Negative electrode sheet and its preparation method, battery cell and power device

Abstract

This application provides a negative electrode sheet and its preparation method, a battery cell, and an electrical device. The negative electrode sheet includes: a negative electrode current collector, a negative electrode active material layer disposed on at least one side of the negative electrode current collector, and a functional coating disposed on the side of the negative electrode active material layer opposite to the negative electrode current collector. The functional coating includes chalcogenide materials, including elemental sulfur, elemental selenium, elemental tellurium, and M. x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, where 0 < x ≤ 2 and 0 < y ≤ 2. The solid electrolyte interface film formed by the chalcogenide materials in this application possesses excellent elasticity and stability, which can adapt to the volume changes caused by the rebound of the negative electrode during charging and discharging. This reduces the compression of the solid electrolyte interface film within the battery cell by the negative electrode, thereby reducing the risk of repeated damage and reformation of the solid electrolyte interface film and improving the interfacial stability between the negative electrode active material and the electrolyte, thus enhancing the cycle performance and storage performance of the battery cell.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a negative electrode sheet and its preparation method, a battery cell, and an electrical device. Background Technology

[0002] A battery cell, also called a rechargeable battery, is a battery that can be repeatedly discharged and recharged for multiple uses. In recent years, with the increasingly widespread application of battery cells, represented by lithium-ion batteries, people have placed higher demands on their performance, especially their cycle performance.

[0003] Therefore, further improving the cycle performance and storage performance of individual battery cells remains a pressing technical problem that needs to be solved. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode sheet that can improve the cycle performance of a battery cell containing the positive electrode sheet; the purpose of this application is also to provide a battery cell and an electrical device containing the above-mentioned positive electrode sheet, thereby achieving improved cycle performance and storage performance of the battery cell.

[0005] In a first aspect, embodiments of this application provide a negative electrode sheet, comprising:

[0006] Negative electrode current collector,

[0007] A negative electrode active material layer is disposed on at least one side of the negative electrode current collector; and

[0008] A functional coating is disposed on the side of the negative electrode active material layer away from the negative electrode current collector. The functional coating includes chalcogenide materials, such as elemental sulfur, elemental selenium, elemental tellurium, and M. x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0 < x ≤ 2, 0 < y ≤ 2.

[0009] The technical solution of this application embodiment provides a negative electrode sheet. The negative electrode active material layer of the negative electrode sheet has a functional coating on the side opposite to the negative electrode current collector. The functional coating contains a specific chalcogenide material. Surprisingly, when a battery cell containing the negative electrode sheet according to the embodiment of this application is formed, an SEI film with excellent elasticity and stability can be formed on the surface of the negative electrode sheet.

[0010] Not intended to be limited to any particular theory or explanation, during the formation of the aforementioned battery cell, the functional coating comes into contact with and interacts with the electrolyte (containing cyclic carbonate solvents such as ethylene carbonate), allowing chalcogenide materials to participate in the formation of the SEI film. The composition of the resulting SEI film can include alkyl sulfates and polyoxyolefin polymers (such as polyethylene oxide (PEO)), thus giving the SEI film excellent elasticity and stability. Such an SEI film can accommodate and adapt to the volume changes caused by the rebound of the negative electrode containing the negative electrode active material layer, reducing or avoiding the negative electrode compressing 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 cycle performance and storage performance of the battery cell containing the negative electrode.

[0011] In addition, a solid electrolyte interface film with excellent elasticity can stabilize the interface stability between the negative electrode and the electrolyte, thereby improving the service life of the battery cell.

[0012] Furthermore, the solid electrolyte interface membrane formed by the participation of chalcogenide materials has good active ion permeability, which can promote the rapid transport of active ions at the interface and improve the ion transport rate. After the chalcogenide materials in the functional coating of the negative electrode sheet participate in the solid electrolyte interface membrane, the porosity of the functional coating is increased, which improves the transport rate of active ions in the negative electrode sheet, thereby comprehensively improving the dynamic performance of the battery cell containing the negative electrode sheet.

[0013] In some alternative implementations, the functional coating comprises 30% to 95% chalcogenide materials based on the total mass of the functional coating.

[0014] According to the embodiments of this application, the chalcogenide material containing the above-mentioned mass content can improve the elasticity of the solid electrolyte interface film, accommodate and adapt to 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 of the solid electrolyte interface film in the battery cell and causing structural damage, reduce the risk of repeated damage and continuous reformation of the solid electrolyte interface film, thereby improving the cycle performance of the battery cell containing the negative electrode sheet.

[0015] In some alternative implementations, the thickness ratio of the negative electrode active material layer to the functional coating is 1:

[0016] (0.01~0.2). Optional: 1: (0.01~0.1).

[0017] According to embodiments of this application, by controlling the ratio of the thickness of the negative electrode active material layer to the thickness of the functional coating within the aforementioned range, the functional coating can provide a sufficient protective layer to protect the negative electrode active material. Components such as metal selenides, sulfur, and selenium can form a protective layer, preventing direct contact between the negative electrode active material and the electrolyte, reducing side reactions with the electrolyte, and improving the cycle stability of the battery cell containing the negative electrode sheet.

[0018] In some alternative embodiments, the thickness of the functional coating is 1–10 μm; alternatively, it is 2–5 μm.

[0019] According to the embodiments of this application, the thickness of the functional coating within the above-mentioned range is beneficial for the insertion and extraction of active ions in the negative electrode sheet within the battery cell, and is beneficial for the kinetic performance and cycle performance of the battery cell.

[0020] In some alternative embodiments, the average particle size D50 of the chalcogenide material is 50–500 nm; alternatively, it is 100–300 nm.

[0021] According to embodiments of this application, the average particle size Dv50 of the chalcogenide material is within the aforementioned range, which is beneficial for the chalcogenide material to participate in the formation of a solid electrolyte interface film during battery cell formation. Furthermore, after decomposition from the negative electrode active material layer, it forms uniformly distributed pores with relatively uniform particle size, which is beneficial for the structural stability of the functional coating and for the kinetic and cycle performance of the battery cell. In some optional embodiments, the porosity of the functional coating is 15% to 40%.

[0022] According to the embodiments of the application, the functional coating has a porosity within the above-mentioned range, which is beneficial for the electrolyte to wet the functional coating during the formation stage, and facilitates the participation of chalcogen materials in the functional coating in the formation of a solid electrolyte interface film, thereby making the solid electrolyte interface film more elastic.

[0023] In some alternative implementations, the functional coating includes chalcogenide materials, conductive agents, and binders.

[0024] According to an embodiment of this application, the functional coating comprises a chalcogenide material, a conductive agent, and a binder. M in the chalcogenide material... x S y M x Se y M x Te y It can be used as a negative electrode active material, exhibiting high lithium / sodium intercalation capacity. The entire functional coating can serve as another new negative electrode active material layer, improving the cycle performance of the battery cell. Elemental sulfur, elemental selenium, and elemental tellurium from the chalcogenide group can also be used as negative electrode active materials.

[0025] In some alternative implementations, the functional coating includes 5% to 10% conductive agent based on the total mass of the functional coating.

[0026] According to the embodiments of this application, when the functional coating contains the above-mentioned amount of conductive agent, the internal resistance of the negative electrode sheet can be reduced, the internal resistance of the entire cell can be reduced, thereby facilitating electron transmission and improving the dynamic performance of the battery cell containing the negative electrode sheet.

[0027] In some alternative implementations, the functional coating includes 3% to 5% binder based on the total mass of the functional coating.

[0028] According to embodiments of this application, when the functional coating contains the aforementioned amount of binder, a balance between the structural stability, conductivity, and ion transport performance of the negative electrode sheet can be ensured. However, excessively high or low binder content may affect the performance of the battery cell containing the negative electrode sheet.

[0029] In some alternative embodiments, based on the total mass of the functional coating, the functional coating comprises 85%–92% of a chalcogenide material containing a metal element, 5%–10% of a conductive agent, and 3%–5% of a binder, wherein the chalcogenide material containing a metal element includes M x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0 < x ≤ 2, 0 < y ≤ 2.

[0030] According to embodiments of this application, the functional coating comprises the aforementioned amounts of chalcogenide materials containing metal elements, conductive agents, and binders. When the negative electrode containing the aforementioned functional coating is formed, the functional coating has a larger porosity. The chalcogenide materials containing metal elements, as negative electrode active materials, have good electronic conductivity and can quickly transfer electrons. They typically have a sub-stoichiometric composition, meaning that the ratio of metals to chalcogenide elements, including selenium, deviates from the stoichiometric ratio. This sub-stoichiometric composition can provide more intercalation / deintercalation sites, promote faster ion transport and higher electrochemical reaction rates, and improve the electrochemical reaction kinetics performance of the battery cell containing the material, thereby achieving high power output and fast charge / discharge rates.

[0031] In some alternative embodiments, the negative electrode active material layer includes a silicon-based material, which includes one or more of silicon, silicon-carbon composite materials, and silicon-oxygen materials.

[0032] According to the embodiments of this application, the negative electrode active material layer containing the above-mentioned silicon-based material in the negative electrode sheet can improve the capacity of the battery cell containing the negative electrode sheet and achieve rapid ion diffusion.

[0033] In some alternative implementations, the negative electrode active material layer comprises 1% to 50% silicon element based on the total mass of the negative electrode active material layer.

[0034] According to embodiments of this application, adding the aforementioned amount of silicon can increase the capacity of the negative electrode active material, thereby improving the energy density of the battery. 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 a high ion diffusion coefficient, 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 kinetic performance of the battery, including charge and discharge rates.

[0035] Preparation method of negative electrode sheet

[0036] Thirdly, embodiments of this application provide a method for preparing a negative electrode sheet, comprising:

[0037] A first slurry containing chalcogenide materials and a second slurry containing a positive electrode active material are provided, wherein the chalcogenide materials include elemental sulfur, elemental selenium, elemental tellurium, and M. x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0 < x ≤ 2, 0 < y ≤ 2;

[0038] 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 a negative electrode sheet according to the first aspect or the second method. The negative electrode sheet includes a negative electrode active material layer disposed on at least one side of the negative electrode current collector and a functional coating disposed on the side of the negative electrode active material layer opposite to the current collector.

[0039] According to embodiments of this application, by forming a functional coating and a negative electrode active material layer from a composition containing chalcogenide materials and a positive electrode active material, respectively, a solid electrolyte interface film formed by the chalcogenide materials in the negative electrode sheet can be formed. The presence of chalcogenide elements in the solid electrolyte interface film enhances its elasticity, allowing it to accommodate and adapt to large volume changes in the negative electrode sheet containing the negative electrode active material layer. This reduces or avoids the negative electrode sheet compressing the structure of the solid electrolyte interface film in the battery cell and causing structural damage, thereby reducing the risk of repeated damage and continuous reformation of the solid electrolyte interface film and improving the cycle performance of the battery cell containing the negative electrode sheet.

[0040] Furthermore, the solid electrolyte interface membrane formed by the participation of chalcogenide materials has good active ion permeability, which can promote the rapid transport of active ions at the interface and improve the ion transport rate. After the chalcogenide materials in the functional coating of the negative electrode sheet participate in the solid electrolyte interface membrane, the porosity of the functional coating is increased, which improves the transport rate of active ions in the negative electrode sheet, thereby comprehensively improving the dynamic performance of the battery cell containing the negative electrode sheet.

[0041] Fourthly, embodiments of this application provide a battery cell including a negative electrode sheet prepared by the first or second method, or a negative electrode sheet prepared by the third method. The battery cell containing this negative electrode sheet possesses at least the advantages of that negative electrode sheet.

[0042] In some alternative embodiments, after the battery cell is formed, the functional coating includes 20% to 30% of chalcogens, including one or more of sulfur, selenium, and tellurium, based on the total mass of the functional coating.

[0043] According to embodiments of this application, after the fresh negative electrode sheet is formed in the battery cell, the functional coating contains the aforementioned amount of chalcogen elements. These chalcogen elements can exist in particulate or porous form, exhibiting a high specific surface area. Furthermore, the pores formed after the decomposition of the chalcogen materials 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 enabling the negative electrode sheet to have a high lithium / sodium intercalation capacity, effectively achieving the insertion and extraction of lithium or sodium ions, thus improving the capacity of the battery cell containing this negative electrode sheet.

[0044] In some alternative embodiments, after cell formation, the porosity of the functional coating is 30% to 60%. According to embodiments of this application, the increased porosity of the functional coating in the negative electrode improves the cell's mass energy density and kinetic performance.

[0045] In some alternative embodiments, the battery cell includes an electrolyte comprising a C3 to C12 cyclic carbonate.

[0046] According to embodiments of this application, the C3-C12 cyclic carbonates can be one or more of ethylene carbonate (EC), fluoroethylene carbonate, difluoroethylene carbonate, and 2,3-butanediol carbonate. The chalcogenide material of this application undergoes a reduction reaction during electrochemical cycling, reacting with C3-C12 cyclic carbonate compounds to generate poly(ethylene oxide) (PEO) polymers. These polymers participate in the formation of a solid electrolyte interface film on the surface of the negative electrode sheet, i.e., the functional coating. This solid electrolyte interface film possesses excellent elasticity, effectively accommodating and allowing the volume expansion of the negative electrode active material layer and the functional coating at the negative electrode-electrolyte interface, stabilizing the stability of the negative electrode sheet-electrolyte interface, and improving the lifespan of the battery cell.

[0047] In some alternative embodiments, the battery cell includes a negative electrode and a solid electrolyte interface membrane, wherein the solid electrolyte interface membrane includes 0.01% to 6% of chalcogens based on the total weight of the solid electrolyte interface membrane, wherein the chalcogens include at least one of sulfur, selenium, and tellurium.

[0048] According to the embodiments of this application, the chalcogen elements in the solid electrolyte interface membrane with the above-mentioned content may generate poly(ethylene oxide) (PEO)-like polymers, which help improve the elasticity of the solid electrolyte interface membrane and facilitate the accommodation and allow the negative electrode to undergo a certain amount of volume change during cycling.

[0049] In some alternative embodiments, the solid electrolyte interface membrane comprises at least one of the compounds shown in formula (1) and formula (2):

[0050]

[0051] Where R represents a chalcogenide, 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.

[0052] According to the embodiments of this application, the compound shown in formula (1) has good elasticity in the solid electrolyte interface film containing the compound shown in formula (1) because it has an alkyl group containing two carbon atoms, the carbon atoms are freely rotating, the chain structure is arranged, and the long chain alkyl group is flexible.

[0053] According to the embodiments of this application, the compound shown in formula (2) itself has ether bonds with relatively large bond lengths. This allows the compound to undergo significant deformation under external force and return to its original shape after the external force is removed. This endows the material with a certain degree of elasticity, enabling it to deform under stress without breaking. The ether bond has a low bond energy, making it relatively easy to break. After breaking, it can rotate freely, thereby increasing the flexibility of the material. The breaking of the ether bond allows the material to undergo reversible deformation under stress without causing material damage. The oxygen atoms surrounding the ether bond have 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 cohesive force of the material, making it more ductile, and comprehensively enhancing the good elasticity of the solid electrolyte interface film containing the compound shown in formula (2).

[0054] In some alternative implementations, the valence states of the chalcogens include at least one of the following: -1, -2, +4, and +6.

[0055] According to embodiments of this application, chalcogenides, existing in the aforementioned valence states within the solid electrolyte interfacial membrane, can form stable chemical bonds, enhancing membrane stability and preventing active ions and electrons from the electrolyte from directly entering the negative electrode active material, thereby reducing battery side reactions. Furthermore, the presence of these valence states of chalcogenides in the solid electrolyte interfacial membrane exhibits good ionic conductivity, providing pathways for active ion transport and promoting the transport of active ions within the solid electrolyte interfacial membrane. In addition, the interaction between chalcogenides and other components (such as polymers) in the solid electrolyte interfacial membrane can regulate the structure and properties of the membrane, increasing the transport rate of active ions within it.

[0056] In some optional embodiments, after the battery cell is formed, the ratio of the sum of the molar amounts of tetravalent and hexavalent chalcogenides in a unit mass of solid electrolyte interfacial membrane n1 to the sum of the molar amounts of chalcogenides in a unit mass of solid electrolyte interfacial membrane n0 is (0.3~3):1, and can be optionally (0.5~1.5):1.

[0057] According to the embodiments of this application, the elastic range of the solid electrolyte interface film can be quantitatively determined by the ratio of the sum of the molar amounts n1 of tetravalent and hexavalent chalcogenides in a unit mass of solid electrolyte interface film to the sum of the molar amounts n0 of chalcogenides in a unit mass of solid electrolyte interface film. This allows for the design of a suitable negative electrode active material layer with appropriate volume expansion based on the elastic solid electrolyte interface film, thereby avoiding the expansion of the negative electrode active material layer of the negative electrode sheet from affecting the electrochemical performance of the battery cell.

[0058] Fifthly, embodiments of this application provide an electrical device including a battery cell according to the first or second aspect. The battery cell or electrical device of this application includes a negative electrode sheet according to the first or second aspect of this application, and therefore has at least the advantage of application with a negative electrode sheet. Attached Figure Description

[0059] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0060] Figure 1 A schematic diagram of one embodiment of the battery cell of this application is shown.

[0061] Figure 2 It shows Figure 1 The diagram shows an exploded view of a single battery cell.

[0062] Figure 3 A schematic diagram of one embodiment of an electrical device incorporating the battery cell of this application as a power source is shown.

[0063] The accompanying drawings are not necessarily drawn to scale. Detailed Implementation

[0064] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode sheet and its preparation method, electrode assembly, battery cell, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0065] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for specific parameters, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, characterized in that a and b are both real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0066] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0067] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0068] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0069] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0070] 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).

[0071] Unless otherwise specified, the terms "connected" and "linked" in this application should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0072] Unless otherwise specified, in this application, the term "attachment" refers to a connection made by means of adhesion, coating, or other similar methods.

[0073] 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 primary / secondary relationship.

[0074] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a battery cell, including but not limited to lithium ions, sodium ions, etc.

[0075] The terms “several” or “multiple” in this application refer to two or more (including two).

[0076] The battery cells mentioned in the embodiments of this application may be lithium-ion batteries, sodium-ion batteries, lithium metal batteries, sodium metal batteries, etc., and the embodiments of this application are not limited to this.

[0077] A battery cell includes electrode components and an electrolyte. The electrode components include a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. During the electrolyte injection and subsequent settling and formation processes, the electrodes undergo volume expansion, increasing the overall thickness of the battery and affecting its performance. During the formation process, the electrode expansion is caused by both volume expansion due to the combination of active ions with electrode material particles (e.g., adsorption, intercalation, or chemical reaction) and stress relaxation expansion. Research has found that the negative electrode also expands during subsequent charging after formation. This is primarily due to the migration of active ions from the positive electrode to the negative electrode and their combination with the negative electrode active material (e.g., adsorption, intercalation, or chemical reaction), increasing the volume of the negative electrode active material and thus causing the negative electrode to expand.

[0078] When the negative electrode expands in volume, it is compressed, generating significant internal stress. This internal stress can lead to damage to the internal materials of the electrode (such as the destruction of active material particles) and deformation of the battery casing. The repeated volume expansion and contraction of the negative electrode during charge and discharge can also cause repeated damage and formation of the solid electrolyte interphase (SEI) film, thus negatively impacting its stability and further affecting the battery's cycle performance. In short, the repeated volume expansion and contraction of electrode sheets, especially the negative electrode sheet, during battery charge and discharge adversely affects the battery's cycle performance, posing a challenge to improving battery cycle performance. This volume expansion effect is even more pronounced for negative electrode sheets containing silicon-based negative electrode materials.

[0079] To mitigate the impact of negative electrode volume expansion on battery cycle performance, current methods primarily focus on improving the structure of the active material itself to reduce its volume expansion and contraction effects during battery charging and discharging. However, research has revealed that these structural improvements to the active material are limited by factors such as the availability of suitable materials and capacity requirements, and they cannot address electrode volume expansion caused by other factors (such as the deposition of active ions outside the active material).

[0080] In view of this, the technical solution of this application provides a negative electrode sheet, which can at least mitigate the adverse effects of repeated volume expansion / contraction of the negative electrode sheet during battery charging and discharging on the cycle performance of the battery, thereby improving the cycle performance of the battery cell containing it.

[0081] Negative electrode sheet

[0082] In a first aspect, embodiments of this application provide a negative electrode sheet, comprising:

[0083] Negative electrode current collector,

[0084] A negative electrode active material layer is disposed on at least one side of the negative electrode current collector; and

[0085] A functional coating is disposed on the side of the negative electrode active material layer away from the negative electrode current collector. The functional coating includes chalcogenide materials, such as elemental sulfur, elemental selenium, elemental tellurium, and M. x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0 < x ≤ 2, 0 < y ≤ 2.

[0086] The technical solution of this application embodiment provides a negative electrode sheet. The negative electrode active material layer of the negative electrode sheet has a functional coating on the side opposite to the negative electrode current collector. The functional coating contains a specific chalcogenide material. Surprisingly, when a battery cell containing the negative electrode sheet according to the embodiment of this application is formed, an SEI film with excellent elasticity and stability can be formed on the surface of the negative electrode sheet.

[0087] Not intended to be limited to any particular theory or explanation, during the formation of the aforementioned battery cell, the functional coating comes into contact with and interacts with the electrolyte (containing cyclic carbonate solvents such as ethylene carbonate), allowing chalcogenide materials to participate in the formation of the SEI film. The composition of the resulting SEI film can include alkyl sulfates and polyoxyolefin polymers (such as polyethylene oxide (PEO)), thus giving the SEI film 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 avoiding the negative electrode sheet compressing 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 cycle performance of the battery cell containing the negative electrode sheet.

[0088] In addition, a solid electrolyte interface film with excellent elasticity can stabilize the interface stability between the negative electrode and the electrolyte, thereby improving the service life of the battery cell.

[0089] Furthermore, the solid electrolyte interface membrane formed by the participation of chalcogenide materials has good active ion permeability, which can promote the rapid transport of active ions at the interface and improve the ion transport rate. After the chalcogenide materials in the functional coating of the negative electrode sheet participate in the solid electrolyte interface membrane, the porosity of the functional coating is increased, which improves the transport rate of active ions in the negative electrode sheet, thereby comprehensively improving the dynamic performance of the battery cell containing the negative electrode sheet.

[0090] According to embodiments of this application, x and y in a 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 to 2). As an example, the chalcogenide material includes molybdenum disulfide.

[0091] Chalcogenide materials often exist in particulate or porous form and have a high specific surface area. The high surface area can provide more reaction interfaces and active sites, thus enabling the negative electrode to have a high lithium / sodium intercalation capacity. It can effectively realize the intercalation and deintercalation of lithium ions or sodium ions, thereby improving the capacity of the battery cell containing the negative electrode.

[0092] 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 metals and chalcogens, including selenium, deviates from the stoichiometric ratio. This sub-stoichiometric composition can provide more intercalation / deintercalation sites, promote faster ion transport and higher electrochemical reaction rates, and improve the electrochemical reaction kinetics of the battery cell containing this composition, so as to achieve high power output and fast charge and discharge rates.

[0093] Elemental sulfur, selenium, and tellurium in chalcogenide materials are nonmetallic elements, typically linked by covalent bonds in their crystal structures. The formation of covalent bonds results in a relatively stable structure for sulfur and selenium within the crystal, but it also restricts the free movement of electrons, leading to poor electronic conductivity. When present in a negative electrode, their presence can improve the safety performance of the electrode.

[0094] In some alternative implementations, the functional coating comprises 30% to 95% chalcogenide materials based on the total mass of the functional coating.

[0095] Optionally, functional coatings include those with mass contents 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%, 6 Chalcogenide materials of any value or range of composition from 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%.

[0096] According to the embodiments of this application, the chalcogenide material containing the above-mentioned mass content can improve the elasticity of the solid electrolyte interface film, accommodate and adapt to 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 of the solid electrolyte interface film in the battery cell and causing structural damage, reduce the risk of repeated damage and continuous reformation of the solid electrolyte interface film, thereby improving the cycle performance of the battery cell containing the negative electrode sheet.

[0097] In some alternative implementations, the thickness ratio of the negative electrode active material layer to the functional coating is 1:

[0098] (0.01~0.2), can be selected as 1: (0.01~0.1).

[0099] According to embodiments of this application, by controlling the ratio of the thickness of the negative electrode active material layer to the thickness of the functional coating within the aforementioned range, the functional coating can provide a sufficient protective layer to protect the negative electrode active material. Components such as metal selenides, sulfur, and selenium can form a protective layer, preventing direct contact between the negative electrode active material and the electrolyte, reducing side reactions with the electrolyte, and improving the cycle stability of the battery cell containing the negative electrode sheet.

[0100] The ratio of the thickness of the negative electrode active material layer to the thickness of the functional coating can affect the transport paths and resistance of electrons and ions. Overall, a smaller ratio may help improve ion transport and electron conduction performance, thereby improving the battery's discharge performance and charging rate.

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

[0102] According to the embodiments of this application, the thickness of the functional coating within the above-mentioned range is beneficial for the insertion and extraction of active ions in the negative electrode sheet within the battery cell, and is beneficial for the kinetic performance and cycle performance of the battery cell.

[0103] When the thickness of the functional coating is too high, the unreacted remaining non-conductive chalcogenide material coating the electrode surface increases the surface impedance, hinders the transport of active ions, and affects the capacity of the active material and 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, which restricts its ability to accommodate the volume expansion of the negative electrode.

[0104] In some alternative embodiments, the average particle size D50 of the chalcogenide material is 0.05–25 μm; alternatively, it is 0.1–5 μm.

[0105] Optionally, the average particle size D50 of the chalcogenide material can be 0.05 μm, 0.10 μm, 0.15 μm, 0.20 μm, 0.25 μm, 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.65 μm, 0.70 μm, 0.75 μm, 0.80 μm, 0.85 μm, 0.90 μm, 0.95 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm. Any value or a range thereof from 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, and 20.0um.

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

[0107] Volume average particle size D v The value of 50 is known in the art and represents the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T19077~2016 Particle Size Distribution Laser Diffraction Method.

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

[0109] Optionally, the porosity of the functional coating can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, etc.

[0110] Any value or range of combinations thereof from 35%, 36%, 37%, 38%, 39%, and 40%. According to the embodiments of the following application, the functional coating has a porosity within the above range, which is beneficial for the electrolyte to wet the functional coating during the formation stage, and facilitates the participation of chalcogen materials in the functional coating in the formation of a solid electrolyte interface film, thereby making the solid electrolyte interface film more elastic.

[0111] In some alternative implementations, the functional coating includes chalcogenide materials, conductive agents, and binders.

[0112] According to an embodiment of this application, the functional coating comprises a chalcogenide material, a conductive agent, and a binder. M in the chalcogenide material... x S y M x Se y M x Te y It can be used as a negative electrode active material, exhibiting high lithium / sodium intercalation capacity. The entire functional coating can serve as another new negative electrode active material layer, improving the cycle performance of the battery cell. Elemental sulfur, elemental selenium, and elemental tellurium from the chalcogenide group can also be used as negative electrode active materials.

[0113] In some alternative implementations, the functional coating includes 5% to 10% conductive agent based on the total mass of the functional coating.

[0114] Optionally, the functional coating may include a conductive agent of any value or range of composition from 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%.

[0115] According to the embodiments of this application, when the functional coating contains the above-mentioned amount of conductive agent, the internal resistance of the negative electrode sheet can be reduced, the internal resistance of the entire cell can be reduced, thereby facilitating electron transmission and improving the dynamic performance of the battery cell containing the negative electrode sheet.

[0116] In some alternative embodiments, the functional coating comprises 3% to 5% binder based on the total mass of the functional coating. Optionally, 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% binder.

[0117] According to embodiments of this application, when the functional coating contains the aforementioned amount of binder, a balance between the structural stability, conductivity, and ion transport performance of the negative electrode sheet can be ensured. However, excessively high or low binder content may affect the performance of the battery cell containing the negative electrode sheet.

[0118] In some optional embodiments, based on the total mass of the functional coating, the functional coating comprises 80%–95% elemental chalcogenides and 5%–20% binder, wherein the chalcogenides include at least one selected from sulfur, selenium, and tellurium. Optionally, the functional coating, by mass percentage, may include 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%, etc.

[0119] Conductive agents comprising any value or range of composition from 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 19.5%, and 20%. According to an embodiment of this application, the functional coating comprises elemental chalcogenides in the aforementioned amounts and a binder in the aforementioned amounts. When the negative electrode containing the aforementioned functional coating is formed, the functional coating comprises only elemental chalcogenides and a binder, as well as voids left by the consumption of some elemental chalcogenides. This coating has an insulating effect and can enhance the safety performance of the battery cell containing the negative electrode.

[0120] In some alternative embodiments, based on the total mass of the functional coating, the functional coating comprises 85%–92% of a chalcogenide material containing a metal element, 5%–10% of a conductive agent, and 3%–5% of a binder, wherein the chalcogenide material containing a metal element includes M x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0 < x ≤ 2, 0 < y ≤ 2.

[0121] According to embodiments of this application, the functional coating comprises the aforementioned amounts of chalcogenide materials containing metal elements, conductive agents, and binders. When the negative electrode containing the aforementioned functional coating is formed, the functional coating has a larger porosity. The chalcogenide materials containing metal elements, as negative electrode active materials, have good electronic conductivity and can quickly transfer electrons. They typically have a sub-stoichiometric composition, meaning that the ratio of metals to chalcogenide elements, including selenium, deviates from the stoichiometric ratio. This sub-stoichiometric composition can provide more intercalation / deintercalation sites, promote faster ion transport and higher electrochemical reaction rates, and improve the electrochemical reaction kinetics performance of the battery cell containing the material, thereby achieving high power output and fast charge / discharge rates.

[0122] In some alternative embodiments, the negative electrode active material layer includes a silicon-based material, which includes one or more of silicon, silicon-carbon composite materials, and silicon-oxygen materials.

[0123] According to the embodiments of this application, the negative electrode active material layer containing the above-mentioned silicon-based material in the negative electrode sheet can improve the capacity of the battery cell containing the negative electrode sheet and achieve rapid ion diffusion.

[0124] In some optional embodiments, the negative electrode active material layer comprises 1% to 50% silicon element based on the total mass of the negative electrode active material layer. Optionally, the negative electrode active material layer comprises any value or range of silicon element selected from 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%, and 50%.

[0125] According to embodiments of this application, adding the aforementioned amount of silicon can increase the capacity of the negative electrode active material, thereby improving the energy density of the battery. 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 a high ion diffusion coefficient, 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 kinetic performance of the battery, including charge and discharge rates.

[0126] The specific composition and structure of the negative electrode sheet can be selected according to the type of battery cell, and the embodiments of this application are not limited in this regard.

[0127] For example, when the battery cell is a lithium-ion battery cell or a sodium-ion battery cell, the negative electrode sheet 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 opposite to each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0128] The negative electrode active material is a material capable of extracting and inserting active ions (such as lithium ions, sodium ions, etc.), and can be any material known in the art. As examples, negative electrode active materials include, but are 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 composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys. This 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.

[0129] In some embodiments, the negative electrode active material layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an 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.

[0130] In some embodiments, the negative electrode active material layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0131] In some embodiments, the negative electrode active material layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0132] 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 polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0133] The negative electrode active material layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0134] The negative electrode sheet does not exclude other additional layers besides the negative electrode active material layer and the functional coating of this application. For example, in some embodiments, the negative electrode sheet of this application may also include a conductive undercoat (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 this application may also include a protective layer covering the surface of the negative electrode active material layer.

[0135] When the battery cell is a lithium metal battery cell, the negative electrode sheet may not include a negative electrode active material capable of extracting and embedding active ions. For example, in some embodiments, the negative electrode sheet may include a lithium sheet or a lithium alloy sheet; in other embodiments, the negative electrode sheet includes a mesh or foam-like three-dimensional framework layer, such as foamed copper (or copper alloy), foamed nickel (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, etc.

[0136] When the battery cell is a sodium metal battery cell, the negative electrode sheet may not include a negative electrode active material capable of releasing and embedding active ions. For example, in some embodiments, the negative electrode sheet may include a sodium sheet or a sodium alloy sheet; in other embodiments, the negative electrode sheet includes a mesh or foam-like three-dimensional framework layer, such as foamed copper (or copper alloy), foamed nickel (or nickel alloy), foamed aluminum (or aluminum alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, aluminum (or aluminum alloy) mesh, etc.

[0137] Preparation method of negative electrode sheet

[0138] Thirdly, embodiments of this application provide a method for preparing a negative electrode sheet, comprising:

[0139] A first slurry containing chalcogenide materials and a second slurry containing a positive electrode active material are provided, wherein the chalcogenide materials include elemental sulfur, elemental selenium, elemental tellurium, and M. x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0 < x ≤ 2, 0 < y ≤ 2;

[0140] 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 a negative electrode sheet according to the first aspect or the second method. The negative electrode sheet includes a negative electrode active material layer disposed on at least one side of the negative electrode current collector and a functional coating disposed on the side of the negative electrode active material layer opposite to the current collector.

[0141] According to embodiments of this application, by forming a functional coating and a negative electrode active material layer from a composition containing chalcogenide materials and a positive electrode active material, respectively, a solid electrolyte interface film formed by the chalcogenide materials in the negative electrode sheet can be formed. The presence of chalcogenide elements in the solid electrolyte interface film enhances its elasticity, allowing it to accommodate and adapt to large volume changes in the negative electrode sheet containing the negative electrode active material layer. This reduces or avoids the negative electrode sheet compressing the structure of the solid electrolyte interface film in the battery cell and causing structural damage, thereby reducing the risk of repeated damage and continuous reformation of the solid electrolyte interface film and improving the cycle performance of the battery cell containing the negative electrode sheet.

[0142] Furthermore, the solid electrolyte interface membrane formed by the participation of chalcogenide materials has good active ion permeability, which can promote the rapid transport of active ions at the interface and improve the ion transport rate. After the chalcogenide materials in the functional coating of the negative electrode sheet participate in the solid electrolyte interface membrane, the porosity of the functional coating is increased, which improves the transport rate of active ions in the negative electrode sheet, thereby comprehensively improving the dynamic performance of the battery cell containing the negative electrode sheet.

[0143] battery cell

[0144] Fourthly, embodiments of this application provide a battery cell including a negative electrode sheet prepared by the first or second method, or a negative electrode sheet prepared by the third method. The battery cell containing this negative electrode sheet possesses at least the advantages of that negative electrode sheet.

[0145] This application does not impose any particular restrictions on the type of battery cell. For example, the battery cell can be a lithium-ion battery, a sodium-ion battery, etc. Sodium-ion batteries are an option.

[0146] In some alternative embodiments, after the battery cell is formed, the functional coating includes 20% to 30% of chalcogens, including one or more of sulfur, selenium, and tellurium, based on the total mass of the functional coating.

[0147] Optionally, based on the total mass of the functional coating, the functional coating may include 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% of chalcogen elements.

[0148] According to embodiments of this application, after formation, the functional coating of a fresh negative electrode sheet contains the aforementioned amount of chalcogen elements. These chalcogen elements can exist in particulate or porous form, exhibiting a high specific surface area. Furthermore, the pores formed by the decomposition of the chalcogen materials 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 enabling the negative electrode sheet to have a high lithium / sodium intercalation capacity. This effectively achieves the insertion and extraction of lithium or sodium ions, thereby improving the capacity of the battery cell containing the negative electrode sheet.

[0149] Chalcogens in the embodiments of this application may be in elemental form or in M ​​form. x S y M x Se y M x Te y The form exists within the functional coating. Chalcogenides typically possess a relatively stable crystal structure, enabling them to maintain structural integrity and stability during battery cycling. This, in turn, improves the cycle stability of battery cells containing chalcogenides, allowing them to maintain high capacity retention and energy efficiency across multiple charge-discharge cycles.

[0150] With M x S y M x Se y M x Te y Chalcogens, existing in their natural form, possess certain electronic conductivity and typically exhibit a sub-stoichiometric composition, meaning that the ratio of metals to chalcogens, including selenium, deviates from the stoichiometric ratio. This sub-stoichiometric composition can provide more intercalation / deintercalation sites, promoting faster ion transport and higher electrochemical reaction rates. This can improve the electrochemical reaction kinetics of the battery cell containing the chalcogens, thereby achieving high power output and rapid charge / discharge rates.

[0151] Chalcogens, existing as elemental sulfur, elemental selenium, and elemental tellurium, are nonmetallic elements, typically linked by covalent bonds in their crystal structures. The formation of covalent bonds results in a relatively stable structure for sulfur and selenium in the crystal, but it also restricts the free movement of electrons, leading to poor electronic conductivity. When present in a negative electrode, they can improve the safety performance of the electrode containing that element.

[0152] In some alternative embodiments, after cell formation, the porosity of the functional coating is 30% to 60%. According to embodiments of this application, the increased porosity of the functional coating in the negative electrode improves the cell's mass energy density and kinetic performance.

[0153] In some alternative embodiments, the battery cell includes an electrolyte comprising a C3 to C12 cyclic carbonate.

[0154] According to embodiments of this application, the C3-C12 cyclic carbonates can be one or more of ethylene carbonate (EC), fluoroethylene carbonate, difluoroethylene carbonate, and 2,3-butanediol carbonate. The chalcogenide material of this application undergoes a reduction reaction during electrochemical cycling, reacting with C3-C12 cyclic carbonate compounds to generate poly(ethylene oxide) (PEO) polymers. These polymers participate in the formation of a solid electrolyte interface film on the surface of the negative electrode sheet, i.e., the functional coating. This solid electrolyte interface film possesses excellent elasticity, effectively accommodating and allowing the volume expansion of the negative electrode active material layer and the functional coating at the negative electrode-electrolyte interface, stabilizing the stability of the negative electrode sheet-electrolyte interface, and improving the lifespan of the battery cell.

[0155] In some alternative embodiments, the battery cell includes a negative electrode and a solid electrolyte interface membrane, wherein the solid electrolyte interface membrane includes 0.01% to 6% of chalcogens based on the total weight of the solid electrolyte interface membrane, wherein the chalcogens include at least one of sulfur, selenium, and tellurium.

[0156] Optionally, the solid electrolyte interface membrane comprises 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 membrane. Chalcogens in any of the following values ​​or ranges: 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%.

[0157] According to the embodiments of this application, the chalcogen elements in the solid electrolyte interface membrane with the above-mentioned content may generate poly(ethylene oxide) (PEO)-like polymers, which help improve the elasticity of the solid electrolyte interface membrane and facilitate the accommodation and allow the negative electrode to undergo a certain amount of volume change during cycling.

[0158] In some alternative embodiments, the solid electrolyte interface membrane comprises at least one of the compounds shown in formula (1) and formula (2):

[0159]

[0160] Where R represents a chalcogenide, 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.

[0161] According to the embodiments of this application, the compound shown in formula (1) has good elasticity in the solid electrolyte interface film containing the compound shown in formula (1) because it has an alkyl group containing two carbon atoms, the carbon atoms are freely rotating, the chain structure is arranged, and the long chain alkyl group is flexible.

[0162] According to the embodiments of this application, the compound shown in formula (2) itself has ether bonds with relatively large bond lengths. This allows the compound to undergo significant deformation under external force and return to its original shape after the external force is removed. This endows the material with a certain degree of elasticity, enabling it to deform under stress without breaking. The ether bond has a low bond energy, making it relatively easy to break. After breaking, it can rotate freely, thereby increasing the flexibility of the material. The breaking of the ether bond allows the material to undergo reversible deformation under stress without causing material damage. The oxygen atoms surrounding the ether bond have 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 cohesive force of the material, making it more ductile, and comprehensively enhancing the good elasticity of the solid electrolyte interface film containing the compound shown in formula (2).

[0163] As an example, the reactants generated by the reaction of chalcogenide materials are shown in reactions 1 to 3.

[0164]

[0165] Where 0 < x ≤ 2.

[0166] According to the embodiments of this application, under the action of the chalcogenide material of this 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 film includes more of the compounds shown in formula (1) and also has the compounds shown in formula (2), which can effectively improve the elasticity of the solid electrolyte interface film. Therefore, the chalcogenide material significantly improves the elasticity of the solid electrolyte interface film.

[0167] According to embodiments of this application, sulfides can exhibit good ionic conductivity under certain conditions. In solid electrolyte interfacial membranes, sulfides can act as channels or bridges for ion transport, providing pathways for active ion transport and promoting the transport of active ions within the solid electrolyte interfacial membrane. Furthermore, the interaction between sulfides and other components (such as polymers) in the solid electrolyte interfacial membrane can regulate the structure and properties of the membrane, thereby increasing the transport rate of active ions within the membrane.

[0168] In addition, sulfides can form stable chemical bonds in the solid electrolyte interface film, enhancing the stability of the film and preventing active ions and electrons in the electrolyte from directly entering the negative electrode active material, thereby reducing the side reactions of the battery.

[0169] In some alternative implementations, the valence states of the chalcogens include at least one of the following: -1, -2, +4, and +6.

[0170] According to embodiments of this application, the valence states of chalcogens include +4 and / or +6, with an S2p peak of 168–172 eV; the valence states of chalcogens include -2 to -1 / 4, with an S2p peak of 160–166 eV. These peaks were obtained by XPS testing of the anode electrode after disassembling the formed battery cell.

[0171] According to embodiments of this application, chalcogenides, existing in the aforementioned valence states within the solid electrolyte interfacial membrane, can form stable chemical bonds, enhancing membrane stability and preventing active ions and electrons from the electrolyte from directly entering the negative electrode active material, thereby reducing battery side reactions. Furthermore, the presence of these valence states of chalcogenides in the solid electrolyte interfacial membrane exhibits good ionic conductivity, providing pathways for active ion transport and promoting the transport of active ions within the solid electrolyte interfacial membrane. In addition, the interaction between chalcogenides and other components (such as polymers) in the solid electrolyte interfacial membrane can regulate the structure and properties of the membrane, increasing the transport rate of active ions within it.

[0172] In some optional embodiments, after the battery cell is formed, the ratio of the sum of the molar amounts of tetravalent and hexavalent chalcogenides in a unit mass of solid electrolyte interfacial membrane n1 to the sum of the molar amounts of chalcogenides in a unit mass of solid electrolyte interfacial membrane n0 is (0.3~3):1, and can be optionally (0.5~1.5):1.

[0173] Optionally, the ratio of n1 to n0 can be any value or a range thereof from 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.

[0174] According to the embodiments of this application, the elastic range of the solid electrolyte interface film can be quantitatively determined by the ratio of the sum of the molar amounts n1 of tetravalent and hexavalent chalcogenides in a unit mass of solid electrolyte interface film to the sum of the molar amounts n0 of chalcogenides in a unit mass of solid electrolyte interface film. This allows for the design of a suitable negative electrode active material layer with appropriate volume expansion based on the elastic solid electrolyte interface film, thereby avoiding the expansion of the negative electrode active material layer of the negative electrode sheet from affecting the electrochemical performance of the battery cell.

[0175] [Positive electrode plate]

[0176] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector and comprising a positive active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0177] The positive electrode active material layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in battery cells.

[0178] 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 lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This 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.

[0179] In some embodiments, to further improve the energy density of a single battery cell, the positive electrode active material may include materials of the general formula Li. a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 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.

[0180] As an example, positive electrode active materials may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 (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.

[0181] 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 the following: sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0182] As an example, positive electrode active materials may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2Ti 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 materials with the general formula X p M' q (PO4) r O x Y 3-x One or more of the materials. In general formula X p M' q (PO4) r O x Y 3-x In the given condition, 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X includes elements selected from H. + Li + Na + K + and NH4 + One or more of the following, M' is a transition metal cation, which may be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, which may be selected from one or more of F, Cl and Br.

[0183] The modified compounds for the above-mentioned positive electrode active materials can be obtained by doping and / or surface coating of the positive electrode active materials.

[0184] In some embodiments, the positive electrode active material layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0185] In some embodiments, the positive electrode active material layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0186] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymer substrate may be one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0187] The positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0188] [Electrolytes]

[0189] In some embodiments, the battery cell includes an electrolyte. The electrolyte acts as a conductor of active ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0190] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0191] 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 difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). As an example, the sodium salt includes one or more selected from NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0192] 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), butyl 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0193] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature power performance, etc.

[0194] In some embodiments, the battery cell may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0195] 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 pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0196] This application does not impose any particular limitation on the shape of the battery cell; it can be a flat, rectangular, or other shape. Figure 1 The example shown is a rectangular battery cell 5.

[0197] In some embodiments, as Figure 2 As shown, the outer packaging may include a shell 51 and a cover 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. An electrode assembly 52 according to the first aspect of this application or an electrode assembly 52 prepared according to the method of the second aspect of this application is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0198] The method for preparing the battery cell of this application is well known, and the method includes at least the step of preparing an electrode assembly according to the second aspect of the embodiments of this application. In some embodiments, the electrode assembly can be placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, shaping and other processes, a battery cell is obtained.

[0199] In some embodiments of this application, the battery cells according to this application can be assembled into a battery module. The number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0200] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells are housed.

[0201] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0202] [Preparation Method]

[0203] The battery manufacturing method described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a single battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After processes such as encapsulation, settling, formation, and shaping, a single battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0204] Electrical devices

[0205] Fifthly, embodiments of this application provide an electrical device including a battery cell according to the first or second aspect. The battery cell or electrical device of this application includes a negative electrode sheet according to the first or second aspect of this application, and therefore has at least the advantage of application with a negative electrode sheet.

[0206] The battery cell can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can be, but is 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 and satellites, energy storage systems, etc.

[0207] Figure 3This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0208] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0209] Example

[0210] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0211] Example 1

[0212] Preparation of positive electrode sheet

[0213] Will Li[Ni 0.9 Co 0.05 Mn 0.05 O2 (NCM90 ternary material), conductive carbon black, binder polyvinylidene fluoride (PVDF), and carbon nanotubes (CNTs) were dry-mixed in a weight ratio of 77.3:10:8.7:2.7:1.3 until homogeneous. The mixture was stirred at a speed of 400–1000 r / s, followed by wetting, kneading, and dispersion to obtain the positive electrode slurry. The slurry was then coated onto aluminum foil, dried, cold-pressed, and slit to obtain the positive electrode sheet of Example 1.

[0214] Preparation of negative electrode sheet

[0215] Preparation of active material coating slurry: The active material artificial graphite, silicon suboxide, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are dry-mixed evenly in a weight ratio of 72.2:25:0.8:0.8:1.2, and then deionized water is added and mixed evenly to prepare the active material coating slurry.

[0216] Preparation of functional coating slurry: Elemental sulfur powder, carbon nanotubes, and styrene-butadiene rubber (SBR) binder are dry-mixed evenly in a weight ratio of 90:7:3, and then deionized water is added and mixed evenly to prepare functional coating slurry.

[0217] Preparation of composite negative electrode sheet: The precursor of the active material layer is uniformly coated on the current collector and dried at 90℃ for 15 min to obtain the active material layer; the precursor of the functional coating is uniformly printed on the active material layer using a gravure roller and dried at 60℃ for 35 min to obtain the functional coating with a thickness of 3 μm. After cold pressing and slitting, the composite negative electrode sheet is obtained.

[0218] Preparation of the separating membrane

[0219] Polyethylene film is used as the separation membrane.

[0220] Preparation of electrolyte

[0221] In an argon atmosphere glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at 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.

[0222] Preparation of lithium-ion battery cells

[0223] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets, and wound to obtain a bare cell. The bare cell is placed in the battery outer packaging, and then electrolyte is injected, encapsulated, left to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery. The lithium-ion battery has a thickness of 14.2 mm, a width of 32 mm, and a length of 82 mm.

[0224] 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, as detailed in Table 1.

[0225] Examples 3-1 to 3-8: The preparation method is similar to that of Example 1, except that the content of chalcogenide materials in the functional coating varies in the preparation steps (see Table 1 for details).

[0226] Examples 4-1 to 4-4

[0227] The preparation method is similar to that in Example 1, except that the particle size of the chalcogenide materials in the functional coating is different, as detailed in Table 1.

[0228] Examples 5-1 to 5-6

[0229] The preparation method is similar to that in Example 1, except that the thickness ratio of the functional coating to the negative electrode active material layer is different, as detailed in Table 1.

[0230] Comparative Example 1

[0231] The difference between this comparative example and Example 1 is as follows: 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 carboxymethyl cellulose (CMC-Na) were dry-mixed evenly in a weight ratio of 97.2:0.8:0.8:1.2, and then deionized water was added and mixed evenly to prepare a negative electrode slurry; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, the negative electrode sheet was obtained.

[0232] Test section

[0233] 1) Method for detecting the content of chalcogenide materials in functional coatings: First, the positive electrode is digested with aqua regia prepared by a 1:1 volume ratio of concentrated nitric acid (HNO3) and concentrated hydrochloric acid (HCl). Digestion methods include plate digestion, acid digestion, and microwave digestion (high temperature and high pressure, approximately 200℃). Then, the digested solution is collected and placed in an inductively coupled plasma optical transilluminator (ICP-OT) for testing, which allows for the quantitative determination of the chalcogenide content.

[0234] 2) DC internal resistance test method: At 25℃, charge the shipped lithium-ion battery and the lithium-ion battery that has undergone 100 cycles at 45℃ to 4.25V with a constant current of 0.33C. Then charge it with a constant voltage of 4.25V until the current is less than 0.05C. Then discharge it at 0.33C for 30 minutes, adjusting the cell charge to 50% SOC. Then connect the positive and negative probes of the TH2523A AC internal resistance tester to the positive and negative terminals of the battery, respectively, and read the internal resistance value of the battery through the internal resistance tester. Record these values ​​as the initial cell internal resistance and the cell internal resistance after 100 cycles.

[0235] 3) The test method for 0.33C capacity retention is as follows: At 25℃, the lithium-ion battery is charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 4.25V until the current is less than 0.05C, and then discharged at a constant current of 0.33C to 3.0V. This constitutes one charge-discharge cycle. This charging and discharging process is repeated, and the capacity retention rate of the lithium-ion battery after 100 cycles is calculated.

[0236] The capacity retention rate (%) of a lithium-ion battery after 100 cycles at 25°C = (discharge capacity of the 100th cycle / discharge capacity of the first cycle) × 100%.

[0237] 4) Test method for storage capacity retention at 60℃:

[0238] The battery capacity recovery rate test process is as follows: Before storage, at 25℃, the battery corresponding to Example 1 is charged to 4.25V with a constant current of 1 / 3C, then charged to 0.05C with a constant voltage of 4.25V, left to rest for 30 minutes, and then discharged to 2.8V with a 1 / 3C. The resulting capacity is recorded as the initial capacity C0. After storage at 60℃ for 100 days, the battery temperature is cooled to room temperature, and the above steps are repeated. The measured capacity is recorded as Cr. Then, the battery capacity recovery rate H after 50 days of storage is H = Cr / C0 * 100%.

[0239] 5) 0.33C overcharge failure boundary test method:

[0240] First, the battery cell is mounted on the fixture, then fully charged to 100% SOC at 0.33C. The appearance of the sample is checked and photographed, and the cell's OCV, IMP, and mass are recorded. After that, the cell is charged at 0.33C at room temperature until it fails, and the cell's SOC state at this time is recorded. The battery voltage change is monitored simultaneously.

[0241] 6) Full-charge shallow spike safety boundary test method:

[0242] First, the battery cell is mounted on the fixture, then fully charged to 100% SOC at 0.33C. The appearance of the sample is checked and photographed, and the cell's OCV, IMP, and mass are recorded. The process is carried out at room temperature. The nail diameter is 1mm, the speed is 0.1mm / s, and it is inserted at a constant speed perpendicular to the direction of the battery plate. The insertion position is close to the geometric center of the punctured surface. The insertion is continued until the battery cell fails, and the insertion depth at this point is recorded.

[0243] 7) Fast charging performance (10%-80% SOC fast charging time)

[0244] The 10%-80% SOC charging time test procedure is as follows: At 25°C, the batteries in the examples and comparative examples are charged from 10% SOC to 80% SOC in steps at 1.0C / 0.8C / 0.5C / 0.33C. The charging time without lithium plating at the negative electrode is the fast charging time of the battery at this point. The shorter the fast charging time, the better the fast charging performance of the battery.

[0245] Test Results

[0246] The test results from Examples 1 to 8 also show that the functional coating of the negative electrode sheet contains chalcogenide materials, which improves the cycle performance, high-temperature storage performance and safety of the battery cell containing the negative electrode sheet.

[0247] The reason for this may be that during the formation of the battery cell, the functional coating comes into contact with and interacts with the electrolyte (containing cyclic carbonate solvents such as ethylene carbonate), allowing chalcogenide materials to participate in the formation of the SEI film. The resulting SEI film can include alkyl sulfates and polyoxyolefin polymers (such as polyethylene oxide (PEO)), thus giving it excellent elasticity and stability. Such an SEI film can accommodate and adapt to large volume changes in the negative electrode containing the negative electrode active material layer, reducing or preventing the negative electrode from compressing the SEI film structure within the battery cell and causing structural damage. This lowers the risk of repeated damage and reformation of the SEI film, thereby improving the cycle performance of the battery cell containing the negative electrode. A solid electrolyte interface film with excellent elasticity can stabilize the interface stability between the negative electrode and the electrolyte, improving the lifespan of the battery cell. Chalcogenide materials often exist in particulate or porous form and have a high specific surface area. The high surface area can provide more reaction interfaces and active sites, thus enabling the negative electrode to have a high lithium / sodium intercalation capacity. It can effectively realize the intercalation and deintercalation of lithium ions or sodium ions, thereby improving the capacity of the battery cell containing the negative electrode.

[0248] M in chalcogenide materials x S y M x Se y M x Te y While possessing certain electronic conductivity, its electrical conductivity is relatively low. Chalcogenide materials, including elemental sulfur, elemental selenium, and elemental tellurium, are non-metallic elements that are typically linked by covalent bonds in their crystal structure. The formation of covalent bonds results in a relatively stable structure for sulfur and selenium in the crystal, but it also restricts the free movement of electrons, leading to poor electronic conductivity. When present in the negative electrode, it is beneficial to improve the safety performance of the negative electrode. As shown in Table 1, compared to Comparative Example 1, the functional coating of the negative electrode in this embodiment contains chalcogenide materials, which improves the cycle performance, lifespan, and safety of the battery cell containing this negative electrode.

[0249] Compared with Example 1, Examples 2-1 to 2-14 use different types of chalcogenide materials, thus exhibiting differentiated cycle performance, high-temperature storage performance, and safety performance.

[0250] As shown in Table 1, compared with Example 1, the content of chalcogenide materials in Examples 3-1 to 3-8 is reduced, which leads to a decrease in their high-temperature storage performance and 0.33C overcharge failure boundary performance.

[0251] As shown in 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 of Example 4, the better the capacity retention rate after 100 cls of cycling and after 50 days of storage. This indicates that a smaller average particle size (DV50) improves the cycle performance and high-temperature storage performance of the battery cells.

[0252] As shown in Table 1, compared with Examples 5-1 to 5-6, the ratio of the thickness of the functional coating to the thickness of the negative electrode active material layer in Example 1 is different, which to some extent affects the cycle performance, high-temperature storage performance, and safety of the battery cell containing the negative electrode. The smaller the ratio of the functional coating thickness to the thickness of the negative electrode active material layer, the better the safety performance in Examples 5-4 and 5-6 as the relative thickness of the functional coating increases. Compared with Comparative Example 1, the charging time of Examples 1, 5-1, and 5-3 was tested to be faster than that of Comparative Example 1. The fast charging performance in the example group increased with the increase of the thickness of the negative electrode active material layer, and the charging time was shorter.

[0253] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

[0254]

[0255]

[0256]

Claims

1. A negative electrode sheet, characterized in that, include: Negative electrode current collector, A negative electrode active material layer is disposed on at least one side of the negative electrode current collector; and A functional coating is disposed on the side of the negative electrode active material layer opposite to the negative electrode current collector. The functional coating comprises a chalcogenide material, including elemental sulfur, elemental selenium, elemental tellurium, and M. x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0 < x ≤ 2, 0 < y ≤ 2; the average particle size D50 of the chalcogenide material is 50~500 nm.

2. The negative electrode sheet according to claim 1, characterized in that, Based on the total mass of the functional coating, the functional coating comprises 30% to 95% of the chalcogenide material.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, The ratio of the thickness of the negative electrode active material layer to the thickness of the functional coating is 1:(0.01~0.2).

4. The negative electrode sheet according to claim 1 or 2, characterized in that, The ratio of the thickness of the negative electrode active material layer to the thickness of the functional coating is 1:(0.01~0.1).

5. The negative electrode sheet according to claim 1 or 2, characterized in that, The thickness of the functional coating is 1~10μm.

6. The negative electrode sheet according to claim 5, characterized in that, The thickness of the functional coating is 2~5μm.

7. The negative electrode sheet according to claim 1, characterized in that, The average particle size D50 of the chalcogenide material is 100~300nm.

8. The negative electrode sheet according to claim 1 or 2, characterized in that, The porosity of the functional coating is 15% to 40%.

9. The negative electrode sheet according to claim 1 or 2, characterized in that, The functional coating comprises chalcogenide materials, conductive agents, and binders.

10. The negative electrode sheet according to claim 9, characterized in that, Based on the total mass of the functional coating, the functional coating comprises 5% to 10% conductive agent; and / or, Based on the total mass of the functional coating, the functional coating comprises 3% to 5% binder.

11. The negative electrode sheet according to claim 1 or 2, characterized in that, Based on the total mass of the functional coating, the functional coating comprises 85%–92% chalcogenide materials containing metal elements, 5%–10% conductive agents, and 3%–5% binders, wherein the chalcogenide materials containing metal elements include M x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and Mo, 0 < x ≤ 2, 0 < y ≤ 2.

12. The negative electrode sheet according to claim 1 or 2, characterized in that, The negative electrode active material layer includes a silicon-based material, which includes one or more of elemental silicon, silicon-carbon composite materials, and silicon-oxygen materials.

13. The negative electrode sheet according to claim 12, characterized in that, Based on the total mass of the negative electrode active material layer, the negative electrode active material layer comprises 1% to 50% silicon.

14. A method for preparing a negative electrode sheet, characterized in that, include: A first slurry comprising chalcogenide materials and a second slurry comprising a negative electrode active material are provided, wherein the chalcogenide materials include elemental sulfur, elemental selenium, elemental tellurium, and M. x S y M x Se y M x Te y One or more of the following, M includes one or more of Li, Na, Mg, Fe, Co, Ni, Cu, Ti, and 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 sheet according to any one of claims 1 to 13, wherein the negative electrode sheet includes the negative electrode active material layer disposed on at least one side of the negative electrode current collector and a functional coating disposed on the side of the negative electrode active material layer opposite to the current collector.

15. A single battery cell, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 13 or the negative electrode sheet prepared by the preparation method described in claim 14.

16. The battery cell according to claim 15, characterized in that, After the battery cell is formed, based on the total mass of the functional coating, the functional coating includes 20% to 30% chalcogenides; and / or, After the battery cell is formed, the porosity of the functional coating is 30% to 60%.

17. The battery cell according to claim 15 or 16, characterized in that, The battery cell includes an electrolyte, which comprises C3 to C12 cyclic carbonates.

18. The battery cell according to claim 15, characterized in that, It includes a negative electrode sheet and a solid electrolyte interface membrane, wherein the solid electrolyte interface membrane includes 0.01% to 6% chalcogens by mass, wherein the chalcogens include at least one of sulfur, selenium, and tellurium.

19. The battery cell according to claim 18, characterized in that, The solid electrolyte interface membrane comprises at least one of the compounds shown in formula (1) and formula (2): Wherein, R represents the chalcogen group 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.

20. The battery cell according to claim 18 or 19, characterized in that, The valence states of the chalcogens include at least one of the following: -1, -2, +4, and +6.

21. The battery cell according to claim 20, characterized in that, After the battery cell is formed, the ratio of the sum of the molar amounts of the tetravalent and hexavalent chalcogenides in the solid electrolyte interfacial membrane per unit mass n1 to the sum of the molar amounts of the chalcogenides in the solid electrolyte interfacial membrane per unit mass n0 is (0.3~3):

1.

22. The battery cell according to claim 20, characterized in that, After the battery cell is formed, the ratio of the sum of the molar amounts of the tetravalent and hexavalent chalcogenides in the solid electrolyte interfacial membrane per unit mass n1 to the sum of the molar amounts of the chalcogenides in the solid electrolyte interfacial membrane per unit mass n0 is (0.5~1.5):

1.

23. An electrical appliance, characterized in that, Includes the battery cell described in any one of claims 15 to 22.

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