Sodium metal battery, electric device comprising same

Abstract

The application provides a sodium metal battery, an electric device comprising the same, a negative electrode tab of the sodium metal battery comprises a negative electrode current collector and a conductive coating on at least one side of the negative electrode current collector. The conductive coating comprises a conductive agent and an aqueous binder, the aqueous binder comprises carboxymethyl cellulose grafted copolymer-blended modified with one or more of acrylic acid, o-hydroxyphenethylamine and polyvinyl alcohol.

Description

[0001] This application is a divisional application based on the invention with application number 202310622552.5, application date May 30, 2023, applicant CATL, entitled "Negative electrode sheet, battery and power-consuming device including the same". Technical Field

[0002] This application relates to the field of battery technology, and more particularly to a negative electrode sheet for sodium batteries, a battery comprising the same, and an electrical device thereof. Background Technology

[0003] Secondary batteries rely on the repeated insertion and extraction of active ions between the positive and negative electrodes for charging and discharging. Lithium-ion batteries, in particular, possess outstanding characteristics such as high energy density, long cycle life, and the absence of pollution and memory effect. Therefore, as a clean energy source, secondary batteries have gradually expanded from electronic products to large-scale devices such as electric vehicles. However, due to the scarcity of active materials for lithium-ion batteries, battery costs remain high, and the industry also faces serious challenges such as resource depletion. Therefore, there is a need to develop other low-cost metal-ion secondary battery systems.

[0004] Sodium-ion batteries have become a popular research area in recent years due to their advantages such as low cost, abundant resources, and manufacturing process similar to lithium-ion batteries. However, the relatively low energy density of sodium-ion batteries remains a bottleneck limiting their widespread application. Summary of the Invention

[0005] To achieve the above objectives, this application provides a negative electrode sheet for sodium batteries, which enables batteries containing the negative electrode sheet to have both high energy density and good cycle performance; this application also provides a battery and an electrical device containing the negative electrode sheet.

[0006] A first aspect of this application provides a negative electrode sheet for a sodium battery, including a negative current collector and a conductive coating, the conductive coating being located on at least one side of the negative current collector. The conductive coating includes a conductive agent and an aqueous binder, the aqueous binder being selected from aqueous binders with a relative permittivity greater than or equal to 2.5.

[0007] Not intended to be limited by any theory or explanation, water-based binders with a relative permittivity greater than or equal to 2.5 can, on the one hand, promote the growth of Na+. +The combination of sodium metal with electrons to form sodium metal facilitates its deposition on the negative electrode and also promotes the interface smoothness of the conductive coating. When the conductive coating has high interface smoothness, the orientation and tendency of sodium metal deposition can be controlled, ensuring uniform deposition of sodium metal on the surface of the negative electrode. This not only suppresses the formation of sodium dendrites, thereby improving battery reliability and long-term cycle performance, but also reduces the difficulty of sodium metal extraction, minimizing irreversible loss of active sodium ions, thus increasing the battery's energy density and cycle life. Furthermore, compared to other binders, aqueous binders with a relative permittivity greater than or equal to 2.5 form a binder network with higher mechanical strength in the conductive layer, providing support for the conductive coating. This improves the structural stability of the conductive coating, reduces the risk of changes in the current collector structure caused by sodium metal extraction, and thus enhances the battery's cycle stability and extends its cycle life. Therefore, the negative electrode of this embodiment, when applied to a sodium battery, enables the sodium battery to possess high energy density, high cycle stability, and long cycle life.

[0008] In any embodiment of this application, the aqueous binder includes at least one of carboxymethyl cellulose and its derivatives, polyacrylic acid and its derivatives, acrylonitrile copolymers, sodium alginate and its derivatives, and polyacrylate and its derivatives.

[0009] Optionally, the waterborne binder includes at least one of carboxymethyl cellulose and its derivatives.

[0010] The aqueous binders selected from the above-mentioned types possess high polarity, which not only allows for strong adhesion to the negative electrode current collector (e.g., copper foil, aluminum foil), thereby enhancing the interfacial adhesion between the conductive coating and the negative electrode current collector, but also enables the formation of hydrogen bonds with the polar functional groups on the conductive agent surface, thereby enhancing the cohesive force of the conductive coating and suppressing structural changes in the conductive coating caused by sodium leaching. This is beneficial for further improving the interfacial smoothness and structural stability of the conductive coating, facilitating the uniform deposition and leaching of sodium metal onto the surface of the negative electrode, and thus further improving the battery's cycle performance. In particular, carboxymethyl cellulose and its derivatives have relatively stable viscosity and are resistant to electrolyte swelling and corrosion, providing stable viscosity and adhesion. This allows the conductive coating and the negative electrode current collector to maintain high interfacial adhesion during battery charge-discharge cycles, thereby improving the structural stability of the negative electrode and reducing the battery's internal resistance. Therefore, the negative electrode of this application, when used in a sodium battery, can significantly improve the battery's cycle performance.

[0011] In any embodiment of this application, the waterborne adhesive includes a chemically blended modified waterborne adhesive.

[0012] Optionally, the waterborne binder includes chemically blended modified carboxymethyl cellulose.

[0013] Chemical blending modification allows for flexible control of the structure of waterborne binders, endowing them with excellent bonding properties, mechanical strength, and suitable viscosity. This, in turn, can improve the interfacial smoothness and structural stability of conductive coatings, increase sodium-affinity nucleation sites in the conductive coating, and thus further enhance the cycle performance of the battery.

[0014] In any embodiment of this application, the waterborne adhesive includes carboxymethyl cellulose grafted copolymerized and blended with one or more of acrylic acid, o-hydroxyphenylethylamine, and polyvinyl alcohol.

[0015] Carboxymethyl cellulose (CMC) grafted and copolymerized with one or more of acrylic acid, o-hydroxyphenylethylamine, and polyvinyl alcohol can contain a large number of polar groups. In conductive coatings, this type of CMC can form hydrogen bonds in situ between molecules through polar groups, thereby further improving the mechanical properties of the binder network. This can further improve the collapse and changes in the electrode structure caused by metal deposition. In addition, polar groups can further reduce the overpotential of sodium deposition. When the aqueous binder includes CMC grafted and copolymerized with the above-mentioned substances, this CMC is uniformly distributed in the conductive coating, allowing sodium metal to be uniformly deposited on the surface of the negative electrode. This not only inhibits the formation of sodium dendrites, thereby improving the reliability and long-term cycle performance of the battery, but also reduces the difficulty of sodium metal extraction and reduces the irreversible loss of active sodium, thereby improving the energy density and cycle life of the battery.

[0016] In any embodiment of this application, the average degree of polymerization of the aqueous binder is 50-2500, optionally 800-2000. When the average degree of polymerization of the aqueous binder is within this range, the aqueous binder can have a suitable viscosity and higher resistance to electrolyte swelling and corrosion. This allows the conductive coating and the negative electrode current collector to maintain a high interfacial adhesion during battery charge-discharge cycles, thereby improving the structural stability of the negative electrode and reducing the battery's internal resistance. Therefore, the negative electrode of this application, when applied to a sodium battery, can significantly improve the battery's cycle performance.

[0017] In any embodiment of this application, the viscosity of the aqueous binder is 600 mPa·s-2000 mPa·s, optionally 600 mPa·s-1200 mPa·s. When the viscosity of the aqueous binder meets the given range, it can provide stable adhesion during battery charge-discharge cycles, ensuring a high interfacial adhesion between the conductive coating and the negative electrode current collector. This improves the structural stability of the negative electrode sheet, reduces the internal resistance of the battery, and thus enhances the battery's cycle performance.

[0018] In any embodiment of this application, the purity of the aqueous binder is 95% or higher, optionally 95%-99% or higher. This improves the adhesion between the conductive coating and the negative electrode current collector, thereby enhancing the structural stability of the negative electrode sheet and ultimately improving the battery's cycle performance.

[0019] In any embodiment of this application, the conductive agent includes a conductive carbon material.

[0020] Optionally, the conductive agent includes one or more of carbon nanotubes, graphene, and conductive carbon fibers.

[0021] Alternatively, the conductive agent may include carbon nanotubes and / or reduced graphene oxide.

[0022] The aforementioned conductive carbon material contains a suitable amount of active oxygen-containing groups on its surface, which can interact with aqueous binders to improve the mechanical properties of the conductive coating. This suppresses structural changes in the negative electrode sheet caused by sodium extraction during charging and discharging, thereby improving the battery's cycle performance.

[0023] In any embodiment of this application, the conductive agent includes a modified conductive carbon material.

[0024] Optionally, the conductive agent includes conductive carbon materials modified with one or more of -OH, -COOH, and -NH2.

[0025] Alternatively, the conductive agent may include carbon nanotubes and / or reduced graphene oxide modified with one or more of -OH, -COOH, and -NH2.

[0026] The modified conductive carbon material described above can interact with aqueous binders to form hydrogen bonds. This further enhances the mechanical properties of the conductive coating and suppresses structural changes caused by sodium insertion and extraction. Furthermore, the presence of polar groups further reduces the overpotential of sodium metal deposition. When the conductive carbon material includes the aforementioned modified groups, sodium metal can be deposited more uniformly on the surface of the negative electrode. This not only suppresses the formation of sodium dendrites, thereby improving battery reliability and long-term cycle performance, but also reduces irreversible loss of active sodium, thus increasing the battery's energy density and cycle life.

[0027] In any embodiment of this application, the sodium deposition potential of the conductive coating is 2.6V-2.75V. This facilitates the uniform deposition of sodium metal on the negative electrode surface, thereby improving the cycle performance of the battery.

[0028] In any embodiment of this application, the thickness of the conductive coating is 1 μm-5 μm, optionally 2 μm-3 μm. This allows for the uniform deposition of sodium metal on the surface of the negative electrode while reducing its thickness, thereby improving the energy density of the battery.

[0029] In any embodiment of this application, the mass percentage of the aqueous binder, based on the total mass of the conductive coating, is less than or equal to 5%, and can be selected as 2%-2.6%. The mass percentage of the aqueous binder within the given range can improve the interfacial smoothness and structural stability of the conductive coating while ensuring the conductive coating has a suitable conductive agent content. This allows the conductive coating surface to have an appropriate number of sodium-affinity nucleation sites, thereby improving the cycle performance of the battery.

[0030] In any embodiment of this application, the Fourier transform infrared (FTIR) spectrum of the conductive coating has at least one of the characteristic peaks located at the following positions: 1300 cm⁻¹ -1 -1050cm -1 3300 cm -1 -2500 cm -1 3400 cm -1 -3200cm -1 Therefore, it can not only suppress the formation of sodium dendrites, thereby improving the reliability and long-term cycle performance of the battery; it can also reduce the difficulty of sodium metal extraction and reduce the irreversible loss of active sodium ions, thereby improving the energy density and cycle life of the battery.

[0031] A second aspect of this application provides a battery, including the negative electrode sheet of the first aspect. Therefore, the battery of this application embodiment can possess high energy density, high cycle stability, and long cycle life.

[0032] A third aspect of this application provides an electrical device, including the battery of the second aspect.

[0033] The electrical device in this application embodiment includes the battery of the second aspect, and thus has at least the same advantages as the battery. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating an embodiment of the battery cell of this application.

[0035] Figure 2 yes Figure 1 An exploded view of an embodiment of the battery cell of this application is shown.

[0036] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0037] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0038] Figure 5 yes Figure 4The diagram shown is an exploded view of an embodiment of the battery pack of this application.

[0039] Figure 6 This is a schematic diagram of one embodiment of the power supply device of this application, which may include a battery pack or battery module as a power source according to the embodiments of this application.

[0040] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0041] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode sheet, the battery comprising it, and the power supply 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0042] 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 a 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 a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. 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 "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are 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.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] 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.

[0046] 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.

[0047] 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).

[0048] In this application, the terms "multiple", "various", etc., refer to two or more kinds.

[0049] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0050] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0051] Sodium-ion batteries have become a popular research area in recent years due to their advantages such as low cost, abundant resources, and manufacturing process similar to lithium-ion batteries. However, the relatively low energy density of sodium-ion batteries remains a bottleneck limiting their widespread application.

[0052] Sodium metal anodes possess extremely high theoretical specific capacity and low reduction potential. They typically include an undercoat. During charging, active sodium ions released from the positive electrode can deposit at sodium-affinity nucleation sites in the undercoat to form a sodium metal layer. However, the sodium deposition interface in the undercoat of these technologies is poor, making it prone to sodium dendrite formation during deposition. This increases the risk of puncturing the separator, leading to reduced battery reliability. Furthermore, when sodium metal is embedded in the undercoat and then extracted, it creates pores. These pores negatively impact the mechanical properties of the undercoat, increasing the probability of structural collapse. Additionally, some sodium metal within these pores may be difficult to extract, potentially forming "dead sodium" and exacerbating irreversible capacity loss. Ultimately, this deteriorates the battery's long-term cycle performance.

[0053] In view of this, embodiments of this application provide a negative electrode sheet for sodium batteries, which enables batteries containing the sheet to have both high energy density and good cycle performance; this application also provides a battery and an electrical device containing the composite conductive agent.

[0054] Negative electrode sheet A first aspect of this application provides a negative electrode sheet for a sodium battery, comprising a negative current collector and a conductive coating, the conductive coating being located on at least one side of the negative current collector. The conductive coating comprises a conductive agent and an aqueous binder, the aqueous binder being selected from aqueous binders with a relative permittivity greater than or equal to 2.5. For example, the aqueous binder may be selected from aqueous binders with relative permittivity of 2.5, 2.8, 3.0, 3.2, 3.5, 3.9, 4.1, 4.4, 4.8, 5.3, 5.7, 6.0, or any two of the above values.

[0055] Not intended to be limited by any theory or explanation, water-based binders with a relative permittivity greater than or equal to 2.5 can, on the one hand, promote the growth of Na+. + The combination of sodium and electrons to form sodium metal facilitates sodium metal deposition on the negative electrode and also promotes the interface smoothness of the conductive coating. When the conductive coating has high interface smoothness, the orientation and tendency of sodium metal deposition can be controlled, ensuring uniform deposition of sodium metal on the surface of the negative electrode. This not only suppresses the formation of sodium dendrites, thereby improving battery reliability and long-term cycle performance, but also reduces the difficulty of sodium metal extraction, minimizing irreversible loss of active sodium ions, thus increasing battery energy density and cycle life. Furthermore, compared to other binders, aqueous binders with a relative permittivity greater than or equal to 2.5 form a binder network with higher mechanical strength in the conductive layer, providing support for the conductive coating. This improves the structural stability of the conductive coating, reduces the risk of changes in the current collector structure caused by sodium metal extraction, and thus enhances battery cycle stability and extends battery cycle life.

[0056] Therefore, the negative electrode sheet of this application embodiment is applied to a sodium battery, which enables the sodium battery to have high energy density, high cycle stability and long cycle life.

[0057] Examples of negative electrode current collectors may include one or more negative electrode current collectors known in the art that can be used in sodium batteries. In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil or aluminum foil may be used as the metal foil. A composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0058] Examples of conductive agents may include one or more conductive materials known in the art.

[0059] Waterborne adhesives generally refer to adhesives that can use water as a dispersant or solvent. Examples of waterborne adhesives may include one or more waterborne adhesives known in the art. Those skilled in the art can select a suitable waterborne adhesive according to the needs of the actual application, provided that the relative permittivity is greater than or equal to 2.5, and no limitation is made herein.

[0060] In this document, the relative permittivity has a meaning known in the art and can be determined using equipment and methods known in the art. For example, it can be determined with reference to the testing standard GB / T 1409-88. The specific test method is as follows: The relative permittivity εr can be measured using an electrostatic field as follows: First, the capacitance C0 of the capacitor is measured when there is a vacuum between the two capacitor plates. Then, for the same capacitor plates, keeping the distance between the plates constant, a dielectric is added between the plates, and the capacitance Cx of the capacitor is measured. The relative permittivity of the dielectric can be calculated using the following formula.

[0061] εr=Cx / C0 At standard atmospheric pressure, the relative permittivity εr of dry air without carbon dioxide is 1.00053. Therefore, using the capacitance Ca in air with this electrode configuration instead of C0 to measure the relative permittivity εr also provides sufficient accuracy.

[0062] In some embodiments, the waterborne binder may include at least one of carboxymethyl cellulose (CMC) and its derivatives, polyacrylic acid (PAA) and its derivatives, acrylonitrile copolymers, sodium alginate and its derivatives, and polyacrylates and their derivatives.

[0063] Optionally, in some embodiments, the aqueous binder may include at least one of carboxymethyl cellulose and its derivatives.

[0064] Derivatives generally refer to products derived from polymers in which hydrogen atoms or groups of atoms are replaced by other atoms or groups of atoms.

[0065] Not intended to be limited to any particular theory or explanation, the aqueous binders selected from the above-mentioned types possess high polarity, which not only allows for strong adhesion to the negative electrode current collector (e.g., copper foil, aluminum foil), thereby enhancing the interfacial adhesion between the conductive coating and the negative electrode current collector, but also enables the formation of hydrogen bonds with the polar functional groups on the conductive agent surface, thereby enhancing the cohesive force of the conductive coating and suppressing structural changes in the conductive coating caused by sodium leaching. This is beneficial for further improving the interfacial smoothness and structural stability of the conductive coating, facilitating the uniform deposition and leaching of sodium metal onto the surface of the negative electrode, and thus further improving the battery's cycle performance. In particular, carboxymethyl cellulose and its derivatives have relatively stable viscosity and are resistant to electrolyte swelling and corrosion, providing stable viscosity and adhesion. This allows the conductive coating and the negative electrode current collector to maintain high interfacial adhesion during battery charge-discharge cycles, thereby improving the structural stability of the negative electrode and reducing the battery's internal resistance. Therefore, the negative electrode of the embodiments of this application, when applied to sodium batteries, can significantly improve the battery's cycle performance.

[0066] In some embodiments, the waterborne adhesive may include a chemically blended modified waterborne adhesive.

[0067] Alternatively, in some embodiments, the aqueous binder may include chemically blended modified carboxymethyl cellulose.

[0068] Chemical blending modification has a well-known meaning in the art, referring to a macroscopically homogeneous and continuous material formed by the chemical mixing of two or more polymers. Examples of chemical blending modification may include copolymerization-blending modification (e.g., graft copolymerization-blending modification, block copolymerization-blending modification, etc.), interpenetrating polymer network (PIN) modification, etc. Those skilled in the art can select appropriate chemical blending modification methods and raw materials according to the needs of actual applications, and no limitations are imposed here.

[0069] Not intended to be limited by any theory or explanation, chemical blending modification can flexibly control the structure of waterborne binders, endowing them with good bonding properties, mechanical strength, and suitable viscosity. This can improve the interfacial smoothness and structural stability of conductive coatings, increase the sodium-affinity nucleation sites in the conductive coating, and thus further improve the cycle performance of the battery.

[0070] In some embodiments, the waterborne binder may include carboxymethyl cellulose grafted copolymerized and blended with one or more of acrylic acid, o-hydroxyphenylethylamine, and polyvinyl alcohol.

[0071] Not intended to be limited to any particular theory or explanation, carboxymethyl cellulose grafted and copolymerized with one or more of acrylic acid, o-hydroxyphenylethylamine, and polyvinyl alcohol can contain a significant number of polar groups. In conductive coatings, this type of carboxymethyl cellulose can form hydrogen bonds in situ between molecules through polar groups, thereby further enhancing the mechanical properties of the binder network. This can further mitigate electrode structure collapse and changes caused by metal layer deposition. Additionally, polar groups can further reduce the overpotential of sodium deposition. When the aqueous binder includes carboxymethyl cellulose grafted and copolymerized with the aforementioned substances, this carboxymethyl cellulose is uniformly distributed in the conductive coating, ensuring uniform deposition of sodium metal on the negative electrode surface. This not only suppresses sodium dendrite formation, thereby improving battery reliability and long-term cycle performance, but also reduces the difficulty of sodium metal extraction, minimizing irreversible loss of active sodium, thus increasing battery energy density and cycle life.

[0072] The carboxymethyl cellulose grafted and copolymerized with one or more of the above-mentioned acrylic acid, o-hydroxyphenylethylamine, and polyvinyl alcohol can be obtained commercially or prepared by methods known in the art, and no limitation is made herein.

[0073] As an example, acrylic acid graft copolymerization-blending modified carboxymethyl cellulose can be obtained by emulsion polymerization. Specifically, carboxymethyl cellulose and acrylic acid can be copolymerized by emulsion polymerization, causing the carboxyl groups on the polyacrylic acid backbone to undergo a condensation reaction with the hydroxyl groups on the carboxymethyl cellulose backbone, thereby obtaining acrylic acid graft copolymerization-blending modified carboxymethyl cellulose. The reaction conditions and other necessary raw materials for emulsion polymerization are well known in the art, and those skilled in the art can adjust them according to actual needs, without limitation. As an example, o-hydroxyphenylethylamine graft copolymerization-blending modified carboxymethyl cellulose can be obtained by amidation reaction of o-hydroxyphenylethylamine with carboxymethyl cellulose. The reaction conditions and other necessary raw materials for amidation reaction are well known in the art, and those skilled in the art can adjust them according to actual needs, without limitation. As an example, polyvinyl alcohol graft copolymerization-blending modified carboxymethyl cellulose can be obtained by solution polymerization. Specifically, carboxymethyl cellulose and polyvinyl alcohol can undergo a condensation reaction by solution polymerization, thereby obtaining polyvinyl alcohol graft copolymerization-blending modified carboxymethyl cellulose. The reaction conditions and other necessary raw materials for solution polymerization are well known in the art, and those skilled in the art can adjust them according to actual needs, without limitation.

[0074] In some embodiments, the average polymer of the water-based adhesive can be 50-2500, for example, it can be 50, 100, 200, 500, 800, 1000, 1200, 1500, 1800, 2000, 2200, 2500, or a range of any two of the above values.

[0075] Optionally, in some embodiments, the average polymer of carboxymethyl cellulose may also be 800-2000, for example, it may be 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, or a range of any two of the above values.

[0076] Not intended to be limited to any particular theory or explanation, when the average degree of polymerization of the aqueous binder is within the aforementioned suitable range, the aqueous binder can possess a suitable viscosity and exhibit higher resistance to electrolyte swelling and corrosion. This allows the conductive coating and the negative electrode current collector to maintain high interfacial adhesion during battery charge-discharge cycles, thereby improving the structural stability of the negative electrode and reducing the battery's internal resistance. Therefore, the negative electrode of this application, when applied to a sodium battery, can significantly improve the battery's cycle performance.

[0077] The average degree of polymerization has a meaning known in the art, and the average molecular weight can be determined using equipment and methods known in the art. The degree of polymerization (total molecular weight / molecular weight of a single repeating unit) is calculated from the average molecular weight. For example, the average molecular weight can be determined using one of the following methods: end-group analysis, boiling point elevation method, freezing point depression method, membrane osmotic pressure method, light scattering method, small-angle laser scattering method, viscometry, gel permeation chromatography, etc.

[0078] In some embodiments, the viscosity of the water-based adhesive can be between 600 mPa·s and 2000 mPa·s, for example, it can be 600 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, 1300 mPa·s, 1400 mPa·s, 1500 mPa·s, 1600 mPa·s, 1700 mPa·s, 1800 mPa·s, 1900 mPa·s, 2000 mPa·s, or any range of two of the above values.

[0079] Optionally, in some embodiments, the viscosity of the water-based adhesive may also be 600 mPa·s-1200 mPa·s, for example, it may be 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, or any range of two of the above values.

[0080] Not intended to be limited by any theory or explanation, when the viscosity of the aqueous binder meets the given range, it can provide stable adhesion during battery charge-discharge cycles, maintaining high interfacial adhesion between the conductive coating and the negative electrode current collector. This helps improve the structural stability of the negative electrode, reduce the battery's internal resistance, and thus improve the battery's cycle performance.

[0081] The viscosity of water-based adhesives has a meaning known in the art and can be determined using equipment and methods known in the art. For example, it can be determined using the capillary viscosity method, referring to GB / T 10247-2008.

[0082] In some embodiments, the purity of the water-based adhesive can be above 95%. Optionally, the purity of the water-based adhesive can be 95%-99%.

[0083] When the purity of the aqueous binder meets the given range, it is beneficial to improve the adhesion between the conductive coating and the negative electrode current collector. This, in turn, can improve the structural stability of the negative electrode sheet, thereby enhancing the battery's cycle performance.

[0084] The purity of water-based adhesives has a meaning known in the art and can be determined using equipment and methods known in the art. For example, it can be determined by gas chromatography.

[0085] In some implementations, the conductive agent may include a conductive carbon material.

[0086] Optionally, in some embodiments, the conductive agent may include one or more of carbon nanotubes, graphene, and conductive carbon fibers.

[0087] Alternatively, in some embodiments, the conductive agent may include carbon nanotubes and / or reduced graphene oxide.

[0088] Not intended to be limited to any particular theory or explanation, the aforementioned conductive carbon material contains a suitable amount of active oxygen-containing groups on its surface, which can interact with aqueous binders to improve the mechanical properties of the conductive coating. This can suppress structural changes in the negative electrode sheet caused by sodium release during charging and discharging, thereby improving the battery's cycle performance.

[0089] In some embodiments, the conductive agent may include a modified conductive carbon material.

[0090] Optionally, in some embodiments, the conductive agent may include a conductive carbon material modified with one or more of -OH, -COOH, and -NH2. For example, the conductive agent may include carbon nanotubes and / or reduced graphene oxide modified with one or more of -OH, -COOH, and -NH2.

[0091] Not intended to be limited to any particular theory or explanation, the modified conductive carbon material described above can interact with aqueous binders to form hydrogen bonds. This further enhances the mechanical properties of the conductive coating and suppresses structural changes caused by sodium insertion and extraction. Furthermore, the presence of polar groups further reduces the overpotential of sodium metal deposition. When the conductive carbon material includes the aforementioned modified groups, sodium metal can be deposited more uniformly on the surface of the negative electrode. This not only suppresses the formation of sodium dendrites, thereby improving battery reliability and long-term cycle performance, but also reduces irreversible loss of active sodium, thus increasing the battery's energy density and cycle life.

[0092] The conductive carbon materials modified with one or more of the above-mentioned -OH, -COOH, and -NH2 can be obtained commercially or prepared by methods known in the art, and are not limited herein.

[0093] As an example, -OH modified carbon nanotubes can be prepared by the following steps: carbon nanotubes are mixed with a mixed solution of concentrated nitric acid and concentrated sulfuric acid (68% by mass and 98% by mass are mixed in a volume ratio of 2:1), and then treated in a constant temperature water bath at 55℃-65℃ for 3 hours to introduce carboxyl groups into the carbon nanotubes; the treated carbon nanotubes are then mixed with a phosphorous acid reducing agent to reduce the carboxyl groups to hydroxyl groups, thus obtaining -OH modified carbon nanotubes.

[0094] As an example, -COOH modified carbon nanotubes can be prepared by the following steps: carbon nanotubes are mixed with a mixed solution of concentrated nitric acid and concentrated sulfuric acid (68% by mass and 98% by mass are mixed in a volume ratio of 2:1) and treated in a constant temperature water bath at 55℃-65℃ for 3 hours; the treated carbon nanotubes are then transferred to a beaker and sodium hydroxide solution is added until the pH reaches 7, and then washed three times with deionized water to obtain -COOH modified carbon nanotubes.

[0095] As an example, -NH2 modified carbon nanotubes can be prepared by reacting -COOH modified carbon nanotubes with amine compounds (such as ethylenediamine, diethylamine, aniline, etc.) to obtain -NH2 modified carbon nanotubes.

[0096] It should be noted that the above-described preparation steps for the modified conductive carbon material are merely examples to explain this application and are not intended to limit this application. Those skilled in the art can adjust the preparation conditions and raw materials according to actual needs to obtain the modified conductive carbon material of the embodiments of this application. In some embodiments, the sodium deposition potential of the conductive coating can be 2.6V-2.75V.

[0097] Not intended to be limited to any theory or explanation, the conductive coating in the negative electrode of this application embodiment has a specific composition that can increase the number of sodium-affinity nucleation sites on the surface of the conductive coating, resulting in the aforementioned lower sodium deposition potential. This facilitates the uniform deposition of sodium metal on the negative electrode surface, thereby improving the cycle performance of the battery.

[0098] Sodium deposition potential has a well-known meaning in the art and can be determined using equipment and methods known in the art. For example, positive electrode active material NFPP (e.g., Na4Fe3(PO4)2P2O7) can be mixed with positive electrode binder and conductive agent in a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) can be added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on aluminum foil, and then dried, cold-pressed, and slit to obtain a positive electrode sheet. The positive and negative electrode sheets are assembled into a coin cell, and the coin cell is charged using a battery charge-discharge instrument to obtain the first voltage-capacity curve. The sodium deposition potential can be determined based on the voltage plateau in the first voltage-capacity curve.

[0099] In some embodiments, the thickness of the conductive coating can be 1μm-5μm, for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, or any range of two of the above values.

[0100] Optionally, in some embodiments, the thickness of the conductive coating can also be 2μm-3μm, for example, it can be 2μm, 2.2μm, 2.5μm, 2.8μm, 3μm, or any range of two of the above values.

[0101] Not intended to be limited to any theory or explanation, the negative electrode sheet in this application embodiment contains a specific aqueous binder that allows the conductive coating to have both a small thickness and high interface smoothness. Therefore, while reducing the thickness of the negative electrode sheet, sodium metal can be uniformly deposited on the surface of the negative electrode sheet, thereby improving the energy density of the battery.

[0102] The thickness of the conductive coating has a meaning known in the art and can be determined using equipment and methods known in the art. For example, a scanning electron microscope (e.g., ZEISS Sigma 300) can be used, referring to JY / T 0584-2020, to obtain cross-sectional scanning electron microscope (SEM) images of the negative electrode sheet. As an example, the test can be performed as follows: multiple areas are randomly selected on the cross-section of the negative electrode sheet, and the thickness of the conductive coating is measured at least five times at a certain magnification. The measured values ​​of different areas are statistically analyzed, and the average value is taken as the thickness of the conductive coating.

[0103] In some implementations, the mass percentage of the water-based adhesive, based on the total mass of the conductive coating, can be less than or equal to 5%, for example, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, or a range of any two of the above values.

[0104] Optionally, in some embodiments, the mass percentage of the water-based adhesive, based on the total mass of the conductive coating, can be 2%-2.6%, for example, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, or a range of any two of the above values.

[0105] Not intended to be limited by any theory or explanation, when the mass percentage of the aqueous binder in the conductive coating meets the given range, it can improve the interfacial smoothness and structural stability of the conductive coating while ensuring a suitable conductive agent content. This allows the conductive coating surface to have an appropriate number of sodium-affinity nucleation sites, thereby improving the battery's cycle performance.

[0106] In some embodiments, the Fourier transform infrared (FTIR) spectrum of the conductive coating has at least one of the characteristic peaks located at: 1300 cm⁻¹ -1 -1050cm -1 3300cm -1 -2500cm -1 3400cm -1 -3200cm -1 .

[0107] The above is located at 1300cm -1 -1050cm -1 The characteristic peak is used to characterize -OH; it is located at 3300 cm⁻¹. -1 -2500cm -1 The characteristic peak is used to characterize -COOH; it is located at 3400 cm⁻¹. -1 -3200cm -1 The characteristic peak is used to characterize -NH2.

[0108] Not intended to be limited to any particular theory or explanation, when the conductive coating contains one or more of the aforementioned characteristic peaks, it indicates that the conductive coating contains conductive agents and / or aqueous binders modified with the aforementioned polar groups. Thus, the molecules modified with the polar groups can interact to form hydrogen bonds. This can further improve the mechanical properties of the conductive coating and suppress structural changes in the conductive coating caused by sodium insertion and extraction. Furthermore, sodium metal has a low binding energy with polar groups. When the conductive coating includes the aforementioned modified groups, sodium metal can be deposited more uniformly on the surface of the negative electrode. This not only suppresses the formation of sodium dendrites, thereby improving battery reliability and long-term cycle performance, but also reduces the difficulty of sodium metal extraction, minimizing the irreversible loss of active sodium ions, thereby increasing the battery's energy density and cycle life.

[0109] The negative electrode includes a negative current collector and a conductive coating disposed on at least one side of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the conductive coating is disposed on either or both of the two opposite surfaces of the negative current collector.

[0110] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned raw materials for preparing the conductive coating, such as conductive agent, aqueous binder and any other components, in a solvent (e.g., deionized water) to form a conductive coating slurry; coating the conductive coating slurry onto one or both surfaces of the negative electrode current collector; and after drying, cold pressing and other processes, the negative electrode sheet of the present application embodiment can be obtained.

[0111] Furthermore, the negative electrode sheet of this application does not exclude other additional functional layers besides the conductive coating. For example, in some embodiments, the negative electrode sheet of this application also includes a protective layer covering the surface of the conductive coating.

[0112] Battery A second aspect of this application provides a battery. The battery mentioned in the embodiments of this application may include one or more battery cells as a single physical module to provide higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or mixed via a busbar.

[0113] The battery cell can be a secondary battery, also known as a rechargeable battery or accumulator, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged. This application does not impose any particular limitation on the type of secondary battery; however, a sodium metal battery may be used.

[0114] Typically, a battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator.

[0115] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0116] [Positive electrode plate] The positive electrode sheet included in the battery of this application embodiment includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer including a positive active material.

[0117] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0118] In the positive electrode sheet of this application embodiment, the positive electrode active material can be a positive electrode active material known in the art for sodium batteries. As an example, the positive electrode active material may include, but is not limited to, at least one of sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0119] 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 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials, with the general formula X p M' q (PO4) r O x Y 3-x At least one of the materials in general formula X. p M' q (PO4) r O x Y 3-x In the given information, 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X is selected from H. + Li + Na + K + and NH4 + At least one of the following, M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, optionally at least one of F, Cl and Br.

[0120] 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.

[0121] In some embodiments, the positive electrode film 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 at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the positive electrode film 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 at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0123] 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 polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. An example of a metal material may be at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymeric material substrate may be at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0124] The positive electrode film 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.

[0125] [Negative electrode plate] The negative electrode included in the battery of this application embodiment includes the negative electrode of the first aspect of this application embodiment. The embodiments of the negative electrode have been described and illustrated in detail above, and will not be repeated here. It is understood that the battery of this application embodiment can achieve the beneficial effects of any of the above embodiments of the negative electrode of this application embodiment.

[0126] [Isolation membrane] A separator is disposed between the positive and negative electrode plates to provide isolation. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0127] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0128] [Electrolytes] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid or gel-like.

[0129] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0130] In some embodiments, the electrolyte salt may include, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium difluorosulfonylimide (NaFSI), sodium difluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0131] In some embodiments, the solvent may include, but is not limited to, at least one of 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 ester 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).

[0132] 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 may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0133] In some embodiments, the battery cell also includes a housing for containing the electrode assembly and electrolyte. The housing of the battery cell can be a rigid housing, such as a hard plastic housing, an aluminum housing, a steel housing, etc. The housing of the battery cell can also be a pouch, such as a pouch-type pouch. The pouch material can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0134] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0135] In some implementations, refer to Figure 2 The outer casing may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0136] The method for preparing the battery cell in this application is well known. In some embodiments, the electrode assembly can be placed in a housing, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, the battery cell is obtained.

[0137] In some embodiments, the battery mentioned in this application refers to a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application may be a battery module or a battery pack. A battery generally includes a housing for encapsulating one or more battery cells. The housing prevents liquids or other foreign matter from affecting the charging or discharging of the battery cells.

[0138] In some implementations, there can be multiple battery cells in the battery, which can be connected in series, parallel, or a combination thereof. A combination thereof means that multiple battery cells are connected in both series and parallel. Multiple battery cells can be directly connected in series, parallel, or a combination thereof, and then the whole assembly of multiple battery cells is housed in a housing. Alternatively, multiple battery cells can first be connected in series, parallel, or a combination thereof to form a battery module, and then multiple battery modules can be connected in series, parallel, or a combination thereof to form a whole assembly, which is then housed in a housing.

[0139] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, there are multiple battery cells 5, which are connected in series, parallel, or a combination thereof to form a battery module 4. The multiple battery cells 5 in the battery module 4 can be electrically connected through a busbar to achieve the series, parallel, or combination connection. In the battery module 4, the multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0140] 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.

[0141] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The multiple battery modules 4 in the battery pack 1 can be electrically connected via a busbar component to achieve series, parallel, or mixed connection. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery housing.

[0142] Electrical appliances This application also provides an electrical device, which includes a battery cell provided in this application embodiment. The battery cell is used to provide electrical energy. 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 may include, 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.

[0143] As the electrical device, a single battery cell, a battery module containing multiple battery cells, or a battery pack can be selected according to its usage requirements.

[0144] Figure 6 This is an example of an 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.

[0145] 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.

[0146] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0147] Example 1 Preparation of negative electrode sheet A water-based binder, carboxymethyl cellulose (CMC), and a conductive agent, carbon nanotubes (CNTs), were mixed at a mass ratio of 2.6:97.4 and dispersed in deionized water to obtain a conductive coating slurry. The conductive coating slurry was uniformly coated onto the surface of an aluminum foil current collector, and after drying, cold pressing, and slitting, a negative electrode sheet was obtained. This negative electrode sheet includes an aluminum foil and a conductive coating on the surface of the aluminum foil. The CMC has an average degree of polymerization of 1500 and a viscosity of 2000 mPa·s, and the water-based binder has a mass percentage (w) of 2.6% in the conductive coating.

[0148] Preparation of positive electrode sheet The positive electrode active material Na4Fe3(PO4)2P2O7, the positive electrode binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black (Super-P) were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on aluminum foil, and then dried, cold-pressed, and slit to obtain a positive electrode sheet.

[0149] Separating membrane Polypropylene film is used as the separator.

[0150] Preparation of electrolyte NaPF6 was dissolved in a solvent prepared by mixing diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether in a volume ratio of 1:1 to obtain an electrolyte with a NaPF6 concentration of 1 mol / L.

[0151] Preparation of secondary batteries The positive electrode, separator, and negative electrode are stacked in sequence to obtain an electrode assembly. The electrode assembly is placed in a packaging shell and subjected to processes such as drying, liquid injection, vacuum sealing, settling, formation, and shaping to obtain a secondary battery.

[0152] Preparation of button cells The negative electrode sheet is punched into small round pieces with a diameter of 14mm using a punch, and the positive electrode sheet is punched into small round pieces with a diameter of 13mm. In a drying room, the small round negative electrode sheet is assembled with a separator (Celgard2300 model), a small round positive electrode sheet, and a coin cell casing to form a coin cell. The electrolyte mentioned above is then added, and the coin cell is sealed using a coin cell encapsulation machine to obtain a coin cell full cell.

[0153] Example 2-22 Based on the preparation process of the negative electrode sheet in Example 1, and according to Table 1, at least one of the following was adjusted: the type of aqueous binder, the average degree of polymerization n of the aqueous binder, the mass percentage w of the aqueous binder in the conductive coating, and the type of conductive agent, to prepare the negative electrode sheets of Examples 2-22. The preparation of the positive electrode sheet, separator, electrolyte, secondary battery, and coin cell of Examples 2-22 was the same as in Example 1. Specifically, the aqueous binder in Examples 12-14 and 20-22 was CMC modified by graft copolymerization-blending with modified raw materials; the conductive agent in Examples 15-22 was a conductive agent modified with modified groups, as detailed in Table 1.

[0154] Comparative Examples 1-2 Based on the preparation process of the positive electrode, negative electrode, separator, electrolyte, secondary battery and coin cell in Example 1, according to Table 1, at least one of the following was adjusted: the type of aqueous binder, the average degree of polymerization n of the aqueous binder, the mass percentage w of the aqueous binder in the conductive coating, and the type of conductive agent, to prepare the positive electrode, negative electrode, separator, electrolyte, secondary battery and coin cell of Comparative Examples 1-2.

[0155] Test section The following tests were conducted on Examples 1-22 and Comparative Examples 1-2, and the test results are shown in Table 2.

[0156] (1) Sodium deposition potential test A battery charge / discharge tester was used to perform a charging test on the button cell battery. The charging voltage of the button cell battery was set to 100mV vs Na / Na. +The current density is set to 1 mA / cm². 2 The voltage-capacity curve is obtained, and the sodium deposition potential can be determined based on the voltage plateau in the voltage-capacity curve.

[0157] (2) DC resistance (DCR) test of the battery At 25℃, the secondary battery was left to stand for 30 minutes, then charged at a constant current rate of 0.33C to 3.65V; then charged at a constant voltage rate of 3.65V to a cutoff current of 0.05C; after standing for 30 minutes, it was discharged at a constant current rate of 0.33C for 90 minutes to a cutoff current of 0.5C, and the voltage at this point was recorded as U0; after standing for 30 minutes, it was discharged at a 4C rate for 30 seconds, and the discharge current was recorded as I. The voltages at the 5th, 10th, 20th, and 30th seconds of discharge were recorded as U. n The values ​​of n are 5, 10, 20, and 30 respectively; let stand for 5 minutes, then end the test.

[0158] Calculate DCR n =(U n U0) / I is used to obtain the DCR at the 5th, 10th, 20th and 30th seconds of discharge, and the average value is taken as the DCR of the battery.

[0159] (3) Room temperature cycling performance test At 25℃, the secondary battery was left to stand for 30 minutes, then discharged at 0.33C to 1.5V. After standing for 30 minutes, it was charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V to the cutoff current of 0.05C; left to stand for 30 minutes; then discharged at 0.33C to 1.5V; left to stand for 30 minutes. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as the discharge capacity of the battery's first cycle. This charge-discharge cycle was repeated, and the number of cycles when the capacity decreased to 80% was recorded.

[0160] Table 1

[0161] Table 2

[0162] As shown in Tables 1 and 2, the negative electrode sheet provided in this application embodiment can effectively improve the cycle performance of sodium batteries.

[0163] In contrast, Comparative Example 1, which uses styrene-butadiene rubber (SBR) as a binder and conventional conductive agent CNT, has a higher sodium deposition potential and DCR, which is detrimental to the uniform deposition of sodium metal and stable battery cycling. Therefore, the cycle performance of the battery in Comparative Example 1 is far inferior to that of Examples 1-22. Although Comparative Example 2 uses -OH modified CNTs, which reduces the sodium deposition potential and DCR to some extent, its battery cycle performance is still unsatisfactory.

[0164] 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.

Claims

1. A sodium metal battery, comprising a negative electrode, said negative electrode comprising: Negative electrode current collector; as well as A conductive coating is located on at least one side of the negative electrode current collector. The conductive coating includes a conductive agent and an aqueous binder. The aqueous binder includes carboxymethyl cellulose grafted and copolymerized with one or more of acrylic acid, o-hydroxyphenylethylamine, and polyvinyl alcohol.

2. The sodium metal battery according to claim 1, wherein, The relative permittivity of the water-based adhesive is greater than or equal to 2.5, and can be selected as 2.5-6.

0.

3. The sodium metal battery according to claim 1 or 2, wherein, The water-based adhesive has an average degree of polymerization of 50-2500, optionally 800-2000.

4. The sodium metal battery according to any one of claims 1-3, wherein, The viscosity of the water-based adhesive is 600 mPa·s-2000 mPa·s, and can be selected as 600 mPa·s-1200 mPa·s.

5. The sodium metal battery according to any one of claims 1-4, wherein, The purity of the water-based adhesive is above 95%, and can be selected as above 95%-99%.

6. The sodium metal battery according to any one of claims 1-5, wherein, The conductive agent includes a conductive carbon material; Optionally, the conductive agent includes one or more of carbon nanotubes, graphene, and conductive carbon fibers; Alternatively, the conductive agent may comprise carbon nanotubes and / or reduced graphene oxide.

7. The sodium metal battery according to any one of claims 1-6, wherein, The conductive agent includes a modified conductive carbon material; Optionally, the conductive agent includes conductive carbon materials modified with one or more of -OH, -COOH, and -NH2; Alternatively, the conductive agent may include carbon nanotubes and / or reduced graphene oxide modified with one or more of -OH, -COOH, and -NH2.

8. The sodium metal battery according to any one of claims 1-7, wherein, The sodium deposition potential of the conductive coating is 2.6V-2.75V.

9. The sodium metal battery according to any one of claims 1-8, wherein, The thickness of the conductive coating is 1μm-5μm, optionally 2μm-3μm.

10. The sodium metal battery according to any one of claims 1-9, wherein, Based on the total mass of the conductive coating, the mass percentage of the water-based adhesive is less than or equal to 5%, and can be selected as 2%-2.6%.

11. The sodium metal battery according to any one of claims 1-10, wherein, The Fourier transform infrared (FTIR) spectrum of the conductive coating has at least one of the characteristic peaks located at the following positions: 1300 cm -1 -1050cm -1 ;3300cm -1 -2500 cm -1 ;3400cm -1 -3200 cm -1 。 12. An electrical device comprising a sodium metal battery according to any one of claims 1-11.

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