Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The invention provides a sodium ion battery electrolyte and a sodium ion battery. The sodium-ion battery electrolyte comprises a sodium salt, an organic solvent and an additive, wherein the additives comprise a flame-retardant additive and a high-temperature additive, and the mass ratio of the flame-retardant additive to the high-temperature additive is (0.1-0.5): (0.5-1.0); the flame-retardant additive comprises at least one of trimethyl phosphate, triethyl phosphate and dimethyl methylphosphate, and the high-temperature additive comprises at least one of 1, 3-propane sultone and ethylene sulfate. By applying the technical scheme of the invention, through the mutual synergistic effect of the flame-retardant additive and the high-temperature additive in a specific mass ratio, the thermal stability of the electrolyte is improved, and the stability of an electrode interface is enhanced, so that the cycle performance and safety of the sodium-ion battery in a high-temperature environment are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a sodium ion battery electrolyte and a sodium ion battery. Background Art

[0002] In recent years, research on sodium-ion batteries has become a hot topic due to the growing shortage of lithium resources. Although sodium-ion batteries lack the capacity of lithium-ion batteries, their low cost makes them highly attractive for applications such as low-speed electric vehicles and large-scale energy storage. However, practical applications of sodium-ion batteries still face numerous challenges, particularly in terms of cycling performance and safety in high-temperature environments.

[0003] The carbonate-based electrolytes in existing sodium-ion batteries are key components for sodium ion transport between the positive and negative electrodes and for stabilizing the electrode interface. However, their inherent flammability makes them the primary mediator of the battery's thermal runaway reaction chain, posing a significant safety risk. Furthermore, the battery's cycling performance and other electrochemical properties significantly degrade under high-temperature conditions, severely hindering the further development of sodium-ion batteries. Therefore, developing an electrolyte that remains stable under high-temperature conditions and exhibits excellent cycling performance is crucial for the advancement of sodium-ion battery technology.

[0004] As a key component in direct contact between the positive and negative electrode materials in a battery, the electrolyte not only plays the important role of conducting sodium ions but also determines the state of the electrode / electrolyte interface. To date, practical sodium-ion batteries have used liquid electrolytes. The requirements for liquid electrolytes generally need to meet the following aspects: high conductivity and an appropriate lithium-ion transference number; a wide electrochemical window, capable of maintaining stability within the operating voltage range of the positive and negative electrodes; good chemical stability, without self-decomposition or chemical reactions with the electrode materials; a wide operating temperature range, capable of remaining liquid in non-extreme environments; non-flammable, environmentally friendly, and low-cost. However, the safety issues and performance degradation of existing carbonate-based electrolytes at high temperatures have become bottlenecks restricting the large-scale application of sodium-ion batteries.

[0005] Therefore, in order to address the problem of reduced performance of existing sodium ion battery electrolytes under high temperature environments, it is urgent to develop a new electrolyte system to improve the electrochemical performance and safety of batteries under high temperature conditions. Summary of the Invention

[0006] The main purpose of the present invention is to provide a sodium ion battery electrolyte and a sodium ion battery to solve the problem of poor high-temperature performance of sodium ion batteries in the prior art.

[0007] To achieve the above-mentioned object, according to one aspect of the present invention, a sodium ion battery electrolyte is provided, which comprises a sodium salt, an organic solvent and an additive; wherein the additive comprises a flame retardant additive and a high-temperature additive, and the mass ratio of the additive and the high-temperature additive is (0.1-0.5): (0.5-1.0); the flame retardant additive comprises at least one of trimethyl phosphate, triethyl phosphate and dimethyl methyl phosphate, and the high-temperature additive comprises at least one of 1,3-propane sultone and vinyl sulfate.

[0008] Furthermore, in the electrolyte, the total content of the flame retardant additive and the high temperature additive is 0.8 wt% to 2 wt%.

[0009] Furthermore, the organic solvent includes ethylene carbonate, propylene carbonate, ethyl methyl carbonate and diethyl carbonate, and the mass ratio of the four is (0.4-0.8): (0.2-0.5): (0.1-0.8): (0.15-1.0).

[0010] Furthermore, in the organic solvent, the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate and diethyl carbonate is (0.4-0.8):(0.2-0.25):(0.1-0.8):0.15.

[0011] Furthermore, in the organic solvent, the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate and diethyl carbonate is (0.5-0.8):0.2:(0.15-0.8):0.15.

[0012] Further, the sodium salt includes NaPF6 and / or NaFSI.

[0013] Furthermore, the sodium salts are NaPF6 and NaFSI, and the mass ratio of the two is (0.5-0.7): (0.5-0.3).

[0014] Furthermore, the concentration of the sodium salt is 1 mol / L to 1.5 mol / L.

[0015] Furthermore, the preparation method of the sodium ion battery electrolyte includes the following steps: mixing a sodium salt, an organic solvent and an additive to obtain the sodium ion battery electrolyte.

[0016] According to another aspect of the present invention, a sodium ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and the sodium ion battery electrolyte provided by the first aspect above.

[0017] By applying the technical solution of the present invention, the sodium ion battery electrolyte provided by the present invention adjusts the chemical properties of the sodium ion battery electrolyte through a flame retardant additive and a high-temperature additive in a specific mass ratio. The phosphate compound as a flame retardant additive improves the thermal stability of the electrolyte, providing a stable environment for the high-temperature additive to form a uniform and dense SEI film on the electrode surface. The SEI film formed by the high-temperature additive further enhances the stability of the electrode interface, reduces the decomposition of the electrolyte and the corrosion of the electrode material at high temperature, thereby significantly improving the electrochemical performance and safety of the sodium ion battery in a high-temperature environment, and achieving a synergistic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0019] Figure 1 The figures show the battery cycle performance of the sodium ion battery provided in Example 1 and Comparative Example 1 according to the present invention at 45°C;

[0020] Figure 2 The battery cycle performance of the sodium ion battery provided by Example 15 of the present invention and Comparative Example 2 at 45° C. is shown. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] As described in the background of this application, the high-temperature performance of sodium-ion batteries is currently poor. To address this problem, this application provides a sodium-ion battery electrolyte and a sodium-ion battery.

[0023] In a first typical embodiment of the present application, a sodium ion battery electrolyte is provided, which includes a sodium salt, an organic solvent and an additive; wherein the additive includes a flame retardant additive and a high-temperature additive, and the mass ratio of the two is (0.1-0.5): (0.5-1.0); the flame retardant additive includes at least one of trimethyl phosphate, triethyl phosphate and dimethyl methyl phosphate, and the high-temperature additive includes at least one of 1,3-propane sultone and vinyl sulfate.

[0024] The sodium ion battery electrolyte provided by the present invention adjusts the chemical properties of the sodium ion battery electrolyte by using a flame retardant additive and a high-temperature additive in a specific mass ratio. The phosphate compound as a flame retardant additive improves the thermal stability of the electrolyte, providing a stable environment for the high-temperature additive to form a uniform and dense SEI film on the electrode surface. The SEI film formed by the high-temperature additive further enhances the stability of the electrode interface, reduces the decomposition of the electrolyte and the corrosion of the electrode material at high temperatures, thereby significantly improving the electrochemical performance and safety of the sodium ion battery in a high-temperature environment and achieving a synergistic effect.

[0025] Typically but not limitatively, in the sodium ion battery electrolyte provided in the present application, the mass ratio of the flame retardant additive and the high temperature additive is, for example, 0.5:0.5, 0.5:1.0, 0.1:0.5, 0.1:1.0, 0.3:0.7 or a range value consisting of any two values.

[0026] In some embodiments, the total content of the flame retardant additive and the high-temperature additive is 0.8 wt% to 2 wt% based on the total mass of the electrolyte as 100%. If the total content of the additives is too low, the flame retardant performance will be reduced or the SEI film will not be fully formed, resulting in an unstable SEI film structure, which will reduce the electrochemical performance and safety of the battery at high temperatures. If the total content of the additives is too high, it will cause excessive side reactions within the battery, affecting the electrochemical stability of the electrolyte and reducing the electrochemical performance of the sodium ion battery.

[0027] Typically but not limitatively, based on the total mass of the electrolyte as 100%, the total content of flame retardant additives and high temperature additives is 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2.0wt% or a range consisting of any two values.

[0028] In some embodiments, the organic solvent includes ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate, and the mass ratio of the four is (0.4-0.8): (0.2-0.5): (0.1-0.8): (0.15-1.0).

[0029] The present invention optimizes the composition of the organic solvent. The organic solvent composed of the above four components and a specific mass ratio can effectively reduce the viscosity of the sodium ion battery electrolyte, thereby improving the transport capacity of sodium ions in the electrolyte; at the same time, the organic solvent has a high dielectric constant, further improving the conductivity of the electrolyte, thereby more effectively improving the electrochemical performance of the sodium ion battery.

[0030] In addition, the organic solvent has good compatibility with flame retardant additives and high-temperature additives, allowing these additives to be evenly dispersed in the organic solvent and fully exert their functions. The flame retardant additive enhances the safety of the battery by improving the thermal stability and flame retardancy of the electrolyte; the high-temperature additive forms a stable solid electrolyte interface (SEI) film on the electrode surface, inhibiting side reactions at high temperatures and improving the electrochemical performance of the battery. Due to the synergistic effect of the organic solvent and the additive, the additive can achieve high efficiency at a smaller dosage, further improving the electrochemical performance and safety of sodium-ion batteries at high temperatures.

[0031] Typically but not limitatively, in the organic solution provided herein, the masses of ethylene carbonate, propylene carbonate, ethyl methyl carbonate and diethyl carbonate are, for example, 0.5:0.2:0.15:0.15, 0.4:0.25:0.1:0.15, 0.5:0.2:0.15:0.15, 0.4:0.25:0.1:0.15, 0.4:0.5:0.1:1.0, 0.8:0.2:0.8:0.15 or a range value consisting of any two numerical values.

[0032] In order to further reduce the viscosity of the sodium ion battery electrolyte, increase its dielectric constant, and thereby more effectively improve the electrochemical performance and flame retardant properties of the sodium ion battery at high temperature, in other embodiments, the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate and diethyl carbonate is preferably (0.4-0.8): (0.2-0.25): (0.1-0.8): 0.15; more preferably (0.5-0.8): 0.2: (0.15-0.8): 0.15.

[0033] In order to further improve the conductivity of the sodium ion battery electrolyte and promote the rapid migration of sodium ions in the electrolyte, the sodium salt preferably includes NaPF6 and / or NaFSI.

[0034] In order to further promote the rapid migration of sodium ions in the electrolyte and further ensure the thermal stability of the electrolyte, the preferred sodium salts are NaPF6 and NaFSI, and the mass ratio of the two is (0.5-0.7): (0.5-0.3).

[0035] Typically, but not limitatively, in the sodium salt provided herein, the mass ratio of NaPF6 to NaFSI is 0.5:0.5, 0.5:0.3, 0.7:0.5, 0.7:0.3 or a range consisting of any two values.

[0036] In order to effectively balance the conductivity and viscosity of the sodium-ion battery electrolyte, ensure a high migration rate of sodium ions in the electrolyte, and thus improve the electrochemical performance of the sodium-ion battery, the preferred sodium salt concentration is 1 mol / L to 1.5 mol / L. When the sodium salt concentration is too low, the conductivity will be insufficient. When the sodium salt concentration is too high, the electrolyte viscosity will increase and the ion migration resistance will increase.

[0037] Typically, but not limited to, the concentration of the sodium salt is 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L or a range consisting of any two values.

[0038] In some embodiments, a method for preparing a sodium ion battery electrolyte comprises the following steps: mixing a sodium salt, an organic solvent, and an additive to obtain a sodium ion battery electrolyte. The method is simple to operate and suitable for large-scale industrial production.

[0039] In a second typical embodiment of the present application, a sodium ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and the sodium ion battery electrolyte provided in the first typical embodiment.

[0040] The sodium ion battery uses the above-mentioned sodium ion battery electrolyte as the electrolyte, and utilizes a flame retardant additive and a high-temperature additive in a specific mass ratio in the sodium ion battery electrolyte to adjust the chemical properties of the sodium ion battery electrolyte. Among them, the phosphate compound as a flame retardant additive improves the thermal stability of the electrolyte, providing a stable environment for the high-temperature additive to form a uniform and dense SEI film on the electrode surface. The SEI film formed by the high-temperature additive further enhances the stability of the electrode interface, reduces the decomposition of the electrolyte and the corrosion of the electrode material at high temperature, thereby significantly improving the electrochemical performance and safety of the sodium ion battery in a high-temperature environment, and achieving a synergistic effect.

[0041] Furthermore, the organic solvent in the sodium-ion battery electrolyte can effectively reduce the viscosity of the sodium-ion battery electrolyte, thereby improving the transport capacity of sodium ions in the electrolyte. Furthermore, the organic solvent has a high dielectric constant, which can enhance the dissociation degree of sodium ions in the electrolyte, further improving the conductivity of the electrolyte, thereby more effectively improving the electrochemical performance of the sodium-ion battery. Furthermore, the organic solvent has good compatibility with flame retardant additives and high-temperature additives, allowing these additives to be evenly dispersed in the organic solvent, more fully exerting their functions and improving the electrochemical performance and safety of the sodium-ion battery in high-temperature environments.

[0042] The beneficial effects of the present application will be further illustrated below with reference to examples and comparative examples.

[0043] Example 1

[0044] This embodiment provides a sodium ion battery electrolyte, the preparation method of which includes the following steps: in an argon-filled glove box, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate are mixed in a mass ratio of 0.5:0.2:0.15:0.15 to obtain an organic solvent; then, sodium salt is stirred and mixed with the organic solvent to obtain a mixed solution with a sodium salt concentration of 1 mol / L. The sodium salt includes NaPF6 and NaFSI, and the mass ratio of the two is 0.7:0.3; based on the total mass of the electrolyte as 100%, 1.4wt% of additives (the total content of flame retardant additives and high-temperature additives) are added to the mixed solution, and stirred and mixed to obtain a sodium ion battery electrolyte. The flame retardant additive is trimethyl phosphate (TMP) and the high-temperature additive is 1,3-propane sultone (PS), and the mass ratio of the two is 0.3:0.7.

[0045] Example 2

[0046] The difference from Example 1 is that the mass ratio of trimethyl phosphate (TMP) and 1,3-propane sultone (PS) in this example is adjusted to be 0.1:0.5.

[0047] Example 3

[0048] The difference from Example 1 is that in this example, the mass ratio of trimethyl phosphate (TMP) and 1,3-propane sultone (PS) is adjusted to be 0.1:1.0.

[0049] Example 4

[0050] The difference from Example 1 is that the mass ratio of trimethyl phosphate (TMP) and 1,3-propane sultone (PS) in this example is adjusted to be 0.5:0.5.

[0051] Example 5

[0052] The difference from Example 1 is that the mass ratio of trimethyl phosphate (TMP) and 1,3-propane sultone (PS) in this example is adjusted to be 0.5:1.0.

[0053] Example 6

[0054] The difference from Example 1 is that in this example, the flame retardant additive is adjusted to dimethyl methyl phosphate (DMMP) and the high-temperature additive is adjusted to 1,3-propane sultone (PS).

[0055] Example 7

[0056] The difference from Example 1 is that the flame retardant additive in this example is adjusted to dimethyl methyl phosphate (DMMP) and the high-temperature additive is diethyl thiosulfate (DTD).

[0057] Example 8

[0058] The difference from Example 1 is that in this example, the flame retardant additive is adjusted to trimethyl phosphate (TMP) and the high-temperature additive is diethyl thiosulfate (DTD).

[0059] Example 9

[0060] The difference from Example 1 is that in this example, the flame retardant additive is adjusted to triethyl phosphate (TEP) and the high-temperature additive is diethyl thioester (DTD).

[0061] Example 10

[0062] The difference from Example 1 is that in this example, the flame retardant additive is adjusted to triethyl phosphate (TEP) and the high-temperature additive is adjusted to 1,3-propane sultone (PS).

[0063] Example 11

[0064] The difference from Example 1 is that this example adjusts the total content of the additives, so that 2 wt% of additives (the total content of the flame retardant additive and the high temperature additive) are added to the mixed solution, based on the total mass of the electrolyte being 100%.

[0065] Example 12

[0066] The difference from Example 1 is that the total content of the additives in this example is adjusted, so that 0.8 wt% of additives (the total content of flame retardant additives and high temperature additives) is added to the mixed solution, based on the total mass of the electrolyte being 100%.

[0067] Example 13

[0068] The difference from Example 1 is that the total content of the additives in this example is adjusted, so that 0.4 wt% of additives (the total content of the flame retardant additives and the high temperature additives) is added to the mixed solution, based on the total mass of the electrolyte being 100%.

[0069] Example 14

[0070] The difference from Example 1 is that this example adjusts the total content of the additives, so that 3 wt% of additives (the total content of the flame retardant additives and the high temperature additives) are added to the mixed solution, based on the total mass of the electrolyte being 100%.

[0071] Example 15

[0072] The difference from Example 1 is that this example adjusts the ratio of the components in the organic solvent so that the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 0.4:0.25:0.1:0.15.

[0073] Example 16

[0074] The difference from Example 1 is that this example adjusts the ratio of the components in the organic solvent so that the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 0.4:0.5:0.1:1.0.

[0075] Example 17

[0076] The difference from Example 1 is that this example adjusts the ratio of the components in the organic solvent so that the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 0.8:0.2:0.8:0.15.

[0077] Example 18

[0078] The difference from Example 1 is that this example adjusts the ratio of the components in the organic solvent so that the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 0.5:0.2:1.2:0.15.

[0079] Example 19

[0080] The difference from Example 1 is that this example adjusts the ratio of the components in the organic solvent so that the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 0.5:0.2:0.04:0.15.

[0081] Example 20

[0082] The difference from Example 1 is that the components of the organic solvent in this example are adjusted so that the organic solvent includes ethylene carbonate, propylene carbonate, and ethyl methyl carbonate, and the mass ratio of the three is 0.5:0.2:0.15.

[0083] Example 21

[0084] The difference from Example 1 is that the present embodiment adjusts the components of the organic solvent so that the organic solvent includes ethylene carbonate and propylene carbonate, and the mass ratio of the two is 0.5:0.2.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that no flame retardant additive and high temperature additive are added to this comparative example.

[0087] Comparative Example 2

[0088] The difference from Example 15 is that no flame-retardant additive and high-temperature additive is added in this comparative example.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that the only additive in this comparative example is the flame-retardant additive trimethyl phosphate (TMP).

[0091] Comparative Example 4

[0092] The difference from Example 1 is that the only additive in this comparative example is the high-temperature additive 1,3 propane sultone (PS).

[0093] Comparative Example 5

[0094] The difference from Example 1 is that the mass ratio of trimethyl phosphate (TMP) and 1,3 propane sultone (PS) is adjusted in this comparative example, so that the mass ratio of the two is 0.1:1.5.

[0095] Comparative Example 6

[0096] The difference from Example 1 is that the mass ratio of trimethyl phosphate (TMP) and 1,3 propane sultone (PS) is adjusted in this comparative example, so that the mass ratio of the two is 1.0:0.5.

[0097] Test Example 1

[0098] The sodium ion battery electrolyte obtained in the above examples and comparative examples is assembled into a sodium ion battery respectively, and the preparation process is as follows:

[0099] (1) Preparation of positive electrode sheet: the positive electrode material NFM (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2), the binder PVDF (polyvinylidene fluoride), and the conductive agent SP (conductive carbon black) are stirred and mixed uniformly in a mass ratio of 96:2.5:1.5 with the solvent NMP (N-methyl-2-pyrrolidone) to obtain a positive electrode slurry with a viscosity of 6000 mP·s. The positive electrode slurry is uniformly coated on the current collector aluminum foil, dried, and rolled to obtain a positive electrode sheet.

[0100] (2) Preparation of negative electrode sheet: the negative electrode material hard carbon, the thickening agent CMC (carboxymethyl cellulose), the binder SBR (styrene-butadiene rubber), and the conductive agent SP (conductive carbon black) are stirred and mixed uniformly in a mass ratio of 96.5:1:2:0.5 with water to obtain a negative electrode slurry with a viscosity of 5500 mP·s. The negative electrode slurry is uniformly coated on the current collector aluminum foil, dried, and rolled to obtain a negative electrode sheet.

[0101] (3) Preparation of diaphragm: PE (polyethylene) or PP (polypropylene) is used as the base material and ceramic is coated on one side to obtain a diaphragm, where the ceramic side corresponds to the positive electrode.

[0102] (4) Preparation of sodium ion batteries: The positive electrode sheet, separator, and negative electrode sheet are stacked and assembled in sequence, the corresponding sodium ion battery electrolyte is injected and sealed, and then the sodium ion battery is prepared through chemical formation.

[0103] The sodium ion batteries prepared using the electrolytes of the examples and comparative examples were subjected to high temperature cycle performance tests. The test conditions are shown below, and the test results are shown in Table 1.

[0104] Capacity retention rate of high temperature cycle at 45℃:

[0105] At 45°C, the sodium ion battery was charged at a constant current and constant voltage of 0.33C, with a voltage limit of 3.9V and a current limit of 0.05C. It was discharged at a constant current of 0.33C and a voltage limit of 1.5V. The discharge capacity of the sodium ion battery at this time was tested, which was the discharge capacity of the first cycle. The battery was cycled multiple times under the above conditions, and the capacity retention rate of the battery after 150 cycles was calculated.

[0106] The capacity retention rate after the cycle was calculated according to the following formula: Capacity retention rate (%) = (discharge capacity corresponding to 150 cycles / discharge capacity of the first cycle) × 100%.

[0107] Table 1

[0108]

[0109]

[0110] Compared with Comparative Examples 1-2 in which no flame retardant additive and high-temperature additive are added to the electrolyte, or Comparative Examples 3-4 in which only flame retardant additive or high-temperature additive is added to the electrolyte, or Comparative Examples 5-6 in which the mass ratio of flame retardant additive and high-temperature additive is too high or too low, when the mass ratio of flame retardant additive and high-temperature additive in Examples 1-10 is (0.1-0.5): (0.5-1.0), the flame retardant additive includes at least one of trimethyl phosphate, triethyl phosphate and dimethyl methyl phosphate, and the high-temperature additive includes at least one of 1,3-propane sultone and vinyl sulfate, the capacity retention rate of the sodium ion battery after 150 cycles at 45°C is high, indicating that the sodium ion battery has excellent electrochemical performance and safety under high temperature environment.

[0111] Figure 1 The battery cycle performance of the sodium ion battery provided by Example 1 and Comparative Example 1 at 45°C is shown. Figure 1It can be seen that compared with the comparative example 1 without adding flame retardant additives and high temperature additives, when flame retardant additives and high temperature additives are added in Example 1, the battery cycle performance is significantly improved, and during the cycle, the capacity retention rate reduction rate is also significantly reduced.

[0112] same, Figure 2 The battery cycle performance of the sodium ion battery provided by Example 15 and Comparative Example 2 at 45°C is shown. Figure 2 It can be seen that compared with Comparative Example 2 in which no flame retardant additives and high-temperature additives are added, when flame retardant additives and high-temperature additives are added in Example 15, the battery cycle performance is significantly improved, and during the cycle, the capacity retention rate reduction rate is also significantly reduced.

[0113] Compared with Examples 13-14 in which the total content of flame retardant additives and high-temperature additives in the electrolyte is too high or too low, when the total content of flame retardant additives and high-temperature additives in Examples 11-12 is 0.8wt% to 2wt% based on the total mass of the electrolyte as 100%, the capacity retention rate of the sodium ion battery after 150 cycles at 45°C is high, indicating that the sodium ion battery has excellent electrochemical performance and safety under high temperature environment.

[0114] Compared with the organic solvents in Examples 18-21 in which the mass of any one of the components of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate is too large or too small, or any one or more components are missing, when the organic solvents in Examples 15-17 include ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate, and the mass ratio of the four is (0.4-0.8): (0.2-0.5): (0.1-0.8): (0.15-1.0), the capacity retention rate of the sodium ion battery after 150 cycles at 45°C is high, indicating that the sodium ion battery has excellent electrochemical performance and safety under high temperature environment.

[0115] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0116] The sodium ion battery electrolyte provided by the present invention adjusts the chemical properties of the sodium ion battery electrolyte by using a flame retardant additive and a high-temperature additive in a specific mass ratio. The phosphate compound as a flame retardant additive improves the thermal stability of the electrolyte, providing a stable environment for the high-temperature additive to form a uniform and dense SEI film on the electrode surface. The SEI film formed by the high-temperature additive further enhances the stability of the electrode interface, reduces the decomposition of the electrolyte and the corrosion of the electrode material at high temperatures, thereby significantly improving the electrochemical performance and flame retardant properties of the sodium ion battery in a high-temperature environment, achieving a synergistic effect.

[0117] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A sodium ion battery electrolyte, characterized in that It includes sodium salt, organic solvent and additives; wherein the additives include flame retardant additives and high-temperature additives, and the mass ratio of the two is (0.1-0.5): (0.5-1.0); the flame retardant additive includes at least one of trimethyl phosphate, triethyl phosphate and dimethyl methyl phosphate, and the high-temperature additive includes at least one of 1,3-propane sultone and vinyl sulfate.

2. The sodium ion battery electrolyte according to claim 1, characterized in that In the electrolyte, the total content of the flame retardant additive and the high-temperature additive is 0.8 wt % to 2 wt %.

3. The sodium ion battery electrolyte according to claim 1, characterized in that The organic solvent includes ethylene carbonate, propylene carbonate, ethyl methyl carbonate and diethyl carbonate, and the mass ratio of the four is (0.4-0.8): (0.2-0.5): (0.1～0.8)：(0.15～1.0)。 4. The sodium ion battery electrolyte according to claim 1, characterized in that In the organic solvent, the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate and diethyl carbonate is (0.4-0.8): (0.2-0.25): (0.1-0.8): 0.

15.

5. The sodium ion battery electrolyte according to claim 1, characterized in that In the organic solvent, the mass ratio of ethylene carbonate, propylene carbonate, ethyl methyl carbonate and diethyl carbonate is (0.5-0.8):0.2:(0.15-0.8):0.

15.

6. The sodium ion battery electrolyte according to claim 1, characterized in that The sodium salt includes NaPF6 and / or NaFSI.

7. The sodium ion battery electrolyte according to claim 1, characterized in that The sodium salts are NaPF6 and NaFSI, and the mass ratio of the two is (0.5-0.7): (0.5-0.3).

8. The sodium ion battery electrolyte according to any one of claims 1 to 7, characterized in that The concentration of the sodium salt is 1 mol / L to 1.5 mol / L.

9. The sodium ion battery electrolyte according to any one of claims 1 to 7, characterized in that The preparation method of the sodium ion battery electrolyte comprises the following steps: The sodium salt, the organic solvent and the additive are mixed to obtain the sodium ion battery electrolyte.

10. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the sodium ion battery electrolyte according to any one of claims 1 to 9.

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