A sodium-ion battery cell, battery device, and power-using device

Abstract

This application provides a sodium-ion battery cell, a battery device, and an electrical device. The sodium-ion battery cell includes an electrolyte, a negative electrode, and a positive electrode. The negative electrode includes a negative current collector and a negative electrode film. The negative electrode film includes a carbon-based material, which comprises a graphite-like sheet and a porous structure. The sodium-ion battery cell provided in this application has better rate performance.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to PCT international application PCT / CN2025 / 110447, filed on July 24, 2025, entitled “A sodium-ion battery cell and related devices thereof,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a sodium-ion battery cell, a battery device, and an electrical device. Background Technology

[0004] In recent years, with the gradual development and application of lithium-ion batteries from portable electronic devices to high-power electric vehicles, large-scale energy storage power stations, and smart grids, the demand for metallic lithium has been increasing across various industries. However, with the depletion of metallic lithium reserves and the increasing difficulty of mining, current metallic lithium resources can no longer meet the needs of the lithium battery industry. Sodium, which belongs to the same group as lithium, has similar chemical properties to lithium and is abundant. Therefore, sodium-ion batteries, which operate on a similar principle to lithium-ion batteries, are currently being developed, with the expectation that they will serve as an important supplement to lithium-ion batteries in large-scale energy storage applications.

[0005] Sodium batteries have better low-temperature discharge performance. However, how to improve the rate performance of sodium batteries is a problem that urgently needs to be solved. Summary of the Invention

[0006] This application is made in view of the above-mentioned issues, and its purpose is to provide a sodium-ion battery cell, battery device and power supply device with better rate performance.

[0007] To achieve the above objectives, this application provides a sodium-ion battery cell, a battery device, and an electrical device.

[0008] The first aspect of this application provides a sodium-ion battery cell, including an electrolyte, a negative electrode, and a positive electrode; wherein the conductivity C of the electrolyte at 25±1℃ satisfies: 7mS / cm≤C≤20mS / cm; the negative electrode includes a negative current collector and a negative electrode film layer, the thickness L of the negative electrode film layer on one side of the negative current collector satisfies: 140μm≤L≤250μm; the negative electrode film layer includes a carbon-based material, the carbon-based material including multiple graphite-like sheet layers and multiple pore structures; at least some of the graphite-like sheet layers form an interlayer spacing between two graphite-like sheet layers, the interlayer spacing satisfies the volume H1 of the space between 0.35nm-0.4nm and the total volume H of the space between the multiple graphite-like sheet layers satisfies: 20%≤H1 / H≤60%; the pore volume V1 of the pore structure with a pore size of 5nm-10nm in the carbon-based material, measured by nitrogen adsorption method, and the total pore volume V in the pore structure satisfy: 2%≤V1 / V≤15%.

[0009] In some implementations, H1 and H satisfy the following condition: 40% ≤ H1 / H ≤ 60%.

[0010] In this embodiment, the spatial proportion of graphite-like sheets with large interlayer spacing in the carbon-based material is within the aforementioned range, which can increase the extraction rate of sodium ions in the carbon-based material. Simultaneously, the pore volume proportion of larger-diameter pores in the carbon-based material is within the aforementioned range, which can shorten the diffusion path of sodium ions from the interior to the surface of the carbon-based material, thereby effectively extending the capacity plateau near the 0.1V cutoff voltage. This improves the effective capacity of the sodium-ion battery cell while also slowing down the rise in negative electrode potential. Furthermore, a thinner negative electrode film layer can also increase the transport rate of sodium ions in the negative electrode. In summary, this reduces the charge transfer impedance of the negative electrode. Further, an electrolyte with higher conductivity can increase the transport rate of sodium ions in the electrolyte at low temperatures. Combining the above technical solutions, sodium ions extracted from the carbon-based material can reach the positive electrode interface more quickly to participate in the reaction, resulting in better rate performance for the sodium-ion battery cell.

[0011] In some implementations, the volume H2 of the space with an interlayer spacing greater than 0.4 nm and the volume H of the total space formed by multiple graphite-like layers satisfy: 30% ≤ H2 / H ≤ 58%.

[0012] In the embodiments of this application, the spatial proportion of the graphite-like sheets with a large interlayer spacing in the carbon-based material is within the above-mentioned range, which can further increase the extraction rate of sodium ions in the carbon-based material, reduce the charge transfer resistance of the negative electrode sheet, and allow the sodium ions extracted from the carbon-based material to reach the positive electrode interface more quickly to participate in the reaction, thereby achieving better rate performance of the sodium-ion battery cell.

[0013] In some implementations, the volume H3 of the space where the interlayer spacing is less than 0.35 nm and the volume H of the total space formed by the multiple graphite-like layers satisfy: 0% ≤ H3 / H ≤ 22%.

[0014] In the embodiments of this application, graphite-like sheets with an interlayer spacing of less than 0.35 nm are difficult to store sodium due to their small space. However, these graphite-like sheets can provide slip, which is beneficial for improving the compaction density of the negative electrode. Therefore, by controlling the proportion of graphite-like sheets with a small interlayer spacing in the carbon-based material within the above-mentioned range, the compaction density of the negative electrode can be improved without significantly reducing the extraction rate of sodium ions in the carbon-based material.

[0015] In some implementations, V1 and V satisfy: 8% ≤ V1 / V ≤ 15%.

[0016] In some embodiments, the pore volume V2 of the carbon-based material with a pore size of less than or equal to 2 nm, as measured by nitrogen adsorption, and the total pore volume V in the pore structure satisfy: 4.5% ≤ V2 / V ≤ 30%.

[0017] In some implementations, 10% ≤ V2 / V ≤ 18%.

[0018] In the embodiments of this application, the proportion of the pore volume of the micropores in the total pore volume is within the above-mentioned range, which is beneficial to improving the capacity of the sodium-ion battery.

[0019] In some embodiments, the pore volume V3 of the pore structure with a pore size of 1nm-2nm in the carbon-based material, as measured by nitrogen adsorption, and the total pore volume V in the pore structure satisfy the following condition: 5%≤V3 / V≤15%.

[0020] In the embodiments of this application, in the pore structure design of carbon-based materials, pores with a diameter less than 1 nm have poor ion intercalation capability, affecting the fast-charging performance of sodium-ion battery cells. A proportion of pores with a diameter between 1 nm and 2 nm within this range can balance the fast-charging performance of sodium-ion battery cells.

[0021] In some embodiments, the pore volume V4 of the pore structure with a pore size greater than 2 nm and less than 5 nm in the carbon-based material, as measured by nitrogen adsorption, satisfies the following condition: 3.5% ≤ V4 / V ≤ 30%.

[0022] In the embodiments of this application, in the pore structure design of the carbon-based material, pores with a diameter greater than 2 nm and less than 5 nm have better ion-intercalation capabilities, which is beneficial to the fast-charging performance of sodium-ion battery cells. Therefore, the proportion of pores with a diameter greater than 2 nm and less than 5 nm within the above range can take into account the fast-charging performance of sodium-ion battery cells.

[0023] In some embodiments, the carbon-based material contains pores with a pore size in the range of 1.0 nm to 1.5 nm, as determined by nitrogen adsorption. The maximum value of the derivative of the cumulative pore volume V0 with respect to the logarithm of the pore size D, dV0 / d(logD), is between 0.001 cm3 / (g·log(nm)) and 0.009 cm3 / (g·log(nm)).

[0024] In the embodiments of this application, the carbon-based material has an optimized pore structure. Specifically, the characteristic dV0 / d(logD) of the pores with a diameter of 1.0nm-1.5nm corresponds to the pore volume contributed by its unit pore diameter, and its maximum value is in the range of 0.001cm3 / (g·log(nm))-0.009cm3 / (g·log(nm)), which is beneficial to reduce gas generation and bubbling during the pulping process.

[0025] In some embodiments, the maximum value of dV0 / d(logD) for pores with a diameter of 1.0 nm to 1.5 nm in the carbon-based material is 0.001 cm. 3 / (g·log(nm))-0.006cm 3 / (g·log(nm)), which is more conducive to reducing gas generation and bubbling during the pulping process.

[0026] In some embodiments, the powder compaction density T of the negative electrode sheet at 2T satisfies: 0.8 g / cm³ 3 ≤T≤1.0g / cm 3 .

[0027] In the embodiments of this application, when the energy density is satisfied and the powder compaction is controlled within the above range, the electrode can have a higher porosity, which increases the contact area between the negative electrode and the electrolyte. Sodium ions can migrate more smoothly through the pores to the surface of the negative electrode active material, reducing the migration resistance from the liquid phase to the solid phase, reducing the charge transfer impedance of the negative electrode, and improving the discharge power of the sodium-ion battery cell.

[0028] In some implementations, the film resistance R of the negative electrode plate satisfies: 60mΩ≤R≤170mΩ.

[0029] In the embodiments of this application, a suitable range of negative electrode film resistance can enable the negative electrode to have higher conductivity and reduce the charge transfer impedance of the negative electrode.

[0030] In some implementations, the negative electrode film layer also includes carbon nanotubes.

[0031] In the embodiments of this application, carbon nanotubes in the negative electrode film can improve electron conduction efficiency, optimize ion diffusion dynamics, reduce charge transfer impedance of the negative electrode sheet, and increase the discharge power of a sodium-ion battery cell by constructing a three-dimensional conductive network.

[0032] In some embodiments, the positive electrode includes a positive current collector, which includes a metal foil and / or a composite current collector.

[0033] In some embodiments, the positive electrode includes a positive active material layer, which includes at least one of the following: sodium transition metal oxide, polyanionic compound, or Prussian blue compound.

[0034] In some embodiments, the transition metal in the sodium transition metal oxide includes at least one of the following: Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, Ce.

[0035] In some embodiments, the sodium transition metal oxide has the general formula Na x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0036] In some embodiments, the sodium transition metal oxide includes at least one of the following: copper-iron-manganese-based oxide, nickel-iron-manganese-based oxide, and ternary oxide.

[0037] In some embodiments, the polyanionic compound includes at least one of the following: phosphate, sulfate, or fluorophosphate.

[0038] In some embodiments, Prussian blue compounds include iron-based Prussian blue and / or manganese-based Prussian blue.

[0039] In some embodiments, the positive electrode active material layer further includes a binder, which includes at least one of the following: polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0040] In some embodiments, the positive electrode active material layer further includes a conductive agent, which includes at least one of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite-like materials, and carbon nanofibers.

[0041] In some embodiments, the sodium-ion battery cell further includes: a housing, which is a hollow structure with an opening, and the electrolyte, negative electrode, and positive electrode are housed within the housing; and a top cover that closes the opening.

[0042] A second aspect of this application provides a battery device including a sodium-ion battery cell from the first aspect of this application.

[0043] A third aspect of this application provides an electrical device comprising a sodium-ion battery cell according to the first aspect of this application and / or a battery device according to the second aspect of this application. The electrical device is used in fields such as new energy vehicles, drones and robots, smart grids, data centers, renewable energy storage, large-scale energy storage systems, and power starters and power tools. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of a sodium-ion battery cell according to one embodiment of this application.

[0045] Figure 2 This is a schematic diagram of a sodium-ion battery cell according to one embodiment of this application.

[0046] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0047] Figure 4 This is a schematic diagram of a battery device according to one embodiment of this application.

[0048] Figure 5 yes Figure 4 An exploded view of a battery device according to an embodiment of this application is shown.

[0049] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0050] Figure 7 The pore size distribution of the hard carbon anode active material prepared in Example 8 of this application is measured by nitrogen adsorption method.

[0051] Figure 8 The pore size distribution of the hard carbon anode active material prepared in Example 9 of this application is measured by nitrogen adsorption method.

[0052] Explanation of reference numerals in the attached figures:

[0053] 1 Battery assembly; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Sodium-ion battery cell; 51 Negative electrode; 52 Separator; 53 Positive electrode. Detailed Implementation

[0054] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrode plates, battery cells, battery modules, battery devices, and power-consuming devices of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0055] 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.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0058] 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.

[0059] Specifically, the term "graphite-like sheet" can refer to a localized layered structure composed of carbon atoms in a carbon-based material, or it can refer to "graphite-like microcrystals," "pseudo-graphitic domains," disordered stacked carbon sheets, symbiotic large-area graphite-like crystals, or "amorphous carbon" and / or "difficult-to-graphitize carbon" as defined in current national standards (such as GB / T 43114-2023 Hard Carbon).

[0060] Specifically, the term "volume of space" refers to the size of the space formed between adjacent graphite sheets.

[0061] In recent years, with the gradual development and application of lithium-ion batteries from portable electronic devices to high-power electric vehicles, large-scale energy storage power stations, and smart grids, the demand for metallic lithium has been increasing across various industries. However, with the depletion of metallic lithium reserves and the increasing difficulty of mining, current metallic lithium resources can no longer meet the needs of the lithium battery industry. Sodium, which belongs to the same group as lithium, has similar chemical properties to lithium and is abundant. Therefore, sodium-ion batteries, which operate on a similar principle to lithium-ion batteries, are currently being developed, with the expectation that they will serve as an important supplement to lithium-ion batteries in large-scale energy storage applications.

[0062] During their research on the performance of sodium-ion batteries, the applicant discovered that sodium batteries exhibit better low-temperature discharge performance. However, in high-power discharge scenarios, sodium batteries sometimes perform poorly, limiting their use in these situations. One manifestation of this is that sodium batteries cannot output high power when they retain a certain amount of charge, especially after repeated discharges, making it difficult to start the power supply and requiring frequent charging to meet user needs, resulting in a poor user experience. One reason for this phenomenon is that the negative electrode potential may rise rapidly during high-power output, thus reducing the voltage difference between the positive and negative electrodes of the sodium battery, leading to discharge cutoff. Ultimately, this manifests macroscopically as the sodium battery having charge but being unable to output a large current. Furthermore, after a period of use, sodium batteries also fail to discharge at the preset rate, with performance declining sharply, affecting normal use.

[0063] The applicant recognized that the main bottleneck restricting the high-power performance of sodium batteries lies in the excessive charge transfer impedance of the negative electrode. Simultaneously, the applicant also discovered that the electrolyte liquid-phase diffusion impedance also affects the high-power discharge of sodium batteries. While the bottleneck for sustained high-current discharge in sodium batteries is primarily the charge transfer impedance on the surface of the negative electrode active material in the short term, the diffusion impedance has a significant impact during long-term discharge. This is because the liquid-phase diffusion impedance accumulates during the discharge process, further exacerbating polarization within the battery and affecting the discharge power of the sodium-ion battery. Simply reducing the charge transfer impedance of the negative electrode without increasing the migration rate of sodium ions in the electrolyte will not achieve instantaneous high-current discharge in sodium batteries. In summary, the bottleneck to achieving high-rate discharge performance in sodium batteries lies in simultaneously reducing the electron transfer impedance on the negative electrode surface and the liquid-phase diffusion impedance; only by solving these bottlenecks can high-current discharge be achieved.

[0064] In view of this, embodiments of this application provide a sodium-ion battery cell, including an electrolyte, a negative electrode, and a positive electrode; wherein, the conductivity C of the electrolyte at 25±1℃ satisfies: 7mS / cm≤C≤20mS / cm; the negative electrode includes a negative current collector and a negative electrode film, the thickness L of the negative electrode film on one side of the negative current collector satisfies: 140μm≤L≤250μm; the negative electrode film includes a carbon-based material, the carbon-based material including multiple graphite-like sheet layers and multiple pore structures; at least some of the graphite-like sheet layers form an interlayer spacing between two graphite-like sheet layers, the interlayer spacing satisfies the following: the volume H1 of the space of 0.35nm-0.4nm and the volume H of the total space formed by the multiple graphite-like sheet layers satisfy: 20%≤H1 / H≤60%; the pore volume V1 of the pore structure with a pore size of 5nm-10nm in the carbon-based material, measured by nitrogen adsorption method, and the total pore volume V in the pore structure satisfy: 8%≤V1 / V≤15%. The sodium-ion battery cell provided in this application embodiment can have better rate performance.

[0065] The applicant discovered that the selection of the negative electrode material significantly affects the surface reaction polarization process of the negative electrode. Improving the surface reaction polarization can smooth the potential rise during negative electrode discharge, maintaining a sufficient voltage difference between the positive and negative electrodes and preventing the voltage from dropping to the cutoff voltage, thus preventing discharge. The applicant also discovered that the microstructure of the negative electrode material significantly affects the surface reaction polarization process of the negative electrode.

[0066] Currently, the mainstream anode material used in sodium batteries is carbon-based material. During the anode selection process, the applicant discovered that increasing the spatial volume ratio of large-interlayer graphite-like layers and reducing macropores in carbon-based materials can improve the surface reaction polarization process of the anode.

[0067] In the interlayer structure design of carbon-based materials, the interlayer spacing between graphene-like sheets affects the overall extraction rate of sodium ions. When the interlayer spacing of graphene-like sheets is larger, the volume of space between layers is greater, making it easier for sodium ions to extract from the carbon-based material. Simultaneously, in the pore structure design of carbon-based materials, the pore size affects the transport path of sodium ions from the interior to the surface. Pores with a diameter of 5nm-10nm (also known as mesopores) have fewer active sites, but larger pores often connect to micropores and pinholes, which have more active sites. Therefore, ions typically migrate to sites with active sites through macropores. Therefore, reducing the proportion of 5nm-10nm pores can effectively shorten the transport path of sodium ions from the interior to the surface of carbon-based materials, facilitating sodium ion extraction. The specific mechanism is speculated to be: hard carbon contains graphene domains (ordered graphene sheets), and different sizes of open or closed pores are formed by the winding of graphene sheets. In hard carbon materials, the capacity is primarily provided by micropores (<2 nm) through surface adsorption and micropore filling (accounting for approximately 60%-80%). Larger mesopores (2-8 nm) are less likely to form stable electrochemical storage sites, and therefore these larger pores often inevitably connect to micropores and small pores. Consequently, ions need to migrate through the macroporous structure to reach active sites. Therefore, controlling the volume fraction of macropores shortens the migration path of ions from the material's interior to the surface, allowing for faster ion extraction. Furthermore, increasing the spatial proportion of larger interlayer spacing can further facilitate rapid ion extraction from the material's interior.

[0068] In summary, by adjusting the interlayer spacing and pore design of the negative electrode material, the ability of ions to escape from the negative electrode can be improved, allowing more ions to escape and enter the electrolyte per unit time. At the same time, the electrolyte has a high ionic conductivity, and when combined with a negative electrode film of appropriate thickness, sodium ions that escape from the carbon-based material can reach the positive electrode interface more quickly to participate in the reaction, avoiding electron accumulation that causes polarization, reducing charge transfer impedance and liquid phase diffusion impedance, improving the battery polarization process, and increasing the battery power density.

[0069] The sodium-ion battery cell, battery module, battery, and power-consuming device of this application are described below with appropriate reference to the accompanying drawings.

[0070] Typically, a sodium-ion battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0071] Sodium-ion battery cell

[0072] In one embodiment of this application, a sodium-ion battery cell 5 is proposed. Figure 1 This is a schematic diagram of the structure of a sodium-ion battery cell according to one embodiment of this application. The sodium-ion battery cell 5 includes a negative electrode 51, a separator 52, a positive electrode 53, and an electrolyte. The conductivity C of the electrolyte at 25±1℃ satisfies: 7mS / cm≤C≤20mS / cm.

[0073] The conductivity C can be 7 mS / cm, 10 mS / cm, 15 mS / cm, 20 mS / cm or any value within the above range.

[0074] The negative electrode 51 includes a negative electrode current collector and a negative electrode film layer, the negative electrode film layer being disposed on at least one side of the surface of the negative electrode current collector; the thickness L of the negative electrode film layer on one side of the negative electrode current collector satisfies: 140μm≤L≤250μm; the negative electrode film layer includes a carbon-based material, the carbon-based material including multiple graphite-like sheet layers and multiple pore structures; at least some of the graphite-like sheet layers form an interlayer spacing between two graphite-like sheet layers, the interlayer spacing satisfies the following: the volume H1 of the space of 0.35nm-0.4nm and the volume H of the total space formed by the multiple graphite-like sheet layers satisfy: 20%≤H1 / H≤60%; the pore volume V1 of the pore structure with a pore size of 5nm-10nm in the carbon-based material, measured by nitrogen adsorption method, and the total pore volume V in the pore structure satisfy: 2%≤V1 / V≤15%.

[0075] Optionally, 40% ≤ H1 / H ≤ 60%.

[0076] Optionally, 8% ≤ V1 / V ≤ 15%.

[0077] L can be 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, or any value within the above range. H1 / H can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any value within the above range. V1 / V can be 2%, 6%, 8%, 10%, 14%, 15%, or any value within the above range.

[0078] Specifically, the negative electrode film layer is disposed on at least one side of the surface of the negative electrode current collector. As an example, the negative electrode current collector may have two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0079] In this embodiment, the spatial proportion of graphite-like sheets with large interlayer spacing in the carbon-based material is within the aforementioned range, which can increase the extraction rate of sodium ions in the carbon-based material. Simultaneously, the pore volume proportion of larger-diameter pores in the carbon-based material is within the aforementioned range, which can shorten the diffusion path of sodium ions from the interior to the surface of the carbon-based material, thereby effectively extending the plateau capacity near the cutoff voltage of 0.1V. This increases the effective capacity of the sodium-ion battery cell while also slowing down the rise of the negative electrode potential. Furthermore, a thinner negative electrode film layer can also increase the transport rate of sodium ions in the negative electrode. In summary, this reduces the charge transfer impedance of the negative electrode. Further, an electrolyte with higher conductivity can increase the transport rate of sodium ions in the electrolyte at low temperatures. Combining the above technical solutions, sodium ions extracted from the carbon-based material can reach the positive electrode interface more quickly to participate in the reaction, achieving better rate performance in the sodium-ion battery cell.

[0080] In some implementations, the volume H2 of the space with an interlayer spacing greater than 0.4 nm and the volume H of the total space formed by multiple graphite-like layers satisfy: 30% ≤ H2 / H ≤ 58%.

[0081] H2 / H can be 30%, 35%, 40%, 45%, 50%, 55%, 58%, or any value within the above range.

[0082] In the embodiments of this application, the spatial proportion of the graphite-like sheets with a large interlayer spacing in the carbon-based material is within the above-mentioned range, which can further increase the extraction rate of sodium ions in the carbon-based material, reduce the charge transfer resistance of the negative electrode sheet, and allow the sodium ions extracted from the carbon-based material to reach the positive electrode interface more quickly to participate in the reaction, thereby achieving better rate performance of the sodium-ion battery cell.

[0083] In some implementations, the volume H3 of the space where the interlayer spacing is less than 0.35 nm and the volume H of the total space formed by the multiple graphite-like layers satisfy: 0% ≤ H3 / H ≤ 22%.

[0084] H3 / H can be 0%, 5%, 10%, 15%, 20%, 22%, or any value within the above range.

[0085] In the embodiments of this application, graphite-like sheets with an interlayer spacing of less than 0.35 nm are difficult to store sodium due to their small space. However, these graphite-like sheets can provide slip, which is beneficial for improving the compaction density of the negative electrode. Therefore, by controlling the proportion of graphite-like sheets with a small interlayer spacing in the carbon-based material within the above-mentioned range, the compaction density of the negative electrode can be improved without significantly reducing the extraction rate of sodium ions in the carbon-based material.

[0086] In some embodiments, the pore volume V2 of the carbon-based material with a pore size of less than or equal to 2 nm, as measured by nitrogen adsorption, and the total pore volume V in the pore structure satisfy the following condition: 4.5% ≤ V2 / V ≤ 30%. Optionally, 10% ≤ V2 / V ≤ 18%.

[0087] V2 / V can be 4.5%, 5%, 10%, 15%, 18%, 20%, 25%, 30%, or any value within the above range.

[0088] In the embodiments of this application, the proportion of the pore volume of the micropores in the total pore volume is within the above-mentioned range, which is beneficial to improving the capacity of the sodium-ion battery.

[0089] In some embodiments, the pore volume V3 of the pore structure with a pore size of 1nm-2nm in the carbon-based material, as measured by nitrogen adsorption, and the total pore volume V in the pore structure satisfy the following condition: 5%≤V3 / V≤15%.

[0090] V3 / V can be 5%, 10%, 15%, or any value within the above range.

[0091] In the embodiments of this application, in the pore structure design of carbon-based materials, pores with a diameter less than 1 nm have poor ion intercalation capability, affecting the fast-charging performance of sodium-ion battery cells. A proportion of pores with a diameter between 1 nm and 2 nm within this range can balance the fast-charging performance of sodium-ion battery cells.

[0092] In some embodiments, the pore volume V4 of the pore structure with a pore size greater than 2 nm and less than 5 nm in the carbon-based material, as measured by nitrogen adsorption, satisfies the following condition: 3.5% ≤ V4 / V ≤ 30%.

[0093] V4 / V can be 3.5%, 5%, 10%, 15%, 20%, 24%, 25%, 30%, or any value within the above range.

[0094] In the embodiments of this application, in the pore structure design of the carbon-based material, pores with a diameter greater than 2 nm and less than 5 nm have better ion-intercalation capabilities, which is beneficial to the fast-charging performance of sodium-ion battery cells. Therefore, the proportion of pores with a diameter greater than 2 nm and less than 5 nm within the above range can take into account the fast-charging performance of sodium-ion battery cells.

[0095] This disclosure proposes that pores with a diameter of 1.0 nm to 1.5 nm have a significant impact on continuous gas production and bubbling. By controlling the pore size within this specific range, the maximum value of the derivative of the cumulative pore volume V0 with respect to the logarithm of the pore diameter D, dV0 / d(logD), can be achieved within 0.001 cm⁻¹. 3 / (g·log(nm))-0.009cm 3 The value of / (g·log(nm)) can significantly reduce continuous bubbling. Studies have found that larger pore sizes (pores larger than 1.5 nm) have less impact on processability, presumably because the bubbling duration caused by these pores is shorter. Smaller pore sizes (pores smaller than 1.0 nm) may have limited impact on processability due to their smaller gas storage capacity. However, by limiting the maximum value of the volume contribution change rate (dV0 / d(logD)) for pores with diameters between 1.0 nm and 1.5 nm to within the aforementioned range, gas generation and bubbling during pulping can be effectively reduced, while also considering the sodium storage effect of this type of pore size.

[0096] For example, the maximum value of dV0 / d(logD) for a pore with a diameter of 1.0 nm to 1.5 nm is 0.001 cm. 3 / (g·log(nm)), 0.002cm 3 / (g·log(nm)), 0.003cm 3 / (g·log(nm)), 0.004cm 3 / (g·log(nm)), 0.005cm 3 / (g·log(nm)), 0.006cm 3 / (g·log(nm)), 0.007cm 3 / (g·log(nm)), 0.008cm 3 / (g·log(nm)), 0.009cm 3 / (g·log(nm)) can be any value between any two of these values.

[0097] The dV0 / d(logD) mentioned in this disclosure reflects the pore volume contributed per unit pore size. This value can be obtained by measuring carbon-based materials using conventional methods in the art. For example, it can be determined using a surface area analyzer-static volumetric method. Specifically, according to embodiments of this disclosure, a flow-type gas adsorption surface area measuring device (device model Micromeritics ASAP-2460) can be used to measure the adsorption and desorption isotherms of nitrogen adsorption, and a DFT model can be used to fit the distribution curve of dV0 / d(logD) relative to the pore size D, with the maximum value read in the pore size range of 1.0-1.5 nm. The carbon-based material can be a carbon-based material used as a raw material, or it can be a carbon-based material obtained from the disassembly and separation of sodium-ion batteries.

[0098] In some embodiments, the maximum value of dV0 / d(logD) for pores with a diameter of 1.0 nm to 1.5 nm in the carbon-based material is 0.001 cm. 3 / (g·log(nm))-0.006cm 3 / (g·log(nm)), which is more conducive to reducing gas generation and bubbling during the pulping process.

[0099] In some embodiments, the carbon-based material has pores with a diameter of 1.0 nm to 1.5 nm and a pore volume of 0.0003 cm³. 3 / g-0.0017cm 3 / g. This is more conducive to reducing gas generation during pulping while also considering specific volume. For example, the pore volume of pores with a pore size of 1.0nm-1.5nm is 0.0003cm³. 3 / g, 0.0005cm 3 / g, 0.0007cm 3 / g, 0.0009cm 3 / g, 0.0011cm 3 / g, 0.0013cm 3 / g, 0.0015cm 3 / g, 0.0017cm 3 / g or a value within a range of any two of these values. Optionally, the total pore volume of pores with a diameter of 1.0 nm to 1.5 nm is 0.0009 cm³. 3 / g-0.0014cm 3 / g.

[0100] The pore volume of the aforementioned 1.0 nm-1.5 nm pores was also obtained by measuring carbon-based materials using conventional methods in the field, such as the N2 adsorption-desorption pore volume and pore size test method. For example, referring to GB / T 19587-2017, the N2 adsorption method can be used to test adsorption and desorption isotherms, and a DFT model can be used to fit the distribution curve of cumulative pore volume relative to pore size, thus obtaining the pore volume of pores in the specific pore size range of 1.0 nm-1.5 nm.

[0101] In some embodiments, the powder compaction density T of the negative electrode sheet 51 at 2T satisfies: 0.8 g / cm³ 3 ≤T≤1.0g / cm 3 .

[0102] T can be 0.8 g / cm³ 3 0.9g / cm 3 1g / cm 3 Or any value within the above range.

[0103] In the embodiments of this application, when the negative electrode sheet has a low powder compaction density, under the condition of satisfying the energy density, when the powder compaction is controlled within the above range, the electrode sheet can have a high porosity, increase the contact area between the negative electrode sheet and the electrolyte, and sodium ions can migrate more smoothly through the pores to the surface of the negative electrode active material, reduce the migration resistance from the liquid phase to the solid phase, reduce the charge transfer impedance of the negative electrode sheet, and improve the discharge power of the sodium-ion battery cell.

[0104] In some implementations, the film resistance R of the negative electrode 51 satisfies: 60mΩ≤R≤170mΩ.

[0105] R can be 60mΩ, 80mΩ, 100mΩ, 120mΩ, 140mΩ, 160mΩ, 170mΩ or any value within the above range.

[0106] In the embodiments of this application, the negative electrode film resistance within the above range can enable the negative electrode to have higher ionic conductivity and reduce the charge transfer impedance of the negative electrode.

[0107] In some implementations, the negative electrode film layer also includes carbon nanotubes.

[0108] In the embodiments of this application, carbon nanotubes in the negative electrode film can improve electron conduction efficiency, optimize ion diffusion dynamics, reduce charge transfer impedance of the negative electrode sheet, and increase the discharge power of a sodium-ion battery cell by constructing a three-dimensional conductive network.

[0109] In some embodiments, the sodium-ion battery cell 5 further includes: a housing, which is a hollow structure with an opening, and the electrolyte, negative electrode 51 and positive electrode 53 are housed within the housing; and a top cover that closes the opening.

[0110] In some embodiments, the electrolyte includes at least one of the following: cyclic carbonate, chain carbonate, ether solvent, carboxylic acid ester solvent, fluorinated solvent, sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

[0111] In some embodiments, the cyclic carbonate includes at least one of the following: propylene carbonate, ethylene carbonate, butene carbonate, vinylene carbonate, fluoroethylene carbonate, vinyl sulfite, propylene sulfite, vinylethylene carbonate, 4-ethynyl-1,3-dioxacyclopentan-2-one, cis-4,5-difluoro-1,3-dioxacyclopentan-2-one, and trans-4,5-difluoro-1,3-dioxacyclopentan-2-one.

[0112] In some embodiments, the chain esters include chain carbonates and / or chain carboxylic acid esters.

[0113] In some embodiments, the chain carbonate includes at least one of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and dibutyl carbonate.

[0114] In some embodiments, the chain carboxylic acid ester includes at least one of the following: methyl acetate, ethyl acetate, ethyl propionate, methyl formate, ethyl formate, methyl propionate, propyl propionate, ethyl butyrate, and propyl acetate.

[0115] In some embodiments, the ether solvent includes at least one of the following: dioxolane, tetrahydrofuran, 1,2-dimethoxyethane, diethylene glycol dimethyl ether (DG), 1,2-diethoxyethane, and 1,2-dibutoxyethane.

[0116] In some embodiments, the positive electrode 53 includes a positive current collector and a positive active material layer.

[0117] In some implementations, the positive current collector includes a metal foil and / or a composite current collector.

[0118] In some embodiments, the metal foil includes copper foil.

[0119] In some embodiments, the positive electrode active material layer includes at least one of the following: sodium transition metal oxide, polyanionic compound, and Prussian blue compound.

[0120] In some embodiments, the transition metal in the sodium transition metal oxide includes at least one of the following: Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, Ce.

[0121] In some embodiments, the sodium transition metal oxide has the general formula Na x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0122] In some embodiments, the sodium transition metal oxide includes at least one of the following: copper-iron-manganese-based oxide, nickel-iron-manganese-based oxide, and ternary oxide.

[0123] In some embodiments, the polyanionic compound includes at least one of the following: phosphate, sulfate, or fluorophosphate.

[0124] In some embodiments, Prussian blue compounds include iron-based Prussian blue and / or manganese-based Prussian blue.

[0125] In some embodiments, the positive electrode active material layer further includes a binder, which includes at least one of the following: polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0126] In some embodiments, the positive electrode active material layer further includes a conductive agent, which includes at least one of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite-like materials, and carbon nanofibers.

[0127] The above H1 / H, H2 / H, and H3 / H can be obtained by peak fitting of the XRD pattern of carbon-based materials.

[0128] Specifically, the XRD diffraction pattern of the carbon-based material was first tested using the following method: The XRD diffraction pattern of the carbon-based material can be tested using an X-ray diffractometer according to JIS K 0131-1996. The test conditions were as follows: the carbon-based material and silicon powder were uniformly mixed at a mass ratio of 5:1, and the sample was prepared using the plate sample preparation method. CuKα rays were used as the radiation source, and a copper target was used as the anode target. The wavelength λ of the copper target was 1.5406 Å, the scanning 2θ angle range was 10º-40º, and the scanning rate was 1º / min. A Bruker D8 Discover X-ray diffractometer could be used as the testing instrument.

[0129] Next, the XRD diffraction pattern of the carbon-based material was fitted using XPS peak software. The XRD pattern of the carbon-based material was fitted into three small peaks, namely the first fitted peak A, the second fitted peak B, and the third fitted peak C. The fitting criteria were: the 2θ angle of the first fitted peak A was 22.2º~24.7º, the 2θ angle of the second fitted peak B was less than 22.2º, and the 2θ angle of the third fitted peak C was greater than 24.7º.

[0130] The interlayer spacing and the 2θ angle satisfy Bragg's law: Where d is the interlayer spacing of the (002) crystal plane of the carbon-based material. Let be the diffraction angle, and k be the reflection order. The wavelength of the copper target is denoted as k. In this disclosure, k is 1. The value is 1.5406 Å. According to Bragg's formula, the 2θ angle corresponding to graphite-like sheets with an interlayer spacing of 0.35 nm to 0.4 nm is 22.2° to 24.7°. The 2θ angle corresponding to graphite-like sheets with an interlayer spacing greater than 0.4 nm is less than 22.2°, and the 2θ angle corresponding to graphite-like sheets with an interlayer spacing less than 0.35 nm is greater than 24.7°.

[0131] Finally, the ratio of the area of ​​the first fitting peak to the total area of ​​the three fitting peaks is equal to the ratio of the spatial volume H1 between graphite-like sheets with an interlayer spacing of 0.35 nm to 0.4 nm to the total spatial volume H between the layers in the graphite-like sheets (H1 / H); the ratio of the area of ​​the second fitting peak to the total area of ​​the three fitting peaks is equal to the ratio of the spatial volume H2 between graphite-like sheets with an interlayer spacing greater than 0.4 nm to the total spatial volume H between the layers in the graphite-like sheets (H2 / H); and the ratio of the area of ​​the third fitting peak to the total area of ​​the three fitting peaks is equal to the ratio of the spatial volume H3 between graphite-like sheets with an interlayer spacing less than 0.35 nm to the total spatial volume H between the layers in the graphite-like sheets (H3 / H).

[0132] The pore volumes V1, V2, V3, V4, and total pore volume Vtotal of the aforementioned carbon-based materials can be determined with reference to GB / T 19587-2017. For example, referring to GB / T 19587-2017, the nitrogen adsorption method can be used to test the adsorption and desorption isotherms, and a DFT model can be used to fit the distribution curve of the cumulative pore volume relative to the pore size, thus obtaining the pore volume for a specific pore size range.

[0133] The compacted density described above has a well-known meaning in the art and can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., a UTM7305 type electronic pressure testing machine) in accordance with GB / T 24533-2009. An exemplary test method is as follows: Weigh 1g of sample powder and add it to a container with a bottom area of ​​1.327cm². 2In the mold, the pressure is increased to 2t, held for 30s, then the pressure is released and held for 10s. The compaction density of the powder under 2t pressure is then recorded and calculated.

[0134] [Positive electrode plate]

[0135] The positive electrode includes a positive current collector and a layer of positive active material disposed on the positive current collector. The positive electrode can be the aforementioned positive electrode 53.

[0136] 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.).

[0137] In some embodiments, the positive electrode active material layer may employ positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0138] In some embodiments, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0139] In some embodiments, the polyanionic compound may be a sodium ion, a transition metal ion, or a tetrahedral (YO4) compound. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state. Polyanionic compounds can also have sodium ions, transition metal ions, or tetrahedral (YO4) ions. n-A class of compounds containing anionic units and halide anions. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si, where n represents (YO4). n- The valence state; halogens can include at least one of F, Cl, and Br. Polyanionic compounds can also have sodium ions, tetrahedral (YO4) valence states. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can include at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents (ZO). y ) m+ The valence state; halogens can include at least one of F, Cl, and Br. Examples of polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' includes one or more of V, Fe, Mn, and Ni), and Na3(VO4). y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0140] In some embodiments, Prussian blue compounds may contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0141] 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.

[0142] 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, graphite-like materials, and carbon nanofibers.

[0143] In some embodiments, the positive electrode sheet can be prepared by dispersing the positive 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 current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0144] [Negative electrode plate]

[0145] The negative electrode includes a negative current collector and a layer of negative active material disposed on the negative current collector. The negative electrode can be the aforementioned negative electrode 51.

[0146] 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 material substrate and a metal layer formed on at least one surface of the polymer 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 polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0147] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0148] In some embodiments, the negative electrode active material layer may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0149] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite-like materials, and carbon nanofibers.

[0150] In some embodiments, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0151] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material layer, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0152] Electrolyte

[0153] 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 may include fluoroethylene carbonate (FEC) and the sodium-containing compound described in any of the above embodiments. The electrolyte can be the electrolyte described in the above embodiments.

[0154] In some embodiments, the electrolyte includes an organic solvent, a sodium electrolyte salt, and optional additives. The types of organic solvent, sodium electrolyte salt, and additives are not specifically limited and can be selected according to requirements.

[0155] In some embodiments, as examples, the electrolyte salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. One of the above electrolyte salts may be used alone, or two or more may be used simultaneously.

[0156] In some embodiments, as examples, the organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), 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). One of the above organic solvents may be used alone, or two or more may be used simultaneously. Optionally, two or more of the above organic solvents may be used simultaneously.

[0157] In some embodiments, the 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.

[0158] In some embodiments, as examples, the additives include, but are not limited to, at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).

[0159] The electrolyte can be prepared according to conventional methods in the art. For example, an organic solvent, a sodium electrolyte salt, and optional additives can be mixed evenly to obtain an electrolyte. There are no particular restrictions on the order of addition of the materials; for example, the sodium electrolyte salt and optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte; or, the sodium electrolyte salt can be added to the organic solvent first, and then the optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte.

[0160] [Isolation membrane]

[0161] In some embodiments, the 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.

[0162] 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.

[0163] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0164] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0165] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0166] 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 2 The sodium-ion battery cell 5 is an example. The sodium-ion battery cell 5 may include a housing and a top cover. The housing may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing has an opening communicating with the receiving cavity, and the top cover can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly using a winding process or a stacking process. The electrode assembly is encapsulated within the housing (or, the receiving cavity). Electrolyte is immersed in the electrode assembly. The sodium-ion battery cell 5 may contain one or more electrode assemblies, which can be selected by those skilled in the art according to specific practical needs.

[0167] In some embodiments, sodium-ion battery cells can be assembled into battery modules, and the number of sodium-ion battery cells contained in a battery module 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 module.

[0168] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple sodium-ion 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-ion battery cells 5 can be fixed in place using fasteners.

[0169] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple sodium-ion battery cells 5 are received.

[0170] In some embodiments, the battery modules described above can also be assembled into a battery device. The number of battery modules contained in the battery device can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery device.

[0171] Figure 4 and Figure 5 This is battery device 1 as an example. (See reference...) Figure 4 and Figure 5 The battery device 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4 and / or sodium-ion battery cells 5. The multiple battery modules 4 may be arranged in any manner within the battery box.

[0172] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery device provided in this application. The battery cell, battery module, or battery device 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.

[0173] As the electrical device, a single battery cell, a battery module, or a battery can be selected according to its usage requirements.

[0174] 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 high power and high energy density requirements of individual battery cells, a battery device or battery module can be used.

[0175] Another example 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.

[0176] In some implementations, the electrical device is an electrical device used in fields such as new energy vehicles, drones and robots, smart grids, data centers, renewable energy storage, large-scale energy storage systems, and power starters and power tools.

[0177] [Example]

[0178] 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.

[0179] Example 1

[0180] (1) Preparation of negative electrode sheet

[0181] I. Preparation of negative electrode active materials

[0182] ① The pre-carbonization and doping steps involve placing the biomass carbon precursor coconut shell in a box furnace and heating it to 600°C at a heating rate of 5°C / min for 3 hours under the condition of introducing carrier gas nitrogen and doping gas oxygen. The volume ratio of oxygen to nitrogen is 0.05:1. The flow rate of the nitrogen and oxygen mixture is 10 mL / min.

[0183] ② Carbonization step: Under nitrogen gas, heat to 1200℃ and hold for 2 hours, then cool to room temperature;

[0184] ③ The sample obtained from the above carbonization step is subjected to crushing, grading, sieving, and demagnetization to finally obtain the hard carbon anode active material. The water content W of the hard carbon anode active material is controlled to be 0.08% ≤ W ≤ 0.1%, and the Dv10 of the hard carbon anode active material is controlled to be 1 μm ≤ Dv10 ≤ 2 μm.

[0185] II. Preparation of the negative electrode sheet

[0186] The prepared negative electrode active material, carboxymethyl cellulose binder, styrene-butadiene rubber binder, and carbon black conductive agent were mixed and homogenized in a weight ratio of 94.5:1.5:2.5:1.5 to obtain a negative electrode film slurry. The negative electrode active material slurry was coated onto the negative electrode current collector and then dried in an oven at 100°C, controlling the water content to be less than 150 ppm, to obtain the negative electrode sheet. The water content W0 of the negative electrode sheet was controlled to satisfy: 0 ≤ W0 ≤ 0.15%. The thickness of the negative electrode film on one side of the negative electrode current collector was 144 μm.

[0187] (2) Preparation of positive electrode sheet

[0188] The positive electrode active material sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), the binder polyvinylidene fluoride, and the conductive agent SP were mixed in a weight ratio of 95:2.5:2.5 and dissolved in the solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto the current collector aluminum foil, and after being fully dried, it was cold-pressed, die-cut, and slit to obtain the positive electrode sheet.

[0189] (3) Separating membrane

[0190] PE porous polymer film is used as the separator.

[0191] (4) Electrolyte

[0192] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1:1 to obtain an organic solvent. NaPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1.4 mol / L and a conductivity of 14.35 mS / cm.

[0193] (5) Preparation of battery cells

[0194] The positive electrode, separator, and negative electrode are arranged in the order of "separator—negative electrode—separator—positive electrode," so that the separator acts as a barrier between the positive and negative electrodes. One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft to wind the positive electrode, negative electrode, and two separators. After baking, electrolyte injection, and formation, a single battery cell is obtained.

[0195] Example 2

[0196] The difference between Example 2 and Example 1 is that the final carbonization temperature in the material preparation process is 1300℃, and the thickness of the negative electrode film layer on one side of the negative electrode current collector is 140μm-250μm.

[0197] Example 3

[0198] The difference between Example 3 and Example 1 is that the final carbonization temperature in the material preparation process is 1100℃, the heating rate is 3℃ / min, and the thickness of the negative electrode film on one side of the negative electrode current collector is 140μm-250μm.

[0199] Comparative Example 1

[0200] The difference between Comparative Example 1 and Example 1 is that the final carbonization temperature in the material preparation process is different. In Comparative Example 1, it is further increased to 1400℃ and the holding time is 3h.

[0201] The specific parameters of the battery cells in Examples 1-3 and Comparative Example 1 are shown in Table 1 below.

[0202] Table 1: Specific parameters of Examples 1-3 and Comparative Example 1

[0203]

[0204] In addition, the battery cells in Examples 1-3 and Comparative Example 1 were subjected to performance tests. The test results are shown in Table 2 below.

[0205] Table 2: Performance test results of Examples 1-3 and Comparative Example 1

[0206]

[0207] Combined with Examples 1-3 and Comparative Example 1, compared to Comparative Example 1, when the spatial proportion of interlayer spacing and the proportion of pores with specific diameters in Examples 1-3 are within the above range, and the electrolyte is a high-conductivity electrolyte, the sodium-ion battery cell still has a higher capacity retention rate after completing the constant current charge-discharge test at a charge rate of 3C, thus proving that the sodium-ion battery cell has better rate performance.

[0208] Examples 4-7 and Comparative Example 2

[0209] The difference between Examples 4-7 and Comparative Example 2 and Example 1 is that different electrolytes with different conductivity were used to prepare sodium-ion battery cells.

[0210] The specific parameters of the battery cells in Examples 4-7 and Comparative Example 2 are shown in Table 3 below.

[0211] Table 3: Specific parameters of Examples 4-7 and Comparative Example 2

[0212]

[0213] In addition, the battery cells in Examples 4-7 and Comparative Example 2 were subjected to performance tests. The test results are shown in Table 4 below.

[0214] Table 4: Performance test results of Examples 4-7 and Comparative Example 2

[0215]

[0216] As shown in Examples 4-7 and Comparative Example 2, when the electrolyte conductivity is within the above range, the sodium-ion battery cell has better low-temperature low-charge discharge voltage, higher cycle capacity retention, and higher storage capacity retention.

[0217] Example 8

[0218] (1) Preparation of hard carbon anode active material with biomass material as carbon source

[0219] ① Pre-carbonization: Using lignin as raw material, it is treated at 400℃ for 2 hours in a hot press furnace (Dingli Technology, VHP-777) under normal pressure and N2 atmosphere to obtain pre-carbonized product.

[0220] ② Crushing; The pre-carbonized product obtained in step ① above is subjected to air jet milling (Shengxing Environmental Protection: SX1210) to obtain products with Dv10 of 2μm, Dv50 of 5μm and Dv90 of 12μm.

[0221] ③ Deashing: The product crushed in step ② above is soaked in a pickling kettle with 2M hydrochloric acid aqueous solution for 10 hours at room temperature, filtered, washed with water 3 times, and then dried in a continuous kiln at 100℃.

[0222] ④ Pre-pressing: The product obtained in step ③ above is pressurized in a hot press furnace (manufacturer: Dingli Technology, model: VHP-777) at a pressure of 50T for 1 hour.

[0223] ⑤ Carbonization; The product obtained in step ④ above is sintered for 2 hours at 1400℃ for a normal pressure under N2 atmosphere and at a heating rate of 2℃ / min. It is then washed with water 3 times and dried at 100℃ in a continuous kiln to obtain hard carbon anode active material.

[0224] (2) Preparation of negative electrode slurry

[0225] The hard carbon negative electrode active material, conductive agent and dispersant prepared above were dispersed in deionized water in a ratio of 8:1:1 to form a uniform negative electrode slurry, wherein the dispersant was sodium carboxymethyl cellulose and the conductive agent was conductive carbon black.

[0226] (3) Preparation of negative electrode sheet

[0227] The uniformly stirred negative electrode slurry is coated onto both sides of the Al foil using a double-sided coating machine. After double-sided coating is completed, the negative electrode sheet is prepared by vacuum drying at 80°C, cold pressing, slitting, and sheet forming.

[0228] (4) Preparation of secondary batteries

[0229] The prepared negative electrode sheet was used for battery assembly in a glove box. The sodium metal sheet was used as the counter electrode. The electrolyte was a solvent in which NaPF6 was dissolved in EC:DMC (volume ratio) = 1:1, and 10 v / v% FEC was added.

[0230] The positive electrode, separator, and negative electrode are stacked in sequence, and the electrolyte is added. After processes such as encapsulation, standing, formation, and aging, a button cell is made.

[0231] Example 9

[0232] Hard carbon anode active materials were prepared using a method similar to that in Example 8, except that the high-temperature carbonization temperature was 1000°C during the preparation of the hard carbon anode active materials.

[0233] Gas adsorption test

[0234] The time it took for the hard carbon anode active material prepared in the above embodiments to stop bubbling was observed during the preparation of the anode slurry. Record the instances where bubbling continued for 2 hours after mixing the components of the anode slurry.

[0235] For the hard carbon anode active materials of Examples 8 and 9 above, adsorption and desorption isotherms were tested using nitrogen and carbon dioxide adsorption methods, respectively, in accordance with GB / T 19587-2017. Both nitrogen and carbon dioxide adsorption methods were analyzed using a specific surface area and porosity analyzer (Micromeritics ASAP-2460, USA). The specific surface area of ​​the hard carbon anode active material was calculated using the BET (Brunauer Emmett Teller) method based on the adsorption and desorption isotherms measured by the nitrogen adsorption method. The distribution curve of dV0 / d(logD) relative to the pore size D was fitted using a DFT model, and the maximum value was read within the pore size range of 1.0 nm to 1.5 nm. Simultaneously, the distribution curve of the cumulative pore volume relative to the pore size was fitted to obtain the pore volume for specific pore size ranges (1.0 nm-1.5 nm and 1 nm-2 nm). The adsorption and desorption isotherms measured by the carbon dioxide adsorption method were used to fit the cumulative pore volume distribution curve relative to the pore size using a DFT model, and the pore volume of pores with a pore size range of less than 1 nm was obtained. The test results of the hard carbon anode active materials prepared in Examples 8 and 9 are shown in Table 5 below. Figure 7 and Figure 8 The graphs show the dV0 / d(logD) versus pore size within a specific range for the hard carbon anode active materials prepared in Examples 8 and 9, respectively, based on nitrogen adsorption. See also... Figure 7 The hard carbon anode active material prepared in Example 8 of this application has a maximum dV0 / d(logD) value of 0.006 cm in the pore size range of 1.0 nm to 1.5 nm. 3 / (g·log(nm)). See also Figure 8 The maximum value of dV0 / d(logD) of the hard carbon anode active material prepared in Example 9 of this application is 0.013 cm in the pore size range of 1.0 nm to 1.5 nm. 3 / (g·log(nm)). It can be seen that the dV0 / d(logD) of the hard carbon in Examples 8 and 9 with pore sizes of 1.0nm-1.5nm are significantly different.

[0236] Testing of bubbling during the preparation of negative electrode slurry

[0237] 50g of the hard carbon anode active material prepared in Examples 8 and 9 were added to sealed reaction vessels equipped with temperature and pressure sensors. After adding 200ml of water, the reaction vessels were quickly closed, and stirring was started until the temperature and pressure remained constant. The volume of gas emitted per unit mass of hard carbon was calculated based on the pressure change and the ideal gas equation, serving as a measure of the bubbling amount. The test results for the hard carbon anode active materials prepared in Examples 8 and 9 are shown in Table 6 below.

[0238] Specific capacity testing of hard carbon anode active materials

[0239] For the coin cells prepared in Examples 8 and 9, the capacity obtained by inserting sodium at a rate of 0.05C to 0V is the initial charge capacity; the capacity obtained by desodiuming at a rate of 0.1C to 2.5V is the initial discharge capacity. The mass of the hard carbon anode active material in the anode electrode was calculated based on the coating weight and area of ​​the slurry during the electrode preparation process. The total sodium storage capacity Q = initial charge capacity / mass of hard carbon anode active material. The test results of the hard carbon anode active materials prepared in Examples 8 and 9 are shown in Table 6 below.

[0240] Table 5 shows the pore characteristics and interlayer spacing characteristics of the hard carbon anode active materials prepared in Examples 8 and 9, and Table 6 shows the bubbling amount and specific capacity test results of the hard carbon anode active materials prepared in Examples 8 and 9.

[0241] Table 5: Specific parameters of Examples 8-9

[0242]

[0243] Table 6: Performance test results of Examples 8-9

[0244]

[0245] As can be seen from Tables 5 and 6, when the maximum value of dV0 / d(logD) is 0.006cm3 / (g·log(nm)), continuous bubbling can be effectively reduced.

[0246] [Testing methods for individual battery cell parameters]

[0247] The battery cells being tested can be newly assembled and unformed, or they can be battery cells removed from electrical devices (such as vehicles).

[0248] (1) Testing of rate performance of individual battery cells

[0249] At 25℃, the battery is charged at a constant current of 1 / 3C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, left to rest for 5 minutes, and then discharged at 1 / 3C to 2V. The average capacity obtained after three cycles is recorded as the initial capacity D0. Then, the battery is charged under the same conditions and discharged at 3C, and the average capacity obtained after three cycles is recorded as the initial capacity D1. The capacity retention rate Q1 of the battery during rate discharge is calculated using the following formula: Qn = (D1 / D0) × 100%.

[0250] (2) Testing of low-capacity, high-rate discharge voltage of individual battery cells

[0251] At -10℃, a single battery cell with 50% SOC was discharged at a rate of 16.7C for 10 seconds, and then the voltage of the single battery cell was measured.

[0252] (3) Test of battery cell capacity retention at 25°C

[0253] At 25℃, the prepared battery was charged at a constant current of 0.5C to the upper limit cutoff voltage of 4.4V, then charged at a constant voltage of 4.4V until the current ≤0.05C, rested for 5 minutes, and then discharged at 0.5C to 2.5V. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded. The battery capacity retention rate after each cycle was Pn = Cn / C0 × 100%. A curve was obtained by plotting the battery capacity retention rate on the ordinate and the corresponding number of cycles on the abscissa.

[0254] (4) Testing of the high-temperature storage performance of individual battery cells at 60℃

[0255] ① Charge the prepared battery cells at a constant current of 1 / 3C to 4.4V, then charge them at a constant voltage of 4.4V until the current is ≤0.05C. Let them rest for 5 minutes, then discharge them at 1 / 3C to 2.5V. Repeat this process twice and record the discharge capacity D0 of the second discharge. ② Charge the battery cells at a constant current of 1 / 3C to 4.4V, then charge them at a constant voltage of 4.4V until the current is ≤0.05C. Store them in a constant temperature environment at 60℃ for a specified number of days. ③ Discharge them at 1 / 3C to 2.5V, let them rest for 5 minutes, then charge them at a constant voltage of 4.4V until the current is ≤0.05C. Let them rest for 5 minutes, then discharge them at 1 / 3C to 2.5V. Record the capacity as Dn. Divide Dn by D0 to get the cell degradation level on the nth day of high-temperature storage. ④ Repeat processes ② and ③ until the cell storage life degradation is recorded.

[0256] 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-ion battery cell, characterized in that, It includes an electrolyte, a negative electrode, and a positive electrode; among which, The conductivity C of the electrolyte at 25±1℃ satisfies: 7mS / cm≤C≤20mS / cm; The negative electrode sheet includes a negative current collector and a negative electrode film layer. The thickness L of the negative electrode film layer on one side of the negative current collector satisfies: 140μm≤L≤250μm. The negative electrode film layer includes a carbon-based material, which includes multiple graphite-like sheets and multiple porous structures; At least some of the graphite-like sheets form an interlayer spacing between two graphite-like sheets, and the interlayer spacing satisfies the following: the volume H1 of the space between 0.35nm and 0.4nm and the total volume H of the space between the multiple graphite-like sheets satisfy: 20%≤H1 / H≤60%; the pore volume V1 of the pore structure with a pore size of 5nm-10nm in the carbon-based material, measured by nitrogen adsorption method, and the total pore volume V in the pore structure satisfy: 2%≤V1 / V≤15%.

2. The sodium-ion battery cell according to claim 1, characterized in that, H1 and H satisfy the condition: 40% ≤ H1 / H ≤ 60%.

3. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The volume H2 of the space where the interlayer spacing is greater than 0.4 nm and the volume H of the total space formed by the multiple graphite-like sheets satisfy the following condition: 30% ≤ H2 / H ≤ 58%.

4. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The volume H3 of the space where the interlayer spacing is less than 0.35 nm and the volume H of the total space formed by the multiple graphite-like sheets satisfy: 0 ≤ H3 / H ≤ 22%.

5. The sodium-ion battery cell according to claim 1 or 2, characterized in that, V1 and V satisfy: 8%≤V1 / V≤15%.

6. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The pore volume V2 of the carbon-based material with a pore size of less than or equal to 2 nm, as measured by nitrogen adsorption, satisfies the following condition: 4.5% ≤ V2 / V ≤ 30%.

7. The sodium-ion battery cell according to claim 6, characterized in that, V2 and V satisfy: 10%≤V2 / V≤18%.

8. The sodium-ion battery cell according to claim 6, characterized in that, The pore volume V3 of the carbon-based material with a pore size of 1nm-2nm, as measured by nitrogen adsorption, and the total pore volume V in the pore structure satisfy the following condition: 5%≤V3 / V≤15%.

9. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The pore volume V4 of the carbon-based material with a pore size greater than 2 nm and less than 5 nm, as measured by nitrogen adsorption, satisfies the following condition: 3.5% ≤ V4 / V ≤ 30%.

10. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The powder compaction density T of the negative electrode sheet at 2T satisfies: 0.8 g / cm³ 3 ≤T≤1.0g / cm 3 .

11. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The film resistance R of the negative electrode sheet satisfies: 60mΩ≤R≤170mΩ.

12. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The negative electrode film also includes carbon nanotubes.

13. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The positive electrode includes a positive current collector, which includes a metal foil and / or a composite current collector.

14. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The positive electrode sheet includes a positive active material layer, which includes at least one of the following: sodium transition metal oxide, polyanionic compound, and Prussian blue compound.

15. The sodium-ion battery cell according to claim 14, characterized in that, The transition metal in the sodium transition metal oxide includes at least one of the following: Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, Ce.

16. The sodium-ion battery cell according to claim 14, characterized in that, The sodium transition metal oxide has the general formula Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

17. The sodium-ion battery cell according to claim 14, characterized in that, The sodium transition metal oxide includes at least one of the following: copper-iron-manganese-based oxide, nickel-iron-manganese-based oxide, and ternary oxide.

18. The sodium-ion battery cell according to claim 14, characterized in that, The polyanionic compound includes at least one of the following: phosphate, sulfate, or fluorophosphate.

19. The sodium-ion battery cell according to claim 14, characterized in that, The Prussian blue compounds include iron-based Prussian blue and / or manganese-based Prussian blue.

20. The sodium-ion battery cell according to claim 14, characterized in that, The positive electrode active material layer further includes a binder, which includes at least one of the following: polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

21. The sodium-ion battery cell according to claim 14, characterized in that, The positive electrode active material layer further includes a conductive agent, which includes at least one of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite-like materials, and carbon nanofibers.

22. The sodium-ion battery cell according to claim 1 or 2, characterized in that, The sodium-ion battery cell also includes: The housing is a hollow structure with an opening, and the electrolyte, the negative electrode, and the positive electrode are housed within the housing. A top cover that closes the opening.

23. A battery device, characterized in that, Includes the sodium-ion battery cell according to any one of claims 1-22.

24. An electrical appliance, characterized in that, Includes the battery device as described in claim 23.

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