Pre-lithiated diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention discloses a pre-lithiation diaphragm and a preparation method thereof, and a lithium ion battery. The pre-lithiation diaphragm comprises a base membrane, the lithium supplementing layers are arranged on the two opposite sides of the base film, and each lithium supplementing layer comprises a lithium-aluminum composite material which is of a porous structure. Therefore, the pre-lithiation diaphragm can compensate active lithium by introducing lithium ions in advance, so that the occurrence of side reaction can be inhibited, and the internal resistance of the battery is reduced; ceramic particles are introduced into the lithium-aluminum composite material, so that the high-temperature resistance and the chemical stability of the pre-lithiated diaphragm can be improved; besides, ceramic particles and a lithium-rich material in the lithium supplementing layer are tightly combined, the coating uniformity is relatively high, so that the interface impedance is relatively low, the adhesiveness of the lithium supplementing layer on the surface of the base membrane is favorably improved, and the lithium-aluminum composite material has a porous structure, so that the interiors of the pre-lithiation diaphragm are mutually communicated, and the lithium ion transmission efficiency is favorably improved; the pre-lithiated diaphragm has relatively high wettability in an electrolyte, so that the activation time of the battery is shortened, and the long-term cycling stability is improved.

Description

Technical Field

[0001] This application relates to the field of lithium battery separator technology, specifically to pre-lithiated separators and their preparation methods, and lithium-ion batteries. Background Technology

[0002] To address the issue of lithium ions consuming active lithium during the formation of an SEI film on the negative electrode surface during lithium-ion battery formation, leading to battery capacity loss, introducing lithium ions in advance can compensate for the active lithium, thereby improving the energy density of lithium-ion batteries. Pre-lithiation can improve the shortcoming of low initial efficiency, fully leverage its high capacity advantage, and further enhance battery cycle performance and energy density.

[0003] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0004] In a first aspect, this application proposes a pre-lithiation separator, comprising: a base film; and a lithium replenishment layer disposed on opposite sides of the base film. The lithium replenishment layer comprises a lithium-aluminum composite material having a porous structure. Thus, this pre-lithiation separator can compensate for active lithium by introducing lithium ions in advance, which helps to suppress side reactions and reduce battery internal resistance. The introduction of ceramic particles in the lithium-aluminum composite material helps to improve the high-temperature resistance and chemical stability of the pre-lithiation separator. Furthermore, the ceramic particles and lithium-rich material in the lithium replenishment layer are tightly bonded, resulting in high coating uniformity and low interfacial impedance, which is beneficial for improving the adhesion of the lithium replenishment layer to the base film surface. The porous structure of the lithium-aluminum composite material allows for internal interconnection within the pre-lithiation separator, which is beneficial for improving lithium-ion transport efficiency and giving the pre-lithiation separator high wettability in the electrolyte, thereby reducing battery activation time and improving long-term cycle stability.

[0005] In some embodiments, the average particle size of the lithium-aluminum composite material is 0.2 μm to 0.3 μm. This prevents large particle protrusions from piercing the separator, and the suitable particle size facilitates the formation of a dense and flat lithium replenishment layer, avoiding localized over- or under-lithiation.

[0006] In some embodiments, the thickness of the lithium replenishment layer is 3 μm to 5 μm. This provides a greater number of active lithium ions, which helps form a dense SEI film on the negative electrode surface, while also preventing the lithium replenishment layer from shedding powder during use.

[0007] In some embodiments, the lithium-aluminum composite material is formed in situ from a lithium-rich material and a ceramic precursor; wherein the lithium-rich material includes LiOH, Li x M y O z, at least one of Li3N, Li2O, Li2S, Co-doped LiO, Co-doped LiF, and Co-doped Li2S; wherein, M includes at least one of Ni, Co, Fe, Si, and Ti, 1 ≤ x ≤ 9, 0 < y ≤ 3, 2 ≤ z ≤ 8. Thus, it helps to generate a LiPS protective film at the cathode interface, thereby effectively inhibiting the dissolution of transition metals and enhancing the high-voltage tolerance of the cathode active material.

[0008] In some embodiments, the ceramic precursor includes at least one of Al(NO3)3, Al2(SO4)3, AlCl3, Al(OC3H6)3, and γ-AlOOH. Thus, it is beneficial to improve the high-temperature resistance and chemical stability of the prelithiated separator.

[0009] In some embodiments, the lithium supplementation layer further includes fibers, and the fibers include at least one of polyimide fibers, aramid fibers, cellulose fibers, glass fibers, alumina fibers, and boehmite fibers. Thus, it helps to improve the toughness of the lithium supplementation layer and prevent the prelithiated separator from losing materials during use. In addition, the fibers have good wettability to the electrolyte, making the battery liquid injection efficiency higher, the liquid absorption faster, the liquid retention rate higher, capable of accelerating the battery charging speed, and improving the fast charging performance of the battery.

[0010] In some embodiments, the lithium-aluminum composite material adheres to the surface of the fibers and / or fills between the fibers. Thus, it is beneficial to improve the uniformity and density of the lithium supplementation layer.

[0011] In the second aspect of the present application, the present application proposes a method for preparing the aforementioned prelithiated separator, including: mixing a lithium-rich material and a ceramic precursor and undergoing a hydrolysis reaction to obtain a lithium-aluminum composite sol; sequentially performing aging treatment and drying treatment on the lithium-aluminum composite sol to obtain a dry gel; performing a hydrothermal reaction on the dry gel to in-situ generate nanoparticles; performing a sintering treatment on the nanoparticles to obtain a lithium-aluminum composite material; and coating the lithium-aluminum composite material on both opposite sides of a base film to form a lithium supplementation layer to obtain the prelithiated separator. In the present application, a lithium-rich material is introduced during the synthesis process of ceramic particles by the in-situ generation method, and a lithium-aluminum composite material with a porous structure is generated through a chemical reaction. After being made into a slurry, it is used for coating the base film. The in-situ generation method makes the lithium-rich material and the ceramic particles combine tightly, which is beneficial to reducing the interfacial impedance and improving the adhesion of the lithium supplementation layer on the base film.

[0012] In some embodiments, the temperature of the hydrothermal reaction is from 120°C to 180°C. Thus, it is beneficial to obtain nanoparticles with a suitable grain size and is beneficial to enhancing the lithium ion diffusion rate.

[0013] In some embodiments, the sintering temperature is 600℃~800℃. As a result, some lithium ions precipitate from the Li-Al-O solid solution to form a lithium-rich region. The lithium-rich region reversibly releases lithium ions during battery charging and discharging, causing the negative electrode active material to undergo partial volume expansion in advance, forming a stable SEI film framework.

[0014] In some embodiments, the nanoparticles have a particle size of less than 50 nm. Therefore, the small particle size of the nanoparticles, after sintering, results in a lithium-aluminum composite material with a suitable particle size, which helps to shorten the lithium-ion transport path and improve the lithium-ion diffusion rate.

[0015] In some embodiments, the porosity of the dry gel is greater than or equal to 98%. This helps to obtain a lithium-aluminum composite material with a porous structure, which in turn makes the lithium replenishment layer structure porous and interconnected, which is beneficial to improve lithium-ion transport efficiency, increase the ionic conductivity of the pre-lithiated separator and its wettability in the electrolyte, thereby reducing the battery activation time and significantly improving long-term cycle stability.

[0016] In some embodiments, the lithium-aluminum composite material and fibers are slurried and then coated onto opposite sides of a base membrane to form a lithium replenishment layer, thereby obtaining the pre-lithiated separator. Thus, the introduction of fibers provides a toughening effect, preventing the pre-lithiated separator from shedding material during use.

[0017] In a third aspect, this application proposes a lithium-ion battery comprising the pre-lithiation separator described in the first aspect of this application or a pre-lithiation separator prepared using the method described in the second aspect of this application. Consequently, this lithium-ion battery exhibits high initial cycle efficiency, energy density, and cycle life.

[0018] In some embodiments, the lithium-ion battery further includes a positive electrode and a negative electrode, with a separator disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer includes a positive active material, which may be at least one of a nickel-cobalt-manganese ternary material, lithium cobalt oxide, or lithium manganese oxide. The negative electrode includes a negative current collector and a negative active material layer located on at least one side of the negative current collector. The negative active material layer includes a negative active material, which may be a silicon-containing material. Therefore, this lithium-ion battery exhibits high initial cycle efficiency, energy density, and cycle life. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein, Figure 1This is a surface SEM image of a pre-lithiated separator according to an embodiment of this application; Figure 2 This is a surface SEM image of a pre-lithiated separator according to an embodiment of this application. Detailed Implementation

[0020] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0021] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0022] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0023] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0024] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0025] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0026] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0027] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0028] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0029] In related technologies, lithium replenishment is achieved by mixing lithium replenishment reagents and ceramic slurries and then coating them onto a base film. Although this method is simple, it is prone to uneven coating, resulting in poor adhesion of the lithium replenishment layer to the base film surface, high interfacial impedance, and low wettability to the electrolyte, leading to poor improvement in battery cycle performance.

[0030] In a first aspect, this application proposes a pre-lithiation separator, comprising: a base film; and a lithium replenishment layer disposed on opposite sides of the base film. The lithium replenishment layer comprises a lithium-aluminum composite material having a porous structure. It is understood that the lithium-aluminum composite material is composed of lithium-rich materials and ceramic particles. Therefore, this pre-lithiation separator can compensate for active lithium by introducing lithium ions in advance, which helps to suppress side reactions and reduce battery internal resistance. The introduction of ceramic particles in the lithium-aluminum composite material helps to improve the high-temperature resistance and chemical stability of the pre-lithiation separator. Furthermore, the ceramic particles and lithium-rich materials in the lithium replenishment layer are tightly bonded, resulting in high coating uniformity and low interfacial impedance, which is beneficial for improving the adhesion of the lithium replenishment layer to the base film surface. The porous structure of the lithium-aluminum composite material allows for internal interconnection within the pre-lithiation separator, which is beneficial for improving lithium-ion transport efficiency and giving the pre-lithiation separator high wettability in the electrolyte, thereby reducing battery activation time and improving long-term cycle stability.

[0031] For cathode active materials containing transition metals (such as nickel-cobalt-manganese ternary materials, lithium cobalt oxide, and lithium manganese oxide), the lithium-rich material in the pre-lithiation separator can provide a lithium source, which helps to form a LiPS protective film at the cathode interface during charge and discharge, effectively suppressing transition metals (such as Mn). 3+ Co 2+ The dissolution of the positive electrode active material improves its high voltage tolerance, thereby improving the first cycle efficiency, energy density and cycle stability of the lithium-ion battery.

[0032] For high-capacity negative electrode active materials (such as silicon-containing materials), the drastic volume changes during cycling (the volume expansion of silicon can reach 300%) can lead to repeated rupture and repair of the SEI film, consuming a large amount of lithium source and accelerating capacity decay. The pre-lithiation separator of this application induces electrode pre-expansion by releasing lithium ions in advance. Specifically, before the first charge, the lithium ions released by the pre-lithiation separator cause partial volume expansion of the negative electrode active material in advance, forming a stable SEI film framework. During subsequent cycles, the magnitude of electrode volume change decreases, reducing the risk of SEI film rupture. A stable SEI film reduces direct contact between the electrode and the electrolyte, suppresses side reactions, thereby reducing the increase in resistance caused by SEI film thickening, lowering battery internal resistance, improving rate performance, and also helping to extend battery life.

[0033] In some embodiments, the average particle size of the lithium-aluminum composite material is 0.2 μm to 0.3 μm, and can be, for example, 0.2 μm, 0.22 μm, 0.24 μm, 0.26 μm, 0.28 μm, or 0.3 μm, etc. Thus, it is possible to prevent large particle protrusions from piercing the separator, and a suitable particle size is beneficial to form a dense and flat lithium supplement layer, avoiding excessive or insufficient local lithium supplementation.

[0034] In some embodiments, the thickness of the lithium supplement layer is 3 μm to 5 μm, and can be, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm, etc. When the thickness of the lithium supplement layer is within the foregoing range, it can provide more active lithium ions, contribute to forming a dense SEI film on the surface of the negative electrode, and at the same time, the lithium supplement layer is not prone to powder falling during use.

[0035] It should be noted that the thickness of the lithium supplement layer in this application refers to the sum of the thicknesses of the lithium supplement layers on both sides opposite to the base film. In some embodiments, the thicknesses of the two lithium supplement layers can be the same, the thickness of the first lithium supplement layer can be 1.5 μm to 2.5 μm, and the thickness of the second lithium supplement layer can be 1.5 μm to 2.5 μm.

[0036] In some embodiments, the lithium-aluminum composite material is in-situ formed from a lithium-rich material and a ceramic precursor; wherein, the lithium-rich material includes at least one of LiOH, Li x M y O z , Li3N, Li2O, Li2S, Co-doped LiO, Co-doped LiF, Co-doped Li2S; wherein, M includes at least one of Ni, Co, Fe, Si, Ti, 1 ≤ x ≤ 9, 0 < y ≤ 3, 2 ≤ z ≤ 8. The foregoing lithium-rich material has a relatively high theoretical specific capacity of lithium ion donation and good industrial compatibility. Thus, it can provide more active lithium ions, contribute to generating a LiPS protective film at the positive electrode interface, and further effectively inhibit the dissolution of transition metals and improve the high-voltage tolerance of the positive electrode active material.

[0037] In some embodiments, the ceramic precursor includes at least one of Al(NO3)3, Al2(SO4)3, AlCl3, Al(OC3H6)3, γ-AlOOH. Thus, it is beneficial to improve the high-temperature resistance and chemical stability of the prelithiated separator.

[0038] In some embodiments, the lithium replenishment layer further includes fibers, including at least one selected from polyimide fibers (PI fibers), aramid fibers, cellulose fibers, glass fibers, alumina fibers, and boehmite fibers. This helps improve the toughness of the lithium replenishment layer and prevents the pre-lithiated separator from shedding material during use. Furthermore, the fibers have good wettability to the electrolyte, resulting in higher battery electrolyte filling efficiency, faster electrolyte absorption, and higher electrolyte retention, thus accelerating battery charging and improving fast-charging performance.

[0039] In some embodiments, the fibers are short fibers. This makes the fibers easy to disperse, which helps improve the smoothness of the lithium replenishment layer.

[0040] In some embodiments, the lithium-aluminum composite material is attached to the fiber surface and / or filled between the fibers. This helps to improve the uniformity and density of the lithium replenishment layer.

[0041] In a second aspect, this application proposes a method for preparing the aforementioned pre-lithiated separator. This method involves introducing lithium-rich materials during the synthesis of ceramic particles via an in-situ generation method, generating a porous lithium-aluminum composite material through a chemical reaction. This composite material is then prepared into a slurry for coating the base film. The in-situ generation method ensures a tight bond between the lithium-rich material and the ceramic particles, which helps reduce interfacial impedance and improves the adhesion of the lithium replenishment layer to the base film. Specifically, the method includes: S1: Lithium-rich materials and ceramic precursors are mixed and hydrolyzed to obtain lithium-aluminum composite sol.

[0042] In this step, the lithium-rich material and ceramic precursor are hydrolyzed in a mixed solution of ethanol and water to generate Li. + and Al(OH)4 - Li ions + Li-Al-O composite sols are formed by embedding into the Al-O network through electrostatic adsorption or chemical bonding.

[0043] S2: The lithium-aluminum composite sol is subjected to aging and drying treatments in sequence to obtain a dry gel.

[0044] In some embodiments, the aging time is 24h-48h, for example, 24h, 28h, 32h, 36h, 40h, 44h, or 48h. After aging, a wet gel is formed, and the wet gel is dried to obtain a dry gel.

[0045] In some embodiments, the drying process includes supercritical drying or vacuum drying. Supercritical drying eliminates surface tension, preventing gel skeleton shrinkage and pore collapse, resulting in a dry gel porosity of over 98%.

[0046] In some embodiments, the porosity of the dry gel is greater than or equal to 98%, for example, it can be 98%, 98.2%, 98.5%, 98.8%, 99%, or 99.5%. This helps to obtain a lithium-aluminum composite material with a porous structure, resulting in a porous and interconnected lithium-ion replenishment layer structure. This improves lithium-ion transport efficiency, enhances the ionic conductivity of the pre-lithiated separator and its wettability in the electrolyte, reduces battery activation time, and significantly improves long-term cycle stability.

[0047] S3: Perform a hydrothermal reaction on the dry gel to generate nanoparticles in situ.

[0048] In some embodiments, the temperature of the hydrothermal reaction is 120°C to 180°C, for example, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C. This is beneficial for obtaining nanoparticles with suitable grain size, and for improving the lithium-ion diffusion rate.

[0049] In some embodiments, the nanoparticles have a particle size of less than 50 nm, such as 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 49 nm. Therefore, the small particle size of the nanoparticles, after sintering, results in a lithium-aluminum composite material with a suitable particle size, which helps to shorten the lithium-ion transport path and improve the lithium-ion diffusion rate.

[0050] As an example, the dry gel was mixed with deionized water and placed in a high-pressure reactor to promote a hydrolysis-condensation reaction under autogenous pressure. Under high temperature and high pressure conditions, Li... + Rapid crystallization with Al-O intermediates forms Li-Al-O nanoparticles with a grain size of <50 nm, significantly improving the lithium-ion diffusion rate.

[0051] S4: The nanoparticles are sintered to obtain a lithium-aluminum composite material.

[0052] In some embodiments, the sintering temperature is 600℃~800℃, for example, 600℃, 650℃, 700℃, 650℃, or 800℃. As a result, some lithium ions precipitate from the Li-Al-O solid solution to form lithium-rich regions. These lithium-rich regions reversibly release lithium ions during battery charging and discharging, causing the negative electrode active material to undergo partial volume expansion prematurely, forming a stable SEI film framework.

[0053] During the sintering process, the chemical potential of lithium increases at high temperatures, and some Li... + Lithium-rich regions (such as Li₂O nanocrystals) precipitate from the Li-Al-O solid solution, and these regions reversibly release Li₂ during battery charging and discharging. + .

[0054] S5: The lithium-aluminum composite material is made into a slurry and then coated on both sides of the base film to form a lithium replenishment layer, so as to obtain the pre-lithiated separator.

[0055] As an example, lithium-aluminum composite materials, dispersants (such as PVP), thickeners (such as CMC), binders (such as SBR), wetting agents (such as polyether) can be formulated into a slurry and coated on both sides of a commercially available base film. After drying, a lithium replenishment layer is formed.

[0056] As an example, the base membrane may include polyethylene (PE), polypropylene (PP), or polyethylene / polypropylene composite membranes, etc.

[0057] In some embodiments, the lithium-aluminum composite material and fibers are slurried and then coated onto opposite sides of a base membrane to form a lithium replenishment layer, thereby obtaining the pre-lithiated separator. Thus, the introduction of fibers provides a toughening effect, preventing the pre-lithiated separator from shedding material during use.

[0058] As an example, lithium-aluminum composite materials and fibers can be mixed and ground in a ball mill, then dispersed in deionized water, and then a slurry can be made by adding dispersants, thickeners, binders, wetting agents, etc., and then coated on both sides of a commercially available base film. After drying, a lithium replenishment layer is formed.

[0059] As an example, the base membrane may include polyethylene (PE), polypropylene (PP), or polyethylene / polypropylene composite membranes, etc.

[0060] In a third aspect, this application proposes a lithium-ion battery comprising the pre-lithiation separator described in the first aspect of this application or a pre-lithiation separator prepared using the method described in the second aspect of this application. Consequently, this lithium-ion battery exhibits high initial cycle efficiency, energy density, and cycle life.

[0061] In some embodiments, the lithium-ion battery further includes a positive electrode and a negative electrode, with a separator disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer includes a positive active material, which may be at least one of a nickel-cobalt-manganese ternary material, lithium cobalt oxide, or lithium manganese oxide. The negative electrode includes a negative current collector and a negative active material layer located on at least one side of the negative current collector. The negative active material layer includes a negative active material, which may be a silicon-containing material. Therefore, this lithium-ion battery exhibits high initial cycle efficiency, energy density, and cycle life.

[0062] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0063] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. 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 this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0064] Example 1 (1) Weigh 5.0g Al(NO3)3·9H2O and 1.2g LiOH·H2O, and dissolve them separately in a mixed solvent of 50mL anhydrous ethanol and 50mL deionized water. Stir on a magnetic stirrer for 30min to ensure complete dissolution. Slowly add the LiOH solution dropwise to the Al(NO3)3 solution while stirring. After the addition is complete, continue stirring for 2h to ensure thorough mixing and hydrolysis reaction to produce Li. + and Al(OH)4 - Li ions + The Al-O network is embedded to form a Li-Al-O composite sol.

[0065] (2) Transfer the prepared Li-Al-O composite sol to a sealed container and age it at room temperature for 36 hours to allow the sol to gradually transform into a wet gel.

[0066] (3) The wet gel was placed in a supercritical drying apparatus and dried for 4 hours under supercritical conditions of 31°C and 7.39 MPa with carbon dioxide as the drying medium to obtain a dry gel.

[0067] (4) Weigh 2.0 g of dry gel, add it to 50 mL of deionized water, stir well, and then transfer it to a 100 mL high-pressure reactor. Seal the reactor, heat it to 150 °C, and maintain it under autogenous pressure for 12 h to promote the hydrolysis-condensation reaction and crystallization process. After the reaction is completed, let it cool naturally to room temperature, centrifuge the product, wash it three times with deionized water, and then dry it at 80 °C for 6 h to obtain Li-Al-O nanoparticles with a grain size of less than 50 nm.

[0068] (5) The Li-Al-O nanoparticles prepared above were placed in a muffle furnace and calcined at 700℃ for 4 hours. At high temperature, the chemical potential of lithium increases, and some Li... + Lithium-rich regions are formed by precipitation from the Li-Al-O solid solution, resulting in a lithium-aluminum composite material with an average particle size of 0.3 μm.

[0069] (6) Weigh 1.5g of lithium aluminum composite material and 0.5g of PI fiber (50nm in diameter and 10μm in length), put them into a zirconia ball mill jar, add an appropriate amount of zirconia balls, and then add 20mL of deionized water. Mill the mixture on a planetary ball mill at a speed of 300r / min for 4h to ensure that the two are fully mixed.

[0070] Add 0.2g of dispersant PVP, 0.1g of thickener CMC, 0.3g of binder SBR and 0.05g of wetting agent polyether to the ball-milled mixture, and continue stirring for 2 hours to prepare a slurry.

[0071] (7) The prepared slurry was uniformly coated on both sides of a commercially available 7μm PE base film using a small doctor blade coating machine, and the total thickness of the lithium replenishment layer was controlled to be 4μm, and the thickness of the lithium replenishment layer on one side was 2μm. The coated separator was dried at 60℃ for 6h to obtain a pre-lithiated separator.

[0072] Example 2 The difference from Example 1 is that PI fibers are not added in step (6).

[0073] Example 3 The difference from Example 1 is that in step (3), the wet gel is placed in a vacuum drying oven and vacuum dried at 60°C for 12 hours to obtain a vacuum-dried dry gel.

[0074] Example 4 The difference from Example 1 is that in step (7), the total thickness of the lithium replenishment layer is controlled to be 3 μm and the thickness of the lithium replenishment layer on one side is 1.5 μm.

[0075] Example 5 The difference from Example 1 is that in step (7), the total thickness of the lithium replenishment layer is controlled to be 5 μm, and the thickness of the lithium replenishment layer on one side is 2.5 μm.

[0076] Example 6 The difference from Example 1 is that in step (6), PI fiber is replaced with alumina fiber.

[0077] Comparative Example 1 The difference from Example 1 is that a 7μm PE base film is used as the separator, without any treatment.

[0078] Comparative Example 2 (1) Directly mechanically mix alumina, lithium-rich material and short fiber. Weigh 1g LiOH material, 0.5g Al2O3 and 0.5g PI fiber (50nm in diameter and 10μm in length), put them into a zirconia ball mill jar, add an appropriate amount of zirconia balls, and then add 20mL of deionized water. Ball mill the mixture on a planetary ball mill at a speed of 300r / min for 4h to ensure that the two are fully mixed and uniform.

[0079] (2) Add 0.2g dispersant PVP, 0.1g thickener CMC, 0.3g binder SBR and 0.05g wetting agent polyether to the ball-milled mixture, and continue stirring for 2 hours to prepare a slurry.

[0080] (3) The prepared slurry was uniformly coated on both sides of a commercially available 7μm PE base film using a small doctor blade coating machine, and the total thickness of the lithium replenishment layer was controlled to be 4μm, and the thickness of the lithium replenishment layer on one side was 2μm. The coated separator was dried at 60℃ for 6h to obtain a pre-lithiated separator.

[0081] Comparative Example 3 The difference from Example 1 is that: (7) a small blade coater was used to uniformly coat the prepared slurry onto one side of a commercially available 7μm PE base film, and the thickness of the lithium replenishment layer was controlled to be 4μm. The coated separator was dried at 60°C for 6 hours to obtain a pre-lithiated separator.

[0082] Comparative Example 4 The difference from Example 1 is that step (5) was not performed; 1.5g and 0.5g of PI fiber Li-Al-O nanoparticles (50nm in diameter and 10μm in length) were directly mixed and then the subsequent operations were carried out.

[0083] The diaphragm prepared above was subjected to the following performance tests, and the test results are shown in Table 1.

[0084] 1. Diaphragm heat shrinkage test: Cut the diaphragm into 10cm×10cm pieces, hold them with A4 paper, place them in an oven, heat them at 180℃ for 1 hour, and measure the transverse heat shrinkage rate TD and longitudinal heat shrinkage rate MD of the diaphragm.

[0085] 2. Air Permeability Test: Under a constant pressure difference (usually 1.21 kPa), the time required for a certain volume of gas (e.g., 100 mL) to pass through the diaphragm is measured. The specific operating steps are as follows: Cut diaphragm samples at regular intervals along the longitudinal direction from the membrane roll. The sample size depends on the diaphragm width. Place the diaphragm sample in the test head of the air permeability tester. Test the time required for 100 mL of air to pass through the diaphragm under a pressure of 1.21 kPa. Take the average of multiple test results as the air permeability of the diaphragm.

[0086] 3. Surface Contact Angle: Cut the diaphragm to a standard size (e.g., 20mm × 20mm), clean the surface with deionized water to remove impurities, and fix it on the test platform after drying. Add 0.5μL~3μL of electrolyte (1.0mol / L LiPF6, EC:EMC:DMC volume ratio = 1:1:1) to the diaphragm surface using a microsyringe, ensuring the droplets are of uniform size. Take images of the droplet-diaphragm contact vertically using a high-speed camera or microscope. Calculate the contact angle using ellipse fitting.

[0087] 4. Button assembly and electrical performance testing: The separator was cut into 18mm diameter discs and assembled into button cells in an argon-filled glove box. The assembly sequence was: negative electrode casing - gasket - stainless steel sheet - lithium sheet - separator - 20μL electrolyte - positive electrode sheet - positive electrode casing. The electrolyte was 1M LiPF6 dissolved in a 1:1 volume ratio mixture of ethylene carbonate and diethyl carbonate. The specific preparation method of the positive electrode sheet is as follows: 95wt% lithium iron phosphate (LFP), 2wt% conductive carbon black, and 3wt% PMMA are added to a certain amount of N-methylpyrrolidine in a certain mass ratio to obtain a positive electrode slurry with a solid content of 40%. Then, the slurry is dispersed at 1000 rpm for 60 min to obtain a uniform positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector aluminum foil using slit coating (300 μm gap) at a speed of 20 m / min, controlling the thickness of the formed positive electrode active material layer to be 120 μm. The coated material is then transferred to a vacuum oven and baked at 80℃ for 10 h. Finally, it is cut into round sheets using a 16mm cutting die for later use.

[0088] The assembled button batteries were left to stand at room temperature for 12 hours before undergoing electrochemical performance testing. The charge-discharge performance and cycle performance of the lithium-ion batteries were characterized using a battery testing system within an electrochemical window of 2.7V to 4.35V.

[0089] Table 1 Test Results

[0090] Figure 1 and Figure 2 The image shows a surface SEM image of the pre-lithiated separator prepared in Example 1 of this application. It can be seen that the introduction of PI fibers forms a good network structure, and the lithium-aluminum composite material is distributed in the fiber network structure.

[0091] As can be seen from the test results in Table 1, the pre-lithiated separator prepared in this application embodiment has a low thermal shrinkage rate at 180°C, exhibiting excellent heat resistance. Simultaneously, the introduction of PI fibers helps form a good network structure, resulting in good electrolyte wettability and permeability. The pre-lithiation function allows for timely replenishment of lithium ions during the first charge and discharge process, thereby improving the battery's initial efficiency and cycle stability.

[0092] Example 2: Due to the absence of PI fiber, the contact angle is large and the electrolyte wettability is poor, resulting in a reduction in the battery's initial efficiency and cycle life.

[0093] Example 3: Due to the use of vacuum drying, the evaporation of moisture under negative pressure may cause the material surface to harden or the porosity to decrease.

[0094] Comparative Example 1 used a PE base film as the separator, but no lithium replenishment layer was formed on the surface, resulting in poor thermal shrinkage performance and rapid capacity decay of the separator. Comparative Example 2 used direct mechanical mixing, which made it difficult to control the particle size. The mixing and ball milling process caused particle agglomeration and uneven coating, leading to a decrease in the heat resistance of the separator. Comparative Example 3 only coated the base film on one side, resulting in a pre-lithiated separator with low strength that could not resist thermal shrinkage. Comparative Example 4 did not sinter the Li-Al-O nanoparticles, so it was impossible to form lithium-rich regions, and therefore Li could not be reversibly released during battery charging and discharging. + This results in poor initial efficiency and cycle performance of the battery.

[0095] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A pre-lithiated separator, characterized in that, include: Base film; A lithium replenishment layer is disposed on opposite sides of the base film. The lithium replenishment layer comprises a lithium-aluminum composite material having a porous structure.

2. The pre-lithiation separator according to claim 1, characterized in that, The average particle size of the lithium-aluminum composite material is 0.2 μm to 0.3 μm.

3. The pre-lithiation separator according to claim 1, characterized in that, The thickness of the lithium replenishment layer is 3μm~5μm.

4. The pre-lithiation separator according to claim 1 or 2, characterized in that, The lithium-aluminum composite material is formed in situ from lithium-rich materials and a ceramic precursor; wherein... The lithium-rich material includes LiOH, Li x M y O z , at least one of Li3N, Li2O, Li2S, Co-doped LiO, Co-doped LiF, and Co-doped Li2S; where M includes at least one of Ni, Co, Fe, Si, and Ti, 1 ≤ x ≤ 9, 0 < y ≤ 3, 2 ≤ z ≤ 8; and / or, The ceramic precursor includes at least one of Al(NO3)3, Al2(SO4)3, AlCl3, Al(OC3H6)3, and γ-AlOOH.

5. The pre-lithiation separator according to claim 1 or 2, characterized in that, The lithium replenishment layer also includes fibers, which include at least one of polyimide fibers, aramid fibers, cellulose fibers, glass fibers, alumina fibers, and boehmite fibers.

6. The pre-lithiation separator according to claim 5, characterized in that, The lithium-aluminum composite material is attached to the surface of the fibers and / or filled between the fibers.

7. A method for preparing the pre-lithiation separator according to any one of claims 1 to 6, characterized in that, include: Lithium-rich materials and ceramic precursors are mixed and hydrolyzed to obtain lithium-aluminum composite sol; The lithium-aluminum composite sol was subjected to aging and drying treatments in sequence to obtain a dry gel. The dry gel was subjected to a hydrothermal reaction to generate nanoparticles in situ. The nanoparticles are sintered to obtain a lithium-aluminum composite material. The lithium-aluminum composite material is made into a slurry and then coated on both sides of the base film to form a lithium replenishment layer, thereby obtaining the pre-lithiated separator.

8. The method according to claim 7, characterized in that, The hydrothermal reaction temperature is 120℃~180℃; and / or The sintering temperature is 600℃~800℃.

9. The method according to claim 7, characterized in that, The nanoparticles have a particle size of less than 50 nm; and / or, The porosity of the dry gel is greater than or equal to 98%.

10. The method according to claim 7, characterized in that, The lithium-aluminum composite material and fiber are made into a slurry and then coated on opposite sides of the base film to form a lithium replenishment layer, thereby obtaining the pre-lithiated separator.

11. A lithium-ion battery, characterized in that, Includes the pre-lithiation separator as described in any one of claims 1 to 6 or the pre-lithiation separator prepared by the method described in any one of claims 7 to 10.

12. The lithium-ion battery according to claim 11, characterized in that, It also includes a positive electrode and a negative electrode, with the separator disposed between the positive electrode and the negative electrode; The positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes at least one of nickel-cobalt-manganese ternary materials, lithium cobalt oxide, and lithium manganese oxide. The negative electrode sheet includes a negative current collector and a negative active material layer located on at least one side of the negative current collector. The negative active material layer includes a negative active material, which includes a silicon-containing material.

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