Negative electrode sheet and preparation method therefor, battery cell and electric device

Abstract

Provided in the present application are a negative electrode sheet and a preparation method therefor, a battery cell and an electric device. The negative electrode sheet comprises: a negative electrode current collector; a negative electrode active material layer, which is arranged on at least one side of the negative electrode current collector; and a functional coating, which is arranged on the side, away from the negative electrode current collector, of the negative electrode active material layer and comprises a chalcogenide material. The chalcogenide material comprises one or more of elemental sulfur, elemental selenium, elemental tellurium, MxSy, MxSey and MxTey, wherein M comprises one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti and Mo, 0＜x≤2, and 0＜y≤2.

Description

Negative electrode sheet and preparation method thereof, battery cell and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application 202310796833.2, filed on June 30, 2023, entitled “Negative electrode sheet and preparation method thereof, battery cell and electrical device,” and the entire contents of that application are incorporated herein by reference. Technical Field

[0003] The present application belongs to the field of battery technology, and specifically relates to a negative electrode plate and a preparation method thereof, a battery cell and an electrical device. Background Art

[0004] Battery cells, also known as rechargeable batteries, are batteries that can be repeatedly discharged and recharged for multiple uses. In recent years, as battery cells, particularly lithium-ion batteries, have become increasingly widely used, higher demands have been placed on their performance, particularly their cycle life.

[0005] Therefore, further improving the cycle performance and storage performance of battery cells remains a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] The purpose of the present application is to provide a positive electrode plate that can improve the cycle performance of a battery cell containing the positive electrode plate; the purpose of the present application is also to provide a battery cell and an electrical device containing the above-mentioned positive electrode plate, so as to obtain improved battery cell cycle performance and storage performance.

[0008] In a first aspect, an embodiment of the present application provides a negative electrode sheet, comprising:

[0009] negative electrode current collector,

[0010] a negative electrode active material layer disposed on at least one side of the negative electrode current collector; and

[0011] The functional coating is provided on the side of the negative electrode active material layer away from the negative electrode current collector, wherein the functional coating comprises a chalcogenide material, and the chalcogenide material comprises elemental sulfur, elemental selenium, elemental tellurium, M x S y 、M x Se y 、M x Te y One or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2.

[0012] The technical solution of the embodiments of the present application provides a negative electrode plate. The negative electrode active material layer of the negative electrode plate is provided with a functional coating comprising a specific chalcogenide material on the side facing away from the negative electrode current collector. Surprisingly, when a battery cell including the negative electrode plate according to the embodiments of the present application is formed, a SEI film with excellent elasticity and stability is formed on the surface of the negative electrode plate.

[0013] Without intending to be bound by any theory or explanation, during formation of the battery cell, the functional coating contacts and interacts with the electrolyte (including a cyclic carbonate solvent such as ethylene carbonate), allowing the chalcogenide material to participate in the formation of the SEI film. The SEI film thus formed may include components such as alkyl sulfates and polyoxyalkylene polymers (such as polyethylene oxide (PEO)), resulting in the SEI film having excellent elasticity and stability. Such an SEI film can accommodate and adapt to volume changes caused by the rebound of the negative electrode sheet containing the negative electrode active material layer, reducing or preventing the negative electrode sheet from squeezing the structure containing the SEI film in the battery cell and causing structural damage. This reduces the risk of repeated damage and reformation of the SEI film and improves the interfacial stability between the negative electrode active material and the electrolyte, thereby improving the cycling performance and storage performance of the battery cell containing the negative electrode sheet.

[0014] In addition, the solid electrolyte interface membrane with excellent elasticity can stabilize the interface stability between the negative electrode and the electrolyte, thereby improving the service life of the battery cell.

[0015] In addition, the solid electrolyte interface membrane formed with the participation of chalcogenide materials has good active ion permeability, which can promote the rapid transmission of active ions at the interface and improve the ion transmission rate; after the chalcogenide materials in the functional coating of the negative electrode plate participate in the solid electrolyte interface membrane, the porosity in the functional coating is improved, and the transmission rate of active ions in the negative electrode plate is improved, thereby comprehensively improving the kinetic performance of the battery cell containing the negative electrode plate.

[0016] In some optional embodiments, the functional coating comprises 30% to 95% of the chalcogenide material based on the total mass of the functional coating.

[0017] According to the embodiments of the present application, the sulfide material containing the above-mentioned mass content can improve the elasticity of the solid electrolyte interface membrane, can accommodate and adapt to large volume changes of the negative electrode plate containing the negative electrode active material layer, reduce or avoid the negative electrode plate squeezing the structure containing the solid electrolyte interface membrane in the battery cell and thereby causing structural damage, reduce the risk of the solid electrolyte interface membrane being repeatedly destroyed and continuously reformed, thereby improving the cycle performance of the battery cell containing the negative electrode plate.

[0018] In some optional embodiments, the ratio of the thickness of the negative electrode active material layer to the thickness of the functional coating layer is 1:(0.01-0.2). Optionally, it is 1:(0.01-0.1).

[0019] According to the embodiments of the present application, controlling the thickness ratio of the negative electrode active material layer to the functional coating layer within the aforementioned range allows the functional coating layer to provide a sufficient protective layer to protect the negative electrode active material. Components such as metal selenide, sulfur, and selenium can form a protective layer that prevents direct contact between the negative electrode active material and the electrolyte, reduces side reactions with the electrolyte, and improves the cycling stability of battery cells containing the negative electrode sheet.

[0020] In some optional embodiments, the thickness of the functional coating is 1 to 10 um; optionally, 2 to 5 um.

[0021] According to the embodiment of the present application, the functional coating has a thickness within the above range, which is beneficial for the negative electrode plate to embed and de-embed active ions in the battery cell, and is beneficial to the dynamic performance and cycle performance of the battery cell.

[0022] In some optional embodiments, the average particle size D50 of the chalcogenide material is 50 to 500 nm; optionally, 100 to 300 nm.

[0023] According to the embodiments of the present application, the average particle size Dv50 of the chalcogenide material is within the above range, which facilitates the chalcogenide material's participation in forming a solid electrolyte interface film during battery cell formation. Furthermore, after decomposition from the negative electrode active material layer, evenly distributed pores with relatively uniform particle size are formed, which is beneficial to the structural stability of the functional coating and the dynamic and cycling performance of the battery cell. In some optional embodiments, the porosity of the functional coating is 15% to 40%.

[0024] According to the embodiments of the application, the functional coating has a porosity within the above range, which is conducive to the electrolyte infiltration of the functional coating during the formation stage, facilitating the participation of the sulfide material in the functional coating in forming a solid electrolyte interface film, thereby making the solid electrolyte interface film have stronger elasticity.

[0025] In some optional embodiments, the functional coating includes a chalcogenide material, a conductive agent, and a binder.

[0026] According to the embodiment of the present application, when the functional coating comprises a chalcogenide material, a conductive agent and a binder. x S y 、M x Se y 、M x Te yIt can be used as a negative electrode active material, with a high lithium / sodium insertion capacity. The entire functional coating can serve as another new negative electrode active material layer, improving the cycle performance of the battery cell. Chalcogenide materials such as elemental sulfur, elemental selenium, and elemental tellurium can also be used as negative electrode active materials.

[0027] In some optional embodiments, the functional coating comprises 5% to 10% of the conductive agent based on the total mass of the functional coating.

[0028] According to the embodiments of the present application, when the functional coating contains the conductive agent in the above-mentioned content, the internal resistance of the negative electrode plate can be reduced, and the internal resistance of the entire battery cell can be reduced, thereby facilitating the transmission of electrons and improving the dynamic performance of the battery cell containing the negative electrode plate.

[0029] In some optional embodiments, the functional coating includes 3% to 5% of the binder based on the total mass of the functional coating.

[0030] According to the embodiments of the present application, when the functional coating contains the above-mentioned binder content, the structural stability, electrical conductivity, and ion transport performance of the negative electrode sheet can be balanced. However, too high or too low a binder content may affect the performance of the battery cell containing the negative electrode sheet.

[0031] In some optional embodiments, based on the total mass of the functional coating, the functional coating comprises 85% to 92% of a chalcogenide material containing a metal element, 5% to 10% of a conductive agent, and 3% to 5% of a binder, wherein the chalcogenide material containing a metal element comprises M x S y 、M x Se y 、M x Te y One or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2.

[0032] According to an embodiment of the present application, the functional coating comprises the above-mentioned content of a chalcogenide material containing a metal element, the above-mentioned content of a conductive agent, and the above-mentioned content of a binder. When the negative electrode sheet comprising the above-mentioned functional coating is chemically formed, the functional coating has a greater porosity. The chalcogenide material containing a metal element serves as a negative electrode active material and has good electronic conductivity and can quickly transfer electrons. It usually has a sub-stoichiometric composition, that is, the ratio of metal to chalcogenide elements including selenium deviates from the stoichiometric ratio. This sub-stoichiometric ratio can provide more embedding / de-embedding sites, promote faster ion transport and higher electrochemical reaction rates, and can improve the electrochemical reaction kinetics of the battery cell to achieve high power output and fast charge and discharge rates.

[0033] In some optional embodiments, the negative electrode active material layer includes a silicon-based material, and the silicon-based material includes one or more of silicon, a silicon-carbon composite material, and a silicon-oxygen material.

[0034] According to an embodiment of the present application, the negative electrode active material layer comprising the above-mentioned silicon-based material is in the negative electrode plate, which can increase the capacity of the battery cell comprising the negative electrode plate and achieve rapid ion diffusion.

[0035] In some optional embodiments, the negative electrode active material layer includes 1% to 50% of silicon based on the total mass of the negative electrode active material layer.

[0036] According to the embodiments of the present application, adding the aforementioned silicon content can increase the capacity of the negative electrode active material, thereby improving the battery's energy density. Silicon has high electrical conductivity, and adding an appropriate amount of silicon can enhance the electronic conductivity of the negative electrode active material layer. Silicon-based materials have high ion diffusion coefficients, and the introduction of an appropriate amount of silicon can promote the rapid transport of active ions in the negative electrode active material, improving the battery's kinetic performance, including charge and discharge rates.

[0037] Preparation method of negative electrode sheet

[0038] In a third aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising:

[0039] A first slurry containing a chalcogenide material and a second slurry containing a positive electrode active material are provided, wherein the chalcogenide material includes elemental sulfur, elemental selenium, elemental tellurium, M x S y 、M x Se y 、M x Te yOne or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2;

[0040] The first slurry and the second slurry are applied to one side of the negative electrode current collector to form a functional coating and a negative electrode active material layer, respectively, to prepare the negative electrode plate of the first aspect or the second method, wherein the negative electrode plate includes a negative electrode active material layer arranged on at least one side of the negative electrode current collector and a functional coating arranged on the side of the negative electrode active material layer facing away from the current collector.

[0041] According to the embodiments of the present application, by respectively forming a functional coating and a negative electrode active material layer with a composition comprising a chalcogenide material and a positive electrode active material, the chalcogenide material in the negative electrode plate can participate in the formation of a solid electrolyte interface membrane. The solid electrolyte interface membrane has the participation of chalcogenide elements, which enhances the elasticity of the solid electrolyte interface membrane and can accommodate and adapt to large volume changes of the negative electrode plate comprising the negative electrode active material layer, thereby reducing or avoiding the negative electrode plate squeezing the structure comprising the solid electrolyte interface membrane in the battery cell and causing structural damage, reducing the risk of the solid electrolyte interface membrane being repeatedly destroyed and continuously reformed, thereby improving the cycle performance of the battery cell comprising the negative electrode plate.

[0042] In addition, the solid electrolyte interface membrane formed with the participation of chalcogenide materials has good active ion permeability, which can promote the rapid transmission of active ions at the interface and improve the ion transmission rate; after the chalcogenide materials in the functional coating of the negative electrode plate participate in the solid electrolyte interface membrane, the porosity in the functional coating is improved, and the transmission rate of active ions in the negative electrode plate is improved, thereby comprehensively improving the kinetic performance of the battery cell containing the negative electrode plate.

[0043] In a fourth aspect, embodiments of the present application provide a battery cell comprising the negative electrode sheet of the first or second aspect or the negative electrode sheet prepared by the preparation method of the third aspect. The battery cell comprising the negative electrode sheet at least has the advantages of the negative electrode sheet.

[0044] In some optional embodiments, after the battery cell is formed, the functional coating includes 20% to 30% of chalcogen elements based on the total mass of the functional coating, and the chalcogen elements include one or more of sulfur, selenium, and tellurium.

[0045] According to the embodiments of the present application, after the battery cell is formed, the functional coating of the fresh negative electrode sheet contains the aforementioned amount of chalcogen elements. The aforementioned amount of chalcogen elements can exist in a particulate or porous form, with a high specific surface area. The pores formed by the decomposition of the chalcogen material in the fresh negative electrode sheet further increase the porosity and specific surface area. The high specific surface area provides more reaction interfaces and active sites, thereby giving the negative electrode sheet a high lithium / sodium insertion capacity, enabling the efficient insertion and deintercalation of lithium or sodium ions, thereby increasing the capacity of the battery cell containing the negative electrode sheet.

[0046] In some optional embodiments, after the battery cell is formed, the porosity of the functional coating is 30% to 60%. According to the embodiments of the present application, the increase in the porosity of the functional coating in the negative electrode sheet improves the mass energy density and dynamic performance of the battery cell.

[0047] In some optional embodiments, the battery cell includes an electrolyte, and the electrolyte includes a C3-C12 cyclic carbonate.

[0048] According to an embodiment of the present application, the C3-C12 cyclic carbonate can be one or more of ethylene carbonate (EC), fluoroethylene carbonate, bisfluoroethylene carbonate, and 2,3-butylene carbonate. The chalcogenide material of the present application undergoes a reduction reaction during the electrochemical cycle and can react with the C3-C12 cyclic carbonate compound to generate a poly(ethylene oxide) (PEO)-type polymer, which participates in the formation of a solid electrolyte interface film on the surface of the negative electrode plate, i.e., the functional coating. The solid electrolyte interface film has excellent elasticity and can effectively accommodate and allow the volume expansion of the negative electrode active material layer and the functional coating at the negative electrode-electrolyte interface, thereby stabilizing the interface stability between the negative electrode plate and the electrolyte and improving the service life of the battery cell.

[0049] In some optional embodiments, the battery cell includes a negative electrode plate and a solid electrolyte interface membrane, the solid electrolyte interface membrane includes 0.01% to 6% of a chalcogen element based on the total weight of the solid electrolyte interface membrane, wherein the chalcogen element includes at least one of sulfur, selenium, and tellurium.

[0050] According to the embodiments of the present application, the sulfur elements having the above-mentioned content in the solid electrolyte interface membrane may generate poly(ethylene oxide) (PEO)-type polymers, which help to improve the elasticity of the solid electrolyte interface membrane, and are conducive to accommodating and allowing a certain amount of volume change of the negative electrode plate during the cycle.

[0051] In some optional embodiments, the solid electrolyte interface film includes at least one of the compounds represented by formula (1) and formula (2):

[0052] Wherein, R represents a chalcogen element, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0<x'≤2, 0<y'≤1, and n represents a natural number.

[0053] According to the embodiments of the present application, the compound represented by formula (1) has an alkyl group containing 2 carbon atoms, and the carbon atoms thereof are in free rotation, the arrangement of the chain structure and the flexibility of the long-chain alkyl group, so that the solid electrolyte interface membrane containing the compound represented by formula (1) has good elasticity.

[0054] According to the embodiments of the present application, the compound shown in formula (2) itself has an ether bond, and the bond length of the ether bond is relatively large, which allows the compound to undergo a large deformation under the action of an external force, and to return to its original shape after the external force is removed. This gives the material a certain elasticity, allowing it to deform without breaking when subjected to force. The ether bond has a low bond energy, which makes the ether bond relatively easy to break, and after breaking, it can rotate freely, thereby increasing the flexibility of the material. The breaking of the ether bond can cause the material to undergo reversible deformation when subjected to force without causing damage to the material. The oxygen atoms around the ether bond have a high electronegativity and can form intermolecular forces such as hydrogen bonds or van der Waals forces with other molecules or groups. These intermolecular forces can increase the cohesion of the material, making it more ductile, and comprehensively enhance the good elasticity of the solid electrolyte interface membrane containing the compound shown in formula (2).

[0055] In some optional embodiments, the valence state of the chalcogen element includes at least one of negative one, negative two, positive four, and positive six.

[0056] According to the embodiments of the present application, the sulfide elements are present in the solid electrolyte interface membrane in the above-mentioned valence states, which can form stable chemical bonds in the solid electrolyte interface membrane, enhance the stability of the membrane, and prevent the active ions and electrons in the electrolyte from directly entering the negative electrode active material, thereby reducing the side reactions of the battery. In addition, the presence of the sulfide elements in the above-mentioned valence states in the solid electrolyte interface membrane can exhibit good ionic conductivity, provide a path for the transmission of active ions, and promote the transmission of active ions in the solid electrolyte interface membrane. In addition, the interaction between the sulfide elements and other components in the solid electrolyte interface membrane (such as polymers, etc.) can regulate the structure and properties of the solid electrolyte interface membrane and improve the transmission rate of active ions in the solid electrolyte interface membrane.

[0057] In some optional embodiments, after the battery cell is formed, the ratio of the sum of the molar amounts n1 of the tetravalent and hexavalent sulfur elements in the unit mass of the solid electrolyte interface membrane to the sum of the molar amounts n0 of the sulfur elements in the unit mass of the solid electrolyte interface membrane is (0.3 to 3):1, and can optionally be (0.5 to 1.5):1.

[0058] According to the embodiments of the present application, the elastic range of the solid electrolyte interface membrane can be quantitatively determined based on the ratio of the sum of the molar amounts of tetravalent and hexavalent sulfur elements in a unit mass of the solid electrolyte interface membrane n1 to the sum of the molar amounts of sulfur elements in a unit mass of the solid electrolyte interface membrane n0, so that a negative electrode active material layer with suitable volume expansion can be designed based on the elastic solid electrolyte interface membrane, thereby avoiding the expansion of the negative electrode active material layer of the negative electrode sheet affecting the electrochemical performance of the battery cell.

[0059] In a fifth aspect, embodiments of the present application provide an electrical device comprising the battery cell of the first or second aspect. The battery cell or electrical device of the present application comprises the negative electrode sheet of the first or second aspect of the present application, and thus has at least the advantages of using the negative electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0061] FIG1 shows a schematic diagram of a battery cell according to an embodiment of the present application.

[0062] FIG. 2 shows an exploded schematic diagram of the battery cell shown in FIG. 1 .

[0063] FIG3 is a schematic diagram showing an embodiment of an electric device including the battery cell of the present application as a power source.

[0064] In the accompanying drawings, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0065] Below, with appropriate reference to the accompanying drawings, detailed descriptions are provided of the negative electrode sheet and its preparation method, electrode assembly battery cell, battery module, battery pack and electric device of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0066] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0067] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0068] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0069] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0070] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0071] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0072] Unless otherwise specified, the terms "connected" and "connection" in this application should be understood broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to direct connection, indirect connection through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0073] If not otherwise specified, in this application, the term "attach" refers to connection by adhesion, coating, etc.

[0074] Unless otherwise specified, in this application, the terms "first", "second", "third", "fourth", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0075] Unless otherwise specified, in this application, the term "active ions" refers to ions that can be intercalated and extracted between the positive and negative electrodes of a battery cell, including but not limited to lithium ions, sodium ions, etc.

[0076] The term "several" or "multiple" used in this application refers to two or more (including two).

[0077] The battery cells mentioned in the embodiments of the present application may be lithium-ion batteries, sodium-ion batteries, lithium metal batteries, sodium metal batteries, etc., and the embodiments of the present application are not limited thereto.

[0078] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The electrode sheet will undergo volume expansion during the static and formation process after the electrolyte is injected, which will increase the overall thickness of the battery, thereby affecting the battery performance. During the formation process of the battery cell, the electrode sheet expands. The reasons include volume expansion and stress relaxation expansion caused by the combination of active ions with electrode material particles (such as adsorption, embedding or combination). Studies have found that during the subsequent charging process after the battery is formed, the negative electrode sheet will also expand in volume. The main reason is that the active ions migrate from the positive electrode sheet to the negative electrode sheet and combine with the negative electrode active material (such as adsorption, embedding or combination), which increases the volume of the negative electrode active material, thereby causing the volume expansion of the negative electrode sheet.

[0079] When the volume of the negative electrode plate expands, the plate is squeezed and generates a large internal stress. Such internal stress may cause damage to the internal materials of the plate (such as damage to the active material particles), deformation of the battery shell, etc. The repeated volume expansion / contraction of the negative electrode plate during the charge and discharge process may also lead to repeated destruction and generation of the solid electrolyte interface membrane (SEI membrane), which is not conducive to the stability of the solid electrolyte interface membrane and further affects the cycle performance of the battery. In short, the repeated volume expansion / contraction of the electrode plate, especially the negative electrode plate, during the charge and discharge process of the battery has an adverse effect on the cycle performance of the battery, which is a challenge to improving the cycle performance of the battery. For the negative electrode plate containing silicon-based negative electrode materials, the volume expansion effect is more obvious.

[0080] To reduce the impact of negative electrode volume expansion on battery cycle performance, current measures primarily focus on improving the structure of the active material itself to mitigate its volume expansion and contraction during battery charge and discharge. However, research has found that improvements to the active material structure for this purpose are subject to numerous limitations, such as the range of active material options and capacity requirements, and cannot address issues related to electrode volume expansion caused by other factors, such as the deposition of active ions outside the active material.

[0081] In view of this, the technical solution of the embodiment of the present application provides a negative electrode plate, which can at least reduce the adverse effects of repeated volume expansion / contraction of the negative electrode plate during the battery charging and discharging process on the cycle performance of the battery, thereby improving the cycle performance of the battery cell containing it.

[0082] Negative electrode

[0083] In a first aspect, an embodiment of the present application provides a negative electrode sheet, comprising:

[0084] negative electrode current collector,

[0085] a negative electrode active material layer disposed on at least one side of the negative electrode current collector; and

[0086] The functional coating is provided on the side of the negative electrode active material layer away from the negative electrode current collector, wherein the functional coating comprises a chalcogenide material, and the chalcogenide material comprises elemental sulfur, elemental selenium, elemental tellurium, M x S y 、M x Se y 、M x Te y One or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2.

[0087] The technical solution of the embodiments of the present application provides a negative electrode plate. The negative electrode active material layer of the negative electrode plate is provided with a functional coating comprising a specific chalcogenide material on the side facing away from the negative electrode current collector. Surprisingly, when a battery cell including the negative electrode plate according to the embodiments of the present application is formed, a SEI film with excellent elasticity and stability is formed on the surface of the negative electrode plate.

[0088] Without intending to be bound by any theory or explanation, during formation of the battery cell, the functional coating contacts and interacts with the electrolyte (including a cyclic carbonate solvent such as ethylene carbonate), allowing the chalcogenide material to participate in the formation of the SEI film. The resulting SEI film may include components such as alkyl sulfates and polyoxyalkylene polymers (such as polyethylene oxide (PEO)), resulting in the SEI film having excellent elasticity and stability. Such an SEI film can accommodate and adapt to large volume changes in the negative electrode sheet containing the negative electrode active material layer, reducing or preventing the negative electrode sheet from squeezing the structure containing the SEI film in the battery cell and causing structural damage. This reduces the risk of repeated damage and reformation of the SEI film, thereby improving the cycling performance of the battery cell containing the negative electrode sheet.

[0089] In addition, the solid electrolyte interface membrane with excellent elasticity can stabilize the interface stability between the negative electrode and the electrolyte, thereby improving the service life of the battery cell.

[0090] In addition, the solid electrolyte interface membrane formed with the participation of chalcogenide materials has good active ion permeability, which can promote the rapid transmission of active ions at the interface and improve the ion transmission rate; after the chalcogenide materials in the functional coating of the negative electrode plate participate in the solid electrolyte interface membrane, the porosity in the functional coating is improved, and the transmission rate of active ions in the negative electrode plate is improved, thereby comprehensively improving the kinetic performance of the battery cell containing the negative electrode plate.

[0091] According to embodiments of the present application, x and y in the chalcogenide material can be understood as the molar ratio of element M to chalcogenide elements including sulfur, selenium, and tellurium. In some embodiments, the ratio of x to y can be 1:(0-2). As an example, the chalcogenide material includes molybdenum disulfide.

[0092] Chalcogenide materials often exist in the form of particles or porous materials and have a high specific surface area. The high surface area can provide more reaction interfaces and active sites, so that the negative electrode plate has a higher lithium / sodium insertion capacity and can effectively insert and deinsert lithium ions or sodium ions, thereby increasing the capacity of the battery cell containing the negative electrode plate.

[0093] M in chalcogenide materials x S y 、M x Sey 、M x Te y It has certain electronic conductivity, but its electrical conductivity is low, and it usually has a sub-stoichiometric composition, that is, the ratio of metal and chalcogen elements including selenium deviates from the stoichiometric ratio. This sub-stoichiometric ratio can provide more embedding / de-embedding sites, promote faster ion transport and higher electrochemical reaction rates, and improve the electrochemical reaction kinetics of the battery cell to achieve high power output and fast charge and discharge rates.

[0094] Elemental sulfur, selenium, and tellurium in chalcogenide materials are non-metallic elements typically linked by covalent bonds in their crystal structures. This covalent bond creates a relatively stable structure for sulfur and selenium within the crystal, but it also restricts the free movement of electrons, resulting in poor electronic conductivity. Their presence in the negative electrode improves the safety of the negative electrode.

[0095] In some optional embodiments, the functional coating comprises 30% to 95% of the chalcogenide material based on the total mass of the functional coating.

[0096] Optionally, the functional coating includes a mass content of 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, 101%, 102%, 103%, 104%, 105%, 106%, 107%, 108%, 109%, 110%, 111%, 112%, 113%, 114%, 115%, 116%, 117%, 118%, 119%, 120%, 121 3%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% or a range of combinations thereof.

[0097] According to the embodiments of the present application, the sulfide material containing the above-mentioned mass content can improve the elasticity of the solid electrolyte interface membrane, can accommodate and adapt to large volume changes of the negative electrode plate containing the negative electrode active material layer, reduce or avoid the negative electrode plate squeezing the structure containing the solid electrolyte interface membrane in the battery cell and thereby causing structural damage, reduce the risk of the solid electrolyte interface membrane being repeatedly destroyed and continuously reformed, thereby improving the cycle performance of the battery cell containing the negative electrode plate.

[0098] In some optional embodiments, the ratio of the thickness of the negative electrode active material layer to the thickness of the functional coating layer is 1:(0.01-0.2), and can be optionally 1:(0.01-0.1).

[0099] According to the embodiments of the present application, controlling the thickness ratio of the negative electrode active material layer to the functional coating layer within the aforementioned range allows the functional coating layer to provide a sufficient protective layer to protect the negative electrode active material. Components such as metal selenide, sulfur, and selenium can form a protective layer that prevents direct contact between the negative electrode active material and the electrolyte, reduces side reactions with the electrolyte, and improves the cycling stability of battery cells containing the negative electrode sheet.

[0100] The thickness ratio of the negative electrode active material layer to the functional coating can affect the transmission path and resistance of electrons and ions. In general, a smaller ratio may help improve ion transport and electron conductivity, thereby improving the discharge performance and charging rate of the battery.

[0101] In some optional embodiments, the thickness of the functional coating is 1-10 μm, or 2-5 μm. Alternatively, the thickness of the functional coating can be any value of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or a range thereof.

[0102] According to the embodiment of the present application, the functional coating has a thickness within the above range, which is beneficial for the negative electrode plate to embed and de-embed active ions in the battery cell, and is beneficial to the dynamic performance and cycle performance of the battery cell.

[0103] When the thickness of the functional coating is too high, the remaining unreacted non-conductive chalcogenide material coats the surface of the electrode, increasing the surface impedance, hindering the transmission of active ions, and affecting the capacity of the active material and the cycle stability; when the thickness of the functional coating is too low, the elasticity improvement effect of the solid electrolyte interface film formed by the chalcogenide material is limited, limiting its ability to accommodate the volume expansion of the negative electrode.

[0104] In some optional embodiments, the average particle size D50 of the chalcogenide material is 0.05 to 25 μm; optionally, 0.1 to 5 μm.

[0105] Optionally, the average particle size D50 of the chalcogenide material can be 0.05um, 0.10um, 0.15um, 0.20um, 0.25um, 0.30um, 0.35um, 0.40um, 0.45um, 0.50um, 0.55um, 0.65um, 0.70um, 0.75um, 0.80um, 0.85um, 0.90um, 0.95um, 1.0um, 1.5um, 2.0um, 2.5um, 3.0um, 3.5um, 4.0um, 4.5um, 5.0um, Any numerical value among 5.5um, 6.0um, 6.5um, 7.0um, 7.5um, 8.0um, 8.5um, 9.0um, 9.5um, 10.0um, 10.5um, 11.0um, 11.5um, 12.0um, 13.0um, 13.5um, 14.0um, 14.5um, 15.0um, 16.0um, 16.5um, 17.0um, 17.5um, 18.0um, 18.5um, 19.0um, 19.5um, 20.0um or a range composed thereof.

[0106] According to the embodiments of the present application, the average particle size Dv50 of the chalcogenide material is within the above-mentioned range, which is beneficial for the chalcogenide material to participate in the formation of a solid electrolyte interface film during the formation of the battery cell, and to form pores with uniform distribution and relatively uniform particle size after decomposition from the negative electrode active material layer, which is beneficial to the structural stability of the functional coating and the dynamic performance and cycle performance of the battery cell.

[0107] Volume average particle size D v The term "50" is generally known in the art and represents the particle size corresponding to the 50% cumulative volume distribution percentage of the material. It can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, with reference to the particle size distribution laser diffraction method according to GB / T 19077-2016.

[0108] In some optional embodiments, the porosity of the functional coating is 15% to 40%.

[0109] Optionally, the porosity of the functional coating can be any value selected from the group consisting of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, and 40%, or a range thereof. According to the embodiments of the application, the functional coating has a porosity within the above range, which is conducive to the electrolyte infiltration of the functional coating during the formation stage, facilitating the chalcogenide material in the functional coating to participate in the formation of the solid electrolyte interface film, thereby making the solid electrolyte interface film have stronger elasticity.

[0110] In some optional embodiments, the functional coating includes a chalcogenide material, a conductive agent, and a binder.

[0111] According to the embodiment of the present application, when the functional coating comprises a chalcogenide material, a conductive agent and a binder. x S y 、M x Se y 、M x Te y It can be used as a negative electrode active material, with a high lithium / sodium insertion capacity. The entire functional coating can serve as another new negative electrode active material layer, improving the cycle performance of the battery cell. Chalcogenide materials such as elemental sulfur, elemental selenium, and elemental tellurium can also be used as negative electrode active materials.

[0112] In some optional embodiments, the functional coating comprises 5% to 10% of the conductive agent based on the total mass of the functional coating.

[0113] Alternatively, the functional coating may include any of 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or a combination thereof of the conductive agent.

[0114] According to the embodiments of the present application, when the functional coating contains the conductive agent in the above-mentioned content, the internal resistance of the negative electrode plate can be reduced, and the internal resistance of the entire battery cell can be reduced, thereby facilitating the transmission of electrons and improving the dynamic performance of the battery cell containing the negative electrode plate.

[0115] In some optional embodiments, the functional coating comprises 3% to 5% of a binder based on the total weight of the functional coating. Alternatively, the functional coating comprises 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, or 5% of a binder.

[0116] According to the embodiments of the present application, when the functional coating contains the above-mentioned binder content, the structural stability, electrical conductivity, and ion transport performance of the negative electrode sheet can be balanced. However, too high or too low a binder content may affect the performance of the battery cell containing the negative electrode sheet.

[0117] In some optional embodiments, based on the total mass of the functional coating, the functional coating comprises 80% to 95% of a simple chalcogen element and 5% to 20% of a binder, wherein the chalcogen element comprises at least one of sulfur, selenium, and tellurium. Alternatively, the functional coating may comprise, by mass percentage, any of 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 19.5%, and 20% of a conductive agent, or a range thereof. According to an embodiment of the present application, the functional coating contains the above-mentioned content of the simple substance of the chalcogen element and the above-mentioned content of the binder. After the negative electrode plate containing the above-mentioned functional coating is formed, the functional coating only contains the simple substance of the chalcogen element and the binder, as well as the gaps left by the consumption of part of the simple substance of the chalcogen element. The coating has an insulating effect and can enhance the safety performance of the battery cell containing the negative electrode plate.

[0118] In some optional embodiments, based on the total mass of the functional coating, the functional coating comprises 85% to 92% of a chalcogenide material containing a metal element, 5% to 10% of a conductive agent, and 3% to 5% of a binder, wherein the chalcogenide material containing a metal element comprises M x S y 、M x Se y 、M x Te y One or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2.

[0119] According to an embodiment of the present application, the functional coating comprises the above-mentioned content of a chalcogenide material containing a metal element, the above-mentioned content of a conductive agent, and the above-mentioned content of a binder. When the negative electrode sheet comprising the above-mentioned functional coating is chemically formed, the functional coating has a greater porosity. The chalcogenide material containing a metal element serves as a negative electrode active material and has good electronic conductivity and can quickly transfer electrons. It usually has a sub-stoichiometric composition, that is, the ratio of metal to chalcogenide elements including selenium deviates from the stoichiometric ratio. This sub-stoichiometric ratio can provide more embedding / de-embedding sites, promote faster ion transport and higher electrochemical reaction rates, and can improve the electrochemical reaction kinetics of the battery cell to achieve high power output and fast charge and discharge rates.

[0120] In some optional embodiments, the negative electrode active material layer includes a silicon-based material, and the silicon-based material includes one or more of silicon, a silicon-carbon composite material, and a silicon-oxygen material.

[0121] According to an embodiment of the present application, the negative electrode active material layer comprising the above-mentioned silicon-based material is in the negative electrode plate, which can increase the capacity of the battery cell comprising the negative electrode plate and achieve rapid ion diffusion.

[0122] In some optional embodiments, the negative electrode active material layer comprises 1% to 50% silicon based on the total mass of the negative electrode active material layer. Alternatively, the negative electrode active material layer comprises 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% silicon.

[0123] According to the embodiments of the present application, adding the aforementioned silicon content can increase the capacity of the negative electrode active material, thereby improving the battery's energy density. Silicon has high electrical conductivity, and adding an appropriate amount of silicon can enhance the electronic conductivity of the negative electrode active material layer. Silicon-based materials have high ion diffusion coefficients, and the introduction of an appropriate amount of silicon can promote the rapid transport of active ions in the negative electrode active material, improving the battery's kinetic performance, including charge and discharge rates.

[0124] The specific composition and structure of the negative electrode plate can be selected according to the type of battery cell, and the embodiments of the present application are not limited thereto.

[0125] For example, when the battery cell is a lithium-ion battery cell or a sodium-ion battery cell, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces that are opposed in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0126] The negative electrode active material is a material that can extract and embed active ions (such as lithium ions, sodium ions, etc.), and the negative electrode active material can adopt materials well known in the art. As an example, the negative electrode active material includes but is not limited to one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite and silicon alloy materials. Tin-based materials may include one or more of 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 may also be used.

[0127] In some embodiments, the negative electrode active material layer may further include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. For example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In some embodiments, the negative electrode active material layer may further include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder. As examples, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0129] In some embodiments, the negative electrode active material layer may further include other auxiliary agents. For example, the other auxiliary agents may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like.

[0130] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0131] The negative electrode active material layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0132] The negative electrode sheet does not exclude other additional layers besides the negative electrode active material layer and the functional coating of the present application. For example, in some embodiments, the negative electrode sheet of the present application may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet of the present application may further include a protective layer covering the surface of the negative electrode active material layer.

[0133] When the battery cell is a lithium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode plate may include a lithium plate or a lithium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam-like three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, etc.

[0134] When the battery cell is a sodium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode plate may include a sodium plate or a sodium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), aluminum foam (or aluminum alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, aluminum (or aluminum alloy) mesh, etc.

[0135] Preparation method of negative electrode sheet

[0136] In a third aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet, comprising:

[0137] A first slurry containing a chalcogenide material and a second slurry containing a positive electrode active material are provided, wherein the chalcogenide material includes elemental sulfur, elemental selenium, elemental tellurium, M x S y 、M x Se y 、M x Te y One or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2;

[0138] The first slurry and the second slurry are applied to one side of the negative electrode current collector to form a functional coating and a negative electrode active material layer, respectively, to prepare the negative electrode plate of the first aspect or the second method, wherein the negative electrode plate includes a negative electrode active material layer arranged on at least one side of the negative electrode current collector and a functional coating arranged on the side of the negative electrode active material layer facing away from the current collector.

[0139] According to the embodiments of the present application, by respectively forming a functional coating and a negative electrode active material layer with a composition comprising a chalcogenide material and a positive electrode active material, the chalcogenide material in the negative electrode plate can participate in the formation of a solid electrolyte interface membrane. The solid electrolyte interface membrane has the participation of chalcogenide elements, which enhances the elasticity of the solid electrolyte interface membrane and can accommodate and adapt to large volume changes of the negative electrode plate comprising the negative electrode active material layer, thereby reducing or avoiding the negative electrode plate squeezing the structure comprising the solid electrolyte interface membrane in the battery cell and causing structural damage, reducing the risk of the solid electrolyte interface membrane being repeatedly destroyed and continuously reformed, thereby improving the cycle performance of the battery cell comprising the negative electrode plate.

[0140] In addition, the solid electrolyte interface membrane formed with the participation of chalcogenide materials has good active ion permeability, which can promote the rapid transmission of active ions at the interface and improve the ion transmission rate; after the chalcogenide materials in the functional coating of the negative electrode plate participate in the solid electrolyte interface membrane, the porosity in the functional coating is improved, and the transmission rate of active ions in the negative electrode plate is improved, thereby comprehensively improving the kinetic performance of the battery cell containing the negative electrode plate.

[0141] battery cells

[0142] In a fourth aspect, embodiments of the present application provide a battery cell comprising the negative electrode sheet of the first or second aspect or the negative electrode sheet prepared by the preparation method of the third aspect. The battery cell comprising the negative electrode sheet at least has the advantages of the negative electrode sheet.

[0143] The present application has no particular limitation on the type of battery cells. For example, the battery cells may be lithium-ion batteries, sodium-ion batteries, etc. Sodium-ion batteries may be selected as the battery cells.

[0144] In some optional embodiments, after the battery cell is formed, the functional coating includes 20% to 30% of chalcogen elements based on the total mass of the functional coating, and the chalcogen elements include one or more of sulfur, selenium, and tellurium.

[0145] Alternatively, the functional coating may include 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% of the chalcogen element based on the total mass of the functional coating.

[0146] According to the embodiments of the present application, after the fresh negative electrode plate undergoes chemical formation, the functional coating contains the aforementioned amount of chalcogen elements, which can exist in a particulate or porous form and have a high specific surface area. Furthermore, the pores formed by the decomposition of the chalcogen material in the fresh negative electrode plate further increase the porosity and specific surface area. The higher specific surface area provides more reaction interfaces and active sites, resulting in a higher lithium / sodium insertion capacity for the negative electrode plate, enabling efficient insertion and deintercalation of lithium or sodium ions, thereby increasing the capacity of the battery cell containing the negative electrode plate.

[0147] The chalcogenide elements in the embodiments of the present application can be in the form of single substance or in the form of M x S y 、M x Se y 、M x Te y Sulfur-containing materials typically have a relatively stable crystal structure, which can maintain structural integrity and stability during battery cycles, thereby improving the cycle stability of battery cells containing such materials and maintaining a high capacity retention rate and energy efficiency over multiple charge and discharge cycles.

[0148] M x S y 、M x Se y 、M x Te y Sulfur elements in the form of have certain electronic conductivity properties, and they usually have a sub-stoichiometric composition, that is, the ratio of metals and sulfide elements including selenium deviates from the stoichiometric ratio. This sub-stoichiometric ratio can provide more embedding / de-embedding sites, promote faster ion transport and higher electrochemical reaction rates, and improve the electrochemical reaction kinetics of the battery cell to achieve high power output and fast charge and discharge rates.

[0149] Chalcogenides, found in elemental sulfur, selenium, and tellurium, are non-metallic elements typically linked by covalent bonds in their crystal structures. This covalent bond creates a relatively stable structure for sulfur and selenium in the crystal, but it also restricts the free movement of electrons, resulting in poor electronic conductivity. Their presence in negative electrode plates improves the safety of the negative electrode.

[0150] In some optional embodiments, after the battery cell is formed, the porosity of the functional coating is 30% to 60%. According to the embodiments of the present application, the increase in the porosity of the functional coating in the negative electrode sheet improves the mass energy density and dynamic performance of the battery cell.

[0151] In some optional embodiments, the battery cell includes an electrolyte, and the electrolyte includes a C3-C12 cyclic carbonate.

[0152] According to an embodiment of the present application, the C3-C12 cyclic carbonate can be one or more of ethylene carbonate (EC), fluoroethylene carbonate, bisfluoroethylene carbonate, and 2,3-butylene carbonate. The chalcogenide material of the present application undergoes a reduction reaction during the electrochemical cycle and can react with the C3-C12 cyclic carbonate compound to generate a poly(ethylene oxide) (PEO)-type polymer, which participates in the formation of a solid electrolyte interface film on the surface of the negative electrode plate, i.e., the functional coating. The solid electrolyte interface film has excellent elasticity and can effectively accommodate and allow the volume expansion of the negative electrode active material layer and the functional coating at the negative electrode-electrolyte interface, thereby stabilizing the interface stability between the negative electrode plate and the electrolyte and improving the service life of the battery cell.

[0153] In some optional embodiments, the battery cell includes a negative electrode plate and a solid electrolyte interface membrane, the solid electrolyte interface membrane includes 0.01% to 6% of a chalcogen element based on the total weight of the solid electrolyte interface membrane, wherein the chalcogen element includes at least one of sulfur, selenium, and tellurium.

[0154] Optionally, the solid electrolyte interface film includes 0.01%, 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.5%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, based on the total weight of the solid electrolyte interface film. 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0% or any other value or composition range of a chalcogenide element.

[0155] According to the embodiments of the present application, the sulfur elements having the above-mentioned content in the solid electrolyte interface membrane may generate poly(ethylene oxide) (PEO)-type polymers, which help to improve the elasticity of the solid electrolyte interface membrane, and are conducive to accommodating and allowing a certain amount of volume change of the negative electrode plate during the cycle.

[0156] In some optional embodiments, the solid electrolyte interface film includes at least one of the compounds represented by formula (1) and formula (2):

[0157] Wherein, R represents a chalcogen element, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0<x'≤2, 0<y'≤2, and n represents a natural number.

[0158] According to the embodiments of the present application, the compound represented by formula (1) has an alkyl group containing 2 carbon atoms, and the carbon atoms thereof are in free rotation, the arrangement of the chain structure and the flexibility of the long-chain alkyl group, so that the solid electrolyte interface membrane containing the compound represented by formula (1) has good elasticity.

[0159] According to the embodiments of the present application, the compound shown in formula (2) itself has an ether bond, and the bond length of the ether bond is relatively large, which allows the compound to undergo a large deformation under the action of an external force, and to return to its original shape after the external force is removed. This gives the material a certain elasticity, allowing it to deform without breaking when subjected to force. The ether bond has a low bond energy, which makes the ether bond relatively easy to break, and after breaking, it can rotate freely, thereby increasing the flexibility of the material. The breaking of the ether bond can cause the material to undergo reversible deformation when subjected to force without causing damage to the material. The oxygen atoms around the ether bond have a high electronegativity and can form intermolecular forces such as hydrogen bonds or van der Waals forces with other molecules or groups. These intermolecular forces can increase the cohesion of the material, making it more ductile, and comprehensively enhance the good elasticity of the solid electrolyte interface membrane containing the compound shown in formula (2).

[0160] As an example, reactants generated by the reaction of the chalcogenide material are shown in Reaction Formulas 1 to 3.

[0161] Where 0<x≤2.

[0162] According to the embodiments of the present application, under the action of the chalcogenide material of the present application, on the basis of Reaction Formula 1, the reactions of Reaction Formula 2 and Reaction Formula 3 continue to occur, so that the solid electrolyte interface membrane includes more compounds represented by Formula (1) and also has the compound represented by Formula (2), which can effectively improve the elasticity of the solid electrolyte interface membrane. Therefore, the chalcogenide material significantly improves the elasticity of the solid electrolyte interface membrane.

[0163] According to the embodiments of the present application, sulfides can exhibit good ionic conductivity under certain conditions. In the solid electrolyte interface membrane, sulfides can serve as a channel or bridge for ion transmission, providing a path for active ion transmission and promoting the transmission of active ions in the solid electrolyte interface membrane. In addition, the interaction between sulfides and other components in the solid electrolyte interface membrane (such as polymers, etc.) can regulate the structure and properties of the solid electrolyte interface membrane and improve the transmission rate of active ions in the solid electrolyte interface membrane.

[0164] In addition, sulfides can form stable chemical bonds in the solid electrolyte interface membrane, enhance the stability of the membrane, and prevent active ions and electrons in the electrolyte from directly entering the negative electrode active material, thereby reducing the side reactions of the battery.

[0165] In some optional embodiments, the valence state of the chalcogen element includes at least one of negative one, negative two, positive four, and positive six.

[0166] According to the embodiments of the present application, chalcogenides with valence states of +4 and / or +6 have S2p peaks of 168 to 172 eV; chalcogenides with valence states of -2 to -1 / 4 have S2p peaks of 160 to 166 eV. These peaks were determined by XPS analysis of the anode electrode of a disassembled battery cell after formation.

[0167] According to the embodiments of the present application, the sulfide elements are present in the solid electrolyte interface membrane in the above-mentioned valence states, which can form stable chemical bonds in the solid electrolyte interface membrane, enhance the stability of the membrane, and prevent the active ions and electrons in the electrolyte from directly entering the negative electrode active material, thereby reducing the side reactions of the battery. In addition, the presence of the sulfide elements in the above-mentioned valence states in the solid electrolyte interface membrane can exhibit good ionic conductivity, provide a path for the transmission of active ions, and promote the transmission of active ions in the solid electrolyte interface membrane. In addition, the interaction between the sulfide elements and other components in the solid electrolyte interface membrane (such as polymers, etc.) can regulate the structure and properties of the solid electrolyte interface membrane and improve the transmission rate of active ions in the solid electrolyte interface membrane.

[0168] In some optional embodiments, after the battery cell is formed, the ratio of the sum of the molar amounts n1 of the tetravalent and hexavalent sulfur elements in the unit mass of the solid electrolyte interface membrane to the sum of the molar amounts n0 of the sulfur elements in the unit mass of the solid electrolyte interface membrane is (0.3 to 3):1, and can optionally be (0.5 to 1.5):1.

[0169] Optionally, the ratio of n1 to n0 can be any value or a range of its composition among 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, and 3.0:1.

[0170] According to the embodiments of the present application, the elastic range of the solid electrolyte interface membrane can be quantitatively determined based on the ratio of the sum of the molar amounts of tetravalent and hexavalent sulfur elements in a unit mass of the solid electrolyte interface membrane n1 to the sum of the molar amounts of sulfur elements in a unit mass of the solid electrolyte interface membrane n0, so that a negative electrode active material layer with suitable volume expansion can be designed based on the elastic solid electrolyte interface membrane, thereby avoiding the expansion of the negative electrode active material layer of the negative electrode sheet affecting the electrochemical performance of the battery cell.

[0171] [Positive electrode]

[0172] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in the thickness direction of the positive electrode current collector, and the positive electrode active material layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0173] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material may be a positive electrode active material commonly known in the art and used in battery cells.

[0174] For example, when the battery cell is a lithium-ion battery cell or a lithium metal battery cell, the positive electrode active material may include one or more of a lithium transition metal oxide, an olivine-structured lithium-containing phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include 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 their respective modified compounds. Examples of lithium phosphates containing an olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may also be used.

[0175] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material may include a general formula of Li a Ni b Co c M d O e A f One or more lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more selected from N, F, S and Cl.

[0176] As an example, the positive electrode active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0177] When the battery cell is a sodium ion battery cell or a sodium metal battery cell, the positive electrode active material may include but is not limited to one or more of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0178] As an example, the positive electrode active material may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2、NaNi 1 / 2 Mn 1 / 2 O2、Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2、NaNi 1 / 3 Co 1 / 3 Mn 1 / 3O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials and general formula X p M' q (PO4) r O x Y 3-x One or more materials. p M' q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X includes H + 、Li + 、Na + , K + and NH4 + One or more of, M' is a transition metal cation, which can be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, which can be selected from one or more of F, Cl and Br.

[0179] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0180] In some embodiments, the positive electrode active material layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0181] In some embodiments, the positive electrode active material layer may further optionally include a positive electrode binder. This application does not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0182] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0183] The positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0184] [Electrolytes]

[0185] In some embodiments, the battery cell includes an electrolyte. The electrolyte conducts active ions between the positive and negative electrode plates. This application does not specifically limit the type of electrolyte, and the electrolyte may be selected based on needs. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte solution).

[0186] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0187] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. For example, the electrolyte salt includes one or more selected from lithium salts for lithium ion batteries and sodium salts for sodium ion batteries. As an example, the lithium salt includes one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium tetrafluorooxalatophosphate (LiTFOP). As an example, the sodium salt includes one or more selected from NaPF6, NaClO4, NaBCl4, NaSO3CF3, Na(CH3)C6H4SO3.

[0188] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl 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 butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0189] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0190] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0191] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0192] The present application has no particular limitation on the shape of the battery cell, which can be a flat body, a rectangular parallelepiped, or other shapes. FIG1 shows a battery cell 5 of a rectangular parallelepiped structure as an example.

[0193] In some embodiments, as shown in Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate together form a accommodating cavity. The shell 51 has an opening connected to the accommodating cavity, and the cover plate 53 is used to cover the opening to close the accommodating cavity. The electrode assembly 52 of the first aspect of the embodiment of the present application or the electrode assembly 52 prepared according to the method of the second aspect of the embodiment of the present application is encapsulated in the accommodating cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be adjusted according to demand.

[0194] The method for preparing the battery cell of the present application is well known and includes at least the step of preparing the electrode assembly according to the second aspect of the embodiment of the present application. In some embodiments, the electrode assembly can be placed in an outer package, dried, injected with electrolyte, and then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell.

[0195] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module. The battery module can contain multiple battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0196] Optionally, the battery module may further include a housing having an accommodation space, wherein the plurality of battery cells are accommodated in the accommodation space.

[0197] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0198] [Preparation method]

[0199] The preparation method of the battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying. After packaging, standing, forming, shaping and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel or in a mixed manner to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed manner to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0200] Electrical devices

[0201] In a fifth aspect, embodiments of the present application provide an electrical device comprising the battery cell of the first or second aspect. The battery cell or electrical device of the present application comprises the negative electrode sheet of the first or second aspect of the present application, and thus has at least the advantages of using the negative electrode sheet.

[0202] The battery cells can be used as power sources or energy storage units for the electrical devices. The electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, 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 trains, ships, satellites, energy storage systems, etc.

[0203] Figure 3 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0204] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0205] Example

[0206] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0207] Example 1

[0208] Preparation of positive electrode

[0209] Will Li[Ni 0.9 Co 0.05 Mn 0.05

[0014] O2 (NCM90 ternary material), conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and carbon nanotubes (CNTs) were dry-mixed and stirred uniformly in a weight ratio of 77.3:10:8.7:2.7:1.3. The mixture was stirred at a speed of 400 to 1000 r / s, and then wetted, kneaded, and dispersed to obtain a positive electrode slurry. The obtained slurry was then coated on aluminum foil, dried, cold-pressed, and slit to obtain the positive electrode sheet of Example 1.

[0210] Preparation of negative electrode sheet

[0211] Preparation of active material layer coating slurry: Active material artificial graphite, silicon oxide, conductive agent carbon black, binder styrene-butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC-Na) in a weight ratio of 72.2:25:0.8:0.8:1.2 are dry-mixed evenly, and then deionized water is added and mixed evenly to prepare an active layer slurry.

[0212] Preparation of functional coating slurry: dry-mix elemental sulfur powder, carbon nanotubes, and binder styrene-butadiene rubber (SBR) in a weight ratio of 90:7:3, and then add deionized water and mix evenly to prepare a functional coating slurry.

[0213] Preparation of composite negative electrode sheets: The precursor of the active material layer is evenly coated on the current collector, and the active material layer is obtained by drying at a temperature of 90°C for 15 minutes; the precursor of the functional coating is evenly printed on the active material layer with a gravure roller, and the functional coating is obtained by drying at a temperature of 60°C for 35 minutes. The thickness of the functional coating is 3um, and the composite negative electrode sheet is obtained after cold pressing and slitting.

[0214] Preparation of isolation membrane

[0215] Polyethylene film is used as the isolation film.

[0216] Preparation of electrolyte

[0217] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 4 / 6, 12.5% ​​LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred evenly to obtain the electrolyte of Example 1.

[0218] Preparation of lithium-ion battery cells

[0219] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive and negative electrode sheets, and then wound to obtain a bare battery cell; the bare battery cell is placed in the battery outer packaging, and then the electrolyte is injected, packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery, wherein the lithium-ion battery has a thickness of 14.2 mm, a width of 32 mm, and a length of 82 mm.

[0220] Examples 2-1 to 2-14: The preparation method is similar to that of Example 1, except that the types of chalcogenide materials are different, see Table 1 for details.

[0221] Examples 3-1 to 3-8: The preparation method is similar to that of Example 1, except that the content of the chalcogenide material in the functional coating in the preparation steps is different. See Table 1 for details.

[0222] Examples 4-1 to 4-4

[0223] The preparation method is similar to that of Example 1, except that the particle size of the chalcogenide material in the functional coating is different, as shown in Table 1.

[0224] Examples 5-1 to 5-6

[0225] The preparation method is similar to that of Example 1, except that the thickness ratio of the functional coating layer to the negative electrode active material layer is different, as shown in Table 1.

[0226] Comparative Example 1

[0227] The difference between this comparative example and Example 1 is: Preparation of the negative electrode sheet: the active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium hydroxymethyl cellulose (CMC-Na) are dry-mixed in a weight ratio of 97.2:0.8:0.8:1.2, and then deionized water is added and mixed to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode collector copper foil, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0228] Test section

[0229] 1) Method for testing the content of chalcogenide materials in the functional coating: First, digest the positive electrode with aqua regia, a digestion reagent made from concentrated nitric acid (HNO3) and concentrated hydrochloric acid (HCl) in a 1:1 volume ratio. Digestion methods include plate digestion, acid digestion, or microwave digestion (high temperature and pressure, approximately 200°C). The digested solution is then collected and tested with an inductively coupled plasma spectrometer to quantitatively determine the chalcogen content.

[0230] 2) DC internal resistance test method: At 25°C, charge the shipped lithium-ion battery and the lithium-ion battery that has been cycled 100 times at 45°C at a constant current of 0.33C to 4.25V. Then, charge at a constant voltage of 4.25V until the current is less than 0.05C. Then, discharge at 0.33C for 30 minutes, adjusting the battery capacity to 50% SOC. Then, touch the positive and negative test leads of the TH2523A AC internal resistance tester to the positive and negative terminals of the battery, respectively. The internal resistance of the battery is read using the internal resistance tester and recorded as the initial cell internal resistance and the cell internal resistance after 100 cycles, respectively.

[0231] 3) The 0.33C capacity retention rate test method is as follows: At 25°C, charge the lithium-ion battery at a constant current of 0.33C to 4.25V, then charge at a constant voltage of 4.25V until the current is less than 0.05C, and then discharge the lithium-ion battery at a constant current of 0.33C to 3.0V. This charge and discharge process is repeated in this way, and the capacity retention rate of the lithium-ion battery after 100 cycles is calculated.

[0232] Capacity retention rate (%) of the lithium ion battery after 100 cycles at 25° C. = (discharge capacity at the 100th cycle / discharge capacity at the first cycle)×100%.

[0233] 4) Test method for 60°C storage capacity retention rate:

[0234] The battery capacity recovery rate test process is as follows: before storage, at 25°C, the battery corresponding to Implementation 1 was charged to 4.25V at a constant current of 1 / 3C, then charged to 0.05C at a constant voltage of 4.25V, left for 30 minutes, and then discharged to 2.8V at 1 / 3C. The obtained capacity was recorded as the initial capacity C0. After storage at 60°C for 100 days, the battery temperature was cooled to room temperature and the above steps were repeated. The measured capacity was recorded as Cr. The battery capacity recovery rate after storage for 50 days is H=Cr / C0*100%.

[0235] 5) 0.33C overcharge failure boundary test method:

[0236] First, the battery cell is installed in the fixture, then fully charged at 0.33C to 100% SOC, the sample appearance is inspected and photographed, and the battery cell OCV, IMP, and mass are recorded; then, the battery cell is charged at a current of 0.33C at room temperature until the cell fails, the battery cell SOC status at this time is recorded, and the battery voltage change is simultaneously monitored.

[0237] 6) Fully charged shallow puncture safety margin test method:

[0238] First, the battery cell is mounted on a fixture and fully charged at 0.33C to 100% SOC. The appearance of the sample is inspected and photographed, and the cell's OCV, IMP, and mass are recorded. This is done at room temperature with a 1mm diameter nail inserted at a speed of 0.1mm / s perpendicular to the battery plate, close to the geometric center of the surface being punctured, until the cell fails. The penetration depth at this point is recorded.

[0239] 7) Fast charging performance (10%-80% SOC fast charging time)

[0240] The 10%-80% SOC charging time test procedure is as follows: At 25°C, the batteries in the examples and comparative examples were charged from 10% SOC to 80% SOC at a step-by-step rate of 1.0C / 0.8C / 0.5C / 0.33C. The charging time until lithium plating does not occur at the negative electrode is the battery's fast charge time at that point. A shorter fast charge time indicates better fast charge performance.

[0241] Test results

[0242] Based on the test results of Examples 1 to 8, it can be seen that the functional coating of the negative electrode plate contains a chalcogenide material, which improves the cycle performance, high-temperature storage performance and safety of the battery cell containing the negative electrode plate.

[0243] Analysis shows that the reason may be that when the battery cell is formed, the functional coating contacts and interacts with the electrolyte (containing a cyclic carbonate solvent such as ethylene carbonate), causing the sulfide material to participate in the formation of the SEI film. The components of the SEI film thus formed may include alkyl sulfates and polyoxyalkylene polymers (such as polyethylene oxide (PEO)), etc., which makes the SEI film have excellent elasticity and stability. Such an SEI film can accommodate and adapt to the large volume changes of the negative electrode sheet containing the negative electrode active material layer, reduce or avoid the negative electrode sheet squeezing the structure containing the SEI film in the battery cell and causing structural damage, reduce the risk of the SEI film being repeatedly damaged and continuously re-formed, thereby improving the cycle performance of the battery cell containing the negative electrode sheet. The solid electrolyte interface film with excellent elasticity can stabilize the interface stability between the negative electrode sheet and the electrolyte, and improve the service life of the battery cell. Chalcogenide materials often exist in the form of particles or porous materials and have a high specific surface area. The high surface area can provide more reaction interfaces and active sites, so that the negative electrode plate has a higher lithium / sodium insertion capacity and can effectively insert and deinsert lithium ions or sodium ions, thereby increasing the capacity of the battery cell containing the negative electrode plate.

[0244] M in chalcogenide materials x S y 、M x Se y 、M x Te y It has certain electronic conductivity, but its electrical conductivity is low. The elemental sulfur, elemental selenium, and elemental tellurium in the chalcogenide materials are non-metallic elements, which are usually connected in the form of covalent bonds in the crystal structure. The formation of covalent bonds allows sulfur and selenium to form a relatively stable structure in the crystal, but it also limits the free movement of electrons, and its electronic conductivity is poor. When it exists in the negative electrode plate, it is beneficial to improve the safety performance of the negative electrode plate. According to Table 1, compared with Comparative Example 1, the functional coating of the negative electrode set in the embodiment includes a chalcogenide material, which improves the cycle performance, service life and safety of the battery cell containing the negative electrode plate.

[0245] Compared with Example 1, Examples 2-1 to 2-14 have different types of chalcogenide materials and thus have differentiated cycle performance, high-temperature storage performance, and safety performance.

[0246] According to Table 1, compared with Example 1, the chalcogenide material content in Examples 3-1 to 3-8 is reduced, resulting in a decrease in their high-temperature storage performance and 0.33C overcharge failure boundary performance.

[0247] According to Table 1, compared with Examples 4-1 to 4-4, the smaller the average particle size DV50 of the chalcogenide material in the functional coating in Example 4, the better the capacity retention rate after 100 cls of cycling and the capacity retention rate after 50 days of storage. This shows that the smaller the average particle size DV50, the better the cycling performance and high-temperature storage performance of the battery cell.

[0248] According to Table 1, compared with Examples 5-1 to 5-6, the ratio of the thickness of the functional coating layer to the thickness of the negative electrode active material layer in Example 1 is different, which to a certain extent affects the cycle performance of the battery cell containing the negative electrode plate, the high-temperature storage performance and safety of the battery cell. The smaller the ratio of the thickness of the functional coating layer to the thickness of the negative electrode active material layer, the safety performance is improved as the relative thickness of the functional coating layer increases in Examples 5-4 and 5-6. Compared with Comparative Example 1, it was tested that the charging time of Example 1, Example 5-1 and Example 5-3 was faster than that of Comparative Example 1. The fast charging performance in the example group is improved as the thickness of the negative electrode active material layer increases, and the charging time is shorter.

[0249] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

[0250]

[0251]

[0252]

Claims

1. A negative electrode sheet, comprising: Negative electrode current collector, A negative electrode active material layer, disposed on at least one side of the negative electrode current collector; and The functional coating is disposed on the side of the negative electrode active material layer away from the negative electrode current collector, wherein the functional coating comprises a chalcogenide material, and the chalcogenide material comprises elemental sulfur, elemental selenium, elemental tellurium, M x S y 、M x Se y 、M x Te y One or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2.

2. The negative electrode sheet according to claim 1, wherein: The functional coating includes 30% to 95% of the chalcogenide material based on the total mass of the functional coating.

3. The negative electrode sheet according to claim 1 or 2, wherein: The ratio of the thickness of the negative electrode active material layer to the thickness of the functional coating layer is 1:(0.01-0.2), optionally, 1:(0.01-0.1).

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The thickness of the functional coating is 1 to 10 um; optionally, 2 to 5 um.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein: The average particle size D50 of the chalcogenide material is 50 to 500 nm; optionally, 100 to 300 nm.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The porosity of the functional coating is 15% to 40%.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: The functional coating comprises a chalcogenide material, a conductive agent and a binder.

8. The negative electrode sheet according to claim 7, wherein: Based on the total mass of the functional coating, the functional coating comprises 5% to 10% of a conductive agent; and / or, The functional coating includes 3% to 5% of a binder based on the total mass of the functional coating.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein: Based on the total mass of the functional coating, the functional coating comprises 85% to 92% of a chalcogenide material containing a metal element, 5% to 10% of a conductive agent, and 3% to 5% of a binder, wherein the chalcogenide material containing a metal element comprises M x S y 、M x Se y 、M x Te y One or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2.

10. The negative electrode sheet according to any one of claims 1 to 9, wherein: The negative electrode active material layer includes a silicon-based material, and the silicon-based material includes one or more of silicon single substance, silicon-carbon composite material, and silicon-oxygen material; Optionally, based on the total mass of the negative electrode active material layer, the negative electrode active material layer includes 1% to 50% of silicon.

11. A method for preparing a negative electrode sheet, comprising: A first slurry containing a chalcogenide material and a second slurry containing a positive electrode active material are provided, wherein the chalcogenide material includes elemental sulfur, elemental selenium, elemental tellurium, M x S y 、M x Se y 、M x Te y One or more of, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, Mo, 0<x≤2, 0<y≤2; The first slurry and the second slurry are coated on one side of the negative electrode current collector to form a functional coating and a negative electrode active material layer, respectively, to obtain the negative electrode plate according to any one of claims 1 to 10, wherein the negative electrode plate comprises the negative electrode active material layer arranged on at least one side of the negative electrode current collector and the functional coating arranged on the side of the negative electrode active material layer away from the current collector.

12. A battery cell, comprising the negative electrode sheet according to any one of claims 1 to 10 or the negative electrode sheet prepared by the preparation method according to claim 11.

13. The battery cell according to claim 12, wherein: After the battery monomer is formed, the functional coating comprises 20% to 30% of the chalcogen element based on the total mass of the functional coating; and / or, After the battery monomer is formed, the porosity of the functional coating is 30% to 60%.

14. The battery cell according to claim 12 or 13, wherein: The battery cell includes an electrolyte, and the electrolyte includes a C3-C12 cyclic carbonate.

15. The battery cell according to any one of claims 12 to 14, wherein: It comprises a negative electrode plate and a solid electrolyte interface film, wherein the solid electrolyte interface film comprises 0.01% to 6% of chalcogen elements by mass, wherein the chalcogen elements comprise at least one of sulfur, selenium and tellurium.

16. The battery cell according to claim 15, wherein: The solid electrolyte interface film comprises at least one of the compounds represented by formula (1) and formula (2): Wherein, R represents the chalcogen element, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0<x'≤2, 0<y'≤2, and n represents a natural number.

17. The battery cell according to claim 15 or 16, wherein: The valence state of the chalcogen element includes at least one of negative monovalent, negative divalent, positive tetravalent and positive hexavalent.

18. The battery cell according to claim 17, wherein: After the battery cell is formed, the ratio of the sum of the molar amounts n1 of the tetravalent and hexavalent sulfide elements in the solid electrolyte interface membrane per unit mass to the sum of the molar amounts n0 of the sulfide elements in the solid electrolyte interface membrane per unit mass is (0.3-3):1, and can be optionally (0.5-1.5):

1.

19. An electrical device comprising the battery cell according to any one of claims 12 to 18.

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