Electrolyte and sodium-ion battery

Abstract

The application discloses an electrolyte and a sodium ion battery, the electrolyte comprising a solvent, a sodium salt and an additive; the additive has at least one of structures of formula I, formula II and formula III. The application provides an electrolyte aiming at the problems existing on the sodium metal electrode side in a sodium battery, and a battery system using the electrolyte can ensure uniform deposition of sodium metal under the condition of high current density. This characteristic significantly inhibits a series of negative phenomena such as dendrite generation, thereby greatly enhancing the reversibility of sodium ion deposition-stripping, and further, a sodium metal full battery also exhibits excellent rate performance and outstanding capacity retention rate.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to an electrolyte and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries, as a novel energy storage device, have received widespread attention in recent years. Compared to lithium-ion batteries, sodium-ion batteries offer higher safety, lower cost, and longer cycle life, making their large-scale application prospects particularly promising given abundant resources. However, the energy density and cycle stability of sodium-ion batteries still need improvement. In the structure of a sodium-ion battery, the electrolyte plays a crucial role, affecting not only the ion transport rate but also directly influencing the battery's safety and performance.

[0003] Introducing additives to modify electrolytes offers advantages such as simplicity, effectiveness, and cost-effectiveness. It helps enhance the electrolyte's high-voltage resistance, rate performance, and safety, which is crucial for the continuous and efficient operation of batteries. Additives are typically salts or solvent molecules with lower LUMO or higher HOMO values. They usually act as sacrificial agents to improve the physicochemical properties of the electrode-electrolyte interface, forming a stable and robust interface.

[0004] However, current electrolyte additives face a series of problems. First, the high cost not only increases battery production costs but also limits the competitiveness of sodium-ion batteries in the market. Second, sodium metal forms an uneven deposition layer on the electrode surface during charging and discharging. This unevenness not only affects the battery's cycle stability but may also cause safety issues such as short circuits. Furthermore, severe dendrite growth is also a major challenge for current electrolyte additives. The formation of sodium dendrites can damage the battery's electrolyte interface, leading to a sharp decline in battery performance and even battery failure.

[0005] In summary, the research and application of electrolyte additives for sodium-ion batteries face numerous challenges. To promote the widespread use of sodium-ion batteries, it is necessary to continuously explore novel, efficient, and low-cost electrolyte additives to solve current problems and improve battery performance and safety.

[0006] Therefore, it is necessary to develop an electrolyte additive that is compatible with electrolyte components, inexpensive, and capable of forming a stable SEI film. Summary of the Invention

[0007] The purpose of this invention is to provide an electrolyte that can form a stable SEI film and allow sodium metal to be deposited uniformly, thereby effectively improving the cycle life of the battery.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] An electrolyte comprising a solvent, a sodium salt, and additives;

[0010] The additive includes at least one having a structure of formula I, formula II and formula III;

[0011]

[0012] In Formula I, R1, R2, and R3 are each independently selected from alkyl, halogen, or hydrogen groups, with at least one of them selected from a halogen group; in Formula II, R4, R5, and R6 are each independently selected from alkyl, halogen, or hydrogen groups, with at least one of them selected from a halogen group; in Formula III, R7, R8, and R9 are each independently selected from alkyl, halogen, or hydrogen groups, with at least one of them selected from a halogen group; M is selected from K, Na, and Li; and A is selected from F, Cl, and Br.

[0013] Preferably, R1, R2, and R3 are independently selected from fluorine groups;

[0014] And / or, R4, R5 and R6 are independently selected from fluorine groups;

[0015] And / or, R7, R8 and R9 are independently selected from fluorine groups.

[0016] Preferably, M is selected from K.

[0017] Preferably, A is selected from Cl.

[0018] Preferably, the amount of the additive is 1 to 100 mM.

[0019] Preferably, the solvent is at least one selected from diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, dioxolane, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0020] Preferably, the sodium salt is at least one selected from sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium perchlorate, sodium bis(trifluoromethanesulfonyl)imide, trimethylammonium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0021] Preferably, the electrolyte further includes one or more auxiliary additives selected from at least one of 1,3-propenesulfonate lactone, vinylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, vinyl sulfate, ethylene carbonate, ethylene sulfite, 1,4-butanesulfonate lactone, fluoroethylene carbonate, difluoroethylene carbonate, ethylene glycol dipropionitrile ether, fluoroethylene carbonate, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

[0022] Preferably, the auxiliary additive accounts for 0.1% to 10% of the mass fraction of the electrolyte.

[0023] The present invention also provides a sodium-ion battery comprising the electrolyte described in any of the preceding paragraphs.

[0024] The beneficial effects of this invention are as follows: Addressing the problems existing on the sodium metal electrode side of sodium-ion batteries, this invention provides an electrolyte that ensures uniform sodium metal deposition even under high current density conditions. This characteristic significantly suppresses a series of negative phenomena such as dendrite formation, thereby greatly enhancing the reversibility of sodium metal deposition. Consequently, the sodium-ion battery exhibits excellent rate performance and outstanding capacity retention. Attached Figure Description

[0025] Figure 1 The LSV negative scan curves of sodium-ion batteries in Example 1 and Comparative Example 1 of this invention are shown.

[0026] Figure 2 The LSV negative scan curves of sodium-ion batteries in Example 1 and Comparative Example 1 of this invention are shown.

[0027] Figure 3 The above are time-voltage curves of sodium-ion batteries of Example 1 and Comparative Example 1 of the present invention at different current densities.

[0028] Figure 4 The above are time-voltage curves of sodium-ion batteries of Example 1 and Comparative Example 1 of the present invention at different current densities and deposition amounts.

[0029] Figure 5 The rate performance diagrams are for sodium-ion batteries of Example 1 and Comparative Example 1 of the present invention.

[0030] Figure 6 Long-cycle testing of sodium-ion batteries in Example 1 and Comparative Example 1 of this invention;

[0031] Figure 7 This is a negative electrode SEM image of Embodiment 1 of the present invention;

[0032] Figure 8 This is a negative electrode SEM image of Comparative Example 1 of the present invention. Detailed Implementation

[0033] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] According to a first aspect of the present invention, an electrolyte is provided, comprising a solvent, a sodium salt, and an additive;

[0035] The additive includes at least one having a structure of formula I, formula II and formula III;

[0036]

[0037] In Formula I, R1, R2, and R3 are each independently selected from alkyl, halogen, or hydrogen groups, with at least one of them selected from a halogen group; in Formula II, R4, R5, and R6 are each independently selected from alkyl, halogen, or hydrogen groups, with at least one of them selected from a halogen group; in Formula III, R7, R8, and R9 are each independently selected from alkyl, halogen, or hydrogen groups, with at least one of them selected from a halogen group; M is selected from K, Na, and Li; and A is selected from F, Cl, and Br.

[0038] The anions of this additive preferentially adsorb and decompose on the surface of the metal anode, forming an SEI layer rich in inorganic components such as NaF, Na3N, and BO. This SEI layer has good electronic insulation properties, which can prevent the direct transfer of electrons between the electrode and the electrolyte, avoid continuous solvent decomposition, and reduce side reactions. The interface also has high conductivity, high interface energy, and mechanical stability, which can reduce the diffusion barrier and nucleation barrier of sodium ions at the interface, which is conducive to the rapid transport of sodium ions at the interface. Under high current density, it avoids the rapid formation of dendrites due to local accumulation of sodium ions, ensuring that the anode interface has less volume expansion and a smoother surface during long-term cycling.

[0039] Secondly, the additive of this invention utilizes the electrostatic shielding of alkali metal ions, allowing anions to preferentially decompose on the surface of the metal anode to form an SEI layer rich in various inorganic components. This effectively reduces the diffusion and nucleation energy barrier of sodium ions, facilitating rapid transport, avoiding rapid dendrite formation under high current density, reducing the volume expansion of the anode interface, and maintaining a smooth surface. At the same time, it changes the solvation structure of the sodium ion electrolyte, promotes the desolvation of sodium ions, improves interfacial dynamics, and achieves stable cycling of sodium metal batteries at high rates.

[0040] Furthermore, pyridine molecules, due to their unique chemical structure, can effectively interact with other components in the electrolyte within sodium-ion batteries, forming a stable chemical environment. This stable environment helps reduce sodium corrosion and dendrite growth during battery charging and discharging, thereby extending battery life.

[0041] More importantly, the presence of pyridine groups can also optimize the ion conductivity of the electrolyte. This is achieved by promoting the ion conductivity of Na+. +The migration and diffusion of ions, particularly the pyridine group, contribute to improving the charge / discharge rate and energy density of the battery. This means that sodium-ion batteries using electrolytes containing pyridine groups can exhibit superior power output and energy storage capabilities.

[0042] In one embodiment of the present invention, R1, R2 and R3 are independently selected from fluorine groups;

[0043] And / or, R4, R5 and R6 are independently selected from fluorine groups;

[0044] And / or, R7, R8 and R9 are independently selected from fluorine groups.

[0045] Compared to fluorine groups, the presence of other halogen groups significantly enhances the overall activity of the molecule, potentially negatively impacting the construction of a stable battery interface. Therefore, this invention further prefers fluorine groups. Fluorine's strong electronegativity and low polarization help form a stable solid electrolyte interphase (SEI) film on the positive and negative electrode surfaces. This film not only has high mechanical strength but also effectively prevents side reactions between the electrolyte and electrode materials, thereby slowing down battery capacity decay and improving cycle stability and capacity retention. Furthermore, fluorine-containing additives can improve the ionic conductivity of the electrolyte, reduce internal resistance and self-discharge rate, and thus enhance charge / discharge efficiency and energy density. Therefore, fluorine-containing electrolyte additives play a crucial role in improving overall battery performance.

[0046] In one embodiment of the present invention, M is selected from K. + A positively charged electrostatic shield is formed at the tip, preventing the entry of Na... + The ions diffuse and deposit in the surrounding area, thereby promoting uniform and orderly ion deposition, effectively suppressing dendrite growth, and facilitating the formation of a stable interface.

[0047] K + Relatively easy to desolvate, forming K + and Na + The two solvation shell structures facilitate the entry of anions into the inner solvation shell, weaken the interaction between sodium ions and the solvent, promote the desolvation of sodium ions, further enhance interfacial dynamics, and enable the battery to achieve rapid, stable, and long-term cycling at high rates.

[0048] Among them, B, F, pyridine groups and K have a synergistic effect. Compared with additives containing only one of these four groups, additives containing all four groups have better overall battery performance when used in sodium-ion batteries. K + A positively charged electrostatic shield accumulates at the tip, effectively promoting the formation of Na + The ions diffuse and deposit in the region near the tip, achieving uniform ion deposition and suppressing the formation of sodium dendrites.

[0049] The PBF3 anion structure design, due to the high electron cloud density of N atoms, allows them to participate in the formation of the primary solvation sheath of Na and migrate to the negative electrode. The pyridine groups are uniformly adsorbed on the sodium metal surface, exhibiting high reactivity and preferentially participating in the formation of the negative electrode interface, which is beneficial for inducing the formation of an interface with high ionic conductivity and low electronic conductivity. The formation of inorganic components such as NaF and NaBO3 can create interfaces with high interfacial energy and mechanical stability. The formed Na3N component can promote the formation of Na... + Rapid transport helps to reduce the energy barriers for ion diffusion and nucleation at the interface.

[0050] In one embodiment of the present invention, A is selected from Cl. Formula III introduces a chlorine group onto the benzene ring. The chlorine group is a fast-charging interface component with better conductivity. Adding this group to the electrolyte helps to improve the overall rate performance of the battery, thereby optimizing the chemical properties of the electrolyte. This optimization further improves the overall performance of the battery, such as increasing energy density and enhancing cycle stability, laying a solid foundation for the widespread application of sodium-ion batteries.

[0051] In one embodiment of the present invention, the amount of additive added is 1 to 100 mM. Appropriate amounts of additive can improve the ion transport performance of the electrolyte, enhance battery performance and safety, reduce costs, and improve sustainability. In specific implementations, the amount of additive should be appropriately adjusted within the range specified in the present invention according to the actual usage scenario.

[0052] In one embodiment of the present invention, the solvent is at least one selected from diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, dioxolane, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0053] In one embodiment of the present invention, the sodium salt is at least one selected from sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium perchlorate, sodium bis(trifluoromethanesulfonyl)imide, trimethylammonium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0054] In one embodiment of the present invention, the electrolyte further includes one or more auxiliary additives selected from at least one of 1,3-propenesulfonate lactone, vinylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, vinyl sulfate, ethylene carbonate, ethylene sulfite, 1,4-butanesulfonate lactone, fluoroethylene carbonate, difluoroethylene carbonate, ethylene glycol dipropionitrile ether, fluoroethylene carbonate, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

[0055] In one embodiment of the present invention, the auxiliary additive accounts for 0.1% to 10% of the mass fraction of the electrolyte.

[0056] According to a second aspect of the present invention, the present invention also provides a sodium-ion battery, comprising a negative electrode, a positive electrode, a separator, and an electrolyte mentioned in any of the preceding paragraphs. The positive electrode, separator, and negative electrode are sequentially stacked and fabricated into a bare cell by winding or stacking, then packaged, and injected with electrolyte. The sodium-ion battery is then obtained through processes such as formation and capacity testing. The negative electrode comprises a negative current collector and a negative active material layer coated on at least one surface of the negative current collector. The negative active material layer may be one or more of the following: graphite, soft carbon, hard carbon, carbonyl compounds, Schiff compounds, organic free radical compounds, organic sulfides, and titanium-based materials. The negative current collector is preferably copper foil.

[0057] The positive electrode includes a positive current collector and a positive active material layer coated on at least one surface of the positive current collector. The positive active material layer can be one or more of the following: Na,CoO2, NaxMnO2 and its doped compounds, polyanionic compounds, NaFePO4, and NASICON-type phosphate Na3V2(PO4)3. The positive current collector is preferably aluminum foil.

[0058] The separator can be selected from various separators used in sodium-ion batteries that are known to those skilled in the art, such as polypropylene microporous membranes, polyethylene felt, glass fiber felt, or ultrafine glass fiber paper.

[0059] To make the technical solution and advantages of the present invention clearer, the present invention will be further described below through specific embodiments.

[0060] Example 1

[0061] Electrolyte preparation:

[0062] Weigh 0.168g of NaPF6 solid and add it to 1mL of DME. After it is fully dissolved, add 0.001g of KPBF3 and dissolve it completely to obtain the electrolyte.

[0063] Preparation method of sodium-ion battery:

[0064] The positive and negative electrode sheets and the separator were cut to the size suitable for the 2032 battery case. In this experiment, the positive electrode material was NVP, and the negative electrode sheet was sodium metal.

[0065] In an anhydrous and oxygen-free environment, the battery was assembled in the following order: negative electrode shell, negative electrode sheet, separator, positive electrode sheet, gasket, spring sheet and positive electrode shell. During the assembly process, 100 μL of electrolyte was injected and the battery was sealed to obtain the 2032 type Newna battery.

[0066] Table 1 shows the preparation parameters for the examples and comparative examples. All other parameters are the same as those in Example 1, and will not be repeated here.

[0067] Table 1

[0068]

[0069]

[0070] Performance testing:

[0071] The sodium-ion batteries of Examples 1-9 and Comparative Example 1 were subjected to electrochemical performance tests, and the test results are as follows: Figures 1-8 As shown in Table 2.

[0072] Table 2

[0073]

[0074]

[0075] As shown in Table 1, the experimental data of Examples 1-9 are all superior to those of Comparative Example 1, indicating that the addition of the additive of the present invention can improve the oxidation stability of the electrolyte and ensure uniform deposition of sodium metal under high current density conditions. This characteristic significantly suppresses a series of negative phenomena such as dendrite formation, thereby greatly enhancing the reversibility of sodium metal deposition. Consequently, the sodium-ion battery also exhibits excellent rate performance and high capacity retention.

[0076] Depend on Figure 1 and Figure 2 It can be seen that the sodium-ion battery of Example 1 exhibits a decomposition peak of the additive at 1.7V, indicating that the additive can decompose at the negative electrode to form an SEI; the solvent decomposition peak intensity decreases at 0.75V, indicating that the SEI layer has good electronic insulation properties, preventing direct electron transfer between the electrode and the electrolyte, avoiding continuous solvent decomposition, and reducing side reactions. Figure 2 The starting potential at which the oxidation current begins to rise significantly in Example 1 is significantly higher than that in Comparative Example 1. This indicates that the electrolyte system of the present invention requires a higher potential to undergo a significant oxidation reaction, demonstrating that the addition of additives can enhance the oxidation stability of the electrolyte.

[0077] Depend on Figure 3 and Figure 4 It can be seen that the polarization voltage of the symmetrical battery in Example 1 is reduced and the curve has no obvious fluctuation, indicating that the electrolyte of the present invention has excellent properties in many aspects, such as reducing charge transfer resistance, increasing ion diffusion rate, enhancing interface stability, and improving battery performance and efficiency.

[0078] Depend on Figure 5 and Figure 6It can be seen that the battery of Example 1 can maintain stable and efficient energy conversion and storage capabilities under different charge and discharge rates. Whether in high-rate fast charge and discharge scenarios or in relatively low-rate conventional charge and discharge processes, it exhibits good adaptability, ensuring that key performance indicators such as voltage and capacity do not show significant attenuation or fluctuation when the battery rapidly absorbs or releases energy. This effectively guarantees that the battery meets different power requirements in various practical application scenarios. Furthermore, the electrolyte system of this invention can ensure that the battery capacity retention rate remains at a high level, the structural integrity of the electrode materials is not significantly damaged, and the interface stability inside the battery is well maintained. There are no adverse phenomena such as a sharp decrease in capacity or a significant increase in internal resistance caused by long-term cyclic use. This fully demonstrates that the sodium metal full battery has a strong ability to withstand cyclic stress and can continuously and stably provide a reliable power supply during long-term use.

[0079] Depend on Figure 7 and Figure 8 It can be seen that the thickness of the sodium metal deposited on the positive electrode in Comparative Example 1 is uneven and the dendrite growth is severe, which also indicates that the mechanical strength of the positive electrode interface in Comparative Example 1 is low and cannot suppress dendrite growth.

[0080] The sodium metal deposited in Example 1 with the addition of additives has a smoother surface and no obvious dendrite growth, indicating that the interface has high mechanical strength, can effectively suppress dendrite growth, and the sodium metal volume does not expand excessively, with uniform thickness.

[0081] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A sodium-ion battery electrolyte, characterized in that, Including solvents, sodium salts, and additives; The additive includes at least one having a structure of formula I, formula II and formula III; Formula I Formula II Formula III In Formulas I, II, and III, R1, R2, and R3 are each independently selected from alkyl, halogen, or hydrogen, and at least one of R1, R2, and R3 is selected from halogen; M is selected from one of K, Na, and Li; the amount of the additive added is 1~100mM.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, R1, R2, and R3 are each independently selected from fluorine.

3. The sodium-ion battery electrolyte according to claim 1, characterized in that, M is selected from K.

4. The sodium-ion battery electrolyte according to claim 1, characterized in that, The solvent is at least one of diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, dioxolane, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

5. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt is at least one of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium perchlorate, sodium bis(trifluoromethanesulfonyl)imide, and sodium bis(fluorosulfonyl)imide.

6. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium-ion battery electrolyte further includes auxiliary additives selected from at least one of 1,3-propenesulfonate lactone, vinylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, vinyl sulfate, ethylene carbonate, ethylene sulfite, 1,4-butanesulfonate lactone, fluoroethylene carbonate, difluoroethylene carbonate, ethylene glycol dipropionitrile ether, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

7. The sodium-ion battery electrolyte according to claim 6, characterized in that, The auxiliary additive accounts for 0.1% to 10% of the mass fraction of the sodium-ion battery electrolyte.

8. A sodium-ion battery, characterized in that, Includes the sodium-ion battery electrolyte according to any one of claims 1 to 7.

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