Negative electrode sheet and battery

Abstract

Provided in the present application are a negative electrode sheet and a battery. The negative electrode sheet comprises a negative-electrode current collector and a functional coating located on at least one surface of the negative-electrode current collector, wherein the functional coating contains lithium; the functional coating comprises a second area and a first area located on at least one side of the second area, and the first area extends to an edge of the negative-electrode current collector in a direction that faces away from the second area; particles are formed on an edge of the first area; and in an X-ray photoelectron spectroscopy analysis result of the functional coating, the ratio of the molar content of oxygen in the first area to the width of the first area is greater than 0.3, and the unit of the width is mm. The present application can solve the problems of there being edge burrs on an edge of an electrode sheet and the edge burrs being prone to piercing a separator to cause potential safety hazards, and can improve the performance, such as the initial Coulombic efficiency and the cycle life, of the battery.

Description

Negative electrode sheet and battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 27, 2023, with application number 202311818939.4 and application name “A Negative Electrode Sheet and Battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical energy storage devices, and in particular to a negative electrode sheet and a battery. Background Art

[0003] Pre-replenishing lithium to the electrode can replenish the irreversible capacity consumed in the first cycle and improve the battery's first efficiency and energy density. This is especially true for silicon-doped negative electrodes. Silicon materials have a high theoretical specific capacity and are ideal materials for replacing graphite negative electrodes and improving the energy density of lithium-ion batteries. However, silicon materials also have an obvious shortcoming in practical applications, that is, the coulombic efficiency of the first charge and discharge cycle is lower than that of the graphite negative electrode (the first efficiency of silicon-based negative electrodes is generally around 70%). An effective method is to pre-replenish lithium to the electrode to replenish the irreversible capacity consumed in the first cycle, improve the first efficiency of silicon-doped batteries, and thereby improve the battery's energy density.

[0004] In the existing technology, the edges of the electrodes that have undergone the lithium replenishment process often have edge burrs, and the edge burrs are difficult to remove. These edge burrs fail to fit with the side end faces of the electrodes and cannot form an active lithium source. Instead, they are free in the battery cell and have the risk of puncturing the diaphragm, posing a safety hazard. Summary of the Invention

[0005] The present application provides a negative electrode sheet and a battery, which at least solve the problem in the prior art that the edge of the electrode sheet has burrs, and the edge burrs easily pierce the diaphragm and cause safety hazards.

[0006] In one aspect of the present application, a negative electrode sheet is provided, comprising a negative electrode current collector and a functional coating located on at least one surface of the negative electrode current collector, wherein the functional coating contains lithium; the functional coating comprises a second region and a first region located on at least one side of the second region, and the first region extends to the edge of the negative electrode current collector in a direction away from the second region; particles are formed on the edge of the first region; in the results of X-ray photoelectron spectroscopy analysis of the functional coating, the ratio of the molar content of oxygen in the first region to the width of the first region is greater than 0.3, and the unit of the width is mm.

[0007] According to one embodiment of the present application, in the X-ray photoelectron spectroscopy analysis results of the functional coating, the molar content of oxygen in the second region is less than or equal to 20%; and / or, in the X-ray photoelectron spectroscopy analysis results of the functional coating, the molar content of oxygen in the first region is greater than 20%.

[0008] According to one embodiment of the present application, the width of the first region is less than or equal to 1 mm.

[0009] According to one embodiment of the present application, the functional coating contains fluorine element, wherein, in the X-ray photoelectron spectroscopy analysis results of the functional coating, the molar content of fluorine element in the first region is less than or equal to 15%; and / or, in the X-ray photoelectron spectroscopy analysis results of the functional coating, the molar content of fluorine element in the second region is greater than or equal to 15%; and / or, in the X-ray photoelectron spectroscopy analysis results of the functional coating, the difference between the molar content of fluorine element in the second region and the molar content of fluorine element in the first region is 5% to 30%.

[0010] According to one embodiment of the present application, in the X-ray photoelectron spectroscopy analysis results of the functional coating, the difference between the molar content of carbon in the second region and the molar content of carbon in the first region is less than or equal to 10%; and / or, the graphite C ratio in the first region is less than or equal to 60%, and / or, the graphite C ratio in the second region is greater than 60%; wherein, the graphite C ratio refers to the ratio of the amount of graphite carbon to the total amount of carbon; and / or, the functional coating contains fluorine, and the CF ratio in the first region is greater than or equal to 15%, and the CF ratio refers to the ratio of the amount of carbon that forms CF chemical bonds with fluorine to the total amount of carbon; and / or, the CF ratio in the second region is less than 15%, and the CF ratio refers to the ratio of the amount of carbon that forms CF chemical bonds with fluorine to the total amount of carbon; and / or, the first CO ratio in the first region is greater than or equal to 20%, and the first CO ratio refers to the ratio of the amount of oxygen that forms CO chemical bonds with carbon to the total amount of oxygen; and / or, the first CO ratio in the second region is less than or equal to 20%, and the first CO ratio refers to the ratio of the amount of oxygen that forms CO chemical bonds with carbon to the total amount of oxygen.

[0011] According to one embodiment of the present application, the functional coating includes a negative electrode active material, and the negative electrode active material includes graphite and / or silicon-based active materials.

[0012] According to one embodiment of the present application, the content of the lithium element in the functional coating is 0.01 mg / cm 2 ~2mg / cm 2 .

[0013] According to one embodiment of the present application, the functional coating further contains phosphorus and / or sulfur.

[0014] According to one embodiment of the present application, the negative electrode sheet further includes a negative electrode ear, wherein the negative electrode ear is located on a side of the first region away from the second region in a first direction, and the first direction is parallel to the direction from the second region to the first region; and / or, the first region includes a first sub-region and a second sub-region distributed along a second direction, and the negative electrode ear is located between the first sub-region and the second sub-region in the second direction, and the second direction intersects with the direction from the second region to the first region; and / or, the first region includes a first sub-region and a second sub-region, and the second region includes an extension area between the first sub-region and the second sub-region, and the projection of the negative electrode ear on the plane where the negative electrode collector is located is connected to the projection of the extension area on the plane where the negative electrode collector is located.

[0015] Another aspect of the present application provides a battery comprising the above-mentioned negative electrode sheet.

[0016] In the negative electrode sheet and battery provided by the present application, the functional coating of the electrode sheet contains lithium element, and particles are formed on the edge of the first region. Under the premise of effectively improving the performance of the battery such as the first effect and cycle life, the metal particles have no sharp corners. Even if the electrode sheet is misaligned or the particles and the diaphragm abut against each other during the battery falling process, they cannot pierce the diaphragm, thereby avoiding contact short circuit between the positive and negative electrode sheets and improving the overall safety of the battery loaded with the electrode sheet; furthermore, the ratio of the molar content of the oxygen element in the first region to the width of the first region is greater than 0.3, which can ensure that the burrs on the edge of the electrode sheet are avoided while giving full play to the electrochemical properties of the electrode sheet without affecting the overall energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1 is a schematic structural diagram of a pole piece in one embodiment of the present application;

[0018] FIG2 is an XPS O 1s analysis spectrum of the first region of the negative electrode sheet in Example 1;

[0019] FIG3 is an XPS O 1s analysis spectrum of the second region of the negative electrode sheet in Example 1;

[0020] FIG4 is an XPS C 1s analysis spectrum of the first region of the negative electrode sheet in Example 1;

[0021] FIG5 is an XPS C 1s analysis spectrum of the second region of the negative electrode sheet in Example 1.

[0022] Explanation of reference numerals: 1: first region; 11: first sub-region; 12: second sub-region; 2: second region; 21: main region; 22: extension region; 3: negative electrode ear. DETAILED DESCRIPTION

[0023] To enable those skilled in the art to better understand the solutions of the present application, the present application is further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present application. The examples cited are only used to explain the present application and do not limit the scope of the present application. Based on the embodiments of the present application, all other implementation methods obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of this application.

[0024] In the description of this application, terms such as "first" and "second" are used for descriptive purposes only, such as distinguishing between components to more clearly illustrate / explain the technical solution, and cannot be understood as indicating or implying the number of technical features indicated or the order with substantive significance.

[0025] Lithium-ion batteries have the characteristics of high energy density and power density, and have been widely used in portable consumer electronics and electric vehicles. With the increasing demand for the quality of electronic products and electric vehicles, the requirements for the energy density and life of lithium-ion batteries are also getting higher and higher.

[0026] The electrode is an important component of the battery. The common negative electrode is the graphite negative electrode. For batteries with a graphite system, the lithium source of the positive electrode is continuously consumed during the cycle, resulting in damage to the positive electrode structure, poor cycle performance, and reduced life. Developing lithium replenishment technology to address the problem of low life and pre-replenishing lithium to the electrode can alleviate this problem to a certain extent.

[0027] In addition, silicon materials (silicon-based active materials) have a high theoretical specific capacity, and introducing silicon materials into negative electrode sheets is an effective means to improve battery energy density. However, silicon materials also have obvious defects in practical applications, that is, the coulombic efficiency (first efficiency) of the first charge and discharge cycle is lower than that of the graphite negative electrode (generally, the first efficiency of the silicon negative electrode is between 69%-85%, and the first efficiency of the graphite negative electrode is between 90%-94%). Pre-replenishing lithium by doping silicon-doped electrodes can replenish the irreversible capacity consumed in the first cycle to a certain extent, improve the first efficiency of the silicon-doped battery, and thus improve the energy density of the battery.

[0028] However, the edges of the electrodes that have undergone the lithium replenishment process often have edge burrs, and the edge burrs are difficult to remove. These edge burrs fail to fit into the side end faces of the electrodes and cannot form an active lithium source. Instead, they are free in the battery cell and have the risk of puncturing the diaphragm, posing a safety hazard.

[0029] In addition, according to the long-term research of the inventors of this application, although the performance of the battery such as the first effect and life can be improved to a certain extent by replenishing lithium to the negative electrode, the degree of improvement is limited. Specifically, under normal circumstances, after replenishing lithium to the electrode, the electrode needs to be laser cut or other processes to form a electrode product of a preset shape. Therefore, for the lithium-replenished electrode, its preparation process involves processes such as lithium replenishment and laser cutting. These processes often affect the elemental composition of each region of the lithium-replenished electrode. For example, according to the long-term research of the inventors of this application, by replenishing lithium to the negative electrode, the active material layer will contain lithium elements. When replenishing lithium through the electrochemical process, structures such as SEI films will also be formed in the negative electrode. At the same time, in the subsequent laser cutting process of the electrode, the heat generated will affect the composition of the electrode slit edge area (heat-affected zone), such as affecting the content of elements such as carbon (C) and oxygen (O), thereby affecting the battery's first effect and cycle life and other performance.

[0030] In view of this, an embodiment of the present application provides a negative electrode sheet, as shown in Figure 1, the negative electrode sheet includes a negative electrode collector and a functional coating located on at least one surface of the negative electrode collector, the functional coating containing lithium; the functional coating includes a second region 2 and a first region 1 located on at least one side of the second region 2, and the first region 1 extends to the edge of the negative electrode collector in a direction away from the second region 2; particles are formed on the edge of the first region; in the X-ray photoelectron spectroscopy (XPS) analysis results of the functional coating, the ratio of the molar content (atomic content) of the oxygen element in the first region 1 to the width of the first region 1 is greater than 0.3, and the unit of width is millimeter (mm).

[0031] In the embodiment of the present application, the edge of the first region 1 (or the outer edge of the first region 1 ) is also the outer edge of the functional coating, which is substantially flush with the edge (outer edge) of the negative electrode current collector.

[0032] The above-mentioned negative electrode sheet can be a negative electrode sheet that has been lithium-supplemented and laser-cut. As mentioned above, by lithium-supplementing, the functional coating contains lithium element (Li), and the lithium element can be basically evenly distributed in the functional coating (or paste layer). Through the subsequent laser cutting process, a negative electrode sheet of a preset shape can be formed, wherein the first area 1 can be specifically a heat-affected zone (that is, the edge area of ​​the cut after laser cutting, which is also the area where the color and other morphology of the cut edge change due to laser cutting), and the second area 2 is a normal area (that is, the normal paste area).

[0033] Among them, particles are formed at the edge of the first area 1. The particles are mainly metal particles formed by melting metal materials such as the negative electrode current collector during the laser cutting process (usually spherical molten beads, that is, during the laser cutting process, due to the high temperature, the negative electrode current collector and other metal materials shrink due to heat to form spherical molten beads). The metal particles have no sharp corners. Even if the pole pieces are misaligned or the particles and the diaphragm abut during the battery falling process, they cannot pierce the diaphragm, thereby avoiding short circuit between the positive and negative pole pieces and improving the overall safety of the battery loaded with the pole pieces.

[0034] For example, in the related art, a lithium metal strip is pressed onto the surface of the electrode to replenish lithium for the electrode. This method of replenishing lithium will cause edge lithium burrs to appear on the edge of the electrode after the lithium replenishment process, and the edge lithium burrs are difficult to remove. These edge lithium burrs fail to adhere to the side end face of the electrode and cannot form an active lithium source. Instead, they are free in the battery cell and have the risk of piercing the diaphragm, causing a safety hazard. In the embodiment of the present application, according to the inventor's research, by synergistically regulating the lithium replenishment process and the laser cutting process, that is, by forming particles on the edge of the first region of the negative electrode, and the ratio of the molar content of oxygen element in the first region to the width of the first region being greater than 0.3, it is possible to effectively solve the problems of edge lithium burrs on the edge of the negative electrode and the resulting easy piercing of the diaphragm by the edge lithium burrs, causing safety hazards.

[0035] Therefore, the edge of the first region 1 of the negative electrode sheet of the embodiment of the present application has no burrs, which can solve the problem of the edge burrs on the edge of the negative electrode sheet and the resulting burrs easily piercing the separator and causing safety hazards.

[0036] In addition, in the XPS analysis results of the functional coating, the ratio of the molar content of the oxygen element in the first region 1 to the width of the first region 1 is greater than 0.3. By synergistically regulating the oxygen content in the first region 1 and the width of the first region 1, the electrochemical properties of the negative electrode sheet can be fully utilized while avoiding edge burrs on the negative electrode sheet, without affecting the overall energy density of the battery, and improving the battery's first efficiency and cycle life.

[0037] In some embodiments, in the XPS analysis results of the functional coating, the ratio of the molar content of the oxygen element in the first region 1 to the width of the first region 1 can be greater than or equal to 0.31, specifically 0.31 to 0.35, for example, 0.31, 0.315, 0.319, 0.32, 0.325, 0.33, 0.332, 0.335, 0.34, 0.345, 0.35 or a range consisting of any two of them.

[0038] Further research has shown that the molar content of oxygen (O) in the second region 2 can be less than or equal to 20%, further improving the negative electrode's initial efficiency and cycle life. The inventors believe that controlling the molar content of oxygen in the second region 2 to less than or equal to 20% is more suitable for the composition of the functional coating after lithium supplementation, for example, allowing the elements in the functional coating to exist in a more suitable form and content, thereby improving the battery's initial efficiency and cycle life. Furthermore, from another perspective, the oxygen content indicates, to a certain extent, the degree of oxidation of the material in the functional coating. The higher the oxygen content, the more material in the functional coating will be oxidized. This is especially true for active materials (such as subsequent graphite and / or silicon-based active materials). The more active material that is oxidized, the less active material is available for use. Therefore, a low oxygen content in the second region 2 (less than or equal to 20%) ensures a low degree of oxidation and quantity of the material in the functional coating, thereby ensuring that more active materials and other materials can function, improving the battery's energy density, initial efficiency, and cycle life.

[0039] Specifically, the functional coating may include a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material may include graphite and / or a silicon-based active material, wherein the silicon-based active material includes, for example, SiOx, such as silicon monoxide.

[0040] Illustratively, the negative electrode active material is graphite, in which case the negative electrode sheet is a graphite negative electrode sheet; or, the negative electrode active material includes graphite and silicon-based active materials, in which case the negative electrode sheet is a silicon-doped graphite negative electrode sheet; or the negative electrode active material is a silicon-based active material, in which case the negative electrode sheet is a silicon negative electrode sheet.

[0041] As mentioned above, by supplementing the negative electrode sheet with lithium so that its negative electrode active material layer contains lithium elements, and at the same time controlling the molar content of oxygen elements in the second region 2 to be less than or equal to 20%, the performance of the battery using these negative electrode sheets, such as the first effect and cycle life, can be improved. Specifically, taking the negative electrode sheet whose negative electrode active material includes graphite (such as the aforementioned graphite negative electrode sheet or silicon-doped graphite negative electrode sheet) as an example, the oxygen content in its functional coating can indicate the degree of oxidation of the graphite to a certain extent, that is, the higher the oxygen content, the greater the degree of oxidation of the graphite, the greater the amount of oxidation, and the less graphite that can be used. By controlling the molar content of oxygen elements in the second region 2 to be less than or equal to 20%, the degree of oxidation and amount of graphite in the functional coating can be ensured to be low, thereby ensuring that more graphite functions are exerted, thereby improving the energy density, first effect and cycle life of the battery.

[0042] In a specific implementation, XPS analysis can be performed on each region of the functional coating (first region 1 and second region 2) to determine characteristics such as elemental composition, molar content (atomic content) of each element, and the presence form of each element. In the embodiments of the present application, the molar content of each element refers to the molar percentage.

[0043] Furthermore, in the XPS analysis results of the functional coating, the molar content of oxygen element in the second region 2 may be less than or equal to 19.5%, or less than or equal to 19%, or less than or equal to 18.5%, or less than or equal to 18%, less than or equal to 17%, less than or equal to 17.5, or less than or equal to 16, etc.

[0044] Generally, the molar content of oxygen in the first region 1 is greater than the molar content of oxygen in the second region 2. In the XPS analysis results of the functional coating, the difference between the molar content of oxygen in the first region 1 and the molar content of oxygen in the second region 2 can be 5% to 50%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or a range consisting of any two of them.

[0045] In some embodiments, in the XPS analysis results of the functional coating, the molar content of oxygen in the first region 1 may be greater than 20%.

[0046] Furthermore, in the XPS analysis results of the functional coating, the molar content of oxygen element in the first region 1 can be 20% to 70%, for example, 20%, 22%, 24%, 25%, 27%, 29%, 30%, 32%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range consisting of any two of them, which can further improve the battery's first efficiency and cycle life performance.

[0047] In some embodiments, the width of the first region 1 can be less than or equal to 1 mm, specifically 0.001 to 1 mm, for example, 0.001 mm, 0.005 mm, 0.01 mm, 0.03 mm, 0.05 mm, 0.08 mm, 0.1 mm, 0.3 mm, 0.5 mm, 0.8 mm, 1 mm or a range consisting of any two of them.

[0048] In the embodiment of the present application, the width direction of the first region 1 is parallel to the direction from the second region 2 to the first region 1 , that is, the width of the first region 1 is specifically the width of the first region 1 in the direction from the second region 2 to the first region 1 .

[0049] Specifically, as shown in FIG1 , the direction from the second region 2 to the first region 1 can be parallel to the length direction of the electrode sheet (also the length direction of the negative electrode current collector or the functional coating). However, this is not limited to this. For example, the direction from the second region 2 to the first region 1 can also be parallel to the width direction of the electrode sheet (also the width direction of the negative electrode current collector or the functional coating).

[0050] In addition, the functional coating (first region 1 and / or second region 2) contains carbon elements (C), which may specifically include carbon elements that form CO chemical bonds (single bonds) with oxygen, carbon elements that form C=O chemical bonds (double bonds) with oxygen, C elements in graphite carbon (C-C bonds and / or C-H bonds), and C elements in corresponding chemical bonds formed with other elements that may be present in the functional coating such as F (for example, when the functional coating contains F elements, CF bonds are formed with F), etc. One or more of the above, that is, the carbon elements in the functional coating may exist in the form of CO, C=O, graphite carbon (C-C bonds and / or C-H bonds), and other carbon-containing groups (such as CF).

[0051] Generally, the molar content of carbon in the second region 2 may be greater than or equal to the molar content of carbon in the first region 1 .

[0052] Specifically, in the XPS analysis results of the functional coating, the difference between the molar content of carbon in the second region 2 and the molar content of carbon in the first region 1 can be less than or equal to 10%, which is conducive to further improving the battery's first efficiency and cycle life and other performance. One of the reasons for the analysis is that controlling the difference in molar content of carbon in the second region 2 and the first region 1 to be less than or equal to 10% can control the degree of burning of the first region 1 during the laser cutting process, reduce capacity loss, ensure the function of the functional coating, and improve the battery's capacity, first efficiency and cycle life and other performance.

[0053] In some embodiments, in the XPS analysis results of the functional coating, the difference between the molar content of carbon element in the second region 2 and the molar content of carbon element in the first region 1 can be specifically 0 to 10%, for example, 0 (that is, the molar content of carbon element in the second region 2 is basically equal to the molar content of carbon element in the first region 1), 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range of any two of them.

[0054] In some embodiments, in the XPS analysis results of the functional coating, the molar content of carbon element in the first region 1 can be 10% to 90%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or a range consisting of any two thereof.

[0055] In some embodiments, in the XPS analysis results of the functional coating, the molar content of carbon element in the second region 2 can be 10% to 90%, for example, 10%, 20%, 30%, 35%, 40%, 50%, 60%, 70%, 80%, 90% or a range consisting of any two thereof.

[0056] Furthermore, the functional coating (first region 1 and / or second region 2) may contain fluorine (F), which can further enhance the battery's initial efficiency and cycle life. The inventors' research suggests that one reason for this is that the inclusion of fluorine enhances compatibility with the lithium-replenished functional coating, further optimizing the composition and morphology of the lithium-replenished functional coating and improving the battery's initial efficiency and cycle life.

[0057] Generally, the F in the functional coating may include F that forms a CF chemical bond with C and F that forms a chemical bond with other elements (for example, F that forms F-Li (lithium fluoride) with Li, etc.), that is, the F in the functional coating (first region 1 and / or second region 2) can exist in the form of CF, and lithium salts (such as lithium fluoride, lithium carbonate, organic lithium salts, etc.).

[0058] Specifically, the molar content of fluorine in the second region 2 may be greater than the molar content of fluorine in the first region 1. In the XPS analysis results of the functional coating, the difference between the molar content of fluorine in the second region 2 and the molar content of fluorine in the first region 1 may be 5% to 30%, for example, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30% or a range consisting of any two of them, which is conducive to further improving the battery's first efficiency and cycle life and other performance.

[0059] In some embodiments, the molar content of fluorine element in the first region 1 may be less than or equal to 15%, specifically 0.1% to 15%, for example, 0.1%, 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof.

[0060] After further study, the molar content of fluorine in the second region 2 can be greater than or equal to 15%, for example, greater than or equal to 16%, greater than or equal to 17%, greater than or equal to 18%, greater than or equal to 19, etc., which is conducive to further improving the performance of the battery such as the first effect and cycle life. According to the research of the inventors, one of the reasons for the analysis is that the fluorine in the functional coating can participate in the formation of the SEI film (for example, when the negative electrode sheet is replenished with lithium through the electrochemical lithium replenishment process, a SEI film can be formed, and the fluorine and lithium elements can specifically form lithium fluoride, lithium carbonate, and other lithium salts in the SEI film). The fluorine content can indicate the content of the SEI film to a certain extent. The lower the fluorine content, the more SEI films are damaged by processes such as laser cutting, and the more difficult it is to function. In the embodiment of the present application, by controlling the fluorine content in the second region 2 to be greater than or equal to 15%, the degree of damage to the SEI film in the second region 2 is reduced, thereby improving the efficiency of lithium ions passing through, reducing the consumption of lithium ions, thereby improving the utilization rate of the second region 2, and thus improving the performance of the battery such as the first effect and cycle life.

[0061] Specifically, both the first region 1 and the second region 2 contain Li, the Li content in the first region 1 may be less than the Li content in the second region 2, and the ratio of the Li content in the second region 2 to the Li content in the first region 1 may be 1.1 to 2, for example, 1.1, 1.15, 1.2, 1.3, 1.4, 1.5, 1.7, 1.9, 2 or a range consisting of any two thereof.

[0062] For example, in the XPS analysis results of the functional coating, the molar content of Li in the first region 1 is 20% to 25%, for example, 20%, 21%, 22%, 23%, 24%, 25% or a range consisting of any two thereof, and the molar content of Li in the second region 2 is 26% to 30%, for example, 26%, 27%, 28%, 29%, 30% or a range consisting of any two thereof.

[0063] In addition, the functional coating (first region 1 and / or second region 2) may also contain phosphorus (P) elements and / or sulfur (S) elements, wherein the phosphorus element can generally form a PO chemical bond with the oxygen element (i.e., the phosphorus element can exist in the form of PO), and the sulfur element can form a SO bond with the oxygen element (i.e., the sulfur element can exist in the form of SO).

[0064] Specifically, the S content in the first region 1 may be less than or equal to the S content in the second region 2, and the ratio of the S content in the second region 2 to the S content in the first region 1 may be 1 to 2, for example, 1, 1.1, 1.14, 1.2, 1.3, 1.4, 1.5, 1.6, 1.8, 2 or a range consisting of any two of them.

[0065] For example, in the XPS analysis results of the functional coating, the molar content of S in the first region 1 is 0.5% to 0.9% (such as 0.6%, 0.7%, or 0.8%, etc.), and the molar content of S in the second region 2 is 0.7% to 1% (such as 0.8% or 0.9%, etc.), but is not limited to this.

[0066] Specifically, the P content in the first region 1 may be less than or equal to the P content in the second region 2, and the ratio of the P content in the second region 2 to the P content in the first region 1 may be 1 to 2, for example, 1, 1.04, 1.08, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.8, 2 or a range consisting of any two of them.

[0067] For example, in the XPS analysis results of the functional coating, the molar content of P in the first region 1 is 2% to 2.5% (such as 2.1%, 2.2%, 2.3% or 2.4%, etc.), and the molar content of P in the second region 2 is 2.1% to 2.7% (such as 2.2%, 2.3%, 2.3%, 2.5%, 2.6% or 2.7%, etc.).

[0068] In addition, the functional coating (first region 1 and / or second region 2) may further contain elements such as nitrogen (N). The N content in the first region 1 may be less than, equal to, or greater than the N content in the second region 2. The ratio of the N content in the second region 2 to the N content in the first region 1 may be 0.4 to 3, for example, 0.4, 0.5, 0.8, 1, 1.1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, or a range consisting of any two of them.

[0069] For example, in the XPS analysis results of the functional coating, the N molar content in the first region 1 may be 0.1% to 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or a range consisting of any two thereof, and the N molar content in the second region 2 may be 0.1% to 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range consisting of any two thereof.

[0070] In the embodiments of the present application, the molar content of an element is also the atomic content. Taking the molar content of oxygen as an example, in the XPS analysis results of the functional coating, the molar content of oxygen in the first region 1 refers to the ratio of the number of oxygen elements in the first region 1 to the total number of all elements in the first region 1 measured by XPS, and the molar content of oxygen in the second region 2 refers to the ratio of the number of oxygen elements in the second region 2 to the total number of all elements in the second region 2 measured by XPS.

[0071] For example, the XPS analysis results of the functional coating show that the elements in the second region 2 are Li, P, S, C, O, F and N. Then, the molar content of the oxygen element in the second region 2 = the amount of O / (the amount of O + the amount of Li + the amount of P + the amount of S + the amount of C + the amount of F + the amount of N), the molar content of the carbon element in the second region 2 = the amount of C / (the amount of O + the amount of Li + the amount of P + the amount of S + the amount of C + the amount of F + the amount of N), and the molar content of the fluorine element in the second region 2 = the amount of F / (the amount of O + the amount of Li + the amount of P + the amount of S + the amount of C + the amount of F + the amount of N). The calculation method for the molar content of other elements is similar and will not be repeated here.

[0072] In addition, the functional coating (first region 1, second region 2) contains graphite C, the graphite C ratio of the first region 1 may be less than or equal to the graphite C ratio of the second region 2, and the ratio of the graphite C ratio of the second region 2 to the graphite C ratio of the first region 1 may specifically be 1 to 1.5, for example, 1, 1.1, 1.2, 1.3, 1.4, 1.5 or a range consisting of any two thereof.

[0073] In some embodiments, the proportion of graphite C in the first region 1 is less than or equal to 60%, specifically 20% to 60%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any two thereof.

[0074] Further research has shown that the proportion of graphite C in the second region 2 can be greater than 60%, which can further improve the battery's initial efficiency and cycle life.

[0075] In some embodiments, the proportion of graphite C in the second region 2 may be 60% to 80%, for example, 60%, 63%, 65%, 68%, 70%, 73%, 75%, 78%, 80% or any two thereof.

[0076] In addition, the functional coating (first region 1, second region 2) may contain CF chemical bonds, and the CF ratio of the first region 1 may be greater than the CF ratio of the second region 2, which is beneficial to further improve the battery's first efficiency and cycle life and other performance. The reason for this is that by controlling the smaller CF ratio in the second region 2, the proportion of other fluorine-containing valence bonds in the second region 2 (i.e., chemical bonds formed by fluorine elements and other elements (such as lithium fluoride in the SEI film)) can be increased, which is beneficial to improving the efficiency of lithium electrons, reducing the consumption of lithium ions, improving the utilization rate of the second region 2, and improving the battery's first efficiency and cycle life and other performance.

[0077] Specifically, the ratio of the CF ratio of the first region 1 to the CF ratio of the second region 2 may be 2 to 5, for example, 2, 2.5, 2.8, 3, 3.5, 4, 4.5, 5 or a range consisting of any two thereof.

[0078] Specifically, the CF ratio of the first region 1 may be greater than or equal to 15%, specifically 15% to 40%, for example, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40% or a range consisting of any two of them.

[0079] Specifically, the CF ratio of the second region 2 may be less than 15%, specifically 0.1% to 15%, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range consisting of any two of them.

[0080] In addition, the functional coating (first region 1, second region 2) may contain CO chemical bonds, the second CO ratio of the first region 1 may be smaller than the second CO ratio of the second region 2, and the difference between the second CO ratio of the second region 2 and the second CO ratio of the first region 1 may be 0.5% to 3.5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or a range consisting of any two thereof.

[0081] Illustratively, the second CO ratio of the first region 1 may be 10% to 15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two thereof; the second CO ratio of the second region 2 may be 15% to 20%, for example, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two thereof.

[0082] In addition, the functional coating (first region 1, second region 2) may contain C=O chemical bonds, the second C=O ratio of the first region 1 may be smaller than the second C=O ratio of the second region 2, and the ratio of the second C=O ratio of the second region 2 to the second C=O ratio of the first region 1 may be 1.1 to 2.5, for example, 1.1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, or a range consisting of any two thereof.

[0083] Illustratively, the second C=O ratio of the first region 1 may be 5% to 10%, for example, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two thereof, and the second C=O ratio of the second region 2 may be 8% to 15%, for example, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range consisting of any two thereof.

[0084] Specifically, in each of the above regions (first region 1 or second region 2), the graphite C ratio (molar content of graphite C) refers to the ratio of the number of graphite C in the region to the total number of C in the region, the CF ratio (CF molar content) refers to the ratio of the number of C in the region that forms CF chemical bonds with F to the total number of C in the region, the second CO ratio (CO molar content) refers to the ratio of the number of C in the region that forms CO chemical bonds with O to the total number of C in the region, and the second C=O ratio refers to the ratio of the number of C in the region that forms C=O chemical bonds with O to the total number of C. More specifically, taking the graphite C ratio as an example, the graphite C ratio of the first region 1 refers to the ratio of the number of graphite C in the first region 1 to the total number of C in the first region 1, and the graphite C ratio of the second region 2 refers to the ratio of the number of graphite C in the second region 2 to the total number of C in the second region 2.

[0085] During specific implementation, the functional coating (first region 1, second region 2, etc.) can be subjected to XPS analysis, and the C1s orbital can be analyzed to determine the C1s valence bond types (such as graphite carbon (CC, CH), CO, C=O, CF, etc.) and their ratios. Taking the graphite C ratio as an example, the graphite C ratio refers to the molar content of graphite C in the C 1s analysis result, that is, the ratio of the number of C corresponding to graphite C (also the number of graphite C) to the total number of C (that is, the sum of the number of C corresponding to all carbon-containing groups).

[0086] For example, the C1s orbital analysis results of the XPS analysis of the functional coating show that the carbon-containing groups in the first region 1 are graphitic carbon (CC and CH), CO, C=O, and CF. Therefore, the graphitic C ratio of the first region 1 = the number of graphitic Cs / (the number of graphitic Cs + the number of COs + the number of C=Os + the number of CFs), and the CF ratio of the first region 1 = the number of CFs / (the number of graphitic Cs + the number of COs + the number of C=Os + the number of CFs). The calculation method for the ratios of other carbon-containing groups is similar and will not be repeated here.

[0087] In addition, the first CO ratio of the first area 1 may be greater than the first CO ratio of the second area 2, and the difference between the first CO ratio of the first area 1 and the first CO ratio of the second area 2 may specifically be 4% to 20%, for example, 4%, 4.5%, 5%, 5.5%, 6%, 8%, 10%, 13%, 15%, 18%, 20% or a range consisting of any two thereof.

[0088] In some embodiments, the first CO ratio of the first region 1 can be greater than or equal to 20%, specifically 20% to 50%, for example, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50% or a range consisting of any two thereof.

[0089] After further research, it was found that the first CO ratio of the second region 2 can be less than or equal to 20%, which can further improve the battery's first efficiency and cycle life and other performance. One of the reasons for the analysis is that the first CO ratio can indicate the degree of oxidation of the carbon element to a certain extent. By controlling the second region 2 to have a lower first CO ratio (less than or equal to 20%), the degree of oxidation of the carbon element in the second region 2 can be reduced, thereby ensuring that more carbon elements participate in the ion insertion and extraction reaction (such as lithium ions) during the battery cycle, thereby improving the battery's first efficiency and cycle life and other performance.

[0090] In some embodiments, the first CO ratio of the second region 2 can specifically be 0.1% to 20%, for example, 0.1%, 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20% or a range consisting of any two thereof.

[0091] In addition, the functional coating (first region 1, second region 2) may contain PO chemical bonds, the PO ratio of the first region 1 may be smaller than the PO ratio of the second region 2, and the ratio of the PO ratio of the second region 2 to the PO ratio of the first region 1 may specifically be 1.01 to 2, for example, 1.01, 1.1, 1.2, 1.3, 1.4, 1.5, 1.8, 2 or a range consisting of any two of them.

[0092] Exemplarily, the PO ratio of the first region 1 may be 30% to 35%, for example, 31%, 32%, 33%, 34%, 35% or a range consisting of any two thereof, and the PO ratio of the second region 2 may be 32% to 38%, for example, 32%, 33%, 34%, 35%, 36%, 37%, 38% or a range consisting of any two thereof.

[0093] In addition, the functional coating (first region 1, second region 2) may contain SO chemical bonds, the SO ratio of the first region 1 may be smaller than the SO ratio of the second region 2, and the ratio of the SO ratio of the second region 2 to the SO ratio of the first region 1 may be 1.01 to 1.5, for example, 1.01, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, or a range consisting of any two thereof.

[0094] Illustratively, the SO ratio of the first region 1 may be 18% to 30%, for example, 18%, 20%, 23%, 25%, 28%, 30% or a range consisting of any two thereof, and the SO ratio of the second region 2 may be 20% to 32%, for example, 20%, 23%, 25%, 28%, 30%, 32% or a range consisting of any two thereof.

[0095] In addition, the first C=O ratio of the first region 1 may be smaller than the first C=O ratio of the second region 2, and the ratio of the first C=O ratio of the second region 2 to the first C=O ratio of the first region 1 may be 1.01 to 2, for example, 1.01, 1.1, 1.2, 1.3, 1.4, 1.5, 1.8, 2, or a range consisting of any two thereof.

[0096] For example, the first C=O ratio of the first region 1 may be 12% to 27%, for example, 12%, 15%, 18%, 20%, 23%, 25%, 27% or a range consisting of any two thereof, and the first C=O ratio of the second region 2 may be 20% to 32%, for example, 20%, 23%, 25%, 28%, 30%, 32% or a range consisting of any two thereof.

[0097] Specifically, in each of the above regions (first region 1 or second region 2), the first CO ratio (CO molar content) refers to the ratio of the number of O that forms CO chemical bonds with C in the region to the total number of O in the region, the PO ratio (PO molar content) refers to the ratio of the number of O that forms PO chemical bonds with P in the region to the total number of O in the region, the SO ratio (SO molar content) refers to the ratio of the number of O that forms SO chemical bonds with S in the region to the total number of O in the region, and the first C=O ratio refers to the ratio of the number of O that forms C=O chemical bonds with C in the region to the total number of O. More specifically, taking the first CO ratio as an example, the first CO ratio of the first region 1 refers to the ratio of the number of CO in the first region 1 to the total number of O in the first region 1, and the first CO ratio of the second region 2 refers to the ratio of the number of CO in the second region 2 to the total number of O in the second region 2.

[0098] During specific implementation, XPS analysis can be performed on the functional coating (first region 1, second region 2, etc.), and the O1s orbital can be analyzed to determine the O1s valence bond types (such as CO, C=O, PO, SO, etc.) and their ratios. Taking the first CO ratio as an example, the first CO ratio refers to the molar content of CO in the O1s analysis result, that is, the ratio of the number of O corresponding to CO to the total number of O (that is, the sum of the number of O corresponding to all oxygen-containing groups).

[0099] For example, the O1s orbital analysis results of the XPS analysis of the functional coating show that the oxygen-containing groups in the first region 1 are CO, C=O, PO, and SO. Therefore, the first CO ratio of the first region 1 = the number of CO / (the number of CO + the number of C=O + the number of PO + the number of SO). The calculation method for the ratio of other oxygen-containing groups is similar and will not be repeated here.

[0100] Generally, the carbon elements in the functional coating (including those in CO chemical bonds, C=O chemical bonds, C=F chemical bonds, and graphite C) primarily come from the graphite in the functional coating, which serves as the negative electrode active material. For negative electrode sheets containing graphite, by controlling parameters such as the oxygen content, first CO ratio, carbon ratio, and CF ratio in the first and second regions 1 and 2 to meet the aforementioned ranges, the initial efficiency and cycle life of batteries using such negative electrode sheets can be improved.

[0101] In some embodiments, the content of lithium in the functional coating can be 0.01 mg / cm 2 ~2mg / cm 2 , for example 0.01 mg / cm 2 , 0.05mg / cm 2 , 0.1mg / cm 2 , 0.3mg / cm 2 , 0.5mg / cm 2 , 0.8mg / cm 2 , 1mg / cm 2 , 1.3mg / cm 2 , 1.5mg / cm 2 , 1.8mg / cm 2 , 2mg / cm 2 or a range consisting of any two of them.

[0102] The content of lithium element refers to the content per unit area (in cm 2 The mass of lithium element in the functional coating (in units of ) can be calculated based on the surface area of ​​the functional coating facing away from the current collector. A region with an area of ​​S is selected, and all the functional coatings in the region are scraped off (that is, after the functional coating in the region is scraped off, the current collector surface is exposed). The mass of lithium element in the scraped coating material is recorded as m, and the ratio of m to S (i.e., m / S) is the content of lithium element.

[0103] Specifically, the area of ​​the first region 1 is usually small, and it basically does not affect the lithium content in the functional coating. Therefore, the lithium content in the second region 2 is generally substantially equal to the lithium content in the above-mentioned functional coating.

[0104] Specifically, the second region 2 is the main region of the functional coating, the projected area of ​​the second region 2 on the current collector and the length of the second region 2 in the first direction are both larger than the first region 1, and the first direction is parallel to the direction from the first region 1 to the second region 2 (or the direction from the second region 2 to the first region 1), that is, the first region 1 and the second region 2 are distributed along the first direction.

[0105] For example, the first direction can be parallel to the length direction of the negative electrode sheet, that is, the first region 1 and the second region 2 can be distributed along the length direction of the negative electrode sheet. At this time, the length direction of the first region 1 is parallel to the width direction of the negative electrode sheet, the width direction of the first region 1 is parallel to the length direction of the negative electrode sheet, the length direction of the second region 2 is parallel to the length direction of the negative electrode sheet, and the width direction of the second region 2 is parallel to the width direction of the negative electrode sheet. The length of the first region 1 in the width direction of the negative electrode sheet can be equal to the width of the second region 2 in the width direction of the negative electrode sheet, and the length of the second region 2 in the length direction of the negative electrode sheet is greater than the width of the first region 1 in the length direction of the negative electrode sheet.

[0106] In addition, as shown in Figure 1, the negative electrode sheet also includes a negative electrode ear 3, which is located on the side of the first region 1 away from the second region 2 in the first direction, that is, in the first direction, the projection of the negative electrode ear 3 on the plane where the negative electrode collector is located is located on the side of the projection of the first region 1 on the plane where the negative electrode collector is located away from the projection of the second region 2 on the plane where the negative electrode collector is located.

[0107] In some embodiments, the negative electrode tab 3 may be formed by extending the negative electrode current collector outward in the direction from the second region 2 to the first region 1. As shown in FIG1 , the negative electrode tab 3 extends outward in the first direction away from the second region 2 (i.e., from the second region 2 to the first region 1) and exceeds an edge of the first region 1 in the first direction away from the second region 2.

[0108] Continuing with reference to FIG1 , the first region 1 may include a first sub-region 11 and a second sub-region 12, which are respectively located on opposite sides of the negative electrode tab 3 in the second direction (i.e., one side of the negative electrode tab 3 is the first sub-region 11, and the other side is the second sub-region 12), that is, the negative electrode tab 3 is located between the first sub-region 11 and the second sub-region 12 in the second direction, that is, in the second direction, the projection of the negative electrode tab 3 on the plane where the negative electrode current collector is located is located between the projection of the first sub-region 11 on the plane where the negative electrode current collector is located and the projection of the second sub-region 12 on the plane where the negative electrode current collector is located.

[0109] Continuing to refer to FIG. 1 , the second region 2 may include a main region 21 and an extension region 22 connected to the main region 21 . The extension region 22 is formed by extending outward from the main region 21 along a direction from the second region 2 to the first region 1 .

[0110] Among them, in the second direction, the extension area 22 of the second region 2 is located between the first sub-region 11 and the second sub-region 12, that is, the first sub-region 11, the extension area 22 and the second sub-region 12 are distributed in sequence along the second direction, and the projection of the negative electrode ear 3 on the plane where the negative electrode collector is located is connected to the projection of the extension area 22 on the plane where the negative electrode collector is located, and the two can be in direct contact, but are not limited to this.

[0111] Specifically, the negative electrode current collector of the second region 2 extends outward in the first direction to form an extension portion located between the first sub-region 11 and the second sub-region 12. At the same time, the functional coating of the second region 2 extends to a partial area of ​​the extension portion, forming an extension region 22 in this partial area, and the remaining area of ​​the extension portion is the negative electrode ear 3.

[0112] In addition, as shown in FIG1 , in the first direction, the side of the extension region 22 away from the main region 21 may extend beyond the edge of the side of the first region 1 away from the second region 2 , that is, the side of the extension region 22 away from the main region 21 is located between the negative electrode ear and the first region 1 .

[0113] Specifically, the second direction intersects with the thickness direction of the functional coating (also the thickness direction of the negative electrode sheet), and the two can be perpendicular; the first direction is basically parallel to the direction from the second region 2 to the first region 1, and the second direction intersects with the first direction, and the two can be perpendicular, for example, the first direction is parallel to the length direction of the negative electrode sheet, and the second direction is parallel to the width direction of the negative electrode sheet.

[0114] Generally, there is a clear boundary between the first area 1 and the second area 2. Specifically, the colors and other forms of the two areas are different. For example, the color of the first area 1 is darker than that of the second area 2. For example, the second area 2 is gray-black, and the second area 2 is darker than the first area 1, so that there is a clear boundary between the two areas.

[0115] As mentioned above, in the negative electrode sheet of the embodiment of the present application, its functional coating may include a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material may include graphite and / or silicon-based active materials, wherein the silicon-based active material may include one or more of silicon, silicon-carbon material, silicon-oxygen-carbon material, etc.

[0116] In addition, the above-mentioned negative electrode active material layer also includes a conductive agent and a binder. The conductive agent includes, for example, at least one of conductive carbon black, acetylene black, carbon nanotubes, conductive graphite, and graphene, and the binder includes, for example, polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, carboxymethyl cellulose sodium (CMC), polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and one or more of styrene-butadiene rubber (SBR).

[0117] In some embodiments, in the negative electrode active material layer, based on the total mass of the negative electrode active material, the binder and the conductive agent, the mass content of the negative electrode active material can be 80% to 99.8%, the mass content of the binder can be 0.1% to 10%, and the mass content of the conductive agent can be 0.1% to 10%.

[0118] Specifically, the negative electrode active material layer can be provided on one surface of the negative electrode current collector, or on both the front and back surfaces of the negative electrode current collector. The negative electrode current collector can be a conventional negative electrode current collector in the art, such as copper foil.

[0119] In the embodiments of the present application, a negative electrode sheet precursor to be pre-lithiated can be prepared by conventional methods in the art, such as coating, and then subjected to lithium replenishment and laser cutting processes to produce a negative electrode sheet. For example, the preparation process of the negative electrode sheet precursor to be pre-lithiated may include: mixing materials for forming a functional coating, such as a negative electrode active material, a binder, and a conductive agent, with a solvent to prepare a negative electrode slurry; then applying the negative electrode slurry to at least one surface of a negative electrode current collector; and then, after drying and rolling processes, forming a functional coating on the surface of the negative electrode current collector to produce the negative electrode sheet precursor to be pre-lithiated.

[0120] In the embodiment of the present application, during specific implementation, the negative electrode sheet precursor to be pre-lithiated (including the negative electrode current collector and the functional coating to be replenished with lithium) can be pre-lithiated (i.e., replenished with lithium) through an electrochemical lithium replenishment process. Specifically, the negative electrode sheet to be pre-lithiated and the counter electrode containing a lithium source can be placed in an electrolytic cell containing a second electrolyte, and the negative electrode sheet to be pre-lithiated and the counter electrode containing a lithium source are connected to form a pathway, so as to replenish lithium for the negative electrode sheet to be pre-lithiated through an electrochemical process to obtain a pre-lithiated negative electrode sheet precursor; and then the pre-lithiated negative electrode sheet precursor is cut into a preset shape through processes such as laser cutting, so as to obtain the negative electrode sheet of the embodiment of the present application.

[0121] Among them, the counter electrode containing a lithium source includes, for example, a lithium metal sheet and / or an electrode containing a lithium salt. Through the electrochemical lithium replenishment process, the lithium in the counter electrode can be embedded into the functional coating of the negative electrode sheet, thereby achieving pre-lithiation of the negative electrode sheet (i.e., lithium replenishment).

[0122] Specifically, the second electrolyte includes an organic solvent and a lithium salt. The organic solvent includes, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MiPC), 1,4-butyrolactone (GBL), dimethyltetrahydrofuran (2Me-THF), tetrahydrofuran (THF), butylene carbonate (BC), 1,2-dimethoxyethane (DME), dibutyl carbonate (DBC), methyl butyl carbonate (BMC), dipropyl carbonate (DPC), methyl ester (PA), ethyl acetate (MA), methyl formate (MF), methyl propionate (MP), etc. One or more.

[0123] In addition, the lithium salt in the second electrolyte may include LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborate, lower aliphatic carboxylic acid lithium, 4-phenylborate, etc. One or more.

[0124] Specifically, the F element, as well as elements such as S and P in the functional coating can be derived from components such as the binder in the second electrolyte and / or the electrode, and generally can be mainly derived from lithium salts and / or organic solvents in the second electrolyte.

[0125] An embodiment of the present application also provides a battery, which includes the aforementioned negative electrode sheet. As mentioned above, the use of the aforementioned negative electrode sheet can improve the battery's initial efficiency and cycle life and other performance.

[0126] Specifically, the battery of the embodiment of the present application may include a lithium-ion battery. By adopting the above-mentioned negative electrode sheet, the performance of the lithium-ion battery, such as the first effect and cycle life, can be significantly improved.

[0127] Generally, a battery includes a cell, a first electrolyte, and a package that encapsulates the cell. The cell includes a positive electrode sheet, a separator, and a negative electrode sheet. The separator is located between the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting.

[0128] Specifically, the battery cell can be a wound battery cell (i.e., the positive electrode sheet, separator and negative electrode sheet are stacked and then wound to form a wound structure), or the battery cell can also be a laminated structure (the positive electrode sheet, separator and negative electrode sheet are stacked in sequence).

[0129] Specifically, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material may include a lithium-containing active material, such as at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, a ternary material, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, and a lithium-rich manganese-based material. The ternary material may include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide, etc. The binder and conductive agent may be conventional materials in the art, such as the binder and conductive agent in the negative electrode active material layer listed above, which will not be repeated here. It should be noted that the binder or conductive agent in the positive electrode active material layer and the negative electrode active material layer may be the same or different, and there is no particular limitation on this.

[0130] Specifically, the mass percentage of the positive electrode active material may be 80% to 99%, the mass percentage of the conductive agent may be 0.1% to 1%, and the mass percentage of the binder may be 0.1% to 1%.

[0131] Specifically, the positive electrode active material layer can be provided on one surface of the positive electrode current collector, or on both the front and back surfaces of the positive electrode current collector. The positive electrode current collector can be a conventional positive electrode current collector in the art, such as aluminum foil.

[0132] Specifically, the first electrolyte used may include an organic solvent and a lithium salt, the organic solvent may include dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MiPC), 1,4-butyrolactone (GBL), dimethyltetrahydrofuran (2Me-THF), tetrahydrofuran (THF), butylene carbonate (BC), 1,2-dimethoxyethane (DME), dibutyl carbonate (DBC), methyl butyl carbonate (BMC), dipropyl carbonate (DPC), methyl ester (PA), ethyl acetate (MA), methyl formate (MF), methyl propionate (MP) in one or more, and the lithium salt may include LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , one or more of LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborate, lower aliphatic carboxylic acid lithium, and 4-phenylborate.

[0133] In addition, the concentration of the lithium salt in the first electrolyte may be 0.1 mol / L to 3 mol / L.

[0134] Specifically, the battery of the embodiment of the present application may be a soft-pack battery (such as a soft-pack lithium-ion battery), and its packaging body may include an aluminum-plastic film, but is not limited thereto.

[0135] The battery of the present application can be manufactured according to conventional methods in the field. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be stacked in sequence, wound (or laminated) to form a bare battery cell, and then the bare battery cell is placed in a package. The electrolyte is then injected into the battery cell in the package (i.e., liquid injection), and then the battery is manufactured after processes such as packaging (such as vacuum packaging), standing, forming, shaping, and capacity testing.

[0136] The steps / processes in the above-mentioned battery preparation process are all conventional operations in the field and are not particularly limited in the embodiments of this application. For example, during formation, the battery can be first charged at a constant current rate of 0.1C to 4% SOC, and then charged at a constant current rate of 0.2C to 10% SOC, thus completing the formation process.

[0137] As mentioned above, during the preparation process of the negative electrode sheet of the embodiment of the present application, it can be pre-lithiated through an electrochemical lithium replenishment process. The electrochemical lithium replenishment process usually forms a partial SEI film, and the SEI film will be further formed in the formation process during the battery preparation process.

[0138] The present application is further described below through specific examples. In the following examples and comparative examples, XPS analysis was performed directly on the negative electrode sheet prepared in step 2 (i.e., the negative electrode sheet before being fabricated into a battery). The analysis results were substantially consistent with the XPS analysis results obtained using the negative electrode sheet disassembled from the battery. Therefore, the following examples and comparative examples only show the XPS analysis data obtained using the negative electrode sheet disassembled from the battery (Tables 1 to 12).

[0139] Example 1

[0140] The structure of the negative electrode sheet of this embodiment 1 is shown in FIG1 , and includes a copper foil (negative electrode current collector) and a negative electrode active material layer located on both the front and back surfaces of the copper foil, wherein the negative electrode active material layer contains lithium.

[0141] The negative electrode active material layer includes a second region and a first region located on one side of the second region, wherein the first region extends to an edge of the copper foil in a direction away from the second region;

[0142] The negative electrode sheet also includes a negative electrode ear formed by extending outward from the copper foil;

[0143] The negative electrode ear is located on a side of the first region away from the second region in a first direction, and the first direction is parallel to a direction from the second region to the first region;

[0144] The first region includes a first subregion and a second subregion distributed along a second direction, the negative electrode tab is located between the first subregion and the second subregion in the second direction, and the second direction is substantially perpendicular to the direction from the second region to the first region;

[0145] The second region includes a main region and an extension region. The extension region is located between the first subregion and the second subregion. The projection of the negative electrode tab on the plane where the copper foil is located is connected to the projection of the extension region on the plane where the copper foil is located.

[0146] The preparation process of the negative electrode sheet and the battery of this embodiment 1 is as follows:

[0147] 1. Preparation of batteries

[0148] 1. Preparation of positive electrode

[0149] Lithium cobalt oxide, conductive carbon black and polyvinylidene fluoride are added to a stirring tank in a mass ratio of 97:1.5:1.5, and then NMP solvent is added to prepare a positive electrode slurry (the solid content of the positive electrode slurry is 70% to 75%); the positive electrode slurry is then coated on the front and back surfaces of the aluminum foil using a coating machine, and then dried at 120°C for 8 hours. After drying, it is first cut into small strips and welded to the aluminum tabs to obtain the positive electrode sheet.

[0150] 2. Preparation of negative electrode sheet

[0151] (1) Graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.5:1:1.5:1:1, and water was added thereto for mixing and homogenization to obtain a negative electrode slurry (solid content of 45%);

[0152] The negative electrode slurry was prepared at a single surface density of 16 mg / cm 2 The slurry was coated on both sides of a copper foil with a thickness of 6 μm, then dried in a 50° C. oven, and then roller-pressed at room temperature to form a substrate (i.e., the negative electrode sheet to be pre-lithiated).

[0153] (2) Pre-lithiation

[0154] Placing the negative electrode sheet to be pre-lithiated and the lithium metal sheet in an electrolytic cell containing a second electrolyte, and connecting the negative electrode sheet to be pre-lithiated with the lithium metal sheet to form a pathway, so as to replenish lithium to the negative electrode sheet to be pre-lithiated through an electrochemical process, thereby obtaining a pre-lithiated negative electrode sheet precursor;

[0155] Among them, a solution prepared by LiPF6 and a non-aqueous organic solvent in a mass ratio of 8:92 is used as the second electrolyte, wherein the non-aqueous organic solvent is composed of ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and vinylene carbonate (VC) in a mass ratio of 8:85:5:2 (i.e. EC:DEC:EMC:VC=8:85:5:2).

[0156] (3) Laser cutting

[0157] A nanosecond laser is used to cut the pre-lithiated negative electrode sheet precursor obtained in step (2) to obtain a negative electrode sheet; wherein, during cutting, the laser power is 540W (the full power of the nanolaser is 1000W, and during cutting, its power is adjusted to 54%, so that the laser power during cutting is 540W), the cutting speed is 50mm / s, and the frequency (pulsed laser frequency) is 3000kHz; after cutting, the width of the first region of the obtained negative electrode sheet is about 1mm, and particles are formed at the edge of the first region. The structural schematic diagram of the obtained negative electrode sheet is shown in Figure 1, which is not repeated here.

[0158] 3. Preparation of lithium-ion batteries

[0159] The positive electrode sheet, separator, and negative electrode sheet are stacked in order (with the separator placed between the positive and negative electrodes to isolate them), and then wound into a bare cell; wherein the separator is composed of a polypropylene substrate with a thickness of 5μm and a ceramic coating of 3μm (the total thickness of the separator is about 8μm);

[0160] Place the bare battery cell in the aluminum-plastic film;

[0161] The first electrolyte is injected into the bare cell in the aluminum-plastic film, and the soft-pack lithium-ion battery is manufactured through vacuum packaging, static standing, formation (charging at a constant current of 0.1C to 4% SOC, then charging at a constant current of 0.2C to 10% SOC), shaping, and capacity testing.

[0162] Among them, a solution prepared by LiPF6 and a non-aqueous organic solvent in a mass ratio of 8:92 is used as the electrolyte (i.e., the first electrolyte) of the lithium-ion secondary battery, wherein the non-aqueous organic solvent is composed of ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and vinylene carbonate (VC) in a mass ratio of 8:85:5:2 (i.e., EC:DEC:EMC:VC=8:85:5:2).

[0163] 2. Testing

[0164] 1. Disassemble the soft-pack lithium-ion battery, select one fold of the negative electrode sheet, clean it with dimethyl carbonate (DMC), and then vacuum dry it;

[0165] 2. XPS testing was performed on the first area (laser cutting area) and the second area (normal area) of the negative electrode active material layer of the dried negative electrode sheet, and C1s and O1s analysis was performed. The results are shown in Table 1, Table 2, Table 3, Figure 2, Figure 3, Figure 4 and Figure 5 (Figure 2 is the O1s analysis spectrum of the XPS analysis of the first area, Figure 3 is the O1s analysis spectrum of the XPS analysis of the second area, Figure 4 is the C1s analysis spectrum of the XPS analysis of the first area, and Figure 5 is the C1s analysis spectrum of the XPS analysis of the second area).

[0166] Table 1 Atomic content percentage in different regions

[0167] Table 2 Types and proportions of XPS O1s valence bonds in different regions

[0168] Table 3 Types and proportions of XPS C1s bonds in different regions

[0169] Comparative Example 1: The difference from Example 1 is that the pre-lithiation process of step (2) is not performed (ie, the negative electrode active material layer is not replenished with lithium), and the other conditions are the same as those of Example 1.

[0170] Referring to the test process of Example 1, the battery of Comparative Example 1 was disassembled, and a fold of the negative electrode sheet was taken. After cleaning and drying, XPS testing was performed on the first area (laser cutting area) and the second area (normal area) of the negative electrode active material layer of the negative electrode sheet, and C1s and O1s analysis were performed. The results are shown in Tables 4, 5 and 6.

[0171] Table 4 Atomic content percentage in different regions

[0172] Table 5 Types and proportions of XPS O1s valence bonds in different regions

[0173] Table 6 XPS C1s bond types and proportions in different regions

[0174] Example 2: The difference from Example 1 is that the negative electrode active material of the negative electrode sheet includes graphite and silicon oxide, and the mass ratio of graphite to silicon oxide is 4:1; the other conditions are the same as Example 1;

[0175] Referring to the test process of Example 1, the battery of Example 2 was disassembled, and a fold of the negative electrode sheet was taken. After cleaning and drying, XPS testing was performed on the first area (laser cutting area) and the second area (normal area) of the negative electrode active material layer of the negative electrode sheet, and C1s and O1s analysis were performed. The results are shown in Tables 7, 8 and 9.

[0176] Table 7 Atomic content percentage in different regions

[0177] Table 8 XPS O1s valence bond types and proportions in different regions

[0178] Table 9 XPS C1s bond types and proportions in different regions

[0179] Comparative Example 2: The difference from Example 2 is that the pre-lithiation process of step (2) is not performed (ie, the negative electrode active material layer is not replenished with lithium), and the other conditions are the same as those of Example 2.

[0180] Referring to the test process of Example 1, the battery of Comparative Example 2 was disassembled, and a fold of the negative electrode sheet was taken. After cleaning and drying, XPS testing was performed on the first area (laser cutting area) and the second area (normal area) of the negative electrode active material layer of the negative electrode sheet, and C1s and O1s analysis were performed. The results are shown in Tables 10, 11 and 12.

[0181] Table 10 Atomic content percentage in different regions

[0182] Table 11 XPS O1s bond types and proportions in different regions

[0183] Table 12 XPS C1s bond types and proportions in different regions

[0184] The lithium replenishment amount of the negative electrode active material layer of the negative electrode sheets in Examples 1 and 2, Comparative Examples 1 and 2, as well as the capacity retention rate of the battery at the first cycle and after 10,000 cycles are shown in Table 13.

[0185] Among them, the first-effect test process is: place the lithium-ion battery on the Blue Electric Battery Charge and Discharge Test Cabinet for charge and discharge cycle test. The test conditions are 30℃, 0.05C / 0.05C charge and discharge, and the charge and discharge start and end voltage is 3.0-4.30V. Record the battery's first cycle (first cycle) charge and discharge capacity, and calculate the battery's first effect according to the battery's first effect = discharge capacity / charge capacity.

[0186] The test process of the capacity retention rate after 1000 cycles is as follows: in a constant temperature box at 25°C, charge at a constant current rate of 1C to a voltage of 4.4V, then charge at a constant voltage of 4.4V to a current of 0.05C, and then discharge at a constant current rate of 1C to a voltage of 3.0V, cycle 1000 times, and measure the capacity retention rate after 1000 cycles (capacity retention rate = capacity at 1000 cycles / initial capacity of the battery).

[0187] Table 13 Amount of lithium supplemented in the negative electrode sheets, initial efficiency of the battery and capacity retention rate of each embodiment and comparative example

[0188] It can be seen from Table 13 that, whether it is a graphite negative electrode or a silicon-doped negative electrode, by supplementing lithium and controlling the content of elements such as oxygen in the first and second regions, the first efficiency, discharge capacity and capacity retention rate of the negative electrode sheet can be effectively improved.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a functional coating located on at least one surface of the negative electrode current collector, and the functional coating contains lithium element; The functional coating includes a second region and a first region located on at least one side of the second region, and the first region extends along a direction away from the second region to the edge of the negative electrode current collector; Particles are formed at the edge of the first region; In the X-ray photoelectron spectroscopy analysis result of the functional coating, the ratio of the molar content of oxygen element in the first region to the width of the first region is greater than 0.3, and the unit of the width is mm.

2. The negative electrode sheet according to claim 1, wherein In the X-ray photoelectron spectroscopy analysis result of the functional coating, the molar content of oxygen element in the second region is less than or equal to 20%; And / or, in the X-ray photoelectron spectroscopy analysis result of the functional coating, the molar content of oxygen element in the first region is greater than 20%.

3. The negative electrode sheet according to claim 1, wherein The width of the first region is less than or equal to 1 mm.

4. The negative electrode sheet according to claim 1, characterized in that, The functional coating contains fluorine element, wherein In the X-ray photoelectron spectroscopy analysis result of the functional coating, the molar content of fluorine element in the first region is less than or equal to 15%; And / or, in the X-ray photoelectron spectroscopy analysis result of the functional coating, the molar content of fluorine element in the second region is greater than or equal to 15%; And / or, in the X-ray photoelectron spectroscopy analysis result of the functional coating, the difference between the molar content of fluorine element in the second region and the molar content of fluorine element in the first region is 5% - 30%.

5. The negative electrode sheet according to claim 1, wherein In the X-ray photoelectron spectroscopy analysis result of the functional coating, the difference between the molar content of carbon element in the second region and the molar content of carbon element in the first region is less than or equal to 10%; And / or, the graphite C ratio in the first region is less than or equal to 60%, and / or, the graphite C ratio in the second region is greater than 60%; wherein, the graphite C ratio refers to the proportion of the number of graphite carbon to the total number of carbon elements; And / or, the functional coating contains fluorine element, and the C-F ratio in the first region is greater than or equal to 15%, and the C-F ratio refers to the proportion of the number of carbon elements forming C-F chemical bonds with fluorine element to the total number of carbon elements; And / or, the C-F ratio in the second region is less than 15%, and the C-F ratio refers to the proportion of the number of carbon elements forming C-F chemical bonds with fluorine element to the total number of carbon elements; And / or, the first C-O ratio in the first region is greater than or equal to 20%, and the first C-O ratio refers to the proportion of the number of oxygen elements forming C-O chemical bonds with carbon elements to the total number of oxygen elements; And / or, the first C-O ratio in the second region is less than or equal to 20%, and the first C-O ratio refers to the proportion of the number of oxygen elements forming C-O chemical bonds with carbon elements to the total number of oxygen elements.

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, The functional coating includes a negative electrode active material, and the negative electrode active material includes graphite and / or a silicon-based active material.

7. The negative electrode sheet according to any one of claims 1-5, characterized in that, The content of the lithium element in the functional coating is 0.01 mg / cm 2 ~2 mg / cm 2 .

8. The negative electrode sheet according to any one of claims 1-5, characterized in that, The functional coating also contains phosphorus element and / or sulfur element.

9. The negative electrode sheet according to any one of claims 1-5, characterized in that, The negative electrode sheet also includes a negative electrode tab, wherein The negative electrode ear is located on a side of the first region away from the second region in a first direction, and the first direction is parallel to a direction from the second region to the first region; And / or, the first region includes a first sub-region and a second sub-region distributed along a second direction, the negative electrode ear is located between the first sub-region and the second sub-region in the second direction, and the second direction intersects with a direction from the second region to the first region; And / or, the first region includes a first sub-region and a second sub-region, the second region includes an extension region located between the first sub-region and the second sub-region, and the projection of the negative electrode ear on the plane where the negative electrode collector is located is connected to the projection of the extension region on the plane where the negative electrode collector is located.

10. A battery, characterized in that, A negative electrode sheet comprising any one of claims 1 to 9.

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