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, the pre-lithiated negative electrode sheet comprising a negative electrode material layer, the negative electrode material layer comprising opposite first and second surfaces. From the first surface to the second surface, the negative electrode material layer comprises a first region, a second region and a third region in sequence, and the third region is located on the surface of a negative electrode current collector. The thickness of the first region accounts for 1 / 3 of the thickness of the negative electrode material layer, the thickness of the second region accounts for 1 / 3 of the thickness of the negative electrode material layer, and the thickness of the third region accounts for 1 / 3 of the thickness of the negative electrode material layer. Based on the mass of the first region, the mass percentage of lithium element is W1, based on the mass of the second region, the mass percentage of lithium element is W2, and based on the mass of the third region, the mass percentage of lithium element is W3, W1>W2>W3, 1.01≤W1 / W2≤2.0, and 1.01≤W2 / W3≤2.0. The pre-lithiated negative electrode sheet meets 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, and 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 the 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 for energy density. Although the theoretical specific capacity of silicon-carbon and silicon-oxygen negative electrode materials is high, they are ideal materials for replacing negative electrode graphite and improving the energy density of lithium ion batteries. However, they have not been widely used due to problems such as low first coulomb efficiency and poor cycle life. The existing methods for improving the first coulomb efficiency and reducing cycle decay of silicon-carbon or silicon-oxygen containing negative electrodes are to pre-supplement lithium to the negative electrode sheet to supplement the irreversible capacity consumed in the first charge, discharge and cycle, thereby improving the first coulomb efficiency of the lithium ion battery containing silicon-carbon or silicon-oxygen negative electrode, and further improving the energy density of the lithium ion battery.

[0003] The existing lithium supplement methods for negative electrode sheets mainly include lithium powder supplement, lithium ribbon supplement and electrochemical supplement. However, the above three lithium supplement methods have certain problems in environmental pollution, lithium supplement uniformity and side reactions after lithium supplement. Therefore, it is urgent to provide a pre-lithiated negative electrode sheet which can improve the first coulomb efficiency of the lithium ion battery containing silicon-carbon or silicon-oxygen negative electrode, reduce the cycle capacity decay and improve the energy density of the lithium ion battery. 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 0.1T / 10mm to 2T / 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 0.1 T / 10 mm to 2 T / 10 mm, the rolling temperature T1 is 25°C to 170°C, and the rolling standing time t1 is 5 min to 50 min, to form a lithium supplement composite layer.

[0008] 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, and the lithium supplement layer comprises at least one of a lithium foil or a lithium alloy foil.

[0009] The lithium supplement composite layer prepared by the above method is then subjected to pre-lithiation treatment, which is beneficial to supplement the negative electrode sheet with lithium, and the pre-lithiated negative electrode sheet is applied to a secondary battery, 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.

[0010] In an embodiment of the present application, 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, or silicon-oxygen material. By selecting the above interface particles, the interface layer has good electron and ion conductivity, which is beneficial to the transmission of electrons and lithium ions to the surface or interior of the negative electrode material layer during the pre-lithiation process, and is beneficial to further supplement the negative electrode sheet with lithium, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing the cycle capacity attenuation, and further improving the energy density of the secondary battery.

[0011] In an embodiment of the present application, the thickness H1 of the interface layer is 0.1 μm to 50 μm, and preferably, the thickness H1 of the interface layer is 1 μm to 20 μm. Lithium atoms in the lithium supplement layer lose electrons to form lithium ions, and the electrons and lithium ions are transmitted to the surface or interior of the negative electrode material layer through the interface layer. By adjusting the thickness of the interface layer within the range of the present application, the interface layer has a suitable thickness, the transmission distance of the electrons and lithium ions is moderate, the electrons and lithium ions can effectively recombine to form lithium intercalation compounds, which is beneficial to further supplement the negative electrode sheet with lithium, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing the cycle capacity attenuation, and further improving the energy density of the secondary battery.

[0012] In an embodiment of the present application, the coverage ratio s1 of the interface particles in the lithium supplement layer is 50% to 100%, preferably, the coverage ratio s1 of the interface particles in the lithium supplement layer is 80% to 100%. The coverage ratio of the interface particles in the lithium supplement layer is within the scope of the present application, the coverage ratio of the interface particles in the lithium supplement layer is higher, the uniformity of lithium supplement in the negative electrode material layer is higher, 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.

[0013] In an embodiment of the present application, the interface particles are embedded in the lithium supplement layer, and the depth of the interface particles embedded in the lithium supplement layer accounts for 10% to 95% of the thickness of the interface layer, preferably, the depth of the interface particles embedded in the lithium supplement layer accounts for 20% to 70% of the thickness of the interface layer. When the interface particles are embedded in the lithium supplement layer and the depth of the interface particles embedded in the lithium supplement layer accounts for a proportion of the thickness of the interface layer within the scope of the present application, the lithium inside the lithium supplement layer can be better promoted to participate in the oxidation reaction, thereby better transferring the lithium inside the lithium supplement layer into the negative electrode material layer, which is beneficial to further supplement lithium to the negative electrode sheet, 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; at the same time, it is also beneficial to the repeated use of the lithium supplement composite layer.

[0014] 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 or a polyethylene film, and the metal foil comprises a copper foil, a nickel foil, a steel foil or a copper-nickel alloy foil. By selecting the above support layer, the support layer can provide better support for the lithium supplement layer and the interface layer, improve the mechanical strength of the lithium supplement composite layer, so that the lithium supplement composite layer can be peeled off from the surface of the negative electrode material layer more smoothly after lithium supplement, reduce the possibility of breaking of the lithium supplement composite layer, and be beneficial to the lithium supplement of the negative electrode sheet, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing the cycle capacity attenuation, and further improving the energy density of the secondary battery.

[0015] The second aspect of the present application provides a lithium supplement method, which comprises the following steps:

[0016] The negative electrode sheet is dried, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector;

[0017] The aforementioned any lithium supplement composite layer and the negative electrode sheet are attached so that the interface layer is in contact with the negative electrode material layer, pre-lithiation treatment is performed, the interface pressure P3 of the interface layer and the negative electrode material layer is 0.1 MPa to 2 MPa, the attachment time t2 of the interface layer and the negative electrode material layer is 0.5 h to 72 h, the attachment temperature T2 of the interface layer and the negative electrode material layer is 50℃ to 180℃, 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 lithium supplement composite layer is prepared by the preparation method of the lithium supplement composite layer provided in the present application, and then the pre-lithiated negative electrode sheet is prepared by the lithium supplement method provided in the present application, which is beneficial to supplement lithium for the negative electrode sheet, and the pre-lithiated negative electrode sheet is applied to a secondary battery, 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.

[0019] The third aspect of the present application provides a pre-lithiated negative electrode sheet prepared by any of the above lithium supplement methods. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer. In the thickness direction of the negative electrode sheet, the negative electrode material layer comprises opposite first and second surfaces. From the first surface to the second surface, the negative electrode material layer comprises a first region, a second region and a third region in sequence, and the third region is located on the surface of the negative electrode current collector. The thickness of the first region accounts for 1 / 3 of the thickness of the negative electrode material layer, the thickness of the second region accounts for 1 / 3 of the thickness of the negative electrode material layer, and the thickness of the third region accounts for 1 / 3 of the thickness of the negative electrode material layer. Based on the mass of the first region, the mass percentage of lithium element is W1, based on the mass of the second region, the mass percentage of lithium element is W2, and based on the mass of the third region, the mass percentage of lithium element is W3, W1>W2>W3, 1.01≤W1 / W2≤2.0, and 1.01≤W2 / W3≤2.0. The above pre-lithiated negative electrode sheet is applied to a secondary battery, 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.

[0020] In an embodiment of the present application, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material comprises at least one of a carbon material or a silicon-containing substance, the carbon material comprises at least one of a graphite material or a hard carbon, and the silicon-containing substance comprises at least one of a silicon-carbon material or a silicon-oxygen material. The negative electrode material layer comprises a negative electrode active material, and the negative electrode active material comprises the above-mentioned substances, the pre-lithiated negative electrode sheet has a higher lithium supplement amount, and the prepared secondary battery has a higher initial coulomb efficiency, a lower cycle capacity attenuation, and a higher energy density.

[0021] In an embodiment of the present application, the negative active material only includes the silicon-containing substance, the mass percentage of silicon element in the negative material layer is w1 based on the mass of the negative material layer, 18.6%≤w1≤63.5%, 11.5%≤W1≤18.4%, 9.2%≤W2<11.5%, 4.6%≤W3<9.2%. The negative active material only includes the silicon-containing substance, the silicon-containing substance has a relatively high specific capacity, the values of w1, W1, W2 and W3 of the mass percentage of silicon element in the negative material layer are within the range of the present application, the capacity of the negative material layer is relatively high, the ionic conductivity and the electronic conductivity are relatively high, the pre-lithiated negative electrode sheet has a relatively high lithium supplement amount, and the above pre-lithiated negative electrode sheet is applied to the secondary battery, 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.

[0022] In an embodiment of the present application, the negative active material includes the carbon material and the silicon-containing substance, the mass percentage of silicon element in the negative material layer is w1 based on the mass of the negative material layer, 1.1%≤w1≤3.4%, 0.38%≤W1≤0.60%, 0.30%≤W2<0.38%, 0.15%≤W3<0.30%. The negative active material includes the carbon material and the silicon-containing substance, the lithium supplement efficiency of different negative active materials is different within the same pre-lithiation treatment time, the lithium supplement amount of the silicon-containing substance is relatively small, and the lithium supplement amount of the carbon material is relatively large, which will affect the lithium supplement amount in the pre-lithiated negative electrode sheet. The values of w1, W1, W2 and W3 of the mass percentage of silicon element in the negative material layer are within the range of the present application, the carbon material and the silicon-containing substance have a suitable mass percentage, the negative active material has a relatively high capacity and a relatively high lithium supplement amount, which can make the pre-lithiated negative electrode sheet have a relatively high capacity and a relatively high lithium supplement amount, and the above pre-lithiated negative electrode sheet is applied to the secondary battery, 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 negative active material includes a carbon material and a silicon-containing substance, and the mass percentage of silicon in the negative material layer is w1, 3.3%≤w1≤10.2%, 2.8%≤w1≤4.5%, 2.2%≤w2<2.8%, 1.1%≤w3<2.2% based on the mass of the negative material layer. The negative active material includes a carbon material and a silicon-containing substance, and the lithium supplementing efficiency of different negative active materials is different within the same pre-lithiation treatment time, the lithium supplementing amount of the silicon-containing substance is relatively small, and the lithium supplementing amount of the carbon material is relatively large, which will affect the lithium supplementing amount in the pre-lithiated negative electrode sheet. Within the range of the mass percentage of silicon w1, w1, w2, and w3 in the negative material layer, the carbon material and the silicon-containing substance have a suitable mass percentage, the negative active material has a high capacity and a high lithium supplementing amount, which can enable the pre-lithiated negative electrode sheet to have a high capacity and a high lithium supplementing amount. When the pre-lithiated negative electrode sheet is applied to a secondary battery, 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.

[0024] In an embodiment of the present application, the porosity of the first region is S1, the porosity of the second region is S2, and the porosity of the third region is S3, S1>S2>S3. S1, S2, and S3 satisfy the above size relationship, which is beneficial to the migration of lithium ions along the thickness direction of the negative electrode sheet and can improve the kinetic performance of the negative electrode sheet.

[0025] In an embodiment of the present application, 1.01≤S1 / S2≤1.5, 1.01≤S2 / S3≤1.5. Within the range of S1 / S2 and S2 / S3, the porosity of the first region is greater than that of the second region, and the porosity of the second region is greater than that of the third region, which is beneficial to the migration of lithium ions along the thickness direction of the negative electrode sheet and can further improve the kinetic performance of the negative electrode sheet.

[0026] In an embodiment of the present application, the negative active material only includes a silicon-containing substance, and the mass percentage of silicon in the negative material layer is w1, 18.6%≤w1≤63.5%, 42.1%≤S1≤57.0%, 38.0%≤S2<42.1%, 25.0%≤S3<38.0% based on the mass of the negative material layer. The negative active material only includes a silicon-containing substance, the silicon-containing substance has a high specific capacity, and the values of the mass percentage of silicon w1, S1, S2, and S3 in the negative material layer are within the range of the present application, which is beneficial to the migration of lithium ions along the thickness direction of the negative electrode sheet and can further improve the kinetic performance of the negative electrode sheet while the negative electrode sheet has a high capacity.

[0027] In an embodiment of the present application, the negative active material comprises a carbon material and a silicon-containing substance, the mass percentage of silicon in the negative active material layer is w1 based on the mass of the negative active material layer, 1.1%≤w1≤3.4%, 26.3%≤S1≤35.5%, 23.7%≤S2<26.3%, and 15.8%≤S3<23.7%. The negative active material comprises a carbon material and a silicon-containing substance, which is conducive to further improving the gram capacity and lithium supplement amount of the negative active material, the values of the mass percentage of silicon w1, S1, S2, and S3 in the negative active material layer are within the range of the present application, which is conducive to the migration of lithium ions along the thickness direction of the negative electrode sheet, and can further improve the kinetic performance of the negative electrode sheet, and the negative electrode sheet has a high capacity.

[0028] In an embodiment of the present application, the negative active material comprises a carbon material and a silicon-containing substance, the mass percentage of silicon in the negative active material layer is w1 based on the mass of the negative active material layer, 3.3%≤w1≤10.2%, 31.6%≤S1≤42.6%, 28.4%≤S2<31.6%, and 18.9%≤S3<28.4%. The negative active material comprises a carbon material and a silicon-containing substance, which is conducive to further improving the gram capacity and lithium supplement amount of the negative active material, the values of the mass percentage of silicon w1, S1, S2, and S3 in the negative active material layer are within the range of the present application, which is conducive to the migration of lithium ions along the thickness direction of the negative electrode sheet, and can further improve the kinetic performance of the negative electrode sheet, and the negative electrode sheet has a high capacity.

[0029] The fourth aspect of the present application provides a secondary battery comprising the pre-lithiated negative electrode sheet in any of the foregoing embodiments. Therefore, the secondary battery of the present application has a high initial coulombic efficiency, a low cycle capacity decay, and a high energy density.

[0030] The fifth aspect of the present application provides an electronic device comprising the secondary battery in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has a high initial coulombic efficiency, a low cycle capacity decay, and a high energy density.

[0031] The beneficial effects of the present application are as follows:

[0032] 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 and a negative electrode material layer. In the thickness direction of the negative electrode sheet, the negative electrode material layer comprises opposite first and second surfaces. From the first surface to the second surface, the negative electrode material layer comprises a first region, a second region and a third region in sequence, and the third region is located on the surface of the negative electrode current collector. The thickness of the first region accounts for 1 / 3 of the thickness of the negative electrode material layer, the thickness of the second region accounts for 1 / 3 of the thickness of the negative electrode material layer, and the thickness of the third region accounts for 1 / 3 of the thickness of the negative electrode material layer. Based on the mass of the first region, the mass percentage of lithium element is W1, based on the mass of the second region, the mass percentage of lithium element is W2, and based on the mass of the third region, the mass percentage of lithium element is W3, W1>W2>W3, 1.01≤W1 / W2≤2.0, and 1.01≤W2 / W3≤2.0. The pre-lithiated negative electrode sheet meets 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.

[0033] 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

[0034] 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.

[0035] Figure 1 Structure schematic diagram of the lithium supplement composite layer of an embodiment of the present application;

[0036] Figure 2 Structure schematic diagram of the negative electrode sheet and the lithium supplement composite layer in the pre-lithiation process of an embodiment of the present application;

[0037] Figure 3 Structure schematic diagram of the pre-lithiated negative electrode sheet of an embodiment of the present application;

[0038] Figure 4 Schematic diagram of the lithium supplement region and the interface region;

[0039] Figure 5 Schematic diagram of the total area of the lithium supplement region and the total area of the interface region;

[0040] Figure 6 Depth H of the interface particle embedded in the lithium supplement layer a Schematic diagram;

[0041] Figure 7 H is the height difference between the upper surface of the interface layer and the lower surface of the interface layer c schematic diagram. DETAILED DESCRIPTION

[0042] 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 a 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.

[0043] It should be noted that in the specific embodiments of the present application, the present application is explained by taking lithium-ion batteries as examples of secondary batteries, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0044] The first aspect of the present application provides a preparation method of a lithium supplement composite layer, comprising the following steps:

[0045] (1) under the condition of ambient temperature ≤ 30℃ and humidity ≤ 1.7%, coating lithium metal powder slurry on the 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 0.1T / 10mm to 2T / 10mm; specifically, the rolling pressure P11 of the lithium metal powder slurry coated on the support layer is 0.1T / 10mm to 2T / 10mm; the rolling pressure P12 of the lithium foil and / or lithium alloy foil calendered to the support layer is 0.1T / 10mm to 2T / 10mm; the rolling pressure P13 of the lithium or lithium alloy molten slurry coated on the support layer is 0.1T / 10mm to 2T / 10mm;

[0046] (2) under the condition 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 0.1T / 10mm to 2T / 10mm, preferably the rolling pressure P2 is 0.2T / 10mm to 0.8T / 10mm; the rolling temperature T1 is 25℃ to 170℃, preferably the rolling temperature T1 is 50℃ to 120℃; the rolling standing time t1 is 5min to 50min, preferably the rolling standing time t1 is 10min to 30min; to form a lithium supplement composite layer.

[0047] Exemplarily, P1 can be 0.1 T / 10 mm, 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, 2 T / 10 mm, or a range consisting of any two of the aforementioned values. P11 can be 0.1 T / 10 mm, 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, 2 T / 10 mm, or a range consisting of any two of the aforementioned values. P12 can be 0.1 T / 10 mm, 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, 2 T / 10 mm, or a range consisting of any two of the aforementioned values. P13 can be 0.1 T / 10 mm, 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, 2 T / 10 mm, or a range consisting of any two of the aforementioned values. P2 can be 0.1 T / 10 mm, 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, 2 T / 10 mm, or a range consisting of any two of the aforementioned values. T1 can be 25 °C, 40 °C, 50 °C, 60 °C, 80 °C, 100 °C, 120 °C, 140 °C, 160 °C, 170 °C, or a range consisting of any two of the aforementioned 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, or a range consisting of any two of the aforementioned values.

[0048] 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 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.

[0049] In an embodiment of the present application, the lithium supplement composite layer includes 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 includes interface particles, and the lithium supplement layer includes at least one of a lithium foil or a lithium alloy foil. Specifically, as shown in Figure 1 the lithium supplement composite layer 10 includes a support layer 11, a lithium supplement layer 12 and an interface layer 13, the lithium supplement layer 12 is arranged between the support layer 11 and the interface layer 13, the interface layer 13 includes interface particles, and the lithium supplement layer 12 includes at least one of a lithium foil or a lithium alloy foil.

[0050] The lithium supplement composite layer is prepared by the preparation method of the lithium supplement composite layer provided by the present application, the lithium supplement composite layer includes 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, and the interface layer has the ability to conduct electrons and ions. The interface layer is in contact with the negative electrode material layer, as shown in Figure 2 the interface layer 13 is in contact with the negative electrode material layer 15 arranged on the two surfaces of the negative electrode current collector 14. It can be understood that the above-mentioned "negative electrode material layer 15" refers to the negative electrode material layer of the negative electrode sheet which has not been pre-lithiated; the lithium supplement layer forms an internal short circuit with the negative electrode material layer, lithium atoms in the lithium supplement layer lose electrons to generate lithium ions by oxidation reaction, and the electrons and lithium ions are transmitted to the surface or inside of the negative electrode material layer through the interface layer, and the electrons and lithium ions form lithium intercalation compounds by reduction reaction in the negative electrode material layer, realizing the pre-lithiation process of the negative electrode material layer. Since the interface layer is arranged between the lithium supplement layer and the negative electrode material layer, the possibility of the lithium supplement layer adhering to the surface of the negative electrode material layer is reduced, thereby reducing the influence of the side reaction of the lithium metal in the lithium supplement layer due to its high activity on the electrochemical performance of the secondary battery. After the pre-lithiation process is completed, the lithium supplement composite layer is peeled off from the negative electrode sheet to obtain a pre-lithiated negative electrode sheet. The above-mentioned peeling process can reduce the influence of the side reaction of the lithium metal in the lithium supplement layer remaining on the surface of the negative electrode material layer on the electrochemical performance of the secondary battery after entering the secondary battery. The lithium supplement composite layer is prepared by the above-mentioned method, and then the negative electrode sheet is pre-lithiated, which is conducive to supplementing the lithium of the negative electrode sheet, and the pre-lithiated negative electrode sheet applied in the secondary battery can improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0051] In an embodiment of the present application, 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; the lithium intercalation material comprises at least one of artificial graphite, natural graphite, hard carbon, silicon-carbon material or silicon-oxygen material. 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 nanometer carbon fiber; 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. By selecting the above interface particles, the interface layer can have better electronic and ionic conductivity, which is conducive to the rapid transfer of electrons and lithium ions through the interface layer to the surface or interior of the negative electrode material layer during the pre-lithiation process, which is conducive to further lithium supplement of the negative electrode sheet, and can further improve the initial coulombic efficiency of the secondary battery, further reduce the cycle capacity decay, and further improve the energy density of the secondary battery.

[0052] In an embodiment of the present application, the thickness H1 of the interface layer is 0.1 μm to 50 μm, preferably, the thickness H1 of the interface layer is 1 μm to 20 μm. Exemplarily, the value of H1 can be 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or a range composed of any two of the above values. The lithium atoms in the lithium supplement layer lose electrons to form lithium ions, and the electrons and lithium ions are transferred to the surface or interior of the negative electrode material layer through the interface layer. By adjusting the thickness of the interface layer within the scope of the present application, the interface layer has a suitable thickness, the transmission distance of the electrons and lithium ions is moderate, the electrons and lithium ions can effectively recombine to form lithium intercalation compounds, which is conducive to further lithium supplement of the negative electrode sheet, thereby further improving the initial coulombic efficiency of the secondary battery, further reducing the cycle capacity decay, and further improving the energy density of the secondary battery.

[0053] In an embodiment of the present application, the coverage ratio s1 of the interface particles in the lithium supplement layer is 50% to 100%, preferably, the coverage ratio s1 of the interface particles in the lithium supplement layer is 80% to 100%. Illustratively, the value of s1 can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or a range consisting of any two of the above values. The coverage ratio of the interface layer in the lithium supplement layer affects the uniformity of lithium supplement in the negative electrode material layer, that is, the greater the coverage ratio of the interface layer in the lithium supplement layer, the higher the uniformity of lithium supplement in the negative electrode material layer. Within the scope of the present application, the higher the coverage ratio of the interface particles in the lithium supplement layer, the higher the uniformity of lithium supplement in the negative electrode material layer, which can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity decay, and further improve the energy density of the secondary battery.

[0054] In an embodiment of the present application, the interface particles are embedded in the lithium supplement layer, and the depth of the interface particles embedded in the lithium supplement layer accounts for 10% to 95% of the thickness of the interface layer, preferably, the depth of the interface particles embedded in the lithium supplement layer accounts for 20% to 70% of the thickness of the interface layer. Illustratively, the ratio of the depth of the interface particles embedded in the lithium supplement layer to the thickness of the interface layer can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range consisting of any two of the above values. When the interface particles are embedded in the lithium supplement layer and the ratio of the depth of the interface particles embedded in the lithium supplement layer to the thickness of the interface layer is within the scope of the present application, the lithium inside the lithium supplement layer can be better promoted to participate in the oxidation reaction, thereby better transferring the lithium inside the lithium supplement layer to the negative electrode material layer, which is beneficial to further supplement lithium to the negative electrode plate, can further improve the initial coulomb efficiency of the secondary battery, further reduce the cycle capacity decay, and further improve the energy density of the secondary battery; at the same time, it is also beneficial to the repeated use of the lithium supplement composite layer.

[0055] In an embodiment of the present application, the thickness H2 of the lithium supplement layer is 0.001 mm to 1 mm, preferably, the thickness H2 of the lithium supplement layer is 0.005 mm to 0.1 mm. Illustratively, the value of H2 can be 0.001, 0.003, 0.005, 0.007, 0.009, 0.01, 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1, or a range consisting of any two of the above values.

[0056] 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 or a polyethylene film, and the metal foil comprises a copper foil, a nickel foil, a steel foil or a copper-nickel alloy foil. By selecting the above support layer, the support layer can provide better support for the lithium supplement layer and the interface layer, improve the mechanical strength of the lithium supplement composite layer, so that the lithium supplement composite layer can be peeled off from the surface of the negative electrode material layer more smoothly after lithium supplement, reduce the possibility of breaking of the lithium supplement composite layer, and be beneficial to the lithium supplement of the negative electrode sheet, thereby further improving the first coulomb efficiency of the secondary battery, further reducing the cycle capacity attenuation, and further improving the energy density of the secondary battery.

[0057] The thickness H3 of the support layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the thickness H3 of the support layer can be 3 μm to 50 μm, preferably, the thickness H3 of the support layer can be 5 μm to 20 μm.

[0058] The second aspect of the present application provides a lithium supplement method, which comprises the following steps:

[0059] The negative electrode sheet is dried until the water content is ≤500 ppm, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector; it can be understood that the above-mentioned negative electrode sheet refers to a negative electrode sheet which has not been pre-lithiated. Under the conditions of an ambient temperature of 25 ℃ to 180 ℃ and a humidity of ≤1.7%, the aforementioned any lithium supplement composite layer and the negative electrode sheet are laminated so that the interface layer is in contact with the negative electrode material layer, pre-lithiation treatment is carried out, the interface pressure P3 between the interface layer and the negative electrode material layer is 0.1 MPa to 2 MPa, preferably, the interface pressure P3 between the interface layer and the negative electrode material layer is 0.2 MPa to 1.0 MPa; the lamination time t2 of the interface layer and the negative electrode material layer is 0.5 h to 72 h, preferably, the lamination time t2 of the interface layer and the negative electrode material layer is 1 h to 48 h; the lamination temperature T2 of the interface layer and the negative electrode material layer is 50 ℃ to 180 ℃, preferably, the lamination temperature T2 of the interface layer and the negative electrode material layer is 60 ℃ to 160 ℃; after the pre-lithiation treatment is completed, the lithium supplement composite layer is peeled off from the negative electrode sheet to form a pre-lithiated negative electrode sheet.

[0060] The present application does not have a particular limitation on the lamination method of the lithium supplement composite layer and the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the lamination method of the lithium supplement composite layer and the negative electrode sheet can be winding into a roll or pressing into a sheet. The present application does not have a particular limitation on the method of regulating the interface pressure of lamination, as long as the purpose of the present application can be achieved. For example, when the lithium supplement composite layer and the negative electrode sheet are wound into a roll, the interface pressure between the interface layer and the negative electrode material layer can be regulated by regulating the winding tension. For example, when the lithium supplement composite layer and the negative electrode sheet are pressed into a sheet, the interface pressure between the interface layer and the negative electrode material layer can be regulated by regulating the pressure of pressing.

[0061] 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 composed of 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 composed of any two of the above values. T2 can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, or a range composed of any two of the above values.

[0062] The preparation method of the lithium supplement composite layer and the method for supplementing lithium are used to prepare the lithium supplement composite layer and the pre-lithiated negative electrode sheet, which is beneficial to supplement lithium to the negative electrode sheet and obtain the pre-lithiated negative electrode sheet applied to the secondary battery, so as to improve the initial coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0063] The third aspect of the present application provides a pre-lithiated negative electrode sheet prepared according to any of the foregoing lithium supplementing methods. The pre-lithiated negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer. In the thickness direction of the negative electrode sheet, the negative electrode material layer comprises opposite first and second surfaces. In the thickness direction of the negative electrode material layer, the negative electrode material layer comprises, in order from the first surface to the second surface, a first region, a second region, and a third region, and the third region is located on the surface of the negative electrode current collector. The thickness of the first region accounts for 1 / 3 of the thickness of the negative electrode material layer, the thickness of the second region accounts for 1 / 3 of the thickness of the negative electrode material layer, and the thickness of the third region accounts for 1 / 3 of the thickness of the negative electrode material layer. The mass percentage content of lithium in the first region is W1, the mass percentage content of lithium in the second region is W2, and the mass percentage content of lithium in the third region is W3, W1 > W2 > W3, 1.01 ≤ W1 / W2 ≤ 2.0, and 1.01 ≤ W2 / W3 ≤ 2.0. Exemplarily, W1 / W2 can be 1.01, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or a range formed by any two of the foregoing values; and W2 / W3 can be 1.01, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or a range formed by any two of the foregoing values. In the present application, the pre-lithiated negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector in the thickness direction of the negative electrode current collector, or can be disposed on two surfaces of the negative electrode current collector in the thickness direction of the negative electrode current collector. It should be noted that the "surface" herein can be the entire region of the negative electrode current collector, or can be a partial region of the negative electrode current collector, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved. Exemplarily, as shown in FIG. 1, the "surface" of the negative electrode current collector can be the entire region of the negative electrode current collector, or can be a partial region of the negative electrode current collector. Figure 3As shown, the pre-lithiated negative electrode sheet 100 includes a negative electrode current collector 14 and a negative electrode material layer 15 arranged on both surfaces of the negative electrode current collector 14, and the negative electrode material layer 15 includes opposite first and second surfaces 1511 and 1522 along the thickness direction of the negative electrode sheet, i.e., the Y direction. From the first surface 1511 to the second surface 1522, the negative electrode material layer 15 includes a first region 151, a second region 152, and a third region 153 in sequence, and the third region 153 is located on the surface of the negative electrode current collector 14. The thickness of the first region 151 accounts for 1 / 3 of the thickness of the negative electrode material layer 15, the thickness of the second region 152 accounts for 1 / 3 of the thickness of the negative electrode material layer 15, and the thickness of the third region 153 accounts for 1 / 3 of the thickness of the negative electrode material layer 15. Based on the mass of the first region, the mass percentage of lithium element is W1, based on the mass of the second region, the mass percentage of lithium element is W2, and based on the mass of the third region, the mass percentage of lithium element is W3, W1>W2>W3, 1.01≤W1 / W2≤2.0, and 1.01≤W2 / W3≤2.0. It can be understood that the "negative electrode material layer 15" in the above "the pre-lithiated negative electrode sheet 100 includes a negative electrode current collector 14 and a negative electrode material layer 15 arranged on both surfaces of the negative electrode current collector 14" refers to the negative electrode material layer after the pre-lithiation treatment of the negative electrode sheet which has not been pre-lithiated.

[0064] The application does not have special restrictions on the method of regulating the mass percentage of lithium element in the first region, the second region, and the third region of the negative electrode material layer of the pre-lithiated negative electrode sheet, as long as the purpose of the application can be achieved. For example, the mass percentage of lithium element in the first region, the second region, and the third region of the negative electrode material layer of the pre-lithiated negative electrode sheet can be regulated by regulating the pre-lithiation method. For example, the pre-lithiation treatment of the negative electrode sheet can be performed by using a lithium supplement composite layer and negative electrode sheet lamination. For example, the amount of lithium supplement and the rate of lithium supplement can be regulated by regulating the interfacial pressure between the interfacial layer of the lithium supplement composite layer and the negative electrode material layer, the lamination time, and the lamination temperature, so as to regulate the mass percentage of lithium element in the first region, the second region, and the third region of the negative electrode material layer of the pre-lithiated negative electrode sheet.

[0065] The application does not have special restrictions on the method of regulating the value of W1 / W2, as long as the purpose of the application can be achieved. For example, the value of W1 / W2 can be regulated by regulating the value of W1 and W2 respectively, and the regulation method of W1 and W2 is as described above. The application does not have special restrictions on the method of regulating the value of W2 / W3, as long as the purpose of the application can be achieved. For example, the value of W2 / W3 can be regulated by regulating the value of W2 and W3 respectively, and the regulation method of W2 and W3 is as described above.

[0066] The inventors have found that a negative electrode sheet without pre-lithiation is taken, the negative electrode sheet without pre-lithiation comprising a negative electrode current collector and a negative electrode material layer, the negative electrode sheet without pre-lithiation is subjected to pre-lithiation treatment to obtain a pre-lithiated negative electrode sheet. The negative electrode material layer comprises a negative electrode active material, the negative electrode active material comprises at least one of a carbon material or a silicon-containing substance, the lithium supplementing efficiency of different negative electrode active materials is different within the same pre-lithiation treatment time, the lithium supplementing amount of the silicon-containing substance is relatively small, and the lithium supplementing amount of the carbon material is relatively large, therefore, the lithium supplementing amount of the pre-lithiated negative electrode sheet obtained is different due to the different types of negative electrode active materials. For the pre-lithiated negative electrode sheet, along the thickness direction of the negative electrode sheet, the negative electrode material layer comprises opposite first and second surfaces; from the first surface to the second surface, the negative electrode material layer comprises a first region, a second region and a third region in sequence, and the third region is located on the surface of the negative electrode current collector. The mass percentage content of lithium elements in the first region, the second region and the third region satisfies: the mass percentage content of lithium elements in the first region > the mass percentage content of lithium elements in the second region > the mass percentage content of lithium elements in the third region, and the ratio of the mass percentage content of lithium elements in the first region to the mass percentage content of lithium elements in the second region, the ratio of the mass percentage content of lithium elements in the second region to the mass percentage content of lithium elements in the third region is within the scope of the present application, the mass percentage content of lithium elements in the first region, the mass percentage content of lithium elements in the second region and the mass percentage content of lithium elements in the third region are all not 0, the lithium elements in the negative electrode material layer are gradiently distributed along the thickness direction, and the pre-lithiated negative electrode sheet has a relatively high lithium supplementing amount. The pre-lithiated negative electrode sheet is applied to a secondary battery, 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.

[0067] In an embodiment of the present application, the negative electrode material layer comprises a negative electrode active material, the negative electrode active material comprises at least one of a carbon material or a silicon-containing substance, the carbon material comprises at least one of a graphite material or a hard carbon, and the silicon-containing substance comprises at least one of a silicon-carbon material or a silicon-oxygen material. In the present application, the graphite material comprises at least one of artificial graphite or natural graphite; the silicon-carbon material is a silicon-carbon composite material, the mass percentage content of silicon elements w Si is 30% to 70%, and the mass percentage content of carbon elements w CThe 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 and oxygen is 1:1). The negative electrode material layer includes a negative electrode active material, the negative electrode active material includes the above-mentioned substances, the pre-lithiated negative electrode sheet has a high lithium supplement amount, and the prepared secondary battery has a high initial coulombic efficiency, a low cycle capacity decay, and a high energy density.

[0068] In the present application, the negative electrode active material includes a carbon material and a silicon-containing substance, and the mass percentage content W Si The mass percentage content of the carbon material Wc is 0 to 95%. Illustratively, the mass percentage content of the silicon-containing substance can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a range composed of any two of the above values; the mass percentage content of the carbon material can be 0, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or a range composed of any two of the above values.

[0069] In an embodiment of the present application, the negative active material only includes the silicon-containing substance, the mass percentage of the element silicon in the negative material layer is w1 based on the mass of the negative material layer, 18.6%≤w1≤63.5%, 11.5%≤W1≤18.4%, 9.2%≤W2<11.5%, 4.6%≤W3<9.2%. Exemplarily, w1 can be 18.6%, 25.5%, 30.5%, 37.5%, 38.5%, 39.5%, 40.5%, 41.5%, 42.5%, 43.5%, 44.5%, 45.5%, 46.5%, 47.5%, 55.5%, 63.5% or a range consisting of any two of the above values; W1 can be 11.5%, 12.5%, 13.5%, 14.5%, 15.5%, 16.5%, 17.5%, 18.4% or a range consisting of any two of the above values; W2 can be 9.2%, 9.4%, 9.6%, 9.8%, 10%, 10.2%, 10.4%, 10.6%, 10.8%, 11%, 11.2%, 11.4% or a range consisting of any two of the above values; W3 can be 4.6%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.1% or a range consisting of any two of the above values. The negative active material only includes the silicon-containing substance, the silicon-containing substance has a relatively high specific capacity, the mass percentage of the element silicon in the negative material layer w1, W1, W2, W3 is within the range of the present application, the capacity of the negative material layer is relatively high, the ionic conductivity and electronic conductivity are relatively high, the pre-lithiated negative electrode sheet has a relatively high lithium supplement amount, and the use of the pre-lithiated negative electrode sheet in a secondary battery 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.

[0070] In an embodiment of the present application, the negative active material comprises a carbon material and a silicon-containing substance, the mass percentage of silicon element in the negative material layer is w1, 1.1%≤w1≤3.4%, 0.38%≤W1≤0.60%, 0.30%≤W2<0.38%, 0.15%≤W3<0.30% based on the mass of the negative material layer. Exemplarily, w1 can be 1.1%, 1.5%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.4% or a range between any two of the above values; W1 can be 0.38%, 0.4%, 0.42%, 0.44%, 0.46%, 0.48%, 0.5%, 0.52%, 0.54%, 0.56%, 0.58%, 0.60% or a range between any two of the above values; W2 can be 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37% or a range between any two of the above values; W3 can be 0.15%, 0.17%, 0.19%, 0.2%, 0.21%, 0.23%, 0.25%, 0.27%, 0.29% or a range between any two of the above values. The negative active material comprises a carbon material and a silicon-containing substance, the supplement lithium efficiency of different negative active materials is different in the same pre-lithiation treatment time, the supplement lithium amount of the silicon-containing substance is relatively small, and the supplement lithium amount of the carbon material is relatively large, which will affect the supplement lithium amount in the pre-lithiated negative electrode sheet. Within the range of the mass percentage of silicon element w1, W1, W2, W3 in the negative material layer, the carbon material and the silicon-containing substance have a suitable mass percentage, the negative active material has a high capacity and a high supplement lithium amount, which can make the pre-lithiated negative electrode sheet have a high capacity and a high supplement lithium amount, and the above pre-lithiated negative electrode sheet is applied to a secondary battery, which can 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.

[0071] In an embodiment of the present application, the negative active material comprises a carbon material and a silicon-containing substance, and the mass percentage of silicon in the negative material layer is w1, 3.3%≤w1≤10.2%, 2.8%≤W1≤4.5%, 2.2%≤W2<2.8%, 1.1%≤W3<2.2%. Illustratively, w1 can be 3.3%, 4%, 4.5%, 5%, 5.7%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 9.6%, 10%, 10.2%, or a range between any two of the above values; W1 can be 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.5%, or a range between any two of the above values; W2 can be 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, or a range between any two of the above values; W3 can be 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, or a range between any two of the above values. The negative active material comprises a carbon material and a silicon-containing substance, and the lithium supplementing efficiency of different negative active materials is different within the same pre-lithiation treatment time, the lithium supplementing amount of the silicon-containing substance is relatively small, and the lithium supplementing amount of the carbon material is relatively large, which will affect the lithium supplementing amount in the pre-lithiated negative electrode sheet. Within the range of the mass percentage of silicon w1, W1, W2, and W3 in the negative material layer, the carbon material and the silicon-containing substance have a suitable mass percentage, the negative active material has a high capacity and a high lithium supplementing amount, which can enable the pre-lithiated negative electrode sheet to have a high capacity and a high lithium supplementing amount, and the application of the pre-lithiated negative electrode sheet in a secondary battery can 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.

[0072] In an embodiment of the present application, the porosity of the first region is S1, the porosity of the second region is S2, and the porosity of the third region is S3, S1>S2>S3. S1, S2, and S3 satisfy the above size relationship, which is beneficial to the migration of lithium ions along the thickness direction of the negative electrode sheet and can improve the kinetic performance of the negative electrode sheet. The present application does not have special restrictions on the way of regulating the porosities of the first region, the second region, and the third region of the negative material layer in the pre-lithiated negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the lithium supplementing amount and the lithium supplementing rate can be regulated by regulating the interfacial pressure, the lamination time, and the lamination temperature of the interface layer of the lithium supplementing composite layer and the negative material layer, so as to regulate the lithium supplementing amount of the first region, the second region, and the third region of the negative material layer in the pre-lithiated negative electrode sheet, and further regulate the porosities of the first region, the second region, and the third region.

[0073] In an embodiment of the present application, 1.01≤S1 / S2≤1.5, 1.01≤S2 / S3≤1.5. Illustratively, S1 / S2 can be 1.01, 1.1, 1.2, 1.3, 1.4, 1.5 or a range between any two of the above values; S2 / S3 can be 1.01, 1.1, 1.2, 1.3, 1.4, 1.5 or a range between any two of the above values. The values of S1 / S2, S2 / S3 within the scope of the present application, the porosity of the first region > the porosity of the second region > the porosity of the third region, are conducive to the migration of lithium ions along the thickness direction of the negative electrode sheet, and can further improve the kinetic performance of the negative electrode sheet. The method for regulating the value of S1 / S2 is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Illustratively, the value of S1 / S2 can be regulated by regulating the values of S1 and S2 respectively, and the regulation method of S1 and S2 is as described above. The method for regulating the value of S2 / S3 is not particularly limited in the present application, as long as the purpose of the present application can be achieved. Illustratively, the value of S2 / S3 can be regulated by regulating the values of S2 and S3 respectively, and the regulation method of S2 and S3 is as described above.

[0074] In an embodiment of the application, the negative active material only includes the silicon-containing substance, the mass percentage of the element silicon in the negative material layer is w1 based on the mass of the negative material layer, 18.6%≤w1≤63.5%, 42.1%≤S1≤57.0%, 38.0%≤S2<42.1%, 25.0%≤S3<38.0%. Exemplarily, w1 can be 18.6%, 25.5%, 37.5%, 38.5%, 39.5%, 40.5%, 41.5%, 42.5%, 43.5%, 44.5%, 45.5%, 46.5%, 47.5%, 55.5%, 63.5% or a range between any two of the above values; S1 can be 42.1%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 57.0% or a range between any two of the above values; S2 can be 38.0%, 38.5%, 39.0%, 39.5%, 40.0%, 40.5%, 41.0%, 41.5%, 42.0% or a range between any two of the above values; S3 can be 25.0%, 26.0%, 27.0%, 28.0%, 29.0%, 30.0%, 31.0%, 32.0%, 33.0%, 34.0%, 35.0%, 36.0%, 37.0%, 37.9% or a range between any two of the above values. The negative active material only includes the silicon-containing substance, the silicon-containing substance has a high specific capacity, the values of the mass percentage of the element silicon in the negative material layer w1, S1, S2, S3 are within the range of the application, which is beneficial to the migration of lithium ions along the thickness direction of the negative electrode sheet, and can further improve the kinetic performance of the negative electrode sheet, while the negative electrode sheet has a high capacity.

[0075] In an embodiment of the present application, the negative active material comprises a carbon material and a silicon-containing substance, the mass percentage of silicon element in the negative active material layer is w1, 1.1%≤w1≤3.4%, 26.3%≤S1≤35.5%, 23.7%≤S2<26.3%, 15.8%≤S3<23.7%, based on the mass of the negative active material layer. Exemplarily, w1 can be 1.1%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.4%, or a range between any two of the above values; S1 can be 26.3%, 27.3%, 28.3%, 29.3%, 30.3%, 31.3%, 32.3%, 33.3%, 34.3%, 35.3%, 35.5%, or a range between any two of the above values; S2 can be 23.7%, 24%, 24.7%, 25%, 25.7%, 26%, 26.2%, or a range between any two of the above values; S3 can be 15.8%, 16.8%, 17.8%, 18.8%, 19.8%, 20.8%, 21.8%, 22.8%, 23.6%, or a range between any two of the above values. The negative active material comprises a carbon material and a silicon-containing substance, which is beneficial to further improve the specific capacity and lithium supplement amount of the negative active material, the values of the mass percentage of silicon element w1, S1, S2, S3 in the negative active material layer are within the range of the present application, which is beneficial to the migration of lithium ions along the thickness direction of the negative electrode sheet, and can further improve the kinetic performance of the negative electrode sheet, while the negative electrode sheet has a high capacity.

[0076] In an embodiment of the present application, the negative active material comprises a carbon material and a silicon-containing substance, the mass percentage of silicon element in the negative active material layer is w1, 3.3%≤w1≤10.2%, 31.6%≤S1≤42.6%, 28.4%≤S2<31.6%, 18.9%≤S3<28.4%, based on the mass of the negative active material layer. Exemplarily, w1 can be 3.3%, 4.5%, 5.7%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 9.6%, 10%, 10.2%, or a range between any two of the above values; S1 can be 31.6%, 32.6%, 33.6%, 34.6%, 35.6%, 36.6%, 37.6%, 38.6%, 39.6%, 40.6%, 41.6%, 42.6%, or a range between any two of the above values; S2 can be 28.4%, 29%, 29.4%, 30%, 30.4%, 31%, 31.4%, 31.5%, or a range between any two of the above values; S3 can be 18.9%, 19.9%, 20.9%, 21.9%, 22.9%, 23.9%, 24.9%, 25.9%, 26.9%, 27.9%, 28.3%, or a range between any two of the above values. The negative active material comprises a carbon material and a silicon-containing substance, which is beneficial to further improve the specific capacity and lithium supplement amount of the negative active material, the mass percentage of silicon element in the negative active material layer w1, S1, S2, S3 is within the range of the present application, which is beneficial to the migration of lithium ions along the thickness direction of the negative electrode sheet, and can further improve the kinetic performance of the negative electrode sheet, while the negative electrode sheet has a high capacity.

[0077] In the present application, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. The present application does not have a particular limitation on the type of negative electrode binder 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 present application does not have a particular limitation on the type of negative electrode conductive agent 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 in particular, 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 present application does not have a particular limitation on the mass ratio of the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent in the negative electrode material layer, 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.

[0078] The present application does not have a particular limitation on the negative electrode current collector as long as the purpose of the present application can be achieved, for example, it 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 (such as a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.), etc.

[0079] The present application does not have a particular limitation on the thickness of the negative electrode current collector as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 μm to 20 μm. The present application does not have a particular limitation on the thickness of the negative electrode material layer as long as the purpose of the present application can be achieved, for example, the thickness of the single-sided negative electrode material layer is 30 μm to 250 μm.

[0080] The fourth aspect of the present application provides a secondary battery including the pre-lithiated negative electrode sheet in any of the preceding embodiments. Therefore, the secondary battery of the present application has a higher initial coulombic efficiency, a lower cycle capacity decay, and a higher energy density.

[0081] In the present application, the secondary battery further includes a positive electrode tab. The positive electrode tab includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces of the positive electrode current collector in the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire area of the positive electrode current collector, or can be a partial area of the positive electrode current collector, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved.

[0082] The present application does not have a particular limitation on the positive electrode current collector as long as the purpose of the present application can be achieved, for example, it can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), etc.

[0083] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance capable of reversibly intercalating and deintercalating active ions such as lithium ions. The positive electrode material layer can be one layer or multiple layers, and each layer of the multiple layers of the positive electrode material layer can include the same or different positive electrode active material. The present application does not have a particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved, for example, the positive electrode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, 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), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3at least one of O2 (NCM111). The positive electrode material layer of the present application further includes a positive electrode conductive agent and a positive electrode binder, and the present application does not have a particular limitation on the positive electrode conductive agent and the positive electrode binder in the positive electrode material layer as long as the purpose of the present application can be achieved. For example, the positive electrode conductive agent in the positive electrode material layer can include at least one of the above-mentioned negative electrode conductive agents; the positive electrode binder in the positive electrode material layer can include at least one of the above-mentioned negative electrode binders. The present application does not have a particular limitation 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 a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0084] The present application does not have a particular limitation 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 a particular limitation 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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 a 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.

[0089] 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.

[0090] 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 a 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.

[0091] 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.

[0092] 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.

[0093] Embodiments

[0094] 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.

[0095] Test methods and apparatus:

[0096] The mass percentage content of lithium element in the first region, the second region and the third region is tested:

[0097] After the pre-lithiation of the negative electrode sheet, the negative electrode material substance on the surface of the negative electrode current collector is scraped by a blade along the thickness direction of the negative electrode sheet, and the negative electrode material substance is used as the negative electrode material substance of the first region, the second region and the third region.

[0098] The mass percentage content of lithium element in the negative electrode material substance in the first region, the second region and the third region is detected by an inductively coupled plasma-optical emission spectrometer (ICP-OES). The ICP-OES used is a PE7000DV spectrometer produced by the American company Platinum Gold Elmer, and the test conditions of the ICP-OES are as follows: the radio frequency (RF) is 40.68 MHz, the radio frequency power is 1300 W, the argon secondary pressure is 0.6 MPa, the auxiliary gas flow is 0.2 L / min, the cooling gas flow is 15 L / min, and the pump speed is 1.5 mL / min.

[0099] The mass percentage content of silicon element in the negative electrode material layer is tested:

[0100] After the pre-lithiation of the negative electrode sheet, the negative electrode material substance on the surface of the negative electrode current collector is scraped by a blade, and the mass percentage content of silicon element in the negative electrode material substance is detected by an inductively coupled plasma-optical emission spectrometer (ICP-OES). The ICP-OES used is a PE7000DV spectrometer produced by the American company Platinum Gold Elmer, and the test conditions of the ICP-OES are as follows: the radio frequency (RF) is 40.68 MHz, the radio frequency power is 1300 W, the argon secondary pressure is 0.6 MPa, the auxiliary gas flow is 0.2 L / min, the cooling gas flow is 15 L / min, and the pump speed is 1.5 mL / min.

[0101] The porosity of the first region, the second region and the third region is tested:

[0102] (1) The total porosity (S1+S2+S3) of the negative electrode material layer is tested:

[0103] a) Sample preparation: after the pre-lithiation of the negative electrode sheet, the negative electrode sheet is wrapped with weighing paper up and down, and is punched by a punching machine to obtain 40 circular sample pieces with a diameter of 16 mm, and the thickness of the circular sample pieces is tested to obtain an average value h1.

[0104] b) Test: the 40 circular sample pieces obtained in step a) are loaded into a sample cup of a true density instrument (model AccuPyc II 1340), the cover is tightened, the test is performed for 3 times, the average value of the test results is taken as the true volume V2 of the circular sample pieces, and the test temperature is recorded.

[0105] c) Result analysis: apparent volume V1 = s x hi x number of wafer samples, wherein s is the surface area of the wafer sample, hi is the thickness of the wafer sample; the porosity of the wafer sample is obtained according to Porosity = (V1-V2) / V1 x 100%, which is S1+S2+S3.

[0106] (2) Total porosity (S2+S3) test of the second region and the third region:

[0107] a) Sample preparation: the wafer sample after step (1) test is scraped by 1 / 3 thickness of the surface layer with a blade, and the thickness of the wafer sample is tested, and the average value h is taken. 1-1 .

[0108] b) Test: 40 wafer samples obtained in step a) are loaded into the sample cup of the true density instrument (model AccuPyc II 1340), the cover is tightened, and the test is performed for 3 times, the average value of the test results is taken, recorded as the true volume V of the wafer sample, and the test temperature is recorded. 2-1 .

[0109] c) Result analysis: apparent volume V 1-1 = s x h 1-1 x number of wafer samples, wherein s is the surface area of the wafer sample, h 1-1 is the thickness of the wafer sample; the porosity of the wafer sample is obtained according to Porosity = (V 1-1 -V 2-1 ) / V 1-1 x 100%, which is S2+S3.

[0110] (3) Porosity (S3) test of the third region:

[0111] a) Sample preparation: the wafer sample after step (2) test is scraped by 1 / 3 thickness of the surface layer with a blade, and the thickness of the wafer sample is tested, and the average value h is taken. 1-2 .

[0112] b) Test: 40 wafer samples obtained in step a) are loaded into the sample cup of the true density instrument (model AccuPyc II 1340), the cover is tightened, and the test is performed for 3 times, the average value of the test results is taken, recorded as the true volume V of the wafer sample, and the test temperature is recorded. 2-2 .

[0113] c) Result analysis: apparent volume V 1-2 = s x h 1-2 x number of wafer samples, wherein s is the surface area of the wafer sample, h 1-2 is the thickness of the wafer sample; the porosity of the wafer sample is obtained according to Porosity = (V 1-2-V 2-2 ) / V 1-2 The porosity of the disc sample is obtained by multiplying by 100%, which is S3.

[0114] (4) Calculation of porosity in the first region and porosity in the second region:

[0115] The porosity of the first region is S1(%) = (S1 + S2 + S3) - (S2 + S3);

[0116] The porosity of the second region is S2(%) = (S2 + S3) - S3.

[0117] Thickness testing of the support layer, lithium replenishment layer, and interface layer:

[0118] Place the sample to be tested on the table, level it, and then measure its thickness as required. Wipe the measuring face of the dial indicator with a non-woven cloth; press the measuring linkage mechanism to make the two measuring faces fully contact, and press the "zero" key; make contact between the two measuring faces of the dial indicator and the face of the sample to be tested, read the displayed data, and record the reading. Measure at 70mm intervals along the direction perpendicular to the belt travel (i.e., the TD direction), and at 100mm intervals along the belt travel direction (i.e., the MD direction); test 12 points along the TD direction of the sample to be tested; test 12 points along the MD direction of the sample to be tested; test a total of 24 points; take the average thickness of the 24 points as the thickness of the sample to be tested.

[0119] Using the support layer as the sample to be tested, the thickness H3 of the support layer is obtained.

[0120] By combining the support layer and the lithium replenishment layer as the sample to be tested, the total thickness H of the support layer and the lithium replenishment layer is obtained. 支撑层&补锂层 The total thickness H of the support layer and the lithium replenishment layer 支撑层&补锂层 The difference between the thickness H3 and the thickness H2 of the lithium replenishment layer is the thickness H2 of the lithium replenishment layer, i.e., H2 = H 支撑层&补锂层 -H3.

[0121] By combining the support layer, lithium replenishment layer, and interface layer into a composite sample, the total thickness H of the support layer, lithium replenishment layer, and interface layer can be obtained. 支撑层&补锂层&界面层 The thickness of the interface layer is H1, i.e., H1 = H 支撑层&补锂层&界面层 -H 支撑层&补锂层 .

[0122] Test on the coverage ratio of interface particles in the lithium replenishment layer:

[0123] (1) Place the sample flat on the sample stage, and then use an optical microscope to magnify and photograph the sample (Keyence VHX-7000, magnification 300x).

[0124] (2) The photographed picture is imported into image processing software IMAGE J, the lithium supplement area and the interface area are distinguished by threshold value, and the area S1 to S of each interface area is counted n , the total area of the interface area is Sinterface=S1+S2+S3+…+S n-1 +S n ; the length L and the width W of the lithium supplement area are measured, the total area S of the lithium supplement area is calculated =WxL; then the coverage ratio s1 of the interface particles in the lithium supplement layer is Sinterface / Slithium. Details are shown in Figure 4 and Figure 5 .

[0125] (3) The average value of 12 s1 is taken as the coverage ratio of the interface particles in the lithium supplement layer.

[0126] The ratio of the depth of the interface particles embedded in the lithium supplement layer to the thickness of the interface layer is tested:

[0127] (1) Sample preparation: the lithium supplement composite layer sample is cut into a size of 6mmx6mm and adhered to a sample stage with conductive glue; then the lithium supplement composite layer sample is cross-section polished with a cross section polisher (model IB-19520 CCP), and the polishing conditions are: vacuum degree is 10 -3 Pa, acceleration voltage is 6kV, and grinding speed is 500 microns / hour.

[0128] (2) Parameter testing: the polished sample is placed on the sample stage of a scanning electron microscope, and the cross section thereof is tested by a scanning electron microscope (SEM, Scanning electron microscope, model Sumu Fei-Apreo S), and the testing conditions are: acceleration voltage is 10kV, grating is 10spot, working distance is 10mm, and magnification is 2000 times.

[0129] The depth H a of the interface particles embedded in the lithium supplement layer is defined as: the height difference between the upper surface of the lithium supplement layer and the lower surface of the interface layer, and details are shown in Figure 6 . H c is defined as: the height difference between the upper surface of the interface layer and the lower surface of the interface layer, and details are shown in Figure 7 . h is defined as: H a / H c . The average value of 12 h is taken as the ratio of the depth of the interface particles embedded in the lithium supplement layer to the thickness of the interface layer.

[0130] First coulomb efficiency test:

[0131] The voltage range marked on the outer packaging of the battery as shipped is used as the reference, for example, when the voltage range marked on the battery as shipped is 3.0 V to 4.45 V, the charge cut-off voltage is 4.45 V and the discharge cut-off voltage is 3.0 V. The specific test procedure is as follows: the lithium ion battery in the example or comparative example is charged at 0.2 C constant current to the cut-off voltage 4.45 V at 25 °C, then charged at constant voltage of 4.45 V until the current is less than 0.05 C, and then discharged at 0.2 C constant current to the cut-off voltage 3.0 V after 5 min of rest. The capacity of the above charging process is recorded as C0, and the capacity of the above discharging process is recorded as C1. The first coulombic efficiency is calculated according to the following formula.

[0132] First coulombic efficiency (%) = C1 / C0 x 100%.

[0133] Cycle performance test:

[0134] The voltage range marked on the outer packaging of the battery as shipped is used as the reference, for example, when the voltage range marked on the battery as shipped is 3.0 V to 4.45 V, the charge cut-off voltage is 4.45 V and the discharge cut-off voltage is 3.0 V. The specific test procedure is as follows: the lithium ion battery in the example or comparative example is charged and discharged for the first time at 0.2 C constant current to the cut-off voltage 4.45 V at 25 °C, then charged at constant voltage of 4.45 V until the current is less than 0.05 C, and then discharged at 0.2 C constant current to the cut-off voltage 3.0 V after 5 min of rest. The discharge capacity of the lithium ion battery is measured as A; then, the lithium ion battery is subjected to 400 cycles of charging and discharging according to the above procedure in an environment at 25 °C, and the discharge capacity of the lithium ion battery at the 400th cycle is measured as B. The cycle capacity retention rate is calculated according to the following formula.

[0135] Cycle capacity retention rate (%) = B / A x 100%.

[0136] The greater the value of the cycle capacity retention rate obtained by the test, the better the cycle performance of the lithium ion battery.

[0137] Energy density test:

[0138] The voltage range marked on the outer packaging of the battery as shipped is used as the reference, for example, when the voltage range marked on the battery as shipped is 3.0 V to 4.45 V, the charge cut-off voltage is 4.45 V and the discharge cut-off voltage is 3.0 V. The specific test procedure is as follows: the lithium ion battery in the example or comparative example is charged at 0.2 C constant current to the cut-off voltage 4.45 V at 25 °C, then charged at constant voltage of 4.45 V until the current is less than 0.05 C, and then discharged at 0.2 C constant current to the cut-off voltage 3.0 V after 5 min of rest. The energy of the above discharging process is recorded as the discharge energy E. The volume V (mm 3 ) of the lithium ion battery is calculated according to the following formula.

[0139] Energy density (Wh / L) = E / V x 10 6 .

[0140] Example 1-1

[0141] Preparation of lithium supplement composite layer

[0142] Under the conditions of ambient temperature 25℃ and humidity 1.0%, a lithium foil was calendered to a copper foil support layer with a thickness of 14μm to form a lithium supplement layer, and the roll pressure P12 was 1.5T / 10mm, to obtain a lithium supplement layer / support layer composite structure.

[0143] Under the conditions of ambient temperature 25℃ and humidity 1.0%, the interface particles artificial graphite were coated on the surface of the lithium supplement layer by rubbing to form an interface layer, and then roll-pressed, with a roll pressure P2 of 0.5T / 10mm, a roll-pressing temperature T1 of 90℃, and a roll-pressing standing time t1 of 30min, to form a lithium supplement composite layer. In the lithium supplement composite layer, the thickness H1 of the interface layer was 8μm, the thickness H2 of the lithium supplement layer was 0.03mm, the coverage ratio s1 of the interface particles in the lithium supplement layer was 85%, and the depth of the interface particles embedded in the lithium supplement layer accounted for 50% of the thickness of the interface layer.

[0144] Preparation of negative electrode sheet

[0145] The negative electrode active material silicon-carbon material, the negative electrode conductive agent acetylene black, the negative electrode binder styrene-butadiene rubber (SBR), and the negative electrode binder carboxymethyl cellulose lithium were mixed according to a weight ratio of 85:5:5:5, and deionized water was added as a solvent, and the mixture was stirred and mixed uniformly to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry was 28wt%; the negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 12μm, and was dried at 90℃ to obtain a negative electrode sheet coated with a negative electrode material layer on one side. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. After drying under vacuum at 90℃ for 1h, the negative electrode sheet was subjected to cold pressing, cutting, and slitting to obtain a negative electrode sheet with a specification of 51mm x 44.2mm. The silicon-carbon material was a silicon-carbon composite material, and the mass percentage content of silicon element w Si was 50%, and the mass percentage content of carbon element w C was 50%; the area density CW of the negative electrode material layer was 2.3mg / cm 2 , and the compaction density during cold pressing was 1.0g / cm 3 .

[0146] Preparation of pre-lithiated negative electrode sheet

[0147] The prepared negative electrode sheet is dried until the water content is ≤500 ppm; under the conditions of ambient temperature 90 ℃ and humidity 1.0%, the prepared lithium supplement composite layer is attached to the prepared negative electrode sheet to make the interface layer contact with the negative electrode material layer, the attachment mode is compression into a sheet, the interface pressure P3 of the interface layer and the negative electrode material layer is 0.6 MPa, the attachment time t2 of the interface layer and the negative electrode material layer is 20 h, the attachment temperature T2 of the interface layer and the negative electrode material layer is 90 ℃, 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. Based on the mass of the first region, the mass percentage of lithium element W1 is 16.5%; based on the mass of the second region, the mass percentage of lithium element W2 is 10.5%; based on the mass of the third region, the mass percentage of lithium element W3 is 6.5%, W1>W2>W3.

[0148] <Preparation of the positive electrode sheet>

[0149] The positive electrode active material lithium cobaltate (LiCoO2), the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.4:1.6, then N-methyl pyrrolidone (NMP) is added as a solvent, and the mixture is stirred and uniformly mixed to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry is 75 wt%; the positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm, and dried at 110 ℃ to obtain a positive electrode sheet coated with a positive electrode material layer on one side. Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. After drying under vacuum conditions at 110 ℃ for 1 h, cold pressing, sheet cutting, and slitting, a positive electrode sheet with a specification of 48 mm x 41.2 mm is obtained. The areal density of the positive electrode material layer is 19.0 mg / cm 2 , and the compaction density during the cold pressing process is 4.15 g / cm 3 .

[0150] <Preparation of the electrolyte>

[0151] 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) are mixed in a weight ratio of 3:1:3:3 to obtain a base solvent, then lithium salt lithium hexafluorophosphate (LiPF6) is added and uniformly mixed to obtain an electrolyte. The mass percentage of lithium salt LiPF6 based on the mass of the electrolyte is 12.5%, and the balance is the base solvent.

[0152] <Preparation of the separator>

[0153] A porous polypropylene film (provided by Celgard) with a thickness of 5 μm is used as the separator.

[0154] <Preparation of lithium ion battery>

[0155] 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 play a role of isolation, to obtain an electrode assembly. After welding the tab, the electrode assembly was placed in an aluminum plastic film packaging bag, and was placed in a vacuum oven at 85°C for 12h to remove water, injected with electrolyte, and subjected to vacuum packaging, standing, formation (charged to 3.5V at 0.02C constant current, and then charged to 3.9V at 0.1C constant current), degassing, edge cutting, and capacity processing procedures to obtain a lithium ion battery.

[0156] Example 1-2 to Example 1-5

[0157] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1-1. Among them, the sum of the mass percentage contents of the negative electrode active material, the negative electrode conductive agent acetylene black, the negative electrode binder styrene-butadiene rubber, and the negative electrode binder carboxymethyl cellulose lithium was 100%, and the mass ratio of the negative electrode conductive agent acetylene black, the negative electrode binder styrene-butadiene rubber, and the negative electrode binder carboxymethyl cellulose lithium was unchanged.

[0158] Example 1-6

[0159] Except that in the <Preparation of negative electrode sheet>, the negative electrode active material was a mixture of silicon-containing substance silicon-carbon material and carbon material artificial graphite, the mass percentage content W Si of the silicon-containing substance was 5%, and the mass percentage content Wc of the carbon material was 95%; the silicon-carbon material was a silicon-carbon composite material, the mass percentage content wsi of silicon element was 30%, and the mass percentage content wc of carbon element was 70% based on the mass of the silicon-carbon composite material, and the rest was the same as Example 1-1. Among them, the sum of the mass percentage contents of the negative electrode active material, the negative electrode conductive agent acetylene black, the negative electrode binder styrene-butadiene rubber, and the negative electrode binder carboxymethyl cellulose lithium was 100%, and the mass ratio of the negative electrode conductive agent acetylene black, the negative electrode binder styrene-butadiene rubber, and the negative electrode binder carboxymethyl cellulose lithium was unchanged.

[0160] Example 1-7 to Example 1-11

[0161] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1-6. Among them, the sum of the mass percentage contents of the negative electrode active material, the negative electrode conductive agent acetylene black, the negative electrode binder styrene-butadiene rubber, and the negative electrode binder carboxymethyl cellulose lithium was 100%, and the mass ratio of the negative electrode conductive agent acetylene black, the negative electrode binder styrene-butadiene rubber, and the negative electrode binder carboxymethyl cellulose lithium was unchanged.

[0162] Example 1-12

[0163] The rest was the same as Example 1-1 except that the related preparation parameters were adjusted according to Table 1.

[0164] Example 1-13

[0165] The rest was the same as Example 1-10 except that the related preparation parameters were adjusted according to Table 1.

[0166] Examples 2-1 to 2-11

[0167] The rest was the same as Example 1-1 except that the related preparation parameters were adjusted according to Table 3.

[0168] Example 2-12

[0169] The rest was the same as Example 1-1 except that the related preparation parameters were adjusted according to Table 3, and the thickness H1 of the interface layer in the lithium supplementing composite layer was 2 μm.

[0170] Examples 2-13 to 2-14

[0171] The rest was the same as Example 1-1 except that the related preparation parameters were adjusted according to Table 3.

[0172] Comparative Example 1-1

[0173] The rest was the same as Example 1-1 except that the interface layer was not set in the preparation of the lithium supplementing composite layer.

[0174] Comparative Examples 2-1 to 2-5

[0175] The rest was the same as Example 1-1 except that the related preparation parameters were adjusted according to Table 3.

[0176] The preparation parameters and electrical performance parameters of each example and comparative example are shown in Tables 1 to 3.

[0177] Table 1

[0178]

[0179]

[0180] Note: In Table 1, " / " means no related preparation parameter.

[0181] Table 2

[0182] First coulombic efficiency (%) Cycle capacity retention rate (%) Energy density (Wh / L) Example 1-1 92.5 90.5 854.4 Example 1-2 91.0 85.0 825.0 Example 1-3 92.9 84.0 840.0 Example 1-4 92.0 91.0 830.0 Example 1-5 92.7 85.0 860.0 Example 1-6 92.5 87.0 753.0 Example 1-7 93.5 92.5 784.4 Example 1-8 94.0 86.0 770.0 Example 1-9 92.0 86.0 785.0 Example 1-10 93.0 91.5 804.3 Example 1-11 93.4 87.0 795.0 Example 1-12 90.8 87.9 823.1 Example 1-13 92.0 92.5 800.0 Comparative Example 1-1 78.2 76.5 722.5

[0183] As can be seen from Example 1-1 to Example 1-13, Comparative Example 1-1, the lithium supplementing composite layer is prepared by the preparation method of the lithium supplementing composite layer provided in the present application, and then the pre-lithiated negative electrode sheet is prepared by the pre-lithiation method provided in the present application, and the pre-lithiated negative electrode sheet is applied to the lithium ion battery, and the lithium ion battery prepared has high initial coulombic efficiency, cycle capacity retention rate and energy density, which indicates 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 Comparative Example 1-1, the preparation method of the lithium supplementing composite layer is not within the scope of the present application, and the lithium ion battery prepared has low initial coulombic efficiency, cycle capacity retention rate and energy density.

[0184] As can be seen from Example 1-1 to Example 1-3, the mass percentage content of the negative electrode active material in the negative electrode material layer increases, the mass percentage content of silicon element in the silicon-carbon material increases, the mass percentage content of silicon element in the negative electrode material layer increases, the porosity of the first region, the second region and the third region increases, and the better the kinetic performance of the pre-lithiated negative electrode sheet, which is beneficial to the upward transmission of lithium ions during lithium supplementing.

[0185] As can be seen from Example 1-1, Example 1-4 and Example 1-5, the mass percentage content of the negative electrode active material in the negative electrode material layer is unchanged, and the mass percentage content of silicon element in the silicon-carbon material increases, which is more beneficial to the surface lithium supplementing.

[0186] The values of W1 / W2 and W2 / W3 will generally affect the initial coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Example 1-1 to Example 1-13, the values of W1 / W2 and W2 / W3 are within the scope of the present application, and the lithium ion battery prepared has high initial coulombic efficiency, cycle capacity retention rate and energy density, which indicates 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.

[0187] The type of negative electrode active material will generally affect the initial coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 1-7 and Example 1-10, or Example 1-2, Example 1-6 and Example 1-9, or Example 1-3, Example 1-8 and Example 1-11, the type of negative electrode active material is within the scope of the present application, and the lithium ion battery prepared has high initial coulombic efficiency, cycle capacity retention rate and energy density, which indicates 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.

[0188] The values of S1 / S2 and S2 / S3 generally affect the first coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Examples 1-1 to 1-13, the values of S1 / S2 and S2 / S3 are within the scope of the present application, and the prepared lithium ion battery has high first coulombic efficiency, cycle capacity retention rate and energy density, indicating 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.

[0189] Table 3

[0190]

[0191]

[0192] Note: (1) In Table 3, in Example 2-13, the "interfacial particle type" is "97% artificial graphite + 3% single-walled carbon nanotubes", indicating that the interfacial particles include artificial graphite and single-walled carbon nanotubes, and the mass percentage of artificial graphite is 97% and the mass percentage of single-walled carbon nanotubes is 3% based on the mass of the interfacial particles.

[0193] As can be seen from Examples 2-1 to 2-14 and Comparative Examples 2-1 to 2-5, the lithium supplement composite layer is prepared by the preparation method provided in the present application, and then the pre-lithiated negative electrode sheet is prepared by the pre-lithiation method provided in the present application, and the pre-lithiated negative electrode sheet is applied to a lithium ion battery, and the prepared lithium ion battery has high first coulombic efficiency, cycle capacity retention rate and energy density, indicating 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. In Comparative Examples 2-1 to 2-5, the preparation method of the lithium supplement composite layer is not within the scope of the present application, and the prepared lithium ion battery has low first coulombic efficiency, cycle capacity retention rate and energy density.

[0194] As can be seen from Examples 1-1, 2-1 to 2-4, as the roll pressure P2 increases, the lithium supplement amount increases, the first coulombic efficiency of the lithium ion battery increases, the energy density increases, and the cycle capacity retention rate first increases and then decreases, indicating that too large lithium supplement amount will affect the cycle performance of the lithium ion battery to some extent.

[0195] The type of interface particles generally affects the first coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Example 1-1, Example 2-12 and Example 2-13, the type of interface particles 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. In Example 2-12, when the type of interface particles is single-walled carbon nanotubes, the thickness of the interface layer is affected by the diameter of the single-walled carbon nanotubes, the thickness of the interface layer is relatively thin, and after lithium supplement, there are more by-products remaining in the negative electrode material layer, which affects the first coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery.

[0196] The type of lithium supplement layer generally affects the first coulombic efficiency, cycle capacity retention rate and energy density of the lithium ion battery. As can be seen from Example 1-1 and Example 2-14, the type of lithium supplement layer 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.

[0197] It should be noted that the relational terms herein such as first and second and the like are used only to differentiate one entity or operation from another, and do not necessarily require or imply that any such actual relationship or order exists between or among the entities or operations. Also, 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.

[0198] Each of the embodiments in the specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment mainly explains the difference from other embodiments.

[0199] The above only describes the preferred embodiments of the present application, and does not 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 protection scope 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 0.1 T / 10 mm to 2 T / 10 mm; (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 0.1 T / 10 mm to 2 T / 10 mm, the rolling temperature T1 is 25℃ to 170℃, and the rolling standing time t1 is 5 min to 50 min, 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, the lithium supplement layer is arranged between the support layer and the interface layer, the interface layer comprises the interface particles, and the lithium supplement layer comprises at least one of a lithium foil or a lithium alloy foil.

3. The production method according to claim 1, wherein 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, or silicon-oxygen material. 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 and a negative electrode material layer arranged on at least one surface of the negative electrode current collector; adhering the lithium supplement composite layer prepared by the preparation method in any one of claims 1 to 3 and the negative electrode sheet so that the interface layer is in contact with the negative electrode material layer, and performing pre-lithiation treatment, wherein the interface pressure P3 between the interface layer and the negative electrode material layer is 0.1 MPa to 2 MPa, the adhering time t2 of the interface layer and the negative electrode material layer is 0.5 h to 72 h, and the adhering temperature T2 of the interface layer and the negative electrode material layer is 50℃ to 180℃, and after the pre-lithiation treatment, the lithium supplement composite layer and the negative electrode sheet are peeled apart to form a pre-lithiated negative electrode sheet. 5.A pre-lithiated negative electrode sheet prepared by the method for supplementing lithium according to claim 4, the negative electrode sheet comprising a negative electrode current collector and a negative electrode material layer, and along the thickness direction of the negative electrode sheet, the negative electrode material layer comprises opposite first and second surfaces; from the first surface to the second surface, the negative electrode material layer comprises a first region, a second region, and a third region in sequence, and the third region is located on the surface of the negative electrode current collector; the thickness of the first region accounts for 1 / 3 of the thickness of the negative electrode material layer, the thickness of the second region accounts for 1 / 3 of the thickness of the negative electrode material layer, and the thickness of the third region accounts for 1 / 3 of the thickness of the negative electrode material layer; based on the mass of the first region, the mass percentage of lithium is W1, based on the mass of the second region, the mass percentage of lithium is W2, and based on the mass of the third region, the mass percentage of lithium is W3, W1>W2>W3, 1.01≤W1 / W2≤2.0, and 1.01≤W2 / W3≤2.

0.

6. The prelithiated negative electrode web of claim 5, wherein, The negative material layer comprises a negative active material, the negative active material comprises at least one of a carbon material or a silicon-containing substance, the carbon material comprises at least one of a graphite material or hard carbon, and the silicon-containing substance comprises at least one of a silicon-carbon material or a silicon-oxygen material.

7. The prelithiated negative electrode web of claim 6, wherein, The negative electrode sheet satisfies one of the following characteristics: (1) The negative active material only comprises the silicon-containing substance, the mass percentage content of silicon element in the negative material layer is w1 based on the mass of the negative material layer, 18.6%≤w1≤63.5%, 11.5%≤W1≤18.4%, 9.2%≤W2<11.5%, 4.6%≤W3<9.2%; (2) The negative active material comprises the carbon material and the silicon-containing substance, the mass percentage content of silicon element in the negative material layer is w1 based on the mass of the negative material layer, 1.1%≤w1≤3.4%, 0.38%≤W1≤0.60%, 0.30%≤W2<0.38%, 0.15%≤W3<0.30%; (3) The negative active material comprises the carbon material and the silicon-containing substance, the mass percentage content of silicon element in the negative material layer is w1 based on the mass of the negative material layer, 3.3%≤w1≤10.2%, 2.8%≤W1≤4.5%, 2.2%≤W2<2.8%, 1.1%≤W3<2.2%.

8. The prelithiated negative electrode web of claim 6, wherein, The porosity of the first region is S1, the porosity of the second region is S2, and the porosity of the third region is S3, S1>S2>S3.

9. The prelithiated negative electrode web of claim 8, wherein, 1.01≤S1 / S2≤1.5, 1.01≤S2 / S3≤1.

5.

10. The prelithiated negative electrode web of claim 8, wherein, The negative electrode sheet satisfies one of the following characteristics: (1) The negative active material only comprises the silicon-containing substance, the mass percentage content of silicon element in the negative material layer is w1 based on the mass of the negative material layer, 18.6%≤w1≤63.5%, 42.1%≤S1≤57.0%, 38.0%≤S2<42.1%, 25.0%≤S3<38.0%; (2) The negative active material comprises the carbon material and the silicon-containing substance, the mass percentage content of silicon element in the negative material layer is w1 based on the mass of the negative material layer, 1.1%≤w1≤3.4%, 26.3%≤S1≤35.5%, 23.7%≤S2<26.3%, 15.8%≤S3<23.7%; (3) The negative active material comprises the carbon material and the silicon-containing substance, the mass percentage content of silicon element in the negative material layer is w1 based on the mass of the negative material layer, 3.3%≤w1≤10.2%, 31.6%≤S1≤42.6%, 28.4%≤S2<31.6%, 18.9%≤S3<28.4%.

11. A secondary battery comprising the pre-lithiated negative electrode sheet of any one of claims 5 to 10.

12. An electronic device comprising the secondary battery of claim 11.

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