Pre-lithiated negative electrode sheet, method for preparing lithium supplementing composite layer, lithium supplementing method, secondary battery, and electronic device

Abstract

The application provides a pre-lithiated negative electrode sheet, a preparation method of a lithium supplement composite layer, a lithium supplement method, a secondary battery and an electronic device. The pre-lithiated negative electrode sheet comprises a negative electrode current collector, a third negative electrode material layer and a fourth negative electrode material layer. The third negative electrode material layer is arranged between the negative electrode current collector and the fourth negative electrode material layer. The third negative electrode material layer comprises a first negative electrode active material. The fourth negative electrode material layer comprises a second negative electrode active material. The second negative electrode active material comprises a silicon-containing substance. The mass percentage of silicon in the third negative electrode material layer is WSi3%. The mass percentage of silicon in the fourth negative electrode material layer is WSi4%. The mass percentage of lithium in the fourth negative electrode material layer is WLi4%. WSi4> WSi3, 1.5%≤ WLi4 / WSi4≤ 44.4%. The pre-lithiated negative electrode sheet satisfies the above characteristics, can improve the initial coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a pre-lithiated negative electrode sheet, a preparation method of a lithium supplement composite layer, a lithium supplement method, a secondary battery and an electronic device. BACKGROUND

[0002] Lithium ion batteries have the advantages of high energy density, high power and long cycle life, and are widely used in consumer electronics, electric bicycles and electric vehicles. With the continuous expansion of its application range, the requirements for energy density and cycle performance of lithium ion batteries are continuously increasing. The current commonly used graphite negative electrode material of lithium ion batteries cannot meet the requirements of energy density. Since the theoretical specific capacity of silicon-carbon or silicon-oxygen negative electrode material is high, it can be used as an ideal material to improve the energy density of lithium ion batteries. However, it has problems such as low first coulomb efficiency and poor cycle life.

[0003] In order to improve the first coulomb efficiency of the negative electrode active material and reduce the cycle decay, the existing method is to pre-supplement lithium to the negative electrode sheet to supplement the irreversible capacity consumed in the first charge, discharge and cycle, improve the first coulomb efficiency of the lithium ion battery, and then improve the energy density of the lithium ion battery. When the negative electrode active material uses silicon-carbon or silicon-oxygen negative electrode material and graphite material mixedly, the lithium supplement efficiency of different negative electrode active materials is different, the lithium supplement amount in the same time is different, and the first coulomb efficiency of different negative electrode active materials is different, which will affect the first coulomb efficiency of the lithium ion battery, and then affect the improvement of the energy density. SUMMARY

[0004] The purpose of the present application is to provide a pre-lithiated negative electrode sheet, a preparation method of a lithium supplement composite layer, a lithium supplement method, a secondary battery and an electronic device to improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity decay and improve the energy density of the secondary battery. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides a preparation method of a lithium supplement composite layer, which comprises the following steps:

[0006] (1) coating a lithium metal powder slurry on a support layer and drying and rolling to form a lithium supplement layer; or calendering a lithium foil and / or a lithium alloy foil to the support layer to form a lithium supplement layer; or coating a lithium or lithium alloy molten slurry on the support layer and cooling and rolling to form a lithium supplement layer; wherein the rolling pressure P1 is 0.2T / 10mm to 1.8T / 10mm;

[0007] (2) coating the interface particles on the surface of the lithium supplement layer to form an interface layer, and then rolling, wherein the rolling pressure P2 is 0.2 T / 10 mm to 1.8 T / 10 mm, preferably, the rolling pressure P2 is 0.2 T / 10 mm to 0.8 T / 10 mm; the rolling temperature T1 is 20°C to 180°C, preferably, the rolling temperature T1 is 50°C to 120°C; the rolling standing time t1 is 5 min to 60 min, preferably, the rolling standing time t1 is 10 min to 30 min, to form a lithium supplement composite layer.

[0008] The lithium supplement composite layer prepared by the above method is then subjected to prelithiation treatment to obtain a prelithiated negative electrode sheet, wherein the second negative electrode active material and the first negative electrode active material both have a high lithium supplement amount, which can improve the initial coulombic efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0009] In an embodiment of the present application, the lithium supplement composite layer comprises a support layer, a lithium supplement layer, and an interface layer, the lithium supplement layer is arranged between the support layer and the interface layer; the interface layer comprises interface particles, the interface particles comprise at least one of a conductive agent or a lithium intercalation material, the conductive agent comprises at least one of conductive carbon black, carbon fiber, graphene, or carbon nanotube, and the lithium intercalation material comprises at least one of artificial graphite, natural graphite, hard carbon, silicon-carbon material, silicon-oxygen material, lithium titanate, tin, or tin-copper alloy; the lithium supplement layer comprises at least one of lithium foil or lithium alloy foil. The lithium supplement composite layer satisfies the above structure, by selecting the above interface particles, the interface layer can have good electron conductivity and ion conductivity, which is conducive to the transmission of electrons and lithium ions through the interface layer to the surface or the interior of the second negative electrode material layer and the first negative electrode material layer during the prelithiation process, which is conducive to further supplementing lithium to the negative electrode sheet, which can further improve the initial coulombic efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0010] In an embodiment of the present application, the interface particles comprise a lithium intercalation material and a conductive agent, the mass percentage of the lithium intercalation material is 80% to 99%, and the mass percentage of the conductive agent is 1% to 20%, based on the mass of the interface particles. When the interface particles comprise a lithium intercalation material and a conductive agent, and the mass percentages of the lithium intercalation material and the conductive agent are within the range of the present application, the electron conductivity and ion conductivity of the interface layer can be further improved, which is conducive to the transmission of electrons and lithium ions through the interface layer to the surface or the interior of the second negative electrode material layer and the first negative electrode material layer during the prelithiation process, which is conducive to further supplementing lithium to the negative electrode sheet, which can further improve the initial coulombic efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0011] In an embodiment of the present application, the thickness of the interface layer is 0.1 μm to 50 μm, preferably, the thickness of the interface layer is 1 μm to 20 μm.

[0012] In an embodiment of the present application, the thickness of the lithium supplement layer is 0.001 mm to 1 mm, preferably, the thickness of the lithium supplement layer is 0.005 mm to 0.1 mm.

[0013] In an embodiment of the present application, the support layer comprises at least one of a metal foil, a polyethylene terephthalate film, a polypropylene film, a polyethylene film or a polyimide film, and the metal foil comprises a copper foil, a nickel foil, a steel foil or a copper-nickel alloy foil.

[0014] In an embodiment of the present application, the tensile strength of the support layer is 0.5 N / 10 mm to 200 N / 10 mm in the tape running direction of the lithium supplement composite layer, preferably, the tensile strength of the support layer is 1 N / 10 mm to 100 N / 10 mm.

[0015] In an embodiment of the present application, the thickness of the support layer is 3 μm to 50 μm, preferably, the thickness of the support layer is 5 μm to 20 μm.

[0016] The second aspect of the present application provides a lithium supplement method, comprising the following steps:

[0017] The negative electrode sheet is dried, the negative electrode sheet comprising a negative electrode current collector, a first negative electrode material layer and a second negative electrode material layer, the first negative electrode material layer being arranged between the negative electrode current collector and the second negative electrode material layer in the thickness direction of the negative electrode sheet, and the second negative electrode material layer comprising a silicon-containing substance; the mass percentage content of silicon in the first negative electrode material layer is WSi1% based on the mass of the first negative electrode material layer, the mass percentage content of silicon in the second negative electrode material layer is WSi2% based on the mass of the second negative electrode material layer, and WSi2> WSi1. The lithium supplement composite layer prepared by the preparation method in any of the foregoing embodiments is attached to the negative electrode sheet so that the interface layer is in contact with the second negative electrode material layer, pre-lithiation treatment is performed, the lithium supplement composite layer is peeled off from the negative electrode sheet after the pre-lithiation treatment is completed, and a pre-lithiated negative electrode sheet is formed.

[0018] The pre-lithiated negative electrode sheet prepared by the lithium supplement method provided by the present application has a high lithium supplement amount of the second negative electrode active material and the first negative electrode active material, which can improve the initial coulombic efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0019] In an embodiment of the present application, during the pre-lithiation process, the interfacial pressure P3 between the interfacial layer and the second negative electrode material layer is 0.1 MPa to 2 MPa, preferably, the interfacial pressure P3 between the interfacial layer and the second negative electrode material layer is 0.2 MPa to 1.0 MPa; the bonding time t2 between the interfacial layer and the second negative electrode material layer is 0.5 h to 72 h, preferably, the bonding time t2 between the interfacial layer and the second negative electrode material layer is 1 h to 48 h, and the bonding temperature T2 between the interfacial layer and the second negative electrode material layer is 50°C to 180°C, preferably, the bonding temperature T2 between the interfacial layer and the second negative electrode material layer is 60°C to 160°C. By adjusting the interfacial pressure, bonding time and bonding temperature within the scope of the present application, the first coulombic efficiency of the secondary battery can be further improved, the cycle capacity decay can be further reduced, and the energy density of the secondary battery can be further improved.

[0020] The third aspect of the present application provides a pre-lithiated negative electrode sheet prepared according to the above-mentioned lithium supplementing method, the negative electrode sheet comprising a negative electrode current collector, a third negative electrode material layer and a fourth negative electrode material layer, the third negative electrode material layer being arranged between the negative electrode current collector and the fourth negative electrode material layer along the thickness direction of the negative electrode sheet, the third negative electrode material layer comprising a first negative electrode active material, and the fourth negative electrode material layer comprising a second negative electrode active material, the second negative electrode active material comprising a silicon-containing substance. The mass percentage content of silicon element in the third negative electrode material layer is WSi3% based on the mass of the third negative electrode material layer, the mass percentage content of silicon element in the fourth negative electrode material layer is WSi4% based on the mass of the fourth negative electrode material layer, and the mass percentage content of lithium element in the fourth negative electrode material layer is WLi4%, WSi4> WSi3, and 1.5%≤ WLi4 / WSi4≤ 44.4%. The use of the above-mentioned pre-lithiated negative electrode sheet in a secondary battery can improve the first coulombic efficiency of the secondary battery, reduce the cycle capacity decay, and improve the energy density of the secondary battery. At the same time, the fourth negative electrode material layer comprises a silicon-containing substance, which is also beneficial to the improvement of the kinetic performance of the secondary battery.

[0021] In an embodiment of the present application, the mass percentage content of lithium element in the third negative electrode material layer is WLi3% based on the mass of the third negative electrode material layer, 1.1≤ WLi4 / WLi3≤ 4.8, preferably, 1.4≤ WLi4 / WLi3≤ 3.3, and 0.2≤ WLi4≤ 4.4. The value of the mass percentage content of lithium element in the fourth negative electrode material layer and the ratio of the mass percentage content of lithium element in the fourth negative electrode material layer to the mass percentage content of lithium element in the third negative electrode material layer are within the scope of the present application, the second negative electrode active material and the first negative electrode active material both have a high lithium supplementing amount, which can further improve the first coulombic efficiency of the secondary battery, further reduce the cycle capacity decay, and further improve the energy density of the secondary battery.

[0022] In an embodiment of the present application, 0.9≤WSi4≤43.5. The negative pole piece satisfies the above structure, the mass percentage of silicon element in the fourth negative pole material layer is within the range of the present application, the second negative pole active material has a high lithium supplement amount, which can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0023] In an embodiment of the present application, the mass percentage of the silicon-containing substance in the second negative pole active material is S2%, 2≤S2≤100, based on the mass of the second negative pole active material. The negative pole piece satisfies the above structure, the mass percentage of the silicon-containing substance in the second negative pole active material is within the range of the present application, the second negative pole active material has a high lithium supplement amount, which can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0024] In an embodiment of the present application, the mass percentage of the first negative pole active material is H1%, based on the mass of the third negative pole material layer, and the mass percentage of the second negative pole active material is H2%, based on the mass of the fourth negative pole material layer, 0.1≤H2-H1≤10, preferably, 1≤H2-H1≤5. The difference between the mass percentage of the second negative pole active material and the mass percentage of the first negative pole active material is within the range of the present application, the mass percentage of the second negative pole active material matches the mass percentage of the first negative pole active material, the mass percentage of silicon element and lithium element in different negative pole material layers can be controlled, the second negative pole active material and the first negative pole active material both have a high lithium supplement amount, which can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0025] In an embodiment of the present application, the area density of the third negative pole material layer is CW3 mg / cm 2 , the area density of the fourth negative pole material layer is CW4 mg / cm 2 , 0.8≤CW3≤50, preferably, 1.0≤CW3≤13.0; 0.25≤CW4 / CW3≤1. The area density of the third negative pole material layer, the area density of the fourth negative pole material layer, and the ratio of the area density of the fourth negative pole material layer to the area density of the third negative pole material layer are within the range of the present application, the area density of the third negative pole material layer matches the area density of the fourth negative pole material layer, the second negative pole active material and the first negative pole active material both have a high lithium supplement amount, which can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0026] In an embodiment of the present application, the silicon-containing substance includes at least one of a silicon-carbon material or a silicon-oxygen material. The negative electrode sheet satisfying the above structure and the silicon-containing substance selected can make the second negative electrode active material have a higher lithium supplement amount, further improve the first coulomb efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0027] The fourth aspect of the present application provides a secondary battery including the pre-lithiated negative electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by the present application has a higher first coulomb efficiency, a lower cycle capacity attenuation, and a higher energy density.

[0028] The fifth aspect of the present application provides an electronic device including the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has a higher first coulomb efficiency, a lower cycle capacity attenuation, and a higher energy density.

[0029] Advantages of the present application:

[0030] The present application provides a pre-lithiated negative electrode sheet, a preparation method of a lithium supplement composite layer, a lithium supplement method, a secondary battery, and an electronic device. The pre-lithiated negative electrode sheet includes a negative electrode current collector, a third negative electrode material layer, and a fourth negative electrode material layer. Along the thickness direction of the negative electrode sheet, the third negative electrode material layer is arranged between the negative electrode current collector and the fourth negative electrode material layer. The third negative electrode material layer includes a first negative electrode active material. The fourth negative electrode material layer includes a second negative electrode active material. The second negative electrode active material includes a silicon-containing substance. Based on the mass of the third negative electrode material layer, the mass percentage of silicon in the third negative electrode material layer is WSi3%. Based on the mass of the fourth negative electrode material layer, the mass percentage of silicon in the fourth negative electrode material layer is WSi4%. The mass percentage of lithium in the fourth negative electrode material layer is WLi4%. WSi4> WSi3, and 1.5%≤ WLi4 / WSi4≤ 44.4%. The pre-lithiated negative electrode sheet satisfying the above characteristics can improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0031] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0033] Figure 1 A schematic diagram of the structure of the lithium supplement composite layer of an embodiment of the present application;

[0034] Figure 2 A schematic diagram of the structure of the negative electrode sheet and the lithium supplement composite layer during prelithiation of an embodiment of the present application;

[0035] Figure 3 A schematic diagram of the structure of the prelithiated negative electrode sheet of an embodiment of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. All other embodiments obtained by a person skilled in the art based on the present application belong to the scope of protection of the present application.

[0037] It should be noted that in the specific embodiments of the present application, the present application is explained by taking a lithium ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium ion battery.

[0038] A first aspect of the present application provides a preparation method of a lithium supplement composite layer, comprising the following steps:

[0039] (1) under the conditions of ambient temperature ≤ 30℃ and humidity ≤ 1.7%, coating lithium metal powder slurry on a support layer and drying and rolling to form a lithium supplement layer; or calendering lithium foil and / or lithium alloy foil to the support layer to form a lithium supplement layer; or coating lithium or lithium alloy molten slurry on the support layer and cooling and rolling to form a lithium supplement layer; wherein the rolling pressure P1 is 0.2T / 10mm to 1.8T / 10mm; specifically, the rolling pressure P11 after coating lithium metal powder slurry on the support layer and rolling is 0.2T / 10mm to 1.8T / 10mm; the rolling pressure P12 after calendering lithium foil and / or lithium alloy foil to the support layer is 0.2T / 10mm to 1.8T / 10mm; the rolling pressure P13 after coating lithium or lithium alloy molten slurry on the support layer and rolling is 0.2T / 10mm to 1.8T / 10mm;

[0040] (2) under the conditions of ambient temperature ≤ 30℃ and humidity ≤ 1.7%, coating interface particles on the surface of the lithium supplement layer to form an interface layer, and then rolling, wherein the rolling pressure P2 is 0.2T / 10mm to 1.8T / 10mm, preferably the rolling pressure P2 is 0.2T / 10mm to 0.8T / 10mm; the rolling temperature T1 is 20℃ to 180℃, preferably the rolling temperature T1 is 50℃ to 120℃; the rolling standing time t1 is 5min to 60min, preferably the rolling standing time t1 is 10min to 30min, to form a lithium supplement composite layer.

[0041] The inventors have found that, by using the preparation method of the lithium supplementing composite layer provided in the present application to prepare the lithium supplementing composite layer, as shown in Figure 1 The lithium supplementing composite layer 10 includes a support layer 11, a lithium supplementing layer 12, and an interface layer 13. The lithium supplementing layer 12 is arranged between the support layer 11 and the interface layer 13. The interface layer has the ability to conduct electrons and ions. As shown in Figure 2 The interface layer 13 is in contact with the second negative electrode material layer 16, and the lithium supplementing layer 12 forms an internal short circuit with the second negative electrode material layer 16. Lithium atoms in the lithium supplementing layer 12 lose electrons to generate lithium ions through oxidation reaction. The electrons and lithium ions are first transmitted to the surface or interior of the second negative electrode material layer 16 through the interface layer 13, and then transmitted to the surface or interior of the first negative electrode material layer 15. The electrons and lithium ions undergo reduction reaction in the first negative electrode material layer 15 and the second negative electrode material layer 16 to form lithium intercalation compounds, thereby realizing the pre-lithiation process of the first negative electrode material layer 15 and the second negative electrode material layer 16. Since the interface layer is arranged between the lithium supplementing layer and the second negative electrode material layer, the possibility of the lithium supplementing layer adhering to the surface of the second negative electrode material layer is reduced, thereby reducing the influence of the side reaction of the lithium metal in the lithium supplementing layer due to its high activity on the electrochemical performance of the secondary battery. After the pre-lithiation process is completed, the lithium supplementing composite layer is peeled off from the negative electrode sheet to obtain a pre-lithiated negative electrode sheet. The peeling process can reduce the influence of the side reaction of the lithium metal in the lithium supplementing layer on the electrochemical performance of the secondary battery after the lithium metal remains on the surface of the second negative electrode material layer and enters the secondary battery. By using the above method to prepare the lithium supplementing composite layer, and then performing pre-lithiation treatment on the negative electrode sheet, a pre-lithiated negative electrode sheet is obtained. In the pre-lithiated negative electrode sheet, both the second negative electrode active material and the first negative electrode active material have a high lithium supplementing amount, which can improve the initial coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0042] Exemplarily, P11 can be 0.2 T / 10 mm, 0.4 T / 10 mm, 0.6 T / 10 mm, 0.8 T / 10 mm, 1 T / 10 mm, 1.2 T / 10 mm, 1.4 T / 10 mm, 1.6 T / 10 mm, 1.8 T / 10 mm, or a range consisting of any two of the above values. P12 can be 0.2 T / 10 mm, 0.4 T / 10 mm, 0.6 T / 10 mm, 0.8 T / 10 mm, 1 T / 10 mm, 1.2 T / 10 mm, 1.4 T / 10 mm, 1.6 T / 10 mm, 1.8 T / 10 mm, or a range consisting of any two of the above values. P13 can be 0.2 T / 10 mm, 0.4 T / 10 mm, 0.6 T / 10 mm, 0.8 T / 10 mm, 1 T / 10 mm, 1.2 T / 10 mm, 1.4 T / 10 mm, 1.6 T / 10 mm, 1.8 T / 10 mm, or a range consisting of any two of the above values. P2 can be 0.2 T / 10 mm, 0.4 T / 10 mm, 0.6 T / 10 mm, 0.8 T / 10 mm, 1 T / 10 mm, 1.2 T / 10 mm, 1.4 T / 10 mm, 1.6 T / 10 mm, 1.8 T / 10 mm, or a range consisting of any two of the above values. T1 can be 20℃, 40℃, 50℃, 60℃, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, or a range consisting of any two of the above values. t1 can be 5 min, 9 min, 10 min, 15 min, 19 min, 20 min, 25 min, 29 min, 30 min, 35 min, 39 min, 40 min, 45 min, 49 min, 50 min, 55 min, 59 min, 60 min, or a range consisting of any two of the above values.

[0043] In the present application, the lithium metal powder slurry can be coated, rolled to form a lithium supplement layer, or a lithium foil and / or lithium alloy foil can be calendered to form a lithium supplement layer, or a lithium or lithium alloy molten slurry can be coated on the support layer and cooled and rolled to form a lithium supplement layer. In the present application, the lithium alloy foil can include but is not limited to lithium aluminum alloy, and the lithium alloy in the lithium alloy molten slurry can include but is not limited to lithium aluminum alloy. The rolling force refers to the force generated by pressing the sample through the roll gap when the two cylindrical rollers are placed in parallel and the pressure between the upper and lower rollers is controlled. The present application does not particularly limit the coating method of coating the interface particles on the surface of the lithium supplement layer, as long as the purpose of the present application can be achieved. For example, the interface particles can be coated on the surface of the lithium supplement layer by electrostatic spraying, rolling or wiping.

[0044] In an embodiment of the present application, the lithium supplement composite layer comprises a support layer, a lithium supplement layer and an interface layer, the lithium supplement layer is arranged between the support layer and the interface layer; the interface layer comprises interface particles, the interface particles comprise at least one of a conductive agent or a lithium intercalation material, the conductive agent comprises at least one of conductive carbon black, carbon fiber, graphene or carbon nanotube, and the lithium intercalation material comprises at least one of artificial graphite, natural graphite, hard carbon, silicon-carbon material, silicon-oxygen material, lithium titanate, tin or tin-copper alloy; the lithium supplement layer comprises at least one of lithium foil or lithium alloy foil. In the present application, the conductive carbon black can comprise but is not limited to at least one of Super P, acetylene black or Ketjen black; the carbon fiber can comprise but is not limited to at least one of vapor grown carbon fiber (VGCF) or nano carbon fiber; and the carbon nanotube can comprise but is not limited to at least one of single-walled carbon nanotube, multi-walled carbon nanotube or few-walled carbon nanotube. The lithium supplement composite layer satisfies the above structure, by selecting the above interface particles, the interface layer can have good electron and ion conductivity, which is conducive to the transmission of electrons and lithium ions to the surface or interior of the second negative electrode material layer and the first negative electrode material layer during the pre-lithiation process, which is conducive to further supplementing lithium to the negative electrode sheet, and can further improve the initial coulombic efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0045] In an embodiment of the present application, the interface particles comprise a lithium intercalation material and a conductive agent, the mass percentage of the lithium intercalation material is 80% to 99% and the mass percentage of the conductive agent is 1% to 20%, based on the mass of the interface particles. Illustratively, the mass percentage of the lithium intercalation material can be 80%, 81%, 83%, 85%, 87%, 89%, 90%, 91%, 93%, 95%, 97%, 99% or a range composed of any two of the above numbers, and the mass percentage of the conductive agent can be 1%, 3%, 5%, 7%, 9%, 10%, 11%, 13%, 15%, 17%, 19%, 20% or a range composed of any two of the above numbers, based on the mass of the interface particles. When the interface particles comprise a lithium intercalation material and a conductive agent, and the mass percentages of the lithium intercalation material and the conductive agent are within the range of the present application, the electron and ion conductivity of the interface layer can be further improved, which is conducive to the transmission of electrons and lithium ions to the surface or interior of the second negative electrode material layer and the first negative electrode material layer during the pre-lithiation process, which is conducive to further supplementing lithium to the negative electrode sheet, and can further improve the initial coulombic efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0046] In an embodiment of the present application, the interface layer has a thickness of 0.1 μm to 50 μm, preferably, the interface layer has a thickness of 1 μm to 20 μm. Exemplarily, the thickness of the interface layer can be 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or a range between any two of the above-mentioned values.

[0047] In an embodiment of the present application, the lithium supplement layer has a thickness of 0.001 mm to 1 mm, preferably, the lithium supplement layer has a thickness of 0.005 mm to 0.1 mm. Exemplarily, the thickness of the lithium supplement layer 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 between any two of the above-mentioned values.

[0048] In an embodiment of the present application, the support layer comprises at least one of a metal foil, a polyethylene terephthalate film, a polypropylene film, a polyethylene film or a polyimide film, and the metal foil comprises a copper foil, a nickel foil, a steel foil or a copper-nickel alloy foil.

[0049] In an embodiment of the present application, the support layer has a tensile strength of 0.5 N / 10 mm to 200 N / 10 mm in the tape running direction of the lithium supplement composite layer, preferably, the support layer has a tensile strength of 1 N / 10 mm to 100 N / 10 mm, exemplarily, the tensile strength of the support layer can be 0.5 N / 10 mm, 1 N / 10 mm, 5 N / 10 mm, 10 N / 10 mm, 50 N / 10 mm, 100 N / 10 mm, 150 N / 10 mm, 200 N / 10 mm or a range between any two of the above-mentioned values.

[0050] In an embodiment of the present application, the support layer has a thickness of 3 μm to 50 μm, preferably, the support layer has a thickness of 5 μm to 20 μm, exemplarily, the thickness of the support layer can be 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or a range between any two of the above-mentioned values.

[0051] The second aspect of the present application provides a lithium supplement method, comprising the following steps:

[0052] The negative electrode sheet is dried until the water content is ≤500 ppm, the negative electrode sheet comprising a negative current collector, a first negative electrode material layer and a second negative electrode material layer, along the thickness direction of the negative electrode sheet, the first negative electrode material layer is arranged between the negative current collector and the second negative electrode material layer, and the second negative electrode material layer comprises a silicon-containing substance; the mass percentage of silicon in the first negative electrode material layer is WSi1% based on the mass of the first negative electrode material layer, the mass percentage of silicon in the second negative electrode material layer is WSi2% based on the mass of the second negative electrode material layer, and WSi2> WSi1. The lithium supplement composite layer prepared by the preparation method in any of the preceding embodiments and the negative electrode sheet are laminated under the condition of an ambient temperature of 25-180 ℃ and a humidity of ≤1.7% so that the interface layer is in contact with the second negative electrode material layer, a prelithiation treatment is performed, the lithium supplement composite layer is peeled off from the negative electrode sheet after the prelithiation treatment is completed, and a prelithiated negative electrode sheet is formed.

[0053] In the present application, the negative electrode sheet that has not been prelithiated comprises a negative current collector, a first negative electrode material layer and a second negative electrode material layer, the negative electrode sheet that has not been prelithiated is subjected to a prelithiation treatment to obtain a prelithiated negative electrode sheet, and the prelithiated negative electrode sheet comprises a negative current collector, a third negative electrode material layer and a fourth negative electrode material layer. It can be understood that the first negative electrode material layer before the prelithiation treatment corresponds to the third negative electrode material layer after the prelithiation treatment, and the second negative electrode material layer before the prelithiation treatment corresponds to the fourth negative electrode material layer after the prelithiation treatment. The first negative electrode material layer comprises a first negative electrode active material, and the second negative electrode material layer comprises a second negative electrode active material.

[0054] The prelithiated negative electrode sheet prepared by the lithium supplement method provided in the present application has a high lithium supplement amount of both the second negative electrode active material and the first negative electrode active material, can improve the initial coulombic efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0055] In an embodiment of the present application, during the prelithiation treatment, the interface pressure P3 between the interface layer and the second negative electrode material layer is 0.1-2 MPa, preferably 0.2-1.0 MPa; the lamination time t2 of the interface layer and the second negative electrode material layer is 0.5-72 h, preferably 1-48 h, and the lamination temperature T2 of the interface layer and the second negative electrode material layer is 50-180 ℃, preferably 60-160 ℃. By adjusting the interface pressure, the lamination time and the lamination temperature within the range of the present application, the initial coulombic efficiency of the secondary battery can be further improved, the cycle capacity attenuation can be further reduced, and the energy density of the secondary battery can be further improved.

[0056] Exemplarily, P3 can be 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1.0 MPa, 1.2 MPa, 1.4 MPa, 1.6 MPa, 1.8 MPa, 2 MPa, or a range between any two of the above values. t2 can be 0.5 h, 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h, 48 h, 50 h, 55 h, 60 h, 65 h, 70 h, 72 h, or a range between any two of the above values. T2 can be 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, or a range between any two of the above values.

[0057] The third aspect of the present application provides a pre-lithiated negative electrode sheet prepared according to the lithium supplementing method in any of the preceding embodiments, such as Figure 3 As shown, the pre-lithiated negative electrode sheet includes a negative current collector 14, a third negative electrode material layer 17, and a fourth negative electrode material layer 18. The third negative electrode material layer 17 is arranged between the negative current collector 14 and the fourth negative electrode material layer 18 along the thickness direction of the negative electrode sheet, i.e., the Y direction. The third negative electrode material layer 17 includes a first negative electrode active material, and the fourth negative electrode material layer 18 includes a second negative electrode active material. The second negative electrode active material includes a silicon-containing substance. The mass percentage of silicon in the third negative electrode material layer is WSi3% based on the mass of the third negative electrode material layer. The mass percentage of silicon in the fourth negative electrode material layer is WSi4% based on the mass of the fourth negative electrode material layer. The mass percentage of lithium in the fourth negative electrode material layer is WLi4% based on the mass of the fourth negative electrode material layer. WSi4> WSi3, and 1.5%≤ WLi4 / WSi4≤ 44.4%. Exemplarily, the value of WLi4 / WSi4may be 1.5%, 5%, 7%, 9%, 10%, 15%, 17%, 19%, 20%, 25%, 27%, 29%, 30%, 35%, 37%, 39%, 40%, 44.4%, or a range between any two of the above values. In the present application, the third negative electrode material layer and the fourth negative electrode material layer can be sequentially arranged on one surface of the negative current collector along the thickness direction of the negative current collector, or the third negative electrode material layer and the fourth negative electrode material layer can be sequentially arranged on two surfaces of the negative current collector along the thickness direction of the negative current collector, respectively. It should be noted that the "surface" herein can be the entire region of the negative current collector or a partial region of the negative current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. In some embodiments of the present application, WSi3= 0.

[0058] The inventors have found that, for the same pre-lithiation treatment time, different negative active materials have different lithium supplement efficiencies, and the silicon-containing substance has a relatively small amount of lithium supplement, and the carbon material has a relatively large amount of lithium supplement, and thus the first coulomb efficiency of the silicon-containing substance is affected. The negative electrode sheet that has not been pre-lithiated includes a negative electrode current collector, a first negative electrode material layer, and a second negative electrode material layer. The first negative electrode material layer is arranged between the negative electrode current collector and the second negative electrode material layer along the thickness direction of the negative electrode sheet. The second negative electrode material layer includes a silicon-containing substance, the first negative electrode material layer does not include the silicon-containing substance, and the first negative electrode material layer includes a carbon material. The pre-lithiation treatment is performed on the above-mentioned negative electrode sheet that has not been pre-lithiated, so as to preferentially supplement lithium to the silicon-containing substance in the second negative electrode material layer, and then supplement lithium to the carbon material in the first negative electrode material layer, to obtain a pre-lithiated negative electrode sheet. The negative electrode sheet satisfies the above-mentioned structure, and the mass percentage content of the silicon-containing substance in different negative electrode material layers is within the range of the present application, which is beneficial to realizing directional lithium supplement to the silicon-containing substance in the second negative electrode material layer, and thus improving the lithium supplement efficiency of the silicon-containing substance. The pre-lithiated negative electrode sheet includes a negative electrode current collector, a third negative electrode material layer, and a fourth negative electrode material layer. The third negative electrode material layer is arranged between the negative electrode current collector and the fourth negative electrode material layer along the thickness direction of the negative electrode sheet. The third negative electrode material layer includes a first negative active material, and the fourth negative electrode material layer includes a second negative active material. The second negative active material includes a silicon-containing substance, the first negative active material does not include the silicon-containing substance, and the first negative active material includes a carbon material. The mass percentage content of silicon in the fourth negative electrode material layer is greater than the mass percentage content of silicon in the third negative electrode material layer, and the ratio of the mass percentage content of lithium to the mass percentage content of silicon in the fourth negative electrode material layer is within the range of the present application. The second negative active material and the first negative active material both have a high amount of lithium supplement. The above-mentioned pre-lithiated negative electrode sheet is applied to a secondary battery, which can improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery. Meanwhile, the fourth negative electrode material layer includes the silicon-containing substance, which is also beneficial to improving the kinetic performance of the secondary battery.

[0059] In the present application, the carbon material includes at least one of artificial graphite, natural graphite, hard carbon, mesocarbon microbeads (MCMB), or soft carbon.

[0060] In an embodiment of the present application, the mass percentage of lithium in the third negative electrode material layer is WLi3%, and 1.1≤WLi4 / WLi3≤4.8, preferably 1.4≤WLi4 / WLi3≤3.3, and exemplarily the value of WLi4 / WLi3may be 1.1, 1.4, 1.5, 2.0, 2.5, 3.0, 3.3, 3.5, 4.0, 4.5, 4.8, or a range between any two of the above values; 0.2≤WLi4≤4.4, and exemplarily the value of WLi4may be 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, or a range between any two of the above values. The value of the mass percentage of lithium in the fourth negative electrode material layer and the ratio of the value of the mass percentage of lithium in the fourth negative electrode material layer to the value of the mass percentage of lithium in the third negative electrode material layer are within the scope of the present application, and the second negative electrode active material and the first negative electrode active material both have a high lithium supplement amount, which can further improve the initial coulombic efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery. In the present application, 0.08≤WLi3≤0.92, and exemplarily the value of WLi3may be 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.92, or a range between any two of the above values.

[0061] The present application does not have a particular limitation on the way of regulating the mass percentage of silicon in the fourth negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the mass percentage of silicon in the fourth negative electrode material layer can be regulated by regulating the mass percentage of the silicon-containing substance added to the fourth negative electrode material layer. The present application does not have a particular limitation on the way of regulating the mass percentage of lithium in the third negative electrode material layer and the mass percentage of lithium in the fourth negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the mass percentage of lithium in the third negative electrode material layer and the mass percentage of lithium in the fourth negative electrode material layer can be regulated by regulating the bonding time, bonding temperature, or interfacial pressure of the pre-lithiation process. The present application does not have a particular limitation on the method of regulating WLi4 / WSi4, as long as the purpose of the present application can be achieved. For example, the value of WLi4 / WSi4may be regulated by regulating the value of WLi4and WSi4, and the regulation method is as described above. The present application does not have a particular limitation on the method of regulating WLi4 / WLi3, as long as the purpose of the present application can be achieved. For example, the value of WLi4 / WLi3may be regulated by regulating the value of WLi4and WLi3, and the regulation method is as described above.

[0062] In an embodiment of the present application, 0.9≤WSi4≤43.5, and exemplary values of WSi4may be 0.9, 1, 5, 10, 15, 20, 25, 30, 35, 40, 42, 43.5, or a range defined by any two of the above values. The negative electrode tab satisfies the above structure, the mass percentage content of silicon element in the fourth negative electrode material layer is within the range of the present application, the second negative electrode active material has a high lithium supplement amount, which can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery.

[0063] In an embodiment of the present application, the mass percentage content of the silicon-containing substance is S2% based on the mass of the second negative electrode active material, and 2≤S2≤100, and exemplary values of S2may be 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or a range defined by any two of the above values. The negative electrode tab satisfies the above structure, the mass percentage content of the silicon-containing substance in the second negative electrode active material is within the range of the present application, the second negative electrode active material has a high lithium supplement amount, which can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery. The present application does not have a particular limitation on the way of regulating the mass percentage content of the silicon-containing substance in the second negative electrode active material, as long as the purpose of the present application can be achieved. For example, the mass percentage content of the silicon-containing substance in the second negative electrode active material can be regulated by regulating the mass percentage content of the added silicon-containing substance.

[0064] In the present application, the second negative electrode active material can further include a carbon material. The mass percentage content of the carbon material is C2% based on the mass of the second negative electrode active material, and 0≤C2≤98, and exemplary values of C2may be 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 98, or a range defined by any two of the above values.

[0065] In an embodiment of the present application, the mass percentage of the first negative active material is H1% based on the mass of the third negative material layer, the mass percentage of the second negative active material is H2% based on the mass of the fourth negative material layer, 0.1≤H2-H1≤10, preferably, 1≤H2-H1≤5, for example, the value of H2-H1 can be 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or a range between any two of the aforementioned values. The difference between the mass percentage of the second negative active material and the mass percentage of the first negative active material is within the scope of the present application, the mass percentage of the second negative active material matches the mass percentage of the first negative active material, which can regulate the mass percentage of silicon and lithium in different negative material layers, so that the second negative active material and the first negative active material both have a high lithium supplement amount, which can further improve the initial coulombic efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery. In the present application, 65≤H1≤98.9, 75≤H2≤99.

[0066] The present application does not have special restrictions on the way of regulating the mass percentage of the first negative active material and the mass percentage of the second negative active material, as long as the purpose of the present application can be achieved. For example, the mass percentage of the first negative active material can be regulated by regulating the mass percentage of the added first negative active material; the mass percentage of the second negative active material can be regulated by regulating the mass percentage of the added second negative active material. The present application does not have special restrictions on the method of regulating H2-H1, as long as the purpose of the present application can be achieved. For example, the value of H2-H1 can be regulated by regulating the value of H2 and H1 respectively, and the regulation method is as described above.

[0067] In an embodiment of the present application, the areal density of the third negative material layer is CW3 mg / cm 2 , the areal density of the fourth negative material layer is CW4 mg / cm 20.8CW3<50, preferably, 1.0CW3<13.0, exemplarily, the value of CW3may be 0.8, 1, 3, 5, 7, 10, 13, 15, 17, 20, 23, 25, 27, 30, 33, 35, 37, 40, 43, 45, 47, 50, or a range between any two of the above values; 0.25CW4 / CW3<1, exemplarily, the value of CW4 / CW3may be 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range between any two of the above values. The ratio of the surface density of the third negative electrode material layer, the surface density of the fourth negative electrode material layer, and the surface density of the third negative electrode material layer is within the scope of the present application, and the surface density of the third negative electrode material layer matches the surface density of the fourth negative electrode material layer, so that the second negative electrode active material and the first negative electrode active material both have a high lithium supplement amount, which can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity attenuation, and further improve the energy density of the secondary battery. In the present application, 0.2CW4<50.

[0068] The present application does not have special restrictions on the way of regulating the surface density of the third negative electrode material layer and the fourth negative electrode material layer, as long as the purpose of the present application can be achieved. It can be understood that the surface density of the third negative electrode material layer is related to the surface density of the first negative electrode material layer, and the surface density of the third negative electrode material layer is the sum of the surface density of the first negative electrode material layer and the lithium supplement surface density; the surface density of the fourth negative electrode material layer is related to the surface density of the second negative electrode material layer, and the surface density of the fourth negative electrode material layer is the sum of the surface density of the second negative electrode material layer and the lithium supplement surface density. The surface density of the third negative electrode material layer can be regulated by regulating the surface density of the first negative electrode material layer and / or the lithium supplement surface density, and the surface density of the fourth negative electrode material layer can be regulated by regulating the surface density of the second negative electrode material layer and / or the lithium supplement surface density. For example, when the first negative electrode slurry is coated on the surface of the negative electrode current collector, the coating amount of the first negative electrode slurry is increased to increase the surface density of the first negative electrode material layer based on the certain solid content of the first negative electrode slurry; when the second negative electrode slurry is coated on the surface of the first negative electrode material layer, the coating amount of the second negative electrode slurry is increased to increase the surface density of the second negative electrode material layer based on the certain solid content of the second negative electrode slurry. For example, the lithium supplement surface density can be regulated by regulating the interfacial pressure, the fitting time, and the fitting temperature during the pre-lithiation process. The present application does not have special restrictions on the method of regulating CW4 / CW3, as long as the purpose of the present application can be achieved. For example, the value of CW4 / CW3may be regulated by regulating the values of CW4and CW3, and the regulation method is as described above.

[0069] In an embodiment of the present application, the silicon-containing substance includes at least one of a silicon-carbon material or a silicon-oxygen material. In the present application, the silicon-carbon material is a silicon-carbon composite material, and the mass percentage of silicon is 30% to 70% and the mass percentage of carbon is 30% to 70% based on the mass of the silicon-carbon composite material. The silicon-carbon composite material is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the silicon-carbon composite material can be a composite material obtained by deposition. Illustratively, the silicon-carbon composite material can be a silicon material deposited on a carbon skeleton or a carbon material deposited on a silicon skeleton. The silicon-oxygen material includes SiOx, where 0 < x < 2. Illustratively, the silicon-oxygen material can include silicon monoxide (SiO, the molar ratio of silicon to oxygen is 1:1). The negative electrode tab satisfies the above structure, and the above silicon-containing substance is selected, so that the second negative electrode active material has a high lithium supplement amount, the first coulomb efficiency of the secondary battery can be further improved, the cycle capacity attenuation can be further reduced, and the energy density of the secondary battery can be further improved.

[0070] In the present application, the first negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the second negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. The type of the negative electrode binder is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the negative electrode binder can include at least one of 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 hydroxymethyl cellulose, or potassium hydroxymethyl cellulose. The type of the negative electrode conductive agent is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the negative electrode conductive agent can include but is not limited to at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, a metal material, or a conductive polymer. The above-mentioned metal material can include but is not limited to metal powder and / or metal fibers, and specifically, the metal can include but is not limited to at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include but is not limited to at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The mass percentage of the negative electrode binder and the negative electrode conductive agent in the first negative electrode material layer is not particularly limited in the present application, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved. The mass percentage of the negative electrode binder and the negative electrode conductive agent in the second negative electrode material layer is not particularly limited in the present application, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0071] The negative current collector according to the present application is not particularly limited as long as the object of the present application can be achieved, and for example, can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector (for example, a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, or the like), and the like.

[0072] The thickness of the negative current collector according to the present application is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness of the negative current collector is 4 μm to 20 μm. The thickness of the first negative material layer and the second negative material layer according to the present application is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness of the single-sided first negative material layer is 8 μm to 265 μm, and the thickness of the single-sided second negative material layer is 2 μm to 265 μm.

[0073] The fourth aspect of the present application provides a secondary battery including the pre-lithiated negative electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery provided by the present application has a higher initial coulombic efficiency, a lower cycle capacity decay, and a higher energy density.

[0074] In the present application, the secondary battery further includes a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive material layer disposed on at least one surface of the positive current collector. The above-mentioned "positive material layer disposed on at least one surface of the positive current collector" means that the positive material layer can be disposed on one surface of the positive current collector in the thickness direction of the positive current collector itself, or can be disposed on both surfaces of the positive current collector in the thickness direction of the positive current collector itself. It should be noted that the "surface" here can be the entire area of the positive current collector, or can be a partial area of the positive current collector, and the present application is not particularly limited as long as the object of the present application can be achieved.

[0075] The positive current collector according to the present application is not particularly limited as long as the object of the present application can be achieved, and for example, can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), and the like.

[0076] The positive material layer according to the present application includes a positive active material, and the positive active material includes a substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. The positive material layer can be one layer or multiple layers, and each layer of the multiple layers of the positive material layer can include the same or different positive active material. The positive active material according to the present application is not particularly limited as long as the object of the present application can be achieved, and for example, the positive 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 material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate. The above-mentioned lithium nickel cobalt manganese oxide can include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM111). The positive electrode material layer of the present application further comprises a positive electrode conductive agent and a positive electrode binder, and the present application does not have special restrictions on the positive electrode conductive agent and the positive electrode binder, as long as the purpose of the present application can be achieved. For example, the positive electrode conductive agent can include at least one of the above-mentioned negative electrode conductive agents; the positive electrode binder can include at least one of the above-mentioned negative electrode binders. The present application does not have special restrictions 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, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0077] The present application does not have special restrictions on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness of the positive electrode current collector is 6 μm to 25 μm. The present application does not have special restrictions on the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved, for example, the thickness of the single-sided positive electrode material layer is 25 μm to 250 μm.

[0078] In the present application, the secondary battery further includes an electrolyte. The electrolyte includes a lithium salt. The kind of the lithium salt is not particularly limited in the present application, and a lithium salt known in the art can be used. Illustratively, the lithium salt can include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis-trifluoromethanesulfonimide (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 difluoro(oxalato)borate (LiBF2(C2O4), LiDFOB). The mass percentage content of the lithium salt in the electrolyte is not particularly limited in the present application, as long as the object of the present application can be achieved. The electrolyte further includes a non-aqueous organic solvent. The non-aqueous organic solvent is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the non-aqueous organic solvent can include at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or other organic solvents. The carbonate compound described above can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluorinated carbonate compound. The chain carbonate compound described above can include, but is 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 cyclic carbonate compound described above can include, but is not limited to, at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound described above can include, but is 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-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. The carboxylic acid ester compound described above can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The ether compound described above can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyl tetrahydrofuran, or tetrahydrofuran. The other organic solvents described above can include, but is not limited to, at least one of 1,3-propanesultone, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphoric acid ester.The mass percentage content of the non-aqueous organic solvent in the electrolyte is not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0079] In the present application, the secondary battery further includes a separator. The separator is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. The present application does not have a particular limitation on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of the separator can include at least one of woven film, non-woven film, microporous film, composite film, calendered film, or spunlaced film.

[0080] In the present application, the separator can include a substrate and a surface treatment layer. The substrate can be a non-woven fabric or a composite film with a porous structure, and the material of the substrate can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing polymer and inorganic matter. For example, the inorganic layer includes inorganic particles and a separator binder, and the present application does not have a particular limitation on the inorganic particles, which can include at least one of aluminum oxide, 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. The present application does not have a particular limitation on the separator binder, which can be at least one of the aforementioned negative electrode binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0081] The secondary battery of the present application further includes a packaging bag for containing the positive electrode sheet, the separator, the pre-lithiated negative electrode sheet, and the electrolyte, as well as other components known in the art for use in the secondary battery, which are not limited in the present application. The packaging bag is not particularly limited in the present application, and can be a packaging bag known in the art, as long as the purpose of the present application can be achieved.

[0082] The kind of the secondary battery according to the present application is not particularly limited, and it can include any device in which an electrochemical reaction occurs. In the present application, the secondary battery can include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery (lithium ion polymer battery), and the like.

[0083] The preparation process of the secondary battery according to the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, it can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the pre-lithiated negative electrode sheet in order, and winding, folding, or the like as needed to obtain an electrode assembly with a winding structure, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator, and the pre-lithiated negative electrode sheet in order, then fixing the four corners of the entire stack structure with adhesive tape to obtain an electrode assembly with a stack structure, placing the electrode assembly into a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, a current overprotection element, a guide plate, or the like can also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0084] The fifth aspect of the present application provides an electronic device comprising the secondary battery according to any one of the preceding embodiments. Therefore, the electronic device provided by the present application has a higher first coulomb efficiency, a lower cycle capacity decay, and a higher energy density.

[0085] The kind of the electronic device according to the present application is not particularly limited, and it can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, and the like.

[0086] Embodiments

[0087] Hereinafter, embodiments and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0088] Test methods and apparatuses:

[0089] Test of mass percentage content of elements in the negative electrode material layer:

[0090] Take the pre-lithiated negative electrode sheet, cut the pre-lithiated negative electrode sheet into a sample with a size of 6mm x 6mm, and stick it to the sample table with conductive glue; then polish the cross section of the sample with a cross section polisher (model IB-19520CCP) under the following polishing conditions: vacuum degree 10 -3 Pa, acceleration voltage 6kV, and polishing speed 500 microns / hour. Place the polished sample on the sample table of a scanning electron microscope (SEM, model Sumu Fei-Apreo S), and test the cross section thereof by SEM under the following test conditions: acceleration voltage 10kV, grating 10spot, working distance WD 10mm, and magnification 2000x. The one containing irregular silicon particles is the fourth negative electrode material layer, and the one not containing irregular silicon particles is the third negative electrode material layer. Test the thickness of the fourth negative electrode material layer at 10 positions respectively, and take the average value Thk4. Test the thickness of the third negative electrode material layer at 10 positions respectively, and take the average value Thk3.

[0091] Select the area including the double-sided negative electrode material layer on the pre-lithiated negative electrode sheet, cut 10 small discs with an area of 1540.25mm 2 using a disc cutter, then wipe off the negative electrode material layer on the surface of the 10 small discs to a thickness of Thk4, and collect the wiped-off powder, which is the fourth negative electrode material layer powder. Use an inductively coupled plasma-optical emission spectrometer (ICP-OES) to analyze the mass percentage of silicon and lithium in the fourth negative electrode material layer powder. Then wipe off the negative electrode material layer on the 10 small discs to a thickness of Thk3, and collect the wiped-off powder, which is the third negative electrode material layer powder. Use an inductively coupled plasma-optical emission spectrometer (ICP-OES) to analyze the mass percentage of silicon and lithium in the third negative electrode material layer powder. The ICP-OES used is a PE7000DV spectrometer produced by American Platinum Gold Elmer Company, and the test conditions of the ICP-OES are as follows: radio frequency (RF) 40.68MHz, radio frequency power 1300W, argon secondary pressure 0.6MPa, auxiliary gas flow rate 0.2L / min, cooling gas flow rate 15L / min, and pump speed 1.5mL / min.

[0092] Surface density test:

[0093] Select the area including the double-sided negative electrode material layer on the pre-lithiated negative electrode sheet, cut 10 small discs with an area of 1540.25mm 2Ten small circular wafers were used as a negative electrode material layer. Thickness Thk4 of this layer was then wiped away from the surface of the wafers, and the removed powder was collected as the fourth negative electrode material layer powder. The wafers were weighed three times, and the average value M4 was taken. Then, the remaining negative electrode material layer with a thickness of Thk3 was wiped away from the ten wafers, and the removed powder was collected as the third negative electrode material layer powder. The wafers were weighed three times, and the average value M3 was taken. The areal density CW4 of the fourth negative electrode material layer (mg / cm³) 2 = (M4×100000) / (2×1540.25), the areal density CW3 of the third negative electrode material layer (mg / cm³) 2 )=(M3×100000) / (2×1540.25). Where M4 is in g and M3 is in g.

[0094] First Coulomb efficiency test:

[0095] 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.

[0096] Initial coulomb efficiency (%) = C1 / C0 × 100%.

[0097] Cyclic performance test:

[0098] 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.

[0099] Cyclic capacity retention rate (%) = B / A × 100%.

[0100] The greater the value of the cycle capacity retention rate obtained by the test, the better the cycle performance of the lithium ion battery.

[0101] Energy density test:

[0102] The voltage range marked on the factory battery outer package is used as the reference, for example, when the factory battery is marked with a voltage range of 3.0V to 4.45V, the charging cutoff voltage is 4.45V and the discharging cutoff voltage is 3.0V. The specific test procedure is as follows: under the condition of 25℃, the lithium ion battery in the example or the comparative example is charged at 0.2C constant current to the cutoff voltage 4.45V, then charged at 4.45V constant voltage until the current is less than 0.05C, and then discharged at 0.2C constant current to the cutoff voltage 3.0V after standing for 5min. The energy of the above discharging process is recorded as the discharging energy E. The volume V(mm 3 ) of the lithium ion battery is calculated as follows: length x width x height.

[0103] Energy density (Wh / L) = E / V x 10 6 .

[0104] Example 1-1

[0105] Preparation of lithium supplementing composite layer

[0106] Under the condition of ambient temperature 25℃ and humidity 1.0%, the lithium foil is calendered to the copper foil support layer with a thickness of 14μm to form a lithium supplementing layer, the roll pressure P12 is 1.5T / 10mm, and the lithium supplementing layer / support layer composite structure is obtained.

[0107] Under the condition of ambient temperature 25℃ and humidity 1.0%, the interface particle artificial graphite is coated on the surface of the lithium supplementing layer by rubbing to form an interface layer, and then roll pressing is performed, the roll pressure P2 is 0.5T / 10mm, the roll pressing temperature T1 is 90℃, and the roll pressing standing time t1 is 30min, and the lithium supplementing composite layer is formed. In the lithium supplementing composite layer, the thickness of the interface layer is 8μm, the thickness of the lithium supplementing layer is 0.03mm, and the tensile strength of the support layer along the walking direction of the lithium supplementing composite layer is 72N / 10mm.

[0108] Preparation of negative electrode sheet

[0109] The first negative electrode active material artificial graphite, the negative electrode conductive agent acetylene black, the negative electrode binder styrene butadiene rubber (SBR), and the negative electrode binder lithium carboxymethyl cellulose are mixed according to the weight ratio of 88:2:6:4, deionized water is added as a solvent, and stirring is performed until the mixture is uniformly mixed, and a first negative electrode slurry is obtained, wherein the solid content of the first negative electrode slurry is 28wt%.

[0110] The second negative electrode active material, the negative electrode conductive agent acetylene black, the negative electrode binder styrene butadiene rubber (SBR), and the negative electrode binder lithium carboxymethyl cellulose are mixed according to a weight ratio of 98:0.5:1:0.5, deionized water is added as a solvent, and stirring is performed until the mixture is uniform, to obtain a second negative electrode slurry, wherein the solid content of the second negative electrode slurry is 28 wt%; the second negative electrode active material comprises a silicon-carbon material and artificial graphite, the silicon-carbon material is a silicon-carbon composite material, the mass percentage of silicon is 50% and the mass percentage of carbon is 50% based on the mass of the silicon-carbon composite material; the mass percentage of silicon-containing substances is 30% and the mass percentage of carbon materials is 70% based on the mass of the second negative electrode active material.

[0111] The first negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm, and is dried at 90 °C to obtain a negative electrode sheet coated with a first negative electrode material layer on one surface; then the second negative electrode slurry is uniformly coated on the surface of the first negative electrode material layer away from the negative electrode current collector copper foil, and is dried at 90 °C to obtain a negative electrode sheet coated with a first negative electrode material layer and a second negative electrode material layer in sequence on one surface. The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet. After drying under vacuum at 90 °C for 1 h, the negative electrode sheet is subjected to cold pressing, sheet cutting, and slitting to obtain a negative electrode sheet with a size of 51 mm x 44.2 mm. The areal density of the first negative electrode material layer is 5.94 mg / cm 2 , the areal density of the second negative electrode material layer is 2.93 mg / cm 2 , and the compaction density during cold pressing is 1.65 g / cm 3 . The mass percentage of silicon in the first negative electrode material layer is WSi1% based on the mass of the first negative electrode material layer, and the mass percentage of silicon in the second negative electrode material layer is WSi2% based on the mass of the second negative electrode material layer, WSi1 = 0, WSi2 = 14.7, and WSi2 > WSi1.

[0112] <Preparation of a pre-lithiated negative electrode sheet>

[0113] The prepared negative electrode sheet is dried until the water content is ≤500 ppm; the prepared lithium supplement composite layer is attached to the prepared negative electrode sheet under the conditions of an environmental temperature of 90 °C and a humidity of 1.0% so that the interface layer contacts the second negative electrode material layer, pre-lithiation treatment is performed, the interface pressure P3 between the interface layer and the second negative electrode material layer is 0.6 MPa, the attachment time t2 of the interface layer and the second negative electrode material layer is 20 h, the attachment temperature T2 of the interface layer and the second negative electrode material layer is 90 °C, the lithium supplement composite layer is peeled off from the negative electrode sheet after the pre-lithiation treatment is completed, and a pre-lithiated negative electrode sheet is formed.

[0114] <Preparation of a positive electrode sheet>

[0115] The positive active material lithium cobaltate (LiCoO2), the positive conductive agent acetylene black, and the positive binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97:1.4:1.6, N-methyl pyrrolidone (NMP) was added as a solvent, and the mixture was stirred and mixed uniformly to obtain a positive slurry, wherein the solid content of the positive slurry was 75 wt%. The positive slurry was uniformly coated on one surface of a positive current collector aluminum foil with a thickness of 12 μm, and was dried at 110°C to obtain a positive electrode sheet coated with a positive material layer on one side. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive material layer on both sides. After drying under vacuum at 110°C for 1 h, the positive electrode sheet was subjected to cold pressing, sheet cutting, and slitting to obtain a positive electrode sheet with a size of 48 mm x 41.2 mm. The areal density of the positive material layer was 19.0 mg / cm 2 , and the compaction density during the cold pressing process was 4.15 g / cm 3 .

[0116] <Preparation of electrolyte>

[0117] In an argon atmosphere 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, and then lithium salt lithium hexafluorophosphate (LiPF6) was added and mixed uniformly to obtain an electrolyte. The mass percentage of lithium salt LiPF6 was 12.5% based on the mass of the electrolyte, and the balance was the base solvent.

[0118] <Preparation of separator>

[0119] A porous polypropylene film (provided by Celgard) with a thickness of 5 μm was used as the separator.

[0120] <Preparation of lithium ion battery>

[0121] The positive electrode sheet, the separator, the pre-lithiated negative electrode sheet, and the separator prepared above were stacked in order, with the separator between the positive electrode sheet and the pre-lithiated negative electrode sheet to serve as a barrier, and were wound to obtain an electrode assembly. After welding the tabs, the electrode assembly was placed in an aluminum-plastic film packaging bag, was dried in a vacuum oven at 85°C for 12 h to remove water, was injected with electrolyte, and was subjected to vacuum packaging, standing, formation (charged to 3.5 V at 0.02 C and then charged to 3.9 V at 0.1 C), degassing, edge cutting, and capacity processing to obtain a lithium ion battery.

[0122] Examples 1-2 to 1-9

[0123] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as in Example 1-1.

[0124] Example 2-1 to Example 2-8

[0125] The rest is the same as Example 1-3, except that the surface densities of the third negative material layer and / or the fourth negative material layer are adjusted as shown in Table 2 by adjusting the coating amount of the first negative slurry and / or the coating amount of the second negative slurry.

[0126] Example 3-1

[0127] The rest is the same as Example 1-3, except that the relevant preparation parameters are adjusted according to Table 3.

[0128] Example 3-2

[0129] The rest is the same as Example 1-3, except that the lithium supplement composite layer is prepared according to the following method.

[0130] <Preparation of lithium supplement composite layer>

[0131] Under the conditions of ambient temperature 25℃ and humidity 1.0%, the lithium foil is calendered to the copper foil support layer with a thickness of 14μm to form a lithium supplement layer, and the roll pressure P12 is 1.5T / 10mm, to obtain a lithium supplement layer / support layer composite structure.

[0132] Under the conditions of ambient temperature 25℃ and humidity 1.0%, the artificial graphite and acetylene black are first mixed uniformly to obtain interface particles, and then the interface particles are coated on the surface of the lithium supplement layer by rubbing to form an interface layer, and then rolled, the roll pressure P2 is 0.5T / 10mm, the roll temperature T1 is 90℃, and the roll standing time t1 is 30min, to form a lithium supplement composite layer. Among them, the mass percentage content of lithium intercalation material is 80% and the mass percentage content of conductive agent is 20% based on the mass of the interface particles; the thickness of the interface layer in the lithium supplement composite layer is 8μm; the thickness of the lithium supplement layer is 0.03mm; and the tensile strength of the support layer along the walking direction of the lithium supplement composite layer is 72N / 10mm.

[0133] Example 3-3 to Example 3-5

[0134] The rest is the same as Example 3-2, except that the relevant preparation parameters are adjusted according to Table 3.

[0135] Comparative Example 1

[0136] The rest is the same as Example 1-1, except that the negative electrode sheet is prepared according to the following method.

[0137] <Preparation of negative electrode sheet>

[0138] The negative active material, the negative conductive agent acetylene black, the negative binder styrene butadiene rubber (SBR), and the negative binder lithium carboxymethyl cellulose are mixed according to a weight ratio of 89:2:6:3, deionized water is added as a solvent, and stirring and mixing are performed until uniformity is achieved, to obtain a negative slurry, wherein the solid content of the negative slurry is 28 wt%; the negative slurry is uniformly coated on one surface of a negative current collector copper foil with a thickness of 12 μm, and drying is performed at 90 °C, to obtain a negative electrode sheet coated with a negative material layer on one side. The above steps are repeated on the other surface of the copper foil, to obtain a negative electrode sheet coated with a negative material layer on both sides. Drying is performed under vacuum at 90 °C for 1 h, and then cold pressing, sheet cutting, and slitting are performed, to obtain a negative electrode sheet with a size of 51 mm x 44.2 mm. The negative active material includes a silicon-carbon material and artificial graphite, the silicon-carbon material is a silicon-carbon composite material, the mass percentage of silicon is 50% and the mass percentage of carbon is 50% based on the mass of the silicon-carbon composite material; the mass percentage of silicon-containing substances is 10% and the mass percentage of carbon materials is 90% based on the mass of the negative active material; and the area density of the negative material layer is 8.97 mg / cm 2 , and the compaction density during the cold pressing process is 1.65 g / cm 3 .

[0139] Comparative Example 2

[0140] The negative electrode sheet was prepared according to the following method, and the rest was the same as in Examples 1-3.

[0141] <Preparation of a negative electrode sheet>

[0142] The first negative active material, the negative conductive agent acetylene black, the negative binder styrene butadiene rubber (SBR), and the negative binder lithium carboxymethyl cellulose are mixed according to a weight ratio of 88:2:6:4, deionized water is added as a solvent, and stirring and mixing are performed until uniformity is achieved, to obtain a first negative slurry, wherein the solid content of the first negative slurry is 28 wt%; the first negative active material includes a silicon-carbon material and artificial graphite, the silicon-carbon material is a silicon-carbon composite material, the mass percentage of silicon is 50% and the mass percentage of carbon is 50% based on the mass of the silicon-carbon composite material; and the mass percentage of silicon-containing substances is 15% and the mass percentage of carbon materials is 85% based on the mass of the first negative active material.

[0143] The second negative active material artificial graphite, the negative conductive agent acetylene black, the negative binder styrene butadiene rubber (SBR), and the negative binder lithium carboxymethyl cellulose are mixed according to a weight ratio of 91:2:4.5:2.5, deionized water is added as a solvent, and stirring and mixing are performed until uniformity is achieved, to obtain a second negative slurry, wherein the solid content of the second negative slurry is 28 wt%.

[0144] The first negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm, dried at 90 °C, to obtain a negative electrode sheet coated with a first negative electrode material layer on one surface; then the second negative electrode slurry was uniformly coated on the surface of the first negative electrode material layer away from the negative electrode current collector copper foil, dried at 90 °C, to obtain a negative electrode sheet coated with a first negative electrode material layer and a second negative electrode material layer in sequence on one surface. The above steps were repeated on the other surface of the copper foil, to obtain a negative electrode sheet. After drying at 90 °C under vacuum for 1 h, cold pressing, sheet cutting and slitting, a negative electrode sheet with a size of 51 mm x 44.2 mm was obtained. The areal density of the first negative electrode material layer was 5.98 mg / cm 2 , the areal density of the second negative electrode material layer was 2.99 mg / cm 2 , and the compaction density in the cold pressing process was 1.65 g / cm 3 .

[0145] The preparation parameters, sheet performance parameters and electrical performance parameters of each example and comparative example are shown in Tables 1 to 3.

[0146]

[0147]

[0148] As can be seen from Examples 1-1 to 1-9 and Comparative Examples 1 to 2, the pre-lithiated negative electrode sheet of the present application, the structure of the pre-lithiated negative electrode sheet is within the scope of the present application, the mass percentage content of silicon element in the fourth negative electrode material layer is greater than that in the third negative electrode material layer, and the ratio of the mass percentage content of lithium element to the mass percentage content of silicon element in the fourth negative electrode material layer is within the scope of the present application, the prepared lithium ion battery has high first coulomb efficiency, cycle capacity retention rate and energy density, which indicates that the first coulomb efficiency of the lithium ion battery can be improved, the cycle capacity decay can be reduced, and the energy density of the lithium ion battery can be improved. The structure of the pre-lithiated negative electrode sheet of Comparative Example 1 is not within the scope of the present application, and the prepared lithium ion battery has low first coulomb efficiency, cycle capacity retention rate and energy density. In Comparative Example 2, the mass percentage content of silicon element in the third negative electrode material layer is greater than that in the fourth negative electrode material layer, and the prepared lithium ion battery has low first coulomb efficiency, cycle capacity retention rate and energy density.

[0149] The value of the mass percentage content of lithium element in the fourth negative electrode material layer and the ratio of the value to the mass percentage content of lithium element in the third negative electrode material layer affect the first coulomb efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Examples 1-1 to 1-9, the value of the mass percentage content of lithium element in the fourth negative electrode material layer and the ratio of the value to the mass percentage content of lithium element in the third negative electrode material layer are within the scope of the present application, the prepared lithium ion battery has a higher first coulomb efficiency, cycle capacity retention rate and energy density, which indicates that the first coulomb efficiency of the lithium ion battery can be improved, the cycle capacity decay can be reduced, and the energy density of the lithium ion battery can be improved.

[0150] The mass percentage content of silicon element in the fourth negative electrode material layer affects the first coulomb efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Examples 1-1 to 1-9, the mass percentage content of silicon element in the fourth negative electrode material layer is within the scope of the present application, the prepared lithium ion battery has a higher first coulomb efficiency, cycle capacity retention rate and energy density, which indicates that the first coulomb efficiency of the lithium ion battery can be improved, the cycle capacity decay can be reduced, and the energy density of the lithium ion battery can be improved.

[0151] The mass percentage content of silicon-containing substance in the second negative electrode active material affects the first coulomb efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Examples 1-3, 1-6 to 1-9, the mass percentage content of silicon-containing substance in the second negative electrode active material is within the scope of the present application, the prepared lithium ion battery has a higher first coulomb efficiency, cycle capacity retention rate and energy density, which indicates that the first coulomb efficiency of the lithium ion battery can be improved, the cycle capacity decay can be reduced, and the energy density of the lithium ion battery can be improved. In Examples 1-3, 1-6 to 1-9, the mass percentage content of the second negative electrode active material is unchanged, and as the mass percentage content of silicon-containing substance in the second negative electrode active material decreases, the lithium supplement amount decreases under the same lithium supplement condition, the first coulomb efficiency of the lithium ion battery is affected by the mass percentage content of silicon-containing substance and the lithium supplement amount, and the first coulomb efficiency of the lithium ion battery first increases and then decreases.

[0152] The difference between the mass percentage content of the second negative electrode active material and the mass percentage content of the first negative electrode active material affects the initial coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Examples 1-1 to 1-5, within the range of the present application, the lithium ion battery prepared has a higher initial coulombic efficiency, cycle capacity retention rate and energy density, indicating that the initial coulombic efficiency of the lithium ion battery can be improved, the cycle capacity decay can be reduced, and the energy density of the lithium ion battery can be improved. In Examples 1-1 to 1-5, the mass percentage content of the silicon-containing substance in the second negative electrode active material remains unchanged, and the mass percentage content of the second negative electrode active material decreases, which affects the kinetic performance of the lithium ion battery. Under the same lithium supplement condition, the lithium supplement amount decreases, and the initial coulombic efficiency of the lithium ion battery decreases.

[0153] Table 2

[0154]

[0155] The ratio of the surface density of the third negative electrode material layer to the surface density of the fourth negative electrode material layer affects the initial coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Examples 1-3, 2-1 to 2-8, within the range of the present application, the lithium ion battery prepared has a higher initial coulombic efficiency, cycle capacity retention rate and energy density, indicating that the initial coulombic efficiency of the lithium ion battery can be improved, the cycle capacity decay can be reduced, and the energy density of the lithium ion battery can be improved.

[0156] In Examples 1-3, 2-2 and 2-1, under the same lithium supplement condition, the surface density of the third negative electrode material layer and the fourth negative electrode material layer gradually decreases, which has the possibility of excessive lithium supplement, affecting the cycle performance of the lithium ion battery, and the cycle capacity retention rate of the lithium ion battery gradually decreases; in Examples 1-3, 2-3 to 2-5, the surface density of the third negative electrode material layer and the fourth negative electrode material layer gradually increases, and the thickness of the third negative electrode material layer and the fourth negative electrode material layer gradually increases, which affects the kinetic performance of the lithium ion battery, and the cycle capacity retention rate of the lithium ion battery gradually decreases. In Examples 1-3, 2-6 to 2-8, the surface density of the fourth negative electrode material layer increases, and the thickness of the fourth negative electrode material layer increases, which affects the kinetic performance of the lithium ion battery, and the cycle capacity retention rate of the lithium ion battery gradually decreases.

[0157] Table 3

[0158]

[0159]

[0160] The composition of the interface particles affects the amount of lithium supplement of the negative active material in the pre-lithiated negative electrode sheet, thereby affecting the first coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Examples 1-3, Examples 3-1 to 3-5, when the interface particles include a lithium intercalation material and a conductive agent, the mass percentage content of the lithium intercalation material and the conductive agent is within the scope of the present application, the prepared lithium ion battery has higher first coulombic efficiency, cycle capacity retention rate and energy density, which indicates that the first coulombic efficiency of the lithium ion battery can be improved, the cycle capacity decay can be reduced, and the energy density of the lithium ion battery can be improved.

[0161] It should be noted that, in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0162] Each of the embodiments in the specification is described in a relevant manner, and the same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments.

[0163] The above description is merely preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a lithium supplement composite layer, comprising the following steps: (1) applying a lithium metal powder slurry to a support layer and drying and rolling to form a lithium supplement layer; or calendering a lithium foil and / or lithium alloy foil to the support layer to form a lithium supplement layer; or applying a lithium or lithium alloy molten slurry to the support layer and cooling and rolling to form a lithium supplement layer; wherein the rolling pressure P1 is 0.2T / 10mm to 1.8T / 10mm; (2) applying interface particles to the surface of the lithium supplement layer to form an interface layer, and then rolling, wherein the rolling pressure P2 is 0.2T / 10mm to 1.8T / 10mm, the rolling temperature T1 is 20℃ to 180℃, and the rolling standing time t1 is 5min to 60min, to form a lithium supplement composite layer.

2. The production method according to claim 1, wherein The lithium supplement composite layer comprises the support layer, the lithium supplement layer, and the interface layer, and the lithium supplement layer is arranged between the support layer and the interface layer; The interface layer comprises the interface particles, and the interface particles comprise at least one of a conductive agent or a lithium intercalation material, the conductive agent comprises at least one of conductive carbon black, carbon fiber, graphene, or carbon nanotube, and the lithium intercalation material comprises at least one of artificial graphite, natural graphite, hard carbon, silicon-carbon material, silicon-oxygen material, lithium titanate, tin, or tin-copper alloy; The lithium supplement layer comprises at least one of a lithium foil or a lithium alloy foil.

3. The production method according to claim 2, wherein, The interface particles comprise a lithium intercalation material and a conductive agent, and the mass percentage of the lithium intercalation material is 80% to 99% and the mass percentage of the conductive agent is 1% to 20%, based on the mass of the interface particles. 4.A method for supplementing lithium, comprising the following steps: drying a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector, a first negative electrode material layer, and a second negative electrode material layer, and the first negative electrode material layer is arranged between the negative electrode current collector and the second negative electrode material layer along the thickness direction of the negative electrode sheet, and the second negative electrode material layer comprises a silicon-containing substance; the mass percentage of silicon in the first negative electrode material layer is WSi1%, based on the mass of the first negative electrode material layer, and the mass percentage of silicon in the second negative electrode material layer is WSi2%, based on the mass of the second negative electrode material layer, and WSi2>WSi1; adhering the lithium supplement composite layer prepared by the preparation method of any one of claims 1 to 3 to the negative electrode sheet so that the interface layer is in contact with the second negative electrode material layer, and performing a pre-lithiation treatment, and then peeling off the lithium supplement composite layer from the negative electrode sheet to form a pre-lithiated negative electrode sheet.

5. The lithium supplementing method according to claim 4, wherein, During the pre-lithiation treatment, the interfacial pressure P3 between the interface layer and the second negative electrode material layer is 0.1MPa to 2MPa, the adhering time t2 of the interface layer to the second negative electrode material layer is 0.5h to 72h, and the adhering temperature T2 of the interface layer to the second negative electrode material layer is 50℃ to 180℃.

6. The prelithiated negative electrode sheet prepared by the method of claim 4 or 5, the negative electrode sheet comprising a negative electrode current collector, a third negative electrode material layer, and a fourth negative electrode material layer, the third negative electrode material layer being disposed between the negative electrode current collector and the fourth negative electrode material layer along a thickness direction of the negative electrode sheet, the third negative electrode material layer comprising a first negative electrode active material, the fourth negative electrode material layer comprising a second negative electrode active material, the second negative electrode active material comprising a silicon-containing substance; a mass percentage content of silicon in the third negative electrode material layer is WSi3% based on a mass of the third negative electrode material layer, a mass percentage content of silicon in the fourth negative electrode material layer is WSi4% based on a mass of the fourth negative electrode material layer, a mass percentage content of lithium in the fourth negative electrode material layer is WLi4% based on the mass of the fourth negative electrode material layer, WSi4> WSi3, 1.5% < WLi4 / WSi4 < 44.4%.

7. The prelithiated negative electrode web of claim 6, wherein, a mass percentage content of lithium in the third negative electrode material layer is WLi3% based on the mass of the third negative electrode material layer, 1.1 < WLi4 / WLi3 < 4.8, 0.2 < WLi4 < 4.

4.

8. The prelithiated negative electrode web of claim 6, wherein, 0.9 < WSi4 < 43.

5.

9. The prelithiated negative electrode web of claim 6, wherein, a mass percentage content of the silicon-containing substance is S2% based on a mass of the second negative electrode active material, 2 < S2 < 100.

10. The prelithiated negative electrode web of claim 6, wherein, a mass percentage content of the first negative electrode active material is H1% based on the mass of the third negative electrode material layer, a mass percentage content of the second negative electrode active material is H2% based on the mass of the fourth negative electrode material layer, 0.1 < H2 - H1 < 10.

11. The prelithiated negative electrode web according to claim 6, wherein, a face density of the third negative electrode material layer is CW3 mg / cm 2 a face density of the fourth negative electrode material layer is CW4 mg / cm 2 0.8 ≤ CW3 ≤ 50, 0.25 ≤ CW4 / CW3 ≤ 1.

12. The prelithiated negative electrode sheet of claim 6, satisfying at least one of the following characteristics: (1) a mass percentage content of lithium in the third negative electrode material layer is WLi3% based on the mass of the third negative electrode material layer, 1.4 < WLi4 / WLi3 < 3.3; (2) a mass percentage content of the first negative electrode active material is H1% based on the mass of the third negative electrode material layer, a mass percentage content of the second negative electrode active material is H2% based on the mass of the fourth negative electrode material layer, 1 < H2 - H1 < 5; (3) the face density of the third negative electrode material layer is CW3 mg / cm 2 , 1.0≤CW3≤13.0; (4) the silicon-containing substance comprises at least one of a silicon-carbon material or a silicon-oxygen material.

13. A secondary battery comprising the prelithiated negative electrode sheet of any one of claims 6 to 12.

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

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