Electrolyte and sodium metal battery containing same
By adding metal oxides to the electrolyte and utilizing in-situ conversion reactions to form Na2O, the sodium metal alloying reaction is promoted, thus solving the SEI fracture and dendrite growth problems of sodium metal batteries and improving the cycle performance and stability of the batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-14
AI Technical Summary
Sodium metal batteries experience continuous SEI breakage and recovery during cycling, leading to loss of active sodium and dendrite growth, which raises safety issues. Furthermore, existing improvement strategies suffer from poor oxidation stability or high costs.
Adding metal oxides to the electrolyte allows Na2O to be formed on the surface of the sodium metal anode through an in-situ conversion reaction, promoting sodium metal alloying reaction, uniform electrodeposition, and improving cycle performance.
This achieved stable operation and improved cycle performance of sodium metal batteries, reduced active sodium loss, and extended battery life.
Smart Images
Figure CN121862848A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of sodium secondary battery technology, and more particularly to an electrolyte and a sodium metal battery comprising the electrolyte. Background Technology
[0002] Compared to conventional hard carbon anodes, sodium metal anodes (without anodes) can significantly improve the energy density of sodium metal batteries due to their high theoretical capacity and low standard electrode potential (-2.71V compared to the standard hydrogen electrode). However, due to the high reactivity of sodium metal, the electrolyte spontaneously decomposes, subsequently forming a solid electrolyte interphase (SEI) that passivates the sodium metal surface.
[0003] During repeated cycling in sodium metal batteries, the sodium anode undergoes significant volume changes. Consequently, the SEI (Sediment Injection Layer) continues to break down and recover, leading to a loss of active sodium. Furthermore, dendritic growth of sodium metal promotes short circuits and the accumulation of porous SEIs, resulting in serious safety issues and the limited cycle life of sodium metal batteries. Therefore, establishing a stable SEI and inducing planar deposition of sodium metal are crucial for achieving highly reversible sodium metal batteries.
[0004] To address these issues, researchers have devoted significant efforts to enhancing SEI and guiding uniform sodium metal electrodeposition.
[0005] First, to obtain inorganic compound-rich SEIs, researchers have developed various electrolyte modification strategies. These methods include designing new solvent molecules, mixing multiple salts or solvents, and introducing additives, primarily aimed at promoting anion-derived SEIs rich in inorganic compounds. Currently, many novel liquid electrolytes have been proposed, such as high-concentration electrolytes or locally high-concentration electrolytes, which can significantly improve coulombic efficiency (CE) and cycle life. However, several challenges remain, particularly for ether-based electrolytes, which have relatively limited oxidative stability and poor ionic conductivity. Another approach to improving sodium metal batteries is to utilize alloying or conversion reactions to induce uniform sodium metal coating / stripping. When a thin coating of metal or metal oxide is introduced onto the negative electrode or current collector, a sodium metal alloy phase can be formed during sodification. The sodium-loving alloy phase makes sodium metal nucleation chemically more favorable and promotes sodium ion surface diffusion, ultimately inducing more uniform electrodeposition. However, although this coating-based strategy can effectively control the sodium metal morphology, this method often suffers from high manufacturing costs or a lack of scalability.
[0006] Therefore, it is necessary to propose an electrolyte scheme that combines the above advantages and is suitable for sodium metal anodes. Summary of the Invention
[0007] To address the aforementioned technical problems, this disclosure provides an electrolyte and a sodium metal battery containing the electrolyte. By adding metal oxides to the electrolyte, this disclosure effectively improves the cycle performance of sodium metal batteries or negative electrode-free sodium batteries, which is beneficial to promoting the industrialization of sodium metal batteries.
[0008] In a first aspect, this disclosure provides an electrolyte comprising, by weight 100%, 5-20 wt% sodium salt and 0.01-3 wt% first additive, with the balance being an organic solvent. The first additive includes oxides of metals capable of alloying with sodium metal.
[0009] The sodium salt content can be 5wt%, 10wt%, 15wt%, or 20wt%, etc., but is not limited to the listed values. Other unlisted values within this range are also applicable.
[0010] The content of the first additive may be 0.01wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, or 3wt%, etc., but is not limited to the listed values. Other unlisted values within this range are also applicable.
[0011] This disclosure involves adding an appropriate amount of metal oxide to the electrolyte and utilizing an in-situ conversion reaction to disperse the metal oxide particles (denoted as MO). x Na2O is formed on the surface of the sodium metal anode. Then, when the alloying reaction is thermodynamically favorable, the metal in the metal oxide can form a Na-M alloy with Na. The alloy phase makes the nucleation of sodium metal more chemically favorable and promotes the diffusion of sodium ions on the surface, ultimately inducing more uniform electrodeposition, thereby enabling the sodium metal battery to operate stably and improving its cycle performance.
[0012] It should be noted that the thermodynamic advantage of the alloying reaction means that during discharge, the metal in the metal oxide can "actively" absorb metal ions into the crystal lattice, providing low potential and high capacity; while during charging, as long as the voltage is increased to a certain level, Na can be "released" again, realizing a reversible cycle.
[0013] Furthermore, the amount of the first additive should not be excessive, as excessive addition will sacrifice too much reversible capacity. Generally, in a negative electrode-less cell design, the amount of active sodium consumed by the total amount of the first additive should be lower than the amount of active sodium lost during the first charge / discharge of the matched positive electrode. Even when sodium foil is used as the negative electrode, the alloy layer should not be too thick, as the alloy layer itself has different conductivity than sodium, which will affect the local current density at the interface.
[0014] The following are preferred technical solutions of this disclosure, but are not intended to limit the technical solutions provided by this disclosure. The technical objectives and beneficial effects of this disclosure can be better achieved through the following technical solutions.
[0015] As a preferred technical solution of this disclosure, the sodium salt includes one or more of the following: sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium hexafluoroantimonate, sodium difluorophosphate, sodium dioxoborate, sodium bis(malonic acid)borate, sodium difluorooxalateborate, sodium bis(difluoromalonic acid)borate, sodium (malonic acid oxalate)borate, sodium tri(oxalate)phosphate, sodium tri(difluoromalonic acid)phosphate, sodium tetrafluorooxalate phosphate, sodium difluorodioxalate phosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, or sodium nitrate.
[0016] As a preferred technical solution of this disclosure, the organic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, sulfolane, dimethyl sulfoxide, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, difluoroacetate, ethyl difluoroacetate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, fluoroether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, or 1,4-dioxane.
[0017] As a preferred technical solution of this disclosure, the oxide of the metal capable of alloying with sodium metal includes one or more of bismuth oxide, tin oxide, or antimony trioxide.
[0018] As a preferred technical solution of this disclosure, the particle size of the metal oxide capable of alloying with sodium metal is no more than 100 nm, such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, but is not limited to the listed values. Other unlisted values within this range are also applicable, preferably 50-100 nm.
[0019] In this invention, a suitable particle size of the first additive helps it to disperse evenly in the electrolyte. If the particle size is too large, it cannot pass through the diaphragm; while a particle size of less than 50 nm can theoretically achieve good results, but currently, it is not possible to obtain small-particle-size metal oxides with stable quality on the market.
[0020] As a preferred technical solution of this disclosure, the electrolyte further includes a second additive; The second additive includes one or more of the following: fluoroethylene carbonate, dimethyl fluorocarbonate, methyl ethyl fluorocarbonate, vinylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, trifluoromethyl ethylene carbonate, dimethyl sulfate, vinyl sulfate, methyl vinyl sulfate, propylene sulfate, vinyl sulfite, succinic anhydride, biphenyl, diphenyl ether, toluene, xylene, cyclohexylbenzene, fluorobenzene, p-fluorotoluene, p-fluoroanisole, tert-butylbenzene, tert-amylbenzene, propylene sulfonate lactone, butane sulfonate lactone, methane disulfonate methylene ether, ethylene glycol bis(propionitrile) ether, hexamethyldisilazane, heptamethyldisilazane, dimethyl methylphosphonate, diethyl ethylphosphonate, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, tri(trimethylsilyl)borate, or tri(trimethylsilyl) phosphate.
[0021] As a preferred technical solution of this disclosure, the electrolyte comprises 5-20 wt% sodium salt, 0.01-3 wt% first additive and 0.1-10 wt% second additive, with the balance being organic solvent, based on the total mass of the electrolyte being 100%.
[0022] The content of the second additive may be 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, etc., but is not limited to the listed values. Other unlisted values within this range are also applicable.
[0023] In a second aspect, this disclosure provides a sodium metal battery, including a positive electrode, a negative electrode, and a separator, and also includes an electrolyte as described in the first aspect.
[0024] As a preferred technical solution of this disclosure, the positive electrode sheet contains a positive electrode active material, which includes one or more of transition metal layered oxides, polyanionic materials or Prussian blue materials, preferably polyanionic materials.
[0025] Preferably, the pore size of the diaphragm is 100-300nm, such as 100nm, 150nm, 200nm, 250nm or 300nm, but is not limited to the listed values. Other unlisted values within this range are also applicable.
[0026] As a preferred technical solution of this disclosure, the negative electrode sheet includes aluminum foil, carbon-coated aluminum foil, sodium metal sheet or composite negative electrode sheet, wherein the composite negative electrode sheet includes a negative current collector and a sodium metal layer disposed on at least one surface of the negative current collector.
[0027] The technical solution provided in this disclosure has the following advantages compared with the prior art: This disclosure involves adding an appropriate amount of metal oxide to the electrolyte and utilizing an in-situ conversion reaction to disperse the metal oxide particles (denoted as MO). x Na2O is formed on the surface of the sodium metal anode. Then, when the alloying reaction is thermodynamically favorable, the metal in the metal oxide can form a Na-M alloy with Na. The alloy phase makes the nucleation of sodium metal more chemically favorable and promotes the diffusion of sodium ions on the surface, ultimately inducing more uniform electrodeposition, thereby enabling the sodium metal battery to operate stably and improving its cycle performance. Attached Figure Description
[0028] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.
[0029] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0030] Figure 1 The diagram shows the cycle performance of sodium batteries prepared using the electrolytes described in Examples 1-6 and Comparative Examples 1-3 of this disclosure. Detailed Implementation
[0031] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.
[0032] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.
[0033] First, this disclosure provides a test sodium battery with reference to the electrolytes provided in the following embodiments and comparative examples, the preparation process of which is as follows: Positive electrode sheet: Take 4800g of sodium vanadium phosphate, 150g of polyvinylidene fluoride, and 50g of conductive carbon black, and use N-methylpyrrolidone as a solvent to wet homogenize the mixture. The slurry is uniformly dispersed and has a viscosity of 5000-6000 mPa·s. It is then coated on both sides of carbon-coated aluminum foil, with a double-sided surface density of 160 g / m³. 2 Then it is rolled and compacted to a density of 1.56 kg / m³. 3 Then, it undergoes die-cutting and baking. The designed single-sided bulk density is 8.45 Ah / m³. 2 ; Negative electrode plate: as shown in Table 1; The electrolyte comprises: sodium salt: NaPF6, organic solvent: diethylene glycol dimethyl ether / tetraethylene glycol dimethyl ether (volume ratio 8:2), first additive: type and content as shown in Table 1, second additive: type and content as shown in Table 1, and the injection coefficient is 8 g / Ah. Separator: PP dry-process separator, with a thickness of 20μm; The battery cells are stacked, the tabs are welded, the casing is installed, and the electrolyte is injected in an inert atmosphere glove box. The designed capacity of the battery cell is 1Ah.
[0034] After electrolyte filling, the cells were vacuum-sealed and placed at room temperature for 36 hours. Pressurized formation at room temperature followed, subjecting the cells to a constant pressure of 0.8 MPa and a temperature of 25°C. The cells were then charged to 3.65V using a constant current of 0.05A, discharged to 2V using a constant current of 0.05A, and then charged again for 7 hours using a constant current of 0.05A, completing the formation process. The final sealed sodium-ion battery was then obtained for testing.
[0035] Table 1
[0036] Continued from Table 1
[0037]
[0038] The sodium batteries obtained from the above embodiments and comparative examples were tested.
[0039] Cyclic performance test: The sodium battery for testing was placed in a constant temperature chamber at 25±2℃ and left to stand for 30 minutes to allow the sodium battery to reach room temperature. Pressure limit test: The sodium battery for testing was placed between two flat steel plates and secured with four M8 bolts at a torque of 2 N·m. The sodium battery, having reached constant temperature, was charged at a constant current of 0.1C to 3.65V, left to stand for 10 minutes, and then discharged at a constant current of 0.2C to 2V. This cycle was repeated, and the discharge capacity of the first and last cycles was recorded. The capacity retention rate was calculated using the following formula. Cycle capacity retention rate (%) in week n = (cycle discharge capacity in week n / initial cycle discharge capacity) × 100%.
[0040] The test results are shown in Table 2 and Figure 1 As shown in Table 2, the capacity retention rates of the sodium batteries used in the tests obtained in Examples 1-6 and Comparative Examples 1-3 during the first week, 100th week, 200th week, and 300th week are presented. Figure 1 Cyclic performance graphs of the sodium batteries used for testing obtained in Examples 1-6 and Comparative Examples 1-3 are shown.
[0041] Table 2
[0042] From Table 2 and Figure 1 It is known that sodium metal batteries prepared using the electrolyte described in this disclosure have excellent cycle performance.
[0043] Furthermore, based on the first discharge capacity, it can be observed that the batteries with aluminum foil and carbon-coated aluminum foil as the negative electrode (Examples 2-6) have lower capacities than the batteries with metallic sodium negative electrodes (Example 1). This is because the sodium source in a sodium-free battery is only the positive electrode, and some sodium remains at the negative electrode during deposition and film formation, thus not being fully utilized. For sodium metal batteries, however, the metallic sodium negative electrode is also a sodium source, which can compensate for the sodium consumed during film formation, resulting in a relatively higher capacity. In addition, metal oxide particles react with sodium to form alloys, which also consumes some of the active sodium. Therefore, batteries with a higher amount of metal oxide particles tend to have lower capacities.
[0044] From Table 2 and Figure 1 It can also be seen that, among Comparative Examples 1-3, the sodium metal battery (Comparative Example 1) has significantly better cycle performance than the sodium battery without a negative electrode (Comparative Examples 2-3). However, its degradation pattern is basically the same as that of the sodium battery without a negative electrode, both exhibiting accelerated degradation after a certain number of cycles. This is generally considered to be caused by the combined effects of increased internal resistance and accelerated electrolyte consumption. In the embodiments of this disclosure, the capacity degradation of each sodium battery is not significantly different during 300 cycles, and its cycle performance is significantly better than that of the comparative examples, further demonstrating the superiority of the electrolyte provided in this disclosure in application.
[0045] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0046] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. An electrolyte, characterized in that, The electrolyte comprises 5-20 wt% sodium salt and 0.01-3 wt% first additive, with the balance being organic solvent, based on the total mass of the electrolyte (100%). The first additive includes oxides of metals capable of alloying with sodium metal.
2. The electrolyte according to claim 1, characterized in that, The sodium salt includes one or more of the following: sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium hexafluoroantimonyate, sodium difluorophosphate, sodium dioxoborate, sodium di(malonic acid)borate, sodium difluorooxalateborate, sodium di(difluoromalonic acid)borate, sodium (malonic acid oxalate)borate, sodium tri(oxalate)phosphate, sodium tri(difluoromalonic acid)phosphate, sodium tetrafluorooxalate phosphate, sodium difluorodioxalate phosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, or sodium nitrate.
3. The electrolyte according to claim 1 or 2, characterized in that, The organic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, sulfolane, dimethyl sulfoxide, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, methyl difluoroacetate, ethyl difluoroacetate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, fluoroether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, or 1,4-dioxane.
4. The electrolyte according to any one of claims 1-3, characterized in that, The oxides of the metals capable of alloying with sodium metal include one or more of bismuth oxide, tin oxide, or antimony trioxide.
5. The electrolyte according to any one of claims 1-4, characterized in that, The particle size of the oxide of the metal capable of alloying with sodium metal is no more than 100 nm, preferably 50-100 nm.
6. The electrolyte according to any one of claims 1-5, characterized in that, The electrolyte also includes a second additive; The second additive includes one or more of the following: fluoroethylene carbonate, dimethyl fluorocarbonate, methyl ethyl fluorocarbonate, vinylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, trifluoromethyl ethylene carbonate, dimethyl sulfate, vinyl sulfate, methyl vinyl sulfate, propylene sulfate, vinyl sulfite, succinic anhydride, biphenyl, diphenyl ether, toluene, xylene, cyclohexylbenzene, fluorobenzene, p-fluorotoluene, p-fluoroanisole, tert-butylbenzene, tert-amylbenzene, propylene sulfonate lactone, butane sulfonate lactone, methane disulfonate methylene ether, ethylene glycol bis(propionitrile) ether, hexamethyldisilazane, heptamethyldisilazane, dimethyl methylphosphonate, diethyl ethylphosphonate, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, tri(trimethylsilyl)borate, or tri(trimethylsilyl) phosphate.
7. The electrolyte according to claim 6, characterized in that, The electrolyte comprises 5-20 wt% sodium salt, 0.01-3 wt% first additive and 0.1-10 wt% second additive, with the balance being organic solvent, based on the total mass of the electrolyte (100%).
8. A sodium metal battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The sodium metal battery further includes the electrolyte as described in any one of claims 1-7.
9. The sodium metal battery according to claim 8, characterized in that, The positive electrode sheet contains a positive electrode active material, which includes one or more of transition metal layered oxides, polyanionic materials, or Prussian blue materials, preferably polyanionic materials.
10. The sodium metal battery according to claim 8 or 9, characterized in that, The negative electrode sheet includes aluminum foil, carbon-coated aluminum foil, sodium metal sheet, or composite negative electrode sheet. The composite negative electrode sheet includes a negative current collector and a sodium metal sheet disposed on at least one surface of the negative current collector.