Separator and preparation method therefor, battery, and electrical device

Abstract

A separator and a preparation method therefor, a battery, and an electrical device. The separator comprises a polymer layer and a pre-lithiation layer; the pre-lithiation layer is formed on one side of the polymer layer; the pre-lithiation layer comprises a lithium supplementing agent; the decomposition potential of the lithium supplementing agent is less than or equal to 4.2 V; and the content of the lithium supplementing agent is 1 wt% to 10 wt% based on the total mass of the pre-lithiation layer.

Description

Isolation film and preparation method thereof, battery and electrical device Technical Field

[0001] The present application belongs to the field of batteries, and specifically relates to an isolation membrane and a preparation method thereof, a battery and an electrical device. Background Art

[0002] Lithium-ion batteries, due to their high operating potential, long lifespan, and environmental friendliness, have become the most popular energy storage system. They are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. In recent years, with the continuous development of electric vehicles and energy storage systems, the demand for battery energy density has also continued to increase. During the formation process of lithium-ion batteries, the formation of the SEI film (solid electrolyte interface) on the negative electrode surface consumes a large amount of active lithium, resulting in reduced initial charge and discharge efficiency and severe irreversible capacity loss.

[0003] To address the problems of low initial charge and discharge efficiency and severe irreversible capacity loss in batteries, lithium supplementation of the positive and negative electrodes is an effective approach. However, the stability of the positive and negative electrodes after lithium supplementation is low, which affects the battery's cycle performance.

[0004] Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides a separator, aiming to improve the cycle performance of the battery containing the separator.

[0006] In order to achieve the above-mentioned purpose, one aspect of the present application proposes an isolation membrane, which includes a polymer layer and a pre-lithiation layer, wherein the pre-lithiation layer is formed on one side of the polymer layer, and the pre-lithiation layer includes a lithium replenisher, wherein the decomposition potential of the lithium replenisher is lower than or equal to 4.2V, and based on the total mass of the pre-lithiation layer, the content of the lithium replenisher is 1wt%-10wt%.

[0007] The present application has at least the following beneficial effects: the isolation membrane of the present application can not only provide active lithium for the battery cycle process, but also reduce the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte under high voltage, thereby improving the capacity and cycle performance of the battery.

[0008] In some embodiments of the present application, the decomposition potential of the lithium supplement is 4.1 V-4.2 V. This can improve the capacity and cycle performance of the battery.

[0009] In some embodiments of the present application, the volume average particle size Dv50 of the lithium supplement agent is 0.2 μm to 4 μm, thereby improving the capacity and cycle performance of the battery.

[0010] In some embodiments of the present application, the volume average particle size Dv50 of the lithium supplement is 0.5 μm - 2 μm. Thus, the capacity and cycle performance of the battery can be improved.

[0011] In some embodiments of the present application, based on the total mass of the prelithiation layer, the content of the lithium supplement is 2 wt% - 7 wt%. Thus, the capacity and cycle performance of the battery can be improved.

[0012] In some embodiments of the present application, the lithium supplement includes Li x AO 0.5(2+x) , at least one of Li2DO3, Li2EO4, Li3GO4, Li5LO4 or Li5MO6, where x ≥ 1, A includes at least one of Ni, Co, Fe, Mn, Zn, Mg, Ca, Cu or Sn; D includes at least one of Ni, Co, Fe, Mn, Sn or Cr; E includes at least one of Ni, Co, Fe, Mn, Sn, Cr, V or Nb; G includes at least one of Ni, Co, Fe, Mn, Sn, Cr, V, Mo or Nb; L includes at least one of Ni, Co, Fe, Mn, Sn, Cr or Mo; M includes at least one of Ni, Co or Mn, and the valence state of each element in A, D, E, G, L, M is lower than its own highest oxidation state. Thus, the capacity and cycle performance of the battery can be improved.

[0013] In some embodiments of the present application, the lithium supplement satisfies at least one of the following conditions: 2 ≤ x ≤ 4; A includes at least one of Ni, Co, Fe or Mn; D includes at least one of Ni, Co or Fe; E includes at least one of Ni, Co, Fe or Sn; G includes at least one of Ni, Co, Fe, Sn or Mo; L includes at least one of Ni, Co or Fe; M includes Ni. Thus, the capacity and cycle performance of the battery can be improved.

[0014] In some embodiments of the present application, the lithium supplement includes at least one of Li2CO3, Li2MnO2, Li5FeO4, Li6CoO4, Li2NiO2, Li2Cu x1 Ni 1-x1-y1 M y1 O2, Li3VO4 or Li3NbO4, 0 < x1 ≤ 1, 0 ≤ y1 ≤ 0.1, M includes at least one of Zn, Sn, Mg, Fe or Mn.

[0015] In some embodiments of the present application, it satisfies at least one of the following conditions: 0.2 ≤ x1 ≤ 0.8; 0.01 ≤ y1 ≤ 0.07. Thus, the capacity and cycle performance of the battery can be improved.

[0016] In some embodiments of the present application, at least one of the following conditions is satisfied: 0.4≤x1≤0.6; 0.03≤y1≤0.06. This can improve the capacity and cycle performance of the battery.

[0017] In some embodiments of the present application, the lithium supplement includes at least one of 2-cyclopropene-1-one-2,3-dihydroxy lithium, 3-cyclobutene-1,2-dione-3,4-dihydroxy lithium, 4-cyclopentene-1,2,3-trione-4,5-dihydroxy lithium, 5-cyclohexene-1,2,3,4-tetraone-5,6-dihydroxy lithium, lithium oxalate, lithium ketomalonate, lithium diketosuccinate, or lithium triketoglutarate. This can improve the capacity and cycle performance of the battery.

[0018] In some embodiments of the present application, the thickness of the pre-lithiation layer is 5 μm to 15 μm, thereby improving the capacity and cycle performance of the battery.

[0019] In some embodiments of the present application, the thickness of the pre-lithiation layer is 7 μm-10 μm, thereby improving the capacity and cycle performance of the battery.

[0020] In some embodiments of the present application, the pre-lithiation layer and the polymer layer include polymers, thereby improving the capacity and cycle performance of the battery.

[0021] In some embodiments of the present application, the polymer forms a network structure, and the lithium supplement is located on the network structure of the polymer.

[0022] In some embodiments of the present application, the weight average molecular weight of the polymer is 30,000-100,000, thereby improving the capacity and cycle performance of the battery.

[0023] In some embodiments of the present application, the weight average molecular weight of the polymer is 50,000-70,000, thereby improving the capacity and cycle performance of the battery.

[0024] In some embodiments of the present application, the polymer includes at least one of a polyolefin polymer, a polynitrile polymer, or a polycarboxylate polymer, thereby improving the capacity and cycle performance of the battery.

[0025] In some embodiments of the present application, the polymer includes at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylene carbonate, polycyanoacrylate, polymethacrylate, polyacrylonitrile, or polymaleic anhydride, thereby improving the capacity and cycle performance of the battery.

[0026] In some embodiments of the present application, the thickness of the polymer layer is 5 μm to 7 μm, thereby improving the capacity and cycle performance of the battery.

[0027] The second aspect of the present application provides a method for preparing the above-mentioned isolation film, comprising:

[0028] electrospinning a first spinning solution comprising a lithium supplement agent and a polymer to obtain a pre-lithiation layer;

[0029] A polymer layer is formed on the pre-lithiation layer to obtain a separator.

[0030] Thus, the above-mentioned isolation membrane can be obtained by the method of the present application, and the decomposition potential of the lithium supplement agent in the isolation membrane is lower than or equal to 4.2V, which can not only provide active lithium for the battery cycle process, but also reduce the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte under high voltage, thereby improving the capacity and cycle performance of the battery.

[0031] In some embodiments of the present application, the electrospinning of the first spinning solution includes at least one of the following conditions: the pushing speed of the spinneret is 0.01 mm / min-0.05 mm / min; the voltage between the spinneret and the receiver is 10 kV-20 kV; the distance between the spinneret and the receiver is 10 cm-30 cm; the temperature of the electrospinning is 20°C-25°C; and the humidity of the electrospinning is 10%-20%.

[0032] In some embodiments of the present application, the electrospinning of the first spinning solution includes at least one of the following conditions: the pushing speed of the spinneret is 0.02 mm / min-0.04 mm / min; the voltage between the spinneret and the receiver is 15 kV-20 kV; the distance between the spinneret and the receiver is 15 cm-20 cm; the temperature of the electrospinning is 22°C-25°C; and the humidity of the electrospinning is 15%-20%.

[0033] In some embodiments of the present application, forming the polymer layer on the pre-lithiation layer is performed by the following steps: placing the pre-lithiation layer on a receiver of an electrospinning device, and then electrospinning a second spinning solution comprising a polymer.

[0034] In some embodiments of the present application, the pre-lithiation layer is carbonized before the polymer layer is formed on the pre-lithiation layer. This allows the lithium replenisher in the pre-lithiation layer to adhere evenly and tightly to the fiber membrane surface. After carbonization, it forms an excellent 3D conductive network, effectively improving the lithium replenishment efficiency of the separator.

[0035] In some embodiments of the present application, the carbonization conditions include: in an inert atmosphere, heating to 300° C.-500° C. at a rate of 2° C. / min-10° C. / min, and keeping the temperature for 1 h-4 h.

[0036] In some embodiments of the present application, the carbonization conditions include: in an inert atmosphere, heating to 450°C-500°C at a rate of 5°C / min-8°C / min, and keeping the temperature for 2h-3h.

[0037] The third aspect of the present application provides a battery comprising the separator of the first aspect or the separator obtained by the method of the second aspect, thereby having excellent capacity and cycle performance.

[0038] In some embodiments of the present application, the battery further includes a positive electrode sheet and a negative electrode sheet, the isolation membrane is disposed between the positive electrode sheet and the negative electrode sheet, and the pre-lithiation layer of the isolation membrane faces the positive electrode sheet.

[0039] A fourth aspect of the present application provides an electrical device, wherein the electrical device includes the battery according to the third aspect.

[0040] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0042] FIG1 is a schematic diagram of an isolation membrane according to an embodiment of the present application.

[0043] FIG2 is a schematic diagram of a battery according to an embodiment of the present application.

[0044] FIG3 is an exploded view of the battery shown in FIG2 according to one embodiment of the present application.

[0045] FIG4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0046] FIG5 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0047] FIG. 6 is an exploded view of the battery pack shown in FIG. 5 according to an embodiment of the present application.

[0048] FIG7 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.

[0049] Explanation of reference numerals: 1 battery; 11 housing; 12 electrode assembly; 13 cover plate; 2 battery module; 3 battery pack; 31 upper case; 32 lower case; 20 isolation membrane; 21 polymer layer; 22 pre-lithiation layer. DETAILED DESCRIPTION

[0050] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0051] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0052] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0055] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0056] Currently, market developments indicate that lithium-ion batteries are becoming increasingly widely used. They are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. As the application of lithium-ion batteries continues to expand, market demand is also growing.

[0057] During the formation process of lithium-ion batteries, the formation of the SEI film on the negative electrode surface consumes a large amount of active lithium, resulting in reduced charge and discharge efficiency of the battery in the first cycle and serious irreversible capacity loss.

[0058] In order to solve the problems of low initial charge and discharge efficiency of batteries and serious irreversible capacity loss, lithium replenishment of positive and negative electrode sheets is an effective solution. Lithium replenishment of negative electrode sheets usually uses lithium sheets. Lithium sheets are very active in the electrolyte and easily react with the electrolyte, resulting in low lithium replenishment efficiency. In addition, when lithium dendrites are generated on the surface of the negative electrode, the SEI film will continue to rupture and reconstruct, continuously consuming lithium, thereby reducing the cycle life of the battery. Positive electrode sheets usually add lithium-rich additives or lithiated active materials as lithium replenishers. This type of lithium replenisher has a high decomposition potential and requires high voltage to decompose. However, high voltage will destroy the structure of the positive electrode active material. At the same time, high voltage will cause the electrolyte to oxidize and decompose, and the side reactions will increase, thereby reducing the cycle performance of the battery. In addition, lithium-rich additives are usually highly alkaline and air-instable, which can easily cause the positive electrode slurry to gel, resulting in easy destruction of the positive electrode sheet structure, thereby reducing the battery cycle performance.

[0059] The present application adopts an isolation membrane including a polymer layer and a pre-lithiation layer, wherein the pre-lithiation layer includes a lithium replenisher having a decomposition potential lower than or equal to 4.2V. Based on the total mass of the pre-lithiation layer, the content of the lithium replenisher is 1wt%-10wt%, which not only provides active lithium during the battery cycle, but also reduces the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte under high voltage, thereby improving the capacity and cycle performance of the battery.

[0060] The isolation membrane disclosed in the embodiments of the present application is suitable for lithium-ion batteries, and the batteries disclosed in the embodiments of the present application can be used in electrical devices that use batteries as power sources or various energy storage systems that use batteries as energy storage elements. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, battery-powered vehicles, electric cars, ships, spacecraft, and the like. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the like, and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, and the like.

[0061] In a first aspect, the present application proposes an isolation membrane. Referring to Figure 1, the isolation membrane 20 includes a polymer layer 21 and a pre-lithiation layer 22, wherein the pre-lithiation layer 22 is formed on one side of the polymer layer 21, and the pre-lithiation layer 22 includes a lithium replenisher. The decomposition potential of the lithium replenisher is lower than or equal to 4.2V, and the content of the lithium replenisher is 1wt%-10wt% based on the total mass of the pre-lithiation layer.

[0062] The pre-lithiation layer 22 of the present application includes a lithium replenisher having a decomposition potential less than or equal to 4.2V. Based on the total mass of the pre-lithiation layer, the content of the lithium replenisher is 1wt%-10wt%, which can not only provide active lithium for the battery cycle process, but also the lithium replenisher can be decomposed at low voltage, reducing the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte under high voltage, thereby improving the capacity and cycle performance of the battery. At the same time, the lithium replenisher releases gas during the delithiation process, forming pores on the isolation membrane 20, thereby increasing the liquid absorption rate of the isolation membrane 20 and improving its electrolyte wettability. In addition, by adding the lithium replenisher to the isolation membrane 20, the risk of slurry gel caused by adding a strong alkaline lithium replenisher to the positive electrode slurry is avoided, thereby protecting the structure of the positive electrode plate from damage and improving the cycle performance of the battery.

[0063] In this application, the decomposition potential of the lithium supplement refers to the starting potential of decomposition during voltammetry testing or charge-discharge cycling. The voltammetry testing method for "the decomposition potential of the lithium supplement" in this application includes cyclic voltammetry or linear sweep voltammetry.

[0064] In some embodiments of the present application, the decomposition potential of the lithium supplement is less than or equal to 4.2V, for example, 3.5V-4.2V, 3.6V-4.1V, 3.7V-4V, 3.8V-3.9V, etc. Therefore, the separator 20 of the present application uses a lithium supplement within this decomposition voltage range. This lithium supplement can decompose at low voltages, reducing damage to the structure of the battery's positive electrode active material and oxidative decomposition of the electrolyte at high voltages, thereby improving the battery's capacity and cycle performance. In other embodiments of the present application, the decomposition potential of the lithium supplement can be 4.1V-4.2V.

[0065] In some embodiments of the present application, the volume average particle size Dv50 of the lithium supplement agent is 0.2μm-4μm, for example, 0.3μm-3.7μm, 0.4μm-3.5μm, 0.5μm-3.2μm, 0.8μm-3μm, 1μm-2.8μm, 1.2μm-2.5μm, 1.5μm-2.3μm, 1.7μm-2μm, etc. As a result, the lithium supplement agent of this particle size in the present application has a lower decomposition voltage. The lithium supplement agent can decompose at low voltage, reducing the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte at high voltage, thereby improving the capacity and cycle performance of the battery. In other embodiments of the present application, the volume average particle size Dv50 of the lithium supplement agent is 0.5μm-2μm.

[0066] In this application, the volume average particle size Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage reaches 50%. For example, the volume average particle size Dv50 test method can refer to the standard GB / T 19077-2016 and be measured using a laser particle size analyzer (such as Malvern Master Size 3000).

[0067] In some embodiments of the present application, based on the total mass of the isolation film 20, the content of the lithium replenisher is 1wt%-10wt%, for example, 1.5wt%-10wt%, 1.5wt%-9.5wt%, 1.5wt%-9wt%, 2wt%-8.5wt%, 2.5wt%-8wt%, 3wt%-7.5wt%, 3.5wt%-7wt%, 4wt%-6.5wt%, 4.5wt%-6wt%, 5wt%-5.5wt%, etc. Therefore, the present application adopts a lithium replenisher with this content to provide sufficient active lithium during the battery cycle, meet the consumption of active lithium ions during the long-term cycle of the battery, and improve the cycle performance of the battery. In other embodiments of the present application, based on the total mass of the pre-lithiation layer, the content of the lithium replenisher is 2wt%-7wt%.

[0068] In some embodiments of the present application, the lithium supplement comprises Li x AO 0.5(2+x), Li2DO3, Li2EO4, Li3GO4, Li5LO4 or Li5MO6, wherein x≥1, A includes at least one of Ni, Co, Fe, Mn, Zn, Mg, Ca, Cu or Sn; D includes at least one of Ni, Co, Fe, Mn, Sn or Cr; E includes at least one of Ni, Co, Fe, Mn, Sn, Cr, V or Nb; G includes at least one of Ni, Co, Fe, Mn, Sn, Cr, V, Mo or Nb; L includes at least one of Ni, Co, Fe, Mn, Sn, Cr or Mo; M includes at least one of Ni, Co or Mn, and the valence state of each element in A, D, E, G, L, M is lower than its own highest oxidation state. Therefore, the isolation membrane of the present application adopts the lithium supplement agent of the above composition, which has a low decomposition voltage and can be decomposed at low voltage, reducing the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte at high voltage, thereby improving the capacity and cycle performance of the battery.

[0069] In some embodiments of the present application, the lithium supplement Li x AO 0.5(2+x) The value of x satisfies 2≤x≤4, for example, 2.2≤x≤3.8, 2.5≤x≤3.5, 2.7≤x≤3.2, 2.8≤x≤3, etc., and A may include at least one of Ni, Co, Fe, or Mn. Therefore, the separator of the present application employing a lithium replenisher of this composition not only provides sufficient active lithium during the battery cycle, but also has a low decomposition voltage and can decompose at low voltage, reducing damage to the active material structure of the battery's positive electrode and oxidative decomposition of the electrolyte at high voltage, thereby improving the battery's capacity and cycle performance.

[0070] In some embodiments of the present application, D in the lithium supplement Li2DO3 may include at least one of Ni, Co, or Fe. Therefore, the separator of the present application employing this lithium supplement not only provides sufficient active lithium during battery cycling, but also has a low decomposition voltage, allowing it to decompose at low voltages. This reduces damage to the active material structure of the battery's positive electrode and oxidative decomposition of the electrolyte at high voltages, thereby improving the battery's capacity and cycle performance.

[0071] In some embodiments of the present application, the E in the lithium supplement Li2EO4 may include at least one of Ni, Co, Fe, or Sn. Therefore, the separator of the present application employing this lithium supplement not only provides sufficient active lithium during battery cycling, but also has a low decomposition voltage, allowing it to decompose at low voltages. This reduces damage to the active material structure of the battery's positive electrode and oxidative decomposition of the electrolyte at high voltages, thereby improving the battery's capacity and cycle performance.

[0072] In some embodiments of the present application, the lithium supplementing agent includes Li3GO4, where G includes at least one of Ni, Co, Fe, Sn, or Mo. Thus, by using the lithium supplementing agent with this composition in the separator of the present application, not only can sufficient active lithium be provided during the battery cycling process, but also the lithium supplementing agent with this composition has a lower decomposition voltage and can decompose at a low voltage, reducing the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte at high voltages, thereby improving the battery capacity and cycling performance.

[0073] In some embodiments of the present application, the lithium supplementing agent includes Li5LO4, where L can include at least one of Ni, Co, or Fe. Thus, by using the lithium supplementing agent with this composition in the separator of the present application, not only can sufficient active lithium be provided during the battery cycling process, but also the lithium supplementing agent with this composition has a lower decomposition voltage and can decompose at a low voltage, reducing the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte at high voltages, thereby improving the battery capacity and cycling performance.

[0074] In some embodiments of the present application, the lithium supplementing agent Li5MO6, where M can include Ni. Thus, by using the lithium supplementing agent with this composition in the separator of the present application, not only can sufficient active lithium be provided during the battery cycling process, but also the lithium supplementing agent with this composition has a lower decomposition voltage and can decompose at a low voltage, reducing the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte at high voltages, thereby improving the battery capacity and cycling performance.

[0075] In some embodiments of the present application, the lithium supplementing agent includes at least one of Li2CO3, Li2MnO2, Li5FeO4, Li6CoO4, Li2NiO2, Li2Cu x1 Ni 1-x1-y1 M y1 O2, Li3VO4, or Li3NbO4, where 0 < x1 ≤ 1, 0 ≤ y1 ≤ 0.1, and M includes at least one of Zn, Sn, Mg, Fe, or Mn. Thus, by using the lithium supplementing agent with this composition in the separator of the present application, not only can sufficient active lithium be provided during the battery cycling process, but also the lithium supplementing agent with this composition has a lower decomposition voltage and can decompose at a low voltage, reducing the damage to the structure of the battery positive electrode active material and the oxidative decomposition of the electrolyte at high voltages, thereby improving the battery capacity and cycling performance.

[0076] In some embodiments of the present application, the lithium supplementing agent Li2Cu x1 Ni 1-x1-y1 M y1In O2, 0 < x1 ≤ 1, for example, 0.001 ≤ x1 ≤ 1, 0.005 ≤ x1 ≤ 1, 0.008 ≤ x1 ≤ 1, 0.01 ≤ x1 ≤ 1, 0.05 ≤ x1 ≤ 1, 0.08 ≤ x1 ≤ 1, 0.1 ≤ x1 ≤ 1, 0.3 ≤ x1 ≤ 1, 0.5 ≤ x1 ≤ 1, 0.8 ≤ x1 ≤ 1, etc. Thus, by adding Cu with this content in the lithium supplement agent, the electrochemical performance of the lithium supplement agent can be improved. In some embodiments of the present application, the lithium supplement agent is Li2Cu x1 Ni 1-x1-y1 M y1 In O2, 0.2 ≤ x1 ≤ 0.8, and further x1 satisfies: 0.4 ≤ x1 ≤ 0.6.

[0077] In some embodiments of the present application, the lithium supplement agent is Li2Cu x1 Ni 1-x1-y1 M y1 In O2, 0 ≤ y1 ≤ 0.1, for example, 0.001 ≤ y1 ≤ 0.1, 0.005 ≤ y1 ≤ 0.1, 0.008 ≤ y1 ≤ 0.1, 0.01 ≤ y1 ≤ 0.1, 0.05 ≤ y1 ≤ 0.1, 0.08 ≤ y1 ≤ 0.1, and M includes Zn, Sn, Mg, Fe or Mn. Thus, by adding the element M with this content in the lithium supplement agent, the electrochemical performance of the lithium supplement agent can be improved. In some embodiments of the present application, the lithium supplement agent is Li2Cu x1 Ni 1-x1-y1 M y1 In O2, 0.01 ≤ y1 ≤ 0.07, and further y1 satisfies: 0.03 ≤ y1 ≤ 0.06.

[0078] In some embodiments of the present application, the lithium supplement agent may include at least one of lithium 2,3-dihydroxy-2-cyclopropen-1-one, lithium 3,4-dihydroxy-3-cyclobutene-1,2-dione, lithium 4,5-dihydroxy-4-cyclopentene-1,2,3-trione, lithium 5,6-dihydroxy-5-cyclohexene-1,2,3,4-tetrone, lithium carbonate, lithium oxalate, lithium ketomalonate, lithium diketosuccinate or lithium trione glutarate. Thus, by using the lithium supplement agent with this composition in the separator of the present application, not only can sufficient active lithium be provided during the battery cycling process, but also the lithium supplement agent with this composition has a lower decomposition voltage and can decompose at a low voltage, reducing the damage to the structure of the battery positive electrode active material and the oxidation decomposition of the electrolyte at a high voltage, thereby improving the capacity and cycling performance of the battery.

[0080] ​​​In some embodiments of the present application, the thickness of the pre-lithiation layer 22 can be 5μm-15μm, for example, 6μm-14μm, 7μm-13μm, 8μm-12μm, 9μm-11μm, 9μm-10μm, etc. Therefore, the separator of the present application uses a lithium replenishment layer of this thickness to provide sufficient active lithium during the battery cycle, thereby improving the battery capacity. In other embodiments of the present application, the thickness of the pre-lithiation layer 22 can be 7μm-10μm.

[0081] In some embodiments of the present application, the pre-lithiation layer 22 and the polymer layer 21 include a polymer, wherein the weight-average molecular weight of the polymer is 30,000-100,000, for example, 35,000-95,000, 40,000-90,000, 45,000-85,000, 50,000-80,000, 55,000-75,000, 60,000-70,000, 65,000-70,000, etc. Thus, the pre-lithiation layer 22 and the polymer layer 21 in the separator 20 of the present application both use polymers of the above-mentioned molecular weights, which not only improves the strength of the separator 20, but also increases the liquid absorption rate of the separator 20 and improves its electrolyte wettability. In other embodiments of the present application, the weight-average molecular weight of the polymer can be 50,000-70,000.

[0082] In the present application, the weight average molecular weight (Mw) of the polymer can be measured using a HLC-8320GPC gel permeation chromatograph (SuperMultiporeHZ series semi-micro SEC column, the standard product is polystyrene) produced by Tosoh Corporation of Japan.

[0083] In some embodiments of the present application, a slurry comprising a polymer and a lithium replenisher can be directly coated on a substrate and dried to form the pre-lithiation layer 22. Alternatively, the slurry comprising a polymer and a lithium replenisher can be used as a spinning solution and electrospun to form the pre-lithiation layer 22. The polymer in the pre-lithiation layer 22 forms a network structure, and the lithium replenisher is located on the network structure. This allows the lithium replenisher to be evenly distributed in the pre-lithiation layer 22, thereby improving the lithium replenishment efficiency of the lithium replenisher.

[0084] In some embodiments of the present application, the polymer may include at least one of a polyolefin polymer, a polynitrile polymer, or a polycarboxylate polymer. Therefore, the use of such polymers in both the pre-lithiation layer 22 and the polymer layer 21 of the separator 20 of the present application not only improves the strength of the separator 20 but also increases its liquid absorption rate and improves its electrolyte wettability.

[0085] As an example, the polymer includes at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylene carbonate, polycyanoacrylate, polymethacrylate, polyacrylonitrile, or polymaleic anhydride.

[0086] In some embodiments of the present application, the thickness of the polymer layer 21 may be 5 μm-7 μm, such as 5.5 μm-6.5 μm, 6 μm-6.5 μm, etc. Therefore, the isolation film 20 of the present application uses a polymer layer 21 of this thickness to improve the puncture resistance of the isolation film 20 .

[0087] The second aspect of the present application provides a method for preparing the above-mentioned isolation film, comprising:

[0088] S100: electrospinning a first spinning solution including a lithium supplement and a polymer

[0089] In some embodiments of the present application, a lithium supplement agent and a polymer are added to an organic solvent and stirred to prepare a first spinning solution, which is then subjected to electrospinning. The ultra-high voltage static electricity applied during the electrospinning process causes the first spinning solution including the polymer and the lithium supplement agent to accelerate under the action of the electric field force, causing the jet to stretch in the electric field, thereby reducing the size of the lithium supplement agent and effectively reducing its decomposition potential.

[0090] In some embodiments of the present application, the volume average particle size Dv50 of the lithium supplement during the mixing process is 1 μm-8 μm, 2 μm-7 μm, 3 μm-6 μm, 4 μm-5 μm, etc.

[0091] In some embodiments of the present application, the pushing speed of the spinneret in the electrospinning of the first spinning solution is 0.01 mm / min-0.05 mm / min, for example, 0.02 mm / min-0.04 mm / min, 0.03 mm / min-0.04 mm / min, etc. In other embodiments of the present application, the pushing speed of the spinneret in the electrospinning of the first spinning solution is 0.02 mm / min-0.04 mm / min.

[0092] In some embodiments of the present application, the voltage between the spinneret and the receiver during the electrospinning of the first spinning solution is 10 kV-20 kV, for example, 11 kV-19 kV, 12 kV-18 kV, 13 kV-17 kV, 14 kV-16 kV, 14 kV-15 kV, etc. In other embodiments of the present application, the voltage between the spinneret and the receiver during the electrospinning of the first spinning solution is 15 kV-20 kV.

[0093] In some embodiments of the present application, the distance between the spinneret and the receiver in the electrospinning of the first spinning solution is 10 cm-30 cm, for example, 15 cm-25 cm, 17 cm-20 cm, etc. In other embodiments of the present application, the distance between the spinneret and the receiver in the electrospinning of the first spinning solution is 15 cm-20 cm.

[0094] In some embodiments of the present application, the electrospinning temperature during the electrospinning of the first spinning solution is 20°C-25°C, for example, 21°C-24°C, 22°C-23°C, etc. In some embodiments of the present application, the electrospinning temperature during the electrospinning of the first spinning solution is 22°C-25°C.

[0095] In some embodiments of the present application, the humidity of the electrospinning process during the electrospinning of the first spinning solution is 10%-20%, for example, 12%-18%, 14%-17%, 15%-16%, etc. In other embodiments of the present application, the humidity of the electrospinning process during the electrospinning of the first spinning solution is 15%-20%.

[0096] S200: forming a polymer layer on the pre-lithiation layer

[0097] In some embodiments of the present application, a slurry including a polymer and an organic solvent may be coated on the pre-lithiation layer, and then dried to form a polymer layer on the pre-lithiation layer.

[0098] In some embodiments of the present application, the polymer layer is formed on the pre-lithiation layer by the following steps: placing the pre-lithiation layer on a receiver of an electrospinning device, and then electrospinning a second spinning solution comprising a polymer and an organic solvent to form a polymer layer on the pre-lithiation layer.

[0099] As an example, the organic solvents in the first spinning solution and the second spinning solution independently include at least one of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, N-methylpyrrolidone, hexafluoroisopropanol or tetrahydrofuran.

[0100] It should be noted that the electrospinning conditions of the second spinning solution comprising a polymer and an organic solvent are the same as the electrospinning conditions of the first spinning solution described above, and will not be described in detail here.

[0101] In some embodiments of the present application, the pre-lithiation layer is carbonized before forming the polymer layer on it. This allows the lithium replenisher in the pre-lithiation layer to adhere evenly and tightly to the fiber membrane surface after electrospinning. Carbonization effectively removes non-carbon components from the polymer, thereby forming an excellent 3D conductive network and effectively improving the lithium replenishment efficiency of the separator.

[0102] In some embodiments of the present application, the carbonization conditions include: in an inert atmosphere, heating to 300°C-500°C at a rate of 2°C / min-10°C / min, and holding for 1h-4h, for example, the heating rate can be 3°C / min-9°C / min, 4°C / min-8°C / min, 5°C / min-7°C / min, 5°C / min-6°C / min; the carbonization temperature is 320°C-480°C, 350°C-450°C, 370°C-420°C, 380°C-400°C, etc.; the holding time is 1.5h-3.5h, 2h-3h, 2.5h-3h, etc. As an example, the carbonization conditions include: in an inert atmosphere, heating to 450°C-500°C at a rate of 5°C / min-8°C / min, and holding for 2h-3h.

[0103] It should be noted that, since the organic lithium replenisher will decompose and become ineffective during the carbonization process, if the pre-lithiation layer is carbonized, a non-organic lithium replenisher is used to prepare the pre-lithiation layer, for example, the following lithium replenishers are not used: at least one of 2-cyclopropene-1-one-2,3-dihydroxylithium, 3-cyclobutene-1,2-dione-3,4-dihydroxylithium, 4-cyclopentene-1,2,3-trione-4,5-dihydroxylithium, 5-cyclohexene-1,2,3,4-tetraketone-5,6-dihydroxylithium, lithium oxalate, lithium ketomalonate, lithium diketosuccinate or lithium triketoglutarate.

[0104] The third aspect of the present application provides a battery comprising the separator of the first aspect or the separator obtained by the method of the second aspect, thereby having excellent capacity and cycle performance.

[0105] Typically, the battery includes a positive electrode sheet and a negative electrode sheet, with a separator disposed between the two, with the pre-lithiation layer of the separator facing the positive electrode sheet. During battery charging, the lithium replenisher in the pre-lithiation layer loses electrons and converts into lithium ions. Upon reaching the negative electrode sheet, these ions are reduced and stored in the negative electrode active material. The lithium stored in the negative electrode active material is then gradually released during subsequent cycles, achieving a long battery cycle life.

[0106] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0107] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0108] In some embodiments of the present application, the positive electrode current collector may be a metal foil or a composite positive electrode current collector. For example, aluminum foil may be used as the metal foil. The composite positive electrode current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite positive electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0109] In some embodiments of the present application, the positive electrode active material may be a positive electrode active material for lithium ion batteries known in the art.

[0110] As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.80 Co 0.15 Al 0.05O2) or at least one of its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, or a composite material of lithium iron manganese phosphate and carbon.

[0111] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0112] In the list of positive electrode materials in this application, the molar content of oxygen is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0113] In some embodiments of the present application, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0114] In some embodiments of the present application, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorine-containing acrylate resin.

[0115] In some embodiments of the present application, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0116] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0117] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0118] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments of the present application, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites or silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds or tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0120] In some embodiments of the present application, the negative electrode active material layer may further optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS).

[0121] In some embodiments of the present application, the negative electrode active material layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0122] In some embodiments of the present application, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0123] In some embodiments of the present application, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0124] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0125] The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or solid.

[0126] In some embodiments of the present application, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0127] In some embodiments of the present application, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, or lithium tetrafluorooxalatophosphate.

[0128] In some embodiments of the present application, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone or diethyl sulfone.

[0129] In some embodiments of the present application, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0130] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0131] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0132] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0133] The present application has no particular limitation on the shape of the battery, which can be cylindrical, square, or any other shape. For example, FIG2 shows a square-structured battery cell 1 as an example.

[0134] In some embodiments, referring to Figure 3, the outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 1 can be one or more, and those skilled in the art can select according to specific actual needs.

[0135] In some embodiments, batteries may be assembled into a battery module. The number of batteries contained in the battery module may be one or more. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0136] Figure 4 shows an example battery module 2. Referring to Figure 4 , within the battery module 2, multiple battery cells 1 may be arranged sequentially along the length of the battery module 2. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 1 may be secured together using fasteners.

[0137] Optionally, the battery module 2 may further include a housing having an accommodation space, and the plurality of battery cells 1 are accommodated in the accommodation space.

[0138] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0139] Figures 5 and 6 illustrate an example battery pack 3. Referring to Figures 5 and 6 , the battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box comprises an upper case 31 and a lower case 32. The upper case 31 can be positioned over the lower case 32 to form an enclosed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0140] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0141] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0142] Figure 7 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0143] Another example device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be light and thin, and may use a battery as a power source.

[0144] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0145] Example 1

[0146] 1. Preparation of positive electrode sheet

[0147] LiFePO4 (volume average particle size Dv50 is 1.2μm), conductive agent acetylene black, and binder polyvinylidene fluoride are added to N-methylpyrrolidone solvent in a weight ratio of 97:1:2. After fully stirring and mixing, the slurry is evenly coated on the surfaces of both sides of the aluminum foil, and then transferred to a vacuum drying oven for complete drying. The obtained electrode is rolled and then punched to obtain the positive electrode.

[0148] 2. Preparation of negative electrode sheet

[0149] The negative electrode active material artificial graphite, the conductive agent carbon black (Super P), the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are mixed evenly in an appropriate amount of solvent deionized water at a mass ratio of 96.5:0.7:1.8:1 to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of the negative electrode current collector copper foil. Through drying and cold pressing, a negative electrode active material layer is formed on both sides of the negative electrode current collector. Finally, after striping and cutting processes, a negative electrode sheet is obtained.

[0150] 3. Preparation of electrolyte

[0151] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the fully dried electrolyte salt LiPF6 was dissolved in a mixed solvent (the mixed solvent included ethylene carbonate (EC) and diethyl carbonate (DEC), and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 50:50), and after mixing evenly, an electrolyte with a concentration of 1.1 mol / L was obtained.

[0152] 4. Preparation of isolation membrane

[0153] The polymer powder polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and lithium ferrite Li5FeO4 were placed in a 60°C oven and dried for 12 hours. 19g of the dried polyvinylidene fluoride-hexafluoropropylene copolymer and 1g of lithium ferrite Li5FeO4 were weighed and added to a certain amount of N,N-dimethylformamide (DMF). The mixture was placed in a 50°C oil bath and mechanically stirred for 3 hours to obtain a uniformly mixed first spinning solution, which was injected into an electrospinning machine. The distance between the spinneret and the receiver was adjusted to 15cm, the spinning solution injection flow rate was 0.03mm / min, and a voltage of 20kV was applied to spin a fiber membrane layer at room temperature. The fiber membrane layer was then heated to 450°C in an argon atmosphere at a heating rate of 5°C / min and kept warm for 3 hours to obtain a pre-lithiation layer (lithium ferrite surface density 0.019g / 1540.25mm 2 ) is placed on the receiver of the electrospinning machine, and a second spinning solution including polymer powder polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and N,N-dimethylformamide (DMF) is injected into the electrospinning machine, the distance between the spinneret and the receiver is adjusted to 15 cm, the spinning solution injection flow rate is 0.03 mm / min, and a voltage of 20 kV is applied to receive a polymer layer on the pre-lithiation layer at room temperature to obtain an isolation membrane.

[0154] 5. Preparation of lithium ions

[0155] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order (with the pre-lithiation layer on the separator facing the positive electrode sheet), so that the separator is located between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried lithium-ion battery. After vacuum packaging, standing, formation (charging at a constant current of 0.33C at 45°C to 60% SOC, and then charging at a small rate of 0.1C to 4.2V), and shaping processes, a lithium-ion battery is obtained.

[0156] The preparation methods of the lithium-ion batteries of Examples 2-38 and Comparative Example 1 are the same as those of Example 1, except that the preparation methods and compositions of the isolation membranes are different, as shown in Table 1.

[0157] Comparative Example 2

[0158] The preparation method of the lithium ion battery of Comparative Example 2 is the same as that of Example 1, except that the method of preparing the isolation membrane is different, as follows:

[0159] The isolation membrane uses a 6μm polyethylene film as a substrate, and a slurry mixed with lithium ferrite Li5FeO4, polyvinylidene fluoride and N,N-dimethylformamide (DMF) is coated on one side of the polyethylene film (the Dv50 of lithium ferrite Li5FeO4 is 5μm, and the decomposition potential is 4.5V). It is dried to form a pre-lithiation layer (9μm thick) on the polyethylene film to obtain an isolation membrane (based on the total mass of the isolation membrane, the mass of lithium ferrite accounts for 5%).

[0160] Table 1

[0161] The decomposition potential of the lithium replenisher in the isolation membranes obtained in Examples 1-38 and Comparative Examples 1-2 was tested, and the characterization results are shown in Table 1. The discharge capacity and cycle performance of the lithium-ion battery were characterized, and the characterization results are shown in Table 2.

[0162] (1) Decomposition potential test of lithium supplement in isolation membrane:

[0163] Preparation of button-type full battery:

[0164] a. Preparation of negative electrode sheet:

[0165] The negative electrode active material graphite, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were mixed in an appropriate amount of deionized water solvent system according to a weight ratio of 96.5:0.7:1.8:1 to obtain a negative electrode slurry. The negative electrode slurry was coated on one side of a copper foil (thickness of 6 μm) (coating surface density of 0.174 g / 1540.25 mm 2 ), then drying and cold pressing to form a negative electrode active material layer (with a thickness of 0.143 mm) on one side of the negative electrode current collector, and finally punching to obtain a negative electrode sheet;

[0166] b. Preparation of positive electrode sheet:

[0167] The positive electrode active material (LiFePO4), conductive carbon (SP), and binder (polyvinylidene fluoride PVDF) were dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 97:1:2, and the mixture was stirred thoroughly to prepare a positive electrode slurry. The positive electrode slurry was coated on one side of the aluminum foil (coating surface density was 0.377 g / 1540.25 mm 2 ), then drying and cold pressing to form a positive electrode active material layer (with a thickness of 0.219 mm) on one surface of the aluminum foil (13 μm), and finally punching to obtain a positive electrode sheet;

[0168] c. Preparation of isolation membrane:

[0169] A slurry (solid content of 60%) comprising polymer powder polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and N,N-dimethylformamide (DMF) was coated on a glass substrate (coating surface density of 0.05 g / 1540.25 mm 2 ), and then dried, cold pressed, and peeled off the glass substrate to obtain a polymer layer (thickness of 15 μm); the polymer powder polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and the lithium supplement agent were placed in a 60°C oven and dried for 12 hours, 19 g of the dried polyvinylidene fluoride-hexafluoropropylene copolymer and 1 g of the lithium supplement agent were weighed and added to N,N-dimethylformamide (DMF), and mechanically stirred for 3 hours to obtain a uniformly mixed pre-lithiation slurry (solid content of 63%), and then the uniformly mixed pre-lithiation slurry was coated on one side of the polymer layer (coating surface density of 0.02 g / 1540.25 mm 2 ), and then through drying and cold pressing, a pre-lithiation layer (with a thickness of 5 μm) is formed on one side of the polymer layer to obtain an isolation membrane.

[0170] d. Preparation of electrolyte

[0171] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a mass ratio of 1:1:1 to obtain a solvent, and fully dried electrolyte salt LiPF6 is dissolved in the above solvent. After mixing evenly, an electrolyte solution with a concentration of 1 mol / L is obtained.

[0172] Assembly: Stack a single positive electrode sheet, a single separator, and a single negative electrode sheet in order (the side of the positive electrode sheet forming the positive electrode active material layer contacts the pre-lithiation layer on the separator, and the side of the negative electrode sheet forming the negative electrode active material layer contacts the polymer layer of the separator), so that the separator is placed between the positive and negative electrodes to play an isolating role, and add electrolyte. Through pressure packaging (50MPa), a CR2032 button-type full battery (capacity ≤4.5mAh) is obtained.

[0173] The above-mentioned button-type full cell was used as an experimental example to perform charge and discharge cycles at a rate of 0.04C at 25°C. The capacity (Q)-voltage (V) curve of the first cycle was recorded and differentiated to obtain a dQ / dV-V curve. At the same time, a dQ / dV-V curve was obtained for a button-type full cell in the control group (no lithium replenisher was added to the separator pre-lithiation layer slurry, and the rest was the same as the above-mentioned button-type full cell) under the same conditions. Comparing the two curves, an additional peak can be seen in the dQ / dV-V curve of the experimental example button-type full cell. This peak is the characteristic peak of the lithium replenisher, and the ordinate corresponding to this peak is the decomposition potential of the lithium replenisher.

[0174] (2) Discharge specific capacity test:

[0175] At room temperature (25°C), the battery is discharged at a constant current rate of 0.33C to a discharge termination voltage of 2.5V, and the discharge capacity is measured to be E d0 , use E d0 Divide by the mass of the battery's positive electrode active material to get the discharge specific capacity, that is, the battery's discharge specific capacity (mAh / g) = first-cycle discharge capacity / positive electrode active material mass.

[0176] (3) Cyclic performance test:

[0177] The ambient temperature was controlled at 25°C. The battery was charged to 3.65V at 1C, then charged to 0.05C at a constant voltage, left to stand for 10 minutes, and then discharged to 2.5V at 1C. The discharge capacity was recorded as C0. 300 cycles were performed according to the above charge and discharge process. The discharge capacity at the 300th cycle was C1. The cycle capacity retention rate of the battery cell = C1 / C0*100%.

[0178] Table 2

[0179] Conclusion: The lithium-ion battery isolation membranes of Examples 1-38 all include a polymer layer and a pre-lithiation layer, and a lithium replenisher with a decomposition potential lower than or equal to 4.2V is used in the pre-lithiation layer, while no lithium replenisher is added to the pre-lithiation layer of the isolation membrane of Comparative Example 1, and a lithium replenisher with a decomposition potential of 4.5V is used in the isolation membrane of Comparative Example 2. It can be seen from the data in Table 2 that the discharge specific capacity and cycle performance of the lithium-ion batteries of Examples 1-38 are better than those of Comparative Examples 1-2, indicating that the pre-lithiation layer of the isolation membrane of the present application uses a lithium replenisher with a decomposition potential lower than or equal to 4.2V, and the content of the lithium replenisher in the pre-lithiation layer is controlled at 1wt%-10wt%, which can improve the capacity and cycle performance of the battery.

[0180] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A separation film, wherein: The invention comprises a polymer layer and a pre-lithiation layer, wherein the pre-lithiation layer is formed on one side of the polymer layer, the pre-lithiation layer comprises a lithium replenisher, the decomposition potential of the lithium replenisher is lower than or equal to 4.2V, and the content of the lithium replenisher is 1wt%-10wt% based on the total mass of the pre-lithiation layer.

2. The isolation film according to claim 1, wherein: The decomposition potential of the lithium supplement is 4.1V-4.2V.

3. The isolation film according to claim 1 or 2, wherein: The volume average particle size Dv50 of the lithium supplement agent is 0.2 μm-4 μm.

4. The isolation film according to any one of claims 1 to 3, wherein: The volume average particle size Dv50 of the lithium supplement agent is 0.5 μm-2 μm.

5. The isolation film according to any one of claims 1 to 4, wherein: Based on the total mass of the pre-lithiation layer, the content of the lithium supplement agent is 2wt%-7wt%.

6. The isolation film according to any one of claims 1 to 5, wherein: The lithium supplement comprises Li x AO 0.5(2+x) , at least one of Li2DO3, Li2EO4, Li3GO4, Li5LO4 or Li5MO6, Where x≥1, A includes at least one of Ni, Co, Fe, Mn, Zn, Mg, Ca, Cu or Sn; D includes at least one of Ni, Co, Fe, Mn, Sn or Cr; E includes at least one of Ni, Co, Fe, Mn, Sn, Cr, V or Nb; G includes at least one of Ni, Co, Fe, Mn, Sn, Cr, V, Mo or Nb; L includes at least one of Ni, Co, Fe, Mn, Sn, Cr or Mo; M includes at least one of Ni, Co or Mn, The valence state of each element in A, D, E, G, L, and M is lower than its own highest oxidation state.

7. The isolation film according to claim 6, wherein: The lithium supplement meets at least one of the following conditions: 2≤x≤4; A includes at least one of Ni, Co, Fe or Mn; D includes at least one of Ni, Co or Fe; E includes at least one of Ni, Co, Fe or Sn; G includes at least one of Ni, Co, Fe, Sn or Mo; L includes at least one of Ni, Co or Fe; M includes Ni.

8. The isolation film according to any one of claims 1 to 7, wherein: The lithium supplement includes at least one of Li2CO3, Li2MnO2, Li5FeO4, Li6CoO4, Li2NiO2, Li2Cu x1 Ni 1-x1-y1 M y1 O2, Li3VO4 or Li3NbO4, where 0 < x1 ≤ 1, 0 ≤ y1 ≤ 0.1, and M includes at least one of Zn, Sn, Mg, Fe or Mn.

9. The isolation film according to claim 8, wherein: Satisfies at least one of the following conditions: 0.2≤x1≤0.8; 0.01≤y1≤0.

07.

10. The isolation film according to claim 8 or 9, wherein: Satisfies at least one of the following conditions: 0.4≤x1≤0.6; 0.03≤y1≤0.

06.

11. The isolation film according to any one of claims 1 to 10, wherein: The lithium supplement includes at least one of 2-cyclopropene-1-one 2,3-dihydroxy lithium, 3-cyclobutene-1,2-dione 3,4-dihydroxy lithium, 4-cyclopentene-1,2,3-trione 4,5-dihydroxy lithium, 5-cyclohexene-1,2,3,4-tetraketone 5,6-dihydroxy lithium, lithium oxalate, lithium ketomalonate, lithium diketosuccinate or lithium triketoglutarate.

12. The isolation film according to any one of claims 1 to 11, wherein: The thickness of the pre-lithiation layer is 5 μm-15 μm.

13. The isolation film according to any one of claims 1 to 12, wherein: The thickness of the pre-lithiation layer is 7 μm-10 μm.

14. The isolation film according to any one of claims 1 to 13, wherein: The pre-lithiation layer and the polymer layer include a polymer.

15. The isolation film according to claim 14, wherein: The polymer forms a network structure, and the lithium supplement is located on the network structure of the polymer.

16. The isolation film according to claim 14 or 15, wherein: The weight average molecular weight of the polymer is 30,000-100,000.

17. The isolation film according to any one of claims 14 to 16, wherein: The weight average molecular weight of the polymer is 50,000-70,000.

18. The isolation film according to any one of claims 14 to 17, wherein: The polymer includes at least one of a polyolefin polymer, a polynitrile polymer or a polycarboxylate polymer.

19. The isolation film according to any one of claims 14 to 18, wherein: The polymer includes at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylene carbonate, polycyanoacrylate, polymethacrylate, polyacrylonitrile or polymaleic anhydride.

20. The isolation film according to any one of claims 1 to 19, wherein: The thickness of the polymer layer is 5 μm-7 μm.

21. A method for preparing the isolation film according to any one of claims 1 to 20, wherein: include: Electrospinning a first spinning solution including a lithium supplement agent and a polymer to obtain a pre-lithiation layer; A polymer layer is formed on the pre-lithiation layer to obtain an isolation membrane.

22. The method according to claim 21, wherein: The electrospinning of the first spinning solution comprises at least one of the following conditions: The push speed of the spinneret is 0.01mm / min-0.05mm / min; The voltage between the spinneret and the receiver is 10kV-20kV; The distance between the spinneret and the receiver is 10cm-30cm; The temperature of electrospinning is 20℃-25℃; The humidity for electrospinning is 10%-20%.

23. The method according to claim 21 or 22, wherein: The electrospinning of the first spinning solution comprises at least one of the following conditions: The push speed of the spinneret is 0.02mm / min-0.04mm / min; The voltage between the spinneret and the receiver is 15kV-20kV; The distance between the spinneret and the receiver is 15cm-20cm; The temperature of electrospinning is 22℃-25℃; The humidity for electrospinning is 15%-20%.

24. The method according to any one of claims 21 to 23, wherein: The polymer layer is formed on the pre-lithiation layer by the following steps: The pre-lithiation layer is placed on a receiver of an electrospinning device, and then a second spinning solution including a polymer is electrospun.

25. The method according to any one of claims 21 to 24, wherein: Before forming the polymer layer on the pre-lithiation layer, the pre-lithiation layer is carbonized in advance.

26. The method according to claim 25, wherein: The carbonization conditions include: in an inert atmosphere, heating to 300° C.-500° C. at a rate of 2° C. / min-10° C. / min, and keeping the temperature for 1 h-4 h.

27. The method according to claim 25 or 26, wherein: The carbonization conditions include: in an inert atmosphere, heating to 450° C.-500° C. at a rate of 5° C. / min-8° C. / min, and keeping the temperature for 2 h-3 h.

28. A battery, comprising the separator according to any one of claims 1 to 20 or the separator obtained by the method according to any one of claims 21 to 27.

29. The battery according to claim 28, wherein The battery further comprises a positive electrode sheet and a negative electrode sheet, the isolation film is arranged between the positive electrode sheet and the negative electrode sheet, and the pre-lithiation layer of the isolation film faces the positive electrode sheet.

30. An electrical device, comprising the battery according to claim 28 or 29.

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