Negative electrode sheet, secondary battery, battery module, battery pack, and power consumption device

Abstract

The present application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack, and a power consumption device, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector, the negative electrode film layer including a first negative electrode film layer and a second negative electrode film layer, the second negative electrode film layer being located between the negative electrode current collector and the first negative electrode film layer, the second negative electrode film layer including a metal element M, and M having an atomic radius r M and atomic radius r of Li Li teeth and a negative electrode film layer that satisfies the above criteria. The present invention effectively inhibits lithium metal deposition on the surface of the negative electrode sheet, thereby significantly improving the dynamic characteristics, cycle characteristics, and safety of the secondary battery.

Description

[Technical Field]

[0001] This application relates to the technical field of secondary batteries, and more specifically to negative electrode sheets, secondary batteries, battery modules, battery packs, and power consumption devices. [Background technology]

[0002] In recent years, with the application and widespread use of secondary batteries in various electronic products and new energy vehicles, their energy density has attracted increasing attention. However, during high-rate charging of secondary batteries, lithium deposition inevitably occurs on the surface of the negative electrode sheet. Furthermore, lithium deposition also occurs on the surface of the negative electrode sheet during overcharging of secondary batteries. [Overview of the Initiative]

[0003] The present invention aims to provide a negative electrode sheet, a secondary battery, a battery module, a battery pack, and a power consumption device in order to solve the lithium deposition problem that occurs in secondary batteries under high-rate charging and overcharging conditions, effectively suppress the deposition of lithium metal on the surface of the negative electrode sheet, and significantly improve the dynamic characteristics, cycle characteristics, and safety of the secondary battery.

[0004] A first aspect of the present application provides a negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector. The negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, wherein the second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer. The second negative electrode film layer contains a metallic element M, and the atomic radius of M is r M and the atomic radius r of Li Li teeth Satisfy the requirements of JPEG0007880320000001.jpg2066.

[0005] The negative electrode film layer of this application has a multilayer structure, and the second negative electrode film layer contains the metal element M. The difference in atomic radii between M and Li is small, resulting in a small lattice misfit. Thus, Li is more easily dissolved on the surface of M. When the secondary battery is subjected to high-rate charging or overcharging, the surface of M acts as a preferential nucleation site for lithium metal, inducing the deposition of lithium metal on the surface of M in the second negative electrode film layer. This effectively suppresses the deposition of lithium metal on the surface of the negative electrode sheet, improving the dynamic characteristics, cycle characteristics, and safety of the secondary battery. When the difference in atomic radii between M and Li is small, the lattice structure of M is better suited to the lattice structure of Li, and Li is more easily nucleated on the surface of M, thus having a greater effect in suppressing the deposition of lithium metal on the surface of the negative electrode sheet. The negative electrode sheet of this application can effectively suppress the deposition of lithium metal on the surface of the negative electrode sheet, and therefore the secondary battery not only has good dynamic characteristics but also a significantly improved cycle life.

[0006] In any embodiment of the present application, the atomic radius r of M M and the atomic radius r of Li Li teeth, Satisfy the requirements for JPEG0007880320000002.jpg2267.

[0007] By controlling the difference in atomic radii between M and Li to an appropriate range, the deposition of lithium metal on the surface of the negative electrode sheet can be more effectively suppressed, further improving the dynamic characteristics, cycle characteristics, and safety of the secondary battery.

[0008] In any embodiment of the present application, M is selected from one or more of Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, Al, Sc, Mo, W, Pt, Pd, In, Re, Ir, Ga, Os, V, Zn, Ru, and Rh. Selectively, M is selected from one or more of Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, and Al.

[0009] When M is selected from the above-mentioned metal elements, its lattice structure is more compatible with the lattice structure of Li, and Li more easily induces nucleation on the surface of M, thus having a greater effect in suppressing the deposition of lithium metal on the surface of the negative electrode sheet, further improving the dynamic characteristics, cycle characteristics, and safety of the secondary battery.

[0010] In any embodiment of the present application, M is located at least in the main body portion of the negative electrode film layer.

[0011] In any embodiment of the present application, the second negative electrode film layer includes, along its own thickness direction, a first surface and a second surface facing each other, the first surface being provided backward from the negative electrode current collector and the second surface being provided toward the negative electrode current collector, and M is located on the first surface of the second negative electrode film layer facing backward from the negative electrode current collector and / or on the second surface of the second negative electrode film layer toward the negative electrode current collector.

[0012] In any embodiment of the present application, the mass percentage content of M is 3% to 7% based on the total mass of the second negative electrode film layer. Selectively, the mass percentage content of M is 3% to 5%.

[0013] Because the mass percentage content of M is within an appropriate range, the deposition of lithium metal on the surface of the negative electrode sheet can be effectively suppressed, and the shortening of the cycle life of the secondary battery can be effectively suppressed.

[0014] In any embodiment of the present application, the mass percentage content of M is 0.5% or less, based on the total mass of the first negative electrode film layer.

[0015] In any embodiment of the present application, the first negative electrode film layer does not contain the metal element M.

[0016] When the first negative electrode film layer does not contain or substantially does not contain the metal element M, it is possible to effectively ensure that lithium metal preferentially deposits on the surface of M in the second negative electrode film layer, and further suppress the deposition of lithium metal on the surface of the negative electrode sheet. In addition, since lithium metal preferentially deposits on the surface of M in the second negative electrode film layer, the first negative electrode film layer on the surface of the second negative electrode film layer can further achieve the effect of suppressing the rapid growth of lithium dendrites, and further extend the cycle life of the secondary battery.

[0017] In any embodiment of the present application, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.3 to 1.2. Optionally, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.5 to 0.8.

[0018] Since the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is within an appropriate range, not only can the deposition of lithium metal on the surface of the negative electrode sheet be effectively suppressed, but also the arrival of lithium dendrites on the surface of the negative electrode sheet can be effectively suppressed.

[0019] In any embodiment of the present application, the second negative electrode film layer contains metal particles, and the metal particles are selected from one or more of single particles of M and alloy particles of M.

[0020] In any embodiment of the present application, the alloy of M includes an alloy formed by two or more elements of M, and an alloy formed by one or more elements of M and one or more elements of another metal element M1.

[0021] In any embodiment of the present application, M 1 includes one or more of Fe, Cu, Ni, Cr, and Mn.

[0022] In any embodiment of the present application, the volume average particle diameter Dv50 of the metal particles is 5 μm or less. Optionally, the volume average particle diameter Dv50 of the metal particles is 1 μm or less.

[0023] By controlling the volume-average particle size Dv50 of the metal particles within an appropriate range, a sufficient number of nucleation sites can be formed in the second negative electrode film layer, and the deposition of lithium metal on the surface of the negative electrode sheet can be effectively suppressed.

[0024] In any embodiment of the present application, the second negative electrode film layer comprises Li-M alloy particles, Li-MM 1 It contains one or more types of alloy particles, M 1 represents a metallic element, and M1 includes one or more of Fe, Cu, Ni, Cr, and Mn.

[0025] A second aspect of the present application provides a secondary battery including the negative electrode sheet of the first aspect of the present application.

[0026] A third aspect of the present application provides a battery module including a secondary battery according to the second aspect of the present application.

[0027] A fourth aspect of the present application provides a battery pack including one of the secondary battery of the second aspect of the present application and one of the battery module of the third aspect of the present application.

[0028] A fifth aspect of the present application provides a power consumption device including one of the secondary battery of the second aspect of the present application, the battery module of the third aspect, and the battery pack of the fourth aspect.

[0029] The battery module, battery pack, and power consumption device of the present application include a secondary battery provided by the present application and therefore have at least the same advantages as the aforementioned secondary battery. [Brief explanation of the drawing]

[0030] To more clearly explain the technical solutions of the embodiments of the present application, the drawings used in the embodiments of the present application are briefly introduced below. Clearly, the drawings described below represent only a few embodiments of the present application, and those skilled in the art can obtain further drawings based on these drawings without any creative work. [Figure 1] Figure 1 is a schematic diagram of one embodiment of the negative electrode sheet according to the present application. [Figure 2] Figure 2 is a schematic diagram of one embodiment of the secondary battery according to the present invention. [Figure 3] Figure 3 is an exploded schematic diagram of one embodiment of the secondary battery according to the present invention. [Figure 4] Figure 4 is a schematic diagram of one embodiment of the battery module according to the present invention. [Figure 5] Figure 5 is a schematic diagram of one embodiment of the battery pack according to the present application. [Figure 6] Figure 6 is an exploded view of Figure 5. [Figure 7] Figure 7 is a schematic diagram of one embodiment of a power consumption device in which a secondary battery according to the present invention is used as a power source. [Figure 8] Figure 8 is a scanning electron microscope image of a cross-section of the negative electrode sheet of Example 1. [Explanation of symbols]

[0031] In drawings, the drawings are not always drawn to actual scale. The symbols used in the drawings are explained as follows: 1 Battery pack 2. Top box 3. Lower box 4 Battery Modules 5 Secondary battery 51 cases 52 Electrode assembly 53 Lid plate 10 Negative electrode sheets 11 Negative electrode current collector 121 First negative electrode layer 122 Second negative electrode film layer 1221 First surface 1222 Second surface [Modes for carrying out the invention]

[0032] The following describes embodiments of the negative electrode sheet, secondary battery, battery module, battery pack, and power consumption device of this application, with appropriate reference to the brief descriptions of the drawings, although unnecessary details may be omitted. For example, detailed explanations of well-known matters and redundant explanations of substantially identical structures may be omitted. This is to avoid the following explanation becoming unnecessarily verbose in order to facilitate understanding by those skilled in the art. The drawings and the following explanation are provided to enable those skilled in the art to fully understand this application and are not intended to limit the essence of the claims.

[0033] The “range” disclosed in this application is limited in the form of a lower limit and an upper limit, and a given range is limited by selecting one lower limit and one upper limit, and the boundaries of the given range are limited by the selected lower limit and upper limit. The range thus limited may include the values ​​at both ends, or it may not include the values ​​at both ends, and can be combined in any way, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​1 and 2, and the maximum range values ​​3, 4 and 5 are listed, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 can all be expected. In this application, unless otherwise specified, the numerical range “a-b” indicates an abbreviation for any combination of real numbers between a and b, and both a and b are real numbers. For example, the numerical range "0~5" means that all real numbers between "0~5" are listed in the text, and "0~5" is simply an abbreviation for combinations of these numbers. Furthermore, explaining that a parameter is an integer greater than or equal to 2 is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and selectable technical features of this application can be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably in order. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method mentioned above may further include step (c), meaning that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), and so on.

[0037] Unless otherwise specified, the terms “inclusion” and “inclusion” as used herein may be open-ended or closed-ended. For example, the terms “inclusion” and “inclusion” may further include or contain other components not listed, or may include or contain only the listed components.

[0038] Unless otherwise specified, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0039] [Secondary battery]

[0040] Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can be used by activating the active material through a method that allows them to be recharged after discharge.

[0041] Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During charging and discharging of the secondary battery, active ions (e.g., lithium ions) are inserted and removed back and forth between the positive and negative electrode sheets. The separator is placed between the positive and negative electrode sheets and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass through. The electrolyte is located between the positive and negative electrode sheets and primarily serves to conduct active ions.

[0042] [Negative electrode sheet]

[0043] During charging of a secondary battery, lithium ions desorb from the positive electrode and are inserted into the negative electrode. However, when a secondary battery is charged at a high rate or overcharged, the negative electrode insertion space becomes insufficient, and lithium ions desorb from the positive electrode too quickly, but cannot be inserted into the negative electrode in equal amounts. Lithium ions that cannot be inserted into the negative electrode in a timely manner have no choice but to gain electrons on the surface of the negative electrode sheet and are reduced to lithium metal, which is the lithium deposition phenomenon. Furthermore, when a secondary battery is charged at a high rate or overcharged, the negative electrode becomes highly polarized, and the surface potential of the negative electrode sheet continuously decreases, resulting in a Li / Li +When the potential is lower than the reference electrode potential, lithium ions obtain electrons on the surface of the negative electrode sheet and are reduced to lithium metal. Lithium precipitation not only degrades the performance of the secondary battery, for example, significantly shortening the cycle life, but after the lithium precipitation phenomenon occurs continuously, the lithium metal grows into a branch-like structure, that is, lithium dendrites. The growth of lithium dendrites destroys the solid electrolyte interface (SEI) film on the surface of the negative electrode active material, leading to irreversible consumption of active ions. The growth of lithium dendrites can further penetrate the separator and cause an internal short circuit, potentially causing safety risks such as combustion and explosion. The inventors found that lithium precipitation is mainly caused by the fact that the negative electrode active material is generally a lithium insertion-type material. The lithium insertion rate of these lithium insertion-type materials is low, making it difficult to meet the demand for high-rate charging of secondary batteries. Moreover, during overcharging of the secondary battery, it is difficult to prevent the generation of lithium metal on the surface of the negative electrode sheet by these lithium insertion-type materials, and it was discovered that the safety risk of the secondary battery increases.

[0044] To solve the problems of lithium precipitation occurring in secondary batteries under high-rate charging and overcharging conditions, and the resulting problems such as shortening of the cycle life and increase in safety risks of secondary batteries, the inventors conducted further extensive studies and found that they can effectively suppress the precipitation of lithium metal on the surface of the negative electrode sheet, significantly improve the kinetic characteristics, cycle characteristics and safety of secondary batteries, and in particular, improve the cycle characteristics and safety of secondary batteries under high-rate charging and overcharging conditions, and provide a negative electrode sheet.

[0045] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer. The second negative electrode film layer contains a metal element M, and the atomic radius r of M M and the atomic radius r of Li Li satisfies JPEG0007880320000003.jpg2365.

[0046] The negative electrode film layer of the present invention has a multilayer structure, and the second negative electrode film layer contains a metal element M, with a small difference in atomic radii between M and Li, resulting in a small lattice misfit. Thus, Li is more readily dissolved on the surface of M. The inventors discovered that after Li is dissolved on the surface of M, the crystalline structure of the formed solid solution is similar to the crystalline structure of Li, resulting in a low interfacial energy for Li nucleation on the surface of M. Interfacial energy is a source of nucleation resistance, and when the nucleation resistance of the surface of M is lower, the surface of M can be guided to precipitate on the surface of M rather than on the surface of the negative electrode sheet, as a preferential nucleation site for lithium metal.

[0047] When a secondary battery is subjected to high-rate charging or overcharging, the negative electrode becomes highly polarized, and the surface potential of the negative electrode sheet attempts to drop to the overpotential for lithium deposition. However, because the nucleation resistance of the surface of M contained in the second negative electrode film layer is lower, the overpotential for lithium deposition on its surface is lower than that of the negative electrode sheet. Therefore, lithium metal is induced to precipitate on the surface of M in the second negative electrode film layer, which serves as a preferential nucleation site for lithium metal. This effectively suppresses the deposition of lithium metal on the surface of the negative electrode sheet, improving the dynamic characteristics, cycle characteristics, and safety of the secondary battery.

[0048] When the difference in atomic radii between M and Li is small, the lattice structure of M better matches the lattice structure of Li, and Li more easily induces nucleation on the surface of M, thus having a greater effect in suppressing the deposition of lithium metal on the surface of the negative electrode sheet. When the difference in atomic radii between M and Li is large, for example, greater than 12%, and the lattice misfit between M and Li is large, the surface of M cannot be a preferential nucleation site for lithium metal, and the effect of inducing preferential nucleation of lithium metal on the surface of M in the second negative electrode film layer cannot be achieved. When the secondary battery is subjected to high-rate charging or overcharging, lithium metal still deposits on the surface of the negative electrode sheet, and the safety of the secondary battery cannot be effectively guaranteed.

[0049] The negative electrode sheet of this invention enables the safe use of conventional negative electrode active materials under high-rate charging and overcharge conditions, and the negative electrode sheet of this invention can effectively suppress the deposition of lithium metal on the surface of the negative electrode sheet. Therefore, the secondary battery not only has good kinetic characteristics but also a significantly improved cycle life.

[0050] In this application, the atomic radii of the metal elements M and Li can be found in Lange's Handbook of Chemistry.

[0051] In some embodiments, the atomic radius r of M M and the atomic radius r of Li Li teeth, Satisfy the requirements of JPEG0007880320000004.jpg2063.

[0052] By controlling the difference in atomic radii between M and Li to an appropriate range, the deposition of lithium metal on the surface of the negative electrode sheet can be more effectively suppressed, further improving the dynamic characteristics, cycle characteristics, and safety of the secondary battery.

[0053] In some embodiments, the mass percentage content of M is 0.5% or less, based on the total mass of the first negative electrode film layer. Selectively, the first negative electrode film layer does not contain the metal element M.

[0054] If the first negative electrode film layer does not contain or substantially does not contain the metal element M, it is possible to effectively ensure that lithium metal preferentially deposits on the surface of M in the second negative electrode film layer, and further suppress the deposition of lithium metal on the surface of the negative electrode sheet. In addition, because lithium metal preferentially deposits on the surface of M in the second negative electrode film layer, the first negative electrode film layer on the surface of the second negative electrode film layer can further suppress the rapid growth of lithium dendrites, thereby further extending the cycle life of the secondary battery.

[0055] In some embodiments, the mass percentage content of M is 1% to 10% based on the total mass of the second negative electrode film layer. Selectively, the mass percentage content of M is 1% to 9%, 1% to 8%, 1% to 7%, 1% to 6%, 1% to 5%, 1% to 4%, 2% to 9%, 2% to 8%, 2% to 7%, 2% to 6%, 2% to 5%, 2% to 4%, 3% to 9%, 3% to 8%, 3% to 7%, 3% to 6%, 3% to 5%, 3% to 4%, 3.5% to 9%, 3.5% to 8%, 3.5% to 7%, 3.5% to 6%, 3.5% to 5%, or 3.5% to 4.5%.

[0056] When the mass percentage content of M is low, the number of nucleation sites on the second negative electrode film layer is small, and the role of the second negative electrode film layer in suppressing the deposition of lithium metal on the surface of the negative electrode sheet when the secondary battery is subjected to high-rate charging or overcharging is unclear. When the mass percentage content of M is high, the consumption of electrolyte also increases, and since the volume of M expands after Li solid-dissolves on the surface of M, the volume of the second negative electrode film layer and the negative electrode sheet expands and becomes larger, shortening the cycle life of the secondary battery to a certain extent. When the mass percentage content of M is within an appropriate range, the deposition of lithium metal on the surface of the negative electrode sheet can be effectively suppressed, and the shortening of the cycle life of the secondary battery can be effectively suppressed.

[0057] In some embodiments, M is selected from one or more of the following: Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, Al, Sc, Mo, W, Pt, Pd, In, Re, Ir, Ga, Os, V, Zn, Ru, Rh. Selectively, M is selected from one or more of the following: Sn, Bi, Cd, Ti, Nb, Ta, Sb, Hf, Mg, Zr, Ag, Au, Al. Further selectively, M is selected from one or more of the following: Nb, Au, Ag, Al, Mg, Ti, Cd, Zr.

[0058] When M is selected from the above-mentioned metal elements, its lattice structure is more compatible with the lattice structure of Li, and Li more easily induces nucleation on the surface of M, thus having a better effect in suppressing the deposition of lithium metal on the surface of the negative electrode sheet, further improving the dynamic characteristics, cycle characteristics, and safety of the secondary battery.

[0059] In some embodiments, the second negative electrode film layer includes a body portion and a first surface and a second surface facing each other along its own thickness direction, wherein the first surface is provided facing away from the negative electrode current collector and the second surface is provided facing the negative electrode current collector. M is located in the body portion of the second negative electrode film layer and is positioned at one or more locations of the first surface facing away from the negative electrode current collector and the second surface facing the negative electrode current collector. For example, (1) M is located only on the main body of the negative electrode film layer, (2) M is located only on the first surface of the second negative electrode film layer facing away from the negative electrode current collector, (3) M is located only on the second surface of the second negative electrode film layer facing the negative electrode current collector, (4) M is simultaneously located at two positions: the main body of the negative electrode film layer and the first surface of the second negative electrode film layer facing away from the negative electrode current collector, (5) M is simultaneously located at two positions: the main body of the negative electrode film layer and the second surface of the second negative electrode film layer facing the negative electrode current collector, (6) M is simultaneously located at two positions: the first surface of the second negative electrode film layer facing away from the negative electrode current collector and the second surface of the second negative electrode film layer facing the negative electrode current collector, and (7) M is simultaneously located at three positions: the main body of the negative electrode film layer, the first surface of the second negative electrode film layer facing away from the negative electrode current collector and the second surface of the second negative electrode film layer facing the negative electrode current collector.

[0060] In some embodiments, M is located in the main body portion of at least the second negative electrode film layer.

[0061] In some embodiments, when M is located on the first surface of the second negative electrode film layer facing the negative electrode current collector, M can form a layered structure on the first surface of the second negative electrode film layer. Selectively, the layered structure is not continuous. For example, M is distributed at intervals or in an array on the first surface of the second negative electrode film layer. In this case, it is advantageous for the electrolyte to sufficiently permeate the second negative electrode film layer, while at the same time, lithium ions from the positive electrode are smoothly inserted into the second negative electrode film layer during charging of the secondary battery, and lithium ions inserted into the second negative electrode film layer are sufficiently detached and smoothly moved to the positive electrode during discharging of the secondary battery.

[0062] In some embodiments, when M is located on the second surface of the second negative electrode film layer facing the negative electrode current collector, M can form a layered structure on the second surface of the second negative electrode film layer. Selectively, the layered structure is not continuous. For example, M is distributed at intervals or in an array on the second surface of the second negative electrode film layer. In this case, it is advantageous for the second negative electrode film layer and the negative electrode current collector to maintain high adhesion strength and prevent powder shedding, while also being advantageous for electron conduction.

[0063] In some embodiments, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.3 to 1.2. Selectively, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is 0.3 to 1, 0.4 to 1, 0.5 to 1, 0.3 to 0.8, 0.4 to 0.8, 0.5 to 0.8, 0.3 to 0.7, 0.4 to 0.7, 0.5 to 0.7, 0.3 to 0.6, 0.4 to 0.6, or 0.5 to 0.6.

[0064] When the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is relatively large, the nucleation sites in the second negative electrode film layer are relatively small, and the effect of suppressing the deposition of lithium metal on the surface of the negative electrode sheet is not clear. When the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is relatively small, the thickness of the first negative electrode film layer is relatively small, and lithium dendrites formed in the second negative electrode film layer pass through the first negative electrode film layer more easily to reach the surface of the negative electrode sheet, increasing the risk of short circuits in the battery. When the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer is within an appropriate range, not only can the deposition of lithium metal on the surface of the negative electrode sheet be effectively suppressed, but the arrival of lithium dendrites at the surface of the negative electrode sheet can also be effectively suppressed.

[0065] In some embodiments, the second negative electrode film layer may contain metal particles, the metal particles being selected from one or more types of elemental particles of M and alloy particles of M.

[0066] In some embodiments, the alloy of M is an alloy formed from two or more elements of M, and one or more elements of M and another metallic element M. 1 This includes alloys formed from one or more of the elements. Selectively, M alloys include alloys formed from two or more of the elements of M.

[0067] In some embodiments, M 1 This includes one or more of the following: Fe, Cu, Ni, Cr, and Mn.

[0068] In some embodiments, the volume-average particle size Dv50 of the metal particles is 5 μm or less. Selectively, the volume-average particle size Dv50 of the metal particles is 1 μm or less. More specifically, the volume-average particle size Dv50 of the metal particles is 0.5 μm or less.

[0069] By controlling the volume-average particle size Dv50 of the metal particles within an appropriate range, a sufficient number of nucleation sites can be formed in the second negative electrode film layer, and the deposition of lithium metal on the surface of the negative electrode sheet can be effectively suppressed.

[0070] In this application, the volume-average particle size Dv50 of the material has an art-known meaning and can be measured by art-known methods and instruments. For example, it can be measured by a laser particle size analyzer (e.g., Malvern Mastersizer 2000E, UK) referring to GB / T19077-2016 Particle Size Distribution Laser Diffraction.

[0071] In some embodiments, the second negative electrode film layer is made of Li-M alloy particles, Li-MM 1 M may contain one or more types of alloy particles. 1 This indicates a metallic element, and M 1 This includes one or more of Fe, Cu, Ni, Cr, and Mn. Li-M alloy refers to an alloy formed from Li and one or more of the metallic elements M, and Li-MM 1 The alloy consists of Li and one or more of the metallic elements M, and the metallic element M 1 This refers to an alloy formed from one or more of the following types.

[0072] As examples, Li-M alloys include Li-Sn, Li-Bi, Li-Cd, Li-Ti, Li-Nb, Li-Ta, Li-Sb, Li-Hf, Li-Mg, Li-Zr, Li-Ag, Li-Au, Li-Al, Li-Sc, Li-Mo, Li-W, Li-Pt, Li-Pd, Li-In , Li-Re, Li-Ir, Li-Ga, Li-Os, Li-V, Li-Zn, Li-Ru, Li-Rh, Li-Mg-Al, Li-Mg-Zr, Li-Mg-Zn, Li-Ag-Al, Li-Ag-Zn, Li-Ag-Mg, and Li-Ti-Al.

[0073] For example, Li-MM 1 The alloy is selected from one or more of the following: Li-Mg-Mn, Li-Al-Mn, Li-Al-Fe, Li-Al-Cu, Li-Ti-Ni, and Li-Ti-Cr.

[0074] In some embodiments, the second negative electrode film layer is composed of the above-mentioned metal particles, Li-M alloy particles, and Li-MM1 In addition to one or more types of alloy particles, the material may further include a second negative electrode active material, a selectable conductive agent, a selectable adhesive, and other optional auxiliary agents.

[0075] In some embodiments, the first negative electrode film layer comprises a first negative electrode active material, a selectable conductive agent, a selectable adhesive, and other optional auxiliary agents.

[0076] In some embodiments, the types of the first and second negative electrode active materials are not particularly limited, and art-known negative electrode active materials used in secondary batteries can be employed. The types of the first and second negative electrode active materials may be the same or different. For example, the first and second negative electrode active materials may each independently include one or more of the following: graphite, soft carbon, hard carbon, mesocarbon microbeads, carbon fiber, carbon nanotubes, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of the following: elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based materials may include one or more of the following: elemental tin, tin oxide, and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may be used further. These negative electrode active materials may be used individually or in combination of two or more.

[0077] In some embodiments, the types and contents of the conductive agent and adhesive are not particularly limited and can be selected according to actual needs. The types of conductive agents in the first and second negative electrode layers may be the same or different. For example, the conductive agent may include one or more of the following: superconducting carbon, carbon black (e.g., acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The types of adhesives in the first and second negative electrode layers may be the same or different. For example, the adhesive may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylate PAA, polymethacrylate PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polybulb alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). The types of other optional additives for the first and second negative electrode layers may be the same or different. For example, other optional additives may include thickeners (e.g., sodium carboxymethylcellulose CMC-Na), PTC thermistor materials, and the like.

[0078] In the negative electrode sheet of the present application, the negative electrode current collector may be a metal foil sheet or a composite current collector. Copper foil may be used as an example of a metal foil sheet. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material may be selected from one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0079] In some embodiments, the negative electrode film layer is provided on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector.

[0080] Figure 1 shows a schematic diagram of one embodiment of the negative electrode sheet 10 according to the present application. The negative electrode sheet 10 may consist of a negative electrode current collector 11, second negative electrode film layers 122 provided on both sides of the negative electrode current collector 11, and a first negative electrode film layer 121 provided on the second negative electrode film layer 122, the second negative electrode film layer 122 being located between the negative electrode current collector 11 and the first negative electrode film layer 121. The second negative electrode film layer 122 includes opposing first surfaces 1221 and second surfaces 1222 along its own thickness direction, the first surface 1221 being provided with its back to the negative electrode current collector 11 and the second surface 1222 being provided facing the negative electrode current collector 11.

[0081] Naturally, the negative electrode sheet 10 of the present application may have other embodiments, for example, the negative electrode sheet 10 is composed of a negative electrode current collector 11, a second negative electrode film layer 122 provided on one side of the negative electrode current collector, and a first negative electrode film layer 121 provided on the second negative electrode film layer 122.

[0082] It should be noted that the negative electrode sheet of the present invention does not exclude any additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the present invention may further include a conductive primer layer (e.g., composed of a conductive agent and an adhesive) provided between the negative electrode current collector and the second negative electrode film layer. In some other embodiments, the negative electrode sheet of the present invention may further include a protective layer coated on the surface of the first negative electrode film layer.

[0083] In some embodiments, the method for manufacturing a negative electrode sheet of the present invention may include the steps of forming a second negative electrode film layer on at least one side of a negative electrode current collector, wherein the second negative electrode film layer comprises metal particles, and the metal particles are selected from one or more types of single particles of M and M-like alloy particles; and forming a first negative electrode film layer on the surface of the second negative electrode film layer.

[0084] The negative electrode film layer is generally formed by applying a negative electrode slurry to a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is generally formed by dispersing a negative electrode active material, a selectable conductive agent, a selectable adhesive, and other selectable auxiliary agents in a solvent and stirring uniformly. The solvent may be, but is not limited to, N-methylpyrrolidinone (NMP) or deionized water. In some embodiments, a first negative electrode slurry is formed by dispersing a first negative electrode active material, a selectable conductive agent, a selectable adhesive, and other selectable auxiliary agents in a solvent and stirring uniformly, and a second negative electrode slurry is formed by dispersing a second negative electrode active material, metal particles, a selectable conductive agent, a selectable adhesive, and other selectable auxiliary agents in a solvent and stirring uniformly.

[0085] In the method for manufacturing a negative electrode sheet, the first negative electrode slurry and the second negative electrode slurry may be applied simultaneously in one step or in two separate steps.

[0086] In some embodiments, the first negative electrode slurry and the second negative electrode slurry are applied simultaneously in a single application. Applying them simultaneously in a single application improves the adhesion between the first and second negative electrode layers, which is advantageous for reducing the interfacial resistance of the entire negative electrode layer and further improves the battery's cycle characteristics.

[0087] In some embodiments, the method for manufacturing the negative electrode sheet may include the steps of forming a second negative electrode film layer on at least one side of the negative electrode current collector, forming a layer of metal M on the surface of the second negative electrode film layer, continuing to form the first negative electrode film layer, and after cold pressing, positioning M on the first surface of the second negative electrode film layer facing the negative electrode current collector. Selectively, the layered structure of the metal M is discontinuous, for example, in a spaced-out or arrayed state. Methods for forming the metal M on the surface of the second negative electrode film layer include, but are not limited to, coating, shot blasting, spraying, and vapor deposition. For example, the metal M is deposited on the surface of the second negative electrode film layer by vapor deposition. The vapor deposition method may be one or more of atomic layer deposition, chemical vapor deposition, and physical vapor deposition.

[0088] In some embodiments, the method for manufacturing the negative electrode sheet may include the steps of forming one layer of metal M on at least one side of the negative electrode current collector, forming a second negative electrode film layer on the surface of the negative electrode current collector, further forming a first negative electrode film layer on the surface of the second negative electrode film layer, and after cold pressing, positioning M on the second surface of the second negative electrode film layer facing the negative electrode current collector. Selectively, the layered structure of metal M is discontinuous, for example, in a spaced-out or arrayed state. Methods for forming metal M on the surface of the negative electrode current collector include, but are not limited to, coating, vapor deposition, and gravure. For example, metal M is deposited on the surface of the negative electrode current collector by vapor deposition. The vapor deposition method may be one or more of atomic layer deposition, chemical vapor deposition, and physical vapor deposition.

[0089] The mass percentage content of M in the second negative electrode film layer is obtained by the following method.

[0090] The thickness of the first and second negative electrode layers is obtained using a scanning electron microscope (e.g., ZEISS Sigma300). First, the negative electrode sheet is cut to a sample of predetermined dimensions (e.g., 2cm x 2cm), and the negative electrode sheet is fixed to the sample stage with paraffin. Then, the sample stage is placed in the sample holder and locked in place, and the power of a cross-section polisher (e.g., IB-19500CP) is turned on to create a vacuum (e.g., 10°C). -4 Set the pressure (Pa), argon flow rate (e.g., 0.15 MPa), voltage (e.g., 8 KV), and polishing time (e.g., 2 hours), adjust the sample stage to the oscillating mode, and start polishing. Sample testing can be performed by referring to JY / T010-1996. To ensure the accuracy of the test results, select several (e.g., five) different areas from the sample to be measured and perform a scanning test. At a predetermined magnification (e.g., 500x), read the thickness of the first and second negative electrode layers in the specific test area, and read the average value of the multiple test areas to obtain the test result.

[0091] Since the content of metal element M in the second negative electrode film layer is low and has little effect on the density of the second negative electrode film layer, it is thought that the density of the first negative electrode film layer matches that of the second negative electrode film layer. Furthermore, the coating weight ratio of the first negative electrode film layer to the second negative electrode film layer can be obtained from the thickness ratio of the first negative electrode film layer to the second negative electrode film layer.

[0092] After cold-pressing a negative electrode sheet coated on one side (or wiping off the negative electrode film layer on one side if both sides are coated), the sheet is cut into a sample of predetermined dimensions (e.g., 2 cm x 2 cm). The powder is then scraped off, and all the resulting powder is tested using an inductively coupled plasma-Optical Emission spectrometer (ICP-OES) to obtain the mass concentration of metal element M in the negative electrode film layer. The mass percentage content of metal element M in the second negative electrode film layer is then calculated based on the coating weight ratio of the first and second negative electrode film layers. To ensure the accuracy of the test results, the negative electrode sheet is cut into multiple samples of predetermined dimensions (e.g., five), and the average value of the multiple test samples is used as the test result.

[0093] [Positive electrode sheet]

[0094] A secondary battery includes a positive electrode sheet, which typically includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and containing a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0095] In the positive electrode sheet of the present application, the positive electrode current collector may be a metal foil sheet or a composite current collector. As an example of a metal foil sheet, the positive electrode current collector may be aluminum foil. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. As an example, the metal material may be selected from one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0096] In the positive electrode sheet of the present application, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material may be a positive electrode active material known in the art used in secondary batteries. For example, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine-type structure, and modified compounds thereof. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Examples of lithium-containing phosphates with an olivine-type structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate-carbon composite materials, lithium manganese phosphate, lithium manganese phosphate-carbon composite materials, lithium iron manganese phosphate, lithium iron manganese phosphate-carbon composite materials, and modified compounds thereof. This invention is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used individually or in combination of two or more.

[0097] In the positive electrode sheet of the present invention, the modified compound of each of the above positive electrode active materials may be modified by doping, surface coating, or doping and surface coating of the positive electrode active material.

[0098] In the positive electrode sheet of the present application, the positive electrode film layer typically comprises a positive electrode active material, a selectable adhesive, and a selectable conductive agent. The positive electrode film layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, a selectable conductive agent, a selectable adhesive, and other selectable components in a solvent and stirring them uniformly. The solvent may, but is not limited to, N-methylpyrrolidinone (NMP). For example, the adhesive used in the positive electrode film layer may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene ternpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. For example, the conductive agent used in the positive electrode film layer may include one or more of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Note that the configuration or parameters of each positive electrode film layer provided in this application all refer to the range of configuration or parameters of the single-sided film layer of the positive electrode current collector. When the positive electrode film layer is provided on two opposing surfaces of the positive electrode current collector, the configuration or parameters of the positive electrode film layer on either of those surfaces are considered to satisfy the requirements of this application and fall within the scope of the claims.

[0099] [Electrolyte]

[0100] The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The secondary battery of this invention is not particularly limited in terms of the type of electrolyte, and can be selected according to the demand. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., electrolyte solution).

[0101] In some embodiments, the electrolyte is an electrolyte solution, which comprises an electrolyte salt and a solvent.

[0102] In some embodiments, there are no particular restrictions on the type of electrolyte salt, and it can be selected according to actual demand. For example, the electrolyte salt may be selected from one or more of the following: LiPF6 (lithium hexafluoride phosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoride arsenide), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bistrifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium bisoxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalate phosphate), and LiTFOP (lithium tetrafluorooxalatophosphanite).

[0103] In some embodiments, there are no particular restrictions on the type of solvent, and it can be selected according to the actual demand. For example, the solvent may be selected from one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butanoate (MB), ethyl butanoate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0104] In some embodiments, the solvent is selectively a non-aqueous solvent.

[0105] In some embodiments, additives are selectively added to the electrolyte. For example, the additives may include additives for negative electrode film formation, additives for positive electrode film formation, and additives that can improve several aspects of the battery's performance, such as additives that can improve the battery's overchargeability, additives that can improve the battery's high-temperature performance, and additives that can improve the battery's low-temperature performance.

[0106] [Separator]

[0107] In secondary batteries employing an electrolyte, and in some secondary batteries employing a solid electrolyte, a separator is further included. The separator is provided between the positive electrode sheet and the negative electrode sheet and serves to separate them. The present application does not particularly limit the type of separator, and any known porous separator having good chemical and mechanical stability may be selected. In some embodiments, the material of the separator may be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene difluoride. The separator may be a single-layer film or a multilayer composite film. If the separator is a multilayer composite film, the materials of each layer may be the same or different.

[0108] In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be manufactured into an electrode assembly by a winding process or a lamination process.

[0109] In some embodiments, the secondary battery may include an outer casing. This casing can be used to enclose the electrode assembly and electrolyte.

[0110] In some embodiments, the casing of the secondary battery may be a rigid case, such as a hard plastic case, an aluminum case, or a steel case. The casing of the secondary battery may also be a soft pack, such as a bag-type soft pack. The material of the soft pack may be one or more of the following plastics: polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0111] This invention does not impose any particular restrictions on the shape of the secondary battery; it may be cylindrical, rectangular, or any other shape. For example, Figure 2 shows a secondary battery 5 having a rectangular structure as an example.

[0112] In some embodiments, referring to Figure 3, the exterior may include a case 51 and a cover plate 53. The case 51 may include a bottom plate, side plates connected to the bottom plate, and a housing chamber formed by the bottom plate and the side plates. The case 51 has an opening that communicates with the housing chamber, and the cover plate 53 is used to cover the opening, thereby sealing the housing chamber. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is sealed in the housing chamber. The electrolyte permeates the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted according to the demand.

[0113] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0114] Figure 4 shows an example of a battery module 4. Referring to Figure 4, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they can be arranged according to any other method. Furthermore, the multiple secondary batteries 5 can be fixed in place by fastening members.

[0115] Selectively, the battery module 4 may further include a case having a housing space, and a plurality of secondary batteries 5 are housed in said housing space.

[0116] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0117] Figures 5 and 6 show an example of a battery pack 1. Referring to Figures 5 and 6, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper box 2 and a lower box 3, the upper box 2 covering the lower box 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box based on any method.

[0118] [Power consumption equipment]

[0119] Embodiments of the present invention further provide a power consumption device comprising at least one of the secondary battery, battery module, or battery pack of the present invention. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device or as an energy storage unit for the power consumption device. The power consumption device may be, but is not limited to, mobile devices (e.g., mobile phones, notebook computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric vehicles, ships and satellites, energy storage systems, etc.

[0120] The aforementioned power consumption device can select a secondary battery, battery module, or battery pack depending on its usage needs.

[0121] Figure 7 shows an example of a power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the demands of this power consumption device for high power output and high energy density, a battery pack or battery module can be employed.

[0122] Another example of a power-consuming device may be a mobile phone, tablet computer, or notebook computer. Such power-consuming devices are generally required to be thin, and can use rechargeable batteries as their power source.

[0123] Examples

[0124] The following examples illustrate the disclosures in this application in more detail, and are provided only as illustrative examples, as various modifications and changes made within the scope of the disclosures would be obvious to those skilled in the art. Unless otherwise specified, all parts, percentages and ratios described in the following examples are by weight, and all reagents used in the examples are commercially available or can be synthesized by conventional methods and used directly without further processing, and the equipment used in the examples is commercially available.

[0125] Example 1

[0126] Manufacturing of positive electrode sheets

[0127] LiNi as a positive electrode active material 0.5 Co 0.2 Mn 0.3 O2 (NCM523), acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as an adhesive are mixed in a mass ratio of 96:2:2. N-methylpyrrolidinone (NMP) solvent is added, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is then uniformly applied to the aluminum foil of the positive electrode current collector, air-dried at room temperature, and then transferred to an oven for further drying. Finally, a positive electrode sheet is obtained by cold pressing and cutting.

[0128] Manufacturing of negative electrode sheets

[0129] Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain the first negative electrode slurry.

[0130] Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, elemental Ag particles (with a volume-average particle size Dv50 of 0.05 μm) are mixed in a mass ratio of 98:2, deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system becomes homogeneous to obtain a second negative electrode slurry.

[0131] The first and second negative electrode slurries are uniformly applied to the two surfaces of the copper foil of the negative electrode current collector simultaneously in a single step. After air-drying at room temperature, the material is transferred to an oven for further drying. Subsequently, a negative electrode sheet is obtained by cold pressing and cutting. The second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer, and the coating weight of the first negative electrode film layer is 4.3 mg / cm². 2 The coating weight of the second negative electrode film layer is 6.7 mg / cm². 2 Therefore, the mass ratio of single Ag particles in the second negative electrode film layer is 2%.

[0132] Manufacturing of electrolyte

[0133] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Subsequently, a thoroughly dried lithium salt LiPF6 is dissolved in the above organic solvent to produce an electrolyte with a LiPF6 concentration of 1 mol / L.

[0134] Manufacturing of separators

[0135] A polyethylene film is used as a separator.

[0136] Manufacturing of rechargeable batteries

[0137] A positive electrode sheet, a separator, and a negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrode sheets to perform the function of separation. Then, the assembly is wound up to obtain an electrode assembly, which is placed in an outer casing. After drying, an electrolyte solution is injected, and after processes such as vacuum sealing, standing, chemical formation, and shaping are performed to obtain a secondary battery.

[0138] Example 2

[0139] The method for manufacturing the secondary battery is similar to that of Example 1, with the following differences: Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, elemental Ag particles (with a volume-average particle size Dv50 of 0.05 μm) are added in a mass ratio of 97:3. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a second negative electrode slurry. The mass ratio of elemental Ag particles in the second negative electrode film layer is 3%.

[0140] Example 3

[0141] The method for manufacturing the secondary battery is similar to that of Example 1, with the following differences: Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, elemental Ag particles (with a volume-average particle size Dv50 of 0.05 μm) are added in a mass ratio of 95:5. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a second negative electrode slurry. The mass ratio of elemental Ag particles in the second negative electrode film layer is 5%.

[0142] Example 4

[0143] The method for manufacturing the secondary battery is similar to that of Example 1, with the following differences: Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, elemental Ag particles (with a volume-average particle size Dv50 of 0.05 μm) are mixed in a mass ratio of 90:10. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a second negative electrode slurry. The mass ratio of elemental Ag particles in the second negative electrode film layer is 10%.

[0144] Example 5

[0145] The method for manufacturing the secondary battery is similar to that of Example 1, with the following differences: Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, Al elemental particles (with a volume-average particle size Dv50 of 0.05 μm) are added in a mass ratio of 95:5. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a second negative electrode slurry. The mass ratio of Al elemental particles in the second negative electrode film layer is 5%.

[0146] Example 6

[0147] The method for manufacturing the secondary battery is similar to that of Example 1, with the following differences: Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, elemental Mg particles (with a volume-average particle size Dv50 of 0.05 μm) are added in a mass ratio of 95:5. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a second negative electrode slurry. The mass ratio of elemental Mg particles in the second negative electrode film layer is 5%.

[0148] Example 7

[0149] The method for manufacturing the secondary battery is similar to that of Example 1, with the following differences: Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, Nb elemental particles (with a volume-average particle size Dv50 of 0.05 μm) are added in a mass ratio of 95:5. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a second negative electrode slurry. The mass ratio of Nb elemental particles in the second negative electrode film layer is 5%.

[0150] Comparative Example 1

[0151] The method for manufacturing the secondary battery is similar to that of Example 1, the difference being the manufacturing process of the negative electrode sheet, which specifically includes the following steps.

[0152] Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a negative electrode slurry. The negative electrode slurry is divided into two parts, the first negative electrode slurry and the second negative electrode slurry. The first and second negative electrode slurries are uniformly applied to the two surfaces of the copper foil of the negative electrode current collector in a single step. After air-drying at room temperature, the material is transferred to an oven for further drying, and then cold-pressed and cut to obtain a negative electrode sheet. The second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer, and the coating weight of the first negative electrode film layer is 4.3 mg / cm². 2 The coating weight of the second negative electrode film layer is 6.7 mg / cm². 2 That is the case.

[0153] Comparative Example 2

[0154] The method for manufacturing the secondary battery is similar to that of Example 1, the difference being the manufacturing process of the negative electrode sheet, which specifically includes the following steps.

[0155] Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, single Ag particles (with a volume-average particle size Dv50 of 0.05 μm) are mixed in a mass ratio of 95:5. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a negative electrode slurry. The negative electrode slurry is uniformly applied to two surfaces of the copper foil of the negative electrode current collector, air-dried at room temperature, then transferred to an oven for further drying, and finally cold-pressed and cut to obtain a negative electrode sheet. The coating weight of the negative electrode film layer is 11.0 mg / cm². 2 That is the case.

[0156] Comparative Example 3

[0157] The secondary battery manufacturing method is similar to that of Example 1, the difference being the manufacturing process of the negative electrode sheet, which specifically includes the following steps.

[0158] Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, elemental Ag particles (with a volume-average particle size Dv50 of 0.05 μm) are mixed in a mass ratio of 95:5, deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system becomes homogeneous to obtain the first negative electrode slurry.

[0159] Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a second negative electrode slurry.

[0160] The first and second negative electrode slurries are uniformly applied simultaneously to the two surfaces of the copper foil of the negative electrode current collector in a single step. After air-drying at room temperature, the material is transferred to an oven for further drying, followed by cold pressing and cutting to obtain a negative electrode sheet. The second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer, and the coating weight of the first negative electrode film layer is 4.3 mg / cm². 2 The coating weight of the second negative electrode film layer is 6.7 mg / cm². 2 Therefore, the mass ratio of single Ag particles in the first negative electrode film layer is 5%.

[0161] Comparative Example 4

[0162] The method for manufacturing the secondary battery is similar to that of Example 1, with the following differences: Graphite as the negative electrode active material, acetylene black as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the adhesive are mixed in a mass ratio of 96.4:1:1.2:1.4. Then, Ni elemental particles (with a volume-average particle size Dv50 of 0.05 μm) are added in a mass ratio of 95:5. Deionized water is added as the solvent, and the mixture is stirred with a vacuum mixer until the reaction system is homogeneous to obtain a second negative electrode slurry. The mass ratio of Nb elemental particles in the second negative electrode film layer is 5%.

[0163] Test section

[0164] (1) Test of the maximum charge rate of secondary batteries

[0165] At 25°C, the secondary battery is discharged at a rate of 1C to 2.8V with a constant current, then charged at a rate of 1C to 4.2V, and then charged at a constant voltage until the current reaches 0.05C, at which point the secondary battery is fully charged. After letting the fully charged secondary battery stand for 5 minutes, it is discharged at a rate of 1C to 2.8V with a constant current, and the discharge capacity at this point is the actual capacity of the secondary battery at a rate of 1C, which is denoted as C0. The secondary battery is then charged at a rate of xC0 (representing gradient charging rates, such as 1C0, 1.1C0, 1.2C0, 1.3C0, 1.4C0...) to 4.2V, and then charged at a constant voltage until the current reaches 0.05C0, and left to stand for 5 minutes. The secondary battery is then disassembled and the lithium deposition status on the surface of the negative electrode sheet is observed. If lithium is not deposited on the surface of the negative electrode sheet, the charging rate is increased and the test is repeated until lithium is deposited on the surface of the negative electrode sheet. Record the maximum charge rate at which lithium is not deposited on the surface of the negative electrode sheet.

[0166] (2) Overcharge performance test of secondary batteries

[0167] At 25°C, the secondary battery is discharged at a constant current rate of 1C to 2.8V, then charged at a constant current rate of 1C, designing gradient charging times of 1h, 1.1h, 1.2h, 1.3h, 1.4h, etc. After each charge cycle, the secondary battery is disassembled, the lithium deposition status on the surface of the negative electrode sheet is observed, and the charging time t(h) when lithium has just deposited on the surface of the negative electrode sheet is recorded. (Charging time t / Time required for full charge) × 100% indicates the state of charge (SOC) where the secondary battery is overcharged until lithium deposition begins.

[0168] (3) Cycle characteristics test of secondary batteries

[0169] At 25°C, the secondary battery is discharged at a constant current rate of 1C to 2.8V, then charged at a constant current rate of 1C to 4.2V, and the constant voltage charging is continued until the current drops to 0.05C. At this point, the secondary battery is fully charged, and the charge capacity at this time is recorded, i.e., the charge capacity of the first cycle. After the secondary battery is left to stand for 5 minutes, it is discharged at a constant current rate of 1C to 2.8V, which is one charge-discharge cycle, and the discharge capacity at this time is recorded, i.e., the discharge capacity of the first cycle. Based on the above method, a cycle charge-discharge test is performed on the secondary battery, and the discharge capacity per cycle is recorded. The cycle characteristics of the secondary battery at a rate of 1C are characterized by the number of cycles until the discharge capacity of the secondary battery decreases to 80% of the discharge capacity of the first cycle. The higher the number of cycles of the secondary battery, the better the cycle characteristics.

[0170] At 25°C, the secondary battery is discharged at a constant current rate of 1C to 2.8V, then charged at a constant current rate of 3C to 4.2V, and the constant voltage charging is continued until the current drops to 0.05C. At this point, the secondary battery is fully charged, and the charge capacity at this time is recorded, i.e., the charge capacity of the first cycle. After the secondary battery is left to stand for 5 minutes, it is discharged at a constant current rate of 3C to 2.8V, which is one charge-discharge cycle, and the discharge capacity at this time is recorded, i.e., the discharge capacity of the first cycle. Based on the above method, a cycle charge-discharge test is performed on the secondary battery, and the discharge capacity per cycle is recorded. The cycle characteristics of the secondary battery at a rate of 3C are characterized by the number of cycles until the discharge capacity of the secondary battery decreases to 80% of the discharge capacity of the first cycle. The higher the number of cycles of the secondary battery, the better the cycle characteristics.

[0171] For details of the specific parameters for Examples 1-7 and Comparative Examples 1-4, please refer to Table 1, and for details of the test results, please refer to Table 2.

[0172] [Table 1]

[0173] [Table 2]

[0174] As can be seen from the data in Table 2, the maximum charge rate of the secondary battery of the present invention is higher and the overcharge performance is better. This effectively solves the lithium deposition problem that occurs in secondary batteries under high-rate charging and overcharge conditions, and significantly improves the dynamic characteristics, cycle characteristics, and safety of the secondary battery. Figure 8 is a scanning electron microscope image of a cross-section of the negative electrode sheet manufactured in Example 1. As can be seen from Figure 8, the Ag elemental particles are uniformly distributed in the main body of the second negative electrode film layer, and the surface of Ag becomes a preferential nucleation site for lithium metal. This achieves the effect of inducing lithium metal nucleation on the surface of Ag in the second negative electrode film layer, and effectively suppresses the deposition of lithium metal on the surface of the negative electrode sheet. Therefore, the secondary battery still has good dynamic characteristics and safety under high-rate charging and overcharge conditions, and the cycle characteristics of the secondary battery are also better.

[0175] In Comparative Example 1, no metal particles were added to the negative electrode film layer, and the negative electrode film layer did not contain nucleation sites. As a result, the deposition of lithium metal on the surface of the negative electrode sheet could not be effectively suppressed, and the kinetic and cycle characteristics of the secondary battery under high-rate charging and overcharge conditions were both poor.

[0176] In Comparative Example 2, the negative electrode film layer is a single layer, and individual Ag particles are added to the negative electrode film layer. This allows the surface of Ag to be a preferred nucleation site for lithium metal. However, because the individual Ag particles are uniformly distributed in the negative electrode film layer, they cannot suppress the deposition of lithium metal on the surface of the negative electrode sheet. Consequently, the dynamic and cycle characteristics of the secondary battery under high-rate charging and overcharge conditions are both low. In Comparative Example 3, no metal particles are added to the second negative electrode film layer, and individual Ag particles are added to the first negative electrode film layer. This allows the surface of Ag to be a preferred nucleation site for lithium metal. However, because the individual Ag particles are uniformly distributed in the first negative electrode film layer, they cannot suppress the deposition of lithium metal on the surface of the negative electrode sheet. Consequently, the dynamic and cycle characteristics of the secondary battery under high-rate charging and overcharge conditions are both low.

[0177] In Comparative Example 4, the metal particles added to the second negative electrode film layer were single Ni particles. Because the difference in atomic radii between Ni and Li was too large, the surface of Ni could not be made a preferential nucleation site for Li. As a result, the effect of inducing Li nucleation on the surface of Ni in the second negative electrode film layer could not be achieved, and the deposition of lithium metal on the surface of the negative electrode sheet could not be effectively suppressed. Consequently, the kinetic characteristics of the secondary battery under high-rate charging and overcharge conditions were very poor, and it was also difficult for the secondary battery to have a longer cycle life.

[0178] The foregoing is merely a specific embodiment of the present application, and the scope of protection of this application is not limited thereto. A person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the art disclosed herein, and all such modifications or substitutions should be included within the claims of this application. Therefore, the scope of protection of this application should be based on the claims.

Claims

1. Negative electrode current collector (11), A negative electrode film layer provided on the negative electrode current collector (11), wherein the negative electrode film layer includes a first negative electrode film layer (121) and a second negative electrode film layer (122). The first negative electrode film layer (121) contains a first negative electrode active material, the first negative electrode active material contains one or more of graphite, soft carbon, hard carbon, mesocarbon microbeads, carbon fiber, and carbon nanotubes, and the first negative electrode film layer (121) does not contain a metallic element M (except that the first negative electrode film layer (121) contains one or more selected elements from indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), zinc (Zn), gold (Au), platinum (Pt), palladium (Pd), iron (Fe), cobalt (Co), chromium (Cr), cesium (Cs), cerium (Ce), and lanthanum (La). The second negative electrode film layer (122) is located between the negative electrode current collector (11) and the first negative electrode film layer (121), and the second negative electrode film layer (122) contains a metal element M, and the atomic radius of M is r Ｍ and the atomic radius r of Li Ｌｉ teeth A negative electrode sheet (10) comprising a negative electrode film layer that satisfies the following conditions and in which M is one of Ag, Al, Mg, and Nb, and the mass percentage content of M is 2% to 5% based on the total mass of the second negative electrode film layer (122).

2. The negative electrode sheet (10) according to claim 1, wherein M is located in the main body portion of at least the second negative electrode film layer (122).

3. The second negative electrode film layer (122) includes a first surface (1221) and a second surface (1222) facing each other along its own thickness direction, the first surface (1221) being provided facing away from the negative electrode current collector, and the second surface (1222) being provided facing the negative electrode current collector (11). The negative electrode sheet (10) according to claim 1 or 2, wherein M is located on a first surface (1221) of the second negative electrode film layer (122) facing away from the negative electrode current collector (11) and / or on a second surface (1222) of the second negative electrode film layer (122) facing the negative electrode current collector (11).

4. The negative electrode sheet (10) according to any one of claims 1 to 3, wherein the mass percentage content of M is 3% to 5% based on the total mass of the second negative electrode film layer (122).

5. The negative electrode sheet (10) according to any one of claims 1 to 4, wherein the mass percentage content of M is 0.5% or less based on the total mass of the first negative electrode film layer (121).

6. The negative electrode sheet (10) according to any one of claims 1 to 5, wherein the coating weight ratio of the first negative electrode film layer (121) and the second negative electrode film layer (122) is 0.3 to 1.

2.

7. The negative electrode sheet (10) according to any one of claims 1 to 6, wherein the second negative electrode film layer (122) contains metal particles, and the metal particles are selected from one or more types of single particles of M and alloy particles of M.

8. Alloys of M include alloys formed from two or more elements of M, and alloys formed from one or more elements of M and another metallic element M. １ The negative electrode sheet (10) according to claim 7, comprising an alloy formed of one or more elements.

9. The negative electrode sheet (10) according to claim 7 or 8, wherein the volume-average particle size Dv50 of the metal particles is 5 μm or less.

10. The second negative electrode film layer (122) consists of Li-M alloy particles, Li-M-M １ Contains one or more types of alloy particles, M １ This indicates a metallic element, and M １ The negative electrode sheet (10) according to any one of claims 1 to 9, comprising one or more of Fe, Cu, Ni, Cr, and Mn.

11. A secondary battery (5) comprising a negative electrode sheet (10) according to any one of claims 1 to 10.

12. A battery module (4) comprising the secondary battery (5) described in claim 11.

13. A battery pack (1) comprising one of the secondary battery (5) described in claim 11 and the battery module (4) described in claim 12.

14. A power consumption device comprising at least one of the secondary battery (5) described in claim 11, the battery module (4) described in claim 12, and the battery pack (1) described in claim 13.

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