Prelithiation composite layer, preparation method therefor, and application thereof

Abstract

Disclosed are a prelithiation composite layer, a preparation method therefor, a prelithiation method, a prelithiated negative electrode sheet resulting from said method, a secondary battery preparation method, and a prepared secondary battery. The prelithiation composite layer of the present invention comprises an interfacial layer and a prelithiation layer arranged in a stacked configuration, wherein the interfacial layer comprises interfacial particles, the interfacial particles are a lithium intercalation material and / or a conductive agent, the lithium intercalation material is selected from at least one of artificial graphite, natural graphite, hard carbon, a silicon-carbon material, a silicon oxide material, lithium titanate, tin, and a tin-copper alloy, and the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjenblack, carbon fiber, graphene, and carbon nanotubes; the prelithiation layer comprises lithium metal and / or a lithium alloy. An interfacial layer of the prelithiation composite layer of the present invention is in contact with a negative electrode active material layer to prevent a prelithiation layer from adhering to a surface of a negative electrode sheet, thereby preventing deterioration of electrochemical performance caused by side reactions of the prelithiation layer.

Description

Lithium-supplemented composite layers, their preparation methods and applications Technical Field

[0001] This invention belongs to the field of chemical power sources, specifically relating to a lithium replenishment structure, its preparation method, lithium replenishment method, pre-lithiated negative electrode sheet, preparation method of secondary battery, and secondary battery prepared by the method. 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 and improve the energy density of lithium-ion batteries, they have not been widely adopted due to problems such as low initial coulombic efficiency and poor cycle life. Existing methods to improve the initial efficiency and 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 cycles, thereby improving the initial efficiency of silicon-carbon or silicon-oxygen batteries and ultimately increasing the energy density of lithium-ion batteries.

[0003] Existing methods for lithium replenishment of negative electrode sheets mainly include lithium powder replenishment, lithium strip calendering replenishment, and electrochemical replenishment. Lithium powder replenishment involves adsorbing lithium powder onto the surface of the negative electrode sheet under the influence of vibration and an electric field. The powder is then compacted onto the surface of the negative electrode sheet through rolling to prevent it from falling off, thus replenishing the lithium content. However, lithium powder tends to float easily, polluting the environment; its relatively large particle size (Dv50 approximately 25μm) leads to uneven replenishment at low replenishment amounts; and the low adhesion of the lithium bonding layer hinders large-scale application. Lithium strip calendering replenishment involves passing a lithium strip through a calendering roller and a composite roller for calendering, causing the lithium strip to adhere to the composite roller. The lithium strip on the surface of the composite roller is then transferred to the surface of the negative electrode sheet, resulting in a lithium-replenished negative electrode sheet. Lithium strip rolling for lithium replenishment typically involves mechanically pressing lithium strips onto the negative electrode. This results in low lithium film utilization; unconverted lithium loses its electronic conductivity, becoming "dead lithium," hindering lithium-ion diffusion, increasing internal resistance and polarization. More seriously, the unconverted lithium promotes lithium-ion nucleation, leading to lithium plating and safety issues. Electrochemical lithium replenishment, on the other hand, assembles lithium foil or alloys with a separator, negative electrode, and electrolyte into a stack, which is then formed. The formed negative electrode is then dried to form a lithium-replenished negative electrode. However, electrochemical lithium replenishment usually requires an electrolyte, which can react with water in the environment to form byproducts that remain in the electrode, worsening cycle performance.

[0004] The above technologies have achieved lithium replenishment of the negative electrode through different methods, but there are certain problems in environmental control, lithium replenishment uniformity, and side reactions after lithium replenishment. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a lithium-replenishing composite layer, a method for preparing the lithium-replenishing composite layer, a lithium-replenishing method, a pre-lithiated negative electrode sheet, a method for preparing a secondary battery, and a secondary battery prepared by the method.

[0006] The first aspect of this invention provides a lithium-replenishing composite layer, comprising an interface layer and a lithium-replenishing layer stacked together. The interface layer includes interface particles, which are lithium-intercalating materials and / or conductive agents. The lithium-intercalating material is selected from at least one of artificial graphite, natural graphite, hard carbon, silicon carbide, silicon oxide, lithium titanate, tin, and tin-copper alloys. The conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon fiber, graphene, and carbon nanotubes. The lithium-replenishing layer comprises lithium metal and / or lithium alloys. The lithium-intercalating material and conductive agent in this application have the ability to intercalate and deintercalate lithium ions and the ability to conduct electrons.

[0007] According to one embodiment of the present invention, the interface particles are embedded in the lithium replenishment layer.

[0008] According to another embodiment of the present invention, the depth to which the interface particles are embedded in the lithium replenishment layer is 10% to 95% of the thickness of the interface layer, preferably 30% to 70%.

[0009] According to another embodiment of the present invention, the flatness of the surface of the interface layer away from the lithium replenishment layer is 0 μm to 20 μm, preferably 0 μm to 5 μm.

[0010] According to another embodiment of the present invention, the coverage ratio of the interface layer in the lithium replenishment layer is 50% to 100%, preferably 80% to 100%.

[0011] According to another embodiment of the present invention, the thickness of the interface layer is 0.1 μm to 50 μm, preferably 1 μm to 20 μm.

[0012] According to another embodiment of the present invention, the mass percentages of the lithium-intercalated material and the conductive agent in the interface layer are 80%–99% and 1%–20%, respectively.

[0013] According to another embodiment of the present invention, the electronic conductivity of the interface particles is 0.1 mS / cm to 1000 mS / cm, preferably 10 mS / cm to 700 mS / cm; and the ionic conductivity of the interface particles is 0.01 mS / cm to 100 mS / cm, preferably 0.1 mS / cm to 10 mS / cm.

[0014] According to another embodiment of the present invention, the thickness of the lithium replenishment layer is 0.001 mm to 1 mm, preferably 0.005 mm to 0.1 mm.

[0015] According to another embodiment of the present invention, a support layer is further included, which is disposed on the surface of the lithium replenishment layer away from the interface layer.

[0016] According to another embodiment of the present invention, the support layer includes at least one of copper foil, nickel foil, steel foil and copper-nickel alloy foil, or the support layer includes at least one of polyethylene terephthalate (PET) film, polypropylene (PP) film, polyethylene (PE) film and polyimide (PI) film.

[0017] According to another embodiment of the present invention, the tensile strength at break in the MD direction (along the belt direction) of the support layer is 0.5 N / 10 mm to 200 N / 10 mm, preferably 1 N / 10 mm to 100 N / 10 mm.

[0018] According to another embodiment of the present invention, the thickness of the support layer is 3μm to 50μm, preferably 5μm to 20μm.

[0019] The second aspect of this invention provides a method for preparing a lithium replenishment composite layer. Under ambient temperatures of 5°C to 30°C and humidity ≤1.7%, lithium metal powder slurry is coated onto a support layer, dried, and rolled to form a lithium replenishment layer. The rolling pressure is 0.1–2 T / 10 mm (in this application, the rolling pressure refers to the weight borne by the rolled object per unit width, with the width perpendicular to the object's conveying direction); or lithium foil and / or lithium alloy foil are rolled onto the support layer to form a lithium replenishment layer; or lithium or lithium alloy molten slurry is coated onto the support layer, cooled, and rolled to form a lithium replenishment layer; under ambient temperatures of 5°C to 30°C and humidity ≤1.7%, interface particles are coated onto the surface of the lithium replenishment layer using electrostatic spraying, roller coating, or wiping, followed by rolling with a rolling pressure of 0.1 T / 10 mm to 2 T / 10 mm, and then allowed to stand at 20°C to 180°C for 5 min to 60 min to form the lithium replenishment composite layer. Preferably, the roller pressure is 0.2T / 10mm to 0.8T / 10mm, and the lithium-replenishing composite layer is formed by standing at 50℃ to 120℃ for 10min to 30min.

[0020] A third aspect of the present invention provides a lithium replenishment method, comprising: providing a negative electrode sheet, wherein a negative electrode active material layer is disposed on the surface of the negative electrode sheet; drying the active material layer until the water content is ≤500ppm; bonding the above-mentioned lithium replenishment composite layer and the negative electrode sheet such that the interface layer is in contact with the negative electrode active material layer, the interface pressure between the interface layer and the negative electrode active material layer is 0.1MPa~2MPa; performing pre-lithiation under the conditions of ambient temperature 25℃~180℃ and humidity ≤1.7%; and after the pre-lithiation is completed, peeling the lithium replenishment composite layer from the negative electrode sheet to form a pre-lithiated negative electrode sheet.

[0021] The fourth aspect of the present invention provides a pre-lithiated negative electrode sheet, which is obtained by the above-described lithium replenishment method.

[0022] The fifth aspect of the present invention provides a method for preparing a secondary battery, wherein the pre-lithiated negative electrode sheet, separator and positive electrode sheet are stacked or stacked and then wound, and the secondary battery is formed by casing, liquid injection, encapsulation, formation and degassing.

[0023] The sixth aspect of the present invention provides a secondary battery prepared by the above-described preparation method.

[0024] The lithium replenishment composite layer of this invention has an interface layer that combines electron and ion conduction capabilities. Therefore, when the lithium replenishment composite layer comes into contact with the negative electrode active material layer, the interface layer causes a short circuit between the lithium replenishment layer and the negative electrode active material layer. Simultaneously, the interface layer possesses lithium insertion / extraction capabilities, allowing it to conduct lithium ions. Furthermore, a potential difference exists between the lithium replenishment layer and the negative electrode active material layer, enabling the lithium replenishment layer to act as the anode, the interface layer as the electrolyte, and the negative electrode active material layer as the cathode, forming a corrosion cell. During the lithium replenishment process, lithium in the lithium replenishment layer undergoes an oxidation reaction, losing electrons to generate lithium ions. Electrons and ions are transferred through the interface layer to the surface or interior of the negative electrode active material layer, where a reduction reaction occurs. Electrons and lithium ions combine to generate lithium metal, thus replenishing the lithium in the negative electrode active material. The lithium replenishment composite layer of this invention has an interface layer that contacts the negative electrode active material layer, preventing the lithium replenishment layer from adhering to the surface of the negative electrode, thereby avoiding electrical performance degradation caused by side reactions in the lithium replenishment layer. In addition, there is a certain pressure between the interface layer and the negative electrode active material layer, which is conducive to more interface particles in the interface layer contacting the negative electrode active material in the negative electrode active material layer, increasing the pathway for conducting electrons and lithium ions, and facilitating the replenishment of lithium to the negative electrode active material. Attached Figure Description

[0025] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0026] Figure 1 is a comparison of the first-efficiency performance before and after lithium supplementation in Comparative Example 1.

[0027] Figure 2 is a comparison of the cycle performance before and after lithium replenishment in Examples 1-2.

[0028] Figures 3 and 4 are schematic diagrams of the test method for the depth of the lithium-filling layer embedded in the interface layer of this application.

[0029] Figure 5 is a schematic diagram of the test method for the flatness of the interface layer in this application.

[0030] Figures 6 and 7 show the coverage ratio of the interface layer in the lithium replenishment layer of this application, and are schematic diagrams of the test method. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments.

[0032] The lithium replenishment composite layer of the present invention includes an interface layer and a lithium replenishment layer stacked together. The interface layer includes interface particles, which are lithium-intercalating materials and / or conductive agents. The lithium-intercalating material is selected from at least one of artificial graphite, natural graphite, hard carbon, silicon-carbon materials, silicon-oxygen materials, lithium titanate, tin, and tin-copper alloys. The conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon fiber, graphene, and carbon nanotubes. The lithium replenishment layer includes lithium metal and / or lithium alloys. The lithium-intercalating material or conductive agent in the interface layer of the lithium replenishment composite layer of the present invention has both electron and ion conduction capabilities. Therefore, when the lithium replenishment composite layer comes into contact with the negative electrode active material layer, the interface layer causes a short circuit between the lithium replenishment layer and the negative electrode active material layer. At the same time, the interface layer acts as an electrolyte to conduct lithium ions, and there is a potential difference between the lithium replenishment layer and the negative electrode active material layer, thereby forming a corrosion cell with the lithium replenishment layer as the anode, the interface layer as the electrolyte, and the negative electrode active material layer as the cathode. During the lithium replenishment process, lithium in the replenishment layer undergoes an oxidation reaction, losing electrons to generate lithium ions. Electrons and ions are transferred through the interface layer to the surface or interior of the active material layer of the negative electrode. A reduction reaction occurs in the active material layer, where electrons and lithium ions combine to form lithium metal, thus replenishing lithium to the negative electrode active material. In this invention, the interface layer of the lithium replenishment composite layer is in contact with the negative electrode active material layer, preventing the replenishment layer from adhering to the surface of the negative electrode and thereby avoiding electrical performance degradation caused by side reactions in the replenishment layer.

[0033] The rate of lithium replenishment can be controlled by the electronic and ionic conductivity of the lithium-intercalating material and / or conductive agent in the interface layer, the potential difference between the lithium replenishment layer and the negative electrode active material layer, the interfacial pressure between the interface layer and the negative electrode active material layer, and the temperature during lithium replenishment. Those skilled in the art can select the specific types and corresponding contents of the lithium-intercalating material and / or conductive agent according to the specific types of components of the negative electrode active material and the lithium replenishment layer, as well as actual needs.

[0034] In optional embodiments, the electronic conductivity of the interfacial particles is 0.1 mS / cm to 1000 mS / cm, preferably 10 mS / cm to 700 mS / cm. The ionic conductivity of the interfacial particles is 0.01 mS / cm to 100 mS / cm, preferably 0.1 mS / cm to 10 mS / cm.

[0035] In an optional embodiment, when the interface layer simultaneously comprises a lithium-intercalating material and a conductive agent, the preferred mass percentages of the lithium-intercalating material and the conductive agent in the interface layer are 80%–99% and 1%–20%, respectively. The appropriate ratio can be selected based on the specific types of the lithium-intercalating material and the conductive agent, for example, but not limited to, mass percentages of 80% and 20%; 85% and 15%; 90% and 10%; 95% and 5%; 99% and 1%, etc.

[0036] In an optional embodiment, interface particles are embedded in the lithium replenishment layer. When interface particles are embedded in the lithium replenishment layer, they can better promote the participation of lithium within the lithium replenishment layer in the oxidation reaction, thereby transferring lithium from the lithium replenishment layer to the negative electrode active material layer. This also facilitates the repeated use of the lithium replenishment composite layer. The embedding depth of the interface particles in the lithium replenishment layer is 10%-95% of the interface layer thickness, preferably 30%-70%. The specific embedding depth is related to the thickness of the lithium replenishment layer, the particle size of the interface particles, and the amount of interface particles; a thicker layer results in a deeper embedding depth, and a thinner layer results in a shallower embedding depth. Larger particle sizes result in deeper embedding depths, and smaller particle sizes result in shallower embedding depths. The interface layer is not completely embedded in the lithium replenishment layer; that is, at least part of the interface layer is exposed to avoid side reactions caused by the lithium replenishment layer adhering to the negative electrode surface during lithium replenishment, which would otherwise occur.

[0037] The depth at which interface particles are embedded in the lithium replenishment layer can be achieved by any feasible method. For example, but not limited to, controlling the embedding depth of interface particles in the lithium replenishment layer by controlling the rolling pressure during the preparation of the interface layer.

[0038] In an optional embodiment, the thickness of the lithium replenishment layer is 0.001 mm to 1 mm, preferably 0.005 mm to 0.1 mm. Preferably, the depth to which the interface particles are embedded in the lithium replenishment layer is 0.05 μm to 10 μm.

[0039] In optional embodiments, the thickness of the interface layer is 0.1 μm to 50 μm. Preferably, the thickness of the interface layer is 1 μm to 20 μm.

[0040] In an optional embodiment, the flatness of the surface of the interface layer away from the lithium replenishment layer is 0 μm to 20 μm. Flatness refers to the height difference between the highest and lowest points on the same end face. The flatness of the surface of the interface layer away from the lithium replenishment layer determines its tightness of bonding with the negative electrode active material layer. The tighter the bonding between the interface layer and the negative electrode active material layer, the easier the conduction of lithium ions and electrons, i.e., the lower the resistance. Preferably, the flatness of the surface of the interface layer away from the lithium replenishment layer is 0 μm to 5 μm. When the process precision allows, the flatness can be 0 μm.

[0041] The smoothness of the interface layer is related to the type, particle size, coating method, and rolling pressure of the interface particles. The smoothness of the interface layer can be adjusted to the expected value by controlling one or more of the above factors in combination.

[0042] The depth and flatness of the interface particles embedded in the lithium replenishment layer described in this patent were measured using the following method:

[0043] 1) Sample preparation:

[0044] The lithium-filled composite layer sample was cut into 6mm × 6mm pieces and attached to the sample stage with conductive adhesive; then, the sample was cross-section polished using a cross-section polisher (IB-19520CCP, vacuum level 10). -3 Pa, accelerating voltage 6-8kV, grinding speed 500 micrometers / hour;

[0045] 2) Parameter testing:

[0046] The polished sample was placed on the SEM stage, and its cross-section was tested using a SEM (Scanning Electron Microscope). (Thermo Fisher Scientific FEI-Apreo S, accelerating voltage 10KV, grating 10 spots, working distance WD 10mm, magnification 500-2000x).

[0047] Depth of lithium replenishment layer embedded in the lithium replenishment layer: H a Defined as: the height difference between the upper surface of the lithium replenishment layer and the lower surface of the interface layer, as shown in Figure 3; H c Defined as: the height difference between the upper surface and the lower surface of the interface layer, as shown in Figure 4. Define h = H a / H c Each sample was tested with 12 parallel samples, and the average value of 12 hours was taken as the embedding depth.

[0048] Interface layer flatness: H b Defined as: the height difference between the highest point and the lowest point on the upper surface of the interface layer, as shown in Figure 5; 12 parallel samples are tested for each sample, and 12 H values ​​are taken. b The average value is flatness.

[0049] In an optional embodiment, the coverage ratio of the interface layer in the lithium replenishment layer can be 50% to 100%. The coverage ratio of the interface layer in the lithium replenishment layer determines the uniformity of lithium replenishment in the negative electrode active material layer; that is, the greater the coverage ratio of the interface layer in the lithium replenishment layer, the higher the uniformity of lithium replenishment in the negative electrode active material layer. Preferably, the coverage ratio of the interface layer in the lithium replenishment layer is 80% to 100%.

[0050] In this patent, the coverage ratio of the interface layer in the lithium replenishment layer was obtained through the following test method:

[0051] 1) Place the sample flat on the sample stage; then take magnified photographs of the sample using an optical microscope (Keyence VHX-7000, magnification 200-500 times);

[0052] 2) Import the captured images into the image processing software IMAGE J, distinguish between the lithium replenishment area and the interface area using a threshold, and calculate the area S1~S of each interface area. nThe total area of ​​the interface region is S 界面 =S1+S2+S3+……+S n-1 +S n Measure the length L and width W of the lithium replenishment area, and calculate the total area S of the lithium replenishment area. 补锂 =W×L; then the coverage ratio s is S 界 面 / S 补锂 As shown in Figures 6 and 7.

[0053] 3) Each sample was tested in 12 parallel samples, and the average of the 12 samples was taken as the mean coverage ratio.

[0054] An interface layer with the desired coverage can be obtained by any suitable method. For example, but not limited to, controlling the area to be sprayed by a stencil, thereby controlling the coverage ratio of the interface layer in the lithium supplement layer.

[0055] In an optional embodiment, the lithium replenishment composite layer further includes a support layer disposed on the surface of the lithium replenishment layer away from the interface layer. The function of the support layer is to provide support for the lithium replenishment layer and the interface layer, improve the mechanical strength of the composite layer, and thus enable it to be smoothly peeled off from the surface of the negative electrode active material layer after lithium replenishment without breaking.

[0056] In optional embodiments, the support layer comprises at least one of copper foil, nickel foil, steel foil, and copper-nickel alloy foil; or, the support layer comprises at least one of PET film, PP film, PE film, and PI film. The tensile strength at break in the MD direction (along the conveyor belt direction) of the support layer is 0.5 N / 10 mm to 200 N / 10 mm to meet the requirements for peeling. Preferably, the tensile strength at break in the conveyor belt direction of the support layer is 1 N / 10 mm to 100 N / 10 mm. The thickness of the support layer is 3 μm to 50 μm, preferably 5 μm to 20 μm.

[0057] The thickness of each layer described in this patent is obtained by measuring it in the following manner:

[0058] Place the sample to be tested on a clean table, level it, and then measure its thickness as required.

[0059] Check the dial indicator's measuring face for cleanliness and damage; wipe the measuring face with a non-woven cloth. Press the measuring linkage mechanism to ensure full contact between the two measuring faces, and press the "zero" button. Ensure the two measuring faces of the dial indicator are in parallel and perpendicular contact with the sample's face, read the displayed data, and measure the reading. Measure at 70mm intervals in the TD direction (perpendicular to the MD direction) and at 100mm intervals in the MD direction (belt travel direction). Release the sample, bring the two measuring faces into contact, and check if the display has returned to zero to confirm the accuracy of the measurement data. Test two points along the TD direction of the sample, with a 70mm interval between the two points. Draw a parallel line along the MD direction from one of these points, and take 12 points along this parallel line, with each adjacent point spaced 100mm apart. Repeat the above operation for the other point in the TD direction, for a total of 24 points. Test all 24 points; take the average thickness of the 24 points as the thickness of the sample.

[0060] Using the support layer as the sample to be tested, the thickness Thk of the support layer is obtained. 支撑 When the support layer and the lithium replenishment layer are combined and used as the sample to be tested, the resulting material is Thk. 支撑&补锂 Thickness; Thk 支撑&补锂 With the thickness of the support layer Thk 支撑 The difference is the thickness of the lithium replenishment layer Thk 补锂 That is, Thk 补锂 =Thk 支撑&补锂 -Thk 支撑 .

[0061] By combining the support layer, lithium replenishment layer, and interface layer into a composite sample, the thickness Thk of the composite layer is obtained. 支撑&补锂&界面 The thickness of the interface layer is Thk 界面 That is, Thk 界面 =Thk 支撑& 补锂&界面 -Thk 支撑&补锂 .

[0062] The method for preparing the lithium replenishment composite layer of the present invention may be as follows: under the conditions of ambient temperature of 5°C to 30°C and humidity ≤1.7%, lithium metal powder slurry is coated onto a support layer and dried and rolled to form a lithium replenishment layer, with a rolling pressure of 0.1T / 10mm to 2T / 10mm; or lithium foil and / or lithium alloy foil are rolled onto the support layer to form a lithium replenishment layer; or lithium or lithium alloy molten slurry is coated onto the support layer and cooled and rolled to form a lithium replenishment layer; under the conditions of ambient temperature of 5°C to 30°C and humidity ≤1.7%, interface particles are coated onto the surface of the lithium replenishment layer by electrostatic spraying, roller coating, or wiping, and then rolled to form a lithium replenishment layer with a rolling pressure of 0.1T / 10mm to 2T / 10mm, and then left to stand at 20°C to 180°C for 5min to 60min to form a lithium replenishment composite layer. Preferably, the rolling pressure is 0.2T / 10mm to 0.8T / 10mm, and the lithium-replenishing composite layer is formed by standing at 50℃ to 120℃ for 10min to 30min. That is, the lithium-replenishing layer can be formed by coating and rolling lithium metal powder slurry, or by using lithium foil and / or lithium alloy foil as the lithium-replenishing layer, or by coating a support layer with lithium or lithium alloy molten slurry, cooling, and rolling to form the lithium-replenishing layer. When using lithium alloy foil or lithium alloy molten slurry, any lithium alloy that does not affect the performance of the negative electrode and the electrochemical device using the negative electrode can be used, such as, but not limited to, lithium-aluminum alloy (generally with a lithium content of 90% to 99.9% and an aluminum content of 10% to 0.1%). Then, interface particles are coated onto the lithium-replenishing layer by spraying or other methods, and after rolling, the interface particles can be embedded into the lithium-replenishing layer. The rolling pressure can be reasonably selected according to the required embedding depth.

[0063] The method for lithium replenishment using the above-mentioned lithium replenishment composite layer can be as follows: A negative electrode sheet is provided, and a negative electrode active material layer is disposed on the surface of the negative electrode sheet; the active material layer is dried until the water content is ≤500ppm; the above-mentioned lithium replenishment composite layer and the negative electrode sheet are bonded together, so that the interface layer is in contact with the negative electrode active material layer, and the interfacial pressure between the interface layer and the negative electrode active material layer is 0.1MPa~2MPa; pre-lithiation is performed under the conditions of ambient temperature 25℃~180℃ and humidity ≤1.7%; after pre-lithiation, the lithium replenishment composite layer is peeled off from the negative electrode sheet to form a pre-lithiated negative electrode. The interfacial pressure between the interface layer and the negative electrode active material layer is applied by the winding pressure of the winding or the pressure of the pressing die. This method separates the lithium replenishment composite layer from the negative electrode active material layer. On the one hand, it avoids the safety issues caused by the rapid reaction and heat generation after the lithium replenishment layer comes into direct contact with the negative electrode sheet. On the other hand, it prevents the lithium replenishment layer from remaining on the surface of the negative electrode sheet and entering the battery, causing side reactions and deteriorating electrical performance. Furthermore, the lithium replenishment composite layer can be reused, avoiding the waste of lithium metal and reducing costs.

[0064] In an optional embodiment, the active material in the active material layer of the negative electrode sheet can be a conventional negative electrode active material of a lithium-ion battery, such as, but not limited to, any one or a combination of at least two of graphite materials, hard carbon materials, silicon-carbon materials, or silicon-oxygen materials. The lithium replenishment method of the present invention is suitable for active material layers of any areal density and compaction density. For example, the areal density of the negative electrode active material layer is 1.3 mg / cm³. 2 ~130mg / cm 2 The preferred concentration is 2.0 mg / cm³. 2 ~13.0mg / cm 2 The compacted density is 0.4 g / cm³. 3 ~1.9g / cm 3 Preferably 0.5 g / cm 3 ~1.8g / cm 3 .

[0065] The pre-lithiated negative electrode sheet can be obtained by the above lithium replenishment method.

[0066] The preparation method of the secondary battery using the pre-lithiated negative electrode sheet can be as follows: the pre-lithiated negative electrode sheet, separator, and positive electrode sheet are stacked, or stacked and wound, and then subjected to casing, electrolyte injection, encapsulation, formation, and degassing to form the secondary battery. The secondary battery obtained by the above preparation method improves the initial efficiency, reduces cycle decay, and increases the battery energy density.

[0067] The present invention is further described below through specific examples. However, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention. Unless otherwise specified, the reagents, materials, and instruments used in the following embodiments and comparative examples are commercially available.

[0068] Example

[0069] 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.

[0070] Test methods and equipment:

[0071] Test method for lithium replenishment capacity:

[0072] Weigh the sample before and after lithium supplementation using an analytical balance with a strength of 1 / 100,000. The sample area is 1540.25 mm². 2The amount of lithium replenishment is the difference between the areal density after lithium replenishment and the density before lithium replenishment. Two points are tested along the TD direction of the sample, with a 70mm interval between the two points. A parallel line is drawn along the MD direction from one of these points, and 12 points are taken along this parallel line. With each point as the center, an area of ​​1540.25mm² is taken. 2 Using circular discs as samples, each adjacent point (i.e., the center of the disc) is spaced 100 mm apart. Repeat the above operation for another point in the TD direction. This results in a total of 24 circular disc samples. Calculate the average value of these 24 samples.

[0073] Initial efficiency test method:

[0074] The assembled battery is subjected to charge-discharge tests. The test procedure is as follows:

[0075] 25℃ Initial Efficiency: A lithium-ion battery is charged at 0.2C constant current to the cutoff voltage at 25℃, then charged at constant voltage until the current < 0.05C. After resting for 5 minutes, it is discharged at 0.2C constant current (DC) to the cutoff voltage. The ratio of the 0.2C / DC capacity to the sum of the capacities during the constant current (CC) and constant voltage (CV) stages is the initial efficiency at 25℃. (If the battery is labeled with a voltage range of 3.0~4.45V at the factory, then the charging cutoff voltage is 4.45V and the discharging cutoff voltage is 3.0V.)

[0076] Loop testing method:

[0077] Capacity retention at 25°C for 400 cycles (400cls): The lithium-ion battery is charged at 0.2C constant current to the cutoff voltage at 25°C, then charged at constant voltage until the current < 0.05C. After resting for 5 minutes, it is discharged at 0.2C DC to the cutoff voltage. This charge-discharge cycle is repeated. The ratio of the 0.2C DC capacity at the 400th cycle to the 0.2C DC capacity at the 1st cycle is the capacity retention at 25°C for 400 cycles. A higher ratio indicates better cycle performance of the lithium-ion battery.

[0078] Volumetric energy density testing method:

[0079] The lithium-ion battery was placed in a constant temperature chamber at 25°C for 30 minutes, then charged at a constant current of 0.5C to the charging cutoff voltage. It was then charged at a constant voltage of the charging cutoff voltage to 0.025C, placed for 5 minutes, and finally discharged at a constant current of 0.2C to the discharging cutoff voltage. The discharge capacity E and discharge voltage plateau U of the lithium-ion battery were recorded. The length, width, and height of the lithium-ion battery at 50% charge were measured to obtain the volume V of the lithium-ion battery. The energy density is calculated as E × U / V. (If the battery is labeled with a voltage range of 3.0V to 4.45V at the factory, then the charging cutoff voltage is 4.45V and the discharging cutoff voltage is 3.0V.)

[0080] Example 1-1

[0081] (1) Preparation of lithium-supplemented composite layer

[0082] Under ambient temperature of 25℃ and humidity of 1.0%, lithium foil is rolled to form a 14μm thick copper support layer to form a lithium replenishment layer. The rolling pressure is 1.5T / 10mm, resulting in a composite structure of lithium replenishment layer and support layer.

[0083] Under ambient temperatures of 25℃ and humidity of 1.0%, graphite with a Dv50 of 8 μm was applied to the surface of the lithium replenishment layer and allowed to stand at 90℃ for 30 min to form a lithium replenishment composite layer. The lithium replenishment layer itself was 30 μm thick, the interface layer was 8 μm thick, and the interface particles were not embedded in the lithium replenishment layer. The interface layer was not subjected to rolling pressure. The interface layer had a flatness of 3 μm, a coverage of 50% of the lithium replenishment layer, and a tensile strength of 72 N / 10 mm along the belt conveyor direction. Dv50 refers to the particle size that, in a volumetric particle size distribution, reaches 50% of the cumulative volume from the smallest particle size side.

[0084] (2) Preparation of negative electrode sheet

[0085] Silicon-carbon (silicon to carbon in a mass ratio of approximately 1:1), conductive carbon black, styrene-butadiene rubber, and lithium carboxymethyl cellulose were mixed in a mass ratio of 85:5:5:5, using deionized water as a solvent to form a negative electrode active material slurry with a solid content of 28%. Copper foil was used as the negative electrode current collector, and the slurry was coated onto it and dried at 90°C. The compacted density of the negative electrode sheet was 1.0 g / cm³. 3 Its surface density is 2.3 mg / cm³. 2 .

[0086] (3) Lithium supplementation yields a pre-lithiated negative electrode sheet.

[0087] The prepared lithium-replenishing composite layer was laminated with the prepared negative electrode sheet under ambient temperature of 90℃ and humidity of 1.0%. The interfacial pressure between the lithium-replenishing composite layer and the negative electrode sheet was 0.6 MPa, allowing the interfacial layer to contact the negative electrode active material layer for pre-lithiation for 20 hours. After pre-lithiation, the lithium-replenishing composite layer was separated from the negative electrode sheet to form the pre-lithiated negative electrode sheet.

[0088] (4) Preparation of positive electrode sheet

[0089] Lithium cobalt oxide (LiCoO2), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent to prepare a positive electrode slurry with a solid content of 75 wt%, and the mixture was stirred evenly. The positive electrode slurry was then uniformly coated onto an aluminum foil current collector, and the positive electrode sheet was dried at 110°C. The compacted density of the positive electrode sheet was 4.15 g / cm³. 3 Its surface density is 19.0 mg / cm³. 2 .

[0090] (5) Battery assembly

[0091] The prepared positive electrode sheet, negative electrode sheet, and a 5μm thick PP film sandwiched between them are stacked sequentially and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging shell and dried in an 85℃ vacuum oven for 12 hours to remove moisture, and then injected with electrolyte.

[0092] The electrolyte is an organic solvent consisting of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP) in a mass ratio of EC:PC:DEC:EP = 3:1:3:3. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0093] After vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), shaping, and capacity treatment, a lithium-ion battery is obtained, with a designed battery capacity of 5000mAh.

[0094] Examples 1-2

[0095] Except for the rolling of the interface layer formed after wiping and the coverage of the interface layer in the lithium replenishment layer, the other steps are the same as in Example 1-1. After rolling the interface layer, the rolling pressure is 0.5T / 10mm (0.5 tons / 10 millimeters), so that the depth of the interface layer embedded in the lithium replenishment layer is 4μm, that is, 50% of the interface layer thickness is embedded in the lithium replenishment layer. The coverage of the interface layer in the lithium replenishment layer is shown in Table 1.

[0096] The test data for the battery assembled in this embodiment are shown in Table 1.

[0097] Examples 1-3

[0098] Except for the use of lithium metal powder to form the lithium replenishment layer and the coverage of the interface layer in the lithium replenishment layer, the other steps are the same as in Examples 1-2. The process of forming the lithium replenishment layer is as follows:

[0099] Under ambient temperature of 25℃ and humidity of 1.0%, lithium metal powder slurry was coated onto a copper support layer with a thickness of 14μm, dried, and rolled to form a lithium replenishment layer. The rolling pressure was 1.5T / 10mm, resulting in a composite structure of lithium replenishment layer and support layer.

[0100] The coverage of the interface layer in the lithium replenishment layer is shown in Table 1. The test data of the battery assembled in this embodiment are shown in Table 1.

[0101] Examples 1-4

[0102] Except for the use of a lithium-aluminum alloy (99.5% lithium and 0.5% aluminum by mass) to form the lithium replenishment layer and the coverage of the interface layer on the lithium replenishment layer, the other steps are the same as in Examples 1-2. The process of forming the lithium replenishment layer is as follows:

[0103] Under ambient temperature of 25℃ and humidity of 1.0%, lithium-aluminum alloy was melted and slurryed, then coated onto a copper support layer with a thickness of 14μm, dried, and rolled to form a lithium replenishment layer. The rolling pressure was 1.5T / 10mm, resulting in a composite structure of lithium replenishment layer and support layer.

[0104] The coverage of the interface layer in the lithium replenishment layer is shown in Table 1. The test data of the battery assembled in this embodiment are shown in Table 1.

[0105] Examples 1-5

[0106] Except for the use of conductive carbon black to form the interface layer and the coverage of the interface layer in the lithium replenishment layer, the other steps are the same as in Examples 1-4. The thickness of the interface layer formed by the conductive carbon black is 1 μm. Due to the difference in the type of interface particles and the thickness of the interface layer compared with Examples 1-4, the resulting thickness of the interface layer embedded in the lithium replenishment layer, the smoothness of the interface layer, and the electronic and ionic conductivity values ​​of the interface layer are different from those in Examples 1-4, as shown in Table 1.

[0107] The coverage of the interface layer in the lithium replenishment layer is shown in Table 1. The test data of the battery assembled in this embodiment are shown in Table 1.

[0108] Examples 1-6

[0109] Except for the use of hard carbon to form the interface layer and the coverage of the interface layer in the lithium replenishment layer, the other steps are the same as in Examples 1-4. Because the type of interface particles is different from that in Examples 1-4, the resulting electronic and ionic conductivity values ​​of the interface layer are different from those in Examples 1-4, as shown in Table 1.

[0110] The coverage of the interface layer in the lithium replenishment layer is shown in Table 1. The test data of the battery assembled in this embodiment are shown in Table 1.

[0111] Examples 1-7

[0112] Except for the use of silicon-oxygen (silicon to oxygen molar ratio of 1:1) and conductive carbon black (SP) (where silicon-oxygen to SP mass ratio of 90:10) to form the interface layer and the coverage of the interface layer on the lithium supplementation layer, the other steps are the same as in Examples 1-4. Because the type of interface particles differs from that in Examples 1-4, the resulting electronic and ionic conductivity values ​​of the interface layer are different from those in Examples 1-4, as shown in Table 1.

[0113] The coverage of the interface layer in the lithium replenishment layer is shown in Table 1. The test data of the battery assembled in this embodiment are shown in Table 1.

[0114] Examples 1-8

[0115] Except for the use of lithium titanate and conductive carbon black (SP) (where the mass ratio of lithium titanate to SP is 90:10) to form the interface layer and the coverage of the interface layer on the lithium replenishment layer, the other steps are the same as in Examples 1-4. Because the type of interface particles is different from that in Examples 1-4, the resulting electronic conductivity and ionic conductivity values ​​of the interface layer are different from those in Examples 1-4, as shown in Table 1.

[0116] The coverage of the interface layer in the lithium replenishment layer is shown in Table 1. The test data of the battery assembled in this embodiment are shown in Table 1.

[0117] Examples 1-9

[0118] Except for the use of tin to form the interface layer and the coverage of the interface layer in the lithium replenishment layer, the other steps are the same as in Examples 1-4. Because the type of interface particles is different from that in Examples 1-4, the resulting electronic and ionic conductivity values ​​of the interface layer are different from those in Examples 1-4, as shown in Table 1.

[0119] The coverage of the interface layer in the lithium replenishment layer is shown in Table 1. The test data of the battery assembled in this embodiment are shown in Table 1.

[0120] Examples 1-10

[0121] Except for the use of silicon-carbon (silicon to carbon mass ratio of 1:1) to form the interface layer and the coverage of the interface layer in the lithium replenishment layer, the other steps are the same as in Examples 1-4. Because the type of interface particles is different from that in Examples 1-4, the resulting electronic and ionic conductivity values ​​of the interface layer are different from those in Examples 1-4, as shown in Table 1.

[0122] The coverage of the interface layer in the lithium replenishment layer is shown in Table 1. The test data of the battery assembled in this embodiment are shown in Table 1.

[0123] Comparative Example 1

[0124] Pre-lithiation was not performed, that is, steps (1) and (3) were omitted in Example 1-1. The test results are shown in Table 1.

[0125] Comparative Example 2

[0126] In Example 1-1, lithium foil was rolled onto the surface of the negative electrode sheet prepared in step (2) to form a lithium-replenished negative electrode sheet. The rolling pressure was 0.1T / 10mm. The preparation of the positive electrode sheet, battery assembly, and testing were the same as in Example 1-1. The test results are shown in Table 1. For ease of comparison, Table 1 shows the parameter values ​​where the parameters changed in the above examples and comparative examples, as well as the performance test data of each example and comparative example.

[0127] Comparing Examples 1-1 to 1-10, Comparative Example 2 and Comparative Example 1, it can be seen that lithium replenishment can improve the initial efficiency, discharge capacity retention rate and energy density.

[0128] Comparing Example 1-1 and Comparative Example 2, it can be seen that under the same amount of lithium replenishment, Example 1-1 has higher initial efficiency, capacity retention after 400 cycles, and energy density than Comparative Example 2. This proves that the lithium replenishment method of the present invention can reduce the generation of dead lithium and improve the utilization rate of Li compared with the traditional lithium foil replenishment method, thereby further improving the initial efficiency, cycle capacity retention, and energy density.

[0129] Comparing Examples 1-4 to 1-10, it can be seen that lithium replenishment can be achieved with interfacial particles having an electronic conductivity ranging from 0.1 S / cm to 1000 S / cm and an ionic conductivity ranging from 0.01 S / cm to 100 mS / cm. Furthermore, the lithium replenishment effect is even better when the electronic conductivity is between 10 S / cm and 700 mS / cm and the ionic conductivity is between 0.1 S / cm and 10 mS / cm.

[0130] Examples 2-1 to 2-4

[0131] Except for the different rolling pressure on the interface layer and the resulting differences in the depth of the interface layer embedded in the lithium replenishment layer and the flatness of the interface layer, the other steps are the same as in Examples 1-4.

[0132] Examples 2-5 to Examples 2-6

[0133] Except for the different rolling pressure on the interface layer and the resulting differences in the depth of the interface layer embedded in the lithium replenishment layer and the flatness of the interface layer, the other steps are the same as in Examples 1-5.

[0134] Table 2 shows some parameters and test data for Examples 2-1 to 2-6. For ease of comparison, Table 2 also shows some parameters and test data for Examples 1-4 and 1-5.

[0135] Table 2

[0136] Comparing the test data of Examples 1-4 and Examples 2-1 to 2-4, it can be seen that when the interface layer is not fully embedded with the lithium replenishment layer, with the same interface particles, the greater the rolling pressure, the greater the thickness of the lithium replenishment layer embedded in the interface layer, and the lower the flatness value of the interface layer. The flatter the interface layer, the greater the amount of lithium replenished in the same time. The greater the amount of lithium replenished, the higher the initial efficiency, discharge capacity retention rate, and energy density increase. This also explains why the lithium replenishment method of the present invention reduces the generation of dead lithium and improves the utilization rate of Li. Similarly, the data of Examples 1-5, 2-5, and 2-6 also illustrate the above problems. When the interface layer is fully embedded with the lithium replenishment layer, during the lithium replenishment process of the negative electrode, the lithium replenishment layer will directly contact the surface of the negative electrode, which will not achieve the lithium replenishment effect of this application. This point has been explained in the background art of this application. Therefore, the thickness of the interface layer embedded with the lithium replenishment layer in this application is less than 100%.

[0137] Example 3-1

[0138] An interface layer with a thickness of 0.1 μm was formed by electrostatic spraying, and the other steps were the same as in Examples 1-5.

[0139] Example 3-2

[0140] An interface layer with a thickness of 5 μm was formed by electrostatic spraying, and the Dv50 of the graphite was 5 μm. Other steps were the same as in Examples 1-4.

[0141] Example 3-3

[0142] An interface layer with a thickness of 20 μm was formed by roller coating, and the Dv50 of the graphite was 20 μm. Other steps were the same as in Examples 1-4.

[0143] Examples 3-4 to 3-6

[0144] Apart from forming interface layers of different thicknesses using graphite with different Dv50, the other steps were the same as in Examples 1-4. Specifically, the Dv50 of the graphite in Examples 3-4 was 30 μm, the Dv50 of the graphite in Examples 3-5 was 40 μm, and the Dv50 of the graphite in Examples 3-6 was 50 μm.

[0145] Table 3 shows some parameters and test data for Examples 3-1 to 3-4. For ease of comparison, Table 3 also shows some parameters and test data for Examples 1-4.

[0146] Table 3

[0147] Comparing Examples 1-4 and Examples 3-1 to 3-3, it can be seen that the preparation process of the interface layer and the performance of different interface particles affect the thickness of the interface layer (for example, the particle size of conductive carbon black is small, ranging from tens to hundreds of nanometers, much smaller than that of graphite; using conductive carbon black as the interface particle allows for a thinner interface layer), the depth of embedding in the lithium replenishment layer, and the interface smoothness. Comparing Examples 3-4 to 3-6, it can be seen that under the same interface layer preparation process, the surface coverage of the interface layer does not change significantly. The thickness and surface smoothness of the interface layer can be adjusted by controlling the particle size of the graphite interface particles. As shown in Table 3, the lithium replenishment efficiency, initial efficiency, and cycle retention can be improved by controlling the interface layer thickness and surface smoothness. The thinner the interface layer, the faster the lithium ion transport; the smoother the interface layer, the more active sites are in contact with the surface of the negative electrode active layer, thus increasing the amount of lithium replenished, improving the utilization rate of Li, and further improving the initial efficiency and cycle capacity retention.

[0148] Examples 4-1 to 4-5

[0149] Except for the different coverage of the interface layer on the lithium replenishment layer, the other steps in each embodiment are the same as those in Embodiments 1-4.

[0150] Table 3 shows some parameters and test data for Examples 4-1 to 4-5. For ease of comparison, Table 3 also shows some parameters and test data for Example 3-2.

[0151] Table 4

[0152] The data above shows that, with the same number of interfacial particles, the higher the coverage, the greater the lithium replenishment efficiency, meaning the greater the amount of lithium replenished per unit area of ​​the negative electrode sheet.

[0153] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A lithium-replenishing composite layer, characterized in that, The device includes a stacked interface layer and a lithium replenishment layer. The interface layer includes interface particles, which are lithium intercalation materials and / or conductive agents. The lithium intercalation materials are selected from at least one of artificial graphite, natural graphite, hard carbon, silicon carbide, silicon oxide, lithium titanate, tin, and tin-copper alloy. The conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon fiber, graphene, and carbon nanotubes. The lithium replenishment layer includes lithium metal and / or lithium alloy.

2. The lithium-supplementing composite layer as described in claim 1, characterized in that, The interface particles are embedded in the lithium replenishment layer.

3. The lithium replenishment composite layer as described in claim 2, wherein the depth to which the interface particles are embedded in the lithium replenishment layer is 10% to 95% of the thickness of the interface layer, preferably 30% to 70%.

4. The lithium-supplementing composite layer as described in claim 2, characterized in that, The flatness of the surface of the interface layer away from the lithium replenishment layer is 0μm to 20μm, preferably 0μm to 5μm.

5. The lithium-supplementing composite layer according to any one of claims 1 to 4, characterized in that, The interface layer covers 50% to 100% of the lithium replenishment layer, preferably 80% to 100%.

6. The lithium-replenishing composite layer according to any one of claims 1 to 5, characterized in that, The thickness of the interface layer is 0.1 μm to 50 μm, preferably 1 μm to 20 μm.

7. The lithium-replenishing composite layer according to any one of claims 1 to 6, characterized in that, The mass percentages of the lithium-intercalating material and the conductive agent in the interface layer are 80%–99% and 1%–20%, respectively.

8. The lithium-replenishing composite layer according to any one of claims 1 to 7, characterized in that, The electronic conductivity of the interface particles is 0.1 mS / cm to 1000 mS / cm, preferably 10 mS / cm to 700 mS / cm; and The ionic conductivity of the interface particles is 0.01 mS / cm to 100 mS / cm, preferably 0.1 mS / cm to 10 mS / cm.

9. The lithium-replenishing composite layer according to any one of claims 1 to 8, characterized in that, The thickness of the lithium replenishment layer is 0.001 mm to 1 mm, preferably 0.005 mm to 0.1 mm.

10. The lithium-replenishing composite layer according to any one of claims 1 to 9, characterized in that, It also includes a support layer disposed on the surface of the lithium replenishment layer away from the interface layer.

11. The lithium-replenishing composite layer as described in claim 10, characterized in that, The support layer includes at least one of copper foil, nickel foil, steel foil, and copper-nickel alloy foil, or the support layer includes at least one of PET film, PP film, PE film, and PI film.

12. The lithium-supplementing composite layer as described in claim 10 or 11, characterized in that, The tensile strength at break in the MD direction of the support layer is 0.5N / 10mm to 200N / 10mm, preferably 1N / 10mm to 100N / 10mm.

13. The lithium-replenishing composite layer according to any one of claims 10 to 12, characterized in that, The thickness of the support layer is 3μm to 50μm, preferably 5μm to 20μm.

14. A method for preparing a lithium-supplemented composite layer, characterized in that, Under ambient temperatures of 5°C to 30°C and humidity ≤1.7%, lithium metal powder slurry is coated onto a support layer, dried, and rolled to form a lithium replenishment layer, with a rolling pressure of 0.1T / 10mm to 2T / 10mm; or lithium foil and / or lithium alloy foil are 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. Under ambient temperatures of 5°C to 30°C and humidity ≤1.7%, the interface particles are coated onto the surface of the lithium replenishment layer using electrostatic spraying, roller coating, or wiping coating. The coating is then rolled at a pressure of 0.1T / 10mm to 2T / 10mm and left to stand at 20°C to 180°C for 5 to 60 minutes to form the lithium replenishment composite layer. Preferably, the rolling pressure is 0.2T / 10mm to 0.8T / 10mm, and the coating is left to stand at 50°C to 120°C for 10 to 30 minutes to form the lithium replenishment composite layer.

15. A lithium replenishment method, characterized in that, A negative electrode sheet is provided, wherein a negative electrode active material layer is disposed on the surface of the negative electrode sheet; The active material layer is dried until the water content is ≤500ppm; The lithium replenishment composite layer according to any one of claims 1-13 is bonded to the negative electrode sheet, such that the interface layer is in contact with the negative electrode active material layer, the interface pressure between the interface layer and the negative electrode active material layer is 0.1 MPa to 2 MPa, and pre-lithiation is performed under the conditions of ambient temperature 25℃ to 180℃ and humidity ≤1.7%. After the pre-lithiation is completed, the lithium replenishment composite layer is peeled off from the negative electrode sheet to form a pre-lithiated negative electrode sheet.

16. A pre-lithiated negative electrode, characterized in that, The pre-lithiated negative electrode sheet is obtained by the lithium replenishment method described in claim 15.

17. A method for preparing a secondary battery, characterized in that, The secondary battery is formed by stacking or winding the pre-lithiated negative electrode, separator and positive electrode as described in claim 16, and then performing processes such as casing, liquid injection, encapsulation, formation and degassing.

18. A secondary battery, characterized in that, The secondary battery is prepared by the preparation method described in claim 17.

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