Pre-lithiated negative pole piece and preparation method thereof, secondary battery and electronic device

Abstract

The invention provides a pre-lithiated negative pole piece and a preparation method thereof, a secondary battery and an electronic device. The pre-lithiated negative electrode piece comprises a negative electrode current collector, a negative electrode material layer and a lithium supplementing layer arranged between the negative electrode current collector and the negative electrode material layer, the negative electrode material layer sequentially comprises a first area, a second area and a third area in the thickness direction of the negative electrode piece, the first area is located on the surface of the lithium supplementing layer, and the second area is located on the surface of the third area. The thicknesses of the first region, the second region and the third region respectively account for 1 / 3 of the thickness of the negative electrode material layer; based on the mass of the first region, the mass percentage content of the lithium element is W1, based on the mass of the second region, the mass percentage content of the lithium element is W2, based on the mass of the third region, the mass percentage content of the lithium element is W3, W1 > W2 > W3, W1 / W2 is larger than or equal to 1.01 and smaller than or equal to 2.0, and W2 / W3 is larger than or equal to 1.01 and smaller than or equal to 2.0. The first coulombic efficiency and the energy density of the secondary battery can be improved, and the cycle capacity attenuation is reduced.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a pre-lithiated negative electrode plate and a preparation method thereof, a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have the advantages of high energy density, high power, and long cycle life. They are widely used in consumer electronics, electric bicycles, and electric vehicles. As their application scope continues to expand, the requirements for the energy density and cycle performance of lithium-ion batteries continue to increase.

[0003] Lithium metal batteries use lithium metal as the negative electrode, which has the characteristics of high energy density, low operating voltage and high specific capacity. However, during the charging and discharging process, lithium metal batteries may form lithium dendrites on the surface of the negative electrode, which will not only reduce the initial coulombic efficiency, but may also pierce the diaphragm, causing short circuits and safety problems, affecting its cycle performance.

[0004] The current common negative electrode active material graphite for lithium-ion batteries can no longer meet the requirements for energy density. Although silicon-carbon and silicon-oxygen negative electrode active materials have high theoretical specific capacity, they are ideal materials to replace negative electrode active material graphite and improve the energy density of lithium-ion batteries. However, they have not been widely used due to their low first coulombic efficiency and poor cycle life. The existing method to improve the first coulombic efficiency and reduce the capacity cyclic attenuation of lithium-ion batteries containing silicon-carbon or silicon-oxygen negative electrode active materials is to pre-replenish lithium to the negative electrode plate to replenish the irreversible capacity consumed during the first charge, discharge and cycle, thereby improving the first coulombic efficiency of lithium-ion batteries containing silicon-carbon or silicon-oxygen negative electrode active materials and thereby improving the energy density of lithium-ion batteries.

[0005] The existing negative electrode plate lithium replenishment methods mainly include lithium powder replenishment, lithium strip replenishment and electrochemical replenishment. However, the above three lithium replenishment methods have certain problems in environmental control, lithium replenishment uniformity, and side reactions after lithium replenishment. Therefore, it is urgent to provide a pre-lithiated negative electrode plate to improve the first coulomb efficiency of lithium-ion batteries containing silicon-carbon or silicon-oxygen negative electrode active materials, reduce cycle capacity attenuation, and improve the energy density of lithium-ion batteries. Summary of the invention

[0006] The purpose of this application is to provide a pre-lithiation negative electrode sheet and a preparation method thereof, a secondary battery and an electronic device, so as to improve the initial coulombic efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery. The specific technical solution is as follows:

[0007] The first aspect of the present application provides a method for preparing a pre-lithiated negative electrode sheet, which comprises the following steps:

[0008] (1) applying a lithium metal powder slurry to the negative electrode current collector, drying it, and rolling it to form a lithium replenishing layer; or rolling a lithium foil and / or a lithium alloy foil to the negative electrode current collector to form a lithium replenishing layer; or applying a lithium or lithium alloy molten slurry to the negative electrode current collector, cooling it, and rolling it to form a lithium replenishing layer;

[0009] (2) coating a negative electrode slurry including a negative electrode active material on the surface of the support layer and drying the negative electrode slurry to form a negative electrode material layer;

[0010] (3) placing a negative electrode material layer and a support layer on the surface of the lithium replenishing layer, wherein the surface of the negative electrode material layer away from the support layer is in contact with the lithium replenishing layer, and after rolling, the support layer and the negative electrode material layer are peeled off to form a pre-lithiated negative electrode sheet.

[0011] The preparation method provided by the present application is used to prepare the pre-lithiated negative electrode sheet, which can realize the pre-lithiation of the negative electrode material layer, replenish the active lithium lost due to the formation of the solid electrolyte interface film (SEI film) during the first charge and discharge process and the active lithium consumed during the cycle process, improve the lithium precipitation on the surface of the negative electrode sheet, reduce the side reaction between the electrolyte and the negative electrode active material, and reduce the generation of lithium dendrites on the surface of the negative electrode sheet, thereby improving the safety of the secondary battery. Therefore, the application of the above-mentioned pre-lithiated negative electrode sheet to the secondary battery can improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, improve the energy density of the secondary battery, and also improve the safety performance of the secondary battery.

[0012] In some embodiments of the present application, the roller pressure P1 of the rolling in step (1) is 0.1T / 10mm to 2T / 10mm; the roller pressure P2 of the rolling in step (3) is 1.0T / 10mm to 2.0T / 10mm. By adjusting the values ​​of the roller pressures P1 and P2 within the above range, a lithium supplement layer and a negative electrode material layer can be formed on the surface of the negative electrode current collector, and the prepared pre-lithiated negative electrode sheet is applied to a secondary battery, which is beneficial to improving the first coulomb efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0013] The second aspect of the present application provides a pre-lithiated negative electrode sheet prepared by the preparation method in any of the aforementioned embodiments, the negative electrode sheet comprising a negative electrode current collector, a lithium replenishing layer and a negative electrode material layer, the lithium replenishing layer being arranged between the negative electrode current collector and the negative electrode material layer, and along the thickness direction of the negative electrode sheet, the negative electrode material layer comprising a first surface and a second surface relative to each other; from the first surface to the second surface, the negative electrode material layer sequentially comprises a first region, a second region and a third region, and the first region is located on the surface of the lithium replenishing layer; 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 content of the lithium element in the first region is W1, based on the mass of the second region, the mass percentage content of the lithium element in the second region is W2, based on the mass of the third region, the mass percentage content of the lithium element in the third region is W3, W1>W2>W3, 1.01≤W1 / W2≤2.0, 1.01≤W2 / W3≤2.0.

[0014] The present application designs the structure of the negative electrode plate, sets the lithium supplement layer between the negative electrode current collector and the negative electrode material layer, and regulates the relationship between W1, W2, and W3 and the values ​​of W1 / W2 and W2 / W3 within the scope of the present application, which can supplement the active lithium lost due to the formation of the SEI film during the first charge and discharge process and the active lithium consumed during the cycle process, improve the lithium precipitation on the surface of the negative electrode plate, reduce the side reaction between the electrolyte and the negative electrode active material, and reduce the generation of lithium dendrites on the surface of the negative electrode plate, reducing the risk of short circuit of the secondary battery. Therefore, applying the pre-lithiated negative electrode plate of the present application to a secondary battery can improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, improve the energy density of the secondary battery, and also improve the safety performance of the secondary battery.

[0015] In some embodiments of the present application, the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes at least one of a carbon material or a silicon-containing material, the carbon material includes at least one of a graphite material or hard carbon, and the silicon-containing material includes at least one of a silicon-carbon material or a silicon-oxygen material. The negative electrode active material includes the above substances, the negative electrode plate has a high lithium supplement amount, and the prepared secondary battery has a high first coulomb efficiency, a low cycle capacity attenuation, and a high energy density.

[0016] In some embodiments of the present application, the pre-lithiated negative electrode sheet satisfies any of the following characteristics: (1) the negative electrode active material includes only silicon-containing substances, and based on the mass of the negative electrode material layer, the mass percentage of silicon element in the negative electrode material layer is w1, 18.6%≤w1≤63.5%, 11.5%≤W1≤18.4%, 9.2%≤W2<11.5%, 4.6%≤W3<9.2%; (2) the negative electrode active material includes carbon material and silicon-containing substances, and based on the mass of the negative electrode material layer, the mass percentage of silicon element in the negative electrode material layer is w1, 18.6%≤w1≤63.5%, 11.5%≤W1≤18.4%, 9.2%≤W2<11.5%, 4.6%≤W3<9.2%; The mass percentage of silicon element is w1, 1.1%≤w1≤3.4%, 0.38%≤W1≤0.60%, 0.30%≤W2<0.38%, 0.15%≤W3<0.30%; (3) the negative electrode active material includes carbon material and silicon-containing material. Based on the mass of the negative electrode material layer, the mass percentage of silicon element in the negative electrode material layer is w1, 3.3%≤w1≤10.2%, 2.8%≤W1≤4.5%, 2.2%≤W2<2.8%, 1.1%≤W3<2.2%. The pre-lithiation negative electrode plate that meets the above characteristics is applied to secondary batteries, which can improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity decay, and improve the energy density of the secondary battery.

[0017] In some embodiments of the present application, based on the mass of the lithium replenishing layer, the mass percentage of lithium in the lithium replenishing layer is 97% to 100%. By regulating the mass percentage of lithium in the lithium replenishing layer within the above range, more lithium ions can be provided to the negative electrode material layer, achieving a better lithium replenishing effect, thereby facilitating improving the first coulombic efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0018] In some embodiments of the present application, the thickness of the lithium replenishment layer is 1 μm to 30 μm, and the thickness of the negative electrode material layer is 16 μm to 72 μm. By adjusting the thickness of the lithium replenishment layer and the negative electrode material layer within the above range, it is beneficial to achieve a better lithium replenishment effect and increase the amount of lithium replenishment of the negative electrode plate, thereby improving the first coulomb efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0019] In some embodiments of the present application, the bonding force between the lithium replenishing layer and the negative electrode current collector is 10N / m to 50N / m, and the bonding force between the negative electrode material layer and the lithium replenishing layer is 5N / m to 10N / m. By regulating the bonding force between the lithium replenishing layer and the negative electrode current collector and the bonding force between the negative electrode material layer and the lithium replenishing layer within the above range, the bonding between the negative electrode current collector, the lithium replenishing layer, and the negative electrode material layer is good, and the above pre-lithiated negative electrode sheet is applied to the secondary battery, which is conducive to improving the first coulomb efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0020] The third aspect of the present application provides a secondary battery, which includes the pre-lithiated negative electrode plate in any of the above embodiments. Therefore, the secondary battery of the present application has a higher first coulombic efficiency, lower cycle capacity decay and higher energy density.

[0021] The fourth aspect of the present application provides an electronic device, which comprises the secondary battery in any of the above embodiments. The electronic device of the present application has a long service life and good performance.

[0022] Beneficial effects of this application:

[0023] The present application provides a pre-lithiated negative electrode plate and a preparation method thereof, a secondary battery and an electronic device. The negative electrode plate prepared by the preparation method of the present application can realize the pre-lithiation of the negative electrode plate, replenish the active lithium lost due to the formation of the SEI film during the first charge and discharge process, and can also continuously generate lithium ions during the cycle process to replenish the active lithium consumed during the cycle process, and the lithium content in the negative electrode material layer gradually decreases in the direction away from the negative electrode current collector, which can improve the lithium precipitation on the surface of the negative electrode plate, reduce the side reaction between the electrolyte and the negative electrode active material, and can also reduce the generation of lithium dendrites on the surface of the negative electrode plate, reduce the risk of short circuit of the secondary battery, and improve the safety of the secondary battery. Therefore, applying the pre-lithiated negative electrode plate of the present application to a secondary battery can improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, improve the energy density of the secondary battery, and also improve the safety performance of the secondary battery.

[0024] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0026] Figure 1 A schematic structural diagram of a process for preparing a pre-lithiated negative electrode sheet according to an embodiment of the present application;

[0027] Figure 2 This is a schematic diagram of the structure of a pre-lithiated negative electrode plate along its thickness direction according to an implementation scheme of the present application.

[0028] Reference numerals: pre-lithiated negative electrode sheet 100 , negative electrode current collector 110 , lithium supplement layer 120 , negative electrode material layer 130 , first region 131 , second region 132 , third region 133 , first surface 1311 , second surface 1332 , support layer 200 . DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0030] It should be noted that in the specific implementation manner of the present application, the present application is explained by taking a lithium-ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium-ion battery.

[0031] The first aspect of the present application provides a method for preparing a pre-lithiated negative electrode sheet, which comprises the following steps:

[0032] (1) applying a lithium metal powder slurry to the negative electrode current collector, drying it, and rolling it to form a lithium replenishing layer; or rolling a lithium foil and / or a lithium alloy foil to the negative electrode current collector to form a lithium replenishing layer; or applying a lithium or lithium alloy molten slurry to the negative electrode current collector, cooling it, and rolling it to form a lithium replenishing layer;

[0033] (2) coating a negative electrode slurry including a negative electrode active material on the surface of the support layer and drying the negative electrode slurry to form a negative electrode material layer;

[0034] (3) placing a negative electrode material layer and a support layer on the surface of the lithium replenishing layer, wherein the surface of the negative electrode material layer away from the support layer is in contact with the lithium replenishing layer, and after rolling, the support layer and the negative electrode material layer are peeled off to form a pre-lithiated negative electrode sheet.

[0035] The preparation method provided by the present application is used to prepare a pre-lithiated negative electrode sheet, and the negative electrode material layer is first formed on the support layer and then transferred to the surface of the lithium supplement layer, which can reduce the risk of heat release and generation of flammable gas by the reaction between the lithium supplement layer and the solvent in the negative electrode material layer slurry, and improve the safety of the preparation process. The prepared pre-lithiated negative electrode sheet includes a negative electrode current collector, a lithium supplement layer and a negative electrode material layer, and the lithium supplement layer and the negative electrode material layer can form an internal short circuit, and the lithium atoms in the lithium supplement layer undergo an oxidation reaction to lose electrons to generate lithium ions, and the electrons and lithium ions are transmitted to the interior of the negative electrode material layer, and then the electrons and lithium ions undergo a reduction reaction in the negative electrode material layer to form a lithium intercalation compound, so as to achieve pre-lithiation of the negative electrode material layer, so as to supplement the active lithium lost due to the formation of a solid electrolyte interface film (SEI film) during the first charge and discharge process, and can also continuously generate lithium ions during the cycle process to supplement the active lithium consumed during the cycle process. At the same time, the lithium supplement layer is arranged between the negative electrode current collector and the negative electrode material layer, which can improve the lithium precipitation on the surface of the negative electrode plate, reduce the side reaction between the electrolyte and the negative electrode active material, and can also reduce the generation of lithium dendrites on the surface of the negative electrode plate, reduce the risk of the diaphragm being pierced and causing the secondary battery to short-circuit, and improve the safety of the secondary battery. Therefore, the pre-lithiated negative electrode plate prepared by the preparation method provided by the present application is applied to the secondary battery, which can improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, improve the energy density of the secondary battery, and also improve the safety performance of the secondary battery.

[0036] In the present application, the material of the lithium alloy foil may include but is not limited to at least one of lithium aluminum alloy, lithium silicon alloy, lithium magnesium alloy, lithium tin alloy or lithium nickel alloy, and the lithium alloy in the lithium alloy molten slurry may include but is not limited to at least one of lithium aluminum alloy, lithium silicon alloy, lithium magnesium alloy, lithium tin alloy or lithium nickel alloy.

[0037] In some embodiments of the present application, the roller pressure P1 of rolling in step (1) is 0.1T / 10mm to 2T / 10mm. Specifically, the roller pressure P11 of rolling after applying the lithium metal powder slurry to the negative electrode current collector is 0.1T / 10mm to 2T / 10mm; the roller pressure P12 of rolling the lithium foil and / or lithium alloy foil to the negative electrode current collector is 0.1T / 10mm to 2T / 10mm; the roller pressure P13 of rolling after applying the lithium or lithium alloy molten slurry to the negative electrode current collector is 0.1T / 10mm to 2T / 10mm. Exemplarily, P1 may be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range consisting of any two of the above values. P11 may be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range consisting of any two of the above values. P12 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range consisting of any two of the above values. P13 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range consisting of any two of the above values. By regulating the roller pressure P1 within the above range, a lithium replenishment layer can be formed on the surface of the negative electrode current collector. The thickness and surface smoothness of the lithium replenishment layer can also be adjusted by regulating the roller pressure P1, so that the lithium replenishment layer has a suitable thickness and good surface smoothness, which is beneficial to realize the lithium replenishment of the negative electrode material layer and make it have a higher lithium replenishment amount, thereby facilitating the improvement of the first coulombic efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0038] In some embodiments, the water content in the negative electrode material layer after drying in step (2) is ≤500 ppm.

[0039] In some embodiments, in step (3), the negative electrode material layer and the support layer are placed on the surface of the lithium supplement layer, wherein the surface of the negative electrode material layer away from the support layer is in contact with the lithium supplement layer. Figure 1 As shown, the lithium replenishing layer 120 is arranged on the two surfaces of the negative electrode current collector 110, and the negative electrode material layer 130 and the support layer 200 are respectively placed on the surfaces of the two layers of lithium replenishing layer 120, wherein the surface of the negative electrode material layer 130 away from the support layer 200 is attached to the lithium replenishing layer 120. It can be understood that the above-mentioned negative electrode material layer 130 refers to the negative electrode material layer of the negative electrode sheet that has not been pre-lithiated.

[0040] In some embodiments of the present application, the roller pressure P2 of the rolling in step (3) is 1.0T / 10mm to 2.0T / 10mm. Exemplarily, P2 can be 1.0T / 10mm, 1.1T / 10mm, 1.2T / 10mm, 1.3T / 10mm, 1.4T / 10mm, 1.5T / 10mm, 1.6T / 10mm, 1.7T / 10mm, 1.8T / 10mm, 1.9T / 10mm, 2T / 10mm or a range consisting of any two of the above values. By regulating the value of the roller pressure P2 within the above range, the negative electrode material layer can be completely peeled off from the support layer and tightly adhered to the lithium replenishment layer, which is conducive to realizing the lithium replenishment of the negative electrode material layer and making the negative electrode material layer have a higher compaction density, thereby facilitating the improvement of the first coulomb efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0041] In some embodiments, in step (3), the time for the surface of the negative electrode material layer away from the support layer to be attached to the lithium supplement layer is 0.5h to 72h, and the attachment temperature is 25°C to 180°C. Exemplarily, the time for the surface of the negative electrode material layer away from the support layer to be attached to the lithium supplement layer can be 0.5h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 72h, or a range consisting of any two of the above values, and the attachment temperature can be 25°C, 40°C, 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, or a range consisting of any two of the above values.

[0042] In some embodiments, the support layer includes at least one of a metal foil, a polyethylene terephthalate (PET) film, a polypropylene (PP) film, or a polyethylene (PE) film, and the metal foil includes a copper foil, a nickel foil, a steel foil, or a copper-nickel alloy foil. The above-mentioned support layer material is selected to better support the negative electrode material layer, improve the mechanical strength of the negative electrode material layer, so that it can be completely peeled off from the support layer relatively smoothly, which is beneficial to the preparation of the pre-lithiation negative electrode sheet, thereby facilitating the improvement of the first coulomb efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery. The present application does not have any particular restrictions on the thickness of the support layer, as long as the purpose of the present application can be achieved. For example, the thickness of the support layer can be 3μm to 50μm, preferably, the thickness of the support layer can be 5μm to 20μm.

[0043] The present application has no particular restrictions on the environmental parameters in the process of preparing the pre-lithiation negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the environmental parameters of step (1) can be temperature ≤ 30°C and humidity ≤ 1.7%, the environmental parameters of coating the negative electrode slurry in step (2) can be temperature ≤ 30°C and humidity ≤ 55%, the environmental parameters of drying the negative electrode material layer can be temperature ≤ 30°C and humidity ≤ 1.7%, and the environmental parameters of step (3) can be temperature ≤ 30°C and humidity ≤ 1.7%.

[0044] The second aspect of the present application provides a pre-lithiated negative electrode sheet prepared by the preparation method in any of the aforementioned embodiments, the negative electrode sheet comprising a negative electrode current collector, a lithium replenishing layer and a negative electrode material layer, the lithium replenishing layer being arranged between the negative electrode current collector and the negative electrode material layer, and along the thickness direction of the negative electrode sheet, the negative electrode material layer comprising a first surface and a second surface relative to each other; from the first surface to the second surface, the negative electrode material layer sequentially comprises a first region, a second region and a third region, and the first region is located on the surface of the lithium replenishing layer; 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 content of the lithium element in the first region is W1, based on the mass of the second region, the mass percentage content of the lithium element in the second region is W2, based on the mass of the third region, the mass percentage content of the lithium element in the third region is W3, W1>W2>W3, 1.01≤W1 / W2≤2.0, 1.01≤W2 / W3≤2.0. Illustratively, 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 consisting of any two of the above values; 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 consisting of any two of the above values.

[0045] The inventors of the present application have discovered through research that, under the same conditions, different negative electrode active materials have different lithium replenishment efficiencies, silicon-containing materials replenish relatively less lithium, and carbon materials replenish relatively more lithium. Therefore, different types of negative electrode active materials have different lithium replenishment amounts, and the resulting pre-lithiated negative electrode sheets have different lithium replenishment amounts. The present application designs the structure of the negative electrode sheet, arranges the lithium replenishing layer between the negative electrode current collector and the negative electrode material layer, and regulates the relationship between W1, W2, and W3 as well as the values ​​of W1 / W2 and W2 / W3 within the scope of the present application. The lithium replenishing layer and the negative electrode material layer can form an internal short circuit, and the lithium atoms in the lithium replenishing layer undergo an oxidation reaction to lose electrons to generate lithium ions. The electrons and lithium ions are transferred to the interior of the negative electrode material layer, and then the electrons and lithium ions undergo a reduction reaction in the negative electrode material layer to form a lithium intercalation compound, thereby realizing pre-lithiation of the negative electrode sheet, replenishing the active lithium lost due to the formation of the SEI film during the first charge and discharge process, and continuously generating lithium ions during the cycle process to replenish the active lithium consumed during the cycle process. In addition, the lithium content in the negative electrode material layer gradually decreases in the direction away from the negative electrode current collector, which can improve lithium precipitation on the surface of the negative electrode sheet, reduce the side reaction between the electrolyte and the negative electrode active material, and reduce the generation of lithium dendrites on the surface of the negative electrode sheet, thereby reducing the risk of short circuit of the secondary battery and improving the safety of the secondary battery.

[0046] When the values ​​of W1 / W2 and W2 / W3 are too small, for example, less than 1.01, the negative electrode plate is not provided with a lithium replenishment layer (no lithium replenishment) or lithium replenishment is performed on the surface of the negative electrode material layer away from the negative electrode current collector. If the negative electrode plate is not provided with a lithium replenishment layer (no lithium replenishment), the consumption of active lithium during the first charge and discharge process and the cycle process cannot be replenished; if lithium replenishment is performed on the surface of the negative electrode material layer away from the negative electrode current collector, the risk of lithium precipitation on the surface of the negative electrode plate increases, the probability of lithium dendrites increases, and it is easy to pierce the diaphragm to cause the secondary battery to short-circuit, and the safety performance deteriorates, thereby affecting the first coulomb efficiency, cycle performance and energy density of the secondary battery. When the values ​​of W1 / W2 and W2 / W3 are too large, for example greater than 2, the negative electrode plate is over-supplemented with lithium, resulting in increased resistance or inability to embed lithium ions released from the positive electrode material layer into the negative electrode plate when the secondary battery is charged. The risk of lithium precipitation on the surface of the negative electrode plate increases, and the probability of lithium dendrites increases, which can easily pierce the diaphragm and cause the secondary battery to short-circuit, deteriorate safety performance, and affect the cycle performance of the secondary battery.

[0047] Therefore, applying the pre-lithiated negative electrode plate of the present application to a secondary battery can improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, increase the energy density of the secondary battery, and also improve the safety performance of the secondary battery.

[0048] In the present application, the pre-lithiated negative electrode plate includes a negative electrode current collector, a lithium replenishing layer arranged on at least one surface of the negative electrode current collector, and a negative electrode material layer arranged on the lithium replenishing layer away from the surface of the negative electrode current collector. The above-mentioned "lithium replenishing layer arranged on at least one surface of the negative electrode current collector" means that the lithium replenishing layer can be arranged on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. This application has no special restrictions as long as the purpose of this application can be achieved. Similarly, the negative electrode material layer can be arranged in the entire area of ​​the lithium replenishing layer or in a partial area of ​​the lithium replenishing layer.

[0049] In some embodiments, such as Figure 2 As shown, the pre-lithiated negative electrode sheet 100 includes a negative electrode current collector 110 and a lithium supplement layer 120 and a negative electrode material layer 130 stacked on the two surfaces of the negative electrode current collector 110 in sequence, and the lithium supplement layer 120 is arranged between the negative electrode current collector 110 and the negative electrode material layer 130. Along the thickness direction of the negative electrode sheet 100, that is, the Y direction, the negative electrode material layer 130 includes a first surface 1311 and a second surface 1332 opposite to each other. From the first surface 1311 to the second surface 1332, the negative electrode material layer 130 includes a first region 131, a second region 132 and a third region 133 in sequence, and the first region 131 is located on the surface of the lithium supplement layer 120. The thickness of the first region 131 accounts for 1 / 3 of the thickness of the negative electrode material layer 130, the thickness of the second region 132 accounts for 1 / 3 of the thickness of the negative electrode material layer 130, and the thickness of the third region 133 accounts for 1 / 3 of the thickness of the negative electrode material layer 130. In other embodiments, the pre-lithiated negative electrode plate includes a negative electrode current collector and a lithium supplement layer and a negative electrode material layer sequentially stacked on one surface of the negative electrode current collector, and the lithium supplement layer is disposed between the negative electrode current collector and the negative electrode material layer.

[0050] In some embodiments, the lithium supplement layer includes at least one of lithium foil or lithium alloy foil. The present application does not particularly limit the type of lithium alloy foil, as long as the purpose of the present application can be achieved. For example, the material of the lithium alloy foil may include but is not limited to at least one of lithium aluminum alloy, lithium silicon alloy, lithium magnesium alloy, lithium tin alloy or lithium nickel alloy.

[0051] In some embodiments of the present application, the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes at least one of a carbon material or a silicon-containing material, the carbon material includes at least one of a graphite material or hard carbon, and the silicon-containing material includes at least one of a silicon-carbon material or a silicon-oxygen material. In the present application, the graphite material includes at least one of artificial graphite or natural graphite; the silicon-carbon material is a composite material of silicon and carbon, and the mass percentage of the silicon element w based on the mass of the silicon-carbon material SiThe mass percentage of carbon is 30% to 70%. C 30% to 70%; silicon oxide materials include silicon dioxide (SiO x (0<x≤2)). The negative electrode active material includes the above substances, the negative electrode plate has a higher lithium supplement amount, and the prepared secondary battery has a higher first coulomb efficiency, lower cycle capacity attenuation and higher energy density.

[0052] In the present application, the negative electrode active material includes a carbon material and a silicon-containing substance. Based on the mass of the negative electrode active material, the mass percentage of the silicon-containing substance is W Si The mass percentage content Wc of the carbon material is 5% to 100%, and the mass percentage content Wc of the carbon material is 0 to 95%. Si The mass percentage Wc of the carbon material may be 0%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% or a range consisting of any two of the above values.

[0053] In some embodiments of the present application, the negative electrode active material only includes silicon-containing substances. Based on the mass of the negative electrode material layer, the mass percentage of silicon element in the negative electrode material layer is w1, 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%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 63.5%, or a range consisting of any two of the above values; W1 can be 11.5%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 18.4%, or a range consisting of any two of the above values; W2 can be 9.2%, 9.5%, 9.8%, 10%, 10.2%, 10.5%, 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%, 9.1%, or a range consisting of any two of the above values. The negative electrode active material only includes silicon-containing substances, and the values ​​of w1, W1, W2, and W3 are regulated within the above range. The theoretical specific capacity of the silicon-containing substance is high, which is beneficial to improving the energy density of the secondary battery, and is also beneficial to making the negative electrode plate have a higher lithium supplement amount, and the lithium supplement amount has little effect on the lithium ion embedding process in the positive electrode plate. Applying the above pre-lithiated negative electrode plate to the secondary battery can further improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, improve the energy density of the secondary battery, and further improve the safety performance of the secondary battery.

[0054] In some embodiments of the present application, the negative electrode active material includes a carbon material and a silicon-containing substance. Based on the mass of the negative electrode material layer, the mass percentage of silicon element in the negative electrode material layer is w1, 1.1%≤w1≤3.4%, 0.38%≤W1≤0.60%, 0.30%≤W2<0.38%, 0.15%≤W3<0.30%. Exemplarily, w1 can be 1.1%, 1.3%, 1.5%, 1.8%, 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, 3.2%, 3.4% or a range consisting of any two of the above values; W1 can be 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.52%, 0.55%, 0.58%, 0.60% or a range consisting of any two of the above values. The range of any two values; W2 can be 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37% or a range of any two of the above values; W3 can be 0.15%, 0.18%, 0.20%, 0.22%, 0.24%, 0.26%, 0.28%, 0.29% or a range of any two of the above values. Under the same treatment conditions, different negative electrode active materials have different lithium replenishment efficiencies, the amount of lithium replenishment of silicon-containing substances is relatively small, and the amount of lithium replenishment of carbon materials is relatively large. The negative electrode active material includes carbon materials and silicon-containing substances, and the values ​​of w1, W1, W2, and W3 are adjusted within the above range, the carbon materials and silicon-containing substances have appropriate mass percentages, and the negative electrode active material has a higher lithium replenishment amount, so that the pre-lithiated negative electrode plate has a higher lithium replenishment amount, and the lithium replenishment amount has little effect on the lithium ion insertion process in the positive electrode plate. Applying the above-mentioned pre-lithiated negative electrode plate to a secondary battery can further improve the initial coulombic efficiency of the secondary battery, reduce the cycle capacity decay, and improve the energy density of the secondary battery.

[0055] In some embodiments of the present application, the negative electrode active material includes a carbon material and a silicon-containing substance. Based on the mass of the negative electrode material layer, the mass percentage of the silicon element in the negative electrode material layer is w1, 3.3%≤w1≤10.2%, 2.8%≤W1≤4.5%, 2.2%≤W2<2.8%, and 1.1%≤W3<2.2%. Exemplarily, w1 can be 3.3%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10.2% or a range consisting of any two of the above values; W1 can be 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.5% or a range consisting of any two of the above values; W2 can be 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7% or a range consisting of 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%, 2.0%, 2.1% or a range consisting of any two of the above values. Under the same treatment conditions, different negative electrode active materials have different lithium replenishment efficiencies, silicon-containing materials have relatively less lithium replenishment, and carbon materials have relatively more lithium replenishment. The negative electrode active materials include carbon materials and silicon-containing materials, and the values ​​of w1, W1, W2, and W3 are regulated within the above ranges. The carbon materials and silicon-containing materials have appropriate mass percentages, and the negative electrode active materials have a higher lithium replenishment amount, so that the pre-lithiated negative electrode plate has a higher lithium replenishment amount, and the lithium replenishment amount has little effect on the lithium ion embedding process in the positive electrode plate. Applying the above-mentioned pre-lithiated negative electrode plate to a secondary battery can further improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0056] The present application has no particular restrictions on the method of regulating the mass percentage w1 of the silicon element in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the mass percentage w1 of the silicon element in the negative electrode material layer can be regulated by regulating the mass percentage of the silicon-containing substance in the negative electrode material layer and the mass percentage of the silicon element in the silicon-containing substance. Normally, when other conditions remain unchanged, the mass percentage of the silicon-containing substance in the negative electrode material layer increases, and w1 increases; the mass percentage of the silicon-containing substance in the negative electrode material layer decreases, and w1 decreases. When other conditions remain unchanged, the mass percentage of the silicon element in the silicon-containing substance increases, and w1 increases; the mass percentage of the silicon element in the silicon-containing substance decreases, and w1 decreases.

[0057] The present application has no particular restrictions on the manner of regulating the mass percentage W1, W2, and W3 of the lithium element in the first region, the second region, and the third region in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the mass percentage W1, W2, and W3 of the lithium element in the first region, the second region, and the third region can be regulated by regulating the bonding time and the temperature during bonding between the negative electrode material layer and the lithium supplement layer. Normally, when other conditions remain unchanged, the bonding time increases, and W1, W2, and W3 increase; the bonding time decreases, and W1, W2, and W3 decrease. When other conditions remain unchanged, the temperature during bonding increases, and W1, W2, and W3 increase; the temperature during bonding decreases, and W1, W2, and W3 decrease.

[0058] The present application has no particular restrictions on the method of regulating W1 / W2 and W2 / W3, as long as the purpose of the present application can be achieved. For example, the value of W1 / W2 can be regulated by regulating the values ​​of W1 and W2, and the method for regulating W1 and W2 is as described above. The value of W2 / W3 can be regulated by regulating the values ​​of W2 and W3, and the method for regulating W2 and W3 is as described above.

[0059] In some embodiments of the present application, based on the mass of the lithium replenishing layer, the mass percentage of lithium in the lithium replenishing layer is 97% to 100%. Exemplarily, the mass percentage of lithium in the lithium replenishing layer can be 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 100% or a range consisting of any two of the above values. By regulating the mass percentage of lithium in the lithium replenishing layer within the above range, more lithium ions can be provided to the negative electrode material layer, achieving a better lithium replenishment effect, replenishing the active lithium lost due to the formation of the SEI film during the first charge and discharge process, and continuously generating lithium ions during the cycle process to replenish the active lithium consumed during the cycle process, thereby helping to improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0060] In the present application, the lithium supplement layer may further include other elements, which may include but are not limited to at least one of aluminum, silicon, magnesium, tin or nickel. Based on the mass of the lithium supplement layer, the mass percentage of other elements in the lithium supplement layer is 0% to 3%.

[0061] In some embodiments of the present application, the thickness of the lithium replenishment layer is 1 μm to 30 μm. Exemplarily, the thickness of the lithium replenishment layer can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm or a range consisting of any two of the above values. By regulating the thickness of the lithium replenishment layer within the above range, the lithium replenishment layer can meet the lithium replenishment demand and achieve a better lithium replenishment effect. It can also reduce the preparation cost of the lithium replenishment layer and reduce the impact of the increase in the thickness of the lithium replenishment layer on the volume energy density of the secondary battery, thereby helping to improve the first coulomb efficiency of the secondary battery, reduce the cycle capacity attenuation, and improve the energy density of the secondary battery.

[0062] The present application does not particularly limit the method of regulating the thickness of the lithium replenishing layer, as long as the purpose of the present application can be achieved. For example, the thickness of the lithium replenishing layer can be regulated by regulating the roller pressure P1 when preparing the lithium replenishing layer. Generally, when other conditions remain unchanged, the roller pressure P1 increases, and the thickness of the lithium replenishing layer decreases; the roller pressure P1 decreases, and the thickness of the lithium replenishing layer increases. For example, the thickness of the lithium replenishing layer can be regulated by selecting different lithium replenishing layer preparation methods. The preparation method of the lithium replenishing layer usually affects the minimum thickness of the lithium replenishing layer. Specifically, the minimum thickness of the lithium replenishing layer prepared by coating with lithium or lithium alloy molten slurry is usually smaller, and the minimum thickness of the lithium replenishing layer prepared by coating with lithium metal powder slurry is usually larger.

[0063] In some embodiments of the present application, the thickness of the negative electrode material layer is 16 μm to 72 μm. Exemplarily, the thickness of the negative electrode material layer can be 16 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 70 μm, 72 μm or a range consisting of any two of the above values. By regulating the thickness of the negative electrode material layer within the above range, lithium ions are more easily diffused from the lithium replenishment layer to the surface of the negative electrode material layer, which is conducive to achieving a better lithium replenishment effect, increasing the amount of lithium replenishment of the negative electrode plate, and the kinetic performance of the negative electrode plate is excellent, which is conducive to improving the first coulomb efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0064] The present application does not particularly limit the method of regulating 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 negative electrode material layer can be regulated by regulating the single-sided coating surface density and the roller pressure P2 of the negative electrode material layer. Under normal circumstances, when other conditions remain unchanged, the single-sided coating surface density of the negative electrode material layer increases, and the thickness of the negative electrode material layer increases; the single-sided coating surface density of the negative electrode material layer decreases, and the thickness of the negative electrode material layer decreases. When other conditions remain unchanged, the roller pressure P2 increases, and the thickness of the negative electrode material layer decreases; the roller pressure P2 decreases, and the thickness of the negative electrode material layer increases.

[0065] In some embodiments of the present application, the bonding force between the lithium replenishment layer and the negative electrode current collector is 10N / m to 50N / m. Exemplarily, the bonding force between the lithium replenishment layer and the negative electrode current collector can be 10N / m, 15N / m, 20N / m, 25N / m, 30N / m, 35N / m, 40N / m, 45N / m, 50N / m or a range consisting of any two of the above values. By regulating the bonding force between the lithium replenishment layer and the negative electrode current collector within the above range, the lithium replenishment layer can be tightly combined with the negative electrode current collector, reducing the risk of the lithium replenishment layer peeling off from the negative electrode current collector. Applying the above-mentioned pre-lithiated negative electrode plate to a secondary battery is beneficial to improving the first coulomb efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0066] In some embodiments of the present application, the bonding force between the negative electrode material layer and the lithium replenishment layer is 5N / m to 10N / m. Exemplarily, the bonding force between the negative electrode material layer and the lithium replenishment layer can be 5N / m, 6N / m, 7N / m, 8N / m, 9N / m, 10N / m or a range consisting of any two of the above values. By regulating the bonding force between the negative electrode material layer and the lithium replenishment layer within the above range, the negative electrode material layer is not easily peeled off from the lithium replenishment layer, which is beneficial to the transfer of lithium ions in the lithium replenishment layer to the negative electrode material layer, thereby achieving a better lithium replenishment effect. Applying the above-mentioned pre-lithiated negative electrode plate to a secondary battery is beneficial to improving the first coulombic efficiency of the secondary battery, reducing the cycle capacity attenuation, and improving the energy density of the secondary battery.

[0067] In the present application, the negative electrode material layer also includes a negative electrode binder and a negative electrode conductor. The present application does not particularly limit the type of negative electrode binder, as long as the purpose of the present application can be achieved, for example, the negative electrode binder may include but is not limited to 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. At least one of the negative electrode conductors is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the negative electrode conductor may include but is not limited to conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers, and specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions 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. Those skilled in the art may select according to actual needs as long as the purpose of the present application can be achieved.

[0068] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or composite current collector (such as lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). The present application has no particular restrictions 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 can be 4μm to 20μm.

[0069] The third aspect of the present application provides a secondary battery, which includes the pre-lithiated negative electrode plate in any of the above embodiments. Therefore, the secondary battery of the present application has a higher first coulombic efficiency, lower cycle capacity decay and higher energy density.

[0070] In the present application, the secondary battery also includes a positive electrode plate. The positive electrode plate includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its own thickness direction, or on two surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or a partial area of ​​the positive current collector. This application is not particularly limited as long as the purpose of this application can be achieved.

[0071] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0072] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance that can reversibly embed and extract active ions such as lithium ions. The positive electrode material layer can be one layer or more layers, and each layer in the multi-layer positive electrode material layer can contain the same or different positive electrode active materials. The present application has no special restrictions 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 may include but is not limited to lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. At least one of the above-mentioned lithium nickel cobalt manganese oxide may include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95),LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of O2 (NCM111). The positive electrode material layer of the present application also includes a positive electrode conductor and a positive electrode binder. The present application has no special restrictions on the positive electrode conductor 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 conductor in the positive electrode material layer may include at least one of the above-mentioned negative electrode conductors; the positive electrode binder in the positive electrode material layer may include at least one of the above-mentioned negative electrode binders. The present application has no special restrictions on the mass ratio of the positive electrode active material, the positive electrode conductor, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0073] The present application has no 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 can be 6 μm to 25 μm. The present application has no 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 can be 25 μm to 250 μm.

[0074] In the present application, the secondary battery also includes an electrolyte. The electrolyte includes a lithium salt. The present application has no particular restrictions on the type of lithium salt, and lithium salts known in the art can be used. For example, the lithium salt may include but is not limited to lithium hexafluorophosphate (LiPF6), lithium bistrifluoromethanesulfonyl imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalate borate) (LiB(C2O4)2, LiBOB) or lithium difluorooxalate borate (LiBF2(C2O4), LiDFOB). The present application has no particular restrictions on the mass percentage of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The electrolyte also includes a non-aqueous organic solvent. The present application has no particular restrictions on the non-aqueous organic solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous organic solvent may contain at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a linear carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may 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 ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate compound may 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 above-mentioned fluorinated carbonate compound may include but is not limited to fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate or propyl propionate. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include, but are 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-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphate ester.The present application has no particular limitation on the mass percentage of the non-aqueous organic solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0075] In the present application, the secondary battery also includes a diaphragm. The diaphragm is used to separate the positive electrode plate and the pre-lithiated negative electrode plate, prevent the internal short circuit of the secondary battery, allow the electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0076] In the present application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a diaphragm binder, and the present application has no particular restrictions on the above-mentioned inorganic particles, for example, it may 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 has no particular restrictions on the above-mentioned diaphragm binder, for example, it may be at least one of the aforementioned negative electrode binders. The polymer layer contains polymers, and the polymer material may include but is not limited to at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.

[0077] The secondary battery of the present application also includes a packaging bag for containing a positive electrode plate, a separator, a pre-lithiated negative electrode plate and an electrolyte, as well as other components known in the art in the secondary battery, and the present application does not limit the above other components. The present application does not specifically limit the packaging bag, and it can be a packaging bag known in the art, as long as it can achieve the purpose of the present application.

[0078] The present application does not particularly limit the type of secondary battery, which may include any device that undergoes an electrochemical reaction. In the present application, the secondary battery may 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), etc.

[0079] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application has no special restrictions. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator, the pre-lithiated negative electrode sheet, and the separator in order, and winding, folding, and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator, the pre-lithiated negative electrode sheet, and the separator in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly of a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, guide plates, etc. may also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0080] The fourth aspect of the present application provides an electronic device, which comprises the secondary battery in any of the above embodiments. The electronic device of the present application has a long service life and good performance.

[0081] The present application does not particularly limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0082] Example

[0083] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0084] Test methods and equipment:

[0085] Test on the mass percentage of lithium in the first, second and third regions

[0086] Take the pre-lithiated negative electrode sheet, and use a blade to scrape the negative electrode material layer materials at the surface 1 / 3 thickness away from the lithium replenishing layer, the middle 1 / 3 thickness, and the bottom 1 / 3 thickness close to the lithium replenishing layer along the thickness direction of the negative electrode sheet to obtain the negative electrode material layer powders in the third region, the second region, and the first region.

[0087] The mass percentage of lithium element in the negative electrode material layer powder of the first region, the second region and the third region was detected by inductively coupled plasma-optical emission spectrometry (ICP-OES). The ICP-OES used was a PE7000DV spectrometer produced by PerkinElmer, USA. The test conditions of ICP-OES were: radio frequency (RF) of 40.68 MHz, RF power of 1300 W, argon secondary pressure of 0.6 MPa, auxiliary gas flow of 0.2 L / min, cooling gas flow of 15 L / min, and pump speed of 1.5 mL / min.

[0088] Test of the mass percentage of silicon in the negative electrode material layer:

[0089] Take the pre-lithiated negative electrode plate, scrape the negative electrode material layer above the lithium supplement layer with a blade, and obtain the negative electrode material layer powder. The mass percentage of silicon in the negative electrode material layer is detected by inductively coupled plasma-optical emission spectrometry (ICP-OES). The ICP-OES used is a PE7000DV spectrometer produced by PerkinElmer, USA. The test conditions of ICP-OES are: radio frequency (RF) is 40.68MHz, radio frequency power is 1300W, argon secondary pressure is 0.6MPa, auxiliary gas flow rate is 0.2L / min, cooling gas flow rate is 15L / min, and pump speed is 1.5mL / min.

[0090] Test of the mass percentage of lithium in the lithium supplement layer

[0091] Take the pre-lithiated negative electrode plate, scrape off all the negative electrode material layers above the lithium replenishment layer with a blade, and obtain a negative electrode current collector provided with a lithium replenishment layer. The mass percentage of lithium element in the lithium replenishment layer is detected by inductively coupled plasma-optical emission spectrometry (ICP-OES). The ICP-OES used is a PE7000DV spectrometer produced by PerkinElmer, USA. The test conditions of ICP-OES are: radio frequency (RF) is 40.68MHz, radio frequency power is 1300W, argon secondary pressure is 0.6MPa, auxiliary gas flow rate is 0.2L / min, cooling gas flow rate is 15L / min, and pump speed is 1.5mL / min.

[0092] Thickness test

[0093] The pre-lithiated negative electrode sheet was taken, and the cross section of the negative electrode sheet along the thickness direction was polished with argon ions. Then, the cross section of the negative electrode sheet was observed using a scanning electron microscope (SEM) to test the thickness of the lithium supplement layer and the negative electrode material layer.

[0094] Adhesion test

[0095] Take the negative electrode current collector with a lithium replenishing layer on one side in the preparation process of the pre-lithiated negative electrode sheet (step (1)), and cut it into test strips with a width of 16 mm and a length of 150 mm. Cut the double-sided tape (length 60 mm to 70 mm) and stick it on the steel plate. Use a blade to cut it 50 mm from the top of the steel plate, and peel off the double-sided tape. Cover the test strip completely with the double-sided tape surface, with the lithium replenishing layer bonded to the double-sided tape downward. Insert a paper tape with a width equal to that of the negative electrode current collector and a length of 80 mm to 100 mm under the negative electrode current collector, fix it with tape, and mark the group. Use a 2kg roller to roll back and forth three times for testing. Use a tensile testing machine (tensile testing machine model: instron 3365) for testing. Fold the paper tape upward 180°, clamp the end of the steel plate without the sample on the fixed fixture of the tensile testing machine, and connect the other end of the paper tape to the movable fixture. The fixture is moved at a constant speed (50 mm / min) until the lithium supplement layer is peeled off from the negative electrode current collector and the test is ended. The force required during the peeling process is recorded. The bonding force between the lithium supplement layer and the negative electrode current collector is calculated based on the force-displacement curve provided by the tensile machine.

[0096] Take the pre-lithiated negative electrode sheet obtained in step (3) of the pre-lithiated negative electrode sheet preparation process, and cut it into test strips with a width of 16 mm and a length of 150 mm. Cut the double-sided tape (length 60 mm to 70 mm) and stick it on the steel plate. Use a blade to cut it 50 mm from the top of the steel plate, and peel off the double-sided tape. Cover the test strip completely with the double-sided tape surface, with the negative electrode material layer bonded to the double-sided tape downward. Insert a paper tape with a width equal to the width of the negative electrode material layer and a length of 80 mm to 100 mm under the negative electrode current collector, and fix it with tape, and mark the group. Use a 2kg roller to roll back and forth three times for testing. Use a tensile testing machine (tensile testing machine model: instron 3365) for testing. Fold the paper tape upward 180°, clamp the end of the steel plate without the sample on the fixed fixture of the tensile testing machine, and connect the other end of the paper tape to the movable fixture. The fixture is moved at a constant speed (50 mm / min) until the lithium supplement layer and the negative electrode material layer are peeled off and the test is ended. The force required during the peeling process is recorded. The bonding force between the negative electrode material layer and the lithium supplement layer is calculated based on the force-displacement curve provided by the tensile machine.

[0097] First coulombic efficiency test

[0098] The voltage range is based on the voltage range marked on the outer packaging of the lithium-ion battery. For example, when the voltage range marked on the lithium-ion battery is 3.0V to 4.45V, the charge cut-off voltage is 4.45V and the discharge cut-off voltage is 3.0V.

[0099] The specific test steps are: charge the lithium-ion battery at 0.2C constant current at 25°C to a cut-off voltage of 4.45V, then charge at 4.45V constant voltage until the current is less than 0.05C, let it stand for 5 minutes, and then discharge it at 0.2C constant current to a cut-off voltage of 3.0V. 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 coulomb efficiency of the lithium-ion battery is calculated according to the following formula: First coulomb efficiency (%) = C1 / C0×100%.

[0100] Cyclic performance test

[0101] The voltage range is based on the voltage range marked on the outer packaging of the lithium-ion battery. For example, when the voltage range marked on the lithium-ion battery is 3.0V to 4.45V, the charge cut-off voltage is 4.45V and the discharge cut-off voltage is 3.0V.

[0102] The specific test steps are as follows: at 25°C, the lithium-ion battery is charged and discharged for the first time, charged at a constant current of 0.2C to a cut-off voltage of 4.45V, then charged at a constant voltage of 4.45V until the current is less than 0.05C, and after standing for 5 minutes, discharged at a constant current of 0.2C to a cut-off voltage of 3.0V, and the discharge capacity of the lithium-ion battery is measured to be A. Then, 400 charging and discharging cycles are performed according to the above steps in an environment of 25°C, and the discharge capacity of the lithium-ion battery at the 400th time is measured to be B. The cycle capacity retention rate of the lithium-ion battery is calculated according to the following formula: Cycle capacity retention rate (%) = B / A × 100%. The larger the value of the cycle capacity retention rate obtained by the test, the better the cycle performance of the lithium-ion battery and the smaller the cycle capacity attenuation.

[0103] Energy density test

[0104] The voltage range is based on the voltage range marked on the outer packaging of the lithium-ion battery. For example, when the voltage range marked on the lithium-ion battery is 3.0V to 4.45V, the charge cut-off voltage is 4.45V and the discharge cut-off voltage is 3.0V.

[0105] The specific test steps are: at 25℃, charge the lithium-ion battery at a constant current of 0.2C to a cut-off voltage of 4.45V, then charge at a constant voltage of 4.45V until the current is less than 0.05C, let it stand for 5 minutes, then discharge at a constant current of 0.2C to a cut-off voltage of 3.0V, and let it stand for 5 minutes. The energy of the above discharge process is recorded as the discharge energy E. Calculate the volume V (mm) of the lithium-ion battery 3) = length × width × height. The energy density of lithium-ion batteries is calculated according to the following formula: Energy density (Wh / L) = E / V × 10 6 .

[0106] Example 1-1

[0107] <Preparation of pre-lithiated negative electrode sheet>

[0108] (1) Under the conditions of ambient temperature of 25°C and humidity of 1.0%, lithium foil was rolled into a negative electrode current collector copper foil with a thickness of 12 μm to form a lithium supplement layer. The roller pressure P1, the mass percentage of lithium element in the lithium supplement layer, and the thickness of the lithium supplement layer are shown in Table 2. The remaining element in the lithium supplement layer is aluminum element.

[0109] (2) After mixing 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 lithium carboxymethyl cellulose in a mass ratio of 85:5:5:5, deionized water was added as a solvent, and the mixture was stirred 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 support layer copper foil with a thickness of 12μm, pre-dried at 90°C for 30min, and then vacuum dried at 90°C for 12h to form a negative electrode material layer (water content <500ppm).

[0110] (3) At 25°C, place the negative electrode material layer and the support layer on the surface of the lithium replenishment layer, wherein the surface of the negative electrode material layer away from the support layer is in contact with the lithium replenishment layer. After rolling, the support layer and the negative electrode material layer are peeled off, and the rolling pressure P2 is shown in Table 2, to obtain a negative electrode sheet with a lithium replenishment layer and a negative electrode material layer on one side of the negative electrode collector. Repeat the above steps on the other surface of the negative electrode collector copper foil to obtain a negative electrode sheet with a lithium replenishment layer and a negative electrode material layer on both sides of the negative electrode collector. Then, after cutting and slitting, a pre-lithiated negative electrode sheet with a specification of 80mm×1000mm is obtained. Among them, the single-sided coating surface density of the negative electrode material layer is 2.3mg / cm 2 The single-sided thickness of the negative electrode material layer is shown in Table 2; the mass percentage content w1 of the silicon element in the negative electrode material layer, the mass percentage content W1 of the lithium element in the first region, the mass percentage content W2 of the lithium element in the second region, and the mass percentage content W3 of the lithium element in the third region are shown in Table 1.

[0111] <Preparation of positive electrode sheet>

[0112] The positive electrode active material lithium cobalt oxide (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, and N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred and mixed to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry is 75wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12μm, and dried at 110°C 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. Dry under vacuum conditions at 110°C for 1h, and then after cold pressing, cutting, and slitting, a positive electrode sheet with a specification of 77mm×995mm is obtained. Among them, the single-sided coating surface density of the positive electrode material layer is 19.0mg / cm 2 The compaction density of the cold pressing process is 4.15g / cm 3 .

[0113] <Preparation of Electrolyte>

[0114] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP) were mixed at a weight ratio of 3:1:3:3 to obtain a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 12.5%, and the remainder was the base solvent.

[0115] <Preparation of Separator>

[0116] A porous polypropylene film with a thickness of 5 μm (provided by Celgard Company) was used as a separator.

[0117] <Preparation of lithium-ion batteries>

[0118] The prepared positive electrode sheet, separator, pre-lithiated negative electrode sheet and separator are stacked in order, so that the separator is placed between the positive electrode sheet and the pre-lithiated negative electrode sheet to play an isolating role, and the electrode assembly is wound. After welding the pole ear, the electrode assembly is placed in an aluminum plastic film packaging bag, placed in an 85°C vacuum oven for 12 hours to remove moisture, and the electrolyte is injected. After vacuum packaging, standing, formation (charging to 3.5V at a constant current of 0.02C, and then charging to 3.9V at a constant current of 0.1C), degassing, trimming, and capacity processing steps, a lithium-ion battery is obtained.

[0119] Example 1-2 to Example 1-5

[0120] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. In Examples 1-2 and 1-3, when the mass percentage of the negative electrode active material in the negative electrode material layer changes, the sum of the mass percentages of the negative electrode conductive agent and the negative electrode binder changes accordingly, and the mass ratio of the negative electrode conductive agent to the negative electrode binder remains unchanged.

[0121] Examples 1-6

[0122] In addition to the negative electrode active material in the preparation of the pre-lithiation negative electrode plate using silicon-containing silicon-carbon material and carbon material artificial graphite, the mass percentage of the negative electrode active material in the negative electrode material layer is adjusted as shown in Table 1, and the mass percentage of the silicon-containing material based on the mass of the negative electrode active material W Si The mass percentage content Wc of the carbon material and the mass percentage content Wc of the negative electrode conductive agent and the negative electrode binder in the negative electrode material layer change accordingly. Except that the mass ratio of the negative electrode conductive agent and the negative electrode binder remains unchanged, the rest is the same as Example 1-1.

[0123] Example 1-7 to Example 1-11

[0124] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-6. When the mass percentage of the negative electrode active material changes, the sum of the mass percentages of the negative electrode conductive agent and the negative electrode binder changes accordingly, and the mass ratio of the negative electrode conductive agent to the negative electrode binder remains unchanged.

[0125] Examples 1-12

[0126] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0127] Example 2-1 to Example 2-12

[0128] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1. In Examples 2-11 and 2-12, the thickness of the negative electrode material layer is regulated by regulating the single-sided coating surface density of the negative electrode material layer.

[0129] Comparative Example 1

[0130] Except that the following preparation method is used for <Preparation of pre-lithiated negative electrode sheet>, the rest is the same as Example 1-1.

[0131] <Preparation of negative electrode sheet>

[0132] 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 lithium carboxymethyl cellulose are mixed in a mass ratio of 85:5:5:5, and deionized water is added as a solvent, and the mixture is stirred and mixed to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry is 28wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12μm, and dried at 90°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. Repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. Dry under vacuum conditions at 90°C for 12h, and then after cold pressing, cutting, and slitting, a negative electrode sheet with a specification of 80mm×1000mm is obtained. Among them, the single-sided coating surface density of the negative electrode material layer is 2.3mg / cm 2 The single-sided thickness of the negative electrode material layer is 23 μm.

[0133] Comparative Example 2

[0134] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. Among them, the mass percentage of lithium element in the first region is adjusted to W1, the mass percentage of lithium element in the second region is adjusted to W2, and the mass percentage of lithium element in the third region is adjusted to W3 by adjusting the standing time after the negative electrode material layer and the lithium supplement layer are laminated.

[0135] Comparative Example 3

[0136] In addition to the negative electrode active material using silicon-containing silicon-carbon material and carbon material artificial graphite as shown in Table 1 in <Preparation of Negative Electrode Sheet>, based on the mass of the negative electrode active material, the mass percentage content of the silicon-containing material W Si The mass percentage content Wc of the carbon material is as shown in Table 1. Except that the mass percentage content of the negative electrode conductive agent and the negative electrode binder in the negative electrode material layer remains unchanged, the rest is the same as Comparative Example 1.

[0137] Comparative Example 4

[0138] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-7. Among them, the mass percentage of lithium element in the first region is adjusted to W1, the mass percentage of lithium element in the second region is adjusted to W2, and the mass percentage of lithium element in the third region is adjusted to W3 by adjusting the standing time after the negative electrode material layer and the lithium supplement layer are laminated.

[0139] Comparative Example 5

[0140] In addition to the negative electrode active material using silicon-containing silicon-carbon material and carbon material artificial graphite as shown in Table 1 in <Preparation of Negative Electrode Sheet>, based on the mass of the negative electrode active material, the mass percentage content of the silicon-containing material W SiThe mass percentage content Wc of the carbon material is as shown in Table 1. Except that the mass percentage content of the negative electrode conductive agent and the negative electrode binder in the negative electrode material layer remains unchanged, the rest is the same as Comparative Example 1.

[0141] Comparative Example 6

[0142] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-10. Among them, the mass percentage of lithium element in the first region is adjusted to W1, the mass percentage of lithium element in the second region is adjusted to W2, and the mass percentage of lithium element in the third region is adjusted to W3 by adjusting the standing time after the negative electrode material layer and the lithium supplement layer are laminated.

[0143] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0144]

[0145] From Examples 1-1 to 1-12 and Comparative Examples 1 to 6, it can be seen that the lithium-ion battery has a higher first coulombic efficiency, cycle capacity retention rate and energy density when the preparation method provided by the present application is used to prepare the pre-lithiated negative electrode sheet and applied to the lithium-ion battery, indicating that the present application can improve the first coulombic efficiency of the lithium-ion battery, reduce the cycle capacity decay, and improve the energy density. However, the negative electrode sheets of Comparative Examples 1, 3, and 5 are not pre-lithiated by the preparation method of the present application, and the first coulombic efficiency, cycle capacity retention rate and energy density of the lithium-ion battery are lower; the W1 / W2 and W2 / W3 of the pre-lithiated negative electrode sheets of Comparative Examples 2, 4, and 6 are not within the scope of the present application, and the cycle capacity retention rate of the lithium-ion battery is lower. The lithium-ion batteries of Comparative Examples 1 to 6 cannot have a higher first coulombic efficiency, cycle capacity retention rate and energy density at the same time, indicating that they cannot simultaneously improve the first coulombic efficiency of the lithium-ion battery, reduce the cycle capacity decay, and improve the energy density.

[0146] The values ​​of w1, W1, W2, and W3 usually affect the first coulombic efficiency, cycle capacity retention rate, and energy density of the lithium-ion battery. From Examples 1-1 to 1-11, it can be seen that when the values ​​of w1, W1, W2, and W3 are within the range of this application, the lithium-ion battery has a higher first coulombic efficiency, cycle capacity retention rate, and energy density, indicating that this application can improve the first coulombic efficiency of the lithium-ion battery, reduce the cycle capacity attenuation, and improve the energy density.

[0147] The type of negative electrode active material usually affects the initial coulombic efficiency, cycle capacity retention rate and energy density of lithium-ion batteries. It can be seen from Examples 1-1 and 1-12 that the lithium-ion battery has a higher initial coulombic efficiency, cycle capacity retention rate and energy density when the negative electrode active material of the present application is selected, indicating that the present application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity attenuation, and improve energy density.

[0148] Table 2

[0149]

[0150]

[0151] Roller pressure P1 usually affects the first coulombic efficiency, cycle capacity retention rate and energy density of lithium-ion batteries. It can be seen from Examples 1-1, 2-1 to 2-4 that when the roller pressure P1 is within the range of this application, the bonding force between the lithium replenishment layer and the negative electrode current collector and the bonding force between the negative electrode material layer and the lithium replenishment layer are large, and the prepared lithium-ion battery has a high first coulombic efficiency, cycle capacity retention rate and energy density, indicating that this application can improve the first coulombic efficiency of lithium-ion batteries, reduce cycle capacity attenuation, and improve energy density.

[0152] Roller pressure P2 usually affects the first coulombic efficiency, cycle capacity retention rate and energy density of lithium-ion batteries. It can be seen from Examples 1-1, 2-5 to 2-8 that when the roller pressure P2 is within the range of this application, the bonding force between the lithium replenishing layer and the negative electrode current collector and the bonding force between the negative electrode material layer and the lithium replenishing layer are large, and the prepared lithium-ion battery has a high first coulombic efficiency, cycle capacity retention rate and energy density, indicating that this application can improve the first coulombic efficiency of lithium-ion batteries, reduce cycle capacity attenuation, and improve energy density.

[0153] The mass percentage of lithium in the lithium replenishment layer usually affects the initial coulombic efficiency, cycle capacity retention rate and energy density of the lithium-ion battery. It can be seen from Examples 1-1, 2-9 and 2-10 that when the mass percentage of lithium in the lithium replenishment layer is within the scope of the present application, the bonding force between the lithium replenishment layer and the negative electrode current collector and the bonding force between the negative electrode material layer and the lithium replenishment layer are large, and the prepared lithium-ion battery has a high initial coulombic efficiency, cycle capacity retention rate and energy density, indicating that the present application can improve the initial coulombic efficiency of the lithium-ion battery, reduce the cycle capacity attenuation, and improve the energy density.

[0154] The thickness of the lithium replenishment layer usually affects the first coulombic efficiency, cycle capacity retention rate and energy density of the lithium-ion battery. It can be seen from Examples 1-1, 2-1 to 2-4 that when the thickness of the lithium replenishment layer is within the range of this application, the bonding force between the lithium replenishment layer and the negative electrode current collector and the bonding force between the negative electrode material layer and the lithium replenishment layer are large, and the prepared lithium-ion battery has a high first coulombic efficiency, cycle capacity retention rate and energy density, indicating that the present application can improve the first coulombic efficiency of the lithium-ion battery, reduce the cycle capacity attenuation, and improve the energy density.

[0155] The thickness of the negative electrode material layer usually affects the first coulombic efficiency, cycle capacity retention rate and energy density of the lithium-ion battery. It can be seen from Examples 1-1, 2-11 and 2-12 that when the thickness of the negative electrode material layer is within the range of this application, the bonding force between the lithium replenishing layer and the negative electrode current collector and the bonding force between the negative electrode material layer and the lithium replenishing layer are large, and the prepared lithium-ion battery has a high first coulombic efficiency, cycle capacity retention rate and energy density, indicating that the present application can improve the first coulombic efficiency of the lithium-ion battery, reduce the cycle capacity attenuation, and improve the energy density.

[0156] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method or article.

[0157] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0158] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a pre-lithiated negative electrode sheet, comprising the following steps: (1) applying a lithium metal powder slurry to the negative electrode current collector, drying it, and rolling it to form a lithium replenishing layer; or rolling a lithium foil and / or a lithium alloy foil to the negative electrode current collector to form a lithium replenishing layer; or applying a lithium or lithium alloy molten slurry to the negative electrode current collector, cooling it, and rolling it to form a lithium replenishing layer; (2) coating a negative electrode slurry including a negative electrode active material on the surface of the support layer and drying the negative electrode slurry to form a negative electrode material layer; (3) placing the negative electrode material layer and the support layer on the surface of the lithium replenishing layer, wherein the surface of the negative electrode material layer away from the support layer is in contact with the lithium replenishing layer, and after rolling, the support layer and the negative electrode material layer are peeled off to form a pre-lithiated negative electrode sheet.

2. The preparation method according to claim 1, wherein The roller pressure P1 of the rolling in the step (1) is 0.1T / 10mm to 2T / 10mm; the roller pressure P2 of the rolling in the step (3) is 1.0T / 10mm to 2.0T / 10mm.

3. A pre-lithiated negative electrode sheet prepared by the preparation method according to claim 1 or 2, the negative electrode sheet comprising a negative electrode current collector, a lithium replenishing layer and a negative electrode material layer, the lithium replenishing layer is arranged between the negative electrode current collector and the negative electrode material layer, and along the thickness direction of the negative electrode sheet, the negative electrode material layer comprises a first surface and a second surface opposite to each other; From the first surface to the second surface, the negative electrode material layer includes a first region, a second region and a third region in sequence, and the first region is located on the surface of the lithium supplement layer; 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 in the first region is W1, based on the mass of the second region, the mass percentage of lithium element in the second region is W2, based on the mass of the third region, the mass percentage of lithium element in the third region is W3, W1>W2>W3, 1.01≤W1 / W2≤2.0, 1.01≤W2 / W3≤2.

0.

4. The pre-lithiated negative electrode sheet according to claim 3, wherein: The negative electrode material layer includes a negative electrode active material, the negative electrode active material includes at least one of a carbon material or a silicon-containing material, the carbon material includes at least one of a graphite material or hard carbon, and the silicon-containing material includes at least one of a silicon-carbon material or a silicon-oxygen material.

5. The pre-lithiated negative electrode sheet according to claim 4, wherein: The pre-lithiated negative electrode plate satisfies any one of the following characteristics: (1) The negative electrode active material only includes silicon-containing substances. Based on the mass of the negative electrode material layer, the mass percentage of silicon element in the negative electrode material layer is w1, 18.6%≤w1≤63.5%, 11.5%≤W1≤18.4%, 9.2%≤W2<11.5%, 4.6%≤W3<9.2%; (2) The negative electrode active material includes a carbon material and a silicon-containing substance. Based on the mass of the negative electrode material layer, the mass percentage of silicon in the negative electrode material layer is w1, 1.1%≤w1≤3.4%, 0.38%≤W1≤0.60%, 0.30%≤W2<0.38%, 0.15%≤W3<0.30%; (3) The negative electrode active material includes a carbon material and a silicon-containing substance. Based on the mass of the negative electrode material layer, the mass percentage of silicon element in the negative electrode material layer is w1, 3.3%≤w1≤10.2%, 2.8%≤W1≤4.5%, 2.2%≤W2<2.8%, and 1.1%≤W3<2.2%.

6. The pre-lithiated negative electrode sheet according to claim 3, wherein: Based on the mass of the lithium replenishing layer, the mass percentage of lithium element in the lithium replenishing layer is 97% to 100%.

7. The pre-lithiated negative electrode sheet according to claim 3, wherein: The thickness of the lithium supplement layer is 1 μm to 30 μm, and the thickness of the negative electrode material layer is 16 μm to 72 μm.

8. The pre-lithiated negative electrode sheet according to claim 3, wherein: The bonding force between the lithium replenishing layer and the negative electrode current collector is 10 N / m to 50 N / m, and the bonding force between the negative electrode material layer and the lithium replenishing layer is 5 N / m to 10 N / m. 9 . A secondary battery, comprising a pre-lithiated negative electrode sheet prepared by the preparation method according to claim 1 or 2 or a pre-lithiated negative electrode sheet according to any one of claims 3 to 8. 10 . An electronic device comprising the secondary battery according to claim 9 .

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