Electrolyte and sodium metal battery containing same

Abstract

The invention provides an electrolyte and a sodium metal battery containing the same. The electrolyte comprises an organic solvent, a sodium salt and an additive, the organic solvent comprises a first solvent and a second solvent; the first solvent is selected from a donor number DNgt; 15 and the dielectric constant epsilonlt; 10 of an organic solvent; the second solvent is selected from a donor number DNlt; the dielectric constant is epsilon gt; 10 of an organic solvent; the additive includes a thermally responsive polymeric additive. Through cooperation of the specific functional solvent, the high sodium salt dissociation degree and the weak solvation effect are achieved, the desolvation energy barrier is effectively reduced, the ionic conductivity is improved, the deposition / stripping kinetics, reversibility and safety of the sodium metal battery especially in the low-temperature environment are remarkably improved, meanwhile, the thermal response additive is combined, and the thermal response performance of the sodium metal battery is improved. And the wide temperature range and high safety of the sodium metal battery are improved.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, and more particularly to an electrolyte and a sodium metal battery containing the electrolyte. Background Technology

[0002] Sodium metal batteries, as a promising next-generation high-energy-density energy storage system, have attracted much attention due to the abundant reserves of sodium, low raw material costs, and the theoretical specific capacity of sodium metal anodes reaching 1166 mAh / g. In particular, anode-free sodium metal batteries, by completely removing sodium metal from the initial anode side, further improve the overall energy density of the battery, reduce processing difficulty and cost, and demonstrate great application potential. However, problems such as sodium dendrite growth, interfacial side reactions, and volume expansion severely limit their practical application. Electroplated anode battery structures can further improve energy density, but place higher demands on the interfacial control capabilities of the anode substrate.

[0003] Several key problems arise in existing sodium metal battery electrolytes: significantly limited battery kinetics at low temperatures, insufficient free ion concentration, and low ionic conductivity; in addition, a single solvent system cannot simultaneously meet multiple requirements such as low freezing point, high degree of dissociation, and weak coordination ability, thus limiting its practical application performance.

[0004] Currently, ethylene glycol ether solvents, widely used in sodium metal battery technology, while possessing the advantage of low reduction potential, still perform poorly at low temperatures. Furthermore, these ether-based electrolytes also present problems such as flammability.

[0005] Therefore, developing a new type of high-safety electrolyte for sodium metal batteries is of great practical significance. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an electrolyte and a sodium metal battery containing the electrolyte. Based on the intrinsic relationship between the number of donors and the dielectric constant, it proposes using a solvent with a low number of donors and a high dielectric constant as a co-solvent, which is then mixed with an ether solvent to enhance the electrolyte's solubility in sodium salts and its ion transport capability, while maintaining the low reduction potential of the ether electrolyte itself. This comprehensively improves the electrochemical performance of the electrolyte. Simultaneously, it combines thermally responsive polymer additives to construct a high-safety, wide-temperature-range sodium metal battery electrolyte.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides an electrolyte for a sodium metal battery, comprising an organic solvent, a sodium salt, and an additive. The organic solvent comprises a first solvent and a second solvent. The first solvent is selected from organic solvents with a donor number DN > 15 and a dielectric constant ε < 10. The second solvent is selected from organic solvents with a donor number DN < 15 and a dielectric constant ε > 10. The additive comprises a thermally responsive polymerizable additive.

[0009] The electrolyte for the sodium metal battery provided by this invention employs a strategy of using a mixture of solvents with high dielectric constant and low donor number, and solvents with low dielectric constant and high donor number, to simultaneously achieve high salt dissociation and moderate solvation capability. This improves the electrolyte conductivity while reducing Na+. + Desolvation energy barrier. Simultaneously, this invention incorporates a thermally responsive polymeric additive, endowing the electrolyte with active protection under thermal abuse conditions, achieving rapid ion transport, interface stability, and high safety in the electrolyte.

[0010] The key technical point of this invention lies in addressing the core contradictions of sodium metal battery electrolytes in terms of wide temperature range and safety through molecular-level design, based on the synergistic regulation of solvent donor number (DN) and dielectric constant (ε). The first solvent ensures interfacial compatibility, while the second solvent provides strong dissociation capability and weakens the overall solvation energy, synergistically achieving high ionic conductivity and a low desolvation energy barrier. The constructed binary solvent system achieves synergistic optimization in bulk transport (high conductivity) and interfacial processes (low energy barrier), specifically improving the low-temperature deposition / stripping kinetics and reversibility of the sodium metal anode. Based on the optimization of transport and interface, a thermally responsive polymerizing additive is introduced to form an integrated "transport-interface-safety" solution, endowing the electrolyte with active safety protection under thermal abuse conditions.

[0011] The number of donors DN of the first solvent is 15.1, 15.2, 15.3, 15.4, 15.5, 15.6, 15.8, 15.9, 16, 16.2, 16.5, 16.8, 17, 18, 18.2, 18.5 or 19, etc.; the dielectric constant ε of the first solvent is 9.9, 9.8, 9.7, 9.5, 9.2, 9.0, 8.9, 8.5, 8.0, 7.5 or 7.0, etc.

[0012] The number of donors DN of the second solvent is 14.9, 14.8, 14.5, 14.2, 14.1, 14.0, 13.8, 13.5, 13.2, 13.0, 12.8, 12.5 or 12.0, etc.; the dielectric constant ε of the second solvent is 10.1, 10.2, 10.5, 10.8, 10.9, 11, 11.2, 11.3, 11.5, 11.8, 11.9, 12, 12.2, 12.5, 12.8 or 3, etc.

[0013] Preferably, the first solvent is selected from any one or a combination of at least two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol ethyl methyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, or 18-crown-6-ether, wherein typical but non-limiting combinations are combinations of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether, combinations of triethylene glycol dimethyl ether and diethylene glycol dimethyl ether, combinations of ethylene glycol dimethyl ether and triethylene glycol dimethyl ether, combinations of ethylene glycol diethyl ether and diethylene glycol ethyl methyl ether, and combinations of 18-crown-6-ether and diethylene glycol dimethyl ether.

[0014] Preferably, the second solvent is selected from any one or a combination of at least two of dichloroethane, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dibutyl sulfite, sulfolane, or ethyl methyl sulfone, wherein typical but non-limiting combinations are combinations of dichloroethane and vinyl sulfite, combinations of propylene sulfite and vinyl sulfite, combinations of diethyl sulfite and sulfolane, combinations of sulfolane and vinyl sulfite, and combinations of dichloroethane and ethyl methyl sulfone.

[0015] Preferably, the volume ratio of the first solvent to the second solvent is (1~9):(9~1), wherein the number of parts of the first solvent can be, for example, 1, 2, 3, 4, 7, 8, or 9, and the number of parts of the second solvent can be, for example, 1, 2, 3, 4, 7, 8, or 9, preferably (3~7):(7~3). When the proportion of the first solvent is too large, the sodium salt dissociation ability and conductivity of the electrolyte will decrease, failing to meet the wide temperature range application conditions. When the proportion of the second solvent is too large, the reduction potential of the electrolyte increases, and the compatibility with sodium metal deteriorates.

[0016] Preferably, the thermoresponsive polymerization additive comprises any one or a combination of at least two of 3-phenyl-7-(trifluoromethyl)-3,4-dihydro-2H-1,3-benzoxazine, poly(p-phenylene terephthalamide), or tetra(glycidyl etheroxy)bis(trifluoroethoxy)cyclotriphosphazene, wherein typical but non-limiting combinations are the combination of poly(p-phenylene terephthalamide) and tetra(glycidyl etheroxy)bis(trifluoroethoxy)cyclotriphosphazene, or the combination of 3-phenyl-7-(trifluoromethyl)-3,4-dihydro-2H-1,3-benzoxazine and poly(p-phenylene terephthalamide).

[0017] Preferably, the mass content of the thermally responsive polymeric additive in the electrolyte is 0.5-2.0%, for example, it can be 0.5%, 0.7%, 0.9%, 1%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9% or 2.0%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] In this invention, if the proportion of thermally responsive polymer additive is too high, it cannot be dissolved and increases costs; if the proportion is too low, it is difficult to improve the safety of the electrolyte.

[0019] Preferably, the sodium salt comprises any one or a combination of at least two of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoroacetate, sodium difluorooxalateborate, sodium bis(oxalateborate), sodium trifluoromethanesulfonate, or sodium nitrate. Typical but non-limiting combinations include the combination of sodium hexafluorophosphate and sodium tetrafluoroborate, the combination of sodium hexafluorophosphate and sodium hexafluoroarsenate, the combination of sodium hexafluoroarsenate and sodium tetrafluoroborate, the combination of sodium difluorooxalateborate and sodium bis(oxalateborate), and the combination of sodium trifluoromethanesulfonate and sodium nitrate.

[0020] Preferably, the concentration of sodium salt in the electrolyte is 0.5~2.0 mol / L, for example, it can be 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.7 mol / L, 1.9 mol / L, or 2.0 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.8~1.5 mol / L. Too high a sodium salt concentration will cause the viscosity of the electrolyte to increase, making it unsuitable for low-temperature applications, while too low a concentration will result in an excessively low sodium ion concentration in the electrolyte, leading to excessively low electrolyte conductivity.

[0021] The present invention does not impose any special restrictions on the preparation process of the electrolyte, and can adopt electrolyte preparation processes well known to those skilled in the art, such as stirring and mixing.

[0022] In a second aspect, the present invention provides a sodium metal battery, the sodium metal battery comprising the electrolyte of the sodium metal battery described in the first aspect.

[0023] This invention does not have any special requirements for the type of sodium metal battery; batteries well known to those skilled in the art can be used, such as sodium-copper batteries.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] (1) The electrolyte for sodium metal batteries provided by this invention breaks through the traditional empirical screening mode. It adopts a strategy of using a mixture of solvents with high dielectric constant and low donor number and solvents with low dielectric constant and high donor number, thereby obtaining high salt dissociation degree and moderate solvation ability. This improves the electrolyte conductivity while reducing Na+. +Desolvation energy barrier. This invention establishes a rational design principle for electrolytes using solvent donor number (DN) and dielectric constant (ε) as intrinsic descriptors, providing a clear theoretical framework for precisely controlling ion solvation structure and transport behavior.

[0026] (2) The electrolyte of the sodium metal battery provided by this invention is a functionally synergistic binary system composed of a high DN / low ε ether solvent and a low DN / high ε solvent (such as sulfite esters and sulfones). Through molecular-level compatibility, it simultaneously achieves high dissociation and weak solvation of sodium salt, overcoming the technical challenge of synergistically optimizing high conductivity and low desolvation energy barrier. This synergistic solvation structure retains the advantage of low reduction potential of ether electrolytes, effectively reduces the desolvation activation energy of sodium ions, and ensures a high concentration of free ions at low temperatures. This significantly improves the low-temperature deposition / stripping kinetics and reversibility of the sodium metal anode, solving the core bottleneck of rapid performance degradation at low temperatures.

[0027] (3) The electrolyte for sodium metal batteries provided by this invention proposes a multifunctional electrolyte integration strategy that integrates "transportation-interface-safety". While optimizing the ion transport and solvation structure using a solvent with low donor number and high dielectric constant, it maintains the weak reducing properties of the first solvent to synergistically stabilize the interface. At the same time, thermally responsive polymeric additives are introduced to endow the electrolyte with active protection under thermal abuse conditions, thus achieving fast ion transport, stable interface, and high safety of the electrolyte. Detailed Implementation

[0028] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0029] It should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0030] In the design of sodium metal battery electrolytes, the optimization of solvent coordination number and ion transport capacity still mainly relies on empirical screening, lacking systematic control over intrinsic physicochemical properties of the solvent, such as donor number (DN) and dielectric constant (ε). This leads to several key problems: battery kinetics are significantly limited at low temperatures, for example, high donor number solvents (such as EC, DN=16.4) and Na + Excessive coordination between them creates a high desolventizing energy barrier, hindering the low-temperature deposition of sodium metal. Simultaneously, low dielectric constant solvents (such as DEC, ε=2.8) negatively impact sodium salt ion pairs (such as Na+).+ -FSI - Insufficient dissociation capacity of free ions leads to a decrease in the concentration of free ions, thus affecting ionic conductivity.

[0031] Ethylene glycol ether solvents (such as DME, DN=20, ε=7.2), while possessing the advantage of low reduction potential, suffer from high donor number and low dielectric constant, leading to Na... + High coordination strength and low conductivity result in unsatisfactory performance at low temperatures. Conventional electrolytes used in sodium metal batteries suffer from kinetic sluggishness and insufficient ionic conductivity at low temperatures due to an unreasonable solvation structure. Current solvent systems cannot simultaneously achieve both low desolvation energy barriers and high salt dissociation. This invention optimizes the sodium ion solvation structure through the synergistic combination of high donor number / low dielectric constant ether solvents and low donor number / high dielectric constant solvents, while incorporating thermally responsive polymeric additives. This achieves rapid ion transport and low interfacial energy barriers simultaneously, significantly improving the battery's low-temperature performance and thermal safety.

[0032] The following detailed description uses specific embodiments.

[0033] For ease of comparison, the electrolyte preparation methods in the following embodiments and comparative examples include the following steps: dissolving sodium salt in a mixed solvent of a first solvent and a second solvent, adding a thermally responsive polymerizing additive, and shaking to obtain a stable and homogeneous electrolyte. However, this does not mean that the electrolyte provided by the present invention can only be prepared using the above-described process; other electrolyte preparation processes well known to those skilled in the art are also feasible.

[0034] Example 1

[0035] This embodiment provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent, a sodium salt, and a thermally responsive polymerizing additive.

[0036] The organic solvents include ethylene glycol dimethyl ether (first solvent, with a donor number DN of 20.0 and a dielectric constant ε of 7.2) and sulfolane (second solvent, with a donor number DN of 14.0 and a dielectric constant ε of 43.3) in a volume ratio of 7:3.

[0037] The thermally responsive polymerizing additive is 3-phenyl-7-(trifluoromethyl)-3,4-dihydro-2H-1,3-benzoxazine, with a mass concentration of 0.5 wt%.

[0038] The sodium salt is sodium bis(fluorosulfonyl)imide and sodium hexafluorophosphate in a molar ratio of 2:1, and the concentration of the sodium salt is 1.5 mol / L.

[0039] Example 2

[0040] This embodiment provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent, a sodium salt, and a thermally responsive polymerizing additive.

[0041] The organic solvents include diethylene glycol dimethyl ether (first solvent, with a donor number DN of 19.5 and a dielectric constant ε of 7.3) and dimethyl sulfite (second solvent, with a donor number DN of 12.0 and a dielectric constant ε of 22.5) in a volume ratio of 3:7.

[0042] The thermally responsive polymerizing additive is poly(p-phenylene terephthalamide) with a mass concentration of 1.0 wt%.

[0043] The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt is 0.8 mol / L.

[0044] Example 3

[0045] This embodiment provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent, a sodium salt, and a thermally responsive polymerizing additive.

[0046] The organic solvents include diethylene glycol dimethyl ether (first solvent, with a donor number DN of 19.5 and a dielectric constant ε of 7.3) and ethyl methyl sulfone (second solvent, with a donor number DN of 14.8 and a dielectric constant ε of 57.5) in a volume ratio of 5:5.

[0047] The thermally responsive polymerization additive is tetra(glycidoxy)bis(trifluoroethoxy)cyclotriphosphazene, with a mass concentration of 2.0 wt%.

[0048] The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt is 0.8 mol / L.

[0049] Example 4

[0050] This embodiment provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent, a sodium salt, and a thermally responsive polymerizing additive.

[0051] The organic solvents include triethylene glycol dimethyl ether (first solvent, with a donor number DN of 17.0 and a dielectric constant ε of 7.5) and ethyl methyl sulfone (second solvent, with a donor number DN of 14.8 and a dielectric constant ε of 57.5) in a volume ratio of 6:4.

[0052] The thermally responsive polymerization additive is tetra(glycidoxy)bis(trifluoroethoxy)cyclotriphosphazene, with a mass concentration of 2.0 wt%.

[0053] The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt is 0.8 mol / L.

[0054] Example 5

[0055] This embodiment provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent, a sodium salt, and a thermally responsive polymerizing additive.

[0056] The organic solvents include tetraethylene glycol dimethyl ether (first solvent, with a donor number DN of 16.6 and a dielectric constant ε of 7.6) and ethyl methyl sulfone (second solvent, with a donor number DN of 14.8 and a dielectric constant ε of 57.5) in a volume ratio of 4:6.

[0057] The thermally responsive polymerization additive is tetra(glycidoxy)bis(trifluoroethoxy)cyclotriphosphazene, with a mass concentration of 1.5 wt%.

[0058] The sodium salt is sodium difluorooxalate borate and sodium bis(trifluoromethanesulfonyl)imide in a molar ratio of 1:3, and the concentration of the sodium salt is 1.2 mol / L.

[0059] Example 6

[0060] This embodiment provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent, a sodium salt, and a thermally responsive polymerizing additive.

[0061] The organic solvents include ethylene glycol dimethyl ether (first solvent, with a donor number DN of 17.0 and a dielectric constant ε of 7.5) and ethyl methyl sulfone (second solvent, with a donor number DN of 14.8 and a dielectric constant ε of 57.5) in a volume ratio of 4:6.

[0062] The thermally responsive polymerizing additive is 3-phenyl-7-(trifluoromethyl)-3,4-dihydro-2H-1,3-benzoxazine, with a mass concentration of 1.0 wt%.

[0063] The sodium salt is sodium difluorooxalate borate, and the concentration of the sodium salt is 0.8 mol / L.

[0064] Example 7

[0065] This embodiment provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent, a sodium salt, and a thermally responsive polymerizing additive.

[0066] The organic solvents include diethylene glycol dimethyl ether (first solvent, with a donor number DN of 19.5 and a dielectric constant ε of 7.3) and sulfolane (second solvent, with a donor number DN of 14.2 and a dielectric constant ε of 43.3) in a volume ratio of 7:3.

[0067] The thermally responsive polymerization additive is tetra(glycidoxy)bis(trifluoroethoxy)cyclotriphosphazene, with a mass concentration of 1.0 wt%.

[0068] The sodium salt is sodium bis(trifluoromethanesulfonyl)imide, and the concentration of the sodium salt is 1.4 mol / L.

[0069] Example 8

[0070] This embodiment provides an electrolyte for a sodium metal battery. Except for the volume ratio of ethylene glycol dimethyl ether to sulfolane being 1:9, the electrolyte is the same as that in Example 1, and will not be described again here.

[0071] Example 9

[0072] This embodiment provides an electrolyte for a sodium metal battery. Except for the volume ratio of ethylene glycol dimethyl ether to sulfolane being 9:1, the electrolyte is the same as that in Example 1, and will not be described again here.

[0073] Example 10

[0074] This embodiment provides an electrolyte for a sodium metal battery. Except for the concentration of sodium salt being 0.5 mol / L, the electrolyte is the same as that in Example 1, and will not be repeated here.

[0075] Example 11

[0076] This embodiment provides an electrolyte for a sodium metal battery. Except for the concentration of sodium salt being 2.5 mol / L, the electrolyte is the same as that in Example 1, and will not be repeated here.

[0077] Example 12

[0078] This embodiment provides an electrolyte for a sodium metal battery. Except for the fact that the mass content of the thermally responsive polymer additive in the electrolyte is 0.1%, the electrolyte is the same as that in Example 1, and will not be described again here.

[0079] Example 13

[0080] This embodiment provides an electrolyte for a sodium metal battery. Except for the fact that the mass content of the thermally responsive polymer additive in the electrolyte is 2.5%, the electrolyte is the same as that in Example 1, and will not be described again here.

[0081] Comparative Example 1

[0082] This comparative example provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent and a sodium salt.

[0083] The organic solvent comprises ethylene carbonate (DN 16.4, dielectric constant ε 89.78) and dimethyl carbonate (DN 17.2, dielectric constant ε 3.12) in a volume ratio of 1:1.

[0084] The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt is 1.0 mol / L.

[0085] Comparative Example 2

[0086] This comparative example provides an electrolyte for a sodium metal battery, the electrolyte comprising an organic solvent and a sodium salt.

[0087] The organic solvent comprises ethylene carbonate (DN 16.4, dielectric constant ε 89.78) and dimethyl carbonate (DN 17.2, dielectric constant ε 3.12) in a volume ratio of 3:7.

[0088] The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt is 1.0 mol / L.

[0089] Comparative Example 3

[0090] This comparative example provides an electrolyte for a sodium metal battery. The electrolyte is the same as that in Example 1 except that the thermally responsive polymerizing additive 3-phenyl-7-(trifluoromethyl)-3,4-dihydro-2H-1,3-benzoxazine is not added. It will not be described again here.

[0091] Comparative Example 4

[0092] This comparative example provides an electrolyte for a sodium metal battery. The electrolyte is the same as that in Example 1 except that sulfolane is not added, and will not be described again here.

[0093] Comparative Example 5

[0094] This comparative example provides an electrolyte for a sodium metal battery. Except for the absence of ethylene glycol dimethyl ether, the electrolyte is the same as that in Example 1, and will not be described again here.

[0095] Battery Assembly: A sodium-copper battery was assembled in an argon-protected glove box using copper foil, a separator, and sodium metal. The electrolytes obtained in the above examples and comparative examples were added dropwise. The assembled sodium-copper batteries were subjected to coulombic efficiency tests at -40°C, 25°C, and 60°C. The amount of sodium metal deposited was 1 mAh·cm³. -2 The current density is 1 mA·cm -2 The battery was then heated to 150°C to determine if an open circuit had occurred.

[0096] The room temperature test results of the above embodiments and comparative examples are shown in Table 1.

[0097] Table 1

[0098]

[0099] In Table 1, " / " indicates that there is no relevant data.

[0100] The following points can be observed from Table 1:

[0101] (1) As can be seen from the comprehensive examples 1 to 7, the sodium metal electrolyte system provided by the present invention has extremely high coulombic efficiency in sodium metal deposition half-cells, and the applicable temperature ranges from -40℃ to 60℃, with a wide temperature threshold. At -40℃, the average coulombic efficiency is above 99.1%, at 25℃, the average coulombic efficiency is above 99.5%, and at 60℃, the average coulombic efficiency is above 99.1%. Moreover, when the battery is heated to 150℃, it can break the circuit. Its performance is significantly superior to that of carbonate electrolyte.

[0102] (2) As can be seen from Examples 1 and 8-9, when the volume ratio of the two organic solvents is not within the preferred range, even with fewer cycle times, the average coulombic efficiency of the battery is significantly lower than that of Example 1. When the proportion of the first solvent is too large, the dissociation ability and conductivity of the electrolyte sodium salt will decrease, failing to meet the wide temperature range application conditions. When the proportion of the second solvent is too large, the electrolyte reduction potential increases, and the compatibility with sodium metal deteriorates. This indicates that the present invention preferably controls the volume ratio of the first solvent and the second solvent within a reasonable range, which can improve the coulombic efficiency, low-temperature performance, and high-temperature performance of the battery.

[0103] (3) It can be seen from the combined examples 1 and 10-11 that when the concentration of sodium salt is too high or too low, its high temperature performance decreases. This indicates that the present invention preferably controls the concentration of sodium salt within a reasonable range, which can improve the coulombic efficiency, low temperature and high temperature performance of the battery.

[0104] (4) It can be seen from the combined examples 1 and 12-13 that the mass content of the thermally responsive polymer additive in example 12 is too low, and no circuit will break when the battery is heated to 150°C, which poses a safety risk; the mass content of the thermally responsive polymer additive in example 13 is too high, which leads to a decrease in the coulombic efficiency of the battery. This shows that the present invention controls the mass content of the thermally responsive polymer additive within a reasonable range, which can improve the coulombic efficiency and high-temperature performance of the battery.

[0105] (5) As can be seen from the combined examples 1 and 2, the sodium metal electrolyte system provided by the present invention can achieve stable deposition of sodium metal in a wide temperature range, and its performance is significantly superior to that of commonly used carbonate electrolytes.

[0106] (6) Comparative Example 3 does not contain 3-phenyl-7-(trifluoromethyl)-3,4-dihydro-2H-1,3-benzoxazine, and the battery does not break the circuit when heated to 150°C, indicating low risk resistance. Comparative Examples 4 and 5 each added only one organic solvent, resulting in a significant decrease in low-temperature performance and a significant decrease in high-temperature performance compared to Example 1. This indicates that the present invention selects two solvents to work together to better improve the coulombic efficiency of the battery.

[0107] The present invention has been illustrated with the above embodiments to illustrate its detailed features, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected technical features, additions of auxiliary technical features, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An electrolyte for a sodium metal battery, characterized in that, The electrolyte includes an organic solvent, a sodium salt, and additives; The organic solvent includes a first solvent and a second solvent; the first solvent is selected from organic solvents with a donor number DN>15 and a dielectric constant ε<10; the second solvent is selected from organic solvents with a donor number DN<15 and a dielectric constant ε>10. The additives include thermally responsive polymerizable additives.

2. The electrolyte according to claim 1, characterized in that, The first solvent is selected from any one or a combination of at least two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol ethyl methyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, or 18-crown-6-ether.

3. The electrolyte according to claim 1, characterized in that, The second solvent is selected from any one or a combination of at least two of the following: dichloroethane, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dibutyl sulfite, sulfolane, or ethyl methyl sulfone.

4. The electrolyte according to any one of claims 1 to 3, characterized in that, The volume ratio of the first solvent to the second solvent is (1~9):(9~1).

5. The electrolyte according to claim 4, characterized in that, The volume ratio of the first solvent to the second solvent is (3~7):(7~3).

6. The electrolyte according to any one of claims 1 to 3, characterized in that, The thermally responsive polymerizing additive includes any one or a combination of at least two of 3-phenyl-7-(trifluoromethyl)-3,4-dihydro-2H-1,3-benzoxazine, poly(p-phenylene terephthalamide), or tetra(glycidyl etheroxy)bis(trifluoroethoxy)cyclotriphosphazene.

7. The electrolyte according to claim 1, characterized in that, The mass content of the thermally responsive polymeric additive in the electrolyte is 0.5~2.0%.

8. The electrolyte according to claim 1, characterized in that, The sodium salt includes any one or a combination of at least two of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoroacetate, sodium difluorooxalateborate, sodium bis(oxalateborate), sodium trifluoromethanesulfonate, or sodium nitrate.

9. The electrolyte according to claim 1, characterized in that, The concentration of sodium salt in the electrolyte is 0.5~2.0 mol / L.

10. A sodium metal battery, characterized in that, The sodium metal battery includes the electrolyte of the sodium metal battery according to any one of claims 1 to 9.

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