Lithium supplementing diaphragm, preparation method thereof and lithium ion battery

Abstract

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

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium-replenishing separator and its preparation method, and a lithium-ion battery. Background Technology

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

[0003] In recent years, many universities and enterprises have conducted a lot of research on lithium replenishment. Publicly available lithium replenishment technologies, such as patent publication number CN105932206A, disclose a lithium replenishment composite membrane. This invention first coats a ceramic layer on the surface of a porous base membrane, and then introduces a lithium-containing layer. However, the lithium source in this lithium-containing layer is metallic lithium powder, which has poor safety. This type of membrane that directly replenishes metallic lithium is not easy to process and store. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, the purpose of the present invention is to provide a lithium-replenishing separator and its preparation method, and a lithium-ion battery. The lithium-replenishing separator uses Li-Al alloy powder as the lithium source, which 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 separator. Moreover, the lithium-replenishing separator is easier to store.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

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

[0007] The lithium replenishment separator provided by this invention uses Li-Al alloy powder as the lithium source, which 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 separator, and the lithium replenishment separator is easier to store.

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

[0009] Furthermore, the thickness of the lithium replenishment layer is 1–5 μm.

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

[0011] Furthermore, the lithium replenishment layer also includes 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 includes at least one of PVA, CMC and PVDF; and the additive includes at least one of PVP and polyoxyethylene dioleate.

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

[0013] S1. Add the binder, additives and Li-Al alloy powder to water and stir to mix to obtain lithium supplementation slurry;

[0014] S2. The lithium replenishing slurry is coated on the porous base film on the side facing the positive electrode, and then dried 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 mixed in water, and then the Li-Al alloy powder is added.

[0016] Furthermore, the mass percentages of each component in the lithium replenishment 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 equipment used is an IKA@EUROSTAR 200control with a stirring speed of 800-2500 r / s;

[0018] And / or, in step S2, the lithium replenishing slurry is coated 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℃ and the drying time is 40-60min.

[0020] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the separator being the lithium-replenishing separator described in the first aspect, or a lithium-replenishing separator prepared by the preparation method described in the second aspect, wherein the lithium-replenishing layer of the lithium-replenishing separator is disposed on the porous base film facing the positive electrode.

[0021] Furthermore, the positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material in the positive active material layer includes at least one of LFP, NCM, LCO, and LMO; the negative electrode sheet includes a negative current collector and a negative active material layer, wherein the negative active material in the negative 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 replenishment diaphragm provided by the present invention uses Li-Al alloy powder as the lithium source, which 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 replenishment diaphragm is easier to store.

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

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

[0026] 4. The method for preparing the lithium-supplementing separator provided by the present invention uses water as a solvent, which is more non-toxic and environmentally friendly, and is simple to operate without the need for a protective atmosphere.

[0027] 5. There is no need to add lithium powder directly to the base film, thus avoiding puncture or blockage of the separator and reducing the risk of cell failure. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1This is a schematic diagram of the structure of the lithium replenishment separator provided by the present invention;

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

[0031] Icons: 1-Porous base film, 2-Lithium replenishment layer, 3-Positive electrode current collector, 4-Positive electrode active material layer, 5-Negative electrode active material layer, 6-Negative electrode current collector. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0033] The endpoints and any values ​​of the ranges disclosed in this 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0034] Figure 1 A schematic diagram of the lithium-supplementing separator provided by the present invention is shown below. Figure 1 As shown, in a first aspect, the present invention provides a lithium replenishing membrane, the lithium replenishing membrane comprising a porous base membrane 1 and a lithium replenishing layer 2, the lithium replenishing layer 2 being disposed on the porous base membrane 1 on the side facing the positive electrode, the lithium replenishing layer 2 comprising 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 replenishment separator provided by this invention uses Li-Al alloy powder as the lithium source, which 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 separator, and the lithium replenishment separator is easier to store.

[0036] In the above-mentioned lithium-supplementing separator, as an optional embodiment, the porous base membrane 1 includes one of PP (polypropylene) porous base membrane and 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-mentioned lithium replenishment membrane, as an optional embodiment, the thickness of the lithium replenishment layer 2 is 1 to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm or 5 μm.

[0038] In the above-mentioned lithium-supplementing separator, as an optional embodiment, the D50 particle size of the Li-Al alloy powder is 0.3-0.6μm, for example, it can be 0.3μm, 0.4μm, 0.5μm or 0.6μm.

[0039] In the above-mentioned lithium replenishing membrane, as an optional embodiment, the lithium replenishing layer 2 further includes a binder and an additive. 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-supplementing separator, as an optional embodiment, the binder includes at least one of PVA (polyvinyl alcohol), CMC (carboxymethyl cellulose), and PVDF (polyvinylidene fluoride).

[0041] In the aforementioned lithium-filled separator, as an optional embodiment, the additive includes at least one of PVP (polyvinylpyrrolidone) and polyoxyethylene dioleate. This additive acts as a thickener and leveling agent, assisting in homogenization and coating processes.

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

[0043] S1. Add the binder, additives and Li-Al alloy powder to water and stir to mix to obtain lithium supplementation slurry;

[0044] S2. The lithium replenishing slurry is coated on the side of the porous base membrane 1 facing the positive electrode, and then dried 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 this invention uses water as a solvent, making it less toxic and more environmentally friendly. It is also simple to operate and does not require a protective atmosphere.

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

[0047] In the above-mentioned method for preparing the lithium-supplementing separator, as an optional embodiment, the mass percentages of each component in the lithium-supplementing slurry are as follows: Li-Al alloy powder: 55%-70% (e.g., 55%, 60%, 65%, or 70%); binder: 4%-6%; water: 24%-40% (e.g., 24%, 30%, 35%, or 40%); additives: 0.2%-0.5%.

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

[0049] In the above-mentioned method for preparing the lithium-replenishing separator, as an optional embodiment, 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-supplemented separator, as an optional embodiment, the drying temperature is 40-60℃ (for example, it can be 40℃, 45℃, 50℃, 55℃ or 60℃), and the drying time is 40-60min (for example, it can be 40min, 45min, 50min, 55min or 60min).

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

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

[0053] In the aforementioned lithium-ion battery, as an optional embodiment, the negative electrode sheet includes 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 includes at least one of artificial graphite, natural graphite, and hard carbon.

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

[0055] In the following embodiments and comparative examples:

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

[0057] Example 1

[0058] This embodiment provides a lithium replenishment membrane, which includes a PP porous base membrane and a lithium replenishment layer. The lithium replenishment layer is disposed on the PP porous base membrane on the side facing the positive electrode. The lithium replenishment 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 0.5 μm, the porosity of the PP porous base membrane is 40%, and the thickness of the PP porous base membrane is 16 μm.

[0059] The preparation method of this lithium-supplemented separator includes the following steps:

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

[0061] S2. Using a scraper, the lithium replenishing slurry is coated onto the positive electrode side of the PP porous base membrane to form a coating with a thickness of 2μm. Then, the coated porous base membrane is placed in a 60℃ vacuum oven for 60 minutes to cure, thereby obtaining the lithium replenishing separator.

[0062] This embodiment also provides a pouch lithium-ion battery, which includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The separator is a lithium-filling separator in this embodiment. The pouch lithium-ion battery preparation method includes the following steps:

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

[0064] Negative electrode sheet: The negative electrode slurry is prepared by stirring and dispersing artificial graphite, conductive agent SP, binder SBR, thickener CMC and water evenly. It is then coated on copper foil and rolled and slit to obtain the 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: The lithium replenishing separator in this embodiment is used, and the lithium replenishing layer of the lithium replenishing separator is placed facing the positive electrode side;

[0067] A soft-pack lithium-ion battery with a capacity of 5.3 Ah was prepared using the positive electrode, negative electrode, electrolyte, and separator prepared above.

[0068] Example 2

[0069] This embodiment provides a lithium replenishment membrane, which includes a PP porous base membrane and a lithium replenishment layer. The lithium replenishment layer is disposed on the PP porous base membrane on the side facing the positive electrode. The lithium replenishment 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 this lithium-supplemented separator includes the following steps:

[0071] S1. Add PVDF and PVP to water and stir thoroughly using an IKA@EUROSTAR 200control stirring device at a 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. 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. Using a scraper, the lithium replenishing slurry is coated onto the positive electrode side of the PP porous base membrane to form a coating with a thickness of 2μm. Then, the coated porous base membrane is placed in a 60℃ vacuum oven for 60 minutes to cure, thereby obtaining the lithium replenishing separator.

[0073] The soft-pack lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that the separator used is the lithium replenishment separator in this embodiment.

[0074] Example 3

[0075] This embodiment provides a lithium replenishment membrane, which includes a PP porous base membrane and a lithium replenishment layer. The lithium replenishment layer is disposed on the PP porous base membrane on the side facing the positive electrode. The lithium replenishment 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 0.4 μm, the porosity of the PP porous base membrane is 40%, and the thickness of the PP porous base membrane is 16 μm.

[0076] The preparation method of this lithium-supplemented separator includes the following steps:

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

[0078] S2. Using a scraper, the lithium replenishing slurry is coated onto the positive electrode side of the PP porous base membrane to form a coating with a thickness of 2μm. Then, the coated porous base membrane is placed in a 60℃ vacuum oven for 60 minutes to cure, thereby obtaining the lithium replenishing separator.

[0079] The soft-pack lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that the separator used is the lithium replenishment separator in this embodiment.

[0080] Example 4

[0081] This embodiment provides a lithium replenishment membrane, which includes a PP porous base membrane and a lithium replenishment layer. The lithium replenishment layer is disposed on the PP porous base membrane on the side facing the positive electrode. The lithium replenishment 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 0.3 μm, the porosity of the PP porous base membrane is 40%, and the thickness of the PP porous base membrane is 16 μm.

[0082] The preparation method of this lithium-supplemented separator includes the following steps:

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

[0084] S2. Using a scraper, the lithium replenishing slurry is coated onto the positive electrode side of the PP porous base membrane to form a coating with a thickness of 2μm. Then, the coated porous base membrane is placed in a 60℃ vacuum oven for 60 minutes to cure, thereby obtaining the lithium replenishing separator.

[0085] The soft-pack lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that the separator used is the lithium replenishment separator in this embodiment.

[0086] Example 5

[0087] This embodiment provides a lithium replenishment membrane, which includes a PP porous base membrane and a lithium replenishment layer. The lithium replenishment layer is disposed on the side of the PP porous base membrane facing the positive electrode. The lithium replenishment 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 0.3 μm, the porosity of the PP porous base membrane is 45%, and the thickness of the PP porous base membrane is 16 μm.

[0088] The preparation method of this lithium-supplemented separator includes the following steps:

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

[0090] S2. Using a scraper, the lithium replenishing slurry is coated onto the positive electrode side of the PP porous base membrane to form a coating with a thickness of 2μm. Then, the coated porous base membrane is placed in a 60℃ vacuum oven for 60 minutes to cure, thereby obtaining the lithium replenishing separator.

[0091] The soft-pack lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that the separator used is the lithium replenishment separator in this embodiment.

[0092] Example 6

[0093] This embodiment provides a lithium replenishment membrane, which includes a PP porous base membrane and a lithium replenishment layer. The lithium replenishment layer is disposed on the PP porous base membrane on the side facing the positive electrode. The lithium replenishment 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 0.3 μm, the porosity of the PP porous base membrane is 50%, and the thickness of the PP porous base membrane is 16 μm.

[0094] The preparation method of this lithium-supplemented separator includes the following steps:

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

[0096] S2. Using a scraper, the lithium replenishing slurry is coated onto the positive electrode side of the PP porous base membrane to form a coating with a thickness of 2μm. Then, the coated porous base membrane is placed in a 60℃ vacuum oven for 60 minutes to cure, thereby obtaining the lithium replenishing separator.

[0097] The soft-pack lithium-ion battery provided in this embodiment is basically the same as that in Embodiment 1, except that the separator used is the lithium replenishment separator 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 membrane with a thickness of 16 μm and a porosity of 40%. A coating layer of Al2O3 with a thickness of 2 μm is provided on the side of the PP porous base membrane facing the positive electrode. This diaphragm is a purchased finished product from ZTE ZT series.

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

[0102] Comparative Example 2

[0103] The lithium-supplementing separator provided in this comparative example is basically 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 basically the same as that in Example 1, except that the separator used is the lithium-filling separator in this comparative example.

[0106] Comparative Example 3

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

[0110] Performance testing

[0111] Electrochemical performance and safety performance tests were conducted on the soft-pack lithium-ion batteries provided in the examples and comparative examples.

[0112] First charge and discharge efficiency of the battery cell: Charged with a constant current of 0.05C for 4 hours, then charged with a constant current of 0.1C for 1 hour, then charged with a constant current and constant voltage of 0.5C to 3.65V, with a cutoff current of 0.02C. After resting for 10 minutes, discharged with a constant current of 0.5C to 2V. The charging capacity and discharging capacity were recorded and the first coulombic efficiency was calculated.

[0113] Cycling performance: Using 1C constant current and constant voltage charging, with an upper limit voltage of 3.65V and a cutoff current of 0.02C, and 1C constant current discharging to 2.0V, the cycle was repeated 1000 times. The capacity retention rate after 1000 charge-discharge cycles was calculated.

[0114] Safety performance test: A 5mm diameter steel needle is inserted into the battery at a speed of 25mm / s and left inside the battery for 60 minutes. Observe whether there is any fire or explosion. If there is no fire or explosion, the test is passed.

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

[0116] Table 1

[0117]

[0118] At least the following points can be observed from Table 1:

[0119] (1) A comparison of Examples 1-6 with Comparative Example 1 shows that the lithium replenishment separator provided by the present invention can significantly improve the initial coulombic efficiency and cycle performance of lithium-ion batteries. When applied to lithium-ion batteries, the lithium replenishment separator provided by the present invention has high safety performance, does not require coating the base film used in the present invention with a ceramic layer, and does not require additional increase in separator thickness, thereby reducing the cost of separator use and increasing the energy density of the cell.

[0120] (2) 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 both decrease, and the safety is low.

[0121] (3) Comparing Example 1 with Comparative Example 3, it can be seen that when the lithium replenishment layer is placed on the side of the PP porous base film facing the negative electrode, both the first efficiency and 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, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 separator, characterized in that, The lithium replenishing membrane is composed of a porous base membrane (1) and a lithium replenishing layer (2), and does not contain a ceramic layer. The lithium replenishing layer (2) is disposed on the porous base membrane (1) on the side facing the positive electrode. The lithium replenishing layer (2) includes Li-Al alloy powder, wherein the mass percentage of Li in the Li-Al alloy powder is 0.3%-15%.

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

3. The lithium-replenishing separator according to claim 1, characterized in that, The thickness of the lithium replenishment layer (2) is 1~5μm.

4. The lithium-supplementing separator 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 separator according to claim 1, characterized in that, The lithium replenishment layer (2) further includes 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 includes at least one of PVA, CMC and PVDF; and the additive includes at least one of PVP and polyoxyethylene dioleate.

6. A method for preparing a lithium-supplemented separator as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: S1. Add the binder, additives and the Li-Al alloy powder to water and stir to mix to obtain a lithium supplement slurry; S2. The lithium replenishing slurry is coated on the porous base membrane (1) on the side facing the positive electrode, and then dried to solidify the lithium replenishing slurry to form the lithium replenishing layer (2), thus obtaining the lithium replenishing separator.

7. The method for preparing the lithium-supplemented separator according to claim 6, characterized in that, In step S1, the binder and the additive are first mixed in water, and then the Li-Al alloy powder is added.

8. The method for preparing the lithium-supplemented separator according to claim 6, characterized in that, The mass percentages of each component in the lithium replenishment 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 equipment used is an IKA@EUROSTAR 200 control with a stirring speed of 800-2500 r / s; And / or, in step S2, the lithium replenishing slurry is coated on the side of the porous base film (1) facing the positive electrode to form a coating with a thickness of 1~5μm; And / or, the drying temperature is 40-60℃ and the drying time is 40-60min.

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

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

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