Separator, preparation method therefor, and battery

Abstract

The present application provides a separator, a preparation method therefor, and a battery. The separator comprises a base film and a lithium-supplementing layer located on the surface of at least one side of the base film. The content of the element lithium in the lithium-supplementing layer is 100-20000 ppm. According to the present application, lithium supplementation can be performed for a battery by means of the separator, thereby reducing the internal resistance of the battery and improving aspects of the performance of the battery such as the first-cycle coulombic efficiency and cycle life.

Description

A separator, a preparation method thereof and a battery TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a separator, a preparation method thereof and a battery. BACKGROUND

[0002] Lithium ion batteries are common electrochemical devices and are widely used, for example, in new energy vehicles, high-end digital products and the like. Due to the formation of a solid electrolyte interface film (SEI film) on the surface of the negative electrode and other factors during the first charge and discharge process of the lithium ion battery, active lithium ions in the lithium ion battery are consumed, resulting in irreversible lithium loss, which leads to irreversible capacity loss of the lithium ion battery, and thus the capacity of the lithium ion battery is reduced.

[0003] For example, the irreversible lithium capacity loss of the current graphite negative electrode can reach about 10%, while the irreversible capacity loss of the silicon-doped negative electrode (the negative electrode is doped with a silicon negative electrode material or uses a silicon negative electrode material) can be as high as more than 30%. Among them, with the development of new energy vehicles, high-end digital products and other technologies, higher requirements are put forward for the energy density, cycle life and safety of lithium ion batteries. Compared with the graphite negative electrode, the silicon-doped negative electrode has higher capacity, so the silicon-doped negative electrode has gradually attracted widespread attention, but the high irreversible lithium loss generated by the silicon-doped negative electrode during the battery cycle process limits its application.

[0004] With the development of science and technology, higher and higher requirements are put forward for the cycle life and other properties of lithium ion batteries, which requires effective lithium supplementation for the battery during the charge and discharge process to alleviate the problems of battery capacity reduction, short cycle life and the like caused by irreversible lithium loss. Although lithium supplementation for the electrode sheet (such as positive electrode lithium supplementation or negative electrode lithium supplementation) can compensate for the irreversible lithium loss generated during the charge and discharge cycle process of the battery to a certain extent, such lithium supplementation methods generally have problems such as the retention of residues in the electrode sheet, high difficulty in electrode sheet lithium supplementation processing, and the influence on the structure or strength of the electrode sheet, which limits the application.

[0005] Therefore, how to effectively supplement lithium for the battery, reduce the internal resistance of the battery, and improve the first cycle coulombic efficiency and cycle life and other properties of the battery, is still a technical problem to be solved by those skilled in the art.

[0006] SUMMARY

[0007] The present application provides a separator, a preparation method thereof and a battery, which can effectively supplement lithium for the battery, reduce the internal resistance of the battery, and improve the first cycle coulombic efficiency and cycle life and other properties of the battery, effectively overcoming the defects of the prior art.

[0008] In one aspect of the present application, a diaphragm is provided, comprising a base film, and a lithium supplement layer on at least one side surface of the base film, wherein the lithium supplement layer has a lithium content of 100 ppm to 20,000 ppm.

[0009] According to an embodiment of the present application, the lithium supplement layer has a lithium content of 500 ppm to 10,000 ppm.

[0010] According to an embodiment of the present application, the lithium supplement layer comprises a nanofiber lithium-containing compound; preferably, the nanofiber lithium-containing compound comprises one or more of lithium sulfonate modified cellulose nanowhisker, lithium carboxylate modified cellulose nanowhisker, lithium sulfonate modified cellulose nanofiber, lithium carboxylate modified cellulose nanofiber, lithium sulfonate modified bacterial cellulose, lithium carboxylate modified bacterial cellulose, lithium sulfonate modified micronized fiber cellulose, and lithium carboxylate modified micronized fiber cellulose; preferably, the nanofiber lithium-containing compound has a lithium content of 50 ppm to 30,000 ppm, preferably 500 ppm to 20,000 ppm; preferably, the nanofiber lithium-containing compound has an average diameter of 2 nm to 1 μm, preferably 5 nm to 200 nm; preferably, the nanofiber lithium-containing compound has an average length of 50 nm to 10 μm, preferably 100 nm to 5 μm; preferably, the nanofiber lithium-containing compound has a mass fraction of 3% to 80% based on the total mass of the lithium supplement layer.

[0011] According to an embodiment of the present application, the lithium supplement layer comprises a polyacrylic lithium-containing adhesive; preferably, the polyacrylic lithium-containing adhesive has a lithium content of 100 ppm to 30,000 ppm, preferably 500 ppm to 20,000 ppm; preferably, the polyacrylic lithium-containing adhesive comprises acrylic structural units and acrylamide structural units; preferably, the acrylic structural units comprise one or more of acrylic acid structural units, methacrylic acid structural units, itaconic acid structural units, and aconitic acid structural units; preferably, the acrylamide structural units comprise one or more of acrylamide structural units, methacrylamide structural units, N,N-dimethylacrylamide structural units, and N-hydroxymethylacrylamide structural units; preferably, the polyacrylic lithium-containing adhesive is prepared by reacting a copolymer of an acrylic monomer and an acrylamide monomer with a lithium source; preferably, the mass ratio of the acrylic monomer to the acrylamide monomer is 1:9 to 9:1, preferably 5:5 to 9:1; preferably, the lithium source comprises lithium hydroxide; preferably, the polyacrylic lithium-containing adhesive has a mass fraction of 2% to 10% based on the total mass of the lithium supplement layer.

[0012] According to an embodiment of the present application, the lithium supplement layer comprises a ceramic material; preferably, the ceramic material comprises one or more of alumina, boehmite, barium titanate, aluminum nitride, silicon oxide, magnesium oxide, magnesium hydroxide; preferably, the particle size D95 of the ceramic material is ≤400 nm; preferably, the mass fraction of the ceramic material is 10% to 95% based on the total mass of the lithium supplement layer.

[0013] According to an embodiment of the present application, the lithium supplement layer comprises a surfactant; preferably, the surfactant comprises one or more of polyether siloxane copolymer, acetylenic diol copolymer, fatty alcohol polyether siloxane copolymer; preferably, the mass fraction of the surfactant is 0.1% to 0.8% based on the total mass of the lithium supplement layer.

[0014] According to an embodiment of the present application, the thickness of the lithium supplement layer is 0.3 μm to 4 μm, preferably 0.5 μm to 2 μm.

[0015] According to an embodiment of the present application, the thickness of the base film is 3 μm to 25 μm, preferably 5 μm to 12 μm.

[0016] According to an embodiment of the present application, the porosity of the base film is 20% to 90%, preferably 30% to 60%.

[0017] According to an embodiment of the present application, the base film comprises one or more of polypropylene film, polyethylene film, polyimide film, aramid, non-woven fabric.

[0018] According to an embodiment of the present application, the heat shrinkage rate of the separator after being heated at 180℃±5℃ for 1h±0.1h is less than 5%.

[0019] It is to be noted that the term "±" used in the present application means that a specific value can vary within a certain range, which is the normal fluctuation in actual process, for example, the above-mentioned 180℃±5℃ means that the test temperature is not necessarily absolute 180℃ when testing the heat shrinkage rate of the separator, but can vary within the range of 175℃ to 185℃, i.e., the heat shrinkage rate of the separator can be tested at any temperature value between 175℃ and 185℃, and the test temperature when testing the heat shrinkage rate of the separator can vary within the range of 175℃ to 185℃.

[0020] In another aspect of the present application, a preparation method of the above-mentioned separator is provided, comprising the following steps: coating a lithium supplement slurry for forming the lithium supplement layer on at least one side surface of the base film, and after drying, forming the lithium supplement layer on at least one side surface of the base film to obtain the separator.

[0021] According to an embodiment of the present application, the lithium supplementing slurry contains nanofiber lithium-containing compound, polyacrylic lithium-containing adhesive, ceramic material and surfactant; preferably, based on the total mass of the nanofiber lithium-containing compound, polyacrylic lithium-containing adhesive, ceramic material and surfactant, the mass fraction of the nanofiber lithium-containing compound is 3% to 80%, the mass fraction of the polyacrylic lithium-containing adhesive is 2% to 10%, the mass fraction of the ceramic material is 10% to 95%, and the mass fraction of the surfactant is 0.1% to 0.8%.

[0022] In another aspect of the present application, a battery is provided, which comprises the above-mentioned separator.

[0023] The separator, the preparation method thereof and the battery provided by the present application can effectively supplement lithium for the battery, reduce the internal resistance of the battery, and improve the first cycle coulombic efficiency and cycle life of the battery.

[0024] In addition, the lithium supplementing layer is arranged on the surface of the base film of the separator, so that the lithium supplementing layer can not only effectively supplement lithium for the battery, but also maintain the mechanical strength and other properties of the separator, thereby achieving a balance between the lithium supplementing and the mechanical properties of the separator.

[0025] In addition, compared with supplementing lithium for the electrode sheet (e.g., supplementing lithium for the positive electrode or supplementing lithium for the negative electrode), the present application supplements lithium for the separator (i.e., arranging the lithium supplementing layer on the surface of the base film of the separator), which can compensate for the irreversible lithium loss caused by the charging and discharging process of the battery, and has the advantages of simple lithium supplementing process, no residual introduced into the electrode sheet, and no influence on the structure or strength of the electrode sheet, thereby further ensuring the electrochemical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a schematic view of the layering structure of a positive electrode sheet, a separator and a negative electrode sheet according to an embodiment of the present application.

[0027] Reference signs: 1: positive electrode sheet; 11: positive electrode current collector; 12: positive electrode coating layer; 2: negative electrode sheet; 21: negative electrode current collector; 22: negative electrode coating layer; 3: separator; 31: base film; 32: lithium supplementing layer. DETAILED DESCRIPTION

[0028] To enable those skilled in the art to better understand the scheme of the present application, the present application is further described in detail below.

[0029] The embodiment of the present application provides a diaphragm 3, as shown in Figure 1, which comprises a base film 31 and a lithium supplement layer 32 on at least one side surface of the base film 31, and the lithium element content in the lithium supplement layer 32 is 100 ppm-10000 ppm.

[0030] In the battery, the diaphragm 3 mainly plays a role of preventing the positive plate 1 and the negative plate 2 from contacting and allowing the active lithium ions to migrate through. Specifically, the diaphragm 3 is spaced between the positive plate 1 and the negative plate 2 to prevent the positive and negative electrodes from being short-circuited and the risk of battery explosion caused thereby, and the active lithium ions pass through the diaphragm 3 and migrate back and forth between the positive and negative electrodes during the charging and discharging cycle of the battery to be deintercalated in the positive and negative electrodes, so as to realize the charging and discharging process of the battery.

[0031] According to the research and analysis of the inventors, by arranging the lithium supplement layer 32 on the surface of the base film 31 of the diaphragm 3 and controlling the lithium element content in the lithium supplement layer 32 to be 100 ppm-20000 ppm, the active lithium ions can be effectively released from the diaphragm 3 during the charging and discharging process of the battery, so as to effectively supplement lithium for the battery, reduce the internal resistance of the battery, improve the first coulomb efficiency (or first week coulomb efficiency) and cycle life of the battery and the like, and overcome the problems of irreversible lithium loss, battery capacity reduction and low cycle life caused thereby during the charging and discharging cycle of the battery.

[0032] In addition, the inventors have found through long-term research that the lithium element content in the lithium supplement layer 32 not only affects the lithium supplement effect of the diaphragm 3, but also affects the moisture content of the lithium supplement layer 32. Specifically, the lithium element in the lithium supplement layer 32 mainly exists in the form of lithium salt, and the lithium salt is easy to absorb water. Therefore, if the lithium element content in the lithium supplement layer 32 is too high, the water content of the lithium supplement layer 32 is easy to be high, which affects the cycle performance of the battery. In the embodiment of the present application, by controlling the lithium element content in the lithium supplement layer 32 to be in the range of 100 ppm-20000 ppm, the moisture content of the lithium supplement layer 32 can be controlled while ensuring the lithium supplement effect, so as to avoid the problem of high moisture affecting the performance and use of the battery.

[0033] Exemplarily, the lithium element content in the lithium supplement layer 32 can be 100 ppm, 400 ppm, 480 ppm, 500 ppm, 520 ppm, 800 ppm, 880 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 2800 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4200 ppm, 4500 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, 20000 ppm or a range formed by any two of them.

[0034] In some preferred embodiments, the lithium element content in the lithium supplement layer 32 can be 500 ppm to 10000 ppm. In other words, the lithium element content in the lithium supplement layer 32 is not less than 500 ppm, which is beneficial to further improve the lithium supplement effect. However, if the lithium element content in the lithium supplement layer exceeds 10000 ppm, the battery production efficiency will be affected. In the process of preparing the battery by using the separator, the battery needs to be baked at a relatively high temperature for a relatively long time after liquid injection to remove the moisture, thereby increasing the battery production cost.

[0035] In the embodiments of the present application, the lithium element content refers to the mass content of lithium element, unless otherwise specified. In the embodiments of the present application, the lithium element content in the lithium supplement layer 32 of the separator 3 can be measured by a conventional method in the art, for example, by an ICP (inductively coupled plasma) method.

[0036] In the embodiments of the present application, the lithium supplement layer 32 comprises a lithium supplement material containing lithium element, which can provide lithium ions as a lithium ion source, so that the separator 3 can effectively release active lithium ions during the charge and discharge process of the battery, thereby achieving effective lithium supplement for the battery.

[0037] According to the research of the inventors, the lithium supplement material in the lithium supplement layer 32 can comprise a nanofiber lithium-containing compound, which can effectively release active lithium ions during the charge and discharge cycle of the battery, thereby achieving effective lithium supplement for the battery. In addition, the nanofiber lithium-containing compound has a one-dimensional nanostructure, which, as a component material of the separator 3, not only forms a more compact stacking structure to enhance the strength and other properties of the separator 3, such as improving the heat shrinkage resistance of the separator 3, but also facilitates the formation of sufficient contact points to provide more sufficient transmission paths for the transmission of lithium ions, thereby further ensuring the electrochemical performance and safety performance of the battery.

[0038] Through further research, the nanofiber lithium-containing compound can comprise a lithium sulfonate and / or lithium carboxylate modified nanofiber compound, that is, the nanofiber lithium-containing compound can comprise a lithium sulfonate modified nanofiber compound, a lithium carboxylate modified nanofiber compound, or a lithium sulfonate and lithium carboxylate modified nanofiber compound. By introducing the lithium sulfonate and / or lithium carboxylate modified nanofiber compound into the lithium supplement layer 32, it is beneficial to release active lithium ions and achieve the lithium supplement effect for the battery, while improving the strength and other properties of the separator 3.

[0039] In the embodiments of the present application, the fiber raw material can be modified by lithium sulfonate and / or lithium carboxylate by a conventional method to obtain a lithium sulfonate and / or lithium carboxylate modified nanofiber compound.

[0040] For example, the preparation process of the lithium sulfonate modified nanofiber compound can include: after the fiber raw material is oxidized by sulfuric acid, the lithium hydroxide (LiOH) is used for neutralization, and the lithium sulfonate modified nanofiber compound is obtained. The fiber raw material includes, for example, cotton.

[0041] For example, the preparation process of the lithium sulfonate modified nanofiber compound can include: (1) etherification reaction of the fiber raw material and chloroacetate under alkaline conditions to obtain a fiber material grafted with acetate; (2) displacement reaction of the fiber material grafted with acetate and acid to form acetate in the fiber material grafted with acetate, and the fiber acetate material is obtained; (3) neutralization reaction of the fiber acetate material and lithium hydroxide (LiOH) to obtain the lithium carboxylate modified nanofiber compound.

[0042] In step (1), the chloroacetate used can specifically include sodium chloroacetate, and sodium hydroxide (NaOH) can be used to provide alkaline conditions during the etherification reaction. The fiber material grafted with acetate obtained is a fiber material grafted with sodium acetate. In step (1), the fiber raw material can be etherified with sodium chloroacetate in the presence of NaOH to obtain a fiber material grafted with sodium acetate. The fiber raw material includes, for example, cotton.

[0043] In step (2), the acid used in the displacement reaction is stronger than acetic acid, and the acid used can specifically include sulfuric acid. The fiber acetate material can be obtained by reacting (displacement reaction) the fiber material grafted with acetate with sulfuric acid to form acetate in the fiber material grafted with acetate.

[0044] Specifically, the nanofiber compound is an organic nanofiber compound, which can include a cellulose nanofiber compound, such as one or more of cellulose nanowhiskers, cellulose nanofibers, bacterial cellulose fibers, and microfibrillated cellulose (MFC). The cellulose nanofiber compound has a sufficient number of reactive active sites on the surface, which is conducive to modification reaction with lithium compounds and to the stability of lithium grafting, and cooperates with the one-dimensional nanostructure of the cellulose nanofiber compound, thereby increasing the lithium grafting density of the compound. By modifying the cellulose nanofiber compound with lithium sulfonate and / or lithium carboxylate, the corresponding lithium sulfonate and / or lithium carboxylate modified nanofiber compound is obtained. The lithium sulfonate and / or lithium carboxylate modified nanofiber compound is introduced into the lithium supplement layer 32 of the separator 3, thereby increasing the lithium content density of the separator 3, which is conducive to the effective release of active lithium ions of the separator 3 during the charging and discharging of the battery, improves the lithium supplement effect, and at the same time, improves the strength and other properties of the separator 3.

[0045] In some preferred embodiments, the nanofiber lithium-containing compound can include one or more of lithium sulfonate modified cellulose nanowhiskers, lithium carboxylate modified cellulose nanowhiskers, lithium sulfonate modified cellulose nanofibers, lithium carboxylate modified cellulose nanofibers, lithium sulfonate modified bacterial cellulose, lithium carboxylate modified bacterial cellulose, lithium sulfonate modified micronized fiber cellulose, and lithium carboxylate modified micronized fiber cellulose. By introducing such nanofiber lithium-containing compounds into the lithium supplement layer 32 of the separator 3, it is more conducive to the effective release of active lithium ions from the separator 3 during battery charging and discharging, thereby improving the lithium supplement effect, while also improving the strength and other properties of the separator 3.

[0046] Generally, the nanofiber lithium-containing compound has a diameter at the nanometer level, i.e., the average diameter of the nanofiber lithium-containing compound in the lithium supplement layer 32 is less than or equal to 1 μm. Thus, by introducing the nanofiber lithium-containing compound into the lithium supplement layer 32 of the separator 3, it is more conducive to the effective release of active lithium ions from the separator 3 during battery charging and discharging, thereby improving the lithium supplement effect. At the same time, the average diameter of the nanofiber lithium-containing compound is less than or equal to 1 μm, which is conducive to reducing the thickness of the lithium supplement layer 3, reducing its impact on the air permeability of the separator 3, while also reducing the thickness of the separator 3, shortening the transmission path of lithium ions in the separator 3, and the average diameter at the nanometer level further improves the lithium density of the separator, thereby reducing the battery impedance and improving the first cycle coulombic efficiency and cycle life of the battery and other properties.

[0047] Further considering the lithium supplement effect, impedance, and mechanical properties of the separator 3, the average diameter of the nanofiber lithium-containing compound can be 2 nm to 1 μm, such as 2 nm, 5 nm, 10 nm, 50 nm, 70 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, or a range defined by any two of these values, and is further preferably 5 nm to 200 nm.

[0048] Generally, the separator 3 can be prepared by a coating method, i.e., the lithium supplement slurry used to form the lithium supplement layer 32 is coated on the surface of the base film 31 to form the lithium supplement layer 32, thereby preparing the separator 3. The lithium supplement slurry contains the nanofiber lithium-containing compound, and the diameter and length of the nanofiber lithium-containing compound affect not only the effective release of active lithium ions from the separator 3 during battery discharging, but also the preparation efficiency and yield of the separator 3.

[0049] Further research shows that, in consideration of the lithium supplement effect, mechanical strength, and preparation efficiency and yield of the diaphragm 3, the average length of the nanofiber lithium-containing compound is preferably 50 nm to 10 μm, such as 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 500 nm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range between any two of them. The nanofiber lithium-containing compound with a suitable average length is conducive to achieving the balance between the improvement of the mechanical properties such as the diaphragm strength and the provision of a suitable lithium grafting space to achieve a good lithium supplement effect, and further optimizes the preparation quality, coating efficiency and yield of the lithium supplement slurry. The average length of the nanofiber lithium-containing compound is further preferably 100 nm to 5 μm.

[0050] The average diameter and average length of the nanofiber lithium-containing compound can be measured by conventional methods in the art, for example, by scanning electron microscopy (SEM) to measure the average diameter and average length of the nanofiber lithium-containing compound in the lithium supplement layer 32.

[0051] According to the research of the inventors, the lithium element content in the nanofiber lithium-containing compound is preferably 50 ppm to 30000 ppm, such as 50 ppm, 100 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 8000 ppm, 10000 ppm, 13000 ppm, 15000 ppm, 17000 ppm, 18000 ppm, 20000 ppm, 25000 ppm, 30000 ppm, or a range between any two of them. The lithium element content in the nanofiber lithium-containing compound is in a suitable range, which not only ensures the lithium supplement effect of the diaphragm and further helps to avoid the influence of high lithium content in the nanofiber on the water content, but also helps to ensure that the nanofiber lithium-containing compound has a suitable crystal content, thereby further improving the heat resistance of the diaphragm 3, and thus improving the electrochemical safety and cycle performance. The lithium element content in the nanofiber lithium-containing compound is further preferably 500 ppm to 20000 ppm.

[0052] In specific implementation, in the process of modifying the nanofiber compound with lithium sulfonate and / or lithium carboxylate, the lithium element content in the obtained nanofiber compound modified with lithium sulfonate and / or lithium carboxylate (nanofiber lithium-containing compound) can be controlled by adjusting the amount of lithium sulfonate and / or lithium carboxylate.

[0053] In the embodiments of the present application, the lithium supplement material in the lithium supplement layer 32 can also include a polyacrylic lithium-containing adhesive. On the one hand, the polyacrylic adhesive can play a bonding role, improve the adhesion between the components (such as nanofiber lithium-containing compounds) in the lithium supplement layer 32 and the adhesion between the lithium supplement layer 32 and the base film 31, thereby improving the structural stability of the separator 3 and further ensuring the heat shrinkage resistance and other properties of the separator 3. On the other hand, the polyacrylic lithium-containing adhesive can serve as a lithium ion source to effectively release active lithium ions during the charging and discharging of the battery, thereby further improving the lithium supplement effect.

[0054] Further research shows that the polyacrylic lithium-containing adhesive can include acrylic structural units and acrylamide structural units. The acrylic structural units refer to structural units formed by polymerization of acrylic monomers, and the acrylamide structural units refer to structural units formed by polymerization of acrylamide monomers.

[0055] Specifically, the polyacrylic lithium-containing adhesive can be prepared by reacting a copolymer of acrylic monomers and acrylamide monomers with a lithium source. That is, the polyacrylic lithium-containing adhesive can be prepared according to the following process: polymerizing (or copolymerizing) acrylic monomers and acrylamide monomers to obtain a copolymer; and then reacting the copolymer with a lithium source to obtain the polyacrylic lithium-containing adhesive. After polymerization, the acrylamide monomers form acrylamide structural units in the polyacrylic lithium-containing adhesive, and the acrylic monomers form acrylic structural units. After the copolymer reacts with the lithium source, the acrylic structural units form lithium acrylate structural units in the polyacrylic lithium-containing adhesive. Thus, the polyacrylic lithium-containing adhesive includes acrylic structural units and acrylamide structural units, and the acrylic polymerization units mainly include lithium acrylate structural units.

[0056] Specifically, the lithium source can include lithium hydroxide (LiOH). In the preparation process of the polyacrylic lithium-containing adhesive, after the acrylic monomers and the acrylamide monomers are copolymerized, the copolymer is neutralized by LiOH (i.e., the copolymer reacts with LiOH) to mainly form lithium acrylate structural units from the acrylic structural units, thereby obtaining the polyacrylic lithium-containing adhesive.

[0057] Specifically, the acrylic structural units can include one or more of acrylic structural units (formed by polymerization of acrylic monomers), methacrylic structural units (formed by polymerization of methacrylic monomers), itaconic structural units (formed by polymerization of itaconic monomers), and aconitic structural units (formed by polymerization of aconitic monomers).

[0058] Correspondingly, in the preparation of the polyacrylic lithium-containing adhesive, the acrylic monomers used can include one or more of acrylic acid, methacrylic acid, itaconic acid, aconitic acid.

[0059] In addition, the acrylamide polymerization units can include one or more of acrylamide structural units (formed after polymerization of acrylamide monomers), methacrylamide structural units (formed after polymerization of methacrylamide monomers), N,N-dimethyl acrylamide structural units (formed after polymerization of N,N-dimethyl acrylamide monomers), and N-hydroxymethyl acrylamide structural units (formed after polymerization of N-hydroxymethyl acrylamide monomers).

[0060] Correspondingly, in the preparation of the polyacrylic lithium-containing adhesive, the acrylamide monomers used can include one or more of acrylamide, methacrylamide, N,N-dimethyl acrylamide, and N-hydroxymethyl acrylamide.

[0061] In the embodiments of the present application, the characteristics of the acrylic structural units and the acrylamide structural units in the polyacrylic lithium-containing adhesive in the lithium supplementing layer 32 can be detected by infrared spectroscopy testing, mass spectrometry testing, and the like.

[0062] In some embodiments, the mass ratio of the acrylic structural units to the acrylamide structural units in the polyacrylic lithium-containing adhesive can be 1:9 to 9:1, for example, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9, or a range consisting of any two of the foregoing, and is further preferably 5:5 to 9:1. By controlling the mass ratio of the acrylic structural units to the acrylamide structural units within the above range, the lithium supplementing effect is further improved, and the adhesion between the components in the lithium supplementing layer 32 and the adhesion between the lithium supplementing layer 32 and the base film 31 are improved, thereby improving the structural stability and the like of the separator 3, while further taking into account the reduction of the water content of the separator 3 and the improvement of the electrochemical performance of the battery.

[0063] In particular implementations, in the preparation of the polyacrylic lithium-containing adhesive, the amount of the acrylic monomers and the amount of the acrylamide monomers can be regulated so that the mass ratio of the acrylic monomers to the acrylamide monomers is 1:9 to 9:1, for example, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9, or a range consisting of any two of the foregoing, and is preferably 5:5 to 9:1, so that the acrylic structural units and the acrylamide structural units in the prepared polyacrylic lithium-containing adhesive also substantially satisfy the mass ratio.

[0064] In some embodiments, the lithium element content in the polyacrylic lithium-containing adhesive can be 100 ppm to 30000 ppm, for example, 100 ppm, 400 ppm, 480 ppm, 500 ppm, 520 ppm, 880 ppm, 1000 ppm, 2800 ppm, 3000 ppm, 4120 ppm, 4200 ppm, 5000 ppm, 8000 ppm, 9940 ppm, 10000 ppm, 12000 ppm, 14000 ppm, 16000 ppm, 18000 ppm, 20000 ppm, 30000 ppm, or a range between any two of them, and further preferably 500 ppm to 20000 ppm, so as to further improve the lithium supplement effect, while further taking into account reducing the moisture content of the lithium supplement layer 32 and improving the battery performance.

[0065] In particular implementation, in the preparation process of the polyacrylic lithium-containing adhesive, the lithium element content in the prepared polyacrylic lithium-containing adhesive can be controlled by adjusting the amount of acrylic monomer and lithium source.

[0066] In the embodiments of the present application, the lithium supplement layer 32 can also include a ceramic material, which is conducive to further taking into account improving the permeability of the separator 3 and the thermal stability of the separator 3, thereby improving the ion conductivity and the electrochemical safety.

[0067] According to the research of the inventors, in the coexisting system of the nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, and the ceramic material in the lithium supplement layer 32, the components can synergistically play the following roles: (1) the nanofiber lithium-containing compound and the polyacrylic lithium-containing adhesive as the lithium source provide active lithium ions to supplement the irreversible lithium loss in the battery charging and discharging process, improve the first coulomb efficiency of the battery, reduce the internal resistance of the battery, and improve the cycle performance of the battery; (2) the nanofiber lithium-containing compound and the ceramic material are intertwined to form a network structure, and the polyacrylic lithium-containing adhesive bonds the components and the network structure formed by the components to the base film 31, which can significantly improve the stability and permeability of the separator 3, and further improve the dimensional stability of the separator 3 under high temperature conditions, inhibit the thermal shrinkage of the separator 3 (the thermal shrinkage rate of the separator 3 after being heated at 180℃±5℃ for 1h±0.1h can be less than 5%), and avoid the problem of thermal runaway of the battery caused by the thermal shrinkage of the separator 3, thereby improving the safety and cycle performance of the battery; (3) the ceramic material as a heat-resistant filler further improves the permeability and heat resistance of the separator 3.

[0068] Specifically, the ceramic material is in the form of particles, i.e., the ceramic material is inorganic ceramic particle powder.

[0069] In general, the particle size of the ceramic material is not particularly limited, but in order to form a film with uniform thickness and suitable porosity, the particle size D95 of the ceramic material is preferably < 800 nm. According to further research by the inventors, it has been found that a particle size D95 of the ceramic particles ≤ 400 nm is beneficial for further improving the cycle life and safety of the battery, the reason being that a smaller particle size of the ceramic material can improve the heat resistance of the separator 3 while reducing the thickness of the lithium supplement layer 32, thereby reducing the thickness of the separator 3 and improving the energy density of the battery. In addition, the nanofiber lithium-containing compound is a one-dimensional nanomaterial, and the use of a ceramic material with a particle size D95 ≤ 400 nm is more beneficial for matching with the nanofiber lithium-containing compound, forming a thinner lithium supplement layer 32, and facilitating the formation of a network structure between the nanofiber lithium-containing compound and other components such as the ceramic material in the lithium supplement layer 32, thereby further improving the permeability and thermal stability of the separator 3 and improving the cycle performance and safety of the battery.

[0070] In some embodiments, the particle size D95 of the ceramic particles can be 40-400 nm, for example 40 nm, 50 nm, 70 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, or a range defined by any two of them.

[0071] The particle size D95 of the ceramic material refers to the particle size at which 95% of the volume is accumulated from the small particle size side in the particle size distribution on a volume basis. The particle size D95 of the ceramic material can be measured by conventional methods in the art, for example, a conventional particle size analyzer can be used for testing, or a scanning electron microscope (SEM) or other electron microscope can be used to detect the particle size and other characteristics of the ceramic particles in the lithium supplement layer 32.

[0072] Specifically, the ceramic material can include one or more of alumina, boehmite, barium titanate, aluminum nitride, silicon oxide, magnesium oxide, and magnesium hydroxide.

[0073] In some embodiments, the lithium supplement layer 32 can also include a surfactant, which can function as a wetting and leveling agent to facilitate the formation of the lithium supplement layer 32 and improve the surface flatness of the lithium supplement layer 32.

[0074] Specifically, the lithium supplement layer 32 can be formed by a coating method, i.e., the lithium supplement slurry used to form the lithium supplement layer 32 is coated on at least one side of the base film 31, and after drying and other treatments, the lithium supplement layer 32 is formed on at least one side of the base film 31 to obtain the separator 3. The lithium supplement slurry used can contain the above-mentioned nanofiber lithium-containing compound, polyacrylic lithium-containing adhesive, and other components such as ceramic materials and surfactants.

[0075] When the lithium supplement slurry contains a surfactant, the leveling property of the lithium supplement slurry coated on the surface of the base film 31 is improved, the surface flatness of the formed lithium supplement layer 32 is improved, and the lithium supplement slurry is facilitated to wet the base film 31, the adhesion between the formed lithium supplement layer 32 and the base film 31 is improved, and the lithium supplement effect of the separator is improved.

[0076] Specifically, the surfactant can include one or more of polyether siloxane copolymer, acetylenic diol copolymer, and fatty alcohol polyether siloxane copolymer, which is suitable for adapting to the nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, and the like in the lithium supplement layer 32, and improves the lithium supplement effect of the separator 3 while improving the adhesion between the lithium supplement layer 32 and the separator 3 and the surface flatness of the lithium supplement layer 32.

[0077] In some embodiments, the mass fraction of the nanofiber lithium-containing compound (i.e., the proportion of the mass of the nanofiber lithium-containing compound to the total mass of the lithium supplement layer 32) can be 3% to 80%, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range formed by any two of them, for example, 5% to 40%.

[0078] In some embodiments, the mass fraction of the polyacrylic lithium-containing adhesive can be 2% to 10% based on the total mass of the lithium supplement layer 32, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range formed by any two of them, for example, 3% to 5%.

[0079] In some embodiments, the mass fraction of the ceramic material can be 10% to 95% based on the total mass of the lithium supplement layer 32, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 75%, 90%, 92%, 95%, or a range formed by any two of them, for example, 55% to 92%.

[0080] In some embodiments, the mass fraction of the surfactant can be 0.1% to 0.8% based on the total mass of the lithium supplement layer 32, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or a range formed by any two of them, for example, 0.1% to 0.3%.

[0081] In some embodiments, the mass fraction of the nanofiber lithium-containing compound can be 3% to 80%, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range formed by any two of them; the mass fraction of the polyacrylic lithium-containing adhesive can be 2% to 10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range formed by any two of them; the mass fraction of the ceramic material can be 10% to 95%, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 75%, 90%, 92%, 95%, or a range formed by any two of them; and the mass fraction of the surfactant can be 0.1% to 0.8%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or a range formed by any two of them, based on the total mass of the lithium supplement layer 32.

[0082] By controlling the content of each component in the lithium supplement layer 32 within the above range, while achieving effective lithium supplementation, the nanofiber lithium-containing compound and the ceramic material in the lithium supplement layer 32 are intertwined to form a network structure, and the polyacrylic lithium-containing adhesive bonds the components and integrates the network structure formed by the components with the base film 31, thereby improving the stability of the separator 3, especially the dimensional stability of the separator 3 under high temperature conditions, inhibiting the thermal shrinkage of the separator 3, avoiding the problems of battery thermal runaway caused by the thermal shrinkage of the separator 3, and thereby improving the safety and cycle life of the battery.

[0083] In the embodiments of the present application, the lithium supplement layer 32 can be formed on one side surface of the base film 31 in the thickness direction, or the lithium supplement layer 32 can be formed on both opposite side surfaces of the base film 31 in the thickness direction. The lithium supplement layer 32 and the base film 31 are stacked, and the thickness direction of the lithium supplement layer 32, the thickness direction of the base film 31, the thickness direction of the separator 3, and the direction from the lithium supplement layer 32 to the base film 31 (or the direction from the base film 31 to the lithium supplement layer 32) are parallel to each other.

[0084] In some embodiments, the thickness of the lithium supplement layer 32 can be 0.3 μm to 4 μm, for example, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or a range formed by any two of them, and further preferably 0.5 μm to 2 μm. By controlling the thickness of the lithium supplement layer 32 within the above range, the lithium supplement effect of the separator 3 and the air permeability of the separator 3 are further improved, and the energy density and electrochemical performance of the battery are improved.

[0085] In the embodiments of the present application, the thickness of the lithium supplement layer 32 (0.3 μm-4 μm) refers to the thickness of the lithium supplement layer 32 on one side (or the thickness of the lithium supplement layer 32 on one surface). Specifically, when the lithium supplement layer 32 is arranged on both sides of the base film 31, the thickness of the lithium supplement layer 32 refers to the thickness of the lithium supplement layer 32 on any one side, rather than the sum of the thicknesses of the lithium supplement layers 32 on both sides.

[0086] In addition, considering the film strength and energy density, the thickness of the base film 31 is preferably 3 μm-25 μm, for example, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 23 μm, 25 μm, or a range formed by any two of them, and further preferably 5 μm-12 μm.

[0087] In addition, considering the strength, voltage resistance, and cycle performance, the porosity of the base film 31 is preferably 20%-90%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or a range formed by any two of them, and further preferably 30%-60%.

[0088] Specifically, the base film 31 can include one or more of a polypropylene (PP) film, a polyethylene (PE) film, a polyimide film, aramid, and non-woven fabric, that is, the base film 31 can be a single-layer film or a composite film composed of at least two layers of film, for example, the base film 31 can include a PP / PE / PP composite film (in the PP / PE / PP composite film, the PP film, the PE film, and the PP film are sequentially stacked). Among them, the non-woven fabric can specifically include a polyethylene terephthalate (PET) non-woven fabric, but is not limited thereto.

[0089] The separator 3 of the embodiments of the present application not only can effectively supplement lithium for the battery, but also has good thermal stability and other properties. Research shows that the thermal shrinkage rate of the separator 3 after being heated at 180℃±5℃ for 1h±0.1h is less than 5%, specifically less than or equal to 3%, further less than or equal to 2.5%, and more further less than or equal to 2.3%.

[0090] Specifically, the thermal shrinkage rate of the separator 3 in the length direction (MD direction) after being heated at 180℃±5℃ for 1h±0.1h is less than 5%, specifically less than or equal to 3%, further less than or equal to 2.3%; and the thermal shrinkage rate of the separator 3 in the width direction (TD direction) after being heated at 180℃±5℃ for 1h±0.1h is less than 5%, specifically less than or equal to 3%, further less than or equal to 2.3%.

[0091] The application further provides a preparation method of the above-mentioned diaphragm 3, comprising the following steps: coating a lithium supplement slurry for forming a lithium supplement layer 32 on at least one side surface of a base film 31, and after drying, forming the lithium supplement layer 32 on the at least one side surface of the base film 31 to obtain the diaphragm 3.

[0092] Specifically, the above-mentioned lithium supplement slurry contains a lithium supplement material and a ceramic material, and the lithium supplement material includes a nanofiber lithium-containing compound and a polyacrylic lithium-containing adhesive.

[0093] In some embodiments, the mass fraction of the nanofiber lithium-containing compound (i.e., the proportion of the mass of the nanofiber lithium-containing compound to the sum of the masses of the nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, the ceramic material and the surfactant) can be 3% to 80%, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range consisting of any two of them.

[0094] In some embodiments, the mass fraction of the polyacrylic lithium-containing adhesive can be 2% to 10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of them, based on the total mass of the solid components of the lithium supplement slurry.

[0095] In some embodiments, the mass fraction of the ceramic material can be 10% to 95%, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 75%, 90%, 92%, 95% or a range consisting of any two of them, based on the total mass of the solid components of the lithium supplement slurry.

[0096] In some embodiments, the lithium supplement slurry further contains a surfactant, and the mass fraction of the surfactant can be 0.1% to 0.8%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or a range consisting of any two of them, based on the total mass of the solid components of the lithium supplement slurry.

[0097] In some embodiments, the mass fraction of the nanofiber lithium-containing compound is 3% to 80%, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range between any two of them, based on the total mass of the nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, the ceramic material, and the surfactant; the mass fraction of the polyacrylic lithium-containing adhesive is 2% to 10%, for example, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range between any two of them; the mass fraction of the ceramic material is 10% to 95%, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 75%, 90%, 92%, 95%, or a range between any two of them; and the mass fraction of the surfactant is 0.1% to 0.8%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or a range between any two of them.

[0098] In addition, the above-mentioned lithium supplement slurry further includes a dispersion medium, and the nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, the ceramic material, and the surfactant are dispersed in the dispersion medium to form the above-mentioned lithium supplement slurry; wherein the dispersion medium can include water, and the solid components of the lithium supplement slurry refer to the remaining components except the dispersion medium.

[0099] In specific implementation, the nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, the ceramic material, the surfactant, and the dispersion medium can be mixed and uniformly dispersed to prepare the lithium supplement slurry; then, the lithium supplement slurry is coated on the surface of the base film 31 by using a micro-gravure coating or other conventional coating method in the field, dried, and wound to prepare the separator 3.

[0100] The embodiments of the present application further provide a battery including the above-mentioned separator 3, which has the advantages corresponding to the above-mentioned separator 3, and details are not repeated.

[0101] Specifically, the above-mentioned battery can be a lithium ion battery.

[0102] Specifically, the battery includes the positive electrode sheet 1, the negative electrode sheet 2, and the above-mentioned separator 3, and the separator 3 is arranged between the positive electrode sheet 1 and the negative electrode sheet 2 to prevent the positive electrode sheet 1 and the negative electrode sheet 2 from being short-circuited, and at the same time, the separator 3 allows the active lithium ions to pass through during the charging and discharging process of the battery, and the active lithium ions pass through the separator 3 and migrate back and forth between the positive and negative electrodes to be deintercalated in the positive and negative electrodes, so as to realize the charging and discharging process of the battery.

[0103] As described above, the base film 31 of the above-mentioned separator 3 is provided with a lithium supplement layer 32 on the surface thereof, which can effectively release active lithium ions during the charging and discharging process of the battery, and the released active lithium ions participate in the charging and discharging process of the battery, thereby supplementing the irreversible lithium loss generated during the charging and discharging process of the battery, improving the first cycle coulombic efficiency of the battery, reducing the internal resistance of the battery, and improving the cycle performance of the battery.

[0104] Generally, the positive electrode sheet 1 includes a positive electrode current collector 11 and a positive electrode coating layer 12 located on at least one side surface of the positive electrode current collector 11. The positive electrode coating layer 12 can be arranged on one side surface of the positive electrode current collector 11, or the positive electrode coating layer 12 can be arranged on both the front and back side surfaces of the positive electrode current collector 11, respectively.

[0105] Specifically, the positive electrode current collector 11 can be a conventional positive electrode current collector 11 in the art, for example, the positive electrode current collector 11 can include an aluminum foil, but is not limited thereto.

[0106] Specifically, the positive electrode coating layer 12 can include a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material, a first conductive agent, and a first binder.

[0107] The positive electrode active material can be a conventional positive electrode active material in the art, for example, the positive electrode active material includes a lithium-containing active material, and the lithium-containing active material can include one or more of nickel-cobalt-manganese ternary material (NCM), lithium iron phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium nickel manganese oxide, lithium-rich manganese-based solid solution, lithium manganese oxide, etc.

[0108] The first conductive agent can be a conventional conductive material in the art, for example, the first conductive agent can include one or more of conductive carbon black (Super P), acetylene black, graphene, ketjen black, carbon fiber, but is not limited thereto.

[0109] The first binder can be a conventional binding material in the art, for example, the first binder can include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, etc., but is not limited thereto.

[0110] Specifically, based on the total mass of the positive electrode active material layer, the mass fraction of the positive electrode active material can be 70% to 99%, the mass fraction of the first conductive agent can be 0.5% to 15%, and the mass fraction of the first binder can be 0.5% to 15%.

[0111] In addition, the negative electrode sheet 2 includes a negative electrode current collector 21, and a negative electrode coating layer 22 present on at least one side surface of the negative electrode current collector 21. The negative electrode coating layer 22 can be provided on one side surface of the negative electrode current collector 21, or the negative electrode coating layer 22 can be respectively provided on both side surfaces of the negative electrode current collector 21.

[0112] Specifically, the negative electrode current collector 21 can be a conventional negative electrode current collector 21 in the art, for example, the negative electrode current collector 21 can include a copper foil, but is not limited thereto.

[0113] Specifically, the negative electrode coating layer 22 can include a negative electrode active material layer including a negative electrode active material, a second conductive agent, and a second binder.

[0114] The negative electrode active material can include graphite and / or a silicon-based material, and the silicon-based material can include silicon-carbon and / or silicon-oxygen material, but is not limited thereto.

[0115] The second conductive agent can be a conventional conductive material in the art, for example, the second conductive agent can include one or more of conductive carbon black (Super P), acetylene black, ketjen black, carbon fiber, graphene, etc., but is not limited thereto.

[0116] The second binder can be a conventional binding material in the art, for example, the second binder can include one or more of PVDF, carboxymethyl cellulose, styrene butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing an oxirane, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, polyacrylic acid sodium, polyacrylonitrile-based copolymer, polyacrylic acid copolymer, etc., but is not limited thereto.

[0117] Specifically, based on the total mass of the negative electrode active material layer, the mass fraction of the negative electrode active material can be 70% to 99%, the mass fraction of the second conductive agent can be 0.5% to 15%, and the mass fraction of the second binder can be 0.5% to 15%.

[0118] In the embodiments of the present application, the positive electrode sheet 1 can be prepared by a conventional method in the art, for example, by a coating method. For example, the preparation process of the positive electrode sheet 1 includes: dispersing components for forming the positive electrode coating layer 12, such as a positive electrode active material, a first conductive agent, and a first binder, in a first solvent, for example, N-methyl pyrrolidone (NMP), to prepare a positive electrode slurry; applying the positive electrode material to the surface of the positive electrode current collector 11, and after drying, rolling, etc., forming the positive electrode coating layer 12 on the surface of the positive electrode current collector 11 to prepare the positive electrode sheet 1.

[0119] In the embodiments of the present application, the negative electrode sheet 2 can be prepared by a conventional method in the art, for example, by a coating method. For example, the preparation process of the negative electrode sheet 2 includes: dispersing the components for forming the negative electrode coating 22, such as the negative electrode active material, the second conductive agent, and the second binder, in a second solvent, for example, water (deionized water can be specifically used), to prepare a negative electrode slurry; coating the negative electrode material on the surface of the negative electrode current collector 21, and after drying, rolling, and other processes, forming the negative electrode coating 22 on the surface of the negative electrode current collector 21 to obtain the negative electrode sheet 2.

[0120] Generally, the battery includes a battery cell and a packaging body for packaging the battery cell. The battery cell includes the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2. The battery cell can be a wound battery cell, that is, the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2 are sequentially stacked and wound to form a wound battery cell (winding core) having a wound structure. Alternatively, the battery cell can be a stacked battery cell (as shown in FIG. 1), that is, the battery cell includes a plurality of positive electrode sheets 1 and a plurality of negative electrode sheets 2 which are stacked and arranged in an interleaved manner, and the positive electrode sheets 1 and the negative electrode sheets 2 are separated by the separator 3.

[0121] In the embodiments of the present application, the packaging body can be a conventional packaging material in the art, for example, the packaging body can include a soft packaging material (that is, the battery can be a soft packaging battery), and the soft packaging material can include an aluminum plastic film, but is not limited thereto.

[0122] In addition, the battery further includes an electrolyte, which can be a conventional electrolyte in the art, and can be a non-aqueous electrolyte.

[0123] For example, the electrolyte can include an organic solvent, an electrolyte salt, and an additive.

[0124] The organic solvent can include one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0125] The electrolyte salt can include a lithium salt, and the lithium salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(difluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0126] The additive can include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinonitrile (SN), and adiponitrile (ADN).

[0127] In the embodiments of the present application, the battery can be prepared according to conventional methods in the art, for example, after assembling the positive sheet 1, the separator 3 and the negative sheet 2 into a battery cell, the battery cell is packaged by using a packaging body, and then the battery is prepared through processes such as liquid injection and formation. These processes are conventional operations in the process of preparing a battery in the art, and are not particularly limited.

[0128] The present application is further described below through specific embodiments.

[0129] 1. Preparation of the positive sheet

[0130] The nickel-cobalt-manganese 811 type ternary material, Super P and PVDF are mixed in a mass ratio of 96:2:2 and added into NMP to prepare a positive slurry;

[0131] The positive slurry is coated on the front and back surfaces of the aluminum foil, and after drying and rolling, the positive active material layers are respectively formed on the front and back surfaces of the aluminum foil to prepare the positive sheet.

[0132] 2. Preparation of the negative sheet

[0133] The graphite, SiO, Super P, CMC and polyacrylic copolymer are mixed in a mass ratio of 85:10:1:1:3 and added into deionized water to prepare a negative slurry;

[0134] The negative slurry is coated on the front and back surfaces of the copper foil, and after drying and rolling, the negative active material layers are respectively formed on the front and back surfaces of the copper foil to prepare the negative sheet.

[0135] 3. Preparation of the separator

[0136] (1) The nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, the aluminum oxide, the polyether siloxane copolymer and water are mixed and uniformly dispersed to obtain a lithium supplement slurry;

[0137] Based on the total mass of the nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, the ceramic material (aluminum oxide) and the surfactant (polyether siloxane copolymer), the mass fraction of each component (also the mass fraction of each component in the formed lithium supplement layer) is as follows: the mass fraction of the nanofiber lithium-containing compound is 10%, the mass fraction of the polyacrylic lithium-containing adhesive is 4%, the mass fraction of the aluminum oxide is 86%, and the mass fraction of the polyether siloxane copolymer is 0.2%.

[0138] The nanofiber lithium-containing compound is a lithium carboxylate modified cellulose nanowhisker with an average diameter of 20 nm, an average length of 200 nm and a lithium content of 11000 ppm.

[0139] The polyacrylic lithium-containing adhesive is obtained by neutralizing a copolymer of methacrylic acid and acrylamide with LiOH, the mass ratio of methacrylic acid to acrylamide is 8:2, and the lithium element content in the polyacrylic lithium-containing adhesive is 16000 ppm.

[0140] The particle size D95 of the aluminum oxide is 100 nm.

[0141] (2) The lithium supplement slurry is coated on the surfaces of the opposite sides of the base film (PE film), and after drying, lithium supplement layers are respectively formed on the surfaces of the opposite sides of the base film, thereby obtaining the separator; wherein the thickness of the base film is 9 μm, the porosity of the base film is 48%, and the thickness of the single-side lithium supplement layer is 1 μm.

[0142] 4. Preparation of the battery

[0143] The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence to form a stacked electrode, and the stacked electrode is placed in an aluminum plastic film, and then the lithium ion battery is prepared through processes such as liquid injection and formation.

[0144] The electrolyte used is composed of organic solvents DMC, EMC, EC, DEC and PC, the volume ratio of DMC, EMC, EC, DEC and PC is 15:35:35:10:5 (i.e. DMC: EMC: EC: DEC: PC = 15:35:35:10:5 (vol)), and the mass content of LiPF6 in the electrolyte is 11%.

[0145] Comparative Example 1: The difference from Example 1 is that (1) the carboxylate sodium modified cellulose nanowhisker (lithium element content is 0) is used to replace the lithium carboxylate modified cellulose nanowhisker; (2) the polyacrylic adhesive (lithium element content is 0) is used to replace the polyacrylic lithium-containing adhesive, wherein the polyacrylic adhesive does not contain lithium element (i.e. the polyacrylic adhesive is not neutralized by LiOH); see Tables 1 and 2 for details, and the rest of the conditions are the same as those in Example 1 except for the differences shown in Tables 1 and 2.

[0146] Examples 2-18 and Comparative Example 2: The difference from Example 1 is that the types, contents and lithium element contents of the components in the lithium supplement layer are different, see Tables 1 and 2 for details, and the rest of the conditions are the same as those in Example 1 except for the differences shown in Tables 1 and 2.

[0147] The performance of the separators and batteries of each example and comparative example is tested according to the following processes, and the performance test results of the separators and batteries are shown in Table 3.

[0148] (1) Diaphragm heat shrinkage rate test: the diaphragm is cut into a size of 160 mm x 130 mm, the length direction is the MD direction, and the width direction is the TD direction; a square frame of 100 mm x 100 mm is drawn in the middle of the diaphragm with a brush (the length L0 and the width w0 of the square frame are both 100 mm), the surfaces on the opposite sides in the thickness direction of the diaphragm are each covered with 5 A4 papers, and then it is placed in an oven at a temperature of 180℃, so that it is heated at 180℃ for 1 h, and then the size of the square frame is measured, the width is recorded as w1, and the length is recorded as L1, then the heat shrinkage rate of the diaphragm in the MD direction = (L0-L1) / L0, and the heat shrinkage rate of the diaphragm in the TD direction = (w0-w1) / w0.

[0149] (2) Battery internal resistance test: at 25℃, the battery is charged at 0.2C to 50% SOC, and the battery internal resistance is measured with a battery internal resistance tester, and the obtained data is the battery internal resistance.

[0150] (3) First week coulomb efficiency test of the battery: at 25℃, the capacity of the battery when it is first fully charged (charged at 0.2C) is recorded as Q1, the capacity of the battery when it is first fully discharged (discharged at 0.2C) is recorded as Q2, and the first week coulomb efficiency = Q2 / Q1 x 100%.

[0151] (4) Capacity retention rate test of the battery after 500 cycles at 25℃: at 25℃, the discharge capacity of the battery in the first week is recorded as Q3 when it is charged at 0.8C constant current and constant voltage (0.05C cutoff) and discharged at 1.0C constant current (2.7V-4.3V), and the discharge capacity after 500 cycles is recorded as Q4, and the capacity retention rate = Q4 / Q3 x 100%.

[0152] Table 1 Thickness, lithium element content and composition of the lithium supplement layer

[0153] Table 2 Related parameters of nanofiber lithium-containing compounds and acrylic lithium-containing adhesives

[0154] Table 3 Test results of the diaphragm and the battery

[0155] It can be seen that, compared with Comparative Example 1 and Comparative Example 2, in Example 1-Example 18, the lithium element content in the lithium supplement layer of the diaphragm is in the range of 100 ppm-20000 ppm, which can effectively supplement lithium for the battery, reduce the internal resistance of the battery, and improve the first coulomb efficiency and the capacity retention rate of the battery.

[0156] Further, compared with Embodiment 2, Embodiment 3 and Embodiment 9, Embodiments 1 and 4-6 are more conducive to effectively supplementing lithium for the battery by further controlling the lithium element content in the lithium supplement layer of the separator within the range of 500 ppm-10,000 ppm, further reducing the internal resistance of the battery, and improving the first cycle coulombic efficiency and capacity retention rate of the battery.

[0157] Further, compared with Embodiment 14, in Embodiment 1, by further controlling the particle size D95 of the ceramic material in the lithium supplement layer of the separator to be ≤400 nm, it is conducive to further reducing the thermal shrinkage of the separator while maintaining the reduced internal resistance of the battery, and the higher first cycle coulombic efficiency and capacity retention rate, and improving the heat resistance of the separator.

[0158] Further, compared with Embodiment 18, in Embodiments 1 and 7, by further controlling the average diameter of the nanofiber lithium-containing compound in the lithium supplement layer of the separator to be within the range of 5 nm-200 nm, and the average length to be within the range of 100 nm-5 μm, it is conducive to further reducing the thermal shrinkage of the separator while reducing the internal resistance of the battery, and improving the first cycle coulombic efficiency and capacity retention rate of the battery, and improving the heat resistance of the separator.

[0159] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A diaphragm, characterized by The lithium supplement layer is located on at least one side surface of the base film, and the lithium element content in the lithium supplement layer is 100 ppm-20,000 ppm.

2. The separator according to claim 1, characterized in that The lithium element content in the lithium supplement layer is 500 ppm-10,000 ppm.

3. The separator of claim 1, wherein The lithium supplement layer comprises a nanofiber lithium-containing compound; Preferably, the nanofiber lithium-containing compound comprises one or more of lithium sulfonate modified cellulose nanowhiskers, lithium carboxylate modified cellulose nanowhiskers, lithium sulfonate modified cellulose nanofibers, lithium carboxylate modified cellulose nanofibers, lithium sulfonate modified bacterial cellulose, lithium carboxylate modified bacterial cellulose, lithium sulfonate modified micronized fiber cellulose, and lithium carboxylate modified micronized fiber cellulose; Preferably, the lithium element content in the nanofiber lithium-containing compound is 50 ppm-30,000 ppm, preferably 500 ppm-20,000 ppm; Preferably, the average diameter of the nanofiber lithium-containing compound is 2 nm-1 μm, preferably 5 nm-200 nm; Preferably, the average length of the nanofiber lithium-containing compound is 50 nm-10 μm, preferably 100 nm-5 μm; Preferably, the mass fraction of the nanofiber lithium-containing compound is 3%-80% based on the total mass of the lithium supplement layer.

4. The separator of claim 1, wherein The lithium supplement layer comprises a polyacrylic lithium-containing adhesive; Preferably, the lithium element content in the polyacrylic lithium-containing adhesive is 100 ppm-30,000 ppm, preferably 500 ppm-20,000 ppm; Preferably, the polyacrylic lithium-containing adhesive comprises acrylic structural units and acrylamide structural units; Preferably, the acrylic structural units comprise one or more of acrylic acid structural units, methacrylic acid structural units, itaconic acid structural units, and aconitic acid structural units; Preferably, the acrylamide structural units comprise one or more of acrylamide structural units, methacrylamide structural units, N,N-dimethyl acrylamide structural units, and N-hydroxymethyl acrylamide structural units; Preferably, the polyacrylic lithium-containing adhesive is prepared by reacting a copolymer of acrylic monomers and acrylamide monomers with a lithium source; Preferably, the mass ratio of the acrylic monomers to the acrylamide monomers is 1:9-9:1, preferably 5:5-9:1; Preferably, the lithium source comprises lithium hydroxide; Preferably, the mass fraction of the polyacrylic lithium-containing adhesive is 2%-10% based on the total mass of the lithium supplement layer.

5. The separator of claim 1, wherein The lithium supplement layer comprises a ceramic material; Preferably, the ceramic material comprises one or more of alumina, boehmite, barium titanate, aluminum nitride, silicon oxide, magnesium oxide, and magnesium hydroxide; Preferably, the particle size D95 of the ceramic material is ≤400 nm; Preferably, the mass fraction of the ceramic material is 10%-95% based on the total mass of the lithium supplement layer.

6. The separator of claim 1, wherein The lithium supplement layer comprises a surfactant; Preferably, the surfactant comprises one or more of polyether siloxane copolymers, acetylenic diol copolymers, and fatty alcohol polyether siloxane copolymers. Preferably, the mass fraction of the surfactant is 0.1% to 0.8% based on the total mass of the lithium supplement layer.

7. The separator according to any one of claims 1 to 6, characterized in that The thickness of the lithium supplement layer is 0.3 μm to 4 μm, preferably 0.5 μm to 2 μm.

8. The separator according to any one of claims 1 to 6, characterized in that The thickness of the base film is 3 μm to 25 μm, preferably 5 μm to 12 μm.

9. The separator according to any one of claims 1 to 6, characterized in that The porosity of the base film is 20% to 90%, preferably 30% to 60%.

10. The separator according to any one of claims 1 to 6, characterized in that The base film comprises one or more of polypropylene film, polyethylene film, polyimide film, aramid, and non-woven fabric.

11. The separator according to any one of claims 1 to 6, characterized in that The heat shrinkage rate of the separator after being heated at 180℃±5℃ for 1h±0.1h is less than 5%.

12. A method of producing the separator according to any one of claims 1 to 11, characterized by, The method comprises the following steps: coating a lithium supplement slurry for forming the lithium supplement layer on at least one side surface of the base film, and forming the lithium supplement layer on at least one side surface of the base film after drying, thereby obtaining the separator.

13. The method of claim 12, wherein the membrane is prepared by a method comprising: The lithium supplement slurry comprises nanofiber lithium-containing compound, polyacrylic lithium-containing adhesive, ceramic material, and surfactant. Preferably, the mass fraction of the nanofiber lithium-containing compound is 3% to 80%, the mass fraction of the polyacrylic lithium-containing adhesive is 2% to 10%, the mass fraction of the ceramic material is 10% to 95%, and the mass fraction of the surfactant is 0.1% to 0.8% based on the total mass of the nanofiber lithium-containing compound, the polyacrylic lithium-containing adhesive, the ceramic material, and the surfactant.

14. A battery, characterized by The separator according to any one of claims 1 to 11.

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