Pre-lithiated negative electrode sheet, preparation method for lithium-supplementing composite layer, lithium supplementation method, secondary battery, and electronic apparatus

Abstract

A pre-lithiated negative electrode sheet, a preparation method for a lithium-supplementing composite layer, a lithium supplementation method, a secondary battery, and an electronic apparatus. The pre-lithiated negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The content W1 of silicone oil in the negative electrode material layer is 0 g / m2 to 0.02 g / m2. The pre-lithiated negative electrode sheet is prepared by using the lithium supplementation method, and the pre-lithiated negative electrode sheet satisfies the above-mentioned features, thus improving the initial coulombic efficiency of secondary batteries, reducing cycle capacity attenuation, and improving the energy density of secondary batteries.

Description

Pre-lithiated negative electrode sheet, preparation method of lithium replenishment composite layer, lithium replenishment method, secondary battery and electronic device Technical Field

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

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

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

[0004] The purpose of this application is to provide a method for preparing a pre-lithiated negative electrode, a lithium replenishment composite layer, a lithium replenishment method, 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 method for preparing a lithium-supplemented composite layer, which includes the following steps:

[0006] (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.

[0007] (2) The interface particles are coated on the surface of the lithium replenishment layer to form an interface layer, and then rolled to form a lithium replenishment composite layer.

[0008] The interface particles include at least one of a conductive agent or a lithium intercalation material; the conductive agent includes at least one of a conductive carbon black, carbon fiber, graphene, or carbon nanotube; the lithium intercalation material includes at least one of a synthetic graphite, natural graphite, hard carbon, silicon carbide, or silicon oxide.

[0009] In one embodiment of this application, the roller pressure P1 in step (1) is 0.1T / 10mm to 2T / 10mm; the roller pressure P2 in step (2) is 0.1T / 10mm to 2T / 10mm, preferably 0.2T / 10mm to 0.8T / 10mm; the roller pressing temperature T1 is 20℃ to 180℃, preferably 50℃ to 120℃; the roller pressing resting time t1 is 5min to 60min, preferably 10min to 30min.

[0010] The lithium-supplemented composite layer is prepared using the method provided in this application, and then the negative electrode sheet is pre-lithiated to obtain a pre-lithiated negative electrode sheet. The negative electrode material layer of the pre-lithiated negative electrode sheet has a relatively low content of silicone oil, which can reduce the impact of silicone oil on the electrical performance of the secondary battery, improve the first coulombic efficiency of the secondary battery, reduce cycle capacity decay, and improve the energy density of the secondary battery.

[0011] In one embodiment of this application, the lithium replenishment composite layer includes a support layer, a lithium replenishment layer, and an interface layer. The lithium replenishment layer is disposed between the support layer and the interface layer. The interface layer includes interface particles, and the lithium replenishment layer includes at least one of lithium foil or lithium alloy foil.

[0012] In one embodiment of this application, the thickness of the interface layer is from 0.1 μm to 50 μm, preferably from 1 μm to 20 μm. Lithium atoms in the lithium replenishment layer lose electrons to form 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 a lithium intercalation compound. 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.

[0013] In one embodiment of this application, the coverage ratio of interface particles in the lithium replenishment layer is 50% to 100%, preferably 80% to 100%. Within the scope of this application, a higher coverage ratio of interface particles in the lithium replenishment layer results in higher lithium replenishment uniformity in the negative electrode material layer, 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, the depth of the interfacial particles embedded in the lithium replenishment layer accounts for 10% to 95% of the thickness of the interfacial layer, preferably 20% to 70% of the thickness of the interfacial layer. When the interfacial particles are embedded in the lithium replenishment layer and the proportion of the depth of the interfacial particles embedded in the lithium replenishment layer to the thickness of the interfacial layer is within the range of this application, it can better promote the participation of lithium in the oxidation reaction inside the lithium replenishment layer, thereby better transferring lithium inside the lithium replenishment layer to the negative electrode material layer, which is beneficial for further lithium replenishment of the negative electrode sheet, 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; it also facilitates the repeated use of the lithium replenishment composite layer.

[0015] In one embodiment of this application, by selecting the aforementioned interface particles, the interface layer can be made to have good electron and ion conduction capabilities. During the pre-lithiation process, it is beneficial for electrons and lithium ions to be transferred more quickly through the interface layer to the surface or interior of the negative electrode material layer, which is beneficial for further lithium replenishment of 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.

[0016] In one embodiment of this application, the thickness 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 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. In addition, the thickness of the lithium replenishment layer within the scope of this application can also save costs.

[0017] In one embodiment of this application, the support layer includes at least one selected from metal foil, polyethylene terephthalate film, polypropylene film, or polyethylene film, wherein the metal foil includes copper foil, nickel foil, steel foil, or copper-nickel alloy foil. By selecting the above-mentioned support layer, the support layer can provide better support for the lithium replenishment layer and the interface layer, improve the mechanical strength of the lithium replenishment composite layer, thereby enabling the lithium replenishment composite layer to be peeled off from the surface of the negative electrode material layer more smoothly after lithium replenishment, reducing the possibility of fracture of the lithium replenishment composite layer, which is beneficial to the 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.

[0018] A second aspect of this application provides a lithium replenishment method, which includes the following steps:

[0019] 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. The lithium-supplement composite layer prepared by the preparation method in any of the foregoing embodiments is bonded to the negative electrode sheet 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 0.5 h to 72 h, preferably 1 h to 48 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.

[0020] The pre-lithiated negative electrode sheet prepared by the lithium replenishment method provided in this application has a relatively low content of silicone oil in the negative electrode material layer, which can reduce the impact of silicone oil on the electrical performance of the secondary battery, improve the first coulombic efficiency of the secondary battery, reduce cycle capacity decay, and improve the energy density of the secondary battery.

[0021] A third aspect of this application provides a pre-lithiated negative electrode sheet prepared according to the lithium replenishment method in any of the foregoing embodiments. 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, wherein the content W1 of silicone oil in the negative electrode material layer is 0 g / m³. 2 Up to 0.02g / m 2 The pre-lithiated negative electrode sheet prepared using the lithium replenishment method provided in this application has a relatively low content of silicone oil in the negative electrode material layer, which can reduce the impact of silicone oil on the electrical performance of the secondary battery, improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0022] In one embodiment of this application, the mass percentage W2 of lithium metal in the negative electrode material layer is between 0 ppm and 5000 ppm, based on the mass of the negative electrode material layer. Using the lithium replenishment method provided in this application to prepare a pre-lithiated negative electrode sheet reduces the possibility of lithium metal remaining on the surface of the negative electrode material layer. The pre-lithiated negative electrode sheet has a lower mass percentage of lithium metal in its negative electrode material layer, reducing the possibility of lithium metal undergoing side reactions, 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.

[0023] In one embodiment of this application, the mass percentage W3 of aluminum in the negative electrode material layer is 0 ppm to 50 ppm, based on the mass of the negative electrode material layer. When the lithium replenishment layer material is a lithium-aluminum alloy, and the pre-lithiated negative electrode sheet is prepared using the lithium replenishment method provided in this application, the possibility of aluminum in the lithium replenishment layer remaining on the surface of the negative electrode material layer can be reduced. The pre-lithiated negative electrode sheet has a lower mass percentage of aluminum in the negative electrode material layer, which can reduce the impact of aluminum on the stability of the solid electrolyte interphase (SEI) film, reduce cycle capacity decay, and thus further improve the cycle performance of the secondary battery.

[0024] In one embodiment of this application, the negative electrode material layer includes a negative electrode active material, which includes at least one of graphite, hard carbon, silicon-carbon, or silicon-oxygen materials. The negative electrode material layer includes a negative electrode active material, which comprises the aforementioned substances. Furthermore, the lithium replenishment method employed in this application can effectively replenish lithium to the negative electrode sheet, resulting in a secondary battery with high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0025] In one embodiment of this application, the areal density (CW) of the negative electrode material layer is 1.3 mg / cm³. 2 Up to 13.0 mg / cm 2 Preferably, the areal density (CW) of the negative electrode material layer is 2.0 mg / cm³. 2 Up to 13.0 mg / cm 2 By adjusting the areal density of the negative electrode material layer within the scope of this application, the negative electrode material layer has a suitable areal density, which is beneficial to improving the fast charging performance and energy density of the secondary battery.

[0026] A fourth aspect of this application provides a secondary battery comprising a pre-lithiated negative electrode as described in any of the foregoing embodiments. Therefore, the secondary battery provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high energy density.

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

[0028] The beneficial effects of this application are:

[0029] This application provides a pre-lithiated negative electrode sheet, a method for preparing a lithium replenishment composite layer, a lithium replenishment method, a secondary battery, and an electronic device. The pre-lithiated 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 content of silicone oil W1 in the negative electrode material layer is 0 g / m³. 2 Up to 0.02g / m 2 The pre-lithiated negative electrode sheet prepared using the lithium replenishment method provided in this application meets the above characteristics, which can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery. Attached Figure Description

[0030] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0031] Figure 1 is a schematic diagram of the structure of the lithium-supplemented composite layer according to one embodiment of this application;

[0032] Figure 2 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;

[0033] Figure 3 is a schematic diagram of the lithium replenishment region and the interface region;

[0034] Figure 4 is a schematic diagram of the total area of ​​the lithium replenishment region and the total area of ​​the interface region;

[0035] Figure 5 shows the depth H of interfacial particles embedded in the lithium replenishment layer. a A schematic diagram;

[0036] Figure 6 shows the height difference H between the upper and lower surfaces of the interface layer. c A schematic diagram;

[0037] Figure 7 shows the smoothness H of the interface layer surface far from the lithium replenishment layer. b A schematic diagram. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely 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.

[0039] 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.

[0040] Conventional rolling and lithium replenishment can lead to the presence of silicone oil on the surface of the negative electrode material layer, thus affecting the electrochemical performance of the secondary battery. In addition, conventional rolling and lithium replenishment can also result in the presence of residual elemental lithium on the surface of the negative electrode material layer. The residual elemental lithium may contain byproducts such as lithium carbonate, lithium fluoride, and lithium oxide, which can also affect the electrochemical performance of the secondary battery.

[0041] The first aspect of this application provides a method for preparing a lithium-supplemented composite layer, which includes the following steps:

[0042] (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 are rolled onto the support layer to form a lithium replenishment layer; or lithium or lithium alloy molten slurry is coated onto the support layer and cooled and rolled to form a lithium replenishment layer.

[0043] (2) Under the conditions of ambient temperature ≤30℃ and humidity ≤1.7%, the interface particles are coated on the surface of the lithium replenishment layer to form an interface layer, and then rolled to form a lithium replenishment composite layer.

[0044] The interface particles include at least one of a conductive agent or a lithium-intercalating material; the conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, or carbon nanotubes; the lithium-intercalating material includes at least one of artificial graphite, natural graphite, hard carbon, silicon-carbon materials, or silicon-oxygen materials. 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 nanotubes; the carbon nanotubes may include, but are not limited to, at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or few-walled carbon nanotubes.

[0045] In one embodiment of this application, the roller pressure P1 in step (1) is 0.1T / 10mm to 2T / 10mm; specifically, the roller pressure P11 for rolling the lithium metal powder slurry after coating it onto the support layer is 0.1T / 10mm to 2T / 10mm; the roller pressure P12 for rolling the lithium foil and / or lithium alloy foil onto the support layer is 0.1T / 10mm to 2T / 10mm; and the roller pressure P13 for rolling the lithium or lithium alloy molten slurry after coating it onto the support layer is 0.1T / 10mm to 2T / 10mm. In step (2), the roller pressure P2 is 0.1T / 10mm to 2T / 10mm, preferably 0.2T / 10mm to 0.8T / 10mm; the roller pressing temperature T1 is 20℃ to 180℃, preferably 50℃ to 120℃; and the roller pressing resting time t1 is 5min to 60min, preferably 10min to 30min.

[0046] 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 5min, 9min, 10min, 15min, 19min, 20min, 25min, 29min, 30min, 35min, 39min, 40min, 45min, 49min, 50min, 55min, 59min, 60min, or a range of any two of the above values.

[0047] In this application, the lithium replenishment layer can be formed by coating and rolling lithium metal powder slurry, or by rolling lithium foil and / or lithium alloy foil onto a support layer, or by coating a support layer with molten lithium or lithium alloy slurry, cooling, and rolling. In this application, the lithium alloy foil may include, but is not limited to, lithium-aluminum alloy, and the lithium alloy in the molten lithium alloy slurry may include, but is not limited to, lithium-aluminum alloy. This application does not impose any particular limitation on the coating method for the interface particles on the surface of the lithium replenishment layer, as long as it achieves the purpose of this application. For example, electrostatic spraying, roller coating, or wiping coating can be used to coat the interface particles onto the surface of the lithium replenishment layer.

[0048] In one embodiment of this application, the lithium replenishment composite layer includes a support layer, a lithium replenishment layer, and an interface layer. The lithium replenishment layer is disposed between the support layer and the interface layer. The interface layer includes interface particles, and the lithium replenishment layer includes at least one of lithium foil or lithium alloy foil. Specifically, as shown in FIG1, the lithium replenishment composite layer 10 includes a support layer 11, a lithium replenishment layer 12, and an interface layer 13. The lithium replenishment layer 12 is disposed between the support layer 11 and the interface layer 13. The interface layer 13 includes interface particles, and the lithium replenishment layer 12 includes at least one of lithium foil or lithium alloy foil.

[0049] The inventors discovered that the lithium-replenishing composite layer prepared using the method provided in this application comprises a support layer, a lithium-replenishing layer, and an interface layer. The lithium-replenishing layer is disposed between the support layer and the interface layer. The interface layer includes interface particles, the types of which are within the scope of this application. The interface layer possesses good electron and ion conduction capabilities. The interface layer is brought into contact with the negative electrode material layer, as shown in Figure 2. 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-replenishing layer and the negative electrode material layer form an internal short circuit. The lithium atoms in the lithium-replenishing 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, thereby realizing the pre-lithiation process of the negative electrode material layer. Because an interface layer is provided between the lithium replenishment layer and the negative electrode material layer, the possibility of the lithium replenishment layer adhering to the surface of the negative electrode material layer can be reduced. This reduces the impact on the electrochemical performance of the secondary battery due to the potential for side reactions caused by the high activity of lithium metal in the lithium replenishment layer. It also reduces the impact of residual silicone oil on the surface of the lithium replenishment layer entering the secondary battery and affecting its electrochemical performance. 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. The above peeling process reduces the impact of residual lithium metal in the lithium replenishment layer entering the secondary battery and causing side reactions that could affect its electrochemical performance. By preparing the lithium replenishment composite layer using the above method and then pre-lithiating the negative electrode sheet, a pre-lithiated negative electrode sheet is obtained. The pre-lithiated negative electrode sheet has a relatively low silicone oil content in its negative electrode material layer, which reduces the impact of silicone oil on the electrical performance of the secondary battery, improves the initial coulombic efficiency, reduces cycle capacity decay, and increases the energy density of the secondary battery.

[0050] In one embodiment of this application, the thickness H1 of the interface layer is from 0.1 μm to 50 μm, preferably from 1 μm to 20 μm. Exemplarily, the value of H1 can be 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range of any two of the above values. Lithium atoms in the lithium replenishment layer lose electrons to form 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 the purpose of this application can be achieved. For example, the thickness of the interface layer can be controlled by controlling the type of interface particles. For example, different types of interface particles have different particle sizes; the larger the particle size, the thicker the interface layer. For instance, the thickness of the interface layer can be controlled by adjusting the preparation method. For example, the thickness of an interface layer prepared by roller coating is greater than that prepared by wiping coating, which in turn is greater than that prepared by electrostatic spraying.

[0051] In one embodiment of this application, the coverage ratio S1 of the interface particles in the lithium replenishment layer is 50% to 100%, preferably 80% to 100%. Exemplarily, the value of S1 can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or a range of any two of the above values. The coverage ratio of the interface layer in the lithium replenishment layer affects the lithium replenishment uniformity in the negative electrode material layer; that is, the higher the coverage ratio of the interface layer in the lithium replenishment layer, the higher the lithium replenishment uniformity in the negative electrode material layer. Within the scope of this application, a higher coverage ratio of interface particles in the lithium replenishment layer results in higher lithium replenishment uniformity in the negative electrode material layer, 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. This application does not particularly limit the method of controlling the coverage ratio of interface particles in the lithium replenishment layer, as long as the purpose of this application can be achieved. For example, the coverage ratio of interface particles in the lithium replenishment layer can be controlled by using a mask to control the area of ​​spraying. Furthermore, the coverage ratio of interface particles in the lithium replenishment layer can be increased by increasing the number of times interface particles are sprayed.

[0052] In one embodiment of this application, interface particles are embedded in a lithium replenishment layer, and the depth of the embedding depth of the interface particles in the lithium replenishment layer accounts for 10% to 95% of the thickness of the interface layer. Preferably, the depth of the embedding depth of the interface particles in the lithium replenishment layer accounts for 20% to 70% of the thickness of the interface layer. Exemplarily, the percentage of the depth of the embedding depth of the interface particles in the lithium replenishment layer to the thickness of the interface layer can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range of any two of the above values. When the interfacial particles are embedded in the lithium replenishment layer, and the embedding depth of the interfacial particles in the lithium replenishment layer is within the range of this application, it can better promote the participation of lithium in the oxidation reaction within the lithium replenishment layer, thereby better transferring lithium from the lithium replenishment layer to the negative electrode material layer. This is beneficial for further lithium replenishment of the negative electrode sheet, 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; it also facilitates the repeated use of the lithium replenishment composite layer. This application does not have any particular limitation on the method of controlling the embedding depth of the interfacial particles in the lithium replenishment layer to the thickness of the interfacial layer, as long as the purpose of this application can be achieved. For example, the embedding depth of the interfacial particles in the lithium replenishment layer to the thickness of the interfacial layer can be controlled by adjusting the roller pressure during the preparation of the interfacial layer.

[0053] In one embodiment of this application, the flatness of the surface of the interface layer away from the lithium replenishment layer is less than or equal to 20 μm, preferably less than or equal to 5 μm. Exemplarily, the flatness of the surface of the interface layer away from the lithium replenishment layer can be less than or equal to 20 μm, 15 μm, 10 μm, 5 μm, 3 μm, or 1 μm. Flatness refers to the height difference between the highest and lowest points on the same end face. The flatness of the surface of the interface layer away from the lithium replenishment layer affects its bonding tightness with the negative electrode material layer. The tighter the bonding between the interface layer and the negative electrode material layer, the easier the conduction of lithium ions and electrons, i.e., the lower the resistance, which is more conducive to lithium replenishment of the negative electrode sheet.

[0054] In one embodiment of this application, when the interface particles comprise a conductive agent and a lithium-intercalating material, this application does not impose any particular limitation on the mass percentage content of the conductive agent and the lithium-intercalating material, as long as the purpose of this application can be achieved. For example, based on the mass of the interface particles, the mass percentage content of the conductive agent can be 1% to 20%, and the mass percentage content of the lithium-intercalating material can be 80% to 99%. Exemplarily, based on the mass of the interface particles, the mass percentage content of the conductive agent can be 1%, 3%, 5%, 7%, 9%, 10%, 11%, 13%, 15%, 17%, 19%, 20%, or a range consisting of any two of the above values, and the mass percentage content of the lithium-intercalating material can correspond to 99%, 97%, 95%, 93%, 91%, 90%, 89%, 87%, 85%, 83%, 81%, 80%, or a range consisting of any two of the above values. When the interface particles include conductive agents and lithium-intercalating materials, the conductivity of electrons and ions in the interface layer can be further improved. During the pre-lithiation process, it is beneficial for electrons and lithium ions to be transferred more quickly through the interface layer to the surface or interior of the negative electrode material layer. This is beneficial for further lithium replenishment of the negative electrode sheet, 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.

[0055] 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. Alternatively, 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.

[0056] In one embodiment of this application, the support layer includes at least one selected from metal foil, polyethylene terephthalate film, polypropylene film, or polyethylene film, wherein the metal foil includes copper foil, nickel foil, steel foil, or copper-nickel alloy foil. By selecting the above-mentioned support layer, the support layer can provide better support for the lithium replenishment layer and the interface layer, improve the mechanical strength of the lithium replenishment composite layer, thereby enabling the lithium replenishment composite layer to be peeled off from the surface of the negative electrode material layer more smoothly after lithium replenishment, reducing the possibility of fracture of the lithium replenishment composite layer, which is beneficial to the 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.

[0057] This application does not impose any particular limitation on the thickness H3 of the support layer, as long as it can achieve the purpose of this application. For example, the thickness H3 of the support layer can be from 3 μm to 50 μm, and preferably, the thickness H3 of the support layer can be from 5 μm to 20 μm.

[0058] A second aspect of this application provides a lithium replenishment method, which includes the following steps:

[0059] 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 been pre-lithiated. 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 0.5 h to 72 h, preferably 1 h to 48 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.

[0060] 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.

[0061] 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 0.5h, 1h, 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 48h, 50h, 55h, 60h, 65h, 70h, 72h, 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.

[0062] The pre-lithiated negative electrode sheet prepared by the lithium replenishment method provided in this application has a relatively low content of silicone oil in the negative electrode material layer, which can reduce the impact of silicone oil on the electrical performance of the secondary battery, improve the first coulombic efficiency of the secondary battery, reduce cycle capacity decay, and improve the energy density of the secondary battery.

[0063] A third aspect of this application provides a pre-lithiated negative electrode sheet prepared according to the lithium replenishment method in any of the foregoing embodiments. The pre-lithiated 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 "negative electrode material layer" in the above-mentioned "the pre-lithiated 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" refers to the negative electrode material layer after pre-lithiating the negative electrode sheet that has not undergone pre-lithiation. The content of silicone oil W1 in the negative electrode material layer is 0 g / m³. 2 Up to 0.02g / m 2For example, the value of W1 can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, or a range of any two of the above values. 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 own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a portion of the negative electrode current collector; this application has no particular limitation, as long as the purpose of this application can be achieved. In this application, the silicone oil includes, but is not limited to, at least one of methyl silicone oil, ethyl silicone oil, phenyl silicone oil, or methylphenyl silicone oil.

[0064] The pre-lithiated negative electrode sheet prepared by the lithium replenishment method provided in this application has a relatively low content of silicone oil in the negative electrode material layer, which can reduce the impact of silicone oil on the electrical performance of the secondary battery, improve the first coulombic efficiency of the secondary battery, reduce cycle capacity decay, and improve the energy density of the secondary battery.

[0065] In one embodiment of this application, the mass percentage W2 of lithium metal in the negative electrode material layer is between 0 ppm and 5000 ppm, based on the mass of the negative electrode material layer. Exemplarily, the value of W2 can be 0, 5, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, or a range of any two of the above values. Using the lithium replenishment method provided in this application to prepare a pre-lithiated negative electrode sheet can reduce the possibility of lithium metal remaining on the surface of the negative electrode material layer in the lithium replenishment layer. The pre-lithiated negative electrode sheet has a lower mass percentage of lithium metal in its negative electrode material layer, reducing the possibility of lithium metal side reactions, 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.

[0066] In one embodiment of this application, the mass percentage W3 of aluminum in the negative electrode material layer is between 0 ppm and 50 ppm, based on the mass of the negative electrode material layer. Exemplarily, the value of W3 can be 0, 1, 3, 5, 7, 9, 10, 15, 19, 20, 25, 29, 30, 35, 39, 40, 45, 49, 50, or a range of any two of the above values. When the lithium replenishment layer material is a lithium-aluminum alloy, and the pre-lithiated negative electrode sheet is prepared using the lithium replenishment method provided in this application, the possibility of aluminum remaining on the surface of the negative electrode material layer in the lithium replenishment layer can be reduced. The pre-lithiated negative electrode sheet has a lower mass percentage of aluminum in its negative electrode material layer, which can reduce the impact of aluminum on the stability of the solid electrolyte interphase (SEI) film, reduce cycle capacity decay, and thus further improve the cycle performance of the secondary battery.

[0067] In one embodiment of this application, the negative electrode material layer includes a negative electrode active material, which includes at least one of graphite material, hard carbon, silicon-carbon material, or silicon-oxygen material. 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, and based on the mass of the silicon-carbon composite material, the mass percentage content of silicon is 30% to 70%, and the mass percentage content of carbon is 30% to 70%. This application does not impose any particular limitation on the silicon-carbon composite material, as long as it can achieve the purpose of this application. For example, the silicon-carbon composite material can be a composite material obtained by deposition. Exemplarily, the silicon-carbon composite material can be silicon material deposited on a carbon skeleton, or carbon material deposited on a silicon skeleton. The silicon-oxygen material includes SiOx, where 0 < x < 2. Exemplarily, the silicon-oxygen material can include silicon suboxide (SiO, where the molar ratio of silicon to oxygen is 1:1). The negative electrode material layer includes a negative electrode active material, which includes the aforementioned substances. Furthermore, the lithium replenishment method described in this application can effectively replenish lithium on the negative electrode sheet, resulting in a secondary battery with high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0068] In one embodiment of this application, the areal density (CW) of the negative electrode material layer is 1.3 mg / cm³. 2 Up to 13.0 mg / cm 2 Preferably, the areal density (CW) of the negative electrode material layer is 2.0 mg / cm³. 2 Up to 13.0 mg / cm 2For example, the value of CW can be 1.3, 1.5, 1.7, 1.9, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, or a range of any two of the above values. By adjusting the areal density of the negative electrode material layer within the scope of this application, the negative electrode material layer has a suitable areal density, which is beneficial to improving the fast-charging performance and energy density of the secondary battery. This application does not particularly limit the method of adjusting the areal density of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, when coating the negative electrode slurry onto the surface of the negative electrode current collector, with a certain solid content of the negative electrode slurry, increasing the coating amount of the negative electrode slurry can increase the coating weight of the negative electrode material layer.

[0069] In this application, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. This application does not particularly limit the type of negative electrode binder, as long as it achieves 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 particularly limit the type of negative electrode conductive agent, as long as it achieves 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 polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode binder, and negative electrode conductive agent in the negative electrode material layer; those skilled in the art can select these according to actual needs, as long as the purpose of this application can be achieved.

[0070] 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.).

[0071] 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.

[0072] A fourth aspect of this application provides a secondary battery comprising a pre-lithiated negative electrode as described in any of the foregoing embodiments. Therefore, the secondary battery provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0073] 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.

[0074] 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).

[0075] The positive electrode material layer of this application includes a positive electrode active material, which comprises a substance capable of reversibly inserting and extracting active ions such as lithium ions. The positive electrode material layer can be one or more layers, and each layer in a multilayer positive electrode material layer can contain the same or different positive electrode active materials. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The aforementioned lithium nickel cobalt manganese oxide can include LiNi... 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2O2(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.

[0076] 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.

[0077] 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(oxalato)borate (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 contain at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate 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.

[0078] 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.

[0079] 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.

[0080] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, pre-lithiated negative electrode, electrolyte, and other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0081] 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.

[0082] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and pre-lithiated negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and pre-lithiated negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0083] A fifth aspect of this application provides an electronic device comprising the secondary battery of any of the foregoing embodiments. Therefore, the electronic device provided by this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0084] 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.

[0085] Example

[0086] 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.

[0087] Test methods and equipment:

[0088] Test of silicone oil content in the negative electrode material layer:

[0089] Disassemble the lithium-ion battery, remove the negative electrode sheet, clean the negative electrode sheet with DMC, and then let it dry. Select the area on the negative electrode sheet that includes the double-sided negative electrode material layer, place it on the black pad, press the sampling fixture and rotate it once to obtain the film disc.

[0090] The above-mentioned film disc was tested using a spectrometer (model Lab-X3500SCL) to obtain the content of silicone oil in the negative electrode material layer.

[0091] Test of the mass percentage of lithium metal in the negative electrode material layer:

[0092] Disassemble the lithium-ion battery, remove the negative electrode, clean it with DMC, and then dry it. Scrape off all the powder from the single-sided negative electrode material layer with a ceramic knife, weigh it, and obtain the mass of the single-sided negative electrode material layer. Peel off the material from the surface of the negative electrode material layer using adhesive tape, and record the mass of the adhesive tape before peeling as m0 g and the mass of the adhesive tape after peeling as m1 g. Then the mass of the surface material peeled off the adhesive tape is m2 g, and m2(g) = m0 - m1.

[0093] The mass percentage of lithium in the surface material after the adhesive tape was peeled off was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The ICP-OES instrument used was a PE7000DV model manufactured by Platinum Elmer, USA. The ICP-OES testing conditions were: radio frequency (RF) of 40.68 MHz, RF power of 1300 W, argon secondary pressure of 0.6 MPa, auxiliary gas flow rate of 0.2 L / min, cooling gas flow rate of 15 L / min, and pump speed of 1.5 mL / min. The mass percentage of lithium in the surface material after the adhesive tape was peeled off was multiplied by the mass of the surface material to obtain the mass of lithium. The ratio of the mass of lithium to the mass of the single-sided negative electrode material layer is the mass percentage of elemental lithium in the negative electrode material layer.

[0094] Test of the mass percentage of aluminum in the negative electrode material layer:

[0095] Disassemble the lithium-ion battery, remove the negative electrode, clean the negative electrode with DMC, and then let the negative electrode dry.

[0096] The mass percentage of elements on the surface of the negative electrode was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The ICP-OES instrument used was a PE7000DV model manufactured by Platinum Elmer, USA. The ICP-OES testing conditions were as follows: radio frequency (RF) of 40.68 MHz, RF power of 1300 W, argon secondary pressure of 0.6 MPa, auxiliary gas flow rate of 0.2 L / min, cooling gas flow rate of 15 L / min, and pump speed of 1.5 mL / min.

[0097] The mass percentage of aluminum in the negative electrode material layer is the mass percentage content of aluminum in the negative electrode material layer.

[0098] Areal density test:

[0099] Disassemble the lithium-ion battery, remove the negative electrode, clean it with DMC, and then let it air dry. Select the area on the negative electrode that includes the double-sided negative electrode material layer, and cut 10 pieces with an area of ​​1540.25 mm² using a cutting machine. 2 Take the small circular pieces, weigh them, and take the average value M; then wipe off the negative electrode material layer on 10 small circular pieces, weigh them, and take the average value m. The surface density of the negative electrode material layer CW=(Mm) / (2×1540.25).

[0100] Thickness testing of the support layer, lithium replenishment layer, and interface layer:

[0101] Place the sample to be tested on the table, level it, and then measure its thickness as required. Wipe the measuring face of the dial indicator with a non-woven cloth; press the measuring linkage mechanism to make the two measuring faces fully contact, and press the "zero" key; make contact between the two measuring faces of the dial indicator and the face of the sample to be tested, read the displayed data, and record the reading. Measure at 70mm intervals along the direction perpendicular to the belt travel (i.e., the TD direction), and at 100mm intervals along the belt travel direction (i.e., the MD direction); test 12 points along the TD direction of the sample to be tested; test 12 points along the MD direction of the sample to be tested; test a total of 24 points; take the average thickness of the 24 points as the thickness of the sample to be tested.

[0102] Using the support layer as the sample to be tested, the thickness H3 of the support layer is obtained.

[0103] When the support layer and the lithium replenishment layer are combined and used 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 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.

[0104] 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 .

[0105] Test on the coverage ratio of interface particles in the lithium replenishment layer:

[0106] (1) Place the sample flat on the sample stage, and then use an optical microscope to magnify and photograph the sample (Keyence VHX-7000, magnification 300x).

[0107] (2) Import the captured images into the image processing software IMAGE J, distinguish between the lithium replenishment area and the interface area using a threshold, and calculate the area S1 to S2 of each interface area. n The total area of ​​the interface region is S_interface = S1 + S2 + S3 + ... + S n-1 +S n Measure the length L and width W of the lithium replenishment area, and calculate the total area S of the lithium replenishment area. 补锂 =W×L; then the coverage ratio of interface particles in the lithium replenishment layer S1 = S 界面 / S 补锂 The details are shown in Figures 3 and 4.

[0108] (3) Each sample was tested in 12 parallel samples, and the average of the 12 S1 samples was taken as the coverage ratio of the interface particles in the lithium replenishment layer.

[0109] The ratio of the depth of interfacial particles embedded in the lithium replenishment layer to the thickness of the interfacial layer, and the flatness test of the surface of the interfacial layer far from the lithium replenishment layer:

[0110] (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.

[0111] (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 2000x.

[0112] The depth H of the interface particles embedded in the lithium replenishment layer a Defined as: the height difference between the upper surface of the lithium replenishment layer and the lower surface of the interface layer, as shown in Figure 5. H c Defined as: the height difference between the upper surface and the lower surface of the interface layer, as shown in Figure 6. Define h = H a / H c Each sample was tested in 12 parallel samples, and the average value over 12 hours was taken as the ratio of the depth of the interfacial particles embedded in the lithium replenishment layer to the thickness of the interfacial layer.

[0113] Smoothness H of the interface layer away from the lithium replenishment layer bDefined as: the height difference between the highest point and the lowest point on the upper surface of the interface layer, as shown in Figure 7. Twelve parallel samples were tested for each sample, and twelve H values ​​were taken. b The average value is the smoothness of the surface of the interface layer far from the lithium replenishment layer.

[0114] First Coulomb efficiency test:

[0115] 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.

[0116] Initial coulomb efficiency (%) = C1 / C0 × 100%.

[0117] Cyclic performance test:

[0118] 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.

[0119] Cyclic capacity retention rate (%) = B / A × 100%.

[0120] The higher the cycle capacity retention rate value obtained from the test, the better the cycle performance of the lithium-ion battery.

[0121] Energy density test:

[0122] The voltage range indicated on the battery's outer packaging should be used as the standard. For example, if the battery's voltage range is 3.0V to 4.45V, the charging cut-off voltage is 4.45V, and the discharging cut-off voltage is 3.0V. The specific test steps are as follows: At 25°C, charge the lithium-ion battery in the example or comparative example at a constant current of 0.2C to the cut-off voltage of 4.45V, then charge it at a constant voltage of 4.45V until the current is less than 0.05C. After resting for 5 minutes, discharge it at a constant current of 0.2C to the cut-off voltage of 3.0V, and then let it rest for 5 minutes. Record the energy of the above discharge process as the discharge energy E. Calculate the volume V (mm²) of the lithium-ion battery. 3 = Length × Width × Height.

[0123] Energy density (Wh / L) = E / V × 10 6 .

[0124] Example 1-1

[0125] <Preparation of Lithium-Supplemental Composite Layer>

[0126] 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.

[0127] Under ambient temperatures of 25℃ and humidity of 1.0%, Super P interfacial particles were coated onto the surface of the lithium replenishment layer using a wiping method to form an interfacial layer. This was followed by roll pressing with a pressure P2 of 0.5T / 10mm, a rolling temperature T1 of 90℃, and a settling time t1 of 30min, resulting in a lithium replenishment composite layer. The thickness H1 of the interfacial layer in the lithium replenishment composite layer was 0.1μm, the thickness H2 of the lithium replenishment layer was 0.03mm, the coverage ratio S1 of the interfacial particles in the lithium replenishment layer was 85%, and the embedding depth of the interfacial particles in the lithium replenishment layer accounted for 50% of the thickness of the interfacial layer.

[0128] <Preparation of Negative Electrode Sheets>

[0129] A mixture of silicon-carbon anode active material, acetylene black anode conductive agent, styrene-butadiene rubber (SBR) binder, and lithium carboxymethyl cellulose 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 a negative electrode slurry with a solid content of 28 wt%. The negative electrode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector and dried at 90°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode material. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode material. The sheet was dried under vacuum at 90°C for 1 hour, then cold-pressed, cut, and slit to obtain a negative electrode sheet with dimensions of 51 mm × 44.2 mm. The silicon-carbon material was a silicon-carbon composite material, with a silicon content of 50% and a carbon content of 50% based on the mass of the composite material. The areal density (CW) of the negative electrode material layer was 2.3 mg / cm³. 2 The compaction density during the cold pressing process is 1.0 g / cm³. 3 .

[0130] <Preparation of pre-lithiated negative electrode>

[0131] 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 90℃. 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.

[0132] <Preparation of the positive electrode>

[0133] Lithium cobalt oxide (LiCoO2), a positive electrode active material, acetylene black, a positive electrode conductive agent, and polyvinylidene fluoride (PVDF), a 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 dimensions of 48 mm × 41.2 mm. The areal density of the positive electrode material layer was 19.0 mg / cm³. 2 The compaction density during the cold pressing process is 4.15 g / cm³.3 .

[0134] <Preparation of Electrolyte>

[0135] 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.

[0136] <Preparation of the diaphragm>

[0137] A porous polypropylene film with a thickness of 5 μm (provided by Celgard) was used as the separator.

[0138] <Preparation of Lithium-ion Batteries>

[0139] The prepared positive electrode, separator, pre-lithiated negative electrode, and separator 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 packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. Electrolyte is then injected, and the battery undergoes 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.

[0140] Examples 1-2 to Examples 1-15

[0141] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0142] Examples 1-16

[0143] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-10.

[0144] Examples 1-17

[0145] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-10.

[0146] Examples 2-1 to 2-12

[0147] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-10.

[0148] Examples 3-1 to 3-2

[0149] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-10.

[0150] Examples 3-3 to 3-6

[0151] Except for adjusting the amount of negative electrode slurry to achieve the areal density of the negative electrode material layer as shown in Table 3, the rest is the same as in Examples 1-10.

[0152] Examples 3-7 to 3-8

[0153] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-10.

[0154] Comparative Example 1-1

[0155] 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.

[0156] Comparative Examples 1-2

[0157] Except for the preparation of the lithium-replenishing composite layer according to the following method and the fact that the interface layer and the negative electrode sheet are not stripped after the pre-lithiation process in the <Preparation of Pre-lithiation Negative Electrode Sheet>, the rest is the same as in Example 1-1.

[0158] <Preparation of Lithium-Supplemental Composite Layer>

[0159] Under ambient temperatures of 25℃ and humidity of 1.0%, interfacial particles of artificial graphite were coated onto the surface of the lithium replenishment layer using a wiping method to form an interfacial layer. This was followed by roll pressing with a pressure P2 of 0.5T / 10mm, a pressing temperature T1 of 90℃, and a settling time t1 of 30min, resulting in a lithium replenishment composite layer. The thickness H1 of the interfacial layer in the lithium replenishment composite layer was 8μm, the thickness H2 of the lithium replenishment layer was 0.03mm, the coverage ratio S1 of the interfacial particles in the lithium replenishment layer was 85%, and the embedding depth of the interfacial particles in the lithium replenishment layer accounted for 50% of the thickness of the interfacial layer.

[0160] Comparative Examples 1-3

[0161] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-10. Among them, the other interface particles are polyvinylidene fluoride.

[0162] Comparative Examples 2-1 to 2-5

[0163] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-10.

[0164] The preparation parameters, material properties, and electrical properties of each embodiment and comparative example are shown in Tables 1 to 3.

[0165] Table 1

[0166] Note: (1) In Table 1, “ / ” indicates that there are no relevant preparation parameters; (2) In Examples 1-6, “interface particle type” is “silicon-oxygen material”, and silicon-oxygen material is SiO; (3) In Examples 1-7, “interface particle type” is “silicon-carbon material”, and 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%; (4) In Examples 1-9, “interface particle type” is “97% artificial graphite + 3% single-walled carbon nanotubes”, indicating that the interface particles include artificial graphite and single-walled carbon nanotubes. Based on the mass of the interface particles, the mass percentage of artificial graphite is 97% and the mass percentage of single-walled carbon nanotubes is 3%.

[0167] Table 2

[0168] As can be seen from Examples 1-1 to 1-17, Examples 2-1 to 2-12, Comparative Examples 1-1 to 1-3, and Comparative Examples 2-1 to 2-5, when a lithium-replenishing composite layer is prepared using the method provided in this application, and then a pre-lithiated negative electrode sheet is prepared using the lithium-replenishing method provided in this application, with the silicone oil content in the negative electrode material layer of the pre-lithiated negative electrode sheet within the range of this application, the prepared lithium-ion battery exhibits high 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. Comparative Example 1-1 uses a lithium-replenishing composite layer that does not include an interface layer, and the prepared lithium-ion battery exhibits lower initial coulombic efficiency, cycle capacity retention, and energy density. In Comparative Example 1-2, the lithium-replenishing composite layer does not include a support layer, and the interface layer and negative electrode sheet are not stripped after the pre-lithiation process, resulting in a lithium-ion battery with lower initial coulombic efficiency, cycle capacity retention, and energy density. As can be seen from Comparative Examples 1-3 and Examples 1-1 to 1-9, Comparative Examples 1-3 used other interface particles, and the types of other interface particles were outside the scope of this application. The resulting lithium-ion batteries had lower initial coulombic efficiency, cycle capacity retention, and energy density. Other interface particles could also be micron-sized copper, etc. In contrast, Examples 1-1 to 1-9 used interface particles within the scope of this application, and the prepared lithium-ion batteries had higher 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 can be reduced, and the energy density of lithium-ion batteries can be increased.

[0169] As can be seen from Examples 1-1 to 1-4, the interface particles include conductive agents and the types of conductive agents are within the scope of this application. The particle size of the conductive agents is relatively small, so the thickness of the interface layer is relatively small. The prepared lithium-ion battery has high initial coulombic efficiency, cycle capacity retention rate and energy density, indicating that it can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay and improve the energy density of lithium-ion batteries.

[0170] As can be seen from Examples 1-10 to 1-15, the interface particles are artificial graphite. The Dv50 of artificial graphite affects the thickness of the interface layer; as the Dv50 of artificial graphite increases, the thickness of the interface layer increases. The prepared lithium-ion battery exhibits high 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. Furthermore, as the Dv50 of artificial graphite increases, the lithium-ion transport distance increases, the lithium replenishment amount of the negative electrode decreases, and the initial coulombic efficiency, cycle capacity retention, and energy density of the lithium-ion battery all decrease.

[0171] The type of lithium replenishment layer typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-10 and 1-16, the lithium-ion batteries prepared using the lithium replenishment layer within the scope of this application exhibit higher initial coulombic efficiency, cycle capacity retention, and energy density, indicating that the type of lithium replenishment layer can improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the energy density of lithium-ion batteries.

[0172] 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 1-10 and 1-17, the types of support layers used within the scope of this application result in lithium-ion batteries with higher 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.

[0173] During the pre-lithiation process, the interfacial pressure, bonding time, and bonding temperature between the interface layer and the negative electrode material layer affect the amount of lithium replenished to the negative electrode, thereby affecting the initial coulombic efficiency, cycle capacity retention, and energy density of the lithium-ion battery. As can be seen from Examples 1-10, Examples 2-1 to 2-12, and Comparative Examples 2-1 to 2-5, during the pre-lithiation process, when the interfacial pressure, bonding time, and bonding temperature between the interface layer and the negative electrode material layer are within the range specified in this application, the prepared lithium-ion batteries exhibit higher 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. In Comparative Example 2-1, the interfacial pressure, bonding time, and bonding temperature between the interface layer and the negative electrode material layer are too low, resulting in insufficient lithium replenishment and consequently, lower initial coulombic efficiency, cycle capacity retention, and energy density of the prepared lithium-ion battery. In Comparative Example 2-2, the interfacial pressure, bonding time, and bonding temperature between the interface layer and the negative electrode material layer are too high, resulting in a large amount of lithium replenishment. However, the content of silicone oil in the negative electrode material layer is too high, and the mass percentage of lithium metal in the negative electrode material layer is also too high, leading to low initial coulombic efficiency, cycle capacity retention, and energy density of the lithium-ion battery. In Comparative Example 2-3, the bonding time and bonding temperature between the interface layer and the negative electrode material layer are outside the scope of this application, and the prepared lithium-ion battery has low initial coulombic efficiency, cycle capacity retention, and energy density. In Comparative Example 2-4, the interfacial pressure and bonding temperature between the interface layer and the negative electrode material layer are outside the scope of this application, and the prepared lithium-ion battery has low initial coulombic efficiency, cycle capacity retention, and energy density. In Comparative Example 2-5, the interfacial pressure and bonding time between the interface layer and the negative electrode material layer are outside the scope of this application, and the prepared lithium-ion battery has low initial coulombic efficiency, cycle capacity retention, and energy density.

[0174] As can be seen from Examples 1-10 and Examples 2-1 to 2-4, the interfacial pressure between the interface layer and the negative electrode material layer increases, while the bonding time and bonding temperature between the interface layer and the negative electrode material layer remain unchanged. The content of silicone oil in the negative electrode material layer increases, the mass percentage of lithium metal in the negative electrode material layer increases, and the amount of lithium replenishment increases. The initial coulombic efficiency, cycle capacity retention rate, and energy density of the lithium-ion battery first increase and then decrease. This is because increasing the amount of lithium replenishment is beneficial to improving the initial coulombic efficiency, cycle capacity retention rate, and energy density of the lithium-ion battery. However, when the amount of lithium replenishment is large, it may lead to lithium plating, thereby affecting the initial coulombic efficiency, cycle capacity retention rate, and energy density of the lithium-ion battery.

[0175] As can be seen from Examples 1-10 and Examples 2-5 to 2-8, the bonding time between the interface layer and the negative electrode material layer increases, while the interface pressure and bonding temperature remain unchanged. The content of silicone oil in the negative electrode material layer increases, the mass percentage of lithium metal in the negative electrode material layer increases, and the amount of lithium replenishment increases. The initial coulombic efficiency, cycle capacity retention rate, and energy density of the lithium-ion battery first increase and then decrease. This is because increasing the amount of lithium replenishment is beneficial to improving the initial coulombic efficiency, cycle capacity retention rate, and energy density of the lithium-ion battery. However, when the amount of lithium replenishment is large, it may lead to lithium plating, thereby affecting the initial coulombic efficiency, cycle capacity retention rate, and energy density of the lithium-ion battery.

[0176] As can be seen from Examples 1-10 and Examples 2-9 to Examples 2-12, the bonding temperature between the interface layer and the negative electrode material layer increases, while the bonding time and interface pressure remain unchanged. The content of silicone oil in the negative electrode material layer increases, the mass percentage of lithium metal in the negative electrode material layer increases, and the amount of lithium replenishment increases. The initial coulombic efficiency, cycle capacity retention, and energy density of the lithium-ion battery first increase and then decrease. This is because increasing the amount of lithium replenishment is beneficial to improving the initial coulombic efficiency, cycle capacity retention, and energy density of the lithium-ion battery. However, when the amount of lithium replenishment is large, it may lead to lithium plating, thereby affecting the initial coulombic efficiency, cycle capacity retention, and energy density of the lithium-ion battery.

[0177] Table 3

[0178] Note: (1) In Table 3, the “type of negative electrode active material” in Examples 1-10 is “silicon-carbon material”. Silicon-carbon material is a silicon-carbon composite material. Based on the mass of the 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 pattern. (2) In Table 3, taking Examples 3-7 as an example, the “type of negative electrode active material” is “10% silicon-carbon material + 90% artificial graphite”, indicating that the negative electrode active material includes silicon-carbon material and artificial graphite. Based on the total mass of the negative electrode active material, the mass percentage of silicon-carbon material is 10% and the mass percentage of artificial graphite is 90%. Other examples follow the same pattern.

[0179] As can be seen from Examples 1-10, 3-1, 3-2, 3-7, and 3-8, the negative electrode material layer includes a negative electrode active material. The types of negative electrode active materials are within the scope of this application. The prepared lithium-ion battery has high initial coulombic efficiency, cycle capacity retention rate, and energy density, indicating that it can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and improve the energy density of lithium-ion batteries.

[0180] The areal density of the negative electrode material layer typically affects the fast-charging performance and energy density of lithium-ion batteries. As shown in Examples 1-10 and 3-3 to 3-6, within the scope of this application, lithium-ion batteries prepared with a lower areal density of the negative electrode material layer exhibit higher initial coulombic efficiency, cycle capacity retention, and energy density, indicating that the initial coulombic efficiency of lithium-ion batteries can be improved, cycle capacity decay reduced, and energy density increased. Furthermore, as the areal density of the negative electrode material layer increases, the lithium-ion transport distance increases, the cycle capacity retention of the lithium-ion battery decreases, and the energy density of the lithium-ion battery increases.

[0181] 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.

[0182] 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.

[0183] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a lithium-supplemented composite layer, comprising the following steps: (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. (2) The interface particles are coated on the surface of the lithium replenishment layer to form an interface layer, and then rolled to form a lithium replenishment composite layer. The interface particles include at least one of a conductive agent or a lithium intercalation material; the conductive agent includes at least one of conductive carbon black, carbon fiber, graphene, or carbon nanotubes; and the lithium intercalation material includes at least one of artificial graphite, natural graphite, hard carbon, silicon carbide, or silicon oxide.

2. The preparation method according to claim 1, wherein, In step (1), the roller pressure P1 is 0.1T / 10mm to 2T / 10mm; in step (2), the roller pressure P2 is 0.1T / 10mm to 2T / 10mm, the roller pressing temperature T1 is 20℃ to 180℃, and the roller pressing resting time t1 is 5min to 60min.

3. The preparation method according to claim 1 or 2, wherein, The lithium replenishment composite layer includes the support layer, the lithium replenishment layer, and the interface layer. The lithium replenishment layer is disposed between the support layer and the interface layer. The interface layer includes the interface particles. The lithium replenishment layer includes at least one of lithium foil or lithium alloy foil.

4. The preparation method according to claim 1 or 2, wherein, The thickness of the interface layer is from 0.1 μm to 50 μm.

5. The preparation method according to claim 4, wherein, The thickness of the interface layer is 1 μm to 20 μm.

6. A lithium replenishment method, comprising the following steps: The negative electrode sheet is dried, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; The lithium-replenishing composite layer prepared by the preparation method according to any one of claims 1 to 5 is bonded to the negative electrode sheet 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, the bonding time t2 between the interface layer and the negative electrode material layer is 0.5 h to 72 h, and the bonding temperature T2 between the interface layer and the negative electrode material layer is 50 °C to 180 °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.

7. A pre-lithiated negative electrode sheet prepared by the lithium replenishment method according to claim 6, wherein the negative electrode sheet comprises a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector, and the content of silicone oil W1 in the negative electrode material layer is 0 g / m 2 Up to 0.02g / m 2 .

8. The pre-lithiated negative electrode according to claim 7, wherein, Based on the mass of the negative electrode material layer, the mass percentage content W2 of elemental lithium metal in the negative electrode material layer is between 0 ppm and 5000 ppm.

9. The pre-lithiated negative electrode according to claim 7, wherein, Based on the mass of the negative electrode material layer, the mass percentage of aluminum W3 in the negative electrode material layer is between 0 ppm and 50 ppm.

10. The pre-lithiated negative electrode according to claim 7, wherein, The negative electrode material layer includes a negative electrode active material, which includes at least one of graphite, hard carbon, silicon carbide, or silicon oxide.

11. The pre-lithiated negative electrode according to claim 7, wherein, The areal density (CW) of the negative electrode material layer is 1.3 mg / cm³. 2 Up to 13.0 mg / cm 2 .

12. The pre-lithiated negative electrode according to claim 11, wherein, The areal density (CW) of the negative electrode material layer is 2.0 mg / cm³. 2 Up to 13.0 mg / cm 2 .

13. A secondary battery comprising a pre-lithiated negative electrode sheet according to any one of claims 7 to 12.

14. An electronic device comprising the secondary battery of claim 13.

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