A pre-lithiated negative electrode sheet and preparation method thereof, secondary battery and electronic device

Abstract

This application provides a pre-lithiated negative electrode sheet, its preparation method, a secondary battery, and an electronic device. The pre-lithiated negative electrode sheet includes a negative electrode current collector, a negative electrode material layer, and a lithium replenishment layer disposed between the negative electrode current collector and the negative electrode material layer. Along the thickness direction of the negative electrode sheet, the negative electrode material layer sequentially includes a first region, a second region, and a third region. The first region is located on the surface of the lithium replenishment layer, and the thicknesses of the first, second, and third regions are each 1 / 3 of the thickness of the negative electrode material layer. Based on the mass of the first region, the mass percentage of lithium is W1; based on the mass of the second region, the mass percentage of lithium is W2; and based on the mass of the third region, the mass percentage of lithium is W3, where W1 > W2 > W3, 1.01 ≤ W1 / W2 ≤ 2.0, and 1.01 ≤ W2 / W3 ≤ 2.0. This application can improve the initial coulombic efficiency and energy density of the secondary battery and reduce cycle capacity decay.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a pre-lithiated negative electrode sheet and its preparation method, a secondary battery, and an electronic device. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, have advantages such as 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 are constantly increasing.

[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 puncture the separator, causing short circuits and safety problems, and affecting its cycle performance.

[0004] Currently, graphite, the commonly used negative electrode active material for lithium-ion batteries, can no longer meet the energy density requirements. Although silicon-carbon and silicon-oxygen negative electrode active materials have high theoretical specific capacities and are ideal materials to replace graphite and improve the energy density of lithium-ion batteries, they have not been widely used due to their low initial coulombic efficiency and poor cycle life. Existing methods to improve the initial coulombic efficiency and reduce capacity cycle decay of lithium-ion batteries containing silicon-carbon or silicon-oxygen negative electrode active materials involve pre-replenishing the negative electrode with lithium to compensate for the irreversible capacity consumed during the first charge, discharge, and cycle, thereby improving the initial coulombic efficiency of lithium-ion batteries containing silicon-carbon or silicon-oxygen negative electrode active materials and thus increasing the energy density of lithium-ion batteries.

[0005] Existing lithium replenishment methods for negative electrode sheets mainly include lithium powder replenishment, lithium strip replenishment, and electrochemical replenishment. However, these three methods all have certain problems in terms of environmental control, replenishment uniformity, and post-replenishment side reactions. Therefore, there is an urgent need to provide a pre-lithiated negative electrode sheet to improve the initial coulombic efficiency of lithium-ion batteries containing silicon-carbon or silicon-oxygen negative electrode active materials, reduce cycle capacity decay, and increase the energy density of lithium-ion batteries. Summary of the Invention

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

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

[0008] (1) Apply lithium metal powder slurry to the negative electrode current collector and dry and roll it to form a lithium replenishment layer; or roll lithium foil and / or lithium alloy foil to the negative electrode current collector to form a lithium replenishment layer; or apply lithium or lithium alloy molten slurry to the negative electrode current collector and cool and roll it to form a lithium replenishment layer.

[0009] (2) A negative electrode slurry including a negative electrode active material is coated on the surface of the support layer and dried to form a negative electrode material layer;

[0010] (3) The negative electrode material layer and the support layer are placed on the surface of the lithium replenishment layer, wherein the surface of the negative electrode material layer away from the support layer is bonded to the lithium replenishment layer. After rolling, the support layer and the negative electrode material layer are peeled off to form a pre-lithiated negative electrode sheet.

[0011] The pre-lithiated negative electrode sheet prepared using the method provided in this application can achieve pre-lithiation of the negative electrode material layer, replenishing the active lithium lost during the first charge-discharge process due to the formation of the solid electrolyte interphase (SEI) film and the active lithium consumed during cycling. This improves lithium plating on the surface of the negative electrode sheet, reduces side reactions between the electrolyte and the negative electrode active material, and also reduces the formation of lithium dendrites on the surface of the negative electrode sheet, thereby improving the safety of the secondary battery. Therefore, applying the above-mentioned pre-lithiated negative electrode sheet to a secondary battery can improve the initial coulombic efficiency, reduce cycle capacity decay, increase the energy density of the secondary battery, and also improve the safety performance of the secondary battery.

[0012] In some embodiments of this application, the rolling pressure P1 in step (1) is 0.1T / 10mm to 2T / 10mm; the rolling pressure P2 in step (3) is 1.0T / 10mm to 2.0T / 10mm. By adjusting the values ​​of rolling pressure P1 and P2 within the above ranges, a lithium replenishment layer and a negative electrode material layer can be formed on the surface of the negative electrode current collector. Applying the prepared pre-lithiated negative electrode sheet to a secondary battery is beneficial to improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery.

[0013] The second aspect of this application provides a pre-lithiated negative electrode sheet prepared according to the preparation method of any of the foregoing embodiments. The negative electrode sheet includes a negative current collector, a lithium replenishment layer, and a negative electrode material layer. The lithium replenishment layer is disposed between the negative current collector and the negative electrode material layer. Along the thickness direction of the negative electrode sheet, the negative electrode material layer includes opposing first and second surfaces. From the first surface to the second surface, the negative electrode material layer sequentially includes a first region, a second region, and a third region. The first region is located on the surface of the lithium replenishment 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 in the first region is W1; based on the mass of the second region, the mass percentage of lithium in the second region is W2; based on the mass of the third region, the mass percentage of lithium in the third region is W3, where W1 > W2 > W3, 1.01 ≤ W1 / W2 ≤ 2.0, and 1.01 ≤ W2 / W3 ≤ 2.0.

[0014] This application designs the negative electrode structure by placing a lithium replenishment layer between the negative electrode current collector and the negative electrode material layer. By controlling the relationships between W1, W2, and W3, and the values ​​of W1 / W2 and W2 / W3 within the range specified in this application, it can replenish the active lithium lost during the initial charge-discharge process due to SEI film formation, as well as the active lithium consumed during cycling. This improves lithium plating on the negative electrode surface, reduces side reactions between the electrolyte and the negative electrode active material, and also reduces the formation of lithium dendrites on the negative electrode surface, lowering the risk of short circuits in the secondary battery. Therefore, applying the pre-lithiated negative electrode of this application to secondary batteries can improve the initial coulombic efficiency, reduce cycle capacity decay, increase the energy density of the secondary battery, and also improve the safety performance of the secondary battery.

[0015] In some embodiments of this application, the negative electrode material layer includes a negative electrode active material, which 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-mentioned substances, and the negative electrode sheet has a high lithium replenishment capacity. The prepared secondary battery has a high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0016] In some embodiments of this application, the pre-lithiated negative electrode sheet satisfies any of the following characteristics: (1) the negative electrode active material consists only of silicon-containing material, and based on the mass of the negative electrode material layer, the mass percentage of silicon 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 material, and based on the mass of the negative electrode material layer, the mass percentage of silicon 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 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 materials and silicon-containing materials. Based on the mass of the negative electrode material layer, the mass percentage of silicon 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-lithiated negative electrode sheet that meets the above characteristics can be applied to secondary batteries to improve the first coulombic efficiency of secondary batteries, reduce cycle capacity decay, and improve the energy density of secondary batteries.

[0017] In some embodiments of this application, the mass percentage of lithium in the lithium replenishment layer is 97% to 100%, depending on the mass of the lithium replenishment layer. By controlling the mass percentage of lithium in the lithium replenishment layer within the above range, more lithium ions can be provided to the negative electrode material layer, achieving a better lithium replenishment effect. This is beneficial for improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery.

[0018] In some embodiments of this application, the thickness of the lithium replenishment layer is from 1 μm to 30 μm, and the thickness of the negative electrode material layer is from 16 μm to 72 μm. By adjusting the thicknesses of the lithium replenishment layer and the negative electrode material layer within the above ranges, it is beneficial to achieve better lithium replenishment effect, increase the lithium replenishment amount of the negative electrode sheet, thereby improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery.

[0019] In some embodiments of this application, the adhesion force between the lithium replenishment layer and the negative electrode current collector is 10 N / m to 50 N / m, and the adhesion force between the negative electrode material layer and the lithium replenishment layer is 5 N / m to 10 N / m. By adjusting the adhesion force between the lithium replenishment layer and the negative electrode current collector, and the adhesion force between the negative electrode material layer and the lithium replenishment layer, within the above ranges, the adhesion between the negative electrode current collector, the lithium replenishment layer, and the negative electrode material layer is good. Applying the above-mentioned pre-lithiated negative electrode sheet to a secondary battery is beneficial to improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery.

[0020] A third aspect of this application provides a secondary battery comprising a pre-lithiated negative electrode as described in any of the foregoing embodiments. Therefore, the secondary battery of this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0021] A fourth aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. The electronic device of this application has a long service life and good performance.

[0022] The beneficial effects of this application are:

[0023] This application provides a pre-lithiated negative electrode sheet, its preparation method, a secondary battery, and an electronic device. The negative electrode sheet prepared using the method described in this application achieves pre-lithiation, replenishing the active lithium lost during the initial charge-discharge process due to SEI film formation. It also continuously generates lithium ions during cycling to replenish the active lithium consumed during cycling. Furthermore, the lithium content in the negative electrode material layer gradually decreases in the direction away from the negative electrode current collector, improving lithium plating on the negative electrode surface, reducing side reactions between the electrolyte and the negative electrode active material, and reducing the formation of lithium dendrites on the negative electrode surface, thus lowering the risk of short circuits in the secondary battery and improving its safety. Therefore, applying the pre-lithiated negative electrode sheet of this application to a secondary battery can improve the initial coulombic efficiency, reduce cycle capacity decay, increase the energy density of the secondary battery, and also improve its safety performance.

[0024] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0026] Figure 1 This is a schematic diagram of the pre-lithiation negative electrode preparation process according to one embodiment of this application;

[0027] Figure 2 This is a schematic diagram of the pre-lithiated negative electrode sheet along its thickness direction, representing one embodiment of this application.

[0028] Reference numerals: pre-lithiated negative electrode 100, negative electrode current collector 110, lithium replenishment 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 Implementation

[0029] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0030] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

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

[0032] (1) Apply lithium metal powder slurry to the negative electrode current collector and dry and roll it to form a lithium replenishment layer; or roll lithium foil and / or lithium alloy foil to the negative electrode current collector to form a lithium replenishment layer; or apply lithium or lithium alloy molten slurry to the negative electrode current collector and cool and roll it to form a lithium replenishment layer.

[0033] (2) A negative electrode slurry including a negative electrode active material is coated on the surface of the support layer and dried to form a negative electrode material layer;

[0034] (3) The negative electrode material layer and the support layer are placed on the surface of the lithium replenishment layer, wherein the surface of the negative electrode material layer away from the support layer is bonded to the lithium replenishment layer. After rolling, the support layer and the negative electrode material layer are peeled off to form a pre-lithiated negative electrode sheet.

[0035] The pre-lithiated negative electrode sheet prepared using the method provided in this application involves first forming the negative electrode material layer on the support layer and then transferring it to the surface of the lithium replenishment layer. This reduces the risk of exothermic reaction and the generation of flammable gases from the solvent in the slurry between the lithium replenishment layer and the negative electrode material layer, thus improving the safety of the preparation process. The prepared pre-lithiated negative electrode sheet includes a negative electrode current collector, a lithium replenishment layer, and a negative electrode material layer. The lithium replenishment layer and the negative electrode material layer can form an internal short circuit. Lithium atoms in the lithium replenishment layer undergo an oxidation reaction, losing electrons to generate lithium ions. Electrons and lithium ions are transported to the interior of the negative electrode material layer, where they undergo a reduction reaction to form a lithium intercalation compound, thus achieving pre-lithiation of the negative electrode material layer. This replenishes the active lithium lost during the first charge and discharge process due to the formation of the solid electrolyte interphase (SEI) film. Furthermore, it can continuously generate lithium ions during cycling to replenish the active lithium consumed during cycling. Meanwhile, the lithium replenishment layer, positioned between the negative electrode current collector and the negative electrode material layer, can improve lithium plating on the surface of the negative electrode sheet, reduce side reactions between the electrolyte and the negative electrode active material, and also reduce the formation of lithium dendrites on the surface of the negative electrode sheet, lowering the risk of short circuits in the secondary battery due to separator puncture, thus improving the safety of the secondary battery. Therefore, the pre-lithiated negative electrode sheet prepared using the method provided in this application, when applied 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.

[0036] In this 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 this application, the rolling pressure P1 in step (1) is 0.1T / 10mm to 2T / 10mm. Specifically, the rolling pressure P11 after coating the lithium metal powder slurry onto the negative electrode current collector is 0.1T / 10mm to 2T / 10mm; the rolling pressure P12 after rolling the lithium foil and / or lithium alloy foil onto the negative electrode current collector is 0.1T / 10mm to 2T / 10mm; and the rolling pressure P13 after coating the lithium or lithium alloy molten slurry onto the negative electrode current collector is 0.1T / 10mm to 2T / 10mm. For example, P1 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range consisting of any two of the above values. P11 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range consisting of any two of the above values. P12 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range of any two of the above values. P13 can be 0.1T / 10mm, 0.2T / 10mm, 0.4T / 10mm, 0.6T / 10mm, 0.8T / 10mm, 1T / 10mm, 1.2T / 10mm, 1.4T / 10mm, 1.6T / 10mm, 1.8T / 10mm, 2T / 10mm, or a range of any two of the above values. By adjusting the value of 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 flatness of the lithium replenishment layer can also be adjusted by adjusting the value of the roller pressure P1, so that the lithium replenishment layer has a suitable thickness and good surface flatness, which is conducive to the lithium replenishment of the negative electrode material layer, so that it has a higher lithium replenishment amount, thereby improving the first coulombic efficiency of the secondary battery, reducing cycle capacity decay, and improving the energy density of the secondary battery.

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

[0039] In some implementations, in step (3), the negative electrode material layer and the support layer are placed on the surface of the lithium replenishment layer, wherein the surface of the negative electrode material layer away from the support layer is bonded to the lithium replenishment layer. For example, as shown... Figure 1 As shown, the lithium replenishment layer 120 is disposed on two surfaces of the negative electrode current collector 110. The negative electrode material layer 130 and the support layer 200 are respectively placed on the surfaces of the two lithium replenishment layers 120, wherein the surface of the negative electrode material layer 130 away from the support layer 200 is in contact with the lithium replenishment layer 120. It can be understood that the aforementioned negative electrode material layer 130 refers to the negative electrode material layer of the negative electrode sheet that has not undergone pre-lithiation.

[0040] In some embodiments of this application, the rolling pressure P2 in step (3) is from 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 adjusting the value of the rolling pressure P2 within the above range, the negative electrode material layer can be completely peeled from the support layer and tightly bonded to the lithium replenishment layer. This facilitates lithium replenishment of the negative electrode material layer and gives it a higher compaction density, thereby improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery.

[0041] In some implementations, the bonding time between the surface of the negative electrode material layer away from the support layer and the lithium replenishment layer in step (3) is 0.5h to 72h, and the bonding temperature is 25°C to 180°C. For example, the bonding time between the surface of the negative electrode material layer away from the support layer and the lithium replenishment layer can be 0.5h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 72h, or any combination of two of the above values, and the bonding temperature can be 25°C, 40°C, 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, or any combination of two of the above values.

[0042] In some embodiments, the support layer includes at least one selected from metal foil, polyethylene terephthalate (PET) film, polypropylene (PP) film, or polyethylene (PE) film, wherein the metal foil includes copper foil, nickel foil, steel foil, or copper-nickel alloy foil. Using the above-mentioned support layer material can better support the negative electrode material layer, improve the mechanical strength of the negative electrode material layer, and allow it to be easily and completely peeled off from the support layer. This is beneficial for the preparation of pre-lithiated negative electrode sheets, thereby improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery. This application does not impose any particular limitation on the thickness of the support layer, as long as it achieves the purpose of this application. For example, the thickness of the support layer can be from 3 μm to 50 μm, preferably from 5 μm to 20 μm.

[0043] This application does not impose any particular restrictions on the environmental parameters during the preparation of the pre-lithiated negative electrode sheet, as long as the purpose of this application can be achieved. For example, the environmental parameters for step (1) can be temperature ≤30℃ and humidity ≤1.7%, the environmental parameters for step (2) coating the negative electrode slurry can be temperature ≤30℃ and humidity ≤55%, the environmental parameters for drying the negative electrode material layer can be temperature ≤30℃ and humidity ≤1.7%, and the environmental parameters for step (3) can be temperature ≤30℃ and humidity ≤1.7%.

[0044] The second aspect of this application provides a pre-lithiated negative electrode sheet prepared according to the preparation method of any of the foregoing embodiments. The negative electrode sheet includes a negative current collector, a lithium replenishment layer, and a negative electrode material layer. The lithium replenishment layer is disposed between the negative current collector and the negative electrode material layer. Along the thickness direction of the negative electrode sheet, the negative electrode material layer includes opposing first and second surfaces. From the first surface to the second surface, the negative electrode material layer sequentially includes a first region, a second region, and a third region. The first region is located on the surface of the lithium replenishment 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 in the first region is W1; based on the mass of the second region, the mass percentage of lithium in the second region is W2; based on the mass of the third region, the mass percentage of lithium in the third region is W3, where W1 > W2 > W3, 1.01 ≤ W1 / W2 ≤ 2.0, and 1.01 ≤ W2 / W3 ≤ 2.0. For example, 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 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 of any two of the above values.

[0045] The inventors of this application have discovered through research that, under the same conditions, different negative electrode active materials have different lithium replenishment efficiencies. Silicon-containing materials have relatively low lithium replenishment, while carbon materials have relatively high lithium replenishment. Therefore, different types of negative electrode active materials result in different lithium replenishment amounts, leading to different lithium replenishment amounts in the pre-lithiated negative electrode sheets. This application designs the negative electrode structure by placing a lithium replenishment layer between the negative electrode current collector and the negative electrode material layer. By controlling the relationships between W1, W2, and W3, as well as the values ​​of W1 / W2 and W2 / W3, within the scope of this application, an internal short circuit can be formed between the lithium replenishment layer and the negative electrode material layer. Lithium atoms in the lithium replenishment layer undergo oxidation, losing electrons to generate lithium ions. Electrons and lithium ions are transferred to the interior of the negative electrode material layer, where they undergo reduction to form a lithium intercalation compound, achieving pre-lithiation of the negative electrode. This replenishes the active lithium lost during the first charge-discharge process due to the formation of the SEI film. Furthermore, lithium ions are continuously generated during cycling to replenish the active lithium consumed during cycling. Moreover, the lithium content in the negative electrode material layer gradually decreases in the direction away from the negative electrode current collector, improving lithium plating on the negative electrode surface, reducing side reactions between the electrolyte and the negative electrode active material, reducing the formation of lithium dendrites on the negative electrode surface, lowering the risk of short circuits in 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, it indicates that the negative electrode sheet does not have a lithium replenishment layer (no lithium replenishment is performed) 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 sheet does not have a lithium replenishment layer (no lithium replenishment is performed), it cannot replenish the active lithium consumed during the first charge-discharge process and during cycling. 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 plating on the surface of the negative electrode sheet increases, the probability of lithium dendrite formation increases, and it is easy to puncture the separator, causing a short circuit in the secondary battery, deteriorating the safety performance, and thus affecting the initial coulombic efficiency, cycle performance, and energy density of the secondary battery. When the values ​​of W1 / W2 and W2 / W3 are too large, such as greater than 2, the negative electrode is over-compensated with lithium. This increases the resistance when lithium ions extracted from the positive electrode material layer are inserted into the negative electrode during the charging of the secondary battery, or they cannot be inserted into the negative electrode at all. This increases the risk of lithium deposition on the surface of the negative electrode, increases the probability of lithium dendrite formation, and makes it easier to puncture the separator, causing a short circuit in the secondary battery, resulting in poor safety performance and affecting the cycle performance of the secondary battery.

[0047] Therefore, applying the pre-lithiated negative electrode sheet of this 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 this application, the pre-lithiated negative electrode includes a negative electrode current collector, a lithium replenishment layer disposed on at least one surface of the negative electrode current collector, and a negative electrode material layer disposed on the lithium replenishment layer away from the surface of the negative electrode current collector. The aforementioned "lithium replenishment layer disposed on at least one surface of the negative electrode current collector" means that the lithium replenishment layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a portion thereof; this application has no particular limitation, as long as the purpose of this application is achieved. Similarly, the negative electrode material layer can be disposed on the entire area of ​​the lithium replenishment layer or only a portion thereof.

[0049] In some implementation schemes, such as Figure 2 As shown, the pre-lithiated negative electrode 100 includes a negative electrode current collector 110 and a lithium replenishment layer 120 and a negative electrode material layer 130 sequentially stacked on the two surfaces of the negative electrode current collector 110. The lithium replenishment layer 120 is disposed between the negative electrode current collector 110 and the negative electrode material layer 130. Along the thickness direction of the negative electrode 100, i.e., 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 sequentially includes a first region 131, a second region 132, and a third region 133. The first region 131 is located on the surface of the lithium replenishment 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 includes a negative current collector and a lithium replenishment layer and a negative electrode material layer sequentially stacked on one surface of the negative current collector, with the lithium replenishment layer disposed between the negative current collector and the negative electrode material layer.

[0050] In some embodiments, the lithium replenishment layer includes at least one of lithium foil or lithium alloy foil. This application does not particularly limit the type of lithium alloy foil, as long as it achieves the purpose of this application. 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 this application, the negative electrode material layer includes a negative electrode active material, which 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 this 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 silicon element w is based on the mass of the silicon-carbon material. SiThe mass percentage of carbon element is 30% to 70%. C The content ranges from 30% to 70%; silicon-oxygen materials include silicon suboxide (SiO2). x (0<x≤2)). The negative electrode active material includes the above-mentioned substances. The negative electrode sheet has a high lithium replenishment capacity, and the prepared secondary battery has a high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0052] In this application, the negative electrode active material includes carbon materials and silicon-containing substances, and the mass percentage W of the silicon-containing substances is based on the mass of the negative electrode active material. Si The carbon content (Wc) of the carbon material ranges from 5% to 100% by mass, and from 0% to 95% by mass. For example, the silicon content (Wc) of the silicon-containing material... Si The percentage of carbon material by mass, Wc, can be 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or any range of two of the above values; the percentage of carbon material by mass, Wc, can be 0%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, 90%, 95%, or any range of two of the above values.

[0053] In some embodiments of this application, the negative electrode active material comprises only silicon-containing material. Based on the mass of the negative electrode material layer, the mass percentage of silicon in the negative electrode material layer is w1, 18.6%≤w1≤63.5%, 11.5%≤W1≤18.4%, 9.2%≤W2<11.5%, and 4.6%≤W3<9.2%. For example, w1 can be 18.6%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 63.5%, or a range of any two of the above values; W1 can be 11.5%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 18.4%, or a range 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 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 of any two of the above values. The negative electrode active material consists only of silicon-containing substances, and the values ​​of w1, W1, W2, and W3 are controlled within the aforementioned range. Silicon-containing substances have a high theoretical specific capacity, which is beneficial for improving the energy density of the secondary battery. They also contribute to a higher lithium replenishment capacity of the negative electrode, with minimal impact on the lithium-ion intercalation process in the positive electrode. Applying the aforementioned pre-lithiated negative electrode to secondary batteries can further improve the initial coulombic efficiency, reduce cycle capacity decay, increase the energy density, and further enhance the safety performance of the secondary battery.

[0054] In some embodiments of this application, the negative electrode active material includes carbon materials and silicon-containing substances. Based on the mass of the negative electrode material layer, the mass percentage of silicon in the negative electrode material layer is w1, where 1.1% ≤ w1 ≤ 3.4%, 0.38% ≤ W1 ≤ 0.60%, 0.30% ≤ W2 < 0.38%, and 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 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 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 any range of any two values ​​above; W3 can be 0.15%, 0.18%, 0.20%, 0.22%, 0.24%, 0.26%, 0.28%, 0.29%, or any range of any two values ​​above. Under the same processing conditions, the lithium replenishment efficiency of different negative electrode active materials is different. Silicon-containing materials have relatively less lithium replenishment, while carbon materials have relatively more. The negative electrode active materials include carbon materials and silicon-containing materials. By controlling the values ​​of w1, W1, W2, and W3 within the above ranges, and having appropriate mass percentages of carbon materials and silicon-containing materials, the negative electrode active materials have a higher lithium replenishment, thus giving the pre-lithiated negative electrode a higher lithium replenishment, and the lithium replenishment has little impact on the lithium ion insertion process in the positive electrode. Applying the aforementioned pre-lithiated negative electrode to a secondary battery can further improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0055] In some embodiments of this application, the negative electrode active material includes carbon materials and silicon-containing substances. Based on the mass of the negative electrode material layer, the mass percentage of silicon 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%. For example, w1 can be 3.3%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10.2%, or a range 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 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 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 of any two of the above values. Under the same processing conditions, different negative electrode active materials exhibit varying lithium replenishment efficiencies. Silicon-containing materials provide relatively less lithium replenishment, while carbon materials provide relatively more. The negative electrode active materials include both carbon and silicon-containing materials. By controlling the values ​​of w1, W2, and W3 within the aforementioned ranges and ensuring appropriate mass percentages of both carbon and silicon materials, the negative electrode active materials achieve higher lithium replenishment. This results in a pre-lithiated negative electrode sheet with a higher lithium replenishment capacity, and the lithium replenishment capacity has minimal impact on the lithium-ion intercalation process in the positive electrode sheet. Applying the aforementioned pre-lithiated negative electrode sheet to secondary batteries can further improve the initial coulombic efficiency, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0056] This application does not impose any particular restrictions on the method of controlling the mass percentage content w1 of silicon in the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the mass percentage content w1 of silicon in the negative electrode material layer can be controlled by adjusting the mass percentage content of the silicon-containing material and the mass percentage content of silicon element in the silicon-containing material. Generally, when other conditions remain unchanged, an increase in the mass percentage content of the silicon-containing material in the negative electrode material layer increases w1; a decrease in the mass percentage content of the silicon-containing material in the negative electrode material layer decreases w1. When other conditions remain unchanged, an increase in the mass percentage content of silicon element in the silicon-containing material increases w1; a decrease in the mass percentage content of silicon element in the silicon-containing material decreases w1.

[0057] This application does not impose any particular restrictions on the method of controlling the mass percentage content W1, W2, and W3 of lithium element in the first, second, and third regions of the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the mass percentage content W1, W2, and W3 of lithium element in the first, second, and third regions can be controlled by adjusting the bonding time between the negative electrode material layer and the lithium replenishment layer and the bonding temperature. Generally, when other conditions remain unchanged, increasing the bonding time increases W1, W2, and W3, and decreasing the bonding time decreases W1, W2, and W3. When other conditions remain unchanged, increasing the bonding temperature increases W1, W2, and W3, and decreasing the bonding temperature decreases W1, W2, and W3.

[0058] This application does not impose any particular restrictions on the methods for adjusting W1 / W2 and W2 / W3, as long as the purpose of this application can be achieved. For example, the value of W1 / W2 can be adjusted by adjusting the values ​​of W1 and W2 respectively, as described above. Similarly, the value of W2 / W3 can be adjusted by adjusting the values ​​of W2 and W3 respectively, as described above.

[0059] In some embodiments of this application, the mass percentage of lithium in the lithium replenishment layer is 97% to 100%, based on the mass of the lithium replenishment layer. Exemplarily, the mass percentage of lithium in the lithium replenishment layer can be 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 100%, or a range of any two of the above values. By controlling the mass percentage of lithium in the lithium replenishment layer within the above range, more lithium ions can be provided to the negative electrode material layer, achieving a better lithium replenishment effect. This replenishes the active lithium lost during the first charge-discharge process due to the formation of the SEI film, and also allows for the continuous generation of lithium ions during cycling to replenish the active lithium consumed during cycling. This, in turn, helps improve the initial coulombic efficiency of the secondary battery, reduces cycle capacity decay, and increases the energy density of the secondary battery.

[0060] In this application, the lithium replenishment layer may also include other elements, including but not limited to at least one of aluminum, silicon, magnesium, tin, or nickel. Based on the mass of the lithium replenishment layer, the mass percentage of other elements in the lithium replenishment layer is from 0% to 3%.

[0061] In some embodiments of this application, the thickness of the lithium replenishment layer is from 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 of any two of the above values. By adjusting the thickness of the lithium replenishment layer within the above range, the lithium replenishment layer can meet the lithium replenishment requirement, achieve a better lithium replenishment effect, reduce the preparation cost of the lithium replenishment layer, and minimize the impact of increased lithium replenishment layer thickness on the volumetric energy density of the secondary battery. This is beneficial for improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery.

[0062] This application does not impose any particular limitation on the method of controlling the thickness of the lithium replenishment layer, as long as the purpose of this application can be achieved. For example, the thickness of the lithium replenishment layer can be controlled by adjusting the roller pressure P1 during the preparation of the lithium replenishment layer. Generally, when other conditions remain unchanged, increasing the roller pressure P1 decreases the thickness of the lithium replenishment layer, and decreasing the roller pressure P1 increases the thickness of the lithium replenishment layer. For example, the thickness of the lithium replenishment layer can be controlled by selecting different lithium replenishment layer preparation methods. The preparation method of the lithium replenishment layer usually affects the minimum thickness of the lithium replenishment layer. Specifically, the minimum thickness of the lithium replenishment layer prepared by coating with lithium or lithium alloy molten slurry is usually smaller, while the minimum thickness of the lithium replenishment layer prepared by coating with lithium metal powder slurry is usually larger.

[0063] In some embodiments of this application, the thickness of the negative electrode material layer is from 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 controlling the thickness of the negative electrode material layer within the above range, lithium ions diffuse more easily from the lithium replenishment layer to the surface of the negative electrode material layer, which is beneficial for achieving a better lithium replenishment effect, increasing the lithium replenishment capacity of the negative electrode sheet, and resulting in excellent kinetic performance of the negative electrode sheet. This, in turn, helps to improve the initial coulombic efficiency of the secondary battery, reduce cycle capacity decay, and increase the energy density of the secondary battery.

[0064] This application does not impose any particular limitation on the method of controlling the thickness of the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode material layer can be controlled by adjusting the single-sided coating density and the roller pressure P2. Generally, when other conditions remain unchanged, increasing the single-sided coating density of the negative electrode material layer increases the thickness of the negative electrode material layer; decreasing the single-sided coating density decreases the thickness of the negative electrode material layer. When other conditions remain unchanged, increasing the roller pressure P2 decreases the thickness of the negative electrode material layer; decreasing the roller pressure P2 increases the thickness of the negative electrode material layer.

[0065] In some embodiments of this application, the adhesion force between the lithium replenishment layer and the negative electrode current collector is from 10 N / m to 50 N / m. Exemplarily, the adhesion force between the lithium replenishment layer and the negative electrode current collector can be 10 N / m, 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, 50 N / m, or a range consisting of any two of the above values. By adjusting the adhesion force between the lithium replenishment layer and the negative electrode current collector within the above range, the lithium replenishment layer can be tightly bonded to 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 sheet to a secondary battery is beneficial for improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery.

[0066] In some embodiments of this application, the adhesion force between the negative electrode material layer and the lithium replenishment layer is from 5 N / m to 10 N / m. Exemplarily, the adhesion force between the negative electrode material layer and the lithium replenishment layer can be 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, or a range consisting of any two of the above values. By controlling the adhesion force between the negative electrode material layer and the lithium replenishment layer within the above range, the negative electrode material layer is less likely to peel off from the lithium replenishment layer, which is beneficial for the transport of lithium ions from the lithium replenishment layer to the negative electrode material layer, achieving a better lithium replenishment effect. Applying the above-mentioned pre-lithiated negative electrode sheet to a secondary battery is beneficial for improving the initial coulombic efficiency of the secondary battery, reducing cycle capacity decay, and increasing the energy density of the secondary battery.

[0067] In this application, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. This application does not particularly limit the type of negative electrode binder, as long as it achieves the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber, SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, lithium polyacrylate, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. This application does not particularly limit the type of negative electrode conductive agent, as long as it achieves the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned metallic materials may include, but are not limited to, metal powder and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the mass ratio of the negative electrode active material, negative electrode binder, and negative electrode conductive agent in the negative electrode material layer; those skilled in the art can select these according to actual needs, as long as the purpose of this application can be achieved.

[0068] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (such as lithium copper composite current collectors, carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.). This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 20 μm.

[0069] A third aspect of this application provides a secondary battery comprising a pre-lithiated negative electrode as described in any of the foregoing embodiments. Therefore, the secondary battery of this application exhibits high initial coulombic efficiency, low cycle capacity decay, and high energy density.

[0070] In this application, the secondary battery further includes a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a portion of it; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0071] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0072] The positive electrode material layer of this application includes a positive electrode active material, which comprises a substance capable of reversibly inserting and extracting active ions such as lithium ions. The positive electrode material layer can be one or more layers, and each layer in a multilayer positive electrode material layer can contain the same or different positive electrode active materials. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can include, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The aforementioned lithium nickel cobalt manganese oxide can include LiNi... 0.95 Co 0.03 Mn 0.02 O2(Ni95), LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of O2 (NCM111). The positive electrode material layer of this application also includes a positive electrode conductive agent and a positive electrode binder. This application does not have any particular limitations on the positive electrode conductive agent and the positive electrode binder in the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the positive electrode conductive agent in the positive electrode material layer may include at least one of the above-mentioned negative electrode conductive agents; the positive electrode binder in the positive electrode material layer may include at least one of the above-mentioned negative electrode binders. This application does not have any particular limitations on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0073] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be from 6 μm to 25 μm. This application also does not impose any particular limitation on the thickness of the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of a single-sided positive electrode material layer can be from 25 μm to 250 μm.

[0074] In this application, the secondary battery also includes an electrolyte. The electrolyte includes a lithium salt. This application does not particularly limit the type of lithium salt; lithium salts known in the art can be used. Exemplarily, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), or lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB). This application does not particularly limit the mass percentage of lithium salt in the electrolyte, as long as the purpose of this application is achieved. The electrolyte also includes a non-aqueous organic solvent. This application does not particularly limit the non-aqueous organic solvent, as long as the purpose of this application is achieved. For example, the non-aqueous organic solvent may contain at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of 1,3-propanesulfonyl lactone, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters.This application does not impose any particular limitation on the mass percentage of non-aqueous organic solvents in the electrolyte, as long as the purpose of this application can be achieved.

[0075] In this application, the secondary battery also includes a separator. The separator is used to separate the positive electrode and the pre-lithiated negative electrode, preventing internal short circuits in the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charge-discharge process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0076] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a diaphragm binder. This application does not particularly limit the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the aforementioned diaphragm binder, and may include at least one of the aforementioned negative electrode binders. The polymer layer contains a polymer, and the polymer material may include, but is not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene copolymer.

[0077] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, pre-lithiated negative electrode, electrolyte, and other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0078] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. In this application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc.

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

[0080] A fourth aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. The electronic device of this application has a long service life and good performance.

[0081] This application does not specifically limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0082] Example

[0083] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0084] Test methods and equipment:

[0085] Lithium content mass percentage test in the first, second and third regions

[0086] Take a pre-lithiated negative electrode sheet, and along the thickness direction of the negative electrode sheet, scrape off the negative electrode material layer material at the top 1 / 3 thickness away from the lithium replenishment layer, the middle 1 / 3 thickness, and the bottom 1 / 3 thickness near the lithium replenishment layer with a blade to obtain negative electrode material layer powder in the third region, the second region, and the first region.

[0087] The mass percentage of lithium in the negative electrode material powder of the first, second, and third regions was determined by inductively coupled plasma-emission spectroscopy (ICP-OES). The ICP-OES instrument used was a PE7000DV model manufactured by Platinum Elmer, USA. The ICP-OES testing conditions were as follows: radio frequency (RF) of 40.68 MHz, RF power of 1300 W, argon secondary pressure of 0.6 MPa, auxiliary gas flow rate of 0.2 L / min, cooling gas flow rate of 15 L / min, and pump speed of 1.5 mL / min.

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

[0089] The pre-lithiated negative electrode sheet was taken, and the negative electrode material layer above the lithium replenishment layer was scraped off with a blade to obtain negative electrode material layer powder. The mass percentage content of silicon in the negative electrode material layer was determined by inductively coupled plasma-emission spectroscopy (ICP-OES). The ICP-OES instrument used was a PE7000DV spectrometer manufactured by Platinum Elmer, USA. The ICP-OES test conditions were: radio frequency (RF) of 40.68 MHz, RF power of 1300 W, argon secondary pressure of 0.6 MPa, auxiliary gas flow rate of 0.2 L / min, cooling gas flow rate of 15 L / min, and pump speed of 1.5 mL / min.

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

[0091] The pre-lithiated negative electrode sheet was taken, and the entire negative electrode material layer above the lithium replenishment layer was scraped off with a blade to obtain the negative electrode current collector with the lithium replenishment layer. The mass percentage of lithium in the lithium replenishment layer was determined by inductively coupled plasma-emitting emission spectrometry (ICP-OES). The ICP-OES instrument used was a PE7000DV spectrometer manufactured by Platinum Elmer, USA. The ICP-OES test conditions were: radio frequency (RF) of 40.68 MHz, RF power of 1300 W, argon secondary pressure of 0.6 MPa, auxiliary gas flow rate of 0.2 L / min, cooling gas flow rate of 15 L / min, and pump speed of 1.5 mL / min.

[0092] Thickness test

[0093] Take a pre-lithiated negative electrode sheet and polish its cross-section along the thickness direction with argon ions. Then, observe the cross-section of the negative electrode sheet using a scanning electron microscope (SEM) and measure the thickness of the lithium replenishment layer and the negative electrode material layer.

[0094] Adhesion test

[0095] The pre-lithiated negative electrode preparation process steps (1) A negative current collector with a lithium replenishment layer on one side is cut into test strips with a width of 16mm and a length of 150mm. Double-sided tape (60mm to 70mm in length) is cut and attached to a steel plate. At a position 50mm from the top of the steel plate, the tape is cut open with a blade and peeled off. The test strip completely covers the double-sided tape, with the lithium replenishment layer facing down and bonded to the tape. A paper strip with a width equal to that of the negative current collector and a length of 80mm to 100mm is inserted under the negative current collector and fixed with tape, and the group is marked. The test can be performed by rolling back and forth three times with a 2kg pressure roller. The test is performed using a tensile testing machine (tensile testing machine model: Instron 3365). The paper strip is folded upwards 180°, and the end of the steel plate without the sample is clamped on the fixed fixture of the tensile testing machine, while the other end of the paper strip is connected to the moving fixture. The fixture was moved at a constant speed (50 mm / min) until the lithium replenishment layer was peeled off from the negative electrode current collector, at which point the test was terminated. The force required during the peeling process was recorded. The adhesion force between the lithium replenishment layer and the negative electrode current collector was calculated based on the force-displacement curve provided by the tensile testing machine.

[0096] After obtaining the pre-lithiated negative electrode sheet in step (3) of the pre-lithiated negative electrode sheet preparation process, cut it into test strips with a width of 16 mm and a length of 150 mm. Cut double-sided tape (60 mm to 70 mm in length) and stick it on the steel plate. Cut it with a blade at a position 50 mm from the top of the steel plate and peel off the double-sided tape. Completely cover the double-sided tape surface with the test strip, with the negative electrode material layer facing down and bonded to the double-sided tape. Insert a paper strip with a width equal to 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, marking the group. Test by rolling it back and forth three times with a 2 kg pressure roller. Test with a tensile testing machine (tensile testing machine model: Instron 3365). Fold the paper strip 180° upwards, 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 strip to the moving fixture. The fixture was moved at a constant speed (50 mm / min) until the lithium replenishment layer was peeled off from the negative electrode material layer, at which point the test ended. The force required during the peeling process was recorded. The adhesion force between the negative electrode material layer and the lithium replenishment layer was calculated based on the force-displacement curve provided by the tensile testing machine.

[0097] First Coulomb Efficiency Test

[0098] The voltage range indicated on the outer packaging of the lithium-ion battery shall prevail. For example, when the voltage range indicated on the outer packaging of the lithium-ion battery is 3.0V to 4.45V, the charging cut-off voltage is 4.45V and the discharging cut-off voltage is 3.0V.

[0099] The specific test steps are as follows: The lithium-ion battery is charged at a constant current of 0.2C at 25℃ to the cutoff voltage of 4.45V, then charged at a constant voltage of 4.45V until the current is less than 0.05C. After resting for 5 minutes, it is discharged at a constant current of 0.2C to the cutoff voltage of 3.0V. The capacity during the above charging process is denoted as C0, and the capacity during the above discharging process is denoted as C1. The initial coulombic efficiency of the lithium-ion battery is calculated according to the following formula: Initial coulombic efficiency (%) = C1 / C0 × 100%.

[0100] Cyclic performance test

[0101] The voltage range indicated on the outer packaging of the lithium-ion battery shall prevail. For example, when the voltage range indicated on the outer packaging of the lithium-ion battery is 3.0V to 4.45V, the charging cut-off voltage is 4.45V and the discharging cut-off voltage is 3.0V.

[0102] The specific test steps are as follows: Under 25℃ conditions, the lithium-ion battery undergoes its first charge and discharge cycle. It is charged at a constant current of 0.2C to the cutoff voltage of 4.45V, then charged at a constant voltage of 4.45V until the current is less than 0.05C. After resting for 5 minutes, it is discharged at a constant current of 0.2C to the cutoff voltage of 3.0V. The discharge capacity of the lithium-ion battery is measured as A. Then, in an environment of 25℃, 400 charge and discharge cycles are performed according to the above steps. The discharge capacity of the lithium-ion battery after the 400th cycle is measured as B. The cycle capacity retention rate of the lithium-ion battery is calculated using the following formula: Cycle capacity retention rate (%) = B / A × 100%. The higher the measured cycle capacity retention rate, the better the cycle performance of the lithium-ion battery and the smaller the cycle capacity decay.

[0103] Energy density test

[0104] The voltage range indicated on the outer packaging of the lithium-ion battery shall prevail. For example, when the voltage range indicated on the outer packaging of the lithium-ion battery is 3.0V to 4.45V, the charging cut-off voltage is 4.45V and the discharging cut-off voltage is 3.0V.

[0105] The specific test steps are as follows: Under 25℃ conditions, the lithium-ion battery is charged at a constant current of 0.2C to the cutoff voltage of 4.45V, then charged at a constant voltage of 4.45V until the current is less than 0.05C. After resting for 5 minutes, it is discharged at a constant current of 0.2C to the cutoff voltage of 3.0V, and then rested for 5 minutes. The energy of the above discharge process is recorded as the discharge energy E. Calculate the volume V (mm²) of the lithium-ion battery. 3= Length × Width × Height. The energy density of a lithium-ion battery is calculated using the following formula: Energy density (Wh / L) = E / V × 10 6 .

[0106] Example 1-1

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

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

[0109] (2) 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. Deionized water is added as a solvent, and the mixture is stirred and mixed evenly to obtain a negative electrode slurry with a solid content of 28 wt%. The negative electrode slurry is uniformly coated on one surface of a 12 μm thick support layer copper foil, pre-dried at 90 °C for 30 min, and then vacuum-dried at 90 °C for 12 h to form a negative electrode material layer (water content < 500 ppm).

[0110] (3) At 25℃, the negative electrode material layer and the support layer are placed on the surface of the lithium replenishment layer, with the surface of the negative electrode material layer away from the support layer bonded to the lithium replenishment layer. After rolling, the support layer is peeled off from the negative electrode material layer. The rolling pressure P2 is shown in Table 2, resulting in a negative electrode sheet with a lithium replenishment layer and a negative electrode material layer on one side of the negative electrode current collector. The above steps are repeated on the other surface of the negative electrode current 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 current collector. After cutting and slitting, a pre-lithiated negative electrode sheet with a size of 80mm×1000mm is obtained. The surface density of the single-sided coating of the negative electrode material layer is 2.3mg / cm³. 2 The thickness of the negative electrode material layer on one side is shown in Table 2; the mass percentage of silicon in the negative electrode material layer, w1, the mass percentage of lithium in the first region, W1, the mass percentage of lithium in the second region, and the mass percentage of lithium in the third region, W3 are shown in Table 1.

[0111] <Preparation of the positive electrode>

[0112] Lithium cobalt oxide (LiCoO2), acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil current collector and dried at 110 °C to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The sheet was dried under vacuum at 110 °C for 1 hour, then cold-pressed, cut, and slit to obtain a positive electrode sheet with dimensions of 77 mm × 995 mm. The areal density of the single-sided coating of the positive electrode material layer was 19.0 mg / cm³. 2 The compaction density during the cold pressing process is 4.15 g / cm³. 3 .

[0113] <Preparation of Electrolyte>

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

[0115] <Preparation of the diaphragm>

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

[0117] <Preparation of Lithium-ion Batteries>

[0118] The prepared positive electrode, separator, pre-lithiated negative electrode, and separator are stacked in sequence, with the separator positioned between the positive electrode and the pre-lithiated negative electrode to act as a separator. The electrode assembly is then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. Electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation (charged at a constant current of 0.02C to 3.5V, then at a constant current of 0.1C to 3.9V), degassing, edge trimming, and capacity processing to obtain the lithium-ion battery.

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

[0120] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1. Among them, 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, while the mass ratio of the negative electrode conductive agent and the negative electrode binder remains unchanged.

[0121] Examples 1-6

[0122] Except for the use of silicon-containing silicon-carbon materials and carbon materials artificial graphite as the negative electrode active material in the <Preparation of Pre-lithiated Negative Electrode Sheet>, the mass percentage content of the negative electrode active material in the negative electrode material layer was adjusted according to Table 1, and the mass percentage content W of the silicon-containing material was adjusted based on the mass of the negative electrode active material. Si The mass percentage of carbon material Wc and the sum of the mass percentages of negative electrode conductive agent and negative electrode binder in the negative electrode material layer change accordingly. Except for the mass ratio of negative electrode conductive agent and negative electrode binder remaining unchanged, the rest is the same as in Example 1-1.

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

[0124] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-6. Specifically, 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, while the mass ratio of the negative electrode conductive agent to the negative electrode binder remains constant.

[0125] Examples 1-12

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

[0127] Examples 2-1 to 2-12

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

[0129] Comparative Example 1

[0130] Except for the preparation method used in <Preparation of Prelithiated Negative Electrode>, the rest is the same as in Example 1-1.

[0131] <Preparation of Negative Electrode Sheets>

[0132] A mixture of silicon carbide (anode active material), acetylene black (anode conductive agent), styrene-butadiene rubber (SBR) (anode binder), and lithium carboxymethyl cellulose (anode binder) in a mass ratio of 85:5:5:5 was prepared. Deionized water was added as a solvent, and the mixture was stirred until homogeneous to obtain a cathode slurry with a solid content of 28 wt%. The cathode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector and dried at 90°C to obtain a cathode sheet with a single-sided cathode material coating. The above steps were repeated on the other surface of the copper foil to obtain a cathode sheet with a double-sided cathode material coating. The cathode sheet was dried under vacuum at 90°C for 12 hours, then cold-pressed, cut, and slit to obtain a cathode sheet with dimensions of 80 mm × 1000 mm. The single-sided coating surface density of the cathode material layer was 2.3 mg / cm³. 2 The thickness of the negative electrode material layer on one side 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 in Example 1-1. Specifically, the mass percentage of lithium in the first region W1, the mass percentage of lithium in the second region W2, and the mass percentage of lithium in the third region W3 are controlled by adjusting the settling time after the negative electrode material layer and the lithium replenishment layer are bonded together.

[0135] Comparative Example 3

[0136] In addition to using silicon-containing silicon-carbon materials and carbon materials such as artificial graphite as shown in Table 1 in the <Preparation of Negative Electrode Sheets>, the mass percentage W of silicon-containing materials is based on the mass of the negative electrode active materials. Si The mass percentage of carbon materials, Wc, is shown in Table 1. Except for the mass percentage of negative electrode conductive agent and negative electrode binder in the negative electrode material layer, the rest are the same as those in 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 in Examples 1-7. Among them, the mass percentage of lithium in the first region W1, the mass percentage of lithium in the second region W2, and the mass percentage of lithium in the third region W3 are controlled by adjusting the standing time after the negative electrode material layer and the lithium replenishment layer are bonded together.

[0139] Comparative Example 5

[0140] In addition to using silicon-containing silicon-carbon materials and carbon materials such as artificial graphite as shown in Table 1 in the <Preparation of Negative Electrode Sheets>, the mass percentage W of silicon-containing materials is based on the mass of the negative electrode active materials. SiThe mass percentage of carbon materials, Wc, is shown in Table 1. Except for the mass percentage of negative electrode conductive agent and negative electrode binder in the negative electrode material layer, the rest are the same as those in 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 in Examples 1-10. Among them, the mass percentage of lithium in the first region W1, the mass percentage of lithium in the second region W2, and the mass percentage of lithium in the third region W3 are controlled by adjusting the standing time after the negative electrode material layer and the lithium replenishment layer are bonded together.

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

[0144]

[0145] As can be seen from Examples 1-1 to 1-12 and Comparative Examples 1 to 6, when the pre-lithiated negative electrode sheet prepared using the preparation method provided in this application is applied to a lithium-ion battery, the lithium-ion battery exhibits higher initial coulombic efficiency, cycle capacity retention, and energy density. This indicates that this application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase energy density. However, the negative electrode sheets of Comparative Examples 1, 3, and 5 were not pre-lithiated using the preparation method of this application, resulting in lower initial coulombic efficiency, cycle capacity retention, and energy density for the lithium-ion batteries. Furthermore, the W1 / W2 and W2 / W3 ratios of the pre-lithiated negative electrode sheets in Comparative Examples 2, 4, and 6 are not within the scope of this application, leading to even lower cycle capacity retention for the lithium-ion batteries. Therefore, the lithium-ion batteries of Comparative Examples 1 to 6 cannot simultaneously possess high initial coulombic efficiency, cycle capacity retention, and energy density, indicating that they cannot simultaneously improve the initial coulombic efficiency, reduce cycle capacity decay, and increase energy density for lithium-ion batteries.

[0146] The values ​​of w1, W1, W2, and W3 typically affect the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1 to 1-11, when the values ​​of w1, W1, W2, and W3 are within the range specified in this application, the lithium-ion battery exhibits higher initial coulombic efficiency, cycle capacity retention, and energy density. This indicates that this application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase energy density.

[0147] The type of negative electrode active material typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1 and 1-12, the lithium-ion battery using the negative electrode active material of this application exhibits higher initial coulombic efficiency, cycle capacity retention, and energy density, indicating that this application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase energy density.

[0148] Table 2

[0149]

[0150]

[0151] Roller pressure P1 typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-4, when the roller pressure P1 is within the range of this application, the adhesion between the lithium replenishment layer and the negative electrode current collector, as well as the adhesion between the negative electrode material layer and the lithium replenishment layer, is relatively large. The prepared lithium-ion batteries exhibit higher initial coulombic efficiency, cycle capacity retention, and energy density, indicating that this application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase energy density.

[0152] Roller pressure P2 typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 2-5 to 2-8, when the roller pressure P2 is within the range of this application, the adhesion between the lithium replenishment layer and the negative electrode current collector, as well as the adhesion between the negative electrode material layer and the lithium replenishment layer, is relatively large. The prepared lithium-ion batteries exhibit higher initial coulombic efficiency, cycle capacity retention, and energy density, indicating that this application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase energy density.

[0153] The mass percentage of lithium in the lithium replenishment layer typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of a lithium-ion battery. As can be seen from Examples 1-1, 2-9 to 2-10, when the mass percentage of lithium in the lithium replenishment layer is within the range specified in this application, the adhesion between the lithium replenishment layer and the negative electrode current collector, as well as the adhesion between the negative electrode material layer and the lithium replenishment layer, is greater. The prepared lithium-ion battery exhibits higher initial coulombic efficiency, cycle capacity retention, and energy density, indicating that this application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase energy density.

[0154] The thickness of the lithium replenishment layer typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-4, when the thickness of the lithium replenishment layer is within the range specified in this application, the adhesion between the lithium replenishment layer and the negative electrode current collector, as well as the adhesion between the negative electrode material layer and the lithium replenishment layer, is greater. The prepared lithium-ion batteries exhibit higher initial coulombic efficiency, cycle capacity retention, and energy density, indicating that this application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase energy density.

[0155] The thickness of the negative electrode material layer typically affects the initial coulombic efficiency, cycle capacity retention, and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 2-11, and 2-12, when the thickness of the negative electrode material layer is within the range specified in this application, the adhesion between the lithium replenishment layer and the negative electrode current collector, as well as the adhesion between the negative electrode material layer and the lithium replenishment layer, is relatively large. The prepared lithium-ion batteries exhibit higher initial coulombic efficiency, cycle capacity retention, and energy density, indicating that this application can improve the initial coulombic efficiency of lithium-ion batteries, reduce cycle capacity decay, and increase energy density.

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

[0157] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

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

Claims

1. A pre-lithiated negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector, a lithium replenishment layer and a negative electrode material layer, the lithium replenishment layer being disposed between the negative electrode current collector and the negative electrode material layer, and the negative electrode material layer comprising opposing first and second surfaces along the thickness direction of the negative electrode sheet; From the first surface to the second surface, the negative electrode material layer sequentially includes a first region, a second region, and a third region, wherein the first region is located on the surface of the lithium replenishment 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 in the first region is W1; based on the mass of the second region, the mass percentage of lithium in the second region is W2; based on the mass of the third region, the mass percentage of lithium in the third region is W3, where W1 > W2 > W3, 1.01 ≤ W1 / W2 ≤ 2.0, and 1.01 ≤ W2 / W3 ≤ 2.

0. The method for preparing the pre-lithiated negative electrode sheet includes the following steps: (1) Lithium metal powder slurry is coated onto the negative electrode current collector and dried and rolled to form a lithium replenishment layer; or lithium foil and / or lithium alloy foil is rolled onto the negative electrode current collector to form a lithium replenishment layer; or lithium or lithium alloy molten slurry is coated onto the negative electrode current collector and cooled and rolled to form a lithium replenishment layer. (2) A negative electrode slurry including a negative electrode active material is coated on the surface of the support layer and dried to form a negative electrode material layer; (3) The negative electrode material layer and the support layer are placed on the surface of the lithium replenishment layer, wherein the surface of the negative electrode material layer away from the support layer is bonded to the lithium replenishment layer. After rolling, the support layer is peeled off from the negative electrode material layer to form a pre-lithiated negative electrode sheet.

2. The pre-lithiated negative electrode according to claim 1, wherein, In step (1), the roller pressure P1 is 0.1T / 10mm to 2T / 10mm; in step (3), the roller pressure P2 is 1.0T / 10mm to 2.0T / 10mm.

3. The pre-lithiated negative electrode according to claim 1, wherein, The negative electrode material layer includes a negative electrode active material, which includes at least one of carbon material or silicon-containing material. The carbon material includes at least one of graphite material or hard carbon, and the silicon-containing material includes at least one of silicon-carbon material or silicon-oxygen material.

4. The pre-lithiated negative electrode according to claim 3, wherein, The pre-lithiated negative electrode sheet satisfies any of the following characteristics: (1) The negative electrode active material consists only of silicon-containing substances. Based on the mass of the negative electrode material layer, the mass percentage of silicon in the negative electrode material layer is w1, 18.6%≤w1≤63.5%, 11.5%≤W1≤18.4%, 9.2%≤W2<11.5%, and 4.6%≤W3<9.2%. (2) The negative electrode active material includes carbon materials and silicon-containing substances. 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%, and 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%, and 1.1%≤W3<2.2%.

5. The pre-lithiated negative electrode according to claim 1, wherein, Based on the mass of the lithium replenishment layer, the mass percentage of lithium in the lithium replenishment layer is 97% to 100%.

6. The pre-lithiated negative electrode according to claim 1, wherein, 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.

7. The pre-lithiated negative electrode according to claim 1, wherein, The adhesion between the lithium replenishment layer and the negative electrode current collector is 10 N / m to 50 N / m, and the adhesion between the negative electrode material layer and the lithium replenishment layer is 5 N / m to 10 N / m.

8. A secondary battery comprising a pre-lithiated negative electrode sheet according to any one of claims 1 to 7.

9. An electronic device comprising the secondary battery of claim 8.

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