP porous base film facing the positive electrode, and the coating layer is Al2O3 with a thickness of 2 μm. The diaphragm is a purchased finished product, and the manufacturer is ZTE ZT series.

[0101] The soft-pack lithium-ion battery provided in this comparative example is substantially the same as that in Example 1, except that the separator used in this comparative example is the separator.

[0102] Comparative Example 2

[0103] The lithium supplementing separator provided in this comparative example is substantially the same as that in Example 1, except that the mass percentage of Li in the Li-Al alloy powder is 30%.

[0104] The lithium supplementing separator was prepared according to the preparation method provided in Example 1.

[0105] The soft-pack lithium-ion battery provided in this comparative example is substantially the same as that in Example 1, except that the separator uses the lithium-supplementing separator in this comparative example.

[0106] Comparative Example 3

[0107] The lithium-replenishing separator provided in this comparative example is substantially the same as that in Example 1, except that the lithium-replenishing layer is disposed on the side of the PP porous base film facing the negative electrode.

[0108] The lithium supplementing separator was prepared according to the preparation method provided in Example 1.

[0109] The soft-pack lithium-ion battery provided in this comparative example is substantially the same as that in Example 1, except that the separator uses the lithium-supplementing membrane in this comparative example, and the lithium-supplementing layer of the lithium-supplementing membrane is placed toward the negative electrode.

[0110] Performance Testing

[0111] The soft-pack lithium-ion batteries provided in the examples and comparative examples were subjected to electrochemical performance tests and safety performance tests.

[0112] The first charge and discharge efficiency of the battery cell: use 0.05C constant current to charge for 4h, then use 0.1C constant current to charge for 1h, then use 0.5C constant current and constant voltage to charge to 3.65V, cut-off current 0.02C, after leaving for 10min, use 0.5C constant current to discharge to 2V, record the charging capacity and discharge capacity and calculate the first coulombic efficiency.

[0113] Cycle performance: Use 1C constant current and constant voltage charging, the upper limit voltage is 3.65V, the cut-off current is 0.02C, and 1C constant current discharge to 2.0V. Cycle this process for 1000 times, and calculate the capacity retention rate after 1000 cycles of charge and discharge.

[0114] Safety performance test: Use a 5mm diameter steel needle to pierce the battery at a speed of 25mm / s. Keep the needle inside the battery for 60 minutes to observe whether there is fire or explosion. If there is no fire or explosion, the test has passed.

[0115] The above test results are shown in Table 1.

[0116] Table 1

[0117]

[0118] From Table 1, we can see at least the following points:

[0119] (1) By comparing Examples 1-6 with Comparative Example 1, it can be seen that the initial coulombic efficiency and cycle performance of lithium-ion batteries can be significantly improved by using the lithium-supplementing diaphragm provided by the present invention. After being applied to lithium-ion batteries, the lithium-supplementing diaphragm provided by the present invention has high safety performance, and there is no need to coat the base film used in the present invention with a ceramic layer, and there is no need to increase the thickness of the diaphragm, thereby reducing the cost of using the diaphragm and improving the energy density of the battery cell.

[0120] (2) By comparing Example 1 with Comparative Example 2, it can be seen that when the mass percentage of Li in the Li-Al alloy powder is too high, the first efficiency and cycle performance are both reduced, and the safety is low.

[0121] (3) By comparing Example 1 with Comparative Example 3, it can be seen that when the lithium supplement layer is disposed on the side of the PP porous base film facing the negative electrode, both the first efficiency and the cycle performance decrease.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention 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 replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium supplementing diaphragm, characterized in that: The lithium replenishing diaphragm comprises a porous base film (1) and a lithium replenishing layer (2), wherein the lithium replenishing layer (2) is arranged on a side of the porous base film (1) facing the positive electrode, and the lithium replenishing layer (2) comprises Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 0.3%-15%.

2. The lithium supplementing diaphragm according to claim 1, characterized in that: The porous base film (1) comprises one of a PP porous base film and a PE porous base film, the porosity of the porous base film (1) is 35%-55%, the thickness of the PP porous base film is 10-22 μm, and the thickness of the PE porous base film is 5-14 μm.

3. The lithium supplementing diaphragm according to claim 1, characterized in that: The thickness of the lithium replenishing layer (2) is 1 to 5 μm.

4. The lithium supplementing diaphragm according to claim 1, characterized in that: The D50 particle size of the Li-Al alloy powder is 0.3-0.6 μm.

5. The lithium supplementing diaphragm according to claim 1, characterized in that: The lithium supplement layer (2) further comprises a binder and an additive, wherein the mass ratio of the Li-Al alloy powder, the binder and the additive is (55-70):6:(0.2-0.5); the binder comprises at least one of PVA, CMC and PVDF; and the additive comprises at least one of PVP and polyoxyethylene dioleate.

6. A method for preparing a lithium supplementing diaphragm according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: S1, adding the binder, additives and Li-Al alloy powder into water, stirring and mixing to obtain lithium supplement slurry; S2, coating the lithium replenishing slurry on the side of the porous base film (1) facing the positive electrode, and then drying to solidify the lithium replenishing slurry to form the lithium replenishing layer (2), thereby obtaining the lithium replenishing separator.

7. The method for preparing a lithium supplementing diaphragm according to claim 6, characterized in that: In step S1, the binder and the additive are first added into water for mixing, and then the Li-Al alloy powder is added.

8. The method for preparing a lithium supplementing diaphragm according to claim 6, characterized in that: The mass percentages of the components in the lithium supplement slurry are as follows: Li-Al alloy powder: 55%-70%; binder: 4%-6%; Water: 24%-40%; Additives: 0.2%-0.5%; And / or, in step S1, the stirring and mixing device is IKA@EUROSTAR 200control, and the stirring speed is 800-2500r / s; and / or, in step S2, coating the lithium supplement slurry on the side of the porous base film (1) facing the positive electrode to form a coating with a thickness of 1 to 5 μm; And / or, the drying temperature is 40-60° C., and the drying time is 40-60 min.

9. A lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, characterized in that: The isolation membrane is the lithium-supplementing membrane described in any one of claims 1 to 5, or a lithium-supplementing membrane prepared by the preparation method described in any one of claims 6 to 8, and the lithium-supplementing layer (2) of the lithium-supplementing membrane is arranged on the side of the porous base membrane (1) facing the positive electrode plate.

10. The lithium ion battery according to claim 9, characterized in that: The positive electrode plate comprises a positive electrode current collector (3) and a positive electrode active material layer (4), wherein the positive electrode active material in the positive electrode active material layer (4) comprises at least one of LFP, NCM, LCO, and LMO; the negative electrode plate comprises a negative electrode current collector (6) and a negative electrode active material layer (5), wherein the negative electrode active material in the negative electrode active material layer (5) comprises at least one of artificial graphite, natural graphite, and hard carbon.

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