Lithium supplementing composite layer and preparation method thereof, lithium supplementing method, pre-lithiated negative electrode sheet, secondary battery and electronic device

Abstract

The application provides a lithium supplementing composite layer, a preparation method of the lithium supplementing composite layer, a lithium supplementing method, a pre-lithiated negative electrode sheet, a secondary battery and an electronic device. The lithium supplementing composite layer comprises an interface layer and a lithium supplementing layer which are arranged in a stack. The interface layer comprises interface particles and a binder. The interface particles comprise 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, silicon-carbon material, silicon-oxygen material, lithium titanate, tin and tin-copper alloy. The conductive agent is selected from at least one of conductive carbon black, carbon fiber, graphene and carbon nanotube. The binder is selected from at least one of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride and polyethylene oxide. The lithium supplementing layer comprises lithium metal and / or lithium alloy. The lithium supplementing composite layer satisfies the above characteristics, supplements the negative electrode sheet, improves the initial coulomb efficiency of the secondary battery, reduces the cycle capacity attenuation, and improves the energy density of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a lithium replenishment composite layer and its preparation method, lithium replenishment method, pre-lithiated negative electrode sheet, secondary battery and 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 methods for lithium replenishment in 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 vibration and an electric field, then compacting it through rolling to prevent detachment and thus replenishing the lithium content. However, lithium powder is prone to floating, polluting the environment; its particle size is relatively large (Dv50 is approximately 25μm), leading 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 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 replenished negative electrode sheet. Lithium strip rolling for lithium replenishment typically involves mechanically rolling lithium strips onto the negative electrode, resulting in low utilization of the coated lithium film. Unconverted lithium film loses its electronic conductivity, becoming "dead lithium," which hinders lithium-ion diffusion, leading to increased internal resistance and polarization in the lithium-ion battery. More seriously, the unconverted lithium promotes lithium-ion nucleation, causing lithium plating and posing safety risks. Electrochemical lithium replenishment involves assembling lithium foil or lithium alloys with a separator, negative electrode, and electrolyte into a stack, then forming the stack, and finally drying the formed negative electrode to form a lithium-replenished negative electrode. Electrochemical lithium replenishment usually requires an electrolyte, and side reactions between the electrolyte and water in the environment can produce byproducts that remain in the negative electrode, affecting cycle performance. Therefore, all three lithium replenishment methods have certain problems regarding environmental impact, lithium replenishment uniformity, and post-replenishment side reactions. Therefore, there is an urgent need to provide a lithium replenishment method that can improve the initial coulombic efficiency of lithium-ion batteries containing silicon-carbon or silicon-oxygen anodes, 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-replenishing composite layer and its preparation method, a lithium-replenishing method, a pre-lithiated negative electrode sheet, a secondary battery, and an electronic device, so as to improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of this application provides a lithium replenishment composite layer, wherein the lithium replenishment composite layer includes an interface layer and a lithium replenishment layer stacked together. The interface layer includes interface particles and a binder. The interface particles include 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, silicon carbide, silicon oxide, lithium titanate, tin, and tin-copper alloy. The conductive agent is selected from at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes. The binder is selected from at least one of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, and polyethylene oxide. The lithium replenishment layer includes lithium metal and / or a lithium alloy. Using the above-mentioned lithium replenishment composite layer to pre-lithiate the negative electrode sheet is beneficial for lithium replenishment of the negative electrode sheet. The resulting pre-lithiated negative electrode sheet, when applied in a secondary battery, can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0006] In one embodiment of this application, based on the mass of the interface layer, the mass percentage W1 of the interface particles is 80% to 98%, and the mass percentage W2 of the binder is 2% to 20%. By adjusting the mass percentages of the interface particles and the binder within the scope of this application, the interface particles and binder have suitable mass percentages, the interface layer has good self-support and mechanical strength, and the conductivity of the interface layer is improved, which is beneficial for 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 improving the energy density of the secondary battery.

[0007] In one embodiment of this application, the interface particles comprise a lithium-intercalating material and a conductive agent. Based on the mass of the interface layer, the mass percentage of the lithium-intercalating material W11 is 60% to 97.5%, the mass percentage of the conductive agent W12 is 0.5% to 20%, and the mass percentage of the binder W2 is 2% to 20%. The interface particles, comprising the lithium-intercalating material and the conductive agent, possess both electron and ion conduction capabilities, thus enhancing the electron and ion conduction capabilities of the interface layer. Furthermore, by controlling the mass percentages of the lithium-intercalating material, the conductive agent, and the binder within the scope of this application, the self-support and mechanical strength of the interface layer can be further improved, as well as its electron and ion conduction capabilities. This facilitates lithium replenishment to the negative electrode, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the energy density of the secondary battery.

[0008] In one embodiment of this application, the thickness H1 of the interface layer is 20 μm to 100 μm, preferably 30 μm to 50 μm. By adjusting the thickness of the interface layer within the range of this application, it is beneficial to further replenish lithium to the negative electrode, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further improving the energy density of the secondary battery.

[0009] In one embodiment of this application, the compaction density (PD) of the interface layer is 0.8 g / cm³. 3 Up to 1.9 g / cm 3 Preferably, the compaction density (PD) of the interface layer is 1.0 g / cm³. 3 Up to 1.5g / cm 3 By adjusting the compaction density of the interface layer within the scope of this application, it is possible to regulate the thickness of the interface layer, increase the contact between interface particles, enhance the conductivity of electrons and ions in the interface layer, facilitate further lithium replenishment to the negative electrode, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the energy density of the secondary battery.

[0010] In one embodiment of this application, the flatness of the two surfaces of the interface layer is 0 μm to 10 μm, preferably 0 μm to 4 μm. By adjusting the flatness of the two surfaces of the interface layer within the scope of this application, it is beneficial to further replenish lithium on the negative electrode, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further improving the energy density of the secondary battery.

[0011] In one embodiment of this application, the electronic conductivity σ1 of the interface particles is from 0.1 mS / cm to 1000 mS / cm, preferably from 10 mS / cm to 700 mS / cm; the ionic conductivity σ2 of the interface particles is from 0.01 mS / cm to 100 mS / cm, preferably from 0.1 mS / cm to 10 mS / cm. By controlling the electronic and ionic conductivity of the interface particles within the range of this application, it is beneficial to further replenish lithium on the negative electrode, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further improving the energy density of the secondary battery.

[0012] In one embodiment of this application, 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 support layer includes at least one of a metal foil, a polyethylene terephthalate film, a polypropylene film, a polyethylene film, or a polyimide film. The metal foil includes copper foil, nickel foil, steel foil, or a copper-nickel alloy foil. The inclusion of the support layer in the lithium replenishment composite layer, and the selection of the aforementioned support layer, provides better support for the lithium replenishment layer and the interface layer. 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, facilitating further lithium replenishment to the negative electrode sheet. Consequently, this further improves the initial coulombic efficiency of the secondary battery, further reduces cycle capacity decay, and further increases the energy density of the secondary battery.

[0013] In one embodiment of this application, along the tape direction of the lithium replenishment composite layer, the tensile strength K1 of the interface layer is from 0.5 N / 10 mm to 50 N / 10 mm, preferably from 1 N / 10 mm to 10 N / 10 mm. Within the range of this application, the interface layer exhibits high tensile strength and good mechanical properties, which can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further increase the energy density of the secondary battery.

[0014] In one embodiment of this application, along the tape direction perpendicular to the lithium replenishment composite layer, the tensile strength K2 of the interface layer is from 0.05 N / 10 mm to 5 N / 10 mm, preferably from 0.1 N / 10 mm to 1 N / 10 mm. Within the range of this application, the interface layer exhibits high tensile strength and good mechanical properties, which can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further increase the energy density of the secondary battery.

[0015] In one embodiment of this application, along the tape direction of the lithium replenishment composite layer, the tensile strength K3 of the support layer is from 1.5 N / 10 mm to 200 N / 10 mm, preferably from 22 N / 10 mm to 100 N / 10 mm. The tensile strength of the support layer within this range along the tape direction of the lithium replenishment composite layer can adequately meet the requirement of peeling the lithium replenishment composite layer from the surface of the negative electrode material layer after lithium replenishment, which is beneficial for further lithium replenishment of the negative electrode sheet. This further improves the initial coulombic efficiency of the secondary battery, further reduces cycle capacity decay, and further increases the energy density of the secondary battery.

[0016] In one embodiment of this application, the tensile strength K1 of the interface layer along the walking direction of the lithium replenishment composite layer is 0.5 N / 10 mm to 50 N / 10 mm, and the tensile strength K2 of the interface layer along the walking direction perpendicular to the lithium replenishment composite layer is 0.05 N / 10 mm to 5 N / 10 mm. The tensile strength of the interface layer along the walking direction of the lithium replenishment composite layer and along the walking direction perpendicular to the lithium replenishment composite layer, within the range of this application, can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0017] In one embodiment of this application, the tensile strength K1 of the interface layer along the lithium replenishment composite layer is 0.5 N / 10 mm to 50 N / 10 mm, and the tensile strength K3 of the support layer along the lithium replenishment composite layer is 1.5 N / 10 mm to 200 N / 10 mm. The tensile strengths of the interface layer and the support layer along the lithium replenishment composite layer, within the range specified in this application, can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0018] In one embodiment of this application, the tensile strength K2 of the interface layer along the direction perpendicular to the lithium replenishment composite layer is 0.05 N / 10 mm to 5 N / 10 mm, and the tensile strength K3 of the support layer along the direction perpendicular to the lithium replenishment composite layer is 1.5 N / 10 mm to 200 N / 10 mm. The tensile strengths of the interface layer and the support layer along the direction perpendicular to the lithium replenishment composite layer, within the range of this application, can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0019] In one embodiment of this application, the tensile strength K1 of the interface layer along the walking direction of the lithium replenishment composite layer is 0.5 N / 10 mm to 50 N / 10 mm, and the tensile strength K2 of the interface layer along the walking direction perpendicular to the lithium replenishment composite layer is 0.05 N / 10 mm to 5 N / 10 mm, and the tensile strength K3 of the support layer along the walking direction of the lithium replenishment composite layer is 1.5 N / 10 mm to 200 N / 10 mm. The tensile strengths of the interface layer and the support layer along the walking direction of the lithium replenishment composite layer, and the tensile strength of the interface layer along the walking direction perpendicular to the lithium replenishment composite layer, within the range of this application, can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0020] 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 range of this application, it is beneficial to further replenish lithium to the negative electrode, which can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0021] 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 range of this application, the support layer has a suitable thickness, which can better meet the need for the lithium-replenishing composite layer to peel off from the surface of the negative electrode material layer after lithium replenishment. This is beneficial for further lithium replenishment of the negative electrode sheet, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further improving the energy density of the secondary battery.

[0022] A second aspect of this application provides a method for preparing the lithium-supplemented composite layer in any of the foregoing embodiments, comprising the following steps:

[0023] (1) Apply lithium metal powder slurry to the support layer and dry and roll it to form a lithium replenishment layer; or roll lithium foil and / or lithium alloy foil to the support layer to form a lithium replenishment layer; or apply lithium or lithium alloy molten slurry to the support layer and cool and roll it to form a lithium replenishment layer; wherein the rolling pressure P1 is 0.1T / 10mm to 2T / 10mm;

[0024] (2) After mixing the interface particles and the binder, the mixture is thinned and dried to form an interface layer; the interface layer is placed on the surface of the lithium replenishment layer and then rolled. The rolling pressure P2 is 0.1T / 10mm to 2T / 10mm, preferably 0.2T / 10mm to 0.8T / 10mm; the rolling temperature T1 is 20℃ to 180℃, preferably 50℃ to 120℃; the rolling and standing time t1 is 10min to 120min, preferably 20min to 100min; thus forming a lithium replenishment composite layer.

[0025] The lithium-replenishing composite layer is prepared using the method provided in this application. The lithium-replenishing composite layer comprises an interface layer and a lithium-replenishing layer stacked together. The interface layer includes interface particles and a binder. The types of interface particles and binder are within the scope of this application. The lithium-intercalating material and / or conductive agent possess both electron and ion conduction capabilities. The interface layer is brought into contact with the negative electrode material layer to achieve the pre-lithiation process of the negative electrode material layer. Simultaneously, the interface layer includes a binder, which increases the mechanical strength of the interface layer and provides self-support. Furthermore, the addition of the binder results in higher coverage of the interface layer, reducing the impact of residual silicone oil on the surface of the lithium-replenishing layer entering the secondary battery and affecting its electrochemical performance. It also reduces the impact of potential side reactions from lithium metal in the lithium-replenishing layer entering the secondary battery on its electrochemical performance. Additionally, the surface flatness of the interface layer can be reduced, and the process is simpler. After the pre-lithiation treatment is completed, the lithium-replenishing composite layer is peeled off from the negative electrode to obtain the pre-lithiated negative electrode. Applying the pre-lithiated negative electrode to a secondary battery can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0026] A third aspect of this application provides a lithium replenishment method, which includes the following steps:

[0027] The negative electrode sheet is dried. 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.

[0028] The lithium-supplement composite layer and the negative electrode sheet prepared by the preparation method in any of the aforementioned embodiments are bonded together so that the interface layer is in contact with the negative electrode material layer, and a pre-lithiation treatment is performed. The interface pressure P3 between the interface layer and the negative electrode material layer is 0.1 MPa to 2 MPa, preferably 0.2 MPa to 1.0 MPa; the bonding time t2 between the interface layer and the negative electrode material layer is 1 h to 144 h, preferably 2 h to 96 h; the bonding temperature T2 between the interface layer and the negative electrode material layer is 50 °C to 180 °C, preferably 60 °C to 160 °C; after the pre-lithiation treatment is completed, the lithium-supplement composite layer is peeled off from the negative electrode sheet to form a pre-lithiated negative electrode sheet.

[0029] The lithium-replenishing composite layer is prepared using the lithium-replenishing composite layer preparation method provided in this application, and then a pre-lithiated negative electrode sheet is prepared using the lithium-replenishing method provided in this application. This facilitates the lithium replenishment of the negative electrode sheet, and the resulting pre-lithiated negative electrode sheet can be applied to secondary batteries, which can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0030] A fourth aspect of this application provides a pre-lithiated negative electrode, which is obtained by the lithium replenishment method in any of the foregoing embodiments. When applied to a secondary battery, the pre-lithiated negative electrode can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0031] A fifth 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 of this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0032] A sixth aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0033] The beneficial effects of this application are:

[0034] This application provides a lithium-replenishing composite layer and its preparation method, lithium-replenishing method, pre-lithiated negative electrode sheet, secondary battery, and electronic device. The lithium-replenishing composite layer includes an interface layer and a lithium-replenishing layer stacked together. The interface layer includes interface particles and a binder. The interface particles include a lithium-intercalating material and / or a conductive agent. 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, carbon fiber, graphene, and carbon nanotubes. The binder is selected from at least one of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, and polyethylene oxide. The lithium-replenishing layer includes lithium metal and / or lithium alloys. The lithium-replenishing composite layer satisfies the above characteristics, and by replenishing lithium on the negative electrode sheet, it can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0035] 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

[0036] 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.

[0037] Figure 1 This is a schematic diagram of the structure of the lithium-supplemented composite layer according to one embodiment of this application;

[0038] Figure 2 This is a schematic diagram of the structure of the negative electrode and the lithium replenishment composite layer during the pre-lithiation process of one embodiment of this application;

[0039] Figure 3 This is a schematic diagram of the lithium-filled composite layer according to another embodiment of this application;

[0040] Figure 4 This is a schematic diagram of the negative electrode and the lithium replenishment composite layer during the pre-lithiation process of another embodiment of this application;

[0041] Figure 5 The flatness H of the interface layer away from the lithium replenishment layer b A schematic diagram;

[0042] Figure 6 The smoothness H of the surface of the interface layer near the lithium replenishment layer d A schematic diagram. Detailed Implementation

[0043] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the 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.

[0044] 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.

[0045] The first aspect of this application provides a lithium replenishment composite layer, wherein the lithium replenishment composite layer includes an interface layer and a lithium replenishment layer stacked thereon, such as... Figure 1 As shown, the lithium replenishment composite layer 10 includes an interface layer 13 and a lithium replenishment layer 12 stacked together. The interface layer includes interface particles and a binder. The interface particles include 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, silicon carbide, silicon oxide, lithium titanate, tin, and tin-copper alloy. The conductive agent is selected from at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes. The binder is selected from at least one of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, and polyethylene oxide. The lithium replenishment layer includes lithium metal and / or lithium alloy. In this application, the conductive carbon black may include, but is not limited to, at least one of Super P, acetylene black, or Ketjen black; the carbon fiber may include, but is not limited to, at least one of vapor-grown carbon fiber (VGCF) or carbon nanofiber; the carbon nanotube may include, but is not limited to, at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or few-walled carbon nanotubes. The lithium alloy may include, but is not limited to, lithium-aluminum alloy.

[0046] The inventors discovered that the lithium-filling composite layer comprises a stacked interface layer and a lithium-filling layer. The interface layer includes interface particles and a binder. The types of interface particles and binder are within the scope of this application. The lithium-intercalating material and / or conductive agent possess both electron and ion conduction capabilities. The interface layer is then brought into contact with the negative electrode material layer, such as... Figure 2 As shown, the interface layer 13 is brought into contact with the negative electrode material layer 15 disposed on the two surfaces of the negative electrode current collector 14. It can be understood that the aforementioned "negative electrode material layer 15" refers to the negative electrode material layer of the negative electrode sheet that has not undergone pre-lithiation. The lithium replenishment layer and the negative electrode material layer form an internal short circuit. Lithium atoms in the lithium replenishment layer undergo an oxidation reaction, losing electrons to generate lithium ions. Electrons and lithium ions are transferred through the interface layer 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, thus achieving the pre-lithiation process of the negative electrode material layer. Simultaneously, the interface layer includes a binder, which increases the mechanical strength of the interface layer and provides self-support. Furthermore, the addition of the binder results in higher coverage of the interface layer, reducing the impact of residual silicone oil on the surface of the lithium replenishment layer entering the secondary battery and affecting its electrochemical performance. It also reduces the impact of potential side reactions from elemental lithium metal entering the secondary battery and affecting its electrochemical performance. Additionally, the surface flatness of the interface layer can be reduced, and the process is simpler. After the pre-lithiation treatment, the lithium replenishment composite layer is peeled off from the negative electrode sheet to obtain a pre-lithiated negative electrode sheet. This peeling process reduces the impact of lithium metal remaining on the surface of the negative electrode material from the lithium replenishment layer, which could lead to side reactions and affect the electrochemical performance of the secondary battery. Using the aforementioned lithium replenishment composite layer for pre-lithiation treatment of the negative electrode sheet facilitates lithium replenishment, resulting in a pre-lithiated negative electrode sheet that, when applied to secondary batteries, can improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0047] In one embodiment of this application, based on the mass of the interface layer, the mass percentage content W1 of the interface particles is 80% to 98%, and the mass percentage content W2 of the binder is 2% to 20%. Exemplarily, W1 can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, or a range consisting of any two of the above values; W2 can be 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of the above values. By adjusting the mass percentage content of the interface particles and the binder within the scope of this application, the interface particles and binder have suitable mass percentages, the interface layer has good self-support and mechanical strength, and the conductivity of the interface layer is improved, which is beneficial for 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 improving the energy density of the secondary battery. This application does not particularly limit the method of adjusting the mass percentage content of the interface particles and the mass percentage content of the binder in the interface layer, as long as the purpose of this application can be achieved. For example, the mass percentage of interface particles can be controlled by adjusting the mass of the interface particles added during the preparation of the interface layer; the mass percentage of binder can be controlled by adjusting the mass of the binder added during the preparation of the interface layer.

[0048] In one embodiment of this application, the interface particles include a lithium-intercalating material and a conductive agent. Based on the mass of the interface layer, the mass percentage of the lithium-intercalating material W11 is 60% to 97.5%, the mass percentage of the conductive agent W12 is 0.5% to 20%, and the mass percentage of the binder W2 is 2% to 20%. Exemplarily, W11 can be 60%, 64%, 66%, 68%, 70%, 74%, 76%, 78%, 80%, 84%, 86%, 88%, 90%, 94%, 96%, 97.5%, or a range consisting of any two of the above values; W12 can be 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of the above values; W2 can be 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of the above values. The interface particles include a lithium-intercalating material and a conductive agent. Both the lithium-intercalating material and the conductive agent possess both electron and ion conduction capabilities, thus enhancing the electron and ion conduction capabilities of the interface layer. Furthermore, by controlling the mass percentage of the lithium-intercalating material, the conductive agent, and the binder within the scope of this application, the self-support and mechanical strength of the interface layer can be further improved, as well as its electron and ion conduction capabilities. Using the aforementioned lithium-replenishing composite layer for pre-lithiation treatment of the negative electrode sheet facilitates lithium replenishment. The resulting pre-lithiated negative electrode sheet, when applied to a secondary battery, can further improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the energy density of the secondary battery. This application does not impose any particular limitation on the method of controlling the mass percentage of the lithium-intercalating material, the conductive agent, and the binder in the interface layer, as long as the purpose of this application is achieved. For example, the mass percentage of lithium intercalation material can be controlled by adjusting the mass of the lithium intercalation material added during the preparation of the interface layer; the mass percentage of conductive agent can be controlled by adjusting the mass of the conductive agent added during the preparation of the interface layer; and the mass percentage of binder can be controlled by adjusting the mass of the binder added during the preparation of the interface layer.

[0049] In one embodiment of this application, the thickness H1 of the interface layer is 20 μm to 100 μm, preferably 30 μm to 50 μm. Exemplarily, the value of H1 can be 20, 30, 40, 50, 60, 70, 80, 90, 100, or a range of any two of the above values. Lithium atoms in the lithium replenishment layer lose electrons to generate lithium ions. Electrons and lithium ions are transferred through the interface layer to the surface or interior of the negative electrode material layer. By controlling the thickness of the interface layer within the scope of this application, the interface layer has a suitable thickness, the electron and lithium ion transport distance is moderate, and electrons and lithium ions can effectively recombine to form lithium intercalation compounds, which is beneficial for further lithium replenishment of the negative electrode sheet, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further improving the energy density of the secondary battery. This application does not particularly limit the method of controlling the thickness of the interface layer, as long as it achieves the purpose of this application. For example, the thickness of the interface layer can be controlled by controlling the type of interface particles; the thickness of the interface layer can also be controlled by controlling the areal density and / or compaction density of the interface layer. For example, different types of interface particles have different particle sizes; the larger the particle size, the thicker the interface layer. For example, increasing the roller pressure P2 increases the compaction density of the interface layer and decreases its thickness; conversely, decreasing the roller pressure P2 decreases the compaction density and increases its thickness. For example, adjusting the areal density of the interface layer before roller pressing results in a decrease in areal density while maintaining a constant compaction density, leading to a decrease in the interface layer thickness; conversely, increasing the areal density while maintaining a constant compaction density results in an increase in the interface layer thickness.

[0050] In one embodiment of this application, the compaction density (PD) of the interface layer is 0.8 g / cm³. 3 Up to 1.9 g / cm 3 Preferably, the compaction density (PD) of the interface layer is 1.0 g / cm³. 3 Up to 1.5g / cm 3 For example, the value of PD can be 0.8, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or a range of any two of the above values. By adjusting the compaction density of the interface layer within the scope of this application, it is helpful to adjust the thickness of the interface layer, increase the contact between interface particles, improve the conductivity of electrons and ions in the interface layer, facilitate further lithium replenishment to the negative electrode, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the energy density of the secondary battery. This application does not particularly limit the method of adjusting the compaction density of the interface layer, as long as it achieves the purpose of this application. For example, the compaction density of the interface layer can be adjusted by controlling the pressure of hot or cold pressing of the interface layer and the size of the roll gap.

[0051] In one embodiment of this application, the flatness of the two surfaces of the interface layer is from 0 μm to 10 μm, preferably from 0 μm to 4 μm. Exemplarily, the flatness values ​​of the two surfaces of the interface layer can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two of the above values. In this application, flatness refers to the height difference between the highest and lowest points of the same end face. The aforementioned "two surfaces of the interface layer" refer to the surface of the interface layer away from the lithium replenishment layer and the surface of the interface layer close to the lithium replenishment layer. The flatness of the surface of the interface layer away from the lithium replenishment layer affects the tightness of its bonding with the negative electrode material layer. The tighter the bonding between the interface layer and the negative electrode material layer, the easier the transport of lithium ions and electrons, i.e., the lower the resistance. The flatness of the surface of the interface layer close to the lithium replenishment layer affects the tightness of its bonding with the lithium replenishment layer. The tighter the bonding between the interface layer and the lithium replenishment layer, the easier the transport of lithium ions and electrons, i.e., the lower the resistance. Within the scope of this application, by controlling the flatness of the two surfaces of the interface layer, the bonding between the interface layer and the negative electrode material layer is relatively tight, and the bonding between the interface layer and the lithium replenishment layer is also relatively tight. This is beneficial for the transport of lithium ions and electrons, and 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 improving the energy density of the secondary battery. This application does not have any particular limitations on the method of controlling the flatness of the two surfaces of the interface layer, as long as it can achieve the purpose of this application. For example, the flatness of the two surfaces of the interface layer can be controlled by adjusting the type of interface particles, the particle size of the interface particles, or the roller pressure P2.

[0052] In one embodiment of this application, the electronic conductivity σ1 of the interface particles is from 0.1 mS / cm to 1000 mS / cm, preferably from 10 mS / cm to 700 mS / cm; the ionic conductivity σ2 of the interface particles is from 0.01 mS / cm to 100 mS / cm, preferably from 0.1 mS / cm to 10 mS / cm. Exemplarily, the value of σ1 can be 0.1, 10, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, or a range consisting of any two of the above values; the value of σ2 can be 0.01, 0.05, 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 40, 60, 80, 100, or a range consisting of any two of the above values. Within the scope of this application, by controlling the electronic and ionic conductivity of the interface particles, the interface particles exhibit both high electronic and ionic conductivity, which is beneficial for the transport of lithium ions and electrons, facilitating further lithium replenishment to the negative electrode, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the energy density of the secondary battery. This application does not impose any particular limitation on the method of controlling the electronic and ionic conductivity of the interface particles, as long as the purpose of this application is achieved. For example, the electronic and ionic conductivity of the interface particles can be controlled by adjusting the type of interface particles.

[0053] In this application, the electronic conductivity and ionic conductivity of the interface layer can be controlled by adjusting the mass percentage of interface particles and binder in the interface layer.

[0054] In one embodiment of this application, 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 support layer includes at least one of a metal foil, a polyethylene terephthalate film, a polypropylene film, a polyethylene film, or a polyimide film. The metal foil includes copper foil, nickel foil, steel foil, or a copper-nickel alloy foil. Figure 3 As shown, the lithium replenishment composite layer 10 includes an interface layer 13 and a lithium replenishment layer 12 stacked together. The lithium replenishment composite layer 10 also includes a support layer 11, which is disposed on the surface of the lithium replenishment layer 12 away from the interface layer 13. The inclusion of the support layer, specifically the aforementioned support layer, provides better support for the lithium replenishment layer and the interface layer, further improving the mechanical strength of the lithium replenishment composite layer. 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 breakage. 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 energy density of the secondary battery.

[0055] In one embodiment of this application, the lithium replenishment composite layer includes an interface layer and a lithium replenishment layer stacked together. The lithium replenishment composite layer also includes a support layer disposed on the surface of the lithium replenishment layer away from the interface layer. The interface layer includes interface particles and a binder. The types of interface particles and binder are within the scope of this application. The lithium intercalation material and / or conductive agent possess both electron and ion conduction capabilities. The interface layer contacts the negative electrode material layer, such as... Figure 4 As shown, the interface layer 13 is brought into contact with the negative electrode material layer 15 disposed on the two surfaces of the negative electrode current collector 14. It can be understood that the aforementioned "negative electrode material layer 15" refers to the negative electrode material layer of the negative electrode sheet that has not undergone pre-lithiation. The lithium replenishment layer and the negative electrode material layer form an internal short circuit. Lithium atoms in the lithium replenishment layer undergo an oxidation reaction, losing electrons to generate lithium ions. Electrons and lithium ions are transferred through the interface layer 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, thus achieving the pre-lithiation process of the negative electrode material layer. Simultaneously, the interface layer includes a binder, which increases the mechanical strength of the interface layer and provides self-support. Furthermore, the addition of the binder results in higher coverage of the interface layer, reducing the impact of residual silicone oil on the surface of the lithium replenishment layer entering the secondary battery and affecting its electrochemical performance. It also reduces the impact of potential side reactions from elemental lithium metal entering the secondary battery and affecting its electrochemical performance. Additionally, the surface flatness of the interface layer can be reduced, and the process is simpler. Because the lithium replenishment composite layer has a support layer, the pre-lithiation treatment allows for smoother peeling of the lithium replenishment composite layer from the surface of the negative electrode material layer after lithium replenishment, resulting in a pre-lithiated negative electrode sheet. This peeling process reduces the impact of lithium metal remaining on the surface of the negative electrode material layer and undergoing side reactions on the electrochemical performance of the secondary battery. Using the aforementioned lithium replenishment composite layer for pre-lithiation treatment of the negative electrode sheet facilitates further lithium replenishment. The resulting pre-lithiated negative electrode sheet, when used in secondary batteries, can further improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0056] In one embodiment of this application, along the tape direction of the lithium-filled composite layer, i.e., the MD direction, the tensile strength K1 of the interface layer is from 0.5 N / 10 mm to 50 N / 10 mm. Preferably, the tensile strength K1 of the interface layer is from 1 N / 10 mm to 10 N / 10 mm. Exemplarily, K1 can be 0.5 N / 10 mm, 1 N / 10 mm, 3 N / 10 mm, 5 N / 10 mm, 7 N / 10 mm, 10 N / 10 mm, 15 N / 10 mm, 20 N / 10 mm, 25 N / 10 mm, 30 N / 10 mm, 35 N / 10 mm, 40 N / 10 mm, 45 N / 10 mm, 50 N / 10 mm, or a range consisting of any two of the above values. Along the tape-running direction of the lithium replenishment composite layer, the interface layer exhibits high tensile strength within the scope of this application. This interface layer possesses good mechanical properties, effectively resisting tensile forces in the tape-running direction and reducing the likelihood of direct contact between the lithium replenishment layer and the negative electrode material layer due to interface layer cracking. This reduces the possibility of residual silicone oil and elemental lithium on the surface of the negative electrode material layer, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further increasing the energy density of the secondary battery. This application does not impose any particular limitation on the method of controlling the tensile strength of the interface layer along the MD direction, as long as the purpose of this application can be achieved. For example, the tensile strength of the interface layer along the MD direction can be controlled by adjusting the mass percentage of the binder and / or the roller pressure P2. Exemplarily, increasing the mass percentage of the binder increases the tensile strength of the interface layer along the MD direction; decreasing the mass percentage of the binder decreases the tensile strength of the interface layer along the MD direction. Increasing the roller pressure P2 increases the tensile strength of the interface layer along the MD direction; decreasing the roller pressure P2 decreases the tensile strength of the interface layer along the MD direction.

[0057] In one embodiment of this application, along the direction perpendicular to the lithium-filled composite layer, i.e., the TD direction, the tensile strength K2 of the interface layer is from 0.05 N / 10 mm to 5 N / 10 mm. Preferably, the tensile strength K2 of the interface layer is from 0.1 N / 10 mm to 1 N / 10 mm. Exemplarily, K2 can be 0.05 N / 10 mm, 0.1 N / 10 mm, 0.3 N / 10 mm, 0.5 N / 10 mm, 0.7 N / 10 mm, 1 N / 10 mm, 3 N / 10 mm, 5 N / 10 mm, or a range consisting of any two of the above values. Along the tape direction perpendicular to the lithium replenishment composite layer, the tensile strength of the interface layer is within the range of this application. The interface layer possesses high tensile strength and good mechanical properties, effectively resisting tensile forces perpendicular to the tape direction. This reduces the possibility of direct contact between the lithium replenishment layer and the negative electrode material layer due to interface layer cracking, thereby reducing the likelihood of residual silicone oil and elemental lithium on the surface of the negative electrode material layer. This further improves the initial coulombic efficiency of the secondary battery, further reduces cycle capacity decay, and further increases the energy density of the secondary battery. This application does not impose any particular limitation on the method of controlling the tensile strength of the interface layer along the TD direction, as long as the purpose of this application can be achieved. For example, the tensile strength of the interface layer along the TD direction can be controlled by adjusting the mass percentage content of the binder.

[0058] In one embodiment of this application, along the tape direction of the lithium-filled composite layer, the tensile strength K3 of the support layer is from 1.5 N / 10 mm to 200 N / 10 mm, preferably from 22 N / 10 mm to 100 N / 10 mm. Exemplarily, K3 can be 1.5 N / 10 mm, 10 N / 10 mm, 20 N / 10 mm, 22 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. Along the lithium replenishment composite layer's belt direction, the tensile strength of the support layer, within the range of this application, can adequately meet the requirement of the lithium replenishment composite layer peeling 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 energy density of the secondary battery. This application does not impose any particular limitation on the method of controlling the tensile strength of the support layer along the MD direction, as long as the purpose of this application can be achieved. For example, the tensile strength of the support layer along the MD direction can be controlled by adjusting the material type and / or thickness of the support layer.

[0059] In one embodiment of this application, the tensile strength K1 of the interface layer along the walking direction of the lithium replenishment composite layer is 0.5 N / 10 mm to 50 N / 10 mm, and the tensile strength K2 of the interface layer along the walking direction perpendicular to the lithium replenishment composite layer is 0.05 N / 10 mm to 5 N / 10 mm. The tensile strength of the interface layer along the walking direction of the lithium replenishment composite layer and along the walking direction perpendicular to the lithium replenishment composite layer, within the range of this application, can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0060] In one embodiment of this application, the tensile strength K1 of the interface layer along the lithium replenishment composite layer is 0.5 N / 10 mm to 50 N / 10 mm, and the tensile strength K3 of the support layer along the lithium replenishment composite layer is 1.5 N / 10 mm to 200 N / 10 mm. The tensile strengths of the interface layer and the support layer along the lithium replenishment composite layer, within the range specified in this application, can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0061] In one embodiment of this application, the tensile strength K2 of the interface layer along the direction perpendicular to the lithium replenishment composite layer is 0.05 N / 10 mm to 5 N / 10 mm, and the tensile strength K3 of the support layer along the direction perpendicular to the lithium replenishment composite layer is 1.5 N / 10 mm to 200 N / 10 mm. The tensile strengths of the interface layer and the support layer along the direction perpendicular to the lithium replenishment composite layer, within the range of this application, can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0062] In one embodiment of this application, the tensile strength K1 of the interface layer along the walking direction of the lithium replenishment composite layer is 0.5 N / 10 mm to 50 N / 10 mm, and the tensile strength K2 of the interface layer along the walking direction perpendicular to the lithium replenishment composite layer is 0.05 N / 10 mm to 5 N / 10 mm, and the tensile strength K3 of the support layer along the walking direction of the lithium replenishment composite layer is 1.5 N / 10 mm to 200 N / 10 mm. The tensile strengths of the interface layer and the support layer along the walking direction of the lithium replenishment composite layer, and the tensile strength of the interface layer along the walking direction perpendicular to the lithium replenishment composite layer, within the range of this application, can further improve the initial coulombic efficiency of the secondary battery, further reduce cycle capacity decay, and further improve the energy density of the secondary battery.

[0063] 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 scope of this application, the lithium replenishment layer has a suitable thickness, which can better meet the lithium replenishment requirements. Secondly, the thickness of the lithium replenishment layer needs to be greater than the embedding depth of the interface particles, thereby effectively avoiding the inability of interface particles to embed, which is beneficial for further lithium replenishment to the negative electrode sheet, further improving the initial coulombic efficiency of the secondary battery, further reducing cycle capacity decay, and further improving the energy density of the secondary battery. Furthermore, the thickness of the lithium replenishment layer within the scope of this application can also save costs. This application does not impose any particular limitation on the method of controlling the thickness of the lithium replenishment layer, as long as the purpose of this application can be achieved. For example, the thickness of the lithium replenishment layer can be controlled by adjusting the roller pressure during the preparation of the lithium replenishment layer. Exemplarily, increasing the roller pressure during the preparation of the lithium replenishment layer results in a decrease in the thickness of the lithium replenishment layer; conversely, decreasing the roller pressure during the preparation of the lithium replenishment layer results in an increase in the thickness of the lithium replenishment layer. For example, the thickness of the lithium replenishment layer can be controlled by adjusting the preparation method of the lithium replenishment layer. The preparation method of the lithium replenishment layer will affect the minimum thickness of the lithium replenishment layer.

[0064] 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 range of this application, 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 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.

[0065] A second aspect of this application provides a method for preparing the lithium-supplemented composite layer in any of the foregoing embodiments, comprising the following steps:

[0066] (1) Under the conditions of ambient temperature ≤30℃ and humidity ≤1.7%, lithium metal powder slurry is coated onto the support layer and dried and rolled to form a lithium replenishment layer; or lithium foil and / or lithium alloy foil is 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. Among them, the rolling pressure P1 is 0.1T / 10mm to 2T / 10mm; specifically, the rolling pressure P11 after coating the lithium metal powder slurry onto the support layer and rolling is 0.1T / 10mm to 2T / 10mm; the rolling pressure P12 after rolling the lithium foil and / or lithium alloy foil onto the support layer is 0.1T / 10mm to 2T / 10mm; the rolling pressure P13 after coating the lithium or lithium alloy molten slurry onto the support layer and rolling is 0.1T / 10mm to 2T / 10mm.

[0067] (2) After mixing the interface particles and binder, the mixture is kneaded, thinned in multiple stages, and dried to form an interface layer. Under the conditions of ambient temperature ≤30℃ and humidity ≤1.7%, the interface layer is placed on the surface of the lithium replenishment layer and then rolled. The rolling pressure P2 is 0.1T / 10mm to 2T / 10mm, preferably 0.2T / 10mm to 0.8T / 10mm. The rolling temperature T1 is 20℃ to 180℃, preferably 50℃ to 120℃. The rolling and standing time t1 is 10min to 120min, preferably 20min to 100min. The lithium replenishment composite layer is formed.

[0068] In step (2) above, the interface particles and binder are mixed and then subjected to intensive mixing, multi-stage thinning, and drying to form an interface layer. Specifically, the interface particles and binder can be mechanically mixed to obtain a mixed intermediate; wherein the temperature of mechanical mixing can be 10℃ to 35℃, the speed of mechanical mixing can be 800r / min to 2000r / min, and the time of mechanical mixing can be 5min to 60min; then the mixed intermediate is passed through an intensive mixer to form a dough-like material, the temperature in the intensive mixer can be 100℃ to 280℃, and the intensive mixing time in the intensive mixer can be 5min to 90min; then the dough-like material is passed through differential rollers for multi-stage thinning, with a speed difference of (1:1.1) to (1:3) to obtain an interface layer; then the above interface layer is dried until the water content is ≤500ppm to obtain the desired interface layer. This application does not have any particular limitation on the above drying method, as long as it can achieve the purpose of this application. For example, the interface layer can be dried by placing it in a vacuum drying oven or baking oven. Roller pressure refers to the force generated by applying pressure to a sample passing through the roll gap when two cylindrical rolls are placed in parallel and the pressure between the roll gap and the upper and lower rolls is controlled.

[0069] For example, P1 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range consisting of any two of the above values. P11 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range consisting of any two of the above values. P12 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range of any two of the above values. P13 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range of any two of the above values. P2 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range of any two of the above values. T1 can be 20℃, 40℃, 50℃, 60℃, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, or a range of any two of the above values. t1 can be 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min, 120min, or a range of any two of the above values.

[0070] The lithium-replenishing composite layer is prepared using the method provided in this application. The lithium-replenishing composite layer comprises an interface layer and a lithium-replenishing layer stacked together. The interface layer includes interface particles and a binder. The types of interface particles and binder are within the scope of this application. The lithium-intercalating material and / or conductive agent possess both electron and ion conduction capabilities. The interface layer is brought into contact with the negative electrode material layer to achieve the pre-lithiation process of the negative electrode material layer. Simultaneously, the interface layer includes a binder, which increases the mechanical strength of the interface layer and provides self-support. Furthermore, the addition of the binder results in higher coverage of the interface layer, reducing the impact of residual silicone oil on the surface of the lithium-replenishing layer entering the secondary battery and affecting its electrochemical performance. It also reduces the impact of potential side reactions from lithium metal in the lithium-replenishing layer entering the secondary battery on its electrochemical performance. Additionally, the surface flatness of the interface layer can be reduced, and the process is simpler. After the pre-lithiation treatment is completed, the lithium-replenishing composite layer is peeled off from the negative electrode to obtain the pre-lithiated negative electrode. Applying the pre-lithiated negative electrode to a secondary battery can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0071] A third aspect of this application provides a lithium replenishment method, which includes the following steps:

[0072] The negative electrode sheet is 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. It is understood that the above-mentioned negative electrode sheet refers to a negative electrode sheet that has not undergone pre-lithiation. Under ambient temperatures of 25°C to 180°C and humidity ≤1.7%, the lithium-replenishing composite layer and the negative electrode sheet prepared by the preparation method in any of the aforementioned embodiments are bonded together so that the interface layer is in contact with the negative electrode material layer for pre-lithiation treatment. The interface pressure P3 between the interface layer and the negative electrode material layer is 0.1 MPa to 2 MPa, preferably 0.2 MPa to 1.0 MPa; the bonding time t2 between the interface layer and the negative electrode material layer is 1 h to 144 h, preferably 2 h to 96 h; the bonding temperature T2 between the interface layer and the negative electrode material layer is 50°C to 180°C, preferably 60°C to 160°C; after the pre-lithiation treatment is completed, the lithium-replenishing composite layer is peeled off from the negative electrode sheet to form a pre-lithiated negative electrode sheet.

[0073] 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 of controlling the bonding interface pressure, 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 interface pressure between the interface layer and the negative electrode material layer can be controlled by adjusting the winding tension. For example, when the lithium-filled composite layer and the negative electrode sheet are pressed into a sheet, the interface pressure between the interface layer and the negative electrode material layer can be controlled by adjusting the pressing pressure.

[0074] For example, P3 can be 0.1MPa, 0.2MPa, 0.4MPa, 0.6MPa, 0.8MPa, 1.0MPa, 1.2MPa, 1.4MPa, 1.6MPa, 1.8MPa, 2MPa, or a range of any two of the above values. t2 can be 1h, 2h, 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 48h, 50h, 55h, 60h, 65h, 70h, 72h, 96h, 144h, or a range of any two of the above values. T2 can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, or a range of any two of the above values.

[0075] In this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "a negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a portion of it; this application has no particular limitation, as long as the purpose of this application is achieved.

[0076] 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 includes 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 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 polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular restrictions on the mass ratio of negative electrode active material, negative electrode binder, and negative electrode conductive agent in the negative 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.

[0077] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, 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.).

[0078] 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 can be from 4 μm to 20 μm. This application also 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 the single-sided negative electrode material layer can be from 30 μm to 250 μm.

[0079] The lithium-replenishing composite layer is prepared using the lithium-replenishing composite layer preparation method provided in this application, and then a pre-lithiated negative electrode sheet is prepared using the lithium-replenishing method provided in this application. This facilitates the lithium replenishment of the negative electrode sheet, and the resulting pre-lithiated negative electrode sheet can be applied to secondary batteries, which can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0080] A fourth aspect of this application provides a pre-lithiated negative electrode, which is obtained by the lithium replenishment method in any of the foregoing embodiments. When applied to a secondary battery, the pre-lithiated negative electrode can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0081] A fifth 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 of this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0082] 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.

[0083] 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).

[0084] The cathode material layer of this application includes a cathode active material, which comprises a substance capable of reversibly inserting and extracting active ions such as lithium ions. The cathode material layer can be one or more layers, and each layer in a multilayer cathode material layer can contain the same or different cathode active materials. This application does not impose any particular limitation on the cathode active material, as long as it can achieve the purpose of this application. For example, the cathode 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 / 3 At 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 in the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the positive electrode conductive agent in the positive electrode material layer may include at least one of the above-mentioned negative electrode conductive agents; the positive electrode binder in the positive electrode material layer 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.

[0085] 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.

[0086] In this application, the secondary battery also includes an electrolyte. The electrolyte includes a lithium salt. This application does not particularly limit 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(oxalatoborate) (LiB(C2O4)2, LiBOB), or lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB). This application does not particularly limit the mass percentage of lithium salt in the electrolyte, as long as the purpose of this application is achieved. The electrolyte also includes a non-aqueous organic solvent. This application does not particularly limit the non-aqueous organic solvent, as long as the purpose of this application is achieved. For example, the non-aqueous organic solvent may include 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 can be achieved.

[0087] In this application, the secondary battery also includes a separator. The separator is used to separate the positive electrode and the negative electrode, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0088] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a diaphragm binder. This application does not particularly limit the aforementioned inorganic particles, and may include 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. This application does not particularly limit the aforementioned diaphragm binder, and may include at least one of the aforementioned negative electrode binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0089] In this application, the secondary battery also includes a casing for housing the positive electrode, separator, pre-lithiated negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[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 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 pre-lithiated negative electrode sheets, separators, and positive electrode sheets in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it; and then encapsulating, forming, and degassing to obtain a secondary battery; or stacking pre-lithiated negative electrode sheets, separators, and positive electrode sheets 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 into a housing; injecting electrolyte into the housing and sealing it; and then encapsulating, forming, and degassing to obtain a secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0092] A sixth aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high 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] Thickness testing of the support layer, lithium replenishment layer, and interface layer:

[0098] Place the sample to be tested on the table, level it, and 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" button; 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.

[0099] Using the support layer as the sample to be tested, the thickness H3 of the support layer is obtained.

[0100] 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&补锂层 The 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.

[0101] By combining the support layer, lithium replenishment layer, and interface layer into a composite sample, the total thickness H of the support layer, lithium replenishment layer, and interface layer can be obtained. 支撑层&补锂层&界面层 The thickness of the interface layer is H1, i.e., H1 = H 支撑层&补锂层&界面层 -H支撑层&补锂层 .

[0102] Compaction density test of the interface layer:

[0103] A 300mm × 200mm interface layer was selected as the test sample, and 10 pieces with an area of ​​1540.25mm² were cut using a cutting machine. 2 Weigh the small circular pieces and take the average value m; then use a micrometer to measure the thickness of 10 small circular pieces and take the average value thk.

[0104] The compaction density of the interface layer is PD = m / (thk × 1540.25).

[0105] Flatness test of the two surfaces of the interface layer:

[0106] (1) Sample preparation: The lithium-supplemented composite layer sample was cut into 6mm×6mm pieces and attached to the sample stage with conductive adhesive; then the cross section polishing of the lithium-supplemented composite layer sample was performed using a cross section polisher (model IB-19520CCP). The polishing conditions were: vacuum degree of 10 -3 Pa, accelerating voltage of 6kV, grinding speed of 500 micrometers / hour.

[0107] (2) Parameter test: The polished sample was placed on the sample stage of the scanning electron microscope and its cross section was tested by the scanning electron microscope (SEM, Scanning electron microscope, model Thermo Fisher FEI-Apreo S). The test conditions were: accelerating voltage of 10kV, grating of 10spot, working distance of 10mm, and magnification of 2000 times.

[0108] Smoothness H of the interface layer away from the lithium replenishment layer b Defined as: the height difference between the highest point and the lowest point of the upper surface of the interface layer, specifically as follows: Figure 5 As shown. Each sample was tested in 12 parallel samples, and 12 H values ​​were taken. b The average value is the smoothness of the surface of the interface layer far from the lithium replenishment layer.

[0109] Smoothness H of the interface layer near the lithium replenishment layer d Defined as: the height difference between the highest point and the lowest point of the lower surface of the interface layer, specifically as follows: Figure 6 As shown. Each sample was tested in 12 parallel samples, and 12 H values ​​were taken. d The average value is the smoothness of the surface of the interface layer near the lithium replenishment layer.

[0110] Electronic conductivity test of interfacial particles:

[0111] (1) The interface particle powder sample is loaded into the mold and compacted. Pressure is applied using a mechanical pressure system (such as a hydraulic press) to form a dense sample.

[0112] (2) Measure the diameter and thickness of the compacted sample to determine the volume.

[0113] (3) Electrodes are set on both sides of the dense sample. The electrodes are cylindrical pure copper electrodes with a diameter of 14 mm.

[0114] (4) Connect the electrodes, apply a known current I through the dense sample, and use a voltmeter to measure the voltage drop V across the electrodes.

[0115] (5) Calculate the resistance R of the dense sample: R = V / I; where V is the measured voltage drop and I is the applied current.

[0116] The formula for calculating the electronic conductivity σ1 of interfacial particles is:

[0117] σ1 = L1 / (A1 × R); where L1 is the thickness of the dense sample, A1 is the cross-sectional area of ​​the test electrode, and R is the resistance of the dense sample.

[0118] Ionic conductivity test of interfacial particles:

[0119] (1) The interface particle powder sample is loaded into a mold and pressed into a dense cylindrical sample, so that the cylindrical sample is uniform and free of cracks.

[0120] (2) Platinum, an ion-conducting material, is coated on both sides of the cylindrical sample to form a symmetrical electrode structure.

[0121] (3) Connect an impedance analyzer to measure the frequency response of the cylindrical sample. The frequency range is 0.00001Hz to 1000000Hz, and the amplitude is 5mV.

[0122] (4) Perform AC impedance measurement to obtain Nyquist plot and Bode plot.

[0123] (5) Based on the equivalent circuit model, the ionic conductivity σ2 of the interfacial particles is calculated using the following formula:

[0124] σ² = L² / (A² × R) b Where: L2 is the thickness of the cylindrical sample, A2 is the cross-sectional area of ​​the cylindrical sample, and R... b It is the volume resistance of the cylindrical sample, obtained from the intersection of the semicircular arc and the oblique line at the high-frequency end.

[0125] Tensile strength test of the interface layer:

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

[0129] Tensile strength in the TD direction = F2 / W; where F2 is the maximum load and W is the width of the standard test strip.

[0130] Tensile strength test of the support layer:

[0131] The tensile strength test procedure in the MD direction is as follows: Cut the support layer into a standard test strip (width W=16mm, length L=150mm), where the width W of the standard test strip 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 strip in the upper and lower clamps of the tensile testing machine, ensuring the standard test strip is centered and free from folding or twisting. Apply a tensile force at a constant speed of 50mm / min until the standard test strip breaks, and record the load and the corresponding elongation. Calculate the tensile strength in the MD direction according to the following formula:

[0132] Tensile strength in the MD direction = F3 / W; where F3 is the maximum load and W is the width of the standard test specimen.

[0133] Lithium replenishment test:

[0134] Weigh the negative electrode sheet before and after lithium replenishment using an analytical balance with a density of 1 / 100,000. The area of ​​the negative electrode sheet is 1540.25 mm². 2The ratio of the mass of the negative electrode sheet before lithium replenishment to the area of ​​the negative electrode sheet is the areal density before lithium replenishment. The ratio of the mass of the negative electrode sheet after lithium replenishment to the area of ​​the negative electrode sheet is the areal density after lithium replenishment. The amount of lithium replenishment is the difference between the areal density after lithium replenishment and the areal density before lithium replenishment. 24 groups of negative electrode sheets were measured and the average value was calculated to obtain the amount of lithium replenishment.

[0135] First Coulomb efficiency 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 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.

[0137] First Coulomb efficiency (%) = C1 / C0 × 100%.

[0138] Cyclic performance test:

[0139] 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.

[0140] Cyclic capacity retention rate (%) = B / A × 100%.

[0141] The higher the cycle capacity retention rate value obtained from the test, the better the cycle performance of the lithium-ion battery.

[0142] Energy density test:

[0143] The voltage range indicated on the battery's outer packaging should be used as the standard. For example, if the indicated 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: Under 25°C conditions, 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.

[0144] Energy density (Wh / L) = E / V × 10 6 .

[0145] Example 1-1

[0146] <Preparation of Lithium-Supplemental Composite Layer>

[0147] Under ambient temperature of 25℃ and humidity of 1.0%, lithium foil is rolled to a copper foil support layer with a thickness of 14μm to form a lithium replenishment layer. The rolling pressure P12 is 1.5T / 10mm, resulting in a lithium replenishment layer / support layer composite structure.

[0148] Interfacial particles (artificial graphite) and a binder (polytetrafluoroethylene) were mechanically mixed to obtain a mixed intermediate. The mechanical mixing temperature was 25°C, the rotation speed was 1500 r / min, and the mixing time was 60 min. The mixed intermediate was then passed through an internal mixer to form a dough-like material. The temperature in the internal mixer was 150°C, and the mixing time was 75 min. The dough-like material was then thinned through multiple stages using differential rollers with a speed difference of 1:2.5 to obtain an interfacial layer. This interfacial layer was then placed in a vacuum drying oven for drying until the water content was ≤500 ppm, yielding the desired interfacial layer. Based on the mass of the interfacial layer, the mass percentage of the interfacial particles (W1) was 95%, and the mass percentage of the binder (W2) was 5%.

[0149] Under ambient temperature of 25℃ and humidity of 1.0%, the interface layer is placed on the surface of the lithium replenishment layer and then rolled. The rolling pressure P2 is 0.6T / 10mm, the rolling temperature T1 is 90℃, and the rolling and standing time t1 is 60min to form a lithium replenishment composite layer.

[0150] The thickness H1 of the interface layer in the lithium replenishment composite layer is 40 μm; the compaction density PD of the interface layer is 1.2 g / cm³. 3 ; Smoothness H of the interface layer surface far from the lithium replenishment layer b The surface smoothness H of the interface layer near the lithium replenishment layer is 1.0 μm. dThe thickness of the interfacial particles is 1.0 μm; the electronic conductivity σ1 of the interfacial particles is 250 mS / cm, and the ionic conductivity σ2 of the interfacial particles is 1 mS / cm; the tensile strength K1 of the interfacial layer along the banding direction of the lithium replenishment composite layer is 5 N / 10 mm; the tensile strength K2 of the interfacial layer along the banding direction perpendicular to the lithium replenishment composite layer is 0.5 N / 10 mm. The thickness H2 of the lithium replenishment layer is 0.03 mm. The tensile strength K3 of the support layer along the banding direction of the lithium replenishment composite layer is 72 N / 10 mm.

[0151] <Preparation of Negative Electrode Sheets>

[0152] A mixture of silicon-carbon anode active material, acetylene black anode conductive agent, styrene-butadiene rubber (SBR) anode binder, and lithium carboxymethyl cellulose anode binder in a weight ratio of 85:5:5:5 was prepared. Deionized water was added as a solvent, and the mixture was stirred until homogeneous to obtain an anode slurry with a solid content of 28 wt%. The anode slurry was uniformly coated onto one surface of a 12 μm thick copper foil anode current collector and dried at 90 °C to obtain a single-sided anode electrode sheet coated with the anode material layer. The above steps were repeated on the other surface of the copper foil to obtain a double-sided anode electrode sheet coated with the anode material layer. After drying under vacuum at 90 °C for 1 hour, the sheet was cold-pressed, cut, and slit to obtain a 51 mm × 44.2 mm anode sheet. Among them, the silicon-carbon material is a silicon-carbon composite material. Based on the mass of the silicon-carbon composite material, the mass percentage of silicon is 50% and the mass percentage of carbon is 50%. The areal density (CW) of the negative electrode material layer is 2.3 mg / cm², and the compaction density during the cold pressing process is 1.0 g / cm². 3 .

[0153] <Preparation of pre-lithiated negative electrode>

[0154] The prepared negative electrode sheet was dried until the water content was ≤500ppm. Under the conditions of ambient temperature of 90℃ and humidity of 1.0%, the prepared lithium replenishment composite layer was bonded to the prepared negative electrode sheet so that the interface layer and the negative electrode material layer were in contact. The bonding method was to press the sheet together and perform pre-lithiation treatment. The interface pressure P3 between the interface layer and the negative electrode material layer was 0.6MPa, the bonding time t2 between the interface layer and the negative electrode material layer was 20h, and the bonding temperature T2 between the interface layer and the negative electrode material layer was 120℃. After the pre-lithiation treatment was completed, the lithium replenishment composite layer was peeled off from the negative electrode sheet to form a pre-lithiated negative electrode sheet.

[0155] <Preparation of the positive electrode>

[0156] 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 a 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 a size of 48 mm × 41.2 mm. The areal density of the positive electrode material layer was 19.0 mg / cm², and the compaction density during the cold pressing process was 4.15 g / cm². 3 .

[0157] <Preparation of Electrolyte>

[0158] 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.

[0159] <Preparation of the diaphragm>

[0160] A porous polypropylene film with a thickness of 5 μm (provided by Celgard) was used as the separator.

[0161] <Preparation of Lithium-ion Batteries>

[0162] The positive electrode, separator, and pre-lithiated negative electrode prepared above are stacked in sequence, with the separator positioned between the positive electrode and the pre-lithiated negative electrode to act as a separator. 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.

[0163] Examples 1-2 to Examples 1-5

[0164] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0165] Examples 1-6

[0166] Except for the method used to obtain the lithium replenishment layer / support layer composite structure in the <Preparation of Lithium Replenishment Composite Layer>, the rest is the same as in Example 1-1.

[0167] Under ambient temperature of 25℃ and humidity of 1.0%, lithium metal powder slurry was coated onto a copper foil support layer with a thickness of 14μm, dried, and rolled to form a lithium replenishment layer. The rolling pressure P11 was 1.5T / 10mm, resulting in a lithium replenishment layer / support layer composite structure. The solvent for the lithium metal powder slurry was n-hexane, and the solid content was 30wt%.

[0168] Examples 1-7

[0169] Except for the method used to obtain the lithium replenishment layer / support layer composite structure in the <Preparation of Lithium Replenishment Composite Layer>, the rest is the same as in Example 1-1.

[0170] Under ambient temperature of 25℃ and humidity of 1.0%, lithium molten slurry was coated onto a copper foil support layer with a thickness of 14μm, cooled, and rolled to form a lithium replenishment layer. The rolling pressure P13 was 1.5T / 10mm, resulting in a lithium replenishment layer / support layer composite structure.

[0171] Examples 1-8 to Examples 1-18

[0172] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0173] Examples 1-19 to Examples 1-22

[0174] Except for adjusting the thickness of the support layer to increase the tensile strength of the support layer along the MD direction as shown in Table 1, the rest is the same as in Example 1-1.

[0175] Examples 1-23

[0176] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0177] Examples 2-1 to 2-8

[0178] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0179] Examples 2-9

[0180] Except for the fact that in the <Preparation of Lithium-Supplemented Composite Layer>, the interface particles include lithium-intercalating materials and conductive agents, and the relevant preparation parameters are adjusted according to Table 3, the rest is the same as in Examples 1-1.

[0181] Example 2-10

[0182] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 2-9.

[0183] Examples 2-11 to 2-18

[0184] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-1.

[0185] Examples 2-19 to 2-23

[0186] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 2-9.

[0187] Examples 3-1 to 3-12

[0188] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-1.

[0189] Comparative Examples 1-1 to 1-4

[0190] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0191] Comparative Example 2-1

[0192] Except for the absence of an interface layer in the <Preparation of Lithium-Supplemented Composite Layer>, the rest is the same as in Example 1-1.

[0193] Comparative Examples 3-1 to 3-5

[0194] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Examples 1-1.

[0195] The preparation parameters, material properties, and electrical properties of each embodiment and comparative example are shown in Tables 1 to 4.

[0196] Table 1

[0197]

[0198] Note: In Table 1, " / " indicates that there are no relevant preparation parameters.

[0199] Table 2

[0200]

[0201] As can be seen from Examples 1-1 to 1-23 and Comparative Examples 1-1 to 1-4, the lithium-replenishing composite layer prepared using the method provided in this application, followed by the preparation of a pre-lithiated negative electrode using the lithium replenishment method provided in this application, results in a lithium-ion battery with high lithium replenishment capacity, high initial coulombic efficiency, high cycle capacity retention, and high energy density. This demonstrates that the method can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase the energy density of lithium-ion batteries. In Comparative Examples 1-1 to 1-4, the lithium-replenishing composite layer preparation method is not within the scope of this application, and the prepared lithium-ion batteries exhibit lower lithium replenishment capacity, lower initial coulombic efficiency, lower cycle capacity retention, and lower energy density. In Comparative Example 1-2, the rolling temperature T1 is 200°C, causing the lithium replenishment layer to melt and undergo severe side reactions, making effective lithium replenishment impossible. The prepared lithium-ion battery exhibits lower initial coulombic efficiency, lower cycle capacity retention, and lower energy density.

[0202] As shown in Examples 1-1 to 1-5, the thickness of the lithium replenishment layer gradually decreases with increasing roller pressure P12. The lithium replenishment amount in Examples 1-1 to 1-4 is 0.19 mg / cm², consuming a lithium replenishment layer thickness of 0.0033 mm. In contrast, the lithium replenishment layer thickness in Example 1-5 is only 0.001 mm, with a lower lithium replenishment amount of only 0.05 mg / cm². Therefore, the lithium replenishment amounts in Examples 1-1 to 1-4 are sufficient, resulting in similar initial coulombic efficiency, cycle capacity retention, and energy density for the lithium-ion batteries. However, the lower lithium replenishment amount in Example 1-5 leads to lower initial coulombic efficiency, cycle capacity retention, and energy density for the lithium-ion batteries. Furthermore, the thicker lithium replenishment layer in Example 1-2 negatively impacts the production efficiency of the lithium-ion batteries.

[0203] The compaction density of the interface layer typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-8 to 1-11, within the scope of this application, the lithium-ion batteries prepared with a compaction density of the interface layer exhibit higher lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density. This indicates that it can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase the energy density of lithium-ion batteries.

[0204] The tensile strength of the interface layer along the MD direction and the tensile strength of the interface layer along the TD direction typically affect the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-8 to 1-11, the lithium-ion batteries prepared with the interface layer along the MD direction exhibit higher lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density within the scope of this application. This indicates that the initial coulombic efficiency of lithium-ion batteries can be improved, cycle capacity decay reduced, and energy density increased. As can be seen from Examples 1-1, 1-8 to 1-11, as the thickness of the interface layer decreases, the compaction density of the interface layer increases. This is due to the increased shear force and increased fibrous degree experienced by the binder during the interface layer preparation process. Increased fibrous degree leads to increased tensile strength of the interface layer.

[0205] The tensile strength of the support layer along the MD direction typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-19 to 1-22, the lithium-ion batteries prepared with the support layer having a high lithium replenishment capacity, high initial coulombic efficiency, high cycle capacity retention, and high energy density exhibit the tensile strength along the MD direction within the scope of this application. This indicates that the initial coulombic efficiency of lithium-ion batteries can be improved, cycle capacity decay reduced, and energy density increased. As shown in Examples 1-1, 1-19 to 1-22, the support layer is copper foil, and the tensile strength per unit width increases with increasing copper foil thickness.

[0206] The thickness of the support layer typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-19 to 1-22, the lithium-ion batteries prepared with a support layer thickness within the range specified in this application exhibit higher lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density. This demonstrates that the support layer thickness can improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the energy density of lithium-ion batteries.

[0207] The type of support layer typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1 and 1-23, the type of support layer used within the scope of this application results in lithium-ion batteries with higher lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density. This indicates that the type of support layer can improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the energy density of lithium-ion batteries.

[0208] Table 3

[0209]

[0210] Note: (1) In Table 3, “ / ” indicates that there are no relevant preparation parameters; (2) In Examples 2-3, “lithium intercalation material type” is “silicon-carbon material”. Silicon-carbon material is silicon-carbon composite material. Based on the mass of silicon-carbon composite material, the mass percentage of silicon element is 50% and the mass percentage of carbon element is 50%. Other examples follow the same principle.

[0211] As can be seen from Examples 1-1, 2-1 to 2-23, and Comparative Example 2-1, the lithium replenishment composite layer includes a stacked interface layer and a lithium replenishment layer. The interface layer includes interface particles and a binder. The types of interface particles and binder are within the scope of this application. The prepared lithium-ion battery has higher lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density, indicating that it can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase the energy density of lithium-ion batteries. Comparative Example 2-1, however, does not have an interface layer in its lithium replenishment composite layer, and the prepared lithium-ion battery has lower lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density.

[0212] As can be seen from Examples 2-5 to 2-8, the interface particles only include conductive agents, the particle size of which is small, and the particle size of the interface particles is much smaller than the thickness of the interface layer. The type of interface particles mainly affects the smoothness of the interface layer surface. Since the interface layer includes binders, the thickness of the interface layer is controlled by the process parameters of the interface layer preparation process.

[0213] The mass percentage of interface particles and the mass percentage of binder typically affect the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 2-14 to 2-23, within the scope of this application, lithium-ion batteries prepared with the appropriate mass percentages of interface particles and binder exhibit higher lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density. This indicates that the initial coulombic efficiency of lithium-ion batteries can be improved, cycle capacity decay reduced, and energy density increased.

[0214] As can be seen from Examples 2-14 to 2-18, as the mass percentage of interface particles increases, the mass percentage of binder decreases, making thinning easier, and thus the thickness of the interface layer decreases.

[0215] When the interface particles include lithium-intercalating materials and conductive agents, the mass percentages of the lithium-intercalating materials, conductive agents, and binders typically affect the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 2-9, 2-10, 2-19 to 2-23, within the scope of this application, the lithium-ion batteries prepared with the appropriate mass percentages of the lithium-intercalating materials, conductive agents, and binders exhibit higher lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density. This indicates that the initial coulombic efficiency of lithium-ion batteries can be improved, cycle capacity decay reduced, and energy density increased.

[0216] Table 4

[0217]

[0218] As can be seen from Examples 3-1 to 3-12 and Comparative Examples 3-1 to 3-5, the pre-lithiated negative electrode sheet prepared using the lithium replenishment method provided in this application, when applied to lithium-ion batteries, exhibits higher lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density. This demonstrates that the method can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase the energy density. In Comparative Examples 3-1 to 3-5, the lithium replenishment method is not within the scope of this application, and the prepared lithium-ion batteries exhibit lower lithium replenishment capacity, initial coulombic efficiency, cycle capacity retention, and energy density. In Comparative Example 3-2, the interfacial pressure between the interface layer and the negative electrode material layer was too high, the bonding time was too long, and the bonding temperature was 200°C. This caused the lithium replenishment layer to melt, resulting in severe side reactions and preventing effective lithium replenishment. Consequently, the prepared lithium-ion battery exhibited lower initial coulombic efficiency, cycle capacity retention, and energy density.

[0219] It should be noted that, in this document, 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.

[0220] 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.

[0221] 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 lithium supplementing composite layer, wherein, The lithium supplement composite layer comprises an interface layer and a lithium supplement layer arranged in a stack, the interface layer is configured to be in contact with the negative electrode sheet, and the lithium supplement layer is configured to be arranged on the surface of the interface layer away from the negative electrode sheet; The interface layer comprises interface particles and a binder, the interface particles comprise a lithium intercalation material and / or a conductive agent, the lithium intercalation material is at least one selected from artificial graphite, natural graphite, hard carbon, silicon-carbon material, silicon-oxygen material, lithium titanate, tin and tin-copper alloy, the conductive agent is at least one selected from conductive carbon black, carbon fiber, graphene and carbon nanotube, and the binder is at least one selected from polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride and polyethylene oxide; and the lithium supplement layer comprises lithium metal and / or lithium alloy. The tensile strength K1 of the interface layer along the running direction of the lithium supplement composite layer is 0.5 N / 10 mm to 50 N / 10 mm. The tensile strength K2 of the interface layer along the direction perpendicular to the running direction of the lithium supplement composite layer is 0.05 N / 10 mm to 5 N / 10 mm.

2. The lithium supplementing composite layer according to claim 1, wherein Based on the mass of the interface layer, the mass percentage W1 of the interface particles is 80% to 98%, and the mass percentage W2 of the binder is 2% to 20%.

3. The lithium supplement composite layer of claim 1, wherein, The interface particles comprise a lithium intercalation material and a conductive agent, based on the mass of the interface layer, the mass percentage W11 of the lithium intercalation material is 60% to 97.5%, the mass percentage W12 of the conductive agent is 0.5% to 20%, and the mass percentage W2 of the binder is 2% to 20%.

4. The lithium supplement composite layer of claim 1, wherein, The thickness H1 of the interface layer is 20 μm to 100 μm.

5. The lithium replenishing composite layer of claim 1, wherein, The compaction density PD of the interface layer is 0.8 g / cm 3 up to 1.9 g / cm 3 .

6. The lithium replenishing composite layer of claim 1, wherein, The flatness of the two surfaces of the interface layer is 0 μm to 10 μm.

7. The lithium replenishing composite layer of claim 1, wherein, The electronic conductivity σ1 of the interface particles is 0.1 mS / cm to 1000 mS / cm, and the ionic conductivity σ2 of the interface particles is 0.01 mS / cm to 100 mS / cm.

8. The lithium replenishing composite layer of claim 1, wherein, The lithium supplement composite layer further comprises a support layer arranged on the surface of the lithium supplement layer away from the interface layer, the support layer comprises at least one of a metal foil, a polyethylene terephthalate film, a polypropylene film, a polyethylene film or a polyimide film, and the metal foil comprises a copper foil, a nickel foil, a steel foil or a copper-nickel alloy foil.

9. The lithium replenishing composite layer of claim 8, wherein, The tensile strength K3 of the support layer along the running direction of the lithium supplement composite layer is 1.5 N / 10 mm to 200 N / 10 mm.

10. The lithium replenishing composite layer of claim 1, wherein, The lithium supplement composite layer satisfies at least one of the following characteristics: (1) the thickness H1 of the interface layer is 30 μm to 50 μm; (2) the interface layer has a compacted density PD of 1.0 g / cm 3 to 1.5 g / cm 3 ; (3) the flatness of the two surfaces of the interface layer is 0 μm to 4 μm; (4) the electronic conductivity σ1 of the interface particles is 10 mS / cm to 700 mS / cm, and the ionic conductivity σ2 of the interface particles is 0.1 mS / cm to 10 mS / cm; (5) the tensile strength K1 of the interface layer along the running direction of the lithium supplement composite layer is 1 N / 10 mm to 10 N / 10 mm; (6) the tensile strength K2 of the interface layer is 0.1 N / 10 mm to 1 N / 10 mm along the tape running direction perpendicular to the lithium supplement composite layer; (7) the thickness H2 of the lithium supplement layer is 0.001 mm to 1 mm; (8) the lithium supplement composite layer further comprises a support layer, and the tensile strength K3 of the support layer is 22 N / 10 mm to 100 N / 10 mm along the tape running direction of the lithium supplement composite layer; (9) the lithium supplement composite layer further comprises a support layer, and the thickness H3 of the support layer is 3 μm to 50 μm.

11. A preparation method of the lithium supplement composite layer according to any one of claims 1 to 10, comprising the following steps: (1) coating a lithium metal powder slurry on a support layer and drying and rolling to form the lithium supplement layer; or calendering a lithium foil and / or lithium alloy foil to the support layer to form the lithium supplement layer; or coating a lithium or lithium alloy molten slurry on the support layer and cooling and rolling to form the lithium supplement layer; wherein the rolling pressure P1 is 0.1 T / 10 mm to 2 T / 10 mm; (2) mixing the interface particles and the binder, then thinning and drying to form the interface layer; placing the interface layer on the surface of the lithium supplement layer, and then rolling, wherein the rolling pressure P2 is 0.1 T / 10 mm to 2 T / 10 mm, the rolling temperature T1 is 20°C to 180°C, and the rolling standing time t1 is 10 min to 120 min, to form the lithium supplement composite layer.

12. A lithium supplement method, comprising the following steps: drying a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector; adhering the lithium supplement composite layer prepared by the preparation method of claim 11 and the negative electrode sheet so that the interface layer is in contact with the negative electrode material layer, and performing pre-lithiation treatment, wherein the interface pressure P3 between the interface layer and the negative electrode material layer is 0.1 MPa to 2 MPa, the adhering time t2 of the interface layer and the negative electrode material layer is 1 h to 144 h, and the adhering temperature T2 of the interface layer and the negative electrode material layer is 50°C to 180°C; and after the pre-lithiation treatment, peeling off the lithium supplement composite layer from the negative electrode sheet to form a pre-lithiated negative electrode sheet.

13. A prelithiated negative electrode web, wherein, The negative electrode sheet is the pre-lithiated negative electrode sheet obtained by the lithium supplement method of claim 12.

14. A secondary battery comprising the pre-lithiated negative electrode sheet of claim 13.

15. An electronic device comprising the secondary battery of claim 14.

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