Lithium supplementing method, pre-lithiated negative electrode sheet, secondary battery, and electronic device

Abstract

The application provides a lithium supplement method, a pre-lithiated negative electrode sheet, a secondary battery and an electronic device. The lithium supplement method comprises the following steps: providing a negative electrode sheet; providing a lithium supplement composite layer, the lithium supplement composite layer comprising a support layer, a lithium supplement layer and a separator film of a pre-impregnated electrolyte, the lithium supplement layer being arranged between the separator film and the support layer. The lithium supplement composite layer and the negative electrode sheet are attached, the separator film is in contact with a negative material layer, the lithium supplement composite layer and the negative electrode sheet are subjected to a discharging treatment, the constant current discharging current of the discharging treatment is 0.1C-3C, and the discharging time is 0.067h-2h. After the discharging treatment is completed, the lithium supplement composite layer and the negative electrode sheet are peeled off, and a pre-lithiated negative electrode sheet is obtained. The negative electrode sheet is subjected to lithium supplement by using the above lithium supplement method, a pre-lithiated negative electrode sheet is obtained, and the pre-lithiated negative electrode sheet is applied to a secondary battery. As a result, the first coulomb efficiency of the secondary battery can be improved, the cycle capacity attenuation can be reduced, and the volume energy density of the secondary battery can be improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a lithium replenishment method, a pre-lithiated negative electrode, a secondary battery, and an electronic device. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, high power, and long cycle life, and are widely used in consumer electronics, electric bicycles, and electric vehicles. As their application scope continues to expand, the requirements for energy density and cycle performance of lithium-ion batteries are constantly increasing. Currently, commonly used graphite anode materials for lithium-ion batteries can no longer meet the energy density requirements. Although silicon-carbon and silicon-oxygen anode materials have high theoretical specific capacity and are ideal materials to replace graphite anode materials and improve the energy density of lithium-ion batteries, they have not been widely adopted due to their low initial coulombic efficiency and poor cycle life. Existing methods to improve the initial coulombic efficiency and reduce cycle decay of silicon-carbon or silicon-oxygen anodes involve pre-lithipping the anode plates to replenish the irreversible capacity consumed during the first charge, discharge, and cycle, thereby improving the initial coulombic efficiency of lithium-ion batteries with silicon-carbon or silicon-oxygen anodes and ultimately increasing the energy density of the lithium-ion battery.

[0003] Existing lithium replenishment methods for negative electrode sheets mainly include lithium powder replenishment, lithium strip replenishment, and electrochemical replenishment. However, these three methods all have certain problems in terms of environmental control, replenishment uniformity, and post-replenishment side reactions. Therefore, there is an urgent need to provide a pre-lithiated negative electrode sheet that can improve the initial coulombic efficiency of lithium-ion batteries containing silicon-carbon or silicon-oxygen negative electrodes, reduce cycle capacity decay, and increase the energy density of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a lithium replenishment method, a pre-lithiated negative electrode, a secondary battery, and an electronic device to improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the volumetric energy density of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of this application provides a lithium replenishment method, comprising the following steps: providing a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector; providing a lithium replenishment composite layer, the lithium replenishment composite layer including a support layer, a lithium replenishment layer and a separator pre-impregnated with electrolyte, the lithium replenishment layer being disposed between the separator and the support layer; bonding the lithium replenishment composite layer and the negative electrode sheet together, so that the separator is in contact with the negative electrode material layer; performing a discharge treatment on the lithium replenishment composite layer and the negative electrode sheet, the constant current discharge current I of the discharge treatment being 0.1C to 3C, and the discharge time t being 0.067h to 2h; after the discharge treatment is completed, peeling the lithium replenishment composite layer from the negative electrode sheet to obtain a pre-lithiated negative electrode sheet. The pre-lithiated negative electrode sheet prepared using the lithium replenishment method of this application, when applied to a secondary battery, can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, increase the volumetric energy density of the secondary battery, and also simplify the manufacturing process of the secondary battery and reduce costs.

[0006] In one embodiment of this application, the negative electrode sheet has a gap structure, which includes a gap structure along the tape delivery direction or a gap structure perpendicular to the tape delivery direction. Having a gap structure for the negative electrode sheet can effectively reduce the thickness of the secondary battery and further improve the volumetric energy density of the secondary battery.

[0007] In one embodiment of this application, when the negative electrode sheet is a gap structure along the tape direction, the negative electrode current collector includes opposing first and second surfaces along the thickness direction of the negative electrode sheet; both the first and second surfaces are provided with negative electrode material layer regions and empty foil regions at intervals; along the tape direction of the negative electrode sheet, the shortest distance D1 between two adjacent negative electrode material layer regions on the first surface is 5 mm to 30 mm, and the shortest distance D2 between two adjacent negative electrode material layer regions on the second surface is 30 mm to 150 mm. The negative electrode sheet satisfies the above characteristics, which can effectively reduce the thickness of the secondary battery and reduce the amount of negative electrode active material used, thereby further improving the volumetric energy density of the secondary battery and reducing the cost of the secondary battery.

[0008] In one embodiment of this application, the separator includes a first separator, which is disposed opposite to a first surface. The first separator has a gap structure along the tape delivery direction. The first separator includes a base film and a separator coating disposed on at least one surface of the base film. A first region and a second region are spaced apart on the surface of the base film. The second region is coated with the separator coating. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the tape delivery direction of the first separator, the shortest distance D3 between two adjacent first regions in the first separator is 5 mm to 30 mm. The first separator, satisfying the above characteristics, can reduce the possibility of lithium plating in the empty foil region, improve the safety performance of the secondary battery, and effectively reduce the thickness of the secondary battery, further improving the volumetric energy density of the secondary battery.

[0009] In one embodiment of this application, the separator includes a second separator, which is disposed opposite to a second surface. The second separator has a gap structure along the tape delivery direction. The second separator includes a base film and a separator coating disposed on at least one surface of the base film. A first region and a second region are spaced apart on the surface of the base film. The second region is coated with the separator coating. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the tape delivery direction of the second separator, the shortest distance D4 between two adjacent first regions in the second separator is 30 mm to 150 mm. The second separator, satisfying the above characteristics, can reduce the possibility of lithium plating in the empty foil region, improve the safety performance of the secondary battery, and effectively reduce the thickness of the secondary battery, further improving the volumetric energy density of the secondary battery.

[0010] In one embodiment of this application, the separator includes a first separator and a second separator. The first separator and a first surface are disposed opposite each other. The first separator has a gap structure along the belt travel direction. The first separator includes a base film and a separator coating disposed on at least one surface of the base film. The surface of the base film has a first region and a second region spaced apart. The second region has the separator coating disposed on it. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the belt travel direction of the first separator, the shortest distance D3 between two adjacent first regions in the first separator is 5 mm to 30 mm. The second separator and a second surface are disposed opposite each other. The second separator has a gap structure along the belt travel direction. The second separator includes a base film and a separator coating disposed on at least one surface of the base film. The surface of the base film has a first region and a second region spaced apart. The second region has the separator coating disposed on it. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the belt travel direction of the second separator, the shortest distance D4 between two adjacent first regions in the second separator is 30 mm to 150 mm. The first and second separators meet the above characteristics, which can reduce the possibility of lithium deposition in the empty foil area, further improve the safety performance of the secondary battery, and also effectively reduce the thickness of the secondary battery, further improving the volumetric energy density of the secondary battery.

[0011] In one embodiment of this application, when the negative electrode sheet is a gap structure perpendicular to the tape direction, the surface of the negative electrode current collector is provided with a negative electrode material layer region and an empty foil region at intervals; along the tape direction perpendicular to the negative electrode sheet, the shortest distance D5 between two adjacent negative electrode material layer regions on the surface of any negative electrode current collector is 5 mm to 150 mm. The negative electrode sheet satisfies the above characteristics, which can reduce the amount of negative electrode active material used and lower the cost of the secondary battery; after the negative electrode sheet is die-cut, the empty foil region can serve as a tab region, reducing the impedance of the secondary battery, improving the dynamic performance of the secondary battery, and increasing the capacity of the secondary battery.

[0012] In one embodiment of this application, the separator includes a third separator, which is a gap structure perpendicular to the tape delivery direction. The third separator includes a base film and a separator coating disposed on at least one surface of the base film. A first region and a second region are spaced apart on the surface of the base film. The second region is coated with the separator coating. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the tape delivery direction perpendicular to the third separator, the shortest distance D6 between two adjacent first regions on the surface of any base film is 5 mm to 150 mm. The third separator, satisfying the above characteristics, can reduce the possibility of lithium plating in the empty foil region and improve the safety performance of the secondary battery.

[0013] In one embodiment of this application, the ionic conductivity σ1 of the separator in the first region is from 0.1 mS / cm to 5 mS / cm. By controlling the ionic conductivity of the separator in the first region within the above range, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the volumetric energy density of the secondary battery can be further improved.

[0014] In one embodiment of this application, the porosity P1 of the separator in the first region is 30% to 45%. By adjusting the porosity of the separator in the first region within the above range, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the volumetric energy density of the secondary battery can be further improved.

[0015] In one embodiment of this application, the permeability G of the separator in the first region is between 6 s / 100 mL and 9 s / 100 mL. By adjusting the permeability of the separator in the first region within the above range, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the volumetric energy density of the secondary battery can be further improved.

[0016] In one embodiment of this application, the ionic conductivity σ2 of the separator in the second region is between 0 mS / cm and 0.1 mS / cm. By controlling the ionic conductivity of the separator in the second region within the above range, it is possible to effectively reduce lithium replenishment in the empty foil region, reduce the possibility of lithium deposition in the empty foil region, and improve the safety performance of the secondary battery.

[0017] In one embodiment of this application, the porosity P2 of the separator in the second region is 0 to 1%. By controlling the porosity of the separator in the second region within the above range, it is possible to effectively reduce lithium replenishment in the empty foil region, reduce the possibility of lithium deposition in the empty foil region, and improve the safety performance of the secondary battery.

[0018] In one embodiment of this application, the interfacial pressure p per unit area between the lithium replenishment composite layer and the negative electrode is 0.1 MPa to 0.6 MPa. By bonding the lithium replenishment composite layer and the negative electrode, and by controlling the interfacial pressure per unit area between the lithium replenishment composite layer and the negative electrode within the above-mentioned range during bonding, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the volumetric energy density of the secondary battery can be further improved.

[0019] In one embodiment of this application, the discharge treatment temperature T is between 25°C and 90°C. By controlling the discharge treatment temperature within the above range, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the volumetric energy density of the secondary battery can be further improved.

[0020] In one embodiment of this application, the areal density CW of the electrolyte on the pre-impregnated electrolyte separator is 3 g / mm². 2 Up to 60g / mm 2 Preferably, the areal density (CW) of the electrolyte on the pre-impregnated separator is 5 g / mm². 2 Up to 30g / mm 2 By controlling the areal density of the electrolyte on the pre-impregnated electrolyte separator within the aforementioned range, it is beneficial to quickly and appropriately replenish lithium in the negative electrode material layer region, and to reduce the possibility of lithium deposition in the empty foil region, thereby improving the safety performance of the secondary battery.

[0021] In one embodiment of this application, the thickness H2 of the lithium replenishment layer is 0.001 mm to 1 mm, preferably 0.005 mm to 0.1 mm. By adjusting the thickness of the lithium replenishment layer within the above range, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the volumetric energy density of the secondary battery can be further improved.

[0022] In one embodiment of this application, the thickness H3 of the support layer is from 3 μm to 50 μm, preferably from 5 μm to 20 μm. By adjusting the thickness of the support layer within the above range, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the volumetric energy density of the secondary battery can be further improved.

[0023] In one embodiment of this application, the support layer includes at least one of copper foil, nickel foil, steel foil, or copper-nickel alloy foil. By selecting the aforementioned support layer, which is a metallic material, high electronic conductivity is achieved, enabling electrochemical external short-circuit lithium replenishment. Furthermore, the support layer provides better support for the lithium replenishment layer, further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the volumetric energy density of the secondary battery.

[0024] In one embodiment of this application, along the tape direction of the lithium replenishment composite layer, the tensile strength K1 of the lithium replenishment layer (including the support layer) is from 0.5 N / 10 mm to 200 N / 10 mm, preferably from 1 N / 10 mm to 100 N / 10 mm. By controlling the tensile strength of the lithium replenishment layer within the above range, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the volumetric energy density of the secondary battery can be further improved.

[0025] A second aspect of this application provides a pre-lithiated negative electrode sheet prepared according to the lithium replenishment method in any of the foregoing embodiments. Applying the aforementioned pre-lithiated negative electrode sheet to a secondary battery can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, increase the volumetric energy density of the secondary battery, and also simplify the secondary battery manufacturing process and reduce costs.

[0026] A third aspect of this application provides a secondary battery comprising a pre-lithiated negative electrode as described in any of the foregoing embodiments. Therefore, the secondary battery provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high volumetric energy density, and its fabrication process is relatively simple and cost-effective.

[0027] A fourth aspect of this application provides an electronic device comprising the secondary battery of any of the foregoing embodiments. Therefore, the electronic device provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high volumetric energy density.

[0028] The beneficial effects of this application are:

[0029] This application provides a lithium replenishment method, a pre-lithiated negative electrode sheet, a secondary battery, and an electronic device. The lithium replenishment method includes the following steps: providing a negative electrode sheet, which includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. Providing a lithium replenishment composite layer, which includes a support layer, a lithium replenishment layer, and a separator pre-impregnated with electrolyte, wherein the lithium replenishment layer is disposed between the separator and the support layer. Bonding the lithium replenishment composite layer and the negative electrode sheet together, so that the separator is in contact with the negative electrode material layer, and performing a discharge treatment on the lithium replenishment composite layer and the negative electrode sheet, wherein the constant current discharge current I of the discharge treatment is 0.1C to 3C, and the discharge time t is 0.067h to 2h. After the discharge treatment is completed, peeling the lithium replenishment composite layer from the negative electrode sheet to obtain a pre-lithiated negative electrode sheet. By using the above-mentioned lithium replenishment method to replenish lithium on the negative electrode sheet, a pre-lithiated negative electrode sheet is obtained. Applying the pre-lithiated negative electrode sheet to a secondary battery can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the volumetric energy density of the secondary battery.

[0030] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0032] Figure 1 This is a schematic diagram of the negative electrode sheet during the lithium replenishment process according to one embodiment of this application;

[0033] Figure 2 This is a schematic diagram of the negative electrode sheet according to one embodiment of this application;

[0034] Figure 3 This is a schematic diagram of the negative electrode sheet according to another embodiment of this application;

[0035] Figure 4 This is a schematic diagram of the structure of the first isolation membrane according to one embodiment of this application;

[0036] Figure 5 This is a schematic diagram of the structure of the second isolation membrane according to one embodiment of this application;

[0037] Figure 6 This is a schematic diagram of the negative electrode sheet according to another embodiment of this application;

[0038] Figure 7 This is a schematic diagram of the structure of the third separator membrane according to one embodiment of this application. Detailed Implementation

[0039] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0040] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0041] The first aspect of this application provides a lithium replenishment method, comprising the following steps: (1) providing a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. It is understood that the aforementioned negative electrode sheet refers to a negative electrode sheet that has not been pre-lithiated. (2) providing a lithium replenishment composite layer, the lithium replenishment composite layer comprising a support layer, a lithium replenishment layer and a separator pre-impregnated with electrolyte, the lithium replenishment layer being disposed between the separator and the support layer. (3) bonding the lithium replenishment composite layer and the negative electrode sheet together, so that the separator is in contact with the negative electrode material layer, and performing a discharge treatment on the lithium replenishment composite layer and the negative electrode sheet, wherein the constant current discharge current I of the discharge treatment is 0.1C to 3C, and the discharge time t is 0.067h to 2h. (4) after the discharge treatment is completed, peeling the lithium replenishment composite layer from the negative electrode sheet to obtain a pre-lithiated negative electrode sheet.

[0042] For example, I can be 0.1C, 0.3C, 0.5C, 0.9C, 1C, 1.3C, 1.5C, 1.9C, 2C, 2.3C, 2.5C, 2.9C, 3C, or a range of any two of the above values; the value of t can be 0.067, 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.1, 1.3, 1.5, 1.7, 1.9, 2, or a range of any two of the above values.

[0043] In step (1), the negative electrode sheet can be dried until the water content is ≤500ppm. The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The aforementioned "negative electrode material layer disposed on at least one surface of the negative current collector" means that the negative electrode material layer can be disposed on one surface of the negative current collector along its own thickness direction, or it can be disposed on two surfaces of the negative current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative current collector or a part of the negative current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0044] In this application, the negative electrode material layer includes a negative electrode active material. The negative electrode active material includes at least one of graphite, hard carbon, silicon-carbon, or silicon-oxygen materials. The graphite material includes at least one of artificial graphite or natural graphite. In this application, the silicon-carbon material is a silicon-carbon composite material, wherein the mass percentage of silicon is 30% to 70%, and the mass percentage of carbon is 30% to 70% based on the mass of the silicon-carbon composite material. This application does not impose any particular limitation on the silicon-carbon composite material, as long as it achieves the purpose of this application. For example, the silicon-carbon composite material can be a composite material obtained by deposition. Exemplarily, the silicon-carbon composite material can be silicon material deposited on a carbon skeleton, or carbon material deposited on a silicon skeleton. The silicon-oxygen material includes SiOx, where 0 < x < 2. Exemplarily, the silicon-oxygen material can include silicon suboxide (SiO, where the molar ratio of silicon to oxygen is 1:1). The negative electrode material layer also includes a negative electrode binder and a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode binder, as long as it can achieve the purpose of this application. For example, the negative electrode binder may include at least one of the following: polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, lithium polyacrylate, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. This application does not impose any particular limitation on the type of negative electrode conductive agent, as long as it can achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of the following: conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned conductive carbon black may include, but is not limited to, at least one of Super P, acetylene black, or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or few-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, at least one of vapor-grown carbon fibers (VGCF) or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powder and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode binder, and negative electrode conductive agent in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0045] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (such as lithium copper composite current collectors, carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.). This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector may be 4 μm to 20 μm. This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided negative electrode material layer may be 30 μm to 250 μm.

[0046] In this application, step (3) involves bonding the lithium-filled composite layer and the negative electrode sheet, bringing the separator into contact with the negative electrode material layer. Specifically, as shown... Figure 1 As shown, for ease of understanding, the thickness direction of the negative electrode sheet and the lithium replenishment composite layer is defined as the Z direction. The negative electrode sheet includes a negative electrode current collector 14 and a negative electrode material layer 15 disposed on both surfaces of the negative electrode current collector 14. The lithium replenishment composite layer 10 includes a support layer 11, a lithium replenishment layer 12, and a separator 13 pre-impregnated with electrolyte. The lithium replenishment layer 12 is disposed between the separator 13 pre-impregnated with electrolyte and the support layer 11. The lithium replenishment composite layer 10 and the negative electrode sheet are bonded together so that the separator 13 contacts the negative electrode material layer 15. It can be understood that the above-mentioned negative electrode sheet refers to a negative electrode sheet that has not undergone pre-lithiation.

[0047] In this application, a voltage control system is used to discharge the lithium replenishment composite layer and the negative electrode. The positive terminal of the voltage control system is connected to the negative electrode, and the negative terminal is connected to the lithium replenishment layer. During this discharge process, the potential of the negative electrode is higher than that of the lithium replenishment layer. The negative electrode acts as the "positive electrode," and the lithium replenishment layer acts as the "negative electrode." Therefore, to achieve lithium replenishment on the negative electrode, allowing lithium ions to transfer from the lithium replenishment layer to the negative electrode, a discharge process is required.

[0048] This application does not impose any special restrictions on the environmental parameters during the lithium replenishment process, as long as the purpose of this application can be achieved. For example, the environmental parameters in step (1) can be temperature ≤30℃ and humidity ≤1.7%, the environmental parameters in step (2) can be temperature ≤30℃ and humidity ≤1.7%, the environmental parameters in step (3) can be humidity ≤1.7%, and the environmental parameters in step (4) can be temperature ≤30℃ and humidity ≤1.7%.

[0049] The inventors discovered that by using the lithium replenishment method provided in this application to replenish lithium in the negative electrode sheet, an electrochemical external short circuit can be formed between the lithium replenishment layer and the negative electrode material layer. Lithium atoms in the lithium replenishment layer undergo an oxidation reaction, losing electrons to generate lithium ions. These lithium ions are transported through a pre-impregnated electrolyte separator to the surface or interior of the negative electrode material layer. Electrons are transported through an external circuit to the negative electrode current collector and then to the surface or interior of the negative electrode material layer. Electrons and lithium ions undergo a reduction reaction in the negative electrode material layer to form a lithium intercalation compound, achieving pre-lithiation of the negative electrode material layer. This replenishes the active lithium lost during the first charge and discharge of the secondary battery due to the formation of the solid electrolyte interphase (SEI) film. This process also addresses the loss of active lithium during cycling. Furthermore, by controlling the discharge treatment conditions, a relatively dense and stable SEI film can be formed on the surface of the negative electrode, reducing the probability of the negative electrode active material being damaged by solvent molecule co-intercalation, improving lithium-ion transport efficiency, and reducing side reactions between the negative electrode and the electrolyte. Simultaneously, since a relatively dense and stable SEI film is formed during the above discharge treatment, the formation step can be omitted in the subsequent preparation of the secondary battery, reducing electrolyte consumption during the formation process and increasing the overall electrolyte content in the secondary battery. Furthermore, omitting the formation step can also improve the production efficiency of the secondary battery and reduce costs. Furthermore, since lithium replenishment is performed on the negative electrode using an electrochemical external short circuit, a pre-impregnated electrolyte separator is placed between the negative electrode material layer and the lithium replenishment layer. This separator has excellent ion-conducting ability, which reduces the probability of the lithium replenishment layer adhering to the surface of the negative electrode material layer. This reduces the impact of side reactions that may occur on the negative electrode material layer due to the high activity of lithium metal in the lithium replenishment layer on the electrochemical performance of the secondary battery. It also reduces the impact of residual silicone oil on the surface of the lithium replenishment layer entering the secondary battery and affecting its electrochemical performance. Therefore, the lithium replenishment method of this application produces a pre-lithiated negative electrode. Applying this pre-lithiated negative electrode to a secondary battery can improve the initial coulombic efficiency, reduce cycle capacity decay, increase the volumetric energy density of the secondary battery, simplify the secondary battery manufacturing process, and reduce costs.

[0050] In one embodiment of this application, the negative electrode sheet has a continuous structure. The aforementioned continuous structure refers to the continuous arrangement of the negative electrode material layer on the surface of the negative electrode current collector. For example... Figure 2 As shown, the negative electrode material layer 15 on the surface of the negative electrode current collector 14 is continuously disposed. Compared with the intermittent structure, the two negative electrode material layers at the end of the continuous structure do not contribute capacity and occupy the thickness, resulting in a relatively low volumetric energy density of the secondary battery. Since the negative electrode sheet is a continuous structure, the lithium replenishment method of this application can be used to replenish lithium on the above-mentioned negative electrode sheet, which can improve the initial coulombic efficiency of the secondary battery and reduce the cycle capacity decay.

[0051] In one embodiment of this application, the separator is a continuous structure, and the ionic conductivity σ3 of the separator is from 0.1 mS / cm to 5 mS / cm. Exemplarily, the value of σ3 can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range consisting of any two of the above values; and / or, the porosity P3 of the separator is from 30% to 45%. Exemplarily, the value of P3 can be 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45%, or a range consisting of any two of the above values. The range of values; and / or, the air permeability G1 of the separator is from 6 s / 100 mL to 9 s / 100 mL. Exemplarily, G1 can be 6 s / 100 mL, 6.3 s / 100 mL, 6.6 s / 100 mL, 6.9 s / 100 mL, 7 s / 100 mL, 7.3 s / 100 mL, 7.6 s / 100 mL, 7.9 s / 100 mL, 8 s / 100 mL, 8.3 s / 100 mL, 8.6 s / 100 mL, 8.9 s / 100 mL, 9 s / 100 mL, or a range consisting of any two of the above values. It is understood that when the negative electrode sheet has a continuous structure, the separator also has a corresponding continuous structure.

[0052] In one embodiment of this application, the negative electrode sheet has a gap structure, which includes a gap structure along the tape delivery direction or a gap structure perpendicular to the tape delivery direction. In this application, the tape delivery direction is also the MD direction, i.e., the length direction; the direction perpendicular to the tape delivery direction is also the TD direction, i.e., the width direction. The aforementioned gap structure refers to the negative electrode material layers on the surface of the negative electrode current collector being spaced apart, with empty foil areas between adjacent negative electrode material layers. The gap structure of the negative electrode sheet can effectively reduce the thickness of the secondary battery, further improving the volumetric energy density of the secondary battery; simultaneously, using the lithium replenishment method of this application to replenish the aforementioned negative electrode sheet can improve the initial coulombic efficiency of the secondary battery and reduce cycle capacity decay.

[0053] In one embodiment of this application, such as Figure 3As shown, when the negative electrode sheet is a gap structure along the tape-carrying direction, along the thickness direction of the negative electrode sheet, i.e., the Z direction, the negative electrode current collector 14 includes a first surface 141 and a second surface 142 opposite to each other; the first surface 141 and the second surface 142 are both provided with negative electrode material layer areas and empty foil areas at intervals; along the tape-carrying direction of the negative electrode sheet, i.e., the X direction, the shortest distance D1 between two adjacent negative electrode material layer areas on the first surface 141 is 5mm to 30mm, and the shortest distance D2 between two adjacent negative electrode material layer areas on the second surface 142 is 30mm to 150mm. For example, the value of D1 can be 5, 7, 9, 10, 13, 15, 17, 20, 23, 25, 27, 30, or a range of any two of the above values; the value of D2 can be 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or a range of any two of the above values. In one embodiment of this application, D1 < D2. The negative electrode sheet satisfies the above characteristics, which can effectively reduce the thickness of the secondary battery and reduce the amount of negative electrode active material used, thereby further improving the volumetric energy density of the secondary battery and reducing the cost of the secondary battery. It is understood that the dimension of the negative electrode material layer region along the X direction is the length of the negative electrode material layer region. In this application, the length of a single negative electrode material layer region on the first surface is 180 mm to 3000 mm; the length of a single negative electrode material layer region on the second surface is 60 mm to 2975 mm.

[0054] In one embodiment of this application, the separator includes a first separator, which is disposed opposite to a first surface. The first separator has a gap structure along the conveying direction. The first separator includes a base film and a separator coating disposed on at least one surface of the base film. The surface of the base film has a first region and a second region spaced apart. The second region is coated with the separator coating. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the conveying direction of the first separator, the shortest distance D3 between two adjacent first regions in the first separator is 5 mm to 30 mm. Exemplarily, the value of D3 can be 5, 7, 9, 10, 13, 15, 17, 20, 23, 25, 27, 30, or a range consisting of any two of the above values. In this application, "the first separator has a gap structure along the conveying direction" means that the separator coating on the surface of the base film in the first separator is spaced apart. The negative electrode sheet has a gap structure along the tape-running direction, and the first separator also has a corresponding gap structure along the tape-running direction. The first separator satisfies the above-mentioned characteristics, which can reduce the possibility of lithium plating in the empty foil area, improve the safety performance of the secondary battery, and effectively reduce the thickness of the secondary battery, further increasing the volumetric energy density. It can be understood that the dimension of the first region along the X direction is the length of the first region. In this application, the length of a single first region in the first separator is 180mm to 3000mm. Specifically, as shown... Figure 4 As shown, the first separator is a gap structure along the belt travel direction. The first separator includes a base film 21 and a separator coating disposed on two surfaces of the base film 21. A first region and a second region are disposed at intervals on the two surfaces of the base film 21. The separator coating is disposed in the second region. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the belt travel direction of the first separator, that is, the X direction, the shortest distance D3 between two adjacent first regions in the first separator is 5mm to 30mm.

[0055] In one embodiment of this application, the separator includes a second separator, which is disposed opposite to a second surface. The second separator has a gap structure along the conveyor belt direction. The second separator includes a base film and a separator coating disposed on at least one surface of the base film. A first region and a second region are spaced apart on the surface of the base film. The second region is coated with the separator coating. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the conveyor belt direction of the second separator, the shortest distance D4 between two adjacent first regions in the second separator is 30 mm to 150 mm. Exemplarily, the value of D4 can be 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or a range consisting of any two of the above values. In this application, "the second separator has a gap structure along the conveyor belt direction" means that the separator coating on the surface of the base film in the second separator is spaced apart. The negative electrode sheet has a gap structure along the tape-running direction, and the second separator also has a corresponding gap structure along the tape-running direction. The second separator satisfies the aforementioned characteristics, which can reduce the possibility of lithium plating in the empty foil area, improve the safety performance of the secondary battery, and effectively reduce the thickness of the secondary battery, further increasing its volumetric energy density. In this application, the length of a single first region in the second separator is 60 mm to 2975 mm. Specifically, as shown... Figure 5 As shown, the second separator has a gap structure along the belt travel direction. The second separator includes a base film 21 and a separator coating disposed on two surfaces of the base film 21. A first region and a second region are spaced apart on each surface of the base film 21. The separator coating is disposed in the second region. The first region is positioned opposite to the negative electrode material layer region, and the second region is positioned opposite to the empty foil region. Along the belt travel direction of the second separator, i.e., the X direction, the shortest distance D4 between two adjacent first regions in the second separator is 30 mm to 150 mm. In one embodiment of this application, D3 < D4.

[0056] In one embodiment of this application, the separator includes a first separator and a second separator. The first separator and a first surface are disposed opposite each other. The first separator has a gap structure along the belt travel direction. The first separator includes a base film and a separator coating disposed on at least one surface of the base film. The surface of the base film has a first region and a second region spaced apart. The second region has the separator coating disposed on it. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the belt travel direction of the first separator, the shortest distance D3 between two adjacent first regions in the first separator is 5 mm to 30 mm. The second separator and a second surface are disposed opposite each other. The second separator has a gap structure along the belt travel direction. The second separator includes a base film and a separator coating disposed on at least one surface of the base film. The surface of the base film has a first region and a second region spaced apart. The second region has the separator coating disposed on it. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the belt travel direction of the second separator, the shortest distance D4 between two adjacent first regions in the second separator is 30 mm to 150 mm. The negative electrode sheet has a gap structure along the tape direction, and the first and second separators also have gap structures along the tape direction. The first and second separators satisfy the above characteristics, which can reduce the possibility of lithium plating in the empty foil area, further improve the safety performance of the secondary battery, and also effectively reduce the thickness of the secondary battery, further improving the volumetric energy density of the secondary battery.

[0057] In one embodiment of this application, when the negative electrode sheet is a gap structure perpendicular to the tape direction, the surface of the negative electrode current collector is provided with a negative electrode material layer region and an empty foil region at intervals; along the tape direction perpendicular to the negative electrode sheet, the shortest distance D5 between two adjacent negative electrode material layer regions on the surface of any negative electrode current collector is 5 mm to 150 mm. For example, the value of D5 can be 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or a range of any two of the above values. The negative electrode sheet, satisfying the above characteristics, can reduce the amount of negative electrode active material used, reducing the cost of the secondary battery; the empty foil region after die-cutting the negative electrode sheet can serve as a tab region, reducing the impedance of the secondary battery, improving the dynamic performance of the secondary battery, and increasing the capacity of the secondary battery. It is understood that the dimension of the negative electrode material layer region along the Y direction is the width of the negative electrode material layer region. In this application, the width of a single negative electrode material layer region is 30 mm to 150 mm. Specifically, as shown... Figure 6 As shown, when the negative electrode sheet is a gap structure perpendicular to the tape direction, the surface of the negative electrode current collector (not shown in the figure) is provided with negative electrode material layer region 151 and empty foil region 152 at intervals; along the tape direction perpendicular to the negative electrode sheet, that is, the Y direction, the shortest distance D5 between two adjacent negative electrode material layer regions 151 on one surface of the negative electrode current collector is 5mm to 150mm.

[0058] In one embodiment of this application, the separator includes a third separator, which is a gap structure perpendicular to the tape delivery direction. The third separator includes a base film and a separator coating disposed on at least one surface of the base film. A first region and a second region are spaced apart on the surface of the base film. The second region is coated with the separator coating. The first region is disposed opposite to the negative electrode material layer region, and the second region is disposed opposite to the empty foil region. Along the tape delivery direction perpendicular to the third separator, the shortest distance D6 between two adjacent first regions on the surface of any base film is 5 mm to 150 mm. Exemplarily, the value of D6 can be 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or a range consisting of any two of the above values. The negative electrode sheet is a gap structure perpendicular to the tape delivery direction, and the third separator also has a corresponding gap structure perpendicular to the tape delivery direction. Since the third separator satisfies the above characteristics, it can reduce the possibility of lithium plating in the empty foil region and improve the safety performance of the secondary battery. It is understood that the dimension of the first region along the Y direction is the width of the first region. In this application, the width of a single first region is 30mm to 150mm. Specifically, as shown... Figure 7 As shown, the third separator is a gap structure perpendicular to the belt conveyor direction. The third separator includes a base film (not shown) and a separator coating disposed on one surface of the base film. A first region 201 and a second region 202 are disposed at intervals on the surface of the base film. The second region 202 is disposed with the separator coating. The first region 201 is disposed opposite to the negative electrode material layer region, and the second region 202 is disposed opposite to the empty foil region. Along the belt conveyor direction perpendicular to the third separator, i.e., the Y direction, the shortest distance D6 between two adjacent first regions 201 on the surface of the base film is 5 mm to 150 mm.

[0059] In one embodiment of this application, the ionic conductivity σ1 of the separator in the first region is from 0.1 mS / cm to 5 mS / cm. Exemplarily, the value of σ1 can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a range consisting of any two of the above values. In this application, the ionic conductivity of the first, second, and third separators in the first region are all within the above range. The porosity and permeability of the separator in the first region affect the ionic conductivity of the separator in the first region, thereby affecting the constant current discharge current during the lithium replenishment process. By controlling the ionic conductivity of the separator in the first region within the aforementioned range, a suitable constant current discharge current can be achieved during the electrochemical external short-circuit lithium replenishment process, reducing the possibility of lithium deposition in the negative electrode material layer. Furthermore, it facilitates rapid and appropriate lithium replenishment in the negative electrode material layer, effectively replenishing the active lithium lost during the initial charge and discharge of the secondary battery due to SEI film formation, as well as the active lithium lost during cycling. This further improves the initial coulombic efficiency of the secondary battery, further reduces cycle capacity decay, and further increases the volumetric energy density of the secondary battery. This application does not impose any particular limitation on the method of controlling the ionic conductivity of the separator in the first region, as long as the purpose of this application is achieved. For example, the ionic conductivity of the separator in the first region can be controlled by adjusting the porosity and / or permeability of the separator. Exemplarily, increasing the porosity of the separator in the first region increases its ionic conductivity; decreasing the porosity of the separator in the first region decreases its ionic conductivity. For example, if the air permeability of the separator in the first region increases, the ionic conductivity of the separator in the first region increases; if the air permeability of the separator in the first region decreases, the ionic conductivity of the separator in the first region decreases.

[0060] In one embodiment of this application, the porosity P1 of the separator in the first region is 30% to 45%. Exemplarily, the value of P1 can be 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45%, or a range consisting of any two of the above values. In this application, the porosity of the first, second, and third separators in the first region is within the above range. By controlling the porosity of the separator in the first region within the above range, the separator in the first region can have a suitable ionic conductivity, enabling a suitable constant current discharge current during the electrochemical external short-circuit lithium replenishment process, reducing the possibility of lithium deposition in the negative electrode material layer region; and facilitating rapid and appropriate lithium replenishment in the negative electrode material layer region, effectively replenishing the active lithium lost during the first charge and discharge of the secondary battery due to the formation of the SEI film and the active lithium lost during cycling, further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further improving the volumetric energy density of the secondary battery. This application does not impose any particular limitation on the method of controlling the porosity of the separator membrane in the first region, as long as the purpose of this application can be achieved. For example, the porosity of the separator membrane in the first region can be controlled by adjusting the amount of pore-forming agent added during the preparation of the separator membrane base film or by adjusting the tensile force during the preparation of the separator membrane base film.

[0061] In one embodiment of this application, the air permeability G of the separator membrane in the first region is between 6 s / 100 mL and 9 s / 100 mL. Exemplarily, G can be 6 s / 100 mL, 6.3 s / 100 mL, 6.6 s / 100 mL, 6.9 s / 100 mL, 7 s / 100 mL, 7.3 s / 100 mL, 7.6 s / 100 mL, 7.9 s / 100 mL, 8 s / 100 mL, 8.3 s / 100 mL, 8.6 s / 100 mL, 8.9 s / 100 mL, 9 s / 100 mL, or a range consisting of any two of the above values. In this application, the air permeability of the first separator membrane, the second separator membrane, and the third separator membrane in the first region are all within the above range. By controlling the permeability of the separator in the first region within the aforementioned range, the separator in the first region can possess suitable ionic conductivity, enabling a suitable constant current discharge current during the electrochemical external short-circuit lithium replenishment process, thereby reducing the possibility of lithium deposition in the negative electrode material layer. Furthermore, it facilitates rapid and appropriate lithium replenishment in the negative electrode material layer, effectively replenishing the active lithium lost during the initial charge and discharge of the secondary battery due to SEI film formation, as well as the active lithium lost during cycling. This further improves the initial coulombic efficiency of the secondary battery, further reduces cycle capacity decay, and further increases the volumetric energy density of the secondary battery. This application does not impose any particular limitation on the method of controlling the permeability of the separator in the first region, as long as the objectives of this application are achieved. For example, the permeability of the separator in the first region can be controlled by adjusting the amount of pore-forming agent added during the preparation of the separator base film or the tensile force during the preparation of the separator base film.

[0062] In one embodiment of this application, the ionic conductivity σ2 of the separator in the second region is from 0 mS / cm to 0.1 mS / cm. Exemplarily, the value of σ2 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a range consisting of any two of the above values. In this application, the ionic conductivity of the first, second, and third separators in the second region are all within the above range. By controlling the ionic conductivity of the separator in the second region to be within the above range, the ionic conductivity of the separator in the second region is relatively low, making lithium-ion transport more difficult. This effectively reduces the need for lithium replenishment in the empty foil region, decreases the possibility of lithium deposition in the empty foil region, and improves the safety performance of the secondary battery. This application does not particularly limit the method of controlling the ionic conductivity of the separator in the second region, as long as the purpose of this application can be achieved. For example, the ionic conductivity of the separator in the second region can be controlled by controlling the porosity of the separator in the second region. For example, if the porosity of the isolation membrane in the second region increases, the ionic conductivity of the isolation membrane in the second region increases; if the porosity of the isolation membrane in the second region decreases, the ionic conductivity of the isolation membrane in the second region decreases.

[0063] In one embodiment of this application, the porosity P2 of the separator in the second region is 0 to 1%. Exemplarily, the value of P2 can be 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range consisting of any two of the above values. In this application, the porosities of the first, second, and third separators in the second region are all within the above range. By controlling the porosity of the separator in the second region to be within the above range, the porosity of the separator in the second region is smaller, the ionic conductivity of the separator in the second region is smaller, lithium-ion transport is more difficult, which can effectively reduce the need for lithium replenishment in the empty foil region, reduce the possibility of lithium deposition in the empty foil region, and improve the safety performance of the secondary battery. This application does not particularly limit the method of controlling the porosity of the separator in the second region, as long as the purpose of this application can be achieved. For example, the porosity of the separator in the second region can be controlled by adjusting the areal density of the separator coating.

[0064] In one embodiment of this application, the interfacial pressure p per unit area between the lithium replenishment composite layer and the negative electrode is 0.1 MPa to 0.6 MPa. Exemplarily, the value of p can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, or a range of any two of the above values. By bonding the lithium replenishment composite layer and the negative electrode, and adjusting the interfacial pressure per unit area between them within the above range during bonding, the lithium replenishment layer adheres more tightly to the pre-impregnated electrolyte separator, resulting in lower interfacial impedance, higher impedance uniformity, higher lithium replenishment efficiency, and higher lithium replenishment uniformity. This further improves the initial coulombic efficiency of the secondary battery, further reduces cycle capacity decay, and further increases the volumetric energy density of the secondary battery.

[0065] This application does not impose any particular restrictions on the bonding method between the lithium-filled composite layer and the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the bonding method between the lithium-filled composite layer and the negative electrode sheet can be winding into a roll or pressing into a sheet. This application does not impose any particular restrictions on the method for controlling the interfacial pressure per unit area between the lithium-filled composite layer and the negative electrode sheet, as long as the purpose of this application can be achieved. For example, when the lithium-filled composite layer and the negative electrode sheet are wound into a roll, the interfacial pressure per unit area between the lithium-filled composite layer and the negative electrode sheet can be controlled by adjusting the winding tension. When other conditions remain unchanged, increasing the winding tension increases the interfacial pressure per unit area; decreasing the winding tension decreases the interfacial pressure per unit area. For example, when the lithium-filled composite layer and the negative electrode sheet are pressed into a sheet, the interfacial pressure per unit area between the lithium-filled composite layer and the negative electrode sheet can be controlled by adjusting the pressing pressure. When other conditions remain unchanged, increasing the pressing pressure increases the interfacial pressure per unit area; decreasing the pressing pressure decreases the interfacial pressure per unit area.

[0066] In one embodiment of this application, the discharge treatment temperature T is between 25°C and 90°C. Exemplarily, the value of T can be 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or a range consisting of any two of the above values. By controlling the discharge treatment temperature within the above range, combined with a suitable constant current discharge during the discharge treatment process, the possibility of lithium deposition in the negative electrode material layer can be reduced; the possibility of electrolyte solvent evaporation can also be reduced, resulting in a suitable electrolyte viscosity and thus a suitable ionic conductivity. This provides a higher lithium replenishment rate and a suitable amount of lithium replenishment, effectively replenishing the active lithium lost during the first charge and discharge of the secondary battery due to the formation of the SEI film, as well as the active lithium lost during cycling. This further improves the initial coulombic efficiency of the secondary battery, further reduces cycle capacity decay, and further increases the volumetric energy density of the secondary battery.

[0067] In one embodiment of this application, the areal density CW of the electrolyte on the pre-impregnated electrolyte separator is 3 g / mm². 2 Up to 60g / mm 2 Preferably, the areal density (CW) of the electrolyte on the pre-impregnated separator is 5 g / mm². 2 Up to 30g / mm 2 For example, the value of CW can be 3, 5, 7, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or a range of any two of the above values. By adjusting the areal density of the electrolyte on the pre-impregnated electrolyte separator within the above range, the electrolyte on the separator has a suitable areal density, enabling a suitable constant current discharge current for the electrochemical external short-circuit lithium replenishment process. This facilitates rapid and appropriate lithium replenishment to the negative electrode material layer region and reduces the possibility of lithium deposition in the empty foil region, thereby improving the safety performance of the secondary battery. This application does not impose any particular limitation on the method of adjusting the areal density of the electrolyte on the pre-impregnated electrolyte separator, as long as the purpose of this application can be achieved. For example, the areal density of the electrolyte on the pre-impregnated electrolyte separator can be adjusted by controlling the immersion time of the separator in the electrolyte. Generally, when other conditions remain constant, increasing the immersion time of the separator in the electrolyte increases the surface density of the electrolyte on the separator pre-impregnated with electrolyte; conversely, decreasing the immersion time decreases the surface density of the electrolyte on the separator pre-impregnated with electrolyte. The type of separator and the composition ratio of the electrolyte also typically affect the surface density of the electrolyte on the separator pre-impregnated with electrolyte.

[0068] In one embodiment of this application, the elongation of the separator under a tensile force of 2N / 10mm to 4N / 10mm is 0% to 1%. Exemplarily, the elongation of the separator under a tensile force of 2N / 10mm to 4N / 10mm can be 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range consisting of any two of the above values. A separator satisfying the above characteristics has high mechanical strength and is less prone to breakage during lithium replenishment, which is beneficial for improving lithium replenishment efficiency.

[0069] In one embodiment of this application, the tensile strength of the separator membrane along the conveyor belt direction is 4000 kg / cm². 2 Up to 7000 kg / cm 2 The tensile strength perpendicular to the conveyor belt direction is 2000 kg / cm². 2 Up to 4000 kg / cm 2 For example, the tensile strength of the separator membrane along the conveyor belt direction can be 4000 kg / cm². 2 4500kg / cm 2 5000kg / cm 2 5500kg / cm 2 6000kg / cm 2 6500kg / cm 2 7000kg / cm 2 Or it can be a range consisting of any two of the above values; the tensile strength of the separator along the direction perpendicular to the conveyor belt can be 2000 kg / cm². 2 2500kg / cm 2 3000kg / cm 2 3500kg / cm 2 4000kg / cm 2 Or it can be a range consisting of any two of the above values. A separator that meets these characteristics has high mechanical strength and is less prone to breakage during lithium replenishment, which helps improve lithium replenishment efficiency.

[0070] The separator in this application is reusable, provided it remains undamaged after lithium replenishment. For example, the separator can be reused more than 5 times. The initial coulombic efficiency of the pre-lithiated negative electrode sheet prepared using the separator in the first use in a secondary battery is a1, and the initial coulombic efficiency of the pre-lithiated negative electrode sheet prepared using the i-th use in a secondary battery is a. i a i / a1 is 99% to 100%, and i is 1 to 15, indicating that the reusable separator has little impact on the initial coulombic efficiency of the secondary battery and can be maintained at a high level, which is beneficial to reducing the cost of the preparation process.

[0071] This application does not impose any particular limitation on the thickness of the base film, as long as it achieves the purpose of this application. For example, the thickness of the base film can be from 4 μm to 20 μm. This application also does not impose any particular limitation on the material of the base film, as long as it achieves the purpose of this application. For example, the material of the base film can include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of base film can include at least one of woven film, nonwoven film, microporous film, composite film, rolled film, or spun film. This application does not impose any particular limitation on the thickness of the separator coating, as long as it achieves the purpose of this application. For example, the thickness of the separator coating can be from 3 μm to 20 μm.

[0072] This application does not impose any particular limitation on the electrolyte pre-impregnated in the separator membrane, as long as it achieves the purpose of this application. The electrolyte includes lithium salts. This application does not impose any particular limitation on the type of lithium salt; lithium salts known in the art can be used. Exemplarily, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), or lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB). This application does not impose any particular limitation on the mass percentage of lithium salt in the electrolyte, as long as it achieves the purpose of this application. The electrolyte also includes non-aqueous organic solvents. This application does not impose any particular limitation on non-aqueous organic solvents, as long as they achieve the purpose of this application. For example, the non-aqueous organic solvent may contain at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.The other organic solvents mentioned above may include, but are not limited to, at least one of 1,3-propanesulfonyl lactone, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters. This application does not impose any particular limitation on the mass percentage of non-aqueous organic solvents in the electrolyte, as long as the purpose of this application is achieved.

[0073] In one embodiment of this application, the lithium replenishment layer comprises at least one of lithium foil or lithium alloy foil. The lithium alloy foil may include, but is not limited to, lithium-aluminum alloy, lithium-magnesium alloy, lithium-nickel alloy, or lithium-silicon alloy.

[0074] In one embodiment of this application, the thickness H2 of the lithium replenishment layer is 0.001 mm to 1 mm, preferably 0.005 mm to 0.1 mm. Exemplarily, the value of H2 can be 0.001, 0.003, 0.005, 0.007, 0.009, 0.01, 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1, or a range of any two of the above values. By adjusting the thickness of the lithium replenishment layer within the above range, the lithium replenishment layer has a suitable thickness, which can better meet the lithium replenishment requirements, facilitating further lithium replenishment to the negative electrode, further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further improving the volumetric energy density of the secondary battery. Furthermore, a lithium replenishment layer thickness within the above range can also save costs. This application does not particularly limit the method of adjusting the thickness of the lithium replenishment layer, as long as the purpose of this application is achieved. For example, the thickness of the lithium replenishment layer can be controlled by adjusting the rolling pressure or calendering force during the preparation of the lithium replenishment layer.

[0075] In one embodiment of this application, the thickness H3 of the support layer is from 3 μm to 50 μm, preferably from 5 μm to 20 μm. Exemplarily, the value of H3 can be 3, 4, 5, 7, 9, 10, 13, 15, 17, 19, 20, 25, 30, 35, 40, 45, 50, or a range of any two of the above values. By adjusting the thickness of the support layer within the above range, the support layer has a suitable thickness, enabling it to have higher mechanical strength. This better meets the requirement of peeling the lithium-replenishing composite layer from the surface of the negative electrode material layer after lithium replenishment, reducing the possibility of fracture in the lithium-replenishing composite layer. This facilitates further lithium replenishment to the negative electrode sheet, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the volumetric energy density of the secondary battery. In this application, commercially available support layers of different thicknesses can be selected; there are no particular limitations, as long as the purpose of this application can be achieved.

[0076] In one embodiment of this application, the support layer includes at least one of copper foil, nickel foil, steel foil, or copper-nickel alloy foil. By selecting the aforementioned support layer, a metallic material is chosen, which possesses high electronic conductivity, enabling electrochemical external short-circuit lithium replenishment. Furthermore, the support layer provides better support for the lithium replenishment layer, further improving the mechanical strength of the lithium replenishment composite layer. This allows the lithium replenishment composite layer to be more easily peeled from the surface of the negative electrode material layer after lithium replenishment, reducing the possibility of breakage of the lithium replenishment composite layer. This facilitates further lithium replenishment to the negative electrode sheet, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the volumetric energy density of the secondary battery.

[0077] In one embodiment of this application, along the tape direction of the lithium replenishment composite layer, the tensile strength K1 of the lithium replenishment layer (including the support layer) is from 0.5 N / 10 mm to 200 N / 10 mm. Preferably, the tensile strength K1 of the lithium replenishment layer (including the support layer) is from 1 N / 10 mm to 100 N / 10 mm. Exemplarily, K1 can be 0.5 N / 10 mm, 1 N / 10 mm, 10 N / 10 mm, 20 N / 10 mm, 30 N / 10 mm, 40 N / 10 mm, 50 N / 10 mm, 60 N / 10 mm, 70 N / 10 mm, 80 N / 10 mm, 90 N / 10 mm, 100 N / 10 mm, 150 N / 10 mm, 200 N / 10 mm, or a range consisting of any two of the above values. By adjusting the tensile strength of the lithium replenishment layer within the aforementioned range, the lithium replenishment layer exhibits both high tensile strength and high mechanical strength. This allows the lithium replenishment composite layer to be more easily peeled off from the surface of the negative electrode material layer after lithium replenishment, reducing the possibility of fracture in the lithium replenishment composite layer. This facilitates further lithium replenishment to the negative electrode sheet, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the volumetric energy density of the secondary battery.

[0078] This application does not impose any particular limitation on the preparation method of the lithium replenishment layer, as long as it achieves the purpose of this application. For example, under the conditions of ambient temperature ≤30℃ and humidity ≤1.7%, lithium metal powder slurry is coated onto the support layer, dried, and rolled to form the lithium replenishment layer; or lithium foil and / or lithium alloy foil is rolled onto the support layer to form the lithium replenishment layer; or lithium or lithium alloy molten slurry is coated onto the support layer, cooled, and rolled to form the lithium replenishment layer. This application does not impose any particular limitation on the rolling pressure during the preparation of the above-mentioned lithium replenishment layer, as long as it achieves the purpose of this application. For example, the rolling pressure p1 can be from 0.1T / 10mm to 2T / 10mm. Specifically, the rolling pressure p11 for rolling the lithium metal powder slurry onto the support layer can be from 0.1T / 10mm to 2T / 10mm; the rolling pressure p12 for rolling the lithium foil and / or lithium alloy foil onto the support layer can be from 0.1T / 10mm to 2T / 10mm; and the rolling pressure p13 for rolling the lithium or lithium alloy molten slurry onto the support layer can be from 0.1T / 10mm to 2T / 10mm.

[0079] This application does not impose any particular limitation on the preparation method of the gap-structured negative electrode sheet, as long as it can achieve the purpose of this application. For example, the preparation method of the gap-structured negative electrode sheet may include the following steps: uniformly mixing negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode solvent to obtain a negative electrode slurry; using extrusion gap coating, gap-coating the negative electrode slurry onto one surface of the negative electrode current collector along the conveying direction, and drying to obtain a negative electrode sheet with a single-sided gap-coated negative electrode material layer; then repeating the above steps on the other surface of the negative electrode current collector to obtain a negative electrode sheet with a double-sided gap-coated negative electrode material layer. For example, the preparation method of the negative electrode sheet with gap structure may include the following steps: mixing negative electrode active material, negative electrode conductive agent, negative electrode binder and negative electrode solvent evenly to obtain negative electrode slurry; using extrusion gap coating, coating the negative electrode slurry gap onto one surface of the negative electrode current collector along the direction perpendicular to the conveyor belt, drying, to obtain a negative electrode sheet with a single-sided gap-coated negative electrode material layer; then repeating the above steps on the other surface of the negative electrode current collector to obtain a negative electrode sheet with a double-sided gap-coated negative electrode material layer.

[0080] This application does not impose any particular limitation on the preparation method of the gap-structured separator membrane, as long as it can achieve the purpose of this application. Exemplarily, the preparation method of the gap-structured separator membrane may include the following steps: uniformly mixing a polymer, inorganic ceramic, and a solvent to obtain a separator membrane coating slurry; applying the separator membrane coating slurry to one surface of a base film along the conveyor belt direction using extrusion gap coating or gravure gap coating (the second region is coated with the separator membrane coating, and the first region is not coated with the separator membrane coating); drying to obtain a single-sided gap-coated separator membrane; then repeating the above steps on another surface of the base film to obtain a double-sided gap-coated separator membrane. Exemplarily, the preparation method of the gap-structured separator membrane may include the following steps: uniformly mixing a polymer, inorganic ceramic, and a solvent to obtain a separator membrane coating slurry; applying the separator membrane coating slurry to one surface of a base film along the conveyor belt direction perpendicular to the conveyor belt direction (the second region is coated with the separator membrane coating, and the first region is not coated with the separator membrane coating); drying to obtain a single-sided gap-coated separator membrane; then repeating the above steps on another surface of the base film to obtain a double-sided gap-coated separator membrane. The polymers mentioned above include, but are not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene copolymer; inorganic ceramics include, but are not limited to, at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate; solvents include, but are not limited to, water or N-methylpyrrolidone (NMP).

[0081] A second aspect of this application provides a pre-lithiated negative electrode sheet prepared according to the lithium replenishment method in any of the foregoing embodiments. Applying the aforementioned pre-lithiated negative electrode sheet to a secondary battery can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, increase the volumetric energy density of the secondary battery, and also simplify the secondary battery manufacturing process and reduce costs.

[0082] A third aspect of this application provides a secondary battery comprising a pre-lithiated negative electrode as described in any of the foregoing embodiments. Therefore, the secondary battery provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high volumetric energy density, and its fabrication process is relatively simple and cost-effective.

[0083] In this application, the secondary battery further includes a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a portion of it; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0084] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0085] The positive electrode material layer of this application includes a positive electrode active material, which comprises a substance capable of reversibly inserting and extracting active ions such as lithium ions. The positive electrode material layer can be one or more layers, and each layer in a multilayer positive electrode material layer can contain the same or different positive electrode active materials. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The aforementioned lithium nickel cobalt manganese oxide can include LiNi... 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3At least one of O2 (NCM111). The positive electrode material layer of this application also includes a positive electrode conductive agent and a positive electrode binder. This application does not have any particular limitations on the positive electrode conductive agent and the positive electrode binder, as long as the purpose of this application can be achieved. For example, the positive electrode conductive agent may include at least one of the above-mentioned negative electrode conductive agents; the positive electrode binder may include at least one of the above-mentioned negative electrode binders. This application does not have any particular limitations on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0086] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be from 6 μm to 25 μm. This application also does not impose any particular limitation on the thickness of the positive electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of a single-sided positive electrode material layer can be from 25 μm to 250 μm.

[0087] In this application, the secondary battery also includes an electrolyte. This application does not impose any particular limitations on the electrolyte in the secondary battery, as long as it achieves the purpose of this application. For example, the electrolyte in the secondary battery can be the same as or different from the electrolyte pre-impregnated in the separator of the lithium replenishment composite layer.

[0088] In this application, the secondary battery also includes a separator. This application does not impose any particular limitations on the separator in the secondary battery, as long as it achieves the purpose of this application. For example, the separator in the secondary battery can be the same as or different from the separator in the lithium replenishment composite layer.

[0089] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, pre-lithiated negative electrode, electrolyte, and other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application.

[0090] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. In this application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc.

[0091] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, pre-lithiated negative electrode, and separator in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, pre-lithiated negative electrode, and separator in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0092] A fourth aspect of this application provides an electronic device comprising the secondary battery of any of the foregoing embodiments. Therefore, the electronic device provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high volumetric energy density.

[0093] This application does not specifically limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0094] Example

[0095] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0096] Test methods and equipment:

[0097] Ionic conductivity tests of the separator membranes in the first and second regions:

[0098] (1) Sample preparation of the isolation membrane: Cut the sample to be tested (isolation membrane of the first region) into the same size (45.3mm×33.7mm), and bake the sample to be tested in an environment of 60℃ for more than 4 hours, and then quickly put it into the glove box for later use.

[0099] (2) Preparation of blank symmetric battery packaging bags: Using copper foil (14μm thick) as the current collector, blank symmetric battery packaging bags without separators are assembled. Before use, the packaging bags are baked at 60℃ for more than 4 hours and then quickly placed in a glove box for later use.

[0100] (3) Preparation of single-sided negative electrode: Cut the single-sided negative electrode into a size of 23mm×38.5mm, which will be used as the electrode for measuring the ionic conductivity of the separator. After baking in vacuum at 105℃ for more than 4 hours, put it into the glove box for later use.

[0101] (4) Symmetrical cell assembly: Assemble a symmetrical cell with negative electrode to negative electrode in a blank symmetrical cell packaging bag. In a glove box, assemble a separator with different numbers of layers (1, 2, 3, 4 layers) in situ to the middle of the symmetrical electrode to form a symmetrical cell (assemble 4 parallel samples of each number of layers of symmetrical cell). Seal the packaging bag with a simple sealing machine, then inject the electrolyte (300μL) with a pipette, and finally seal the bottom.

[0102] (5) Installing symmetrical cells into the fixture: Place the packaged symmetrical cells in the glove box overnight to allow the electrolyte to fully wet the separator.

[0103] (6) Electrochemical Impedance Spectroscopy (EIS) Test: Before measuring EIS, symmetrical cells with different numbers of separator layers were placed in a high-low temperature chamber at 45°C for half an hour, and the EIS at the set temperature was measured. The test conditions for EIS were: the frequency range was set to 1MHz to 1kHz, and the perturbation voltage was set to 5mV. The ionic conductivity σ1 of the separator in the first region was calculated based on the test results.

[0104] A scatter plot of the resistance values ​​obtained from symmetrical cells with different numbers of separator layers against the number of layers n is plotted, and then a linear fit is performed. The slope is the resistance value k of the separator. The ionic conductivity σ1 of the separator in the first region can be calculated according to the following formula.

[0105] The ionic conductivity of the isolation membrane in the first region is σ1 = l0 / (k×S); where l0 is the thickness of a single-layer isolation membrane, and S is the effective area (153.86 mm²) of the isolation membrane capable of transmitting ions when the impedance is tested. 2 .

[0106] The composition and preparation method of the electrolyte are the same as in Example 1-1, and the preparation method of the single-sided negative electrode sheet is as follows:

[0107] The negative electrode slurry from Example 1-1 was uniformly coated onto one surface of a 12 μm thick copper foil used as a negative electrode current collector. The coating was then dried at 90°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. This was dried under vacuum at 90°C for 1 hour, followed by cold pressing to obtain a single-sided negative electrode sheet. The areal density of the negative electrode material layer was 2.3 mg / cm³. 2 The compaction density during the cold pressing process is 1.0 g / cm³. 3 .

[0108] (7) Refer to steps (1) to (6) to test the ionic conductivity σ2 of the isolation membrane in the second region.

[0109] Porosity testing of the isolation membranes in the first and second regions:

[0110] (1) Sample preparation: Take the isolation film of the first region, wrap it with weighing paper on the top and bottom, lay it flat on the die, and press it with a punch to obtain 40 round samples with a diameter of 16mm. Test the thickness of the round sample and take its average value h1.

[0111] (2) Test: The 40 disc samples obtained in step (1) are placed into the sample cup of the true density instrument (model AccuPyc II1340), the lid is tightened, the test is performed 3 times, the average value of the test results is taken and recorded as the true volume V2 of the disc sample, and the test temperature is also recorded.

[0112] (3) Results analysis: The apparent volume of the disc sample V1 = s × h1 × number of disc samples, where s is the surface area of ​​the disc sample and h1 is the thickness of the disc sample; the porosity of the disc sample is obtained according to the porosity = (V1-V2) / V1 × 100%, which is the porosity of the isolation membrane in the first region.

[0113] (4) Refer to steps (1) to (3) to take the isolation membrane of the second region and test the porosity of the isolation membrane of the second region.

[0114] Air permeability test of the isolation membrane in the first region:

[0115] (1) Lift and fix the upper cylinder of the air permeability tester (model: Langguang TQD-G1);

[0116] (2) Unscrew the bottom stopcock of the air permeability tester, and place the isolation membrane (size greater than 6.5cm) in the first area. 2 Place the rectangular sample on the bottom disk and then tighten the stopcock;

[0117] (3) Gently lower the cylinder. When the white area on the cylinder passes the sensor, the digital timer will start counting automatically.

[0118] (4) When the white area has completely passed through the sensor, the digital timer will automatically stop timing and record the value on the digital timer, which is the air permeability of the isolation membrane in the first area.

[0119] Test of the areal density of electrolyte on the pre-impregnated separator:

[0120] Before the separator is immersed in the electrolyte, weigh the separator and record the mass as M1 g, and measure the area of ​​the separator and record it as S mm. 2 After the separator membrane is soaked in the electrolyte, its mass is measured and recorded as M2 g. The areal density (g / mm²) of the electrolyte on the pre-soaked separator membrane is also measured. 2 ) = (M2-M1) / S.

[0121] Thickness testing of lithium replenishment layer and support layer:

[0122] Place the sample to be tested on the table, level it, and then measure its thickness as required. Wipe the measuring face of the dial indicator with a non-woven cloth; press the measuring linkage mechanism to make the two measuring faces fully contact, and press the "zero" key; make contact between the two measuring faces of the dial indicator and the face of the sample to be tested, read the displayed data, and record the reading. Measure at 70mm intervals along the direction perpendicular to the belt travel (i.e., the TD direction), and at 100mm intervals along the belt travel direction (i.e., the MD direction); test 12 points along the TD direction of the sample to be tested; test 12 points along the MD direction of the sample to be tested; test a total of 24 points; take the average thickness of the 24 points as the thickness of the sample to be tested.

[0123] Using the support layer as the sample to be tested, the thickness H3 of the support layer is obtained.

[0124] By combining the support layer and the lithium replenishment layer as the sample to be tested, the total thickness H of the support layer and the lithium replenishment layer is obtained. 支撑层&补锂 Layer; Total thickness H of the support layer and the lithium replenishment layer 支撑层&补锂层 The difference between the thickness H3 and the thickness H2 of the lithium replenishment layer is the thickness H2 of the lithium replenishment layer, i.e., H2 = H 支撑层&补锂层 -H3.

[0125] Tensile strength test of lithium replenishment layer:

[0126] The tensile strength test procedure in the MD direction is as follows: Cut the lithium-filled layer (including the support layer) into a standard test specimen (width W = 16 mm, length L = 150 mm), where the width W of the standard test specimen is along the TD direction and the length L is along the MD direction. Using a tensile testing machine (model Instron 3365), clamp both ends of the standard test specimen in the upper and lower clamps of the tensile testing machine, ensuring the standard test specimen is centered and free from folding or twisting. Apply a tensile force at a constant speed of 50 mm / min until the standard test specimen breaks, and record the load and the corresponding elongation. Calculate the tensile strength in the MD direction according to the following formula:

[0127] Tensile strength in the MD direction = F1 / W; where F1 is the maximum load and W is the width of the standard test specimen.

[0128] First Coulomb efficiency test:

[0129] The voltage range indicated on the battery's outer packaging should be used as the standard. For example, if the battery's voltage range is 3.0V to 4.45V, the charging cut-off voltage is 4.45V, and the discharging cut-off voltage is 3.0V. The specific testing steps are as follows: Charge the lithium-ion battery from the example or comparative example at 25°C with a constant current of 0.2C to the cut-off voltage of 4.45V. Then, charge it at 4.45V with a constant voltage until the current is less than 0.05C. After resting for 5 minutes, discharge it at a constant current of 0.2C to the cut-off voltage of 3.0V. The capacity during the above charging process is denoted as C0, and the capacity during the above discharging process is denoted as C1. Calculate the initial coulombic efficiency according to the following formula.

[0130] Initial coulomb efficiency (%) = C1 / C0 × 100%.

[0131] Cyclic performance test:

[0132] The voltage range indicated on the battery's outer packaging should be used as the standard. For example, if the battery's voltage range is 3.0V to 4.45V, the charging cut-off voltage is 4.45V, and the discharging cut-off voltage is 3.0V. The specific testing steps are as follows: Under 25°C conditions, the lithium-ion battery in the example or comparative example is charged and discharged for the first time. It is charged at a constant current of 0.2C to the cut-off voltage of 4.45V, and then charged at a constant voltage of 4.45V until the current is less than 0.05C. After resting for 5 minutes, it is discharged at a constant current of 0.2C to the cut-off voltage of 3.0V. The discharge capacity of the lithium-ion battery is measured as A. Then, in an environment at 25°C, 400 charge and discharge cycles are performed according to the above steps. The discharge capacity of the lithium-ion battery after the 400th cycle is measured as B. The cycle capacity retention rate is calculated according to the following formula.

[0133] Cyclic capacity retention rate (%) = B / A × 100%.

[0134] The higher the cycle capacity retention rate value obtained from the test, the better the cycle performance of the lithium-ion battery.

[0135] Volumetric energy density test:

[0136] The voltage range indicated on the battery's outer packaging should be used as the standard. For example, if the battery's voltage range is 3.0V to 4.45V, the charging cut-off voltage is 4.45V, and the discharging cut-off voltage is 3.0V. The specific test steps are as follows: At 25°C, charge the lithium-ion battery in the example or comparative example at a constant current of 0.2C to the cut-off voltage of 4.45V, then charge it at a constant voltage of 4.45V until the current is less than 0.05C. After resting for 5 minutes, discharge it at a constant current of 0.2C to the cut-off voltage of 3.0V, and then let it rest for 5 minutes. Record the energy of the above discharge process as the discharge energy E. Calculate the volume V (mm²) of the lithium-ion battery. 3 = Length × Width × Height.

[0137] Volumetric energy density (Wh / L) = E / V × 10 6 .

[0138] Thermal safety performance test:

[0139] (1) At 25°C, the lithium-ion battery in the example or comparative example is charged at a constant current of 0.2C to the cutoff voltage of 4.45V, and then charged at a constant voltage of 4.45V until the current is less than 0.05C, and then left to stand for 5 minutes.

[0140] (2) Inspect the appearance of the lithium-ion battery and take photos before conducting thermal safety performance tests;

[0141] (3) Place the temperature sensing wire in the middle of the lithium-ion battery body;

[0142] (4) Place the lithium-ion battery vertically in the box and heat it to the target temperature (e.g., 135±2℃) at a heating rate of 5±2℃ and hold it for 60 minutes;

[0143] (5) Determine whether the lithium-ion battery has caught fire or exploded and take photos;

[0144] (6) The highest temperature at which a lithium-ion battery will not catch fire or explode is the highest temperature that a lithium-ion battery can withstand, also known as the thermal safety pass temperature.

[0145] Example 1-1

[0146] <Preparation of Negative Electrode Sheets>

[0147] The negative electrode active material (silicon-carbon material), negative electrode conductive agent (acetylene black), negative electrode binder (styrene-butadiene rubber (SBR), and negative electrode binder (lithium carboxymethyl cellulose)) were mixed in a weight ratio of 85:5:5:5. Deionized water was then added as the negative electrode solvent, and the mixture was stirred until homogeneous to obtain a negative electrode slurry. The solid content of the negative electrode slurry was 28 wt%. The silicon-carbon material was a silicon-carbon composite material, with a silicon content of 50% and a carbon content of 50% based on the mass of the composite material.

[0148] A gap-coating method was used to uniformly coat the negative electrode slurry onto the first surface of a 12μm thick copper foil negative electrode current collector along the tape direction. The coating was then dried at 90℃ to obtain a negative electrode sheet with a single-sided gap-coated negative electrode material layer. The shortest distance D1 between two adjacent negative electrode material layer regions on the first surface along the tape direction of the negative electrode sheet is 20mm, and the length of a single negative electrode material layer region on the first surface is 1000mm. The above steps were then repeated on the second surface of the copper foil to obtain a negative electrode sheet with a double-sided gap-coated negative electrode material layer. The shortest distance D2 between two adjacent negative electrode material layer regions on the second surface along the tape direction of the negative electrode sheet is 80mm, and the length of a single negative electrode material layer region on the second surface is 940mm. After drying under vacuum at 90℃ for 1 hour, the sheet was cold-pressed, cut, and slit to obtain a negative electrode sheet with dimensions of 80mm × 1020mm. The areal density of the negative electrode material layer was 2.3mg / cm³. 2 The compaction density during the cold pressing process is 1.0 g / cm³. 3 .

[0149] <Preparation of pre-lithiated negative electrode>

[0150] Under ambient temperature of 25℃ and humidity of 1.0%, lithium foil was rolled to a copper foil support layer with a thickness of 14μm to form a lithium replenishment layer. The rolling pressure p12 was 1.5T / 10mm, resulting in a lithium replenishment layer / support layer composite structure. The thickness H2 of the lithium replenishment layer was 0.03mm.

[0151] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP) were mixed in a weight ratio of 3:1:3:3 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) was added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 12.5%, with the remainder being the base solvent.

[0152] Polyvinylidene fluoride (PVDF) and inorganic alumina were mixed at a weight ratio of 9:1, and NMP was added as a solvent. The mixture was thoroughly mixed to obtain a slurry with a solid content of 12 wt%. Using an extrusion-type gap coating method, the slurry was coated onto one surface of a 5 μm thick polypropylene (PP) base film along the conveyor belt direction (the second region was coated with the slurry, while the first region was not). After drying, a single-sided gap-coated slurry was obtained. The shortest distance D3 between two adjacent first regions along the conveyor belt direction was 20 mm, and the length of a single first region was 1000 mm. The above steps were then repeated on the other surface of the base film to obtain the first slurry. The ionic conductivity σ11 of the first slurry in the first region was 3 mS / cm, the porosity P11 was 40%, and the air permeability G2 was 8 s / 100 mL. The ionic conductivity σ21 of the first separator in the second region is 0.05 mS / cm, and the porosity P21 of the first separator in the second region is 0.5%. The elongation of the first separator under a tensile force of 2 N / 10 mm is 1%, and the tensile strength of the first separator along the conveyor belt direction is 5500 kg / cm. 2 The thickness of the separator coating is 10 μm. The areal density of the separator coating is 12 mg / 5000 mm². 2 .

[0153] The first separator membrane described above is immersed in the electrolyte to obtain a first separator membrane pre-impregnated with electrolyte. The areal density CW1 of the electrolyte on the first separator membrane pre-impregnated with electrolyte is 20 g / mm². 2 .

[0154] The first separator pre-impregnated with electrolyte is placed on the surface of the lithium replenishment layer to obtain a first lithium replenishment composite layer. The first lithium replenishment composite layer includes a support layer, a lithium replenishment layer, and the first separator pre-impregnated with electrolyte. The lithium replenishment layer is disposed between the first separator and the support layer. The tensile strength K1 of the lithium replenishment layer (including the support layer) along the tape direction of the lithium replenishment composite layer is 72 N / 10 mm.

[0155] Polyvinylidene fluoride (PVDF) and inorganic alumina were mixed at a weight ratio of 9:1, and NMP was added as a solvent. The mixture was thoroughly mixed to obtain a slurry with a solid content of 12 wt%. Using an extrusion-type gap coating method, the slurry was coated onto one surface of a 5 μm thick polypropylene (PP) base film along the belt direction (the second region was coated with the slurry, while the first region was not). After drying, a single-sided gap-coated slurry was obtained. The shortest distance D4 between two adjacent first regions along the belt direction was 80 mm, and the length of a single first region was 940 mm. The above steps were then repeated on the other surface of the base film to obtain the second slurry. The ionic conductivity σ12 of the second slurry in the first region was 3 mS / cm, the porosity P12 was 40%, and the air permeability G3 was 8 s / 100 mL. The ionic conductivity σ22 of the second separator in the second region is 0.05 mS / cm, and the porosity P22 of the second separator in the second region is 0.5%. The elongation of the second separator under a tensile force of 2 N / 10 mm is 1%, and the tensile strength of the second separator along the conveyor belt direction is 5500 kg / cm. 2 The thickness of the separator coating is 10 μm. The areal density of the separator coating is 12 mg / 5000 mm². 2 .

[0156] The second separator membrane described above is immersed in the electrolyte to obtain a second separator membrane pre-impregnated with electrolyte. The areal density CW2 of the electrolyte on the pre-impregnated second separator membrane is 20 g / mm². 2 .

[0157] The second separator pre-impregnated with electrolyte is placed on the surface of the lithium replenishment layer to obtain the second lithium replenishment composite layer. The second lithium replenishment composite layer includes a support layer, a lithium replenishment layer and the second separator pre-impregnated with electrolyte, with the lithium replenishment layer disposed between the second separator and the support layer.

[0158] The first lithium replenishment composite layer and the negative electrode sheet are bonded together, so that the first separator is in contact with the negative electrode material layer on the first surface. The bonding method is to press them into a sheet. The first region is opposite to the negative electrode material layer region, and the second region is opposite to the empty foil region. The interfacial pressure p2 per unit area between the first lithium replenishment composite layer and the negative electrode sheet is 0.4 MPa. The first lithium replenishment composite layer and the negative electrode sheet are discharged through a voltage control system. The positive terminal of the voltage control system is connected to the negative electrode sheet, and the negative terminal of the voltage control system is connected to the lithium replenishment layer of the first lithium replenishment composite layer. The constant current discharge current I1 of the discharge treatment is 1C, the discharge time t1 is 0.2h, and the discharge temperature T1 is 55℃. Simultaneously, the second lithium replenishment composite layer and the negative electrode sheet are bonded together, so that the second separator is in contact with the negative electrode material layer on the second surface. The bonding method is to press them into a sheet. The first region is opposite to the negative electrode material layer region, and the second region is opposite to the empty foil region. The interfacial pressure p3 per unit area between the second lithium replenishment composite layer and the negative electrode sheet is 0.4 MPa. The second lithium replenishment composite layer and the negative electrode sheet are discharged through a voltage control system. The positive terminal of the voltage control system is connected to the negative electrode sheet, and the negative terminal of the voltage control system is connected to the lithium replenishment layer of the second lithium replenishment composite layer. The constant current discharge current I2 of the discharge treatment is 1C, the discharge time t2 is 0.2h, and the discharge temperature T2 is 55℃.

[0159] After the discharge process is completed, the first lithium replenishment composite layer and the second lithium replenishment composite layer are peeled off from the negative electrode sheet to obtain the pre-lithiated negative electrode sheet.

[0160] <Preparation of the positive electrode>

[0161] Lithium cobalt oxide (LiCoO2), a positive electrode active material, acetylene black, a positive electrode conductive agent, and polyvinylidene fluoride (PVDF), a positive electrode binder, were mixed in a weight ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as the positive electrode solvent, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil current collector and dried at 110 °C to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The sheet was dried under vacuum at 110 °C for 1 hour, and then cold-pressed, cut, and slit to obtain a positive electrode sheet with dimensions of 77 mm × 10¹⁵ mm. The areal density of the positive electrode material layer was 19.0 mg / cm³. 2 The compaction density during the cold pressing process is 4.15 g / cm³. 3 .

[0162] <Preparation of Electrolyte in Lithium-ion Batteries>

[0163] The electrolyte pre-impregnated in the separator of the above-mentioned lithium replenishment composite layer is used as the electrolyte in the lithium-ion battery.

[0164] <Preparation of separator membrane in lithium-ion batteries>

[0165] A porous polypropylene film with a thickness of 5 μm (provided by Celgard) was used as the separator.

[0166] <Preparation of Lithium-ion Batteries>

[0167] The positive electrode, separator, pre-lithiated negative electrode, and separator prepared above are stacked in sequence, with the separator positioned between the positive electrode and the pre-lithiated negative electrode to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film and dried in an 85°C vacuum oven for 12 hours to remove moisture. Electrolyte is then injected, followed by vacuum sealing, settling, formation (charged at a constant current of 0.02C to 3.5V, then at a constant current of 0.1C to 3.9V), degassing, edge trimming, and capacity processing to obtain the lithium-ion battery.

[0168] Examples 1-2

[0169] Except for adjusting the relevant preparation parameters according to Tables 1 and 2, and the specification of the negative electrode sheet being 80mm×1005mm in <Preparation of the negative electrode sheet> and the specification of the positive electrode sheet being 77mm×1000mm in <Preparation of the positive electrode sheet>, the rest is the same as in Example 1-1.

[0170] Examples 1-3

[0171] Except for adjusting the relevant preparation parameters according to Tables 1 and 2, and the specification of the negative electrode sheet being 80mm×1030mm in <Preparation of the negative electrode sheet> and the specification of the positive electrode sheet being 77mm×1025mm in <Preparation of the positive electrode sheet>, the rest is the same as in Example 1-1.

[0172] Examples 1-4 to Examples 1-7

[0173] Except for adjusting the porosity and permeability of the isolation membrane in the first region to achieve the ionic conductivity of the isolation membrane in the first region as shown in Tables 1 and 2, the rest is the same as in Example 1-1.

[0174] Examples 1-8 to Examples 1-10

[0175] Except for adjusting the porosity of the isolation membrane in the second region to achieve the ionic conductivity of the isolation membrane in the second region as shown in Tables 1 and 2, the rest is the same as in Example 1-1.

[0176] Examples 1-11 to Examples 1-16

[0177] Except for adjusting the soaking time of the separator in the electrolyte to achieve the areal density of the electrolyte on the separator pre-soaked in the electrolyte as shown in Tables 1 and 2, the rest is the same as in Example 1-1.

[0178] Examples 1-17 to Examples 1-27

[0179] Except for adjusting the relevant preparation parameters according to Tables 1 and 2, the rest is the same as in Example 1-1.

[0180] Example 2-1

[0181] Except for the preparation of the negative electrode and positive electrode according to the following methods, the rest is the same as in Example 1-1.

[0182] <Preparation of Negative Electrode Sheets>

[0183] The negative electrode slurry from Example 1-1 was used for extrusion-type gap coating. The negative electrode slurry was gap-coated uniformly onto one surface of a 12μm thick copper foil for the negative electrode current collector along a direction perpendicular to the tape travel. The foil was then dried at 90°C to obtain a negative electrode sheet with a single-sided gap-coated negative electrode material layer. The shortest distance D5 between two adjacent negative electrode material layer regions along a direction perpendicular to the tape travel was 50mm, and the width of a single negative electrode material layer region was 80mm. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided gap-coated negative electrode material layer. After drying under vacuum at 90°C for 1 hour, the sheet was cold-pressed, cut, and slit to obtain a negative electrode sheet with dimensions of 80mm × 1020mm. The areal density of the negative electrode material layer was 2.3mg / cm³. 2 The compaction density during the cold pressing process is 1.0 g / cm³. 3 .

[0184] <Preparation of pre-lithiated negative electrode>

[0185] Under ambient temperature of 25℃ and humidity of 1.0%, lithium foil was rolled to a copper foil support layer with a thickness of 14μm to form a lithium replenishment layer. The rolling pressure p12 was 1.5T / 10mm, resulting in a lithium replenishment layer / support layer composite structure. The thickness H2 of the lithium replenishment layer was 0.03mm.

[0186] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP) were mixed in a weight ratio of 3:1:3:3 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) was added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 12.5%, with the remainder being the base solvent.

[0187] Polyvinylidene fluoride (PVDF) and inorganic alumina were mixed at a weight ratio of 9:1, and NMP was added as a solvent. The mixture was thoroughly mixed to obtain a slurry with a solid content of 12 wt%. Using an extrusion-type gap coating method, the slurry was coated onto one surface of a 5 μm thick polypropylene (PP) base film along a direction perpendicular to the film's travel direction (the second region was coated with the slurry, while the first region was not). After drying, a single-sided gap-coated slurry was obtained. The shortest distance D6 between two adjacent first regions along the film's travel direction perpendicular to the slurry was 50 mm, and the width of a single first region was 80 mm. The above steps were then repeated on another surface of the base film to obtain the third slurry. The ionic conductivity σ13 of the third slurry in the first region was 3 mS / cm, the porosity P13 was 40%, and the air permeability G4 was 8 s / 100 mL. The ionic conductivity σ23 of the third separator in the second region is 0.05 mS / cm, and the porosity P23 of the third separator in the second region is 0.5%. The elongation of the third separator under a tensile force of 2 N / 10 mm is 1%, and the tensile strength of the third separator along the conveyor belt direction is 5500 kg / cm. 2 The thickness of the separator coating is 10 μm. The areal density of the separator coating is 12 mg / 5000 mm². 2 .

[0188] The third separator membrane described above is immersed in the electrolyte to obtain a third separator membrane pre-impregnated with electrolyte. The areal density (CW3) of the electrolyte on the pre-impregnated third separator membrane is 20 g / mm³. 2 .

[0189] The third separator with the pre-impregnated electrolyte is placed on the surface of the lithium replenishment layer to obtain the third lithium replenishment composite layer. The third lithium replenishment composite layer includes a support layer, a lithium replenishment layer and the third separator with the pre-impregnated electrolyte, with the lithium replenishment layer disposed between the third separator and the support layer.

[0190] The aforementioned third lithium-replenishing composite layer and the aforementioned negative electrode sheet are bonded together, so that the third separator is in contact with the negative electrode material layer on one surface. The first region is positioned opposite to the negative electrode material layer region, and the second region is positioned opposite to the empty foil region. The bonding method is to press them into a sheet. The interfacial pressure p4 per unit area between the third lithium-replenishing composite layer and the negative electrode sheet is 0.4 MPa. The third lithium-replenishing composite layer and the negative electrode sheet are discharged using a voltage control system. The positive terminal of the voltage control system is connected to the negative electrode sheet, and the negative terminal of the voltage control system is connected to the lithium-replenishing layer of the third lithium-replenishing composite layer. The constant current discharge current I3 is 1C, the discharge time t3 is 0.2h, and the discharge temperature T3 is 55℃. Simultaneously, the negative electrode material layer on the other surface is pre-lithiated according to the above steps.

[0191] After the discharge process is completed, the third lithium replenishment composite layer is peeled off from the negative electrode to obtain the pre-lithiated negative electrode.

[0192] <Preparation of the positive electrode>

[0193] Lithium cobalt oxide (LiCoO2), a positive electrode active material, acetylene black, a positive electrode conductive agent, and polyvinylidene fluoride (PVDF), a positive electrode binder, were mixed in a weight ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as the positive electrode solvent, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil current collector and dried at 110 °C to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The sheet was dried under vacuum at 110 °C for 1 hour, and then cold-pressed, cut, and slit to obtain a positive electrode sheet with dimensions of 77 mm × 10¹⁵ mm. The areal density of the positive electrode material layer was 19.0 mg / cm³. 2 The compaction density during the cold pressing process is 4.15 g / cm³. 3 .

[0194] Examples 2-2 to 2-4

[0195] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Example 2-1.

[0196] Examples 3-1 to 3-10

[0197] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-1.

[0198] Comparative Examples 1 to 6

[0199] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0200] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0201]

[0202]

[0203]

[0204] As can be seen from Examples 1-1 to 1-27 and Comparative Examples 1 to 6, the pre-lithiated negative electrode sheet prepared using the lithium replenishment method provided in this application, when applied to lithium-ion batteries, exhibits higher thermal safety pass temperature, initial coulombic efficiency, cycle capacity retention, and volumetric energy density. This demonstrates that the method can improve the safety performance and initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase the volumetric energy density. In Comparative Examples 1 to 6, the lithium replenishment method is not within the scope of this application, and the prepared lithium-ion batteries exhibit lower thermal safety pass temperature, initial coulombic efficiency, cycle capacity retention, and volumetric energy density.

[0205] The structure of the negative electrode and separator typically affects the safety performance and volumetric energy density of lithium-ion batteries. As can be seen from Examples 1-1 to 1-3, the lithium-ion batteries prepared using the negative electrode and separator structures within the scope of this application exhibit higher thermal safety passing temperature, higher initial coulombic efficiency, higher cycle capacity retention, and higher volumetric energy density. This demonstrates that the structure can improve the safety performance and volumetric energy density of lithium-ion batteries, while also exhibiting higher initial coulombic efficiency and lower cycle capacity decay.

[0206] The ionic conductivity of the separator in the first region typically affects the safety performance, initial coulombic efficiency, cycle capacity retention, and volumetric energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-4 to 1-7, the ionic conductivity of the separator in the first region is within the range specified in this application. The resulting lithium-ion batteries exhibit higher thermal safety passing temperature, initial coulombic efficiency, cycle capacity retention, and volumetric energy density, indicating that the separator can improve the safety performance and initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase the volumetric energy density.

[0207] The ionic conductivity of the separator in the second region typically affects the safety performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-8 to 1-10, the ionic conductivity of the separator in the second region, within the scope of this application, results in lithium-ion batteries with higher thermal safety passing temperature, higher initial coulombic efficiency, higher cycle capacity retention, and higher volumetric energy density. This indicates that the safety performance of lithium-ion batteries can be improved, while the lithium-ion batteries exhibit higher initial coulombic efficiency, lower cycle capacity decay, and higher volumetric energy density.

[0208] The areal density of the electrolyte on the pre-impregnated separator typically affects the safety performance, initial coulombic efficiency, cycle capacity retention, and volumetric energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-11 to 1-16, the lithium-ion batteries prepared with the areal density of the electrolyte on the pre-impregnated separator within the scope of this application exhibit higher thermal safety passing temperature, initial coulombic efficiency, cycle capacity retention, and volumetric energy density. This indicates that it can improve the safety performance and initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase the volumetric energy density of lithium-ion batteries.

[0209] The interfacial pressure per unit area between the lithium-filled composite layer and the negative electrode typically affects the initial coulombic efficiency, cycle capacity retention, and volumetric energy density of a lithium-ion battery. As can be seen from Examples 1-1, 1-17 to 1-20, within the scope of this application, the interfacial pressure per unit area between the lithium-filled composite layer and the negative electrode results in lithium-ion batteries with higher thermal safety pass temperature, higher initial coulombic efficiency, higher cycle capacity retention, and higher volumetric energy density. This indicates that the initial coulombic efficiency of lithium-ion batteries can be improved, cycle capacity decay reduced, and volumetric energy density increased. Furthermore, the lithium-ion batteries also exhibit good safety performance.

[0210] The temperature of the discharge treatment typically affects the safety performance, initial coulombic efficiency, cycle capacity retention, and volumetric energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-25 to 1-27, the lithium-ion batteries prepared within the temperature range of this application exhibit higher thermal safety pass temperature, initial coulombic efficiency, cycle capacity retention, and volumetric energy density. This demonstrates that the discharge treatment can improve the safety performance and initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase the volumetric energy density.

[0211] Table 3

[0212]

[0213] The structure of the negative electrode and separator typically affects the safety performance and volumetric energy density of lithium-ion batteries. As can be seen from Examples 2-1 to 2-4, the lithium-ion batteries prepared using the negative electrode and separator structures within the scope of this application exhibit higher thermal safety passing temperature, higher initial coulombic efficiency, higher cycle capacity retention, and higher volumetric energy density. This demonstrates that the structure can improve the safety performance and volumetric energy density of lithium-ion batteries, while also exhibiting higher initial coulombic efficiency and lower cycle capacity decay.

[0214] Table 4

[0215]

[0216]

[0217] The thickness of the lithium replenishment layer typically affects the initial coulombic efficiency, cycle capacity retention, and volumetric energy density of lithium-ion batteries. As can be seen from Examples 1-1 and 3-1 to 3-4, the lithium-ion batteries prepared with a lithium replenishment layer thickness within the range of this application exhibit higher thermal safety passing temperature, lower initial coulombic efficiency, higher cycle capacity retention, and higher volumetric energy density. This indicates that the initial coulombic efficiency of lithium-ion batteries can be improved, cycle capacity decay reduced, and volumetric energy density increased, while the lithium-ion batteries also exhibit better safety performance. In Examples 1-1 and 3-1 to 3-4, the lithium replenishment layer in Example 3-4 is thicker, which may affect the production efficiency of the lithium-ion battery.

[0218] The thickness of the support layer typically affects the initial coulombic efficiency, cycle capacity retention, and volumetric energy density of lithium-ion batteries. As can be seen from Examples 1-1, 3-5 to 3-8, the lithium-ion batteries prepared with a support layer thickness within the range specified in this application exhibit higher thermal safety passing temperature, lower initial coulombic efficiency, higher cycle capacity retention, and higher volumetric energy density. This indicates that the support layer thickness can improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the volumetric energy density of lithium-ion batteries, while also providing better safety performance.

[0219] The type of support layer typically affects the initial coulombic efficiency, cycle capacity retention, and volumetric energy density of lithium-ion batteries. As can be seen from Examples 1-1, 3-9 to 3-10, the types of support layers used within the scope of this application result in lithium-ion batteries with higher thermal safety passing temperature, lower initial coulombic efficiency, higher cycle capacity retention, and higher volumetric energy density. This indicates that the support layer can improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the volumetric energy density of lithium-ion batteries, while also exhibiting better safety performance.

[0220] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0221] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0222] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for lithium supplementing, comprising the following steps: providing a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; providing a lithium supplementing composite layer, the lithium supplementing composite layer comprising a support layer, a lithium supplementing layer and a separator film of a pre-impregnated electrolyte, the lithium supplementing layer being disposed between the separator film and the support layer; adhering the lithium supplementing composite layer and the negative electrode sheet, so that the separator film is in contact with the negative electrode material layer, and performing a discharging treatment on the lithium supplementing composite layer and the negative electrode sheet, the discharging treatment having a constant current discharging current I of 0.1C to 3C and a discharging time t of 0.067h to 2h; after the discharging treatment, peeling the lithium supplementing composite layer from the negative electrode sheet to obtain a pre-lithiated negative electrode sheet.

2. The lithium supplementing method according to claim 1, wherein, the negative electrode sheet is a gap structure, the gap structure comprising a gap structure along a tape running direction or a gap structure perpendicular to the tape running direction.

3. The lithium supplementing method according to claim 2, wherein, when the negative electrode sheet is a gap structure along the tape running direction, along a thickness direction of the negative electrode sheet, the negative electrode current collector comprises opposite first and second surfaces; the first and second surfaces are both spaced apart from a negative electrode material layer region and an empty foil region; along the tape running direction of the negative electrode sheet, a shortest distance D1 between two adjacent negative electrode material layer regions on the first surface is 5mm to 30mm, and a shortest distance D2 between two adjacent negative electrode material layer regions on the second surface is 30mm to 150mm.

4. The lithium supplementing method according to claim 3, wherein the separator film comprises a first separator film and / or a second separator film, and the separator film satisfies at least one of the following characteristics: (1) the first separator film is opposite to the first surface, the first separator film is a gap structure along the tape running direction, the first separator film comprises a base film and a separator film coating layer disposed on at least one surface of the base film, a surface of the base film is spaced apart from a first region and a second region, the second region is provided with the separator film coating layer, the first region is opposite to the negative electrode material layer region, and the second region is opposite to the empty foil region; along the tape running direction of the first separator film, a shortest distance D3 between two adjacent first regions in the first separator film is 5mm to 30mm; (2) the second separator film is opposite to the second surface, the second separator film is a gap structure along the tape running direction, the second separator film comprises a base film and a separator film coating layer disposed on at least one surface of the base film, a surface of the base film is spaced apart from a first region and a second region, the second region is provided with the separator film coating layer, the first region is opposite to the negative electrode material layer region, and the second region is opposite to the empty foil region; along the tape running direction of the second separator film, a shortest distance D4 between two adjacent first regions in the second separator film is 30mm to 150mm.

5. The lithium supplementing method according to claim 2, wherein When the negative electrode sheet is a gap structure along a direction perpendicular to the tape running direction, the surface of the negative current collector is spaced apart from the negative material layer region and the empty foil region; along a direction perpendicular to the tape running direction of the negative electrode sheet, the shortest distance D5 between any two adjacent negative material layer regions on the surface of the negative current collector is 5 mm to 150 mm.

6. The lithium supplementing method according to claim 5, wherein The isolation film includes a third isolation film, the third isolation film is a gap structure along a direction perpendicular to the tape running direction, the third isolation film includes a base film and an isolation film coating layer arranged on at least one surface of the base film, the surface of the base film is spaced apart from the first region and the second region, the second region is provided with an isolation film coating layer, the first region is arranged opposite to the negative material layer region, and the second region is arranged opposite to the empty foil region; along a direction perpendicular to the tape running direction of the third isolation film, the shortest distance D6 between any two adjacent first regions on the surface of the base film is 5 mm to 150 mm.

7. The lithium supplementing method according to claim 4 or 6, which satisfies at least one of the following characteristics: (1) the ion conductivity σ1 of the isolation film in the first region is 0.1 mS / cm to 5 mS / cm; (2) the porosity P1 of the isolation film in the first region is 30% to 45%; (3) the air permeability G of the isolation film in the first region is 6 s / 100 mL to 9 s / 100 mL.

8. The lithium supplementing method according to claim 4 or 6, which satisfies at least one of the following characteristics: (1) the ion conductivity σ2 of the isolation film in the second region is 0 mS / cm to 0.1 mS / cm; (2) the porosity P2 of the isolation film in the second region is 0 to 1%.

9. The lithium supplementing method according to claim 1, wherein, The interfacial pressure p per unit area between the lithium supplementing composite layer and the negative electrode sheet is 0.1 MPa to 0.6 MPa.

10. The lithium supplementing method according to claim 1, wherein, The temperature T of the discharging treatment is 25°C to 90°C.

11. The lithium supplementing method according to claim 1, which satisfies at least one of the following characteristics: (1) the thickness H2 of the lithium supplementing layer is 0.001 mm to 1 mm; (2) the thickness H3 of the support layer is 3 μm to 50 μm; (3) the support layer includes at least one of a copper foil, a nickel foil, a steel foil, or a copper-nickel alloy foil; (4) along the tape running direction of the lithium supplementing composite layer, the tensile strength K1 of the lithium supplementing layer is 0.5 N / 10 mm to 200 N / 10 mm.

12. The lithium supplementing method according to claim 1, which satisfies at least one of the following characteristics: (1) the thickness H2 of the lithium supplementing layer is 0.005 mm to 0.1 mm; (2) the thickness H3 of the support layer is 5 μm to 20 μm; (3) along the tape running direction of the lithium supplementing composite layer, the tensile strength K1 of the lithium supplementing layer is 1 N / 10 mm to 100 N / 10 mm.

13. A prelithiated negative electrode sheet prepared by the lithium supplementing method according to any one of claims 1 to 12.

14. A secondary battery including the prelithiated negative electrode sheet according to claim 13.

15. An electronic device including the secondary battery according to claim 14.

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