Sodium battery, energy storage device and energy storage system

Abstract

The invention provides a sodium battery, an energy storage device and an energy storage system. The sodium battery comprises a positive pole piece, a diaphragm, a negative pole piece and electrolyte, wherein the diaphragm is positioned between the positive pole piece and the negative pole piece; the negative electrode plate comprises a negative electrode current collector and a negative electrode active layer, the negative electrode active layer is arranged on the surface of the negative electrode current collector, the negative electrode active layer comprises an interfacial film, the interfacial film comprises a sulfur element and a sodium element, and the mass ratio f of the sulfur element to the sodium element in the interfacial film is greater than or equal to 0.005 and less than or equal to 5.000.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a sodium battery, an energy storage device, and an energy storage system. Background Technology

[0002] Sodium-ion batteries, due to their abundant sodium resources and low cost, have shown great development potential and broad application prospects. Compared with lithium-ion batteries, sodium-ion batteries have poorer thermal safety performance. The fundamental mechanism lies in the difference in the chemical environment for cation storage in the negative electrode. The quasi-metallic sodium clusters formed by sodium ions in the hard carbon negative electrode will trigger a self-heating reaction in the sodium-ion battery during the conventional sodification process, leading to the decomposition of the solid electrolyte interphase (SEI) film. This accelerates the reaction between the electrolyte and the hard carbon negative electrode, promoting the accumulation of heat inside the sodium-ion battery. As a result, the thermal runaway trigger temperature (the decomposition temperature of the interphase film) and the thermal runaway initiation temperature of sodium-ion batteries are relatively low. Summary of the Invention

[0003] This application provides a sodium battery with a high interfacial film decomposition temperature and a high thermal runaway initiation temperature.

[0004] The first aspect of this application provides a sodium battery, which includes a positive electrode, a separator, a negative electrode, and an electrolyte. The separator is located between the positive electrode and the negative electrode. The negative electrode includes a negative current collector and a negative active layer. The negative active layer is disposed on the surface of the negative current collector and includes an interface film. The interface film includes sulfur and sodium elements, and the mass ratio f of the sulfur to the sodium elements in the interface film is in the range of 0.005 ≤ f ≤ 5.000.

[0005] Furthermore, the electrolyte includes an electrolyte salt, which includes a sulfur-containing sodium salt and a non-sulfur-containing sodium salt, and the mass ratio n of the sulfur-containing sodium salt to the non-sulfur-containing sodium salt in the electrolyte is in the range of 0.25 ≤ n ≤ 15.

[0006] Further, the sulfur-containing sodium salt includes at least one of sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide; and / or, the non-sulfur-containing sodium salt includes at least one of sodium hexafluorophosphate and sodium perchlorate.

[0007] Further, the separator includes a base membrane and a ceramic layer, the ceramic layer being disposed on two opposite surfaces of the base membrane. The thickness of the base membrane is x, in μm, and the thickness of the ceramic layer is y, in μm. The electrolyte wettability of the separator is z, in mm. The electrolyte wettability z refers to the length of time the electrolyte spreads on a 5mm wide separator after 1 minute when 0.02g of the electrolyte is dropped onto the separator. The sodium battery satisfies the relationship: 0.0004 ≤ (x + y) × f / z ≤ 12.5.

[0008] Furthermore, the thickness x of the base film is in the range of 3μm≤x≤15μm.

[0009] Furthermore, the thickness y of the ceramic layer is in the range of 0.5μm≤y≤10μm.

[0010] Furthermore, the electrolyte wettability z of the diaphragm is in the range of 10 mm ≤ z ≤ 50 mm.

[0011] Furthermore, the sodium battery satisfies at least one of the following conditions: The mass fraction e of the electrolyte salt in the electrolyte solution is in the range of 1% ≤ e ≤ 16%; The electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates. In the electrolyte, the mass fraction a of the cyclic carbonate is in the range of 30% ≤ a ≤ 45%, and the mass fraction b of the chain carbonate is in the range of 35% ≤ b ≤ 60%.

[0012] A second aspect of this application provides an energy storage device, the energy storage device comprising: one or more sodium batteries as described in the embodiments of this application.

[0013] A third aspect of this application provides an energy storage system, which includes: a high-voltage cable, a first power conversion device, a second power conversion device, and the energy storage device described in the embodiments of this application; the high-voltage cable is electrically connected to the energy storage device, the first power conversion device, and the second power conversion device, respectively, the first power conversion device and the second power conversion device are both used to generate electrical energy, and the energy storage device is used to store the electrical energy.

[0014] In this embodiment, if the mass ratio f of sulfur to sodium in the interface film is too small, the content of sulfur-containing inorganic salts in the interface film is too low, failing to improve the stability of the interface film, reducing its thermal stability, and consequently lowering the thermal safety and cycle performance of the sodium battery. If the mass ratio f of sulfur to sodium in the interface film is too large, the mass ratio of sulfur-containing sodium salts to non-sulfur-containing sodium salts in the electrolyte is too high, increasing the electrolyte viscosity, decreasing conductivity, increasing the internal resistance of the sodium battery, and deteriorating its cycle performance. Furthermore, sulfur-containing sodium salts undergo redox reactions during charging and discharging, releasing a large amount of heat, which may cause safety problems in the sodium battery. Moreover, if the mass ratio of sulfur-containing sodium salts to non-sulfur-containing sodium salts in the electrolyte is too high, the electrolyte releases a large amount of heat during thermal runaway, accelerating the occurrence of thermal runaway. In related technologies, the instability of the interface film of sodium batteries, combined with the metallic properties of sodium clusters, results in sodium batteries having lower interface film decomposition temperatures and thermal runaway initiation temperatures, leading to poorer thermal safety. This application designs the mass ratio of sodium to sulfur in the interface film of a sodium battery, thereby effectively increasing the decomposition temperature and thermal runaway initiation temperature of the interface film, reducing the heat generated during thermal runaway, and improving the thermal safety and cycle performance of the sodium battery. When the mass ratio f of sulfur to sodium in the interface film is between 0.005 and 5, the thermal decomposition temperature of the interface film of the sodium battery can be further increased, the thermal runaway initiation temperature of the sodium battery can be increased, the heat release from the reaction between the negative electrode active layer and the electrolyte can be reduced, and the thermal safety and cycle performance of the sodium battery can be improved. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of an energy storage system according to an embodiment of this application.

[0017] Figure 2 This is a schematic diagram of the structure of an energy storage system according to another embodiment of this application.

[0018] Figure 3 This is a schematic diagram of the structure of an energy storage system according to another embodiment of this application.

[0019] Figure 4 This is a schematic diagram of the structure of an electrical system according to an embodiment of this application.

[0020] Figure 5 This is a schematic diagram of the structure of an energy storage device according to an embodiment of this application.

[0021] Figure 6 This is a schematic diagram of the structure of a sodium battery according to an embodiment of this application.

[0022] Figure 7 A sodium battery according to an embodiment of this application Figure 6 A schematic diagram of the cross-sectional structure along the AA direction.

[0023] Figure 8 This is a cross-sectional view of the negative electrode sheet according to an embodiment of this application.

[0024] Figure 9 This is a cross-sectional view of a diaphragm according to an embodiment of this application.

[0025] Figure 10 This is a cross-sectional view of the positive electrode sheet according to an embodiment of this application.

[0026] Figure 11 The thermal safety performance test curves of the sodium batteries in Example 1 and Comparative Example 1 are shown.

[0027] Explanation of reference numerals in the attached figures: 100 - Energy storage system; 110 - First power conversion device; 120 - First user load; 130 - Second user load; 140 - High-voltage cable; 150 - Second power conversion device; 160 - Photovoltaic-energy storage-charging station; 170 - Automobile; 200 - Energy storage device; 210 - Single cell battery; 100' - Power system; 110' - Power equipment; 300 - Sodium battery; 310 - Positive electrode sheet; 311 - Positive current collector; 312 - Positive active layer; 320 - Separator; 321 - Base film; 322 - Ceramic layer; 330 - Negative electrode sheet; 331 - Negative current collector; 332 - Negative active layer; 3321 - Interface film; 340 - Housing; 341 - Reception cavity; 350 - End cap assembly. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0029] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0030] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0031] It should be noted that, for ease of explanation, the same reference numerals denote the same components in the embodiments of this application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0032] Because the energy we need is highly time- and space-dependent, in order to utilize energy rationally and improve energy efficiency, it is necessary to store one form of energy in the same way or by converting it into another, and then release it in a specific energy form based on future application needs. Currently, the main way to generate green electricity is to develop green energy sources such as photovoltaics and wind power to replace fossil fuels.

[0033] Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0034] Taking electrochemical energy storage as an example, this solution provides an energy storage device for use in energy storage systems. The energy storage device is equipped with a set of chemical batteries, which mainly use the chemical elements in the batteries as energy storage media. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage media. Simply put, the electrical energy generated by wind and solar energy is stored in the chemical batteries. When the use of external electrical energy reaches its peak, the stored electricity is released for use, or transferred to places with a shortage of electricity for use.

[0035] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding types of energy storage devices include: (1) Large-scale energy storage power stations (composed of multiple prefabricated energy storage modules) applied to wind power and photovoltaic power stations can help renewable energy power generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power regulation power source on the power supply side, the energy storage power station realizes the load matching of power in time and space, enhances the renewable energy absorption capacity, reduces instantaneous power changes, reduces the impact on the power grid, improves the problem of new energy power generation absorption, and is of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation. (2) The energy storage prefabricated cabin applied on the grid side mainly functions as peak regulation, frequency regulation and grid congestion relief. In terms of peak regulation, it can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption. (3) Small energy storage cabinets applied to the electricity consumption side mainly function as self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improvement of power supply reliability. Depending on the application scenario, electricity consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley pricing, by charging the energy storage system when the electricity price is low and discharging the energy storage system when the electricity price is high, peak-valley price arbitrage can be achieved, reducing electricity costs. In addition, industrial enterprises subject to two-part tariffs can use energy storage systems to store energy during off-peak hours and discharge during peak loads, thereby reducing peak power and the maximum demand declared, achieving the goal of reducing capacity costs. Household photovoltaics with energy storage can improve the level of self-consumption of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations is driven. Given that photovoltaic power generation occurs during the day, while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0036] In some embodiments, see Figure 1 , Figure 1 This is a schematic diagram of the structure of an energy storage system 100 according to an embodiment of this application. Figure 1 The embodiments are illustrated using a home energy storage scenario in user-side energy storage as an example. The energy storage device 200 of this application is not limited to the home energy storage scenario.

[0037] This application provides an energy storage system 100, which includes a first power conversion device 110 (photovoltaic panel), a first user load 120 (household lighting fixture), a second user load 130 (e.g., household appliances such as air conditioners), and an energy storage device 200. The energy storage device 200 is a small energy storage box that can be wall-mounted on an outdoor wall. However, the energy storage device 200 is not limited to wall mounting and can also be placed in a user's residence in other ways. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 200 stores this electrical energy and supplies it to lighting fixtures and household appliances during peak electricity prices, or provides power during power outages / power interruptions.

[0038] In some embodiments, see Figure 2 , Figure 2 This is a schematic diagram of the structure of an energy storage system 100 according to another embodiment of this application, and this application Figure 2 The embodiments are illustrated using a shared energy storage scenario on the generation / distribution side as an example. The energy storage device 200 of this application is not limited to its generation / distribution side energy storage scenario.

[0039] This application provides an energy storage system 100, which includes: a high-voltage cable 140, a first power conversion device 110, a second power conversion device 150, and an energy storage device 200 provided in this application. In some embodiments of the power generation scenario, the second power conversion device 150 can be a wind power conversion device. Since the electricity generated by wind power conversion is volatile, random, and intermittent, the unstable electricity output by the wind power conversion device can be stored in the energy storage device 200 through grid connection. The energy storage device 200 is connected to the high-voltage cable 140 and outputs smooth electricity to the power consumption side of the distribution network, realizing peak shaving and frequency regulation, and stable grid operation; or, wind power conversion... The power conversion device is always connected to the high-voltage cable 140. Under normal power generation conditions, the power output of the wind power conversion device is supplied to the power consumption side of the distribution network through the high-voltage cable 140. When the current power load is low and the wind power conversion device generates excess power, the excess power is first stored in the energy storage device 200 to reduce wind and solar curtailment rates and improve the problem of new energy power generation consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 200 together with the high-voltage cable 140 in grid-connected mode to supply power to the power consumption side. This provides the power grid with various services such as peak shaving, frequency regulation, and backup, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure of the power grid.

[0040] In some embodiments on the distribution network side, the first power conversion device 110 can be a photovoltaic panel, and the energy storage device 200 is connected to the high-voltage cable 140 and installed downstream of the high-voltage cable 140 between the user load and the photovoltaic power conversion device. The electrical energy output by the photovoltaic power conversion device is stored in the energy storage device 200, which can respond in a timely manner to act as a backup power source when the power grid / distribution network fails; or, it can provide power supply support to alleviate line congestion when the high-voltage cable 140 transmission line is blocked, and to delay the economic pressure caused by the expansion of the power grid / distribution capacity when the power grid is planned to be expanded.

[0041] In some embodiments, see Figure 3 , Figure 3 This is a schematic diagram of the structure of an energy storage system 100 according to another embodiment of this application, and this application Figure 3 The embodiments are illustrated using an industrial and commercial energy storage scenario as an example. The energy storage device 200 of this application is not limited to industrial and commercial energy storage scenarios.

[0042] This application provides an energy storage system 100, which includes: an energy storage device 200, a high-voltage cable 140, a factory equipped with a first power conversion device 110, a photovoltaic-energy storage-charging station 160, and a vehicle 170. In some embodiments of industrial and commercial scenarios, the first power conversion device 110 can be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage device 200 in the factory. In the event of a power grid failure, the energy storage device 200 provides power to ensure the safe and stable operation of the factory without interruption. Alternatively, when the factory's power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 200 in conjunction with the high-voltage cable 140 in a grid-connected mode to supply the factory with electricity, providing various services such as peak shaving / frequency regulation and backup for the power grid operation. In addition, the first power conversion device 110 can also convert solar energy into electrical energy and store it in the energy storage device 200 of the photovoltaic-energy storage-charging station 160, which can directly charge the vehicle 170, making it fast and convenient.

[0043] Optionally, the first power conversion device 110 may include, but is not limited to, a photovoltaic panel, and the second power conversion device 150 may include, but is not limited to, a wind power conversion device. The first power conversion device 110 and the second power conversion device 150 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0044] Figure 4 This is a schematic diagram of the structure of an electrical system 100' according to an embodiment of this application.

[0045] Please see Figure 4This application embodiment also provides an electrical system 100', which includes an electrical device 110' and an energy storage device 200. The energy storage device 200 is electrically connected to the electrical device 110' and is used to supply power to the energy storage device 200.

[0046] Optionally, the electrical equipment 110' can be, but is not limited to, at least one of the following: power grid, base station, household appliances (such as air conditioner, refrigerator, washing machine, etc.).

[0047] Optionally, the electrical equipment 110' and the energy storage device 200 can be electrically connected via a high-voltage cable 140.

[0048] Please see Figure 5 , Figure 5 This is a schematic diagram of the structure of an energy storage device 200 according to an embodiment of this application.

[0049] Optionally, the energy storage device 200 includes one or more individual battery cells 210.

[0050] The term "multiple" refers to two or more, such as, but not limited to, 2, 5, 10, 30, 50, 100, 200, 300, 400, 800, 1000, etc. The number of individual battery cells 210 included in the energy storage device 200 can be determined based on the rated capacity of the individual battery cells 210 and the rated capacity to be achieved by the energy storage device 200.

[0051] Optionally, the energy storage device 200 can be used, but is not limited to, energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and is also applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0052] Optionally, the energy storage device 200 may include, but is not limited to, battery integrated systems such as single-cell batteries, or battery modules, battery packs, battery clusters, power banks, and energy storage cabinets / prefabricated energy storage containers composed of single-cell batteries. In other words, when the energy storage device 200 includes a single-cell battery 210, the energy storage device 200 may exist in the form of a single-cell battery 210. When the energy storage device 200 includes multiple single-cell batteries 210, the multiple single-cell batteries 210 may be stacked, arranged, assembled, and other processes to form battery integrated systems such as battery modules, battery packs, battery clusters, power banks, and energy storage cabinets / energy storage containers; that is, the energy storage device 200 exists in the form of battery integrated systems such as battery modules, battery packs, battery clusters, power banks, and energy storage cabinets / energy storage containers. The actual application form of the energy storage device 200 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 200. This application embodiment only illustrates the case where the energy storage device 200 is a multi-cell battery (i.e., multiple single-cell batteries 210).

[0053] Optionally, the single cell 210 can be, but is not limited to, at least one of cylindrical, square, prismatic, or other shaped cells.

[0054] Optionally, the single cell 210 can be a rechargeable battery, which refers to a single cell 210 that can be recharged after discharge to activate the active materials and continue to be used. The single cell 210 can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application does not specifically limit it.

[0055] Understandably, the single cell 210 can be, but is not limited to, a sodium battery, a lithium battery, a magnesium battery, a nickel-metal hydride battery, a nickel-cadmium battery, a lead-acid battery, etc. In the following embodiments of this application, the single cell 210 is illustrated using a sodium battery 300 as an example.

[0056] Sodium-ion batteries, due to their abundant sodium resources and low cost, have shown great development potential and broad application prospects. Compared with lithium-ion batteries, sodium-ion batteries have poorer thermal safety performance. The fundamental mechanism lies in the difference in the chemical environment for cation storage in the negative electrode. The quasi-metallic sodium clusters formed by sodium ions in the hard carbon negative electrode will trigger a self-heating reaction in the sodium-ion battery during the conventional sodification process, leading to the decomposition of the solid electrolyte interphase (SEI) film. This accelerates the reaction between the electrolyte and the hard carbon negative electrode, promoting the accumulation of heat inside the sodium-ion battery. As a result, the thermal runaway trigger temperature (the decomposition temperature of the interphase film) and the thermal runaway initiation temperature of sodium-ion batteries are relatively low.

[0057] Figure 6This is a schematic diagram of the structure of a sodium battery 300 according to an embodiment of this application. Figure 7 A sodium battery 300 according to an embodiment of this application Figure 6 A schematic diagram of the cross-sectional structure along the AA direction. Figure 8 This is a cross-sectional view of the negative electrode 330 according to an embodiment of this application.

[0058] Please see Figures 6 to 8 This application provides a sodium battery 300, which includes a positive electrode 310, a separator 320, a negative electrode 330, and an electrolyte. The separator 320 is located between the positive electrode 310 and the negative electrode 330. The negative electrode 330 includes a negative current collector 331 and a negative active layer 332. The negative active layer 332 is disposed on the surface of the negative current collector 331. The negative active layer 332 includes an interface film 3321, which includes sulfur and sodium elements. The mass ratio f of the sulfur to sodium elements in the interface film 3321 is in the range of 0.005 ≤ f ≤ 5.000.

[0059] It should be noted that the interface film 3321 refers to the solid electrolyte interphase (SEI) film 3321.

[0060] Optionally, the sodium battery 300 of this application may be, but is not limited to, at least one of sodium-ion batteries, sodium metal batteries, lithium sodium-ion batteries, etc.

[0061] Understandably, the positive electrode 310 and the negative electrode 330 are located on opposite sides of the separator 320, that is, the separator 320 is located between the positive electrode 310 and the negative electrode 330, separating the positive electrode 310 and the negative electrode 330. The positive electrode 310, the separator 320, and the negative electrode 330 are stacked sequentially and then wound to obtain a core. That is, the core includes the positive electrode 310, the separator 320, and the negative electrode 330.

[0062] It should be noted that the positive electrode 310, the separator 320, and the negative electrode 330 are all at least partially immersed in the electrolyte.

[0063] It should be noted that the negative electrode active layer 332 can be disposed on one or more surfaces (greater than or equal to two surfaces) of the negative electrode current collector 331. In the schematic diagram of the accompanying drawings of this application, the negative electrode active layer 332 is disposed on two opposite surfaces of the negative electrode current collector 331 as an example, which should not be construed as a limitation on the negative electrode active layer 332 and the negative electrode sheet 330 of the embodiments of this application.

[0064] Specifically, the mass ratio f of sulfur to sodium in the interface film 3321 can be, but is not limited to, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc.

[0065] In this embodiment, if the mass ratio f of sulfur to sodium in the interface film 3321 is too small, the content of sulfur-containing inorganic salts in the interface film 3321 will be too low, failing to improve the stability of the interface film 3321, thus reducing its thermal stability and the thermal safety and cycle performance of the sodium battery 300. If the mass ratio f of sulfur to sodium in the interface film 3321 is too large, the mass ratio of sulfur-containing sodium salts to non-sulfur-containing sodium salts in the electrolyte will be too high, increasing the electrolyte viscosity, decreasing conductivity, increasing the internal resistance of the sodium battery 300, and deteriorating its cycle performance. Furthermore, the sulfur-containing sodium salts undergo redox reactions during charging and discharging, releasing a large amount of heat, which may cause safety problems for the sodium battery 300. Moreover, if the mass ratio of sulfur-containing sodium salts to non-sulfur-containing sodium salts in the electrolyte is too high, the electrolyte will release a large amount of heat during thermal runaway, accelerating the occurrence of thermal runaway. In related technologies, the instability of the interface film 3321 of the sodium battery 300, combined with the metallic properties of sodium clusters, results in a lower decomposition temperature and thermal runaway initiation temperature for the interface film 3321, leading to poor thermal safety. This application addresses this by designing the mass ratio of sodium to sulfur in the interface film 3321 of the sodium battery 300. This effectively increases the decomposition temperature and thermal runaway initiation temperature of the interface film 3321, reduces the heat generated during thermal runaway, and improves the thermal safety and cycle performance of the sodium battery 300. When the mass ratio f of sulfur to sodium in the interface film 3321 is between 0.005 and 5, the thermal decomposition temperature of the interface film 3321 can be further increased, the thermal runaway initiation temperature can be raised, and the exothermic reaction between the negative electrode active layer 332 and the electrolyte can be reduced, thus improving the thermal safety and cycle performance of the sodium battery 300.

[0066] In this application embodiment, when the numerical range m to n is involved, unless otherwise specified, the numerical value can be any value between m and n, including the endpoint value m and the endpoint value n.

[0067] Optionally, the negative electrode current collector 331 can be, but is not limited to, a copper sheet, copper foil, etc.

[0068] Optionally, the negative electrode active layer 332 includes at least one of the following: negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode thickener.

[0069] Optionally, the negative electrode active material can be, but is not limited to, hard carbon.

[0070] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0071] Optionally, the negative electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexanefluoropropylene, and polymerized styrene-butadiene rubber (SBR).

[0072] Optionally, the negative electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethyl methacrylate (PMA).

[0073] In some embodiments, the electrolyte includes an electrolyte salt, which includes a sulfur-containing sodium salt and a non-sulfur-containing sodium salt, and the mass ratio n of the sulfur-containing sodium salt to the non-sulfur-containing sodium salt in the electrolyte is in the range of 0.25 ≤ n ≤ 15.

[0074] Specifically, the mass ratio n of the sulfur-containing sodium salt to the non-sulfur-containing sodium salt in the electrolyte can be, but is not limited to, 0.25, 0.5, 0.8, 1.0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 15, etc.

[0075] In this embodiment, by adjusting the mass ratio of sulfur-containing sodium salt to non-sulfur-containing sodium salt in the electrolyte, the mass ratio of sulfur to sodium in the interface film 3321 of the negative electrode 330 can be optimized. This effectively increases the decomposition temperature and thermal runaway initiation temperature of the interface film 3321 of the sodium battery 300, significantly reduces the heat generation during thermal runaway, and improves the cycle performance of the sodium battery 300. The reduction potential of the sulfur-containing sodium salt is higher than that of the organic solvent in the electrolyte, allowing it to decompose earlier on the surface of the negative electrode active layer 332, forming an SEI film rich in NaF, organic sulfides, and sulfonates. This effectively inhibits electrolyte decomposition during cycling / storage, reducing heat and gas generation in the sodium battery 300. Simultaneously, at higher temperatures, the anions of sulfur-containing sodium salts can catalyze the in-situ ring-opening polymerization of organic solvents in the electrolyte to generate polymers such as polyethers. This polymerization reaction causes the liquid electrolyte to rapidly gel or even solidify, thus physically isolating the positive electrode 310 from the negative electrode 330, preventing large-area internal short circuits, and significantly improving the thermal runaway performance of the sodium battery 300. If the mass ratio of sulfur-containing sodium salts to non-sulfur-containing sodium salts in the electrolyte is too low, the mass ratio of sulfur to sodium in the interface film 3321 of the sodium battery 300 will be too low, failing to improve the stability of the interface film 3321. If the mass ratio of sulfur-containing sodium salts to non-sulfur-containing sodium salts in the electrolyte is too high, the mass ratio of sulfur to sodium in the interface film 3321 of the sodium battery 300 will be too high, increasing the electrolyte viscosity, decreasing conductivity, increasing the internal resistance of the sodium battery 300, deteriorating cycle performance, and causing the electrolyte to release a large amount of heat during thermal runaway, accelerating the occurrence of the thermal runaway process.

[0076] In some embodiments, the sulfur-containing sodium salt includes at least one of sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide.

[0077] In some embodiments, the non-sulfur-containing sodium salt includes at least one of sodium hexafluorophosphate and sodium perchlorate.

[0078] In this embodiment, using these sulfur-containing sodium salts and non-sulfur-containing sodium salts as electrolyte salts can better increase the decomposition temperature of the interface film 3321 of the sodium battery 300, increase the thermal runaway initiation temperature of the sodium battery 300, reduce the heat release from the reaction between the negative electrode active layer 332 of the sodium battery 300 and the electrolyte, and improve the room temperature and high temperature cycle performance of the sodium battery 300.

[0079] In some embodiments, the mass fraction e of the electrolyte salt in the electrolyte is in the range of 1% ≤ e ≤ 16%.

[0080] Specifically, the mass fraction e of the electrolyte salt in the electrolyte can be, but is not limited to, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, etc.

[0081] In this embodiment, if the mass fraction e of the electrolyte salt in the electrolyte is too low, the concentration of free ions in the electrolyte will be too low, reducing the conductivity of the electrolyte and thus reducing the rate performance and cycle performance of the sodium battery 300. If the mass fraction e of the electrolyte salt in the electrolyte is too high, some electrolyte salt may not dissociate, which will increase the viscosity of the electrolyte and reduce the conductivity of the electrolyte, thus also reducing the rate performance and cycle performance of the sodium battery 300.

[0082] In some embodiments, the electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates. Cyclic carbonates have high dielectric constants and high ionic conductivity, enabling the formation of a stable SEI film on the surface of the negative electrode 330, but they have a relatively high viscosity. Chain carbonates have lower viscosity than cyclic carbonates, better electrochemical stability, and can improve the low-temperature performance of the electrolyte. Therefore, using a mixed solvent of cyclic and chain carbonates allows the electrolyte to have a suitable viscosity and low-temperature stability, while also enabling better film formation in the sodium battery 300 using this electrolyte.

[0083] Optionally, the cyclic carbonate may include, but is not limited to, at least one of ethylene carbonate (EC) and propylene carbonate (PC). Ethylene carbonate has a much higher dielectric constant than propylene carbonate, and can better promote the formation of the SEI film.

[0084] Optionally, the chain carbonate may include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0085] Optionally, the mass fraction 'a' of the cyclic carbonate in the electrolyte ranges from 30% to 45%. Specifically, the mass fraction 'a' of the cyclic carbonate in the electrolyte can be, but is not limited to, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 45%, etc. If the mass fraction 'a' of the cyclic carbonate in the electrolyte is too low, the solubility of the electrolyte salt is limited, the conductivity of the electrolyte is low, the impedance of the sodium battery 300 increases, and the room temperature cycling performance of the sodium battery 300 deteriorates. If the mass fraction 'a' of the cyclic carbonate in the electrolyte is too high, the viscosity of the electrolyte is high, and the low-temperature performance and rate performance of the sodium battery 300 deteriorate.

[0086] Optionally, the mass fraction b of the chain carbonate in the electrolyte is in the range of 35% ≤ b ≤ 60%. The mass fraction b of the chain carbonate in the electrolyte can be, but is not limited to, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, etc. If the mass fraction b of the chain carbonate in the electrolyte is too low, the electrolyte viscosity will be too high, and the low-temperature performance and rate performance of the sodium battery 300 will deteriorate. If the mass fraction b of the chain carbonate in the electrolyte is too high, the solubility of the electrolyte salt will be limited, the conductivity of the electrolyte will be low, the impedance of the sodium battery 300 will increase, and the room-temperature cycling performance of the sodium battery 300 will deteriorate.

[0087] In one specific example, the mass fraction 'a' of the cyclic carbonate in the electrolyte ranges from 30% to 45%, and the mass fraction 'b' of the chain carbonate in the electrolyte ranges from 35% to 60%. This results in an electrolyte with higher conductivity, lower viscosity, and a wider liquid range, thus achieving good high and low temperature cycling performance of the sodium battery 300.

[0088] In some embodiments, the electrolyte further includes organic additives. Optionally, the organic additives include at least one of fluoroethylene carbonate (FEC), vinylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, vinyl sulfite, and tris(trimethylsilane) phosphate.

[0089] Optionally, the mass fraction c of the organic additive in the electrolyte is in the range of 1% ≤ c ≤ 5%. Specifically, the mass fraction c of the organic additive in the electrolyte can be, but is not limited to, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. If the mass fraction c of the organic additive in the electrolyte is too low, the interface film 3321 (i.e., SEI film) formed by the sodium battery 300 is loose and porous, resulting in poor water removal and acid suppression effects, increased internal resistance of the sodium battery 300, and deteriorated cycle performance. If the mass fraction c of the organic additive in the electrolyte is too high, the thickness of the interface film 3321 formed by the sodium battery 300 increases, the impedance of the sodium battery 300 increases, the rate performance and low-temperature performance of the sodium battery 300 deteriorate, and the initial coulombic efficiency decreases. When the mass fraction c of the organic additive in the electrolyte is in the range of 1%≤c≤5%, the organic additive can preferably enter the inner layer of the solvation structure of sodium ions, forming an organic-inorganic interface film 3321 with high ionic conductivity and low solubility on the surface of the negative electrode active layer 332, isolating the reaction between the electrolyte and the negative electrode active layer 332, and suppressing the consumption of electrolyte during the charge-discharge cycle of the sodium battery 300.

[0090] In some embodiments, the electrolyte further includes a sodium salt additive. Optionally, the sodium salt additive includes at least one of sodium difluorooxalate borate, sodium bis(oxalate)borate, sodium tetrafluoroborate, sodium difluorophosphate (NaDFP), and sodium difluorobis(oxalate) phosphate.

[0091] Optionally, the mass fraction d of the sodium salt additive in the electrolyte is in the range of 0.2% ≤ d ≤ 1.5%. Specifically, the mass fraction d of the sodium salt additive in the electrolyte can be, but is not limited to, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, etc. If the mass fraction d of the sodium salt additive in the electrolyte is too low, organic solvent molecules in the electrolyte can easily enter the first solvation shell of sodium ions (i.e., the inner layer of the sodium ion solvation structure) to participate in the formation of a loose and porous interface film 3321. The interface film 3321 continuously dissolves and reorganizes during storage / cycling, accelerating the consumption of electrolyte and reducing the cycle performance of the sodium battery 300. If the mass fraction d of the sodium salt additive in the electrolyte is too high, the sodium salt additive has limited solubility in the electrolyte. In addition, it will increase the impedance of the sodium battery 300 and deteriorate the rate performance and low-temperature performance of the sodium battery 300. When the mass fraction d of the sodium salt additive in the electrolyte is in the range of 0.2%≤d≤1.5%, the sodium salt additive (such as the anion of the sodium salt additive) can preferably enter the inner layer of the solvation structure of sodium ions, forming an organic-inorganic interface film 3321 with high ionic conductivity and low solubility on the surface of the negative electrode active layer 332, isolating the reaction between the electrolyte and the negative electrode active layer 332, and suppressing the consumption of electrolyte during the charge and discharge cycle of the sodium battery 300.

[0092] Figure 9 This is a cross-sectional view of a diaphragm 320 according to an embodiment of this application.

[0093] Please see Figure 9 In some embodiments, the separator 320 includes a base film 321 and a ceramic layer 322. The ceramic layer 322 is disposed on two opposite surfaces of the base film 321. The thickness of the base film 321 is x (in μm), the thickness of the ceramic layer 322 is y (in μm), and the electrolyte wettability of the separator 320 is z (in mm). The electrolyte wettability z of the separator 320 refers to the length of time the electrolyte spreads on the separator 320 after 1 minute when 0.02 g (one drop) of the electrolyte is dropped onto a 5 mm wide section of the separator 320. The sodium battery 300 satisfies the relationship: 0.0004 ≤ (x + y) × f / z ≤ 12.5.

[0094] It should be noted that ceramic layers 322 are provided on both opposite surfaces of the base film 321, and y refers to the thickness of a single ceramic layer 322.

[0095] Understandably, the base membrane 321 and the ceramic layer 322 are stacked together, and the structure of the diaphragm 320 is that the ceramic layer 322, the base membrane 321 and the ceramic layer 322 are stacked sequentially along the thickness direction of the diaphragm 320.

[0096] Specifically, (x+y)×f / z can be, but is not limited to, 0.0004, 0.0007, 0.001, 0.003, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 12.5, etc.

[0097] If x is too small, the positive electrode 310 and the negative electrode 330 are prone to short-circuit connection, reducing the safety of the sodium battery 300. As the thickness x of the base film 321 increases, the mechanical strength of the separator 320 improves, reducing the thermal shrinkage rate of the separator 320 in the initial stage of thermal runaway, delaying the direct contact between the positive electrode 310 and the negative electrode 330, and postponing the trigger time of thermal runaway of the sodium battery 300. At the same time, the thicker base film 321 has a higher heat capacity per unit area, which can absorb more heat to delay the temperature rise and reduce the local heat conduction rate. If y is too small, the thermal runaway initiation temperature of the sodium battery 300 is reduced, and the reaction between the negative electrode active layer 332 and the electrolyte of the sodium battery 300 has a large amount of exothermic heat, reducing the cycle performance of the sodium battery 300. If f is too small, the content of sulfur-containing inorganic salts in the interface film 3321 will be too low, failing to improve the stability of the interface film 3321 and reducing its thermal stability, thus lowering the thermal safety and cycle performance of the sodium battery 300. If z is too large, it means excessively high porosity and pore size distribution, promoting side reactions between excessive electrolyte and more surfaces of the positive electrode 310 and negative electrode 330. Especially under high temperature and high pressure conditions, this accelerates the decomposition of the electrolyte and the growth of the interface film 3321, which will also worsen the thermal safety and cycle performance of the sodium battery 300.

[0098] If x is too large, it leads to a longer sodium ion transport path, increased ohmic impedance, and a greater likelihood of localized overheating under high current conditions. Simultaneously, the electrolyte filling efficiency decreases, potentially causing uneven sodium ion concentration at the interface of the negative electrode 330, exacerbating sodium deposition. Therefore, this lowers the thermal runaway initiation temperature of the sodium battery 300 and worsens its cycle performance. If y is too large, the densification of the nanoparticles in the ceramic layer 322 leads to a significant reduction in porosity, decreasing the electrolyte's liquid retention capacity and sodium ion diffusion capacity. This deteriorates the thermal safety and cycle performance of the sodium battery 300, gradually reducing its thermal runaway initiation temperature and capacity retention rates at both room temperature and high temperatures. If f is too large, the mass ratio of sulfur-containing sodium salt to non-sulfur-containing sodium salt in the electrolyte will be too high, increasing the electrolyte viscosity, decreasing conductivity, increasing the internal resistance of the sodium battery 300, and deteriorating its cycle performance. Furthermore, the sulfur-containing sodium salt undergoes a redox reaction during charging and discharging, releasing a large amount of heat, which may cause safety issues with the sodium battery 300. Moreover, an excessively high mass ratio of sulfur-containing sodium salt to non-sulfur-containing sodium salt in the electrolyte will release a large amount of heat during thermal runaway, accelerating the occurrence of thermal runaway. If z is too small, uneven electrolyte wetting is likely to occur, leading to localized sodium deposition, which will significantly lower the internal short-circuit temperature. Side reactions will exacerbate the release of heat and flammable gases, worsening the thermal safety and cycle performance of the sodium battery 300.

[0099] In this embodiment, if (x+y)×f / z is too small, then at least one of x, y, and f is too small or z is too large. This will reduce the decomposition temperature of the interface film 3321 and the thermal runaway initiation temperature of the sodium battery 300, increase the heat release, and reduce the room temperature and high temperature cycle capacity retention rate of the sodium battery 300. If (x+y)×f / z is too large, then at least one of x, y, and f is too large or z is too small. This will also reduce the decomposition temperature of the interface film 3321 and the thermal runaway initiation temperature of the sodium battery 300, increase the heat release, and reduce the room temperature and high temperature cycle capacity retention rate of the sodium battery 300. When 0.0004≤(x+y)×f / z≤12.5, the decomposition temperature of the interface film 3321 of the sodium battery 300 can be better increased, the thermal runaway initiation temperature of the sodium battery 300 and the heat release from the reaction between the negative electrode active layer 332 and the electrolyte can be increased, thereby improving the thermal safety of the sodium battery 300 and improving the cycle performance of the sodium battery 300.

[0100] In some embodiments, the thickness x of the base film 321 ranges from 3 μm ≤ x ≤ 15 μm.

[0101] Specifically, the thickness x of the base film 321 can be, but is not limited to, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc.

[0102] In this embodiment, if the thickness x of the base film 321 is too small, the positive electrode 310 and the negative electrode 330 are prone to short-circuit connection, reducing the safety of the sodium battery 300. As the thickness x of the base film 321 increases, the mechanical strength of the separator 320 increases, reducing the thermal shrinkage rate of the separator 320 in the early stage of thermal runaway, delaying the direct contact between the positive electrode 310 and the negative electrode 330, and postponing the triggering time of thermal runaway of the sodium battery 300. At the same time, the thicker base film 321 has a higher heat capacity per unit area, which can absorb more heat to delay the temperature rise and reduce the local heat conduction rate. However, when the thickness of the base film 321 increases to a certain extent, further increasing the thickness of the base film 321 will lead to a longer transport path for sodium ions, an increase in ohmic resistance, and a greater likelihood of local overheating under high current conditions. At the same time, the filling efficiency of the electrolyte will decrease, which may cause uneven sodium ion concentration at the interface of the negative electrode 330, exacerbating sodium deposition. Therefore, it lowers the thermal runaway initiation temperature of the sodium battery 300 and deteriorates the cycle performance of the sodium battery 300.

[0103] In some embodiments, the thickness y of the ceramic layer 322 is in the range of 0.5 μm ≤ y ≤ 10 μm.

[0104] Specifically, the thickness y of the ceramic layer 322 can be, but is not limited to, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.

[0105] In this embodiment, if the thickness y of the ceramic layer 322 is too thin, the thermal runaway initiation temperature of the sodium battery 300 is reduced. The reaction between the negative electrode active layer 332 of the sodium battery 300 and the electrolyte has a large amount of heat release, which reduces the cycle performance of the sodium battery 300. As the thickness y of the ceramic layer 322 increases, the thermal runaway initiation temperature of the sodium battery 300 gradually increases, while the heat release from the reaction between the negative electrode active layer 332 and the electrolyte gradually decreases. This reduces the room temperature and high temperature cycle capacity retention rate of the sodium battery 300, which in turn gradually increases. This is because the ceramic layer 322 has a high melting point, which can suppress the thermal shrinkage of the base film 321 at high temperatures and reduce the risk of short circuits in the sodium battery 300. Therefore, as the thickness of the ceramic layer 322 increases, the thermal runaway temperature of the sodium battery 300 gradually increases. At the same time, the microporous structure and polar oxides of the ceramic layer 322 have a strong affinity for the electrolyte, which can improve the wetting rate and saturation of the separator 320 and improve the cycle performance of the sodium battery 300. Therefore, as the thickness of the ceramic layer 322 increases, the cycle capacity retention rate of the sodium battery 300 after 2000 cycles at 25℃ (room temperature) and 60℃ (high temperature) gradually increases. If the thickness y of the ceramic layer 322 is too thick, the porosity will be significantly reduced due to the densification of the nanoparticles in the ceramic layer 322, resulting in a decrease in the electrolyte's liquid retention capacity and sodium ion diffusion capacity. This will deteriorate the thermal safety performance and cycle performance of the sodium battery 300, and gradually reduce the thermal runaway initiation temperature, room temperature and high temperature cycle capacity retention rate of the sodium battery 300.

[0106] In some embodiments, the electrolyte wettability z of the diaphragm 320 is in the range of 10 mm ≤ z ≤ 50 mm.

[0107] It should be noted that the electrolyte wettability z of the diaphragm 320 can be achieved by adjusting the porosity and pore size distribution of the diaphragm 320, for example, by adjusting the porosity and pore size distribution of the base membrane 321 and / or the ceramic layer 322. Alternatively, it can be achieved by adjusting the materials of the base membrane 321 and the ceramic layer 322 of the diaphragm 320. This application does not specifically limit which method of adjustment is used; in this embodiment, the electrolyte wettability of the diaphragm 320 is used as the adjustment variable.

[0108] Specifically, the electrolyte wettability z of the diaphragm 320 can be, but is not limited to, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm, 22mm, 24mm, 26mm, 28mm, 30mm, 32mm, 34mm, 36mm, 38mm, 40mm, 42mm, 44mm, 46mm, 48mm, 50mm, etc.

[0109] In this embodiment, if the electrolyte wettability z of the separator 320 is too small, uneven electrolyte wetting is likely to occur, leading to localized sodium deposition, which significantly lowers the internal short-circuit temperature. This exacerbates the release of heat and flammable gases through side reactions, worsening the thermal safety and cycle performance of the sodium battery 300. Conversely, if the electrolyte wettability z of the separator 320 is too large, it implies excessive porosity and pore size distribution, promoting side reactions between excess electrolyte and more surfaces of the positive electrode 310 and negative electrode 330. Especially under high temperature and high pressure conditions, this accelerates electrolyte decomposition and the growth of the interface film 3321, similarly worsening the thermal safety and cycle performance of the sodium battery 300.

[0110] Optionally, the base film 321 can be, but is not limited to, at least one of polypropylene film (PP film), polyethylene film (PE film), etc.

[0111] Figure 10 This is a cross-sectional view of the positive electrode 310 according to an embodiment of this application.

[0112] Please see Figure 10 Optionally, the positive electrode 310 includes a positive current collector 311 and a positive active layer 312, wherein the positive active layer 312 is disposed on the surface of the positive current collector 311.

[0113] It should be noted that the positive electrode active layer 312 can be disposed on one or more surfaces (greater than or equal to two surfaces) of the positive electrode current collector 311. In the schematic diagram of the accompanying drawings of this application, the positive electrode active layer 312 is disposed on two opposite surfaces of the positive electrode current collector 311 as an example, which should not be construed as a limitation on the positive electrode active layer 312 and the positive electrode sheet 310 of the embodiments of this application.

[0114] Optionally, the positive current collector 311 can be, but is not limited to, an aluminum sheet, aluminum foil, etc.

[0115] Optionally, the positive electrode active layer 312 includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0116] Optionally, the positive electrode active material may be, but is not limited to, sodium iron pyrophosphate.

[0117] Optionally, the positive electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0118] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexanefluoropropylene, and polymerized styrene-butadiene rubber (SBR).

[0119] Please see again Figure 6 and Figure 7 Optionally, the sodium battery 300 further includes a housing 340 and an end cap assembly 350, the housing 340 and the end cap assembly 350 forming a closed receiving cavity 341 for housing the electrolyte, the positive electrode 310, the separator 320, and the negative electrode 330. Understandably, the end cap assembly 350 electrically connects the positive electrode 310 and the negative electrode 330, leading them out for electrical connection to external devices or other sodium batteries 300.

[0120] The sodium battery 300 of this application will be further described below through specific embodiments.

[0121] Example 1 The sodium batteries 300 of each embodiment and comparative example were prepared by the following steps: (1) Preparation of non-aqueous electrolyte: Under an environment with a water content of less than 10 ppm, propylene carbonate (PC, cyclic carbonate) and diethyl carbonate (DEC, chain carbonate) are mixed at a mass ratio of 30:51 to obtain a mixed solvent. Then, electrolyte salts and additives are added to the mixed solvent to obtain an electrolyte. The additives include organic additives and sodium salt additives. The organic additive is fluoroethylene carbonate (FEC), and the sodium salt additive is sodium difluorophosphate (NaDFP). In this embodiment, the mass fraction a of cyclic carbonate is 30%, the mass fraction b of chain carbonate is 51%, the mass fraction of sulfur-containing sodium salt is 6%, and the mass fraction of non-sulfur-containing sodium salt is 9%. (2) Preparation of positive electrode 310: Sodium iron pyrophosphate, acetylene black and polyvinylidene fluoride are dissolved in N-methylpyrrolidone solution in a weight ratio of 97:1:2 to form positive electrode slurry; aluminum foil is used as positive electrode current collector 311, the positive electrode slurry is coated on the positive electrode current collector 311, and after drying, cold pressing and die cutting, positive electrode 310 is obtained; (3) Preparation of negative electrode sheet 330: Hard carbon (negative electrode active material), acetylene black, styrene-butadiene rubber and sodium carboxymethyl cellulose are dissolved in deionized water in a weight ratio of 95:2:2:1 and stirred to obtain negative electrode slurry; copper foil is used as negative electrode current collector 331, and the negative electrode slurry is coated on negative electrode current collector 331. After drying, cold pressing and die cutting, negative electrode sheet 330 is obtained. (4) Separator 320: The separator 320 includes a base membrane 321 and a ceramic layer 322 disposed on two opposite surfaces of the base membrane 321. The thickness of the base membrane 321 is 9 μm and the material of the base membrane 321 is a porous polyethylene polymer film. The thickness of the ceramic layer 322 is 4 μm and the electrolyte wettability of the separator 320 is 30 mm. (5) Assembly of soft-pack sodium battery 300: The positive electrode 310, separator 320 and negative electrode 330 prepared above are stacked in sequence, so that the separator 320 is placed between the positive electrode 310 and the negative electrode 330 to play a role in isolation. The bare cell is obtained by winding. The middle area, top area and bottom area of ​​the termination part of the bare cell (i.e. the end of the bare cell) are respectively pasted with termination tape. Then the bare cell is put into polypropylene plastic outer packaging and electrolyte is injected. After vacuum sealing, standing and formation processes, soft-pack sodium battery 300 is obtained.

[0122] Example 2 The difference between this embodiment and Embodiment 1 is that the thickness of the base film 321 in this embodiment is 3 μm.

[0123] Example 3 The difference between this embodiment and Embodiment 1 is that the thickness of the base film 321 in this embodiment is 15 μm.

[0124] Example 4 The difference between this embodiment and Embodiment 1 is that the thickness of the ceramic layer 322 in this embodiment is 0.5 μm.

[0125] Example 5 The difference between this embodiment and Embodiment 1 is that the thickness of the ceramic layer 322 in this embodiment is 10 μm.

[0126] Example 6 The difference between this embodiment and Embodiment 1 is that the electrolyte wettability of the diaphragm 320 in this embodiment is 10 mm.

[0127] Example 7 The difference between this embodiment and Embodiment 1 is that the electrolyte wettability of the diaphragm 320 in this embodiment is 50 mm.

[0128] Example 8 The difference between this embodiment and Embodiment 1 is that the mass fraction of sulfur-containing sodium salt in the electrolyte is 3%, and the mass fraction of non-sulfur-containing sodium salt is 12%.

[0129] Example 9 The difference between this embodiment and Embodiment 1 is that the mass fraction of sulfur-containing sodium salt in the electrolyte is 9%, and the mass fraction of non-sulfur-containing sodium salt is 6%.

[0130] Example 10 The difference between this embodiment and Embodiment 1 is that the mass fraction of sulfur-containing sodium salt in the electrolyte is 15%, and the mass fraction of non-sulfur-containing sodium salt is 1%.

[0131] Example 11 The difference between this embodiment and Embodiment 1 is that the thickness of the base film 321 is 15 μm, the thickness of the ceramic layer 322 is 10 μm, the electrolyte wettability of the separator 320 is 10 mm, the mass fraction of the sulfur-containing sodium salt in the electrolyte is 15%, and the mass fraction of the non-sulfur-containing sodium salt is 1%.

[0132] Example 12 The difference between this embodiment and Embodiment 1 is that the thickness of the base film 321 is 3μm, the thickness of the ceramic layer 322 is 0.5μm, the electrolyte wettability of the separator 320 is 50mm, the mass fraction of the sodium salt containing sulfur in the electrolyte is 3%, and the mass fraction of the sodium salt not containing sulfur is 12%.

[0133] Comparative Examples 1 to 8 The differences between each comparative example and Example 1 are as follows: the thickness of the base film 321, the thickness of the ceramic layer 322, the wettability of the electrolyte, and the mass ratio f of sulfur to sodium in the interface film 3321 are different, as shown in Table 1 below.

[0134] The following performance tests were performed on the sodium battery 300 of the above embodiments and comparative examples: (1) 25℃ 2P / 2P cycle performance test: The sodium battery 300 was placed in a constant temperature oven at 25℃ and charged to 3.3V with a constant power of 1P. After resting for 10 minutes, it was discharged to 1.5V with a constant power of 1P. After resting for 10 minutes, it was charged to 3.3V with a constant power of 2P. After resting for 10 minutes, it was discharged to 1.5V with a constant power of 2P. The discharge capacity was recorded as the discharge capacity of the first cycle. The charge and discharge cycles were performed 2000 times with 2P / 2P power. The discharge capacity of the 2000th cycle was calculated according to the formula: capacity retention rate (%) = discharge capacity of the 2000th cycle / discharge capacity of the first cycle × 100%. The capacity retention rate of the sodium battery 300 after 2000 cycles was calculated.

[0135] (2) 60℃ 2P / 2P cycle performance test: The sodium battery 300 was placed in a constant temperature oven at 60℃ and charged to 3.3V at a constant power of 1P. After resting for 10 minutes, it was discharged to 1.5V at a constant power of 1P. After resting for 10 minutes, it was charged to 3.3V at a constant power of 2P. After resting for 10 minutes, it was discharged to 1.5V at a constant power of 2P. The discharge capacity was recorded as the first discharge capacity. The charge and discharge cycle was performed 2000 times at a power of 2P / 2P. The discharge capacity of the 2000th cycle was recorded. According to the formula, the capacity retention rate (%) = discharge capacity of the 2000th cycle / discharge capacity of the first cycle × 100%, the capacity retention rate of the sodium battery 300 after 2000 cycles was calculated.

[0136] (3) Thermal safety performance test (the onset temperature of thermal runaway): The sodium battery 300 was placed in a constant temperature oven at 25℃ and discharged at a constant power of 1P to 1.5V. After standing for 10 minutes, it was charged at a constant power of 1P to 3.3V. The sodium battery 300 was placed in a heating test chamber and heated from 25℃ ambient temperature to 200℃ at a heating rate of 5℃ / min. After maintaining this temperature for 30 minutes, the heating was stopped. After the heating was stopped, the chamber door was opened within 3 minutes to cool down. After the test, the chamber was observed for 1 hour or cooled down to 30% of the highest temperature rise. The presence of expansion, leakage, smoke, fire, or explosion was recorded. The temperature at which the heating rate of the sodium battery 300 exceeds the heating rate from the externally applied heat source by 1.0℃ / min is recorded as the thermal runaway initiation temperature of the sodium battery 300. That is, when the externally applied heat source causes the heating rate of the sodium battery 300 to be 5℃ / min, the temperature at which the heating rate of the sodium battery 300 reaches 6.0℃ / min is recorded as the thermal runaway initiation temperature of the sodium battery 300.

[0137] (4) Decomposition temperature test of interface film 3321: The sodium battery 300 was disassembled inside gloves under an inert gas atmosphere. The disassembled negative electrode 330 was soaked in dimethyl carbonate (DMC) for 2 hours (repeated three times) to remove residual sodium salts. The negative electrode active layer 332 was scraped off and mixed with electrolyte at a mass ratio of 0.78:1. The electrolyte was based on the electrolytes corresponding to each embodiment and comparative example. Differential scanning calorimetry (DSC) was performed in a temperature range of 35°C to 350°C at a heating rate of 5°C / min under a nitrogen atmosphere. Peak values ​​and peak areas were recorded. The onset temperature of the exothermic peak was defined as the decomposition temperature of the SEI film (interface film 3321), and the peak area of ​​the DSC spectrum was the heat of exothermic reaction, i.e., the heat of reaction between the negative electrode active layer 332 and the electrolyte.

[0138] (5) Electrolyte wettability z of diaphragm 320: A drop of electrolyte (approximately 0.02 g in weight) is dropped onto diaphragm 320 with a width of 5 mm, and the length of the electrolyte spreading on diaphragm 320 after 1 minute is measured as the value of z.

[0139] The performance parameters of the sodium battery 300 in each embodiment and comparative example are shown in Tables 1 and 2 below.

[0140] Table 1 Performance parameters of sodium batteries 300 in various embodiments and comparative examples

[0141] Table 2 Performance parameters of sodium battery 300 in each embodiment and comparative example

[0142] The test results from Examples 1 to 3 show that as the thickness of the base film 321 increases, the thermal runaway initiation temperature of the sodium battery 300 first gradually increases and then gradually decreases. This is because initially, the increased thickness of the base film 321 improves the mechanical strength of the separator 320, reduces the thermal shrinkage rate of the separator 320 in the early stage of thermal runaway, delays the direct contact between the positive electrode 310 and the negative electrode 330, and postpones the triggering time of thermal runaway of the sodium battery 300. Simultaneously, the thicker base film 321 has a higher heat capacity per unit area, which can absorb more heat to delay the temperature rise and reduce the local heat conduction rate. However, with further increases in the thickness of the base film 321, the thermal runaway initiation temperature of the sodium battery 300 decreases significantly, and the cycle performance deteriorates. This is because the increased thickness of the base film 321 leads to a longer sodium ion transport path, increased ohmic impedance, and a greater likelihood of local overheating under high current conditions. Simultaneously, the electrolyte filling efficiency decreases, which may cause uneven sodium ion concentration at the interface of the negative electrode 330, exacerbating sodium deposition. The test results from Examples 1 to 3 show that as the thickness of the base film 321 increases, the decomposition temperature of the interface film 3321 of the sodium battery 300 first gradually increases and then gradually decreases; the heat release of the sodium battery 300 first gradually decreases and then gradually increases; and the cycle capacity retention rate of the sodium battery 300 after 2000 cycles at 25°C and 60°C both first gradually increase and then gradually decrease.

[0143] Figure 11 The thermal safety performance test curves of sodium battery 300 in Example 1 and Comparative Example 1 are provided by... Figure 11 It can be seen that the sodium battery 300 in Example 1 had a stable heating rate and did not experience thermal runaway. In contrast, the sodium battery 300 in Comparative Example 1 experienced a rapid temperature rise after reaching 156.9°C, indicating that thermal runaway occurred at this point. Both Example 1 and Comparative Example 1 used two samples for parallel testing.

[0144] The test results of Examples 1, 4 and 5 show that as the thickness of the ceramic layer 322 increases, the decomposition temperature and thermal runaway initiation temperature of the interface film 3321 of the sodium battery 300 first gradually increase and then gradually decrease; the heat release of the sodium battery 300 first gradually decreases and then gradually increases; and the cycle capacity retention rate of the sodium battery 300 after 2000 cycles at 25°C and 60°C first gradually increases and then gradually decreases. This is because the ceramic layer 322 has a high melting point, which can suppress the thermal shrinkage of the base film 321 at high temperatures and reduce the risk of short circuits in the sodium battery 300. Therefore, as the thickness of the ceramic layer 322 increases, the thermal runaway temperature of the sodium battery 300 gradually increases. At the same time, the microporous structure and polar oxides of the ceramic layer 322 have a strong affinity for the electrolyte, which can improve the wetting rate and saturation of the separator 320 and improve the cycle performance of the sodium battery 300. Therefore, as the temperature of the ceramic layer 322 increases, the cycle capacity retention rate of the sodium battery 300 after 2000 cycles at 25℃ and 60℃ gradually increases. However, when the thickness of the ceramic layer 322 increases to a certain extent, further increases in the thickness of the ceramic layer 322 will result in a significant decrease in porosity due to the densification of the nanoparticles in the ceramic layer 322. This will reduce the electrolyte's liquid retention capacity and sodium ion diffusion capacity, thereby deteriorating the thermal safety and cycle performance of the sodium battery 300.

[0145] It should be noted that although the thickness of the base film 321 or the ceramic layer 322 itself does not affect the decomposition temperature of the interface film 3321, the thickness of the base film 321 or the ceramic layer 322 will affect the "SEI decomposition behavior" observed during the actual thermal runaway of the sodium battery 300 through the heat transfer effect. An increase in the thickness of the base film 321 or the ceramic layer 322 means greater thermal resistance and a longer heat transfer path. When the sodium battery 300 starts to heat up at some point outside or inside, it takes longer for the heat to reach the surface of the negative electrode 330, which is manifested as the measured exothermic peak shifting towards a higher temperature. However, if the thickness of the base film 321 or the ceramic layer 322 continues to increase after reaching a certain level, it will lead to a longer sodium ion diffusion path, an increased impedance of the sodium battery 300, a decrease in electrolyte filling efficiency, and may cause local overheating or sodium deposition, shortening the thermal runaway trigger time, which is manifested as a decrease in the decomposition temperature of the interface film.

[0146] The test results of Examples 1, 6 and 7 show that adjusting the electrolyte wettability z of the separator 320 can significantly improve the thermal safety and cycle performance of the sodium battery 300. This is because uneven electrolyte wetting leads to local sodium deposition, which significantly reduces the temperature at which internal short circuits occur, and the side reactions exacerbate the release of heat and combustible gases. In addition, excessive electrolyte wettability of the separator 320 means excessive porosity and excessive pore size distribution, which promotes the side reactions of excessive electrolyte with more positive electrode 310 and negative electrode 330 surfaces. Especially under high temperature and high pressure conditions, this accelerates the decomposition of electrolyte and the growth of the interface film 3321. Therefore, as the wettability of the electrolyte in the separator 320 increases, the decomposition temperature and thermal runaway initiation temperature of the interfacial membrane 3321 of the sodium battery 300 first gradually increase and then gradually decrease; the heat release of the sodium battery 300 first gradually decreases and then gradually increases; the cycle capacity retention rate of the sodium battery 300 after 2000 cycles at 25℃ and 60℃ first gradually increases and then gradually decreases.

[0147] The test results from Examples 1, 8 to 10 show that by adjusting the mass ratio of sulfur-containing sodium salt to non-sulfur-containing sodium salt in the electrolyte, the mass ratio of sulfur to sodium in the interface film 3321 of the negative electrode 330 can be optimized. This effectively increases the decomposition temperature and thermal runaway initiation temperature of the interface film 3321 of the sodium battery 300, significantly reduces the heat generation during thermal runaway, and improves the cycle performance of the sodium battery 300. The reduction potential of the sulfur-containing sodium salt is higher than that of the organic solvent in the electrolyte, allowing it to decompose earlier on the surface of the negative electrode active layer 332, forming an SEI film rich in NaF, organic sulfides, and sulfonates. This effectively inhibits electrolyte decomposition during cycling / storage, reducing heat and gas generation in the sodium battery 300. Simultaneously, at higher temperatures, the anions of sulfur-containing sodium salts can catalyze in-situ ring-opening polymerization of the organic solvent in the electrolyte to generate polymers such as polyethers. This polymerization reaction causes the liquid electrolyte to rapidly gel or even solidify, thereby physically isolating the positive electrode 310 and the negative electrode 330, preventing large-area internal short circuits, and significantly improving the thermal runaway performance of the sodium battery 300. If the mass ratio of sulfur-containing sodium salts to non-sulfur-containing sodium salts in the electrolyte is too low, the mass ratio of sulfur to sodium in the interface film 3321 of the sodium battery 300 will be too low, failing to improve the stability of the interface film 3321. If the mass ratio of sulfur-containing sodium salt to non-sulfur-containing sodium salt in the electrolyte is too high, the mass ratio of sulfur to sodium in the interfacial film 3321 of the sodium battery 300 will be too high, resulting in increased electrolyte viscosity, decreased conductivity, increased internal resistance of the sodium battery 300, and deteriorated cycle performance. In addition, the sulfur-containing sodium salt undergoes a redox reaction during charging and discharging and releases a large amount of heat, which may cause safety problems for the sodium battery 300. Furthermore, if the mass ratio of sulfur-containing sodium salt to non-sulfur-containing sodium salt in the electrolyte is too high, the electrolyte will release a large amount of heat during thermal runaway, accelerating the occurrence of thermal runaway.

[0148] The test results from Examples 1 to 12 and Comparative Examples 1 to 8 show that by adjusting the thickness x of the base film 321, the thickness y of the ceramic layer 322, the electrolyte wettability z of the separator 320, and the mass ratio f of sulfur to sodium in the interface film 3321, such that 0.0004≤M=(x+y)×f / z≤12.5, the interface film 3321 can have a higher decomposition temperature, the sodium battery 300 has a higher thermal runaway initiation temperature, less heat release, and higher room temperature cycle capacity retention and high temperature cycle capacity retention of the sodium battery 300. In other words, the sodium battery 300 has better thermal safety and cycle performance. As can be seen from Comparative Examples 1, 3, 6 and 7, when the thickness x of the base film 321, the thickness y of the ceramic layer 322, the electrolyte wettability z of the separator 320 and the mass ratio f of sulfur to sodium in the interface film 3321 are adjusted, so that M is too small, the decomposition temperature of the interface film 3321 is greatly reduced, the onset temperature of thermal runaway of the sodium battery 300 is reduced, the heat release is greatly increased, and the room temperature cycle capacity retention rate and high temperature cycle capacity retention rate of the sodium battery 300 are greatly reduced. As can be seen from Comparative Examples 2, 4, 5 and 8, when the thickness x of the base film 321, the thickness y of the ceramic layer 322, the electrolyte wettability z of the separator 320 and the mass ratio f of sulfur to sodium in the interface film 3321 are adjusted to make M too large, the decomposition temperature of the interface film 3321 is greatly reduced, the thermal runaway initiation temperature of the sodium battery 300 is reduced, the heat release is greatly increased, and the room temperature cycle capacity retention rate and high temperature cycle capacity retention rate of the sodium battery 300 are greatly reduced.

[0149] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A sodium battery, characterized in that, The sodium battery includes a positive electrode, a separator, a negative electrode, and an electrolyte. The separator is located between the positive electrode and the negative electrode. The negative electrode includes a negative current collector and a negative active layer. The negative active layer is disposed on the surface of the negative current collector. The negative active layer includes an interface film. The interface film includes sulfur and sodium elements. The mass ratio f of the sulfur to the sodium elements in the interface film is in the range of 0.005 ≤ f ≤ 5.

000.

2. The sodium battery according to claim 1, characterized in that, The electrolyte includes an electrolyte salt, which includes a sulfur-containing sodium salt and a non-sulfur-containing sodium salt. The mass ratio n of the sulfur-containing sodium salt to the non-sulfur-containing sodium salt in the electrolyte is in the range of 0.25 ≤ n ≤ 15.

3. The sodium battery according to claim 2, characterized in that, The sulfur-containing sodium salt includes at least one of sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide; and / or, the non-sulfur-containing sodium salt includes at least one of sodium hexafluorophosphate and sodium perchlorate.

4. The sodium battery according to claim 1, characterized in that, The separator includes a base membrane and a ceramic layer. The ceramic layer is disposed on two opposite surfaces of the base membrane. The thickness of the base membrane is x (in μm), and the thickness of the ceramic layer is y (in μm). The electrolyte wettability of the separator is z (in mm). The electrolyte wettability z refers to the length of time the electrolyte spreads on the separator after 1 minute when 0.02 g of the electrolyte is dropped onto a 5 mm wide section of the separator. The sodium battery satisfies the following relationship: 0.0004 ≤ (x + y) × f / z ≤ 12.

5.

5. The sodium battery according to claim 4, characterized in that, The thickness x of the base film is in the range of 3μm≤x≤15μm.

6. The sodium battery according to claim 4, characterized in that, The thickness y of the ceramic layer is in the range of 0.5μm≤y≤10μm.

7. The sodium battery according to claim 4, characterized in that, The electrolyte wettability z of the diaphragm is in the range of 10 mm ≤ z ≤ 50 mm.

8. The sodium battery according to claim 2, characterized in that, The sodium battery satisfies at least one of the following conditions: The mass fraction e of the electrolyte salt in the electrolyte solution is in the range of 1% ≤ e ≤ 16%; The electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates. In the electrolyte, the mass fraction a of the cyclic carbonate is in the range of 30% ≤ a ≤ 45%, and the mass fraction b of the chain carbonate is in the range of 35% ≤ b ≤ 60%.

9. An energy storage device, characterized in that, The energy storage device includes one or more sodium batteries as described in any one of claims 1-8.

10. An energy storage system, characterized in that, The energy storage system includes: a high-voltage cable, a first power conversion device, a second power conversion device, and the energy storage device as described in claim 9; the high-voltage cable is electrically connected to the energy storage device, the first power conversion device, and the second power conversion device respectively, the first power conversion device and the second power conversion device are both used to generate electrical energy, and the energy storage device is used to store the electrical energy.

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