Sodium secondary battery monomer and preparation method thereof, sodium supplementing agent and preparation method thereof, and electric equipment

Abstract

The invention discloses a sodium secondary battery monomer and a preparation method thereof, a sodium supplementing agent and a preparation method thereof and electric equipment, the sodium secondary battery monomer comprises a positive pole piece, the positive pole piece comprises a positive pole current collector and a positive pole film layer located on at least one side of the positive pole current collector, the positive pole film layer comprises the sodium supplementing agent, and the negative pole piece comprises a negative pole current collector and a negative pole film layer located on at least one side of the negative pole current collector. The sodium supplementing agent comprises a matrix, at least part of the surface of the matrix is provided with a coating layer, and the coating layer comprises an oxygen-containing polymer; the negative electrode plate comprises a negative electrode current collector; and the isolating membrane is arranged between the positive pole piece and the negative pole piece. Therefore, before the battery voltage in the formation stage reaches the decomposition potential of the sodium supplementing agent, the stability of the sodium supplementing agent is improved; and after the battery voltage reaches the decomposition potential of the sodium supplementing agent, the sodium supplementing agent is decomposed to release sodium ions so as to compensate the sodium ions consumed by forming the SEI membrane, and further the cycle performance of the sodium secondary battery monomer is improved.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to sodium secondary battery cells and their preparation methods, sodium supplementation agents and their preparation methods, and electrical equipment. Background Technology

[0002] Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. During the first charge and discharge cycle, a battery forms an electrolyte interface film (SEI film). This SEI film formation irreversibly consumes active metal ions (such as sodium ions in sodium-ion batteries), reducing the battery's initial efficiency and energy density. Related technologies compensate for the loss of active ions by adding sodium-based additives to the positive electrode; however, these additives have poor air stability and are easily oxidized, rendering them unusable. Summary of the Invention

[0003] The first aspect of this application provides a sodium secondary battery cell, comprising a positive electrode sheet, the positive electrode sheet including 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 sodium replenishing agent, the sodium replenishing agent including a matrix, at least a portion of the surface of the matrix having a coating layer, the coating layer including an oxygen-containing polymer; a negative electrode sheet, the negative electrode sheet including a negative current collector; and a separator membrane disposed between the positive electrode sheet and the negative electrode sheet. This improves the stability of the sodium replenishing agent in air, allowing the sodium replenishing agent to effectively decompose and replenish sodium during the formation stage, thereby improving the initial charge specific capacity and cycle performance of the sodium secondary battery cell.

[0004] According to some embodiments of this application, the sodium secondary battery cell undergoes in-situ deposition of metallic sodium on the negative electrode current collector during charging. Therefore, the absence of a negative electrode sodium current collector can improve the energy density of the sodium secondary battery cell.

[0005] According to some embodiments of this application, the positive electrode film layer includes: a positive electrode active material layer located on at least one side of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material; and a pre-sodiumization layer located on the side of the positive electrode active material layer away from the positive electrode current collector, the pre-sodiumization layer comprising the sodium supplementing agent. This improves the coating effect of the oxygen-containing polymer on the matrix and reduces the impact on lithium insertion / extraction / deintercalation of the positive electrode active material.

[0006] According to some embodiments of this application, the average thickness of the coating layer is 0.5 μm-20 μm. This improves the coating effect on the substrate, reduces the risk of direct contact between the substrate and air, and enhances the stability of the substrate in air.

[0007] According to some embodiments of this application, the decomposition potential of the sodium replenishing agent is less than or equal to 4.25V. This improves the sodium replenishment effect and enhances the cycle performance of the sodium secondary battery cell.

[0008] According to some embodiments of this application, the decomposition potential of the sodium replenishing agent is 2.2V-4.25V. This improves the sodium replenishment effect and enhances the cycle performance of the sodium-ion battery cell.

[0009] According to some embodiments of this application, the matrix includes Na2S, N a2 One or more of C2O4 and Na2C4O4. Therefore, the matrix materials of the above types have low decomposition potentials, which can further improve the sodium replenishment effect and enhance the cycle performance of sodium secondary battery cells.

[0010] According to some embodiments of this application, the average particle size of the sodium replenishing agent matrix is ​​0.5 μm-10 μm. This improves the sodium replenishment effect and enhances the cycle performance of the sodium-ion battery cell.

[0011] According to some embodiments of this application, the sodium secondary battery cell satisfies one or two of the following conditions: the molecular weight of the oxygen-containing polymer is 5000-200000; the oxygen-containing polymer includes one or more of polyethylene oxide, polymethyl methacrylate, polyimide, polysiloxane, and polyetherketone. Therefore, the above-mentioned types of oxygen-containing polymers can improve the stability of the sodium supplement matrix while reducing the impact on the decomposition potential of the sodium supplement, thereby improving the sodium supplementation effect and enhancing the cycle performance of the sodium secondary battery cell.

[0012] According to some embodiments of this application, the pre-sodium layer further includes a positive conductive agent. This improves the electronic conductivity of the pre-sodium layer.

[0013] According to some embodiments of this application, the thickness of the pre-sodiumization layer is 0.5 μm-20 μm. This improves the sodium replenishment effect and enhances the cycle performance of the sodium-ion battery cell.

[0014] According to some embodiments of this application, the sodium secondary battery cell satisfies one or more of the following conditions: the mass percentage of the sodium supplement agent is 30%-98% based on the total mass of the pre-sodium layer; the mass percentage of the positive electrode conductive agent is 1%-40% based on the total mass of the pre-sodium layer; and the mass percentage of the oxygen-containing polymer is 1%-69% based on the total mass of the pre-sodium layer.

[0015] According to some embodiments of this application, the sodium secondary battery cell satisfies one or more of the following conditions: the mass percentage of the sodium supplement agent is 50%-90% based on the total mass of the pre-sodium layer; the mass percentage of the positive electrode conductive agent is 5%-20% based on the total mass of the pre-sodium layer; and the mass percentage of the oxygen-containing polymer is 5%-30% based on the total mass of the pre-sodium layer.

[0016] Therefore, while improving the sodium supplementation effect, the electronic conductivity of the positive electrode is also increased.

[0017] According to some embodiments of this application, the positive electrode active material includes Na. a Ni b Fe c Mn d M e O f Or Na x1 M1 y1 M2 y2 (X z2 O z3 ) z1 Z w One or two of the following are present: 0.85≤a≤1, 0≤b≤0.3, 0.3≤c≤0.4, 0.3≤d≤0.4, 0.02≤e≤0.1, 1.8≤f≤2; M includes one or more of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, Ir, and Ca; M1 includes one or more of Ti, V, Cr, Mn, Fe, Ca, Mg, Al, Nb, Co, and Zr; M2 includes Ni; X includes one or more of Si, S, P, As, B, Mo, W, and Ge; Z includes one or more of F, O, and OH; 2≤x1≤7, 1≤y1≤4, 0≤y2≤0.05, 0.2≤z2 / z3≤0.3, 1≤z1≤4, and 0≤w≤3. This improves the energy density and cycle performance of sodium-ion secondary batteries.

[0018] According to some embodiments of this application, the sodium secondary battery cell satisfies one or two of the following conditions: the compaction density of the positive electrode sheet is 1.6 g / cm³. 3 -3.5g / cm 3 The coating weight of the positive electrode sheet is 12 mg / cm³. 2 -20mg / cm 2 This increases the energy density of sodium secondary battery cells.

[0019] According to some embodiments of this application, the negative electrode further includes an interface modification layer located on at least one side of the negative current collector, the interface modification layer comprising a negative electrode conductive agent and a binder. This improves the electronic conductivity of the negative electrode.

[0020] According to some embodiments of this application, the thickness of the interface modification layer is 2μm-10μm. This improves the electronic conductivity of the negative electrode.

[0021] A second aspect of this application provides a method for preparing a sodium-ion battery cell. The method includes: mixing a matrix material, an oxygen-containing polymer, and a solvent; drying the mixture; forming a coating layer containing the oxygen-containing polymer on at least a portion of the surface of the matrix material to obtain a sodium-replenishing agent; forming a positive electrode film layer on at least one side of a positive electrode current collector, the positive electrode film layer including the sodium-replenishing agent; preparing a negative electrode sheet, the negative electrode sheet including a negative electrode current collector; and assembling the positive electrode sheet, the negative electrode sheet, and a separator into a sodium-ion battery cell. Therefore, the sodium-ion battery cell prepared by this method exhibits high initial charge specific capacity and excellent cycle performance.

[0022] According to some embodiments of this application, a method for preparing the positive electrode film layer includes: forming a positive electrode active material layer on at least one side of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material; mixing the matrix material, the oxygen-containing polymer, and the solvent to form a slurry; forming the slurry on the side of the positive electrode active material layer away from the positive electrode current collector; and drying it to form a pre-sodiumized layer. This simultaneously improves the energy density and cycle performance of the sodium secondary battery cell.

[0023] According to some embodiments of this application, the method further includes mixing the matrix material, the oxygen-containing polymer, the positive electrode conductive agent, and the solvent. This improves the electronic conductivity of the positive electrode.

[0024] According to some embodiments of this application, the method further includes the step of forming an interface modification layer on at least one side of the negative electrode current collector. This improves the electronic conductivity of the negative electrode.

[0025] A third aspect of this application provides a sodium supplement agent comprising a matrix, at least a portion of the surface of which has a coating layer comprising an oxygen-containing polymer. This improves the stability of the sodium supplement agent in air.

[0026] According to some embodiments of this application, the average thickness of the coating layer is 0.5 μm-20 μm. This improves the protective effect on the substrate and reduces the risk of the substrate coming into contact with air.

[0027] According to some embodiments of this application, the decomposition potential of the sodium supplement is less than or equal to 4.25V.

[0028] According to some embodiments of this application, the decomposition potential of the sodium supplement is 2.2V-4.25V.

[0029] This allows the sodium supplement to decompose and release active sodium ions at a lower potential, thus improving the sodium supplementation effect.

[0030] According to some embodiments of this application, the matrix includes Na2S, N a2 One or more of C2O4 and Na2C4O4. Therefore, the matrix materials of the above types have low decomposition potentials, which can further improve the sodium replenishment effect and enhance the cycle performance of sodium secondary battery cells.

[0031] According to some embodiments of this application, the average particle size of the sodium replenishing agent matrix is ​​0.5 μm-10 μm. This improves the sodium replenishment effect and enhances the cycle performance of the sodium-ion battery cell.

[0032] According to some embodiments of this application, the molecular weight of the oxygen-containing polymer is 5000-200000; the oxygen-containing polymer includes one or more of polyethylene oxide, polymethyl methacrylate, polyimide, polysiloxane, and polyetherketone. Therefore, the above-mentioned types of oxygen-containing polymers can improve the stability of the sodium supplement matrix while reducing the impact on the decomposition potential of the sodium supplement, thereby improving the sodium supplementation effect and enhancing the cycle performance of the sodium secondary battery cell.

[0033] A fourth aspect of this application provides a method for preparing a sodium supplement, the method comprising mixing a matrix material, an oxygen-containing polymer, and a solvent, followed by drying to obtain the sodium supplement. The sodium supplement prepared by this method exhibits excellent air stability.

[0034] According to some embodiments of this application, the method further includes mixing the matrix material, the oxygen-containing polymer, the positive electrode conductive agent, and the solvent. This improves the electronic conductivity of the sodium supplement.

[0035] The fifth aspect of this application provides an electrical device, including a sodium secondary battery cell provided in the first aspect of this application or a sodium secondary battery cell prepared by the method provided in the second aspect of this application.

[0036] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0037] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0038] Figure 1 This is a schematic diagram of a sodium secondary battery cell according to one embodiment of this application.

[0039] Figure 2 yes Figure 1 An exploded view of a sodium secondary battery cell according to an embodiment of this application is shown.

[0040] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0041] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0042] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0043] Figure 6 This is a schematic diagram of an electrical device using a sodium secondary battery cell as a power source according to an embodiment of this application.

[0044] Explanation of reference numerals in the attached figures:

[0045] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Sodium secondary battery cell; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0046] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0047] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0050] 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.

[0051] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0052] During the first charge of a battery, an SEI film forms on the negative electrode. This SEI formation irreversibly consumes active metal ions (such as sodium ions in sodium-ion batteries), deteriorating the cycle performance of the individual battery cell. Pre-sodiumization is a crucial method for improving the cycle performance of individual battery cells. Pre-sodiumization includes pre-sodiumization of both the positive and negative electrodes. Positive electrode pre-sodiumization involves adding a high-capacity sodium-containing material as a sodium replenisher to the positive electrode side. This material decomposes at a certain potential to release sodium ions, compensating for the lost sodium ions. During the preparation of the positive electrode sheet, the sodium replenisher, positive electrode active material, and solvent are mixed to form a slurry. The entire process of slurry stirring, coating, and cold pressing of the positive electrode sheet is exposed to air. The sodium replenisher has poor air stability and is easily oxidized and decomposed, reducing the initial charge capacity and cycle performance of the individual battery cell.

[0053] This application discloses a sodium secondary battery cell, wherein the positive electrode of the sodium secondary battery cell includes a sodium replenishing agent, and at least a portion of the surface of the sodium replenishing agent matrix has a coating layer, the coating layer comprising an oxygen-containing polymer, wherein the oxygen-containing polymer contains O 2- Sodium in sodium supplements +The strong interactions between them easily form chemical bonds, resulting in a more stable coating layer on the surface of the substrate. At the same time, the oxygen-containing polymer is a flexible organic material, which can better form a film on the surface of the substrate, reducing coating defects on the substrate surface, thereby improving the coating effect on the substrate, reducing direct contact between the substrate and air, improving the stability of the sodium replenishing agent in air, and enabling the sodium replenishing agent to effectively replenish sodium during the formation process, thereby improving the initial charge specific capacity and cycle performance of sodium secondary battery cells.

[0054] The sodium secondary battery cell proposed in this application can be used in electrical devices that use sodium secondary battery cells as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0055] The first aspect of this application provides a sodium secondary battery cell, the sodium secondary battery cell comprising a positive electrode sheet, the positive electrode sheet comprising 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 comprising a sodium supplement agent, the sodium supplement agent comprising a matrix, at least a portion of the surface of the matrix having a coating layer comprising an oxygen-containing polymer; a negative electrode sheet, the negative electrode sheet comprising a negative current collector; and a separator membrane disposed between the positive electrode sheet and the negative electrode sheet.

[0056] The sodium secondary battery cell proposed in this application has at least a portion of the surface of the sodium replenishment matrix having a coating layer formed by an oxygen-containing polymer, wherein the oxygen-containing polymer contains O 2- Sodium in sodium supplements + The strong interactions between them easily form chemical bonds, improving the stability of the coating layer. Simultaneously, the oxygen-containing polymer is a flexible organic material, which can improve the density of the coating layer, reduce coating defects on the substrate surface, and thus reduce the risk of direct contact between the sodium supplement agent matrix and air. This lowers the risk of moisture absorption or oxidation of the sodium supplement agent during the entire process of preparing the positive electrode sheet, allowing the sodium supplement agent to effectively decompose and release Na during the formation stage. + This improves the initial charge capacity and cycle performance of sodium secondary battery cells.

[0057] In this application, the longitudinal section of the positive electrode sheet along the thickness direction can be obtained by plasma, and the longitudinal section can be observed by scanning electron microscopy (SEM). The positive electrode active material and the sodium supplement can be distinguished by SEM and energy dispersive spectroscopy (EDS). The material containing Na and transition metal elements is the positive electrode active material, and the material containing Na, C, O, S and P elements is the sodium supplement. The oxygen-containing polymer in the sodium supplement coating layer can be confirmed by infrared spectroscopy.

[0058] According to some embodiments of this application, the sodium secondary battery cell deposits metallic sodium in situ on the negative electrode current collector during charging. That is, the sodium secondary battery cell can be a sodium metal battery cell without a negative electrode. Specifically, in the sodium metal battery cell without a negative electrode, no negative electrode active material is disposed on the negative electrode sheet; instead, a sodium metal layer is formed on the negative electrode current collector as the negative electrode active material during charging.

[0059] According to some embodiments of this application, in order to increase the content of positive electrode active material on the positive electrode sheet while setting a sodium supplement, the positive electrode film layer may include: a positive electrode active material layer, the positive electrode active material layer being located on at least one side of the positive electrode current collector, the positive electrode active material layer comprising positive electrode active material; and a pre-sodiumization layer, the pre-sodiumization layer being located on the side of the positive electrode active material layer away from the positive electrode current collector, the pre-sodiumization layer comprising the sodium supplement. Thus, while improving the sodium supplementation effect, the energy density of the sodium secondary battery cell is increased, and the cycle performance of the sodium secondary battery cell is improved.

[0060] In this application, the method for identifying the positive electrode active material layer and the pre-sodiumization layer is to obtain a longitudinal section of the positive electrode sheet along the thickness direction by plasma, and observe the longitudinal section by SEM. The positive electrode active material and the sodium supplement can be distinguished by SEM and EDS. The area enriched by the positive electrode active material is the positive electrode active material layer, and the area enriched by the sodium supplement is the pre-sodiumization layer.

[0061] According to some embodiments of this application, the average thickness of the coating layer can be 0.5 μm-20 μm. For example, it can be 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, or 20 μm, or any range of the above values. This improves the coating effect on the substrate and enhances the stability of the coating layer.

[0062] In this application, the cross-section of the positive electrode sheet along the thickness direction can be obtained by plasma, and at least 5 sodium supplement particles can be taken by SEM. The thickness of the coating layer at 4 points in the transverse and longitudinal directions of each particle can be measured. The average value of the 20 thickness data is the average thickness of the coating layer.

[0063] In this application, the decomposition potential of the sodium replenishing agent can be less than or equal to 4.25V. For example, it can be 4.25V, 4.1V, 4.0V, 3.9V, 3.8V, 3.7V, 3.6V, 3.5V, 3.4V, 3.3V, 3.2V, 3.1V, 3.0V, or 2.9V, or any range of the above values. Therefore, the lower decomposition potential of the sodium replenishing agent improves sodium replenishment efficiency. Simultaneously, since at least a portion of the matrix surface has a coating layer formed by an oxygen-containing polymer, the stability of the sodium replenishing agent matrix in air is improved, enabling the sodium replenishing agent to effectively replenish sodium during the formation stage, thereby improving the initial charge specific capacity and cycle performance of the sodium secondary battery cell. According to some specific embodiments of this application, the decomposition potential of the sodium replenishing agent is 2.2V-4.25V.

[0064] According to some embodiments of this application, the matrix may include one or more of Na2S, Na2C2O4, and Na2C4O4. Therefore, the above-mentioned sodium replenishing agents have low decomposition potentials, and their air stability is improved by forming oxygen-containing polymers on their surfaces, thereby obtaining sodium replenishing agents with low decomposition potentials and high air stability, thus improving the cycle performance of sodium secondary battery cells.

[0065] According to some embodiments of this application, the average particle size of the sodium replenishing agent matrix can be 0.5 μm-10 μm, for example, it can be 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, or 10 μm, or any range of the above values. This increases the sodium ion removal rate, improves the sodium replenishment effect of the sodium replenishing agent, and enhances the cycle performance of the sodium secondary battery cell.

[0066] In this application, the average particle size of the sodium supplement matrix can be measured by SEM. Specifically, a longitudinal section of the positive electrode sheet along its thickness direction is obtained by plasma. The SEM magnification is 30,000x. The diameter of the sodium supplement matrix is ​​calibrated using SEM, and the average value is taken after statistically analyzing the particle size of the sodium supplement matrix within the field of view.

[0067] According to some embodiments of this application, the molecular weight of the oxygen-containing polymer can be 5,000-600,000. For example, it can be 5,000, 10,000, 100,000, 200,000, 300,000, 400,000, 500,000, or 600,000, or any range of the above values. This improves the coating effect of the oxygen-containing polymer on the sodium supplement matrix, enhances the stability of the sodium supplement matrix, and improves the cycle performance of the sodium secondary battery cell.

[0068] According to some embodiments of this application, the oxygen-containing polymer includes one or more of polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyimide (PI), polysiloxane (PDMS), and polyetherketone (PEK). Therefore, the coating layer formed by the above-mentioned types of oxygen-containing polymers can improve the stability of the sodium supplement matrix while reducing the impact of the coating layer on sodium ion release, allowing the sodium supplement to still decompose and release sodium ions at low potentials, thereby improving the sodium supplement efficiency and enhancing the cycle performance of the sodium secondary battery cell.

[0069] According to some embodiments of this application, the oxygen-containing polymer includes PEO.

[0070] According to some embodiments of this application, the thickness of the pre-sodiumization layer can be 0.5μm-20μm, for example, it can be 0.5μm, 1μm, 5μm, 10μm, 15μm or 20μm, or any range of the above values. This improves the sodium replenishment effect.

[0071] According to some embodiments of this application, the pre-sodium layer further includes a positive electrode conductive agent. This improves the electronic conductivity of the positive electrode.

[0072] As an example, positive electrode conductive agents include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0073] According to some embodiments of this application, based on the total mass of the pre-sodiumized layer, the mass percentage of the sodium-replenishing agent is 30%-98%, for example, it can be 30%, 40%, 50%, 60%, 70%, 80%, 90%, 94%, 96%, or 98%, or any range of the above values. This increases the sodium-replenishing agent content in the positive electrode, improves the sodium-replenishing effect, and increases the initial charge specific capacity and cycle performance of the sodium secondary battery cell. According to some specific embodiments of this application, the mass percentage of the sodium-replenishing agent can be 50%-90%.

[0074] According to some embodiments of this application, based on the total mass of the pre-sodium layer, the mass percentage of the positive electrode conductive agent is 1%-40%, for example, it can be 1%, 5%, 10%, 20%, 30%, or 40%, or any range of the above values. This improves the electronic conductivity of the positive electrode. According to some specific embodiments of this application, the mass percentage of the positive electrode conductive agent is 5%-20%.

[0075] According to some embodiments of this application, based on the total mass of the pre-sodiumized layer, the mass percentage of the oxygen-containing polymer can be 1%-69%, for example, it can be 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, or 69%, or any range of the above values. This improves the coating effect on the sodium supplement matrix, reduces the risk of direct contact between the sodium supplement matrix and air, and improves the stability of the sodium supplement in air. According to some specific embodiments of this application, the mass percentage of the oxygen-containing polymer can be 5%-30%.

[0076] According to some embodiments of this application, the positive electrode active material includes Na. a Ni b Fe c Mn d M e O f Or Na x1 M1 y1 M2 y2 (X z2 O z3 ) z1 Z w One or two of the following are present: 0.85≤a≤1, 0≤b≤0.3, 0.3≤c≤0.4, 0.3≤d≤0.4, 0.02≤e≤0.1, 1.8≤f≤2; M includes one or more of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, Ir, and Ca; M1 includes one or more of Ti, V, Cr, Mn, Fe, Ca, Mg, Al, Nb, Co, and Zr; M2 includes Ni; X includes one or more of Si, S, P, As, B, Mo, W, and Ge; Z includes one or more of F, O, and OH; 2≤x1≤7, 1≤y1≤4, 0≤y2≤0.05, 0.2≤z2 / z3≤0.3, 1≤z1≤4, and 0≤w≤3. This improves the energy density of sodium-ion battery cells.

[0077] According to some embodiments of this application, the compaction density of the positive electrode sheet can be 1.6 g / cm³. 3 -3.5g / cm 3 .

[0078] When the positive electrode active material includes Na a Ni b Fe c Mn d M e O f At that time, the compaction density of the positive electrode sheet can be 2.8 g / cm³. 3 -3.5g / cm 3For example, it could be 2.8 g / cm³. 3 2.9g / cm 3 3.0g / cm 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 Or 3.5g / cm 3 The range can be any of the values ​​mentioned above. This increases the energy density of a single sodium-ion battery cell.

[0079] When the positive electrode active material includes Na x1 M1 y1 M2 y2 (X z2 O z3 ) z1 Z w At that time, the compaction density of the positive electrode sheet can be 1.6 g / cm³. 3 -2.5g / cm 3 For example, it could be 1.6 g / cm³. 3 1.8g / cm 3 2.0g / cm 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 Or 2.5g / cm 3 The range can be any of the values ​​mentioned above. This increases the energy density of a single sodium-ion battery cell.

[0080] In this application, the compaction density of the positive electrode sheet is determined by measuring the mass of the positive electrode sheet per unit area (g / cm³). 2 The positive electrode thickness (cm) was determined by the number of sampling points > 14. The compaction density PD of the positive electrode is calculated as: PD = (mass of the positive electrode per unit area, g / cm³) 2 ) / Thickness of positive electrode (cm).

[0081] According to some embodiments of this application, the coating weight of the positive electrode sheet can be 12 mg / cm³. 2 -20mg / cm 2 For example, it could be 12 mg / cm³ 2 14mg / cm 2 16mg / cm 2 18mg / cm 2 Or 20mg / cm 2 The range can be any of the values ​​mentioned above. This increases the energy density of a single sodium-ion battery cell.

[0082] It should be noted that the coating weight of the positive electrode film referred to here refers to the coating weight of the positive electrode film on one side of the positive electrode current collector.

[0083] In this application, a fixed-size mold is used to punch and coat the middle area and the tab area. The mass of the positive active material layer on both sides of the positive electrode sheet in the middle area is m1, and the mass of the positive film layer on both sides of the positive electrode sheet in the tab area is m2. The coating mass of one side of the positive film layer is ((m1-m2) / 2) / S, where S is the mold area.

[0084] According to some embodiments of this application, the negative electrode further includes an interface modification layer located on at least one side of the negative current collector, the interface modification layer comprising a negative electrode conductive agent and a binder. This improves the electronic conductivity of the negative electrode.

[0085] According to some embodiments of this application, the thickness of the interface modification layer can be 2μm-10μm. For example, it can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, or 10μm, or any range of the above values. This improves the electronic conductivity of the negative electrode.

[0086] In this application, the longitudinal section of the negative electrode sheet along its thickness direction is obtained by plasma, and the thickness of the interface modification layer is obtained by SEM.

[0087] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0088] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0089] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer 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 polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0091] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0092] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0093] In some embodiments of this application, when the sodium secondary battery cell is a sodium metal battery without a negative electrode, the electrolyte sodium salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, or sodium bis(trifluoromethanesulfonyl)imide.

[0094] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0095] 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.

[0096] In some embodiments, the sodium secondary battery cell also includes a separator. 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.

[0097] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0098] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0099] In some embodiments, the sodium secondary battery cell may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0100] In some embodiments, the outer packaging of a sodium secondary battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a sodium secondary battery cell can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0101] This application does not impose any particular limitation on the shape of the sodium secondary battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured sodium secondary battery cell, 5.

[0102] In some implementations, refer to Figure 2 The outer packaging 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 be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may 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 sodium secondary battery cell 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0103] In some embodiments, sodium secondary battery cells can be assembled into battery modules. The number of sodium secondary battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0104] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3In battery module 4, multiple sodium secondary battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple sodium secondary battery cells 5 can be secured with fasteners.

[0105] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple sodium secondary battery cells 5 are received.

[0106] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0107] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0108] A second aspect of this application provides a method for preparing a sodium-ion battery cell according to the first aspect of this application. The method includes: mixing a matrix material, an oxygen-containing polymer, and a solvent; drying the mixture; forming a coating layer containing the oxygen-containing polymer on at least a portion of the surface of the matrix to obtain a sodium supplement; forming a positive electrode film layer on at least one side of a positive current collector, the positive electrode film layer including the sodium supplement; preparing a negative electrode sheet including a negative current collector; and assembling the positive electrode sheet, the negative electrode sheet, and a separator into a battery. Thus, by mixing the matrix material and the oxygen-containing polymer solution and forming an oxygen-containing polymer coating layer on at least a portion of the surface of the matrix, the stability of the matrix is ​​improved during the formation stage, the sodium supplementation effect is enhanced, and the cycle performance of the sodium-ion battery cell is improved.

[0109] According to some embodiments of this application, a method for preparing the positive electrode film layer includes: forming a positive electrode active material layer on at least one side of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material; mixing the matrix material, the oxygen-containing polymer, and the solvent to form a slurry; forming the slurry on the side of the positive electrode active material layer away from the positive electrode current collector; and drying it to form a pre-sodium-modified layer. This increases the content of positive electrode active material on the positive electrode sheet, thereby increasing the energy density of the sodium secondary battery cell.

[0110] In some embodiments, the positive electrode active material layer can be prepared by dispersing the components used to prepare the positive electrode active material layer, such as positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0111] According to some embodiments of this application, a method for preparing the positive electrode film layer includes: forming a positive electrode active material layer on at least one side of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material; mixing the matrix material, the oxygen-containing polymer, the conductive agent, and the solvent to form a slurry; forming the slurry on the side of the positive electrode active material layer away from the positive electrode current collector; and drying it to form a pre-sodium-modified layer. This increases the content of positive electrode active material on the positive electrode sheet, thereby increasing the energy density of the sodium secondary battery cell. This also increases the electronic conductivity of the pre-sodium-modified layer.

[0112] As an example, the solvent used in preparing the pre-sodium layer slurry may include one or more of acetonitrile, dimethyl sulfoxide (DOL), and dimethylformamide (DMF).

[0113] According to some embodiments of this application, the method further includes the step of forming an interface modification layer on at least one side of the negative electrode current collector. Specifically, the material for forming the interface modification layer is mixed with a solvent to form a slurry, the slurry is formed on at least one side of the negative electrode current collector, and then subjected to processes such as drying and cold pressing to form the interface modification layer. This improves the electronic conductivity of the negative electrode sheet.

[0114] A third aspect of this application provides a sodium supplement agent comprising a matrix, at least a portion of the surface of which has a coating layer comprising an oxygen-containing polymer. This improves the stability of the sodium supplement agent in air.

[0115] According to some embodiments of this application, the average thickness of the coating layer is 0.5 μm-20 μm. For example, it can be 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, or 20 μm, or any range of the above values. This improves the coating effect on the substrate and enhances the stability of the coating layer.

[0116] According to some embodiments of this application, the decomposition potential of the sodium replenishing agent is less than or equal to 4.25V. For example, it can be 4.25V, 4.1V, 4.0V, 3.9V, 3.8V, 3.7V, 3.6V, 3.5V, 3.4V, 3.3V, 3.2V, 3.1V, 3.0V, or 2.9V, or a range of any of the above values. Therefore, the lower decomposition potential of the sodium replenishing agent improves sodium replenishment efficiency. Simultaneously, since at least a portion of the matrix surface has a coating layer formed by an oxygen-containing polymer, the stability of the sodium replenishing agent matrix in air is improved, enabling the sodium replenishing agent to effectively replenish sodium during the formation stage, thereby improving the initial charge specific capacity and cycle performance of the sodium secondary battery cell. According to some specific embodiments of this application, the decomposition potential of the sodium replenishing agent is 2.2V-4.25V.

[0117] This allows the sodium supplement to decompose and release active sodium ions at a lower potential, thus improving the sodium supplementation effect.

[0118] According to some embodiments of this application, the matrix includes Na2S, N a2 One or more of C2O4 and Na2C4O4. Therefore, the above-mentioned sodium supplements have low decomposition potentials, and their air stability is improved by forming oxygen-containing polymers on their surface, thus obtaining sodium supplements with low decomposition potentials and good air stability.

[0119] According to some embodiments of this application, the average particle size of the sodium replenishing agent matrix can be 0.5 μm-10 μm, for example, it can be 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, or 10 μm, or any range of the above values. This increases the sodium ion removal rate, improves the sodium replenishment effect of the sodium replenishing agent, and enhances the cycle performance of the sodium secondary battery cell.

[0120] According to some embodiments of this application, the molecular weight of the oxygen-containing polymer can be 5,000-600,000. For example, it can be 5,000, 10,000, 100,000, 200,000, 300,000, 400,000, 500,000, or 600,000, or any range of the above values. This improves the coating effect of the oxygen-containing polymer on the sodium supplement matrix, enhances the stability of the sodium supplement matrix, and improves the cycle performance of the sodium secondary battery cell.

[0121] According to some embodiments of this application, the oxygen-containing polymer includes one or more of polyethylene oxide, polymethyl methacrylate, polyimide, polysiloxane, and polyetherketone. Therefore, the coating layer formed by the above-mentioned types of oxygen-containing polymers can improve the stability of the sodium supplement matrix while reducing the impact of the coating layer on sodium ion release, allowing the sodium supplement to still decompose and release sodium ions at low potentials, thereby improving the sodium supplement efficiency and enhancing the cycle performance of the sodium secondary battery cell.

[0122] A fourth aspect of this application provides a method for preparing a sodium supplement, the method comprising mixing a matrix material, an oxygen-containing polymer, and a solvent, followed by drying to obtain the sodium supplement. The sodium supplement prepared by this method exhibits excellent air stability.

[0123] According to some embodiments of this application, the method further includes mixing the matrix material, the oxygen-containing polymer, the positive electrode conductive agent, and the solvent. This improves the electronic conductivity of the sodium supplement.

[0124] In addition, this application also provides an electrical device, which includes at least one of the battery, battery module, or battery pack provided in this application. The battery, battery module, or battery pack 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.

[0125] As the electrical equipment, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0126] 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 batteries, a battery pack or battery module can be used.

[0127] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0128] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0129] Example 1

[0130] 1. Positive electrode sheet

[0131] The positive electrode sheet includes a positive current collector aluminum foil, with positive active material layers on both surfaces of the aluminum foil. A pre-sodium coating layer is located on the surface of the positive active material layer away from the aluminum foil. Based on the total mass of the single-sided positive active material layer, the positive active material layer comprises 90% sodium iron pyrophosphate, 5% conductive carbon black (Super P), and 5% binder polyvinylidene fluoride (PVDF) by mass. Based on the total mass of the single-sided pre-sodium coating layer, the pre-sodium coating layer comprises 98% Na₂S, 1% Super P, and 1% PEO by mass. The average particle size of the sodium-supplementing matrix is ​​5 μm, and the compaction density of the positive electrode sheet is 2.1 g / cm³. 3 .

[0132] 2. Negative electrode plate

[0133] The negative electrode includes a negative current collector copper foil, and an interface modification layer on both surfaces of the copper foil. Based on the total mass of the interface modification layer on one side, the interface modification layer includes carbon nanotubes (CNTs) and sodium carboxymethyl cellulose (CMC-Na) with a mass ratio of 50% and 50% respectively, and the thickness of the interface modification layer is 5 μm.

[0134] 3. Electrolyte

[0135] The electrolyte consists of a solvent and an electrolyte salt. The solvent is dimethyl ethylene glycol (DME), and the electrolyte salt is NaPF6 with a molar concentration of 1 mol / L.

[0136] 4. Separating membrane

[0137] Polyethylene film.

[0138] 5. Sodium metal battery without negative electrode

[0139] It includes the positive electrode, the separator, the negative electrode, and the electrolyte.

[0140] Performance testing

[0141] 1. Initial Charge Capacity Test Method

[0142] At 25°C, the sodium metal battery without a negative electrode was first charged to 4.2V with a constant current of 0.1C, and then further charged to 0.05C with a constant voltage of 3.65V; the initial formation charge capacity parameters were collected.

[0143] 2. Cyclic Capacity Retention Test Method

[0144] At 25°C, the corresponding battery was charged to 3.65V at a constant current of 1 / 3C, then charged to 0.05C at a constant voltage of 3.65V. After resting for 30 minutes, it was discharged to 1.5V at 1 / 3C. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity C of the battery after the 200th cycle was recorded. n Then the battery capacity retention rate P n =C n / C0×100%.

[0145] Examples 2-6

[0146] The negative electrode, electrolyte, and separator in the sodium metal battery without a negative electrode are the same as in Example 1, except that the contents of the sodium-supplementing agent matrix, oxygen-containing polymer, and positive electrode conductive agent in the pre-sodiumization layer of the positive electrode are different.

[0147] Comparative Example 1

[0148] The negative electrode, electrolyte, and separator in the sodium metal battery without a negative electrode are the same as in Example 1, except that a pre-sodium coating layer is not provided on the positive electrode.

[0149] Comparative Example 2 and Comparative Example 3

[0150] The negative electrode, electrolyte, and separator in the sodium metal battery without a negative electrode are the same as in Example 1. The difference is that the sodium replenishing agent on the positive electrode is not coated and the content is different. Since the pre-sodiumization layer does not include PEO, the pre-sodiumization layer does not include a conductive agent.

[0151] The detailed differences between Examples 1-6 and Comparative Examples 1-3 are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] As can be seen from the comparison between Examples 1-6 and Comparative Examples 1-3, the sodium metal battery without a negative electrode proposed in this application has a higher initial charge specific capacity and cycle capacity retention rate. This indicates that by forming a PEO coating layer on the surface of the sodium-adding agent matrix, the air stability of the sodium-adding agent matrix can be improved throughout the entire process of slurry stirring, coating, and cold pressing of the positive electrode sheet, enabling it to decompose effectively and add sodium during the formation stage.

[0156] As can be seen from Examples 3-5, based on the total mass of the pre-sodium layer, when the mass percentage of the sodium supplement matrix is ​​50%-90%, the mass percentage of the oxygen-containing polymer is 5%-30%, and the mass percentage of the positive electrode conductive agent is 5%-20%, the sodium metal battery without a negative electrode has both a high initial charge specific capacity and a high cycle capacity retention rate.

[0157] Examples 7 and 8

[0158] The negative electrode, electrolyte, and separator in the sodium metal battery without a negative electrode are the same as in Example 1, except that the molecular weight of PEO is different.

[0159] Examples 9 and 10

[0160] The negative electrode, electrolyte, and separator in the sodium metal battery without a negative electrode are the same as in Example 1, except that the type of oxygen-containing polymer is different.

[0161] The detailed differences between Examples 7-10 are shown in Table 2.

[0162] Table 2

[0163]

[0164] As can be seen from Examples 3, 7 and 8, coating with PEO of different molecular weights can improve the initial charge specific capacity and cycle capacity retention of the sodium metal battery without a negative electrode, indicating that coating with PEO of different molecular weights has a good coating effect.

[0165] As can be seen from Examples 3, 9 and 10, coating with different types of oxygen-containing polymers can improve the initial charge capacity and cycle capacity retention of the sodium metal battery without a negative electrode, indicating that different types of oxygen-containing polymers have good coating effects.

[0166] Examples 11 and 12

[0167] The negative electrode, electrolyte, and separator in the sodium metal battery without a negative electrode are the same as in Example 1, except that the material of the sodium supplement matrix is ​​different.

[0168] Examples 13 and 14

[0169] The negative electrode, electrolyte, and separator in the non-negative electrode sodium metal battery are the same as in Example 1, except that the thickness of the pre-sodiumization layer is different.

[0170] The detailed differences between Examples 11-14 are shown in Table 3.

[0171] Table 3

[0172]

[0173] As can be seen from Examples 3, 11 and 12, for different sodium supplement matrix materials, oxygen-containing polymers can be used for coating to improve their air stability, thereby improving the initial charge specific capacity and cycle capacity retention of the sodium-free secondary battery.

[0174] As can be seen from Examples 3, 13 and 14, by forming a pre-sodium layer of different thickness on the positive electrode, the initial charge specific capacity and cycle capacity retention of the sodium-free secondary battery can be improved.

[0175] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium secondary battery cell, characterized in that, include: A positive electrode sheet, the positive electrode sheet comprising 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 comprising a sodium supplement agent, the sodium supplement agent comprising a matrix, at least a portion of the surface of the matrix having a coating layer, the coating layer comprising an oxygen-containing polymer; The negative electrode includes a negative current collector; A separator is disposed between the positive electrode and the negative electrode.

2. The sodium secondary battery cell according to claim 1, characterized in that, During charging, the sodium secondary battery cell deposits metallic sodium in situ on the negative electrode current collector to form sodium metal.

3. The sodium secondary battery cell according to claim 1 or 2, characterized in that, The positive electrode film layer includes: A positive electrode active material layer, wherein the positive electrode active material layer is located on at least one side of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material; A pre-sodium layer is located on the side of the positive electrode active material layer away from the positive electrode current collector, and the pre-sodium layer includes the sodium supplementing agent.

4. The sodium secondary battery cell according to any one of claims 1-3, characterized in that, The average thickness of the coating layer is 0.5μm-20μm.

5. The sodium secondary battery cell according to any one of claims 1-4, characterized in that, The decomposition potential of the sodium supplement is less than or equal to 4.25V.

6. The sodium secondary battery cell according to any one of claims 1-5, characterized in that, The decomposition potential of the sodium supplement is 2.2V-4.25V.

7. The sodium secondary battery cell according to any one of claims 1-6, characterized in that, The matrix includes Na2S and N. a2 One or more of C2O4 and Na2C4O4.

8. The sodium secondary battery cell according to any one of claims 1-7, characterized in that, The average particle size of the sodium supplement matrix is ​​0.5 μm-10 μm.

9. The sodium secondary battery cell according to any one of claims 1-8, characterized in that, One or two of the following conditions must be met: The molecular weight of the oxygen-containing polymer is 5,000-200,000; The oxygen-containing polymer includes one or more of polyethylene oxide, polymethyl methacrylate, polyimide, polysiloxane, and polyetherketone.

10. The sodium secondary battery cell according to any one of claims 3-9, characterized in that, The pre-sodium-treated layer also includes a positive conductive agent.

11. The sodium secondary battery cell according to any one of claims 3-10, characterized in that, The thickness of the pre-sodiumized layer is 0.5 μm-20 μm.

12. The sodium secondary battery cell according to claim 10 or 11, characterized in that, One or more of the following conditions must be met: Based on the total mass of the pre-sodiumized layer, the mass percentage of the sodium supplement is 30%-98%; Based on the total mass of the pre-sodium layer, the mass percentage of the positive electrode conductive agent is 1%-40%. Based on the total mass of the pre-sodiumized layer, the mass percentage of the oxygen-containing polymer is 1%-69%.

13. The sodium secondary battery cell according to any one of claims 10-12, characterized in that, One or more of the following conditions must be met: Based on the total mass of the pre-sodiumized layer, the mass percentage of the sodium supplement is 50%-90%; Based on the total mass of the pre-sodium layer, the mass percentage of the positive electrode conductive agent is 5%-20%. Based on the total mass of the pre-sodiumized layer, the mass percentage of the oxygen-containing polymer is 5%-30%.

14. The sodium secondary battery cell according to any one of claims 2-13, characterized in that, The positive electrode active material includes Na. a Ni b Fe c Mn d M e O f Or Na x1 M1 y1 M2 y2 (X z2 O z3 ) z1 Z w One or two of the following, wherein 0.85≤a≤1, 0≤b≤0.3, 0.3≤c≤0.4, 0.3≤d≤0.4, 0.02≤e≤0.1, 1.8≤f≤2, M includes one or more of Zn, V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Cu, Ru, Ir, Ca, M1 includes one or more of Ti, V, Cr, Mn, Fe, Ca, Mg, Al, Nb, Co, Zr, M2 includes Ni, X includes one or more of Si, S, P, As, B, Mo, W, Ge, Z includes one or more of F, O, OH, 2≤x1≤7, 1≤y1≤4, 0≤y2≤0.05, 0.2≤z2 / z3≤0.3, 1≤z1≤4, 0≤w≤3.

15. The sodium secondary battery cell according to any one of claims 1-14, characterized in that, One or two of the following conditions must be met: The compaction density of the positive electrode sheet is 1.6 g / cm³. 3 -3.5g / cm 3 ; The coating weight of the positive electrode sheet is 12 mg / cm³. 2 -20mg / cm 2 .

16. The sodium secondary battery cell according to any one of claims 1-15, characterized in that, The negative electrode sheet further includes an interface modification layer, which is located on at least one side of the negative electrode current collector, and the interface modification layer includes a negative electrode conductive agent and a binder.

17. The sodium secondary battery cell according to claim 16, characterized in that, The thickness of the interface modification layer is 2μm-10μm.

18. A method for preparing sodium secondary battery cells, characterized in that, include: A base material, an oxygen-containing polymer, and a solvent are mixed and dried to form a coating layer with the oxygen-containing polymer on at least a portion of the surface of the base material, thereby obtaining a sodium supplement. A positive electrode film layer is formed on at least one side of the positive electrode current collector, the positive electrode film layer including the sodium supplementing agent; Prepare a negative electrode sheet, wherein the negative electrode sheet includes a negative current collector; The positive electrode, the negative electrode, and the separator are assembled into a sodium secondary battery cell.

19. The method according to claim 18, characterized in that, The method for preparing the positive electrode film includes: A positive electrode active material layer is formed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material; The matrix material, the oxygen-containing polymer, and the solvent are mixed to form a slurry. The slurry is formed on the side of the positive electrode active material layer away from the positive electrode current collector and then dried to form a pre-sodiumized layer.

20. The method according to claim 18 or 19, characterized in that, Also includes: The matrix material, the oxygen-containing polymer, the positive electrode conductive agent, and the solvent are mixed.

21. The method according to any one of claims 18-20, characterized in that, Also includes: The step of forming an interface modification layer on at least one side of the negative electrode current collector.

22. A sodium supplement, characterized in that, It includes a matrix, at least a portion of the surface of which has a coating layer comprising an oxygen-containing polymer.

23. The sodium supplement according to claim 22, characterized in that, The average thickness of the coating layer is 0.5μm-20μm.

24. The sodium supplement according to claim 22 or 23, characterized in that, The decomposition potential of the sodium supplement is less than or equal to 4.25V.

25. The sodium supplement according to any one of claims 22-24, characterized in that, The decomposition potential of the sodium supplement is 2.2V-4.25V.

26. The sodium supplement according to any one of claims 22-25, characterized in that, The matrix includes Na2S and N. a2 One or more of C2O4 and Na2C4O4.

27. The sodium supplement according to any one of claims 22-26, characterized in that, The average particle size of the sodium supplement matrix is ​​0.5 μm-10 μm.

28. The sodium supplement according to any one of claims 22-27, characterized in that, The oxygen-containing polymer includes one or more of polyethylene oxide, polymethyl methacrylate, polyimide, polysiloxane, and polyetherketone.

29. A method for preparing a sodium supplement, characterized in that, The method includes mixing a matrix material, an oxygen-containing polymer, and a solvent, and then drying them to obtain the sodium supplement.

30. The method according to claim 29, characterized in that, The matrix material, the oxygen-containing polymer, the positive electrode conductive agent, and the solvent are mixed.

31. An electrical appliance, characterized in that, Includes the sodium secondary battery cell according to any one of claims 1-17 or the sodium secondary battery cell prepared by the method according to any one of claims 18-21.

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