An electrolyte and its preparation method and application

Abstract

The present invention discloses an electrolyte and its preparation method and application, belonging to the field of battery technology. The electrolyte comprises the following raw materials: 1-ethoxy-1-trimethylsilylcyclopropane. The present invention uses 1-ethoxy-1-trimethylsilylcyclopropane as a high-voltage electrolyte additive, and through its own Si-C and electron-loss oxidation reaction, it combines with oxygen free radicals to form a new organosilicon compound to produce Si-O, which participates in the formation of a stable CEI film, which is covered on the surface of the positive electrode material, effectively suppresses the oxidative decomposition of the electrolyte under high voltage (above 4.5V), prevents the dissolution of transition metal ions in the positive electrode material, and improves the stability of the positive electrode material; thereby improving the cycle performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrolyte and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries (SIBs) have attracted significant attention in the energy storage field due to their abundance in the Earth's crust and lower cost compared to lithium-based materials. However, their widespread application is hampered by poor rate and cycle performance, as well as low initial efficiency. The electrolyte, the "bridge" connecting the positive and negative electrodes in a SIB, influences the battery's cycling and rate performance.

[0003] Carbonate electrolytes have a simple process and low cost; however, the carbonate electrolytes in related technologies have a low oxidation stability potential. At 4.5V, they will undergo irreversible oxidative decomposition on the surface of the highly oxidatively active positive electrode material, generating products such as CO2, H2O and polyvinyl carbonate (PEC), causing battery bloating, changes in the electrode interface composition, increased polarization, etc., which will lead to problems such as a significant deterioration in the cycle performance of the high-voltage positive electrode material, causing serious attenuation of the electrode cycle capacity, and failing to meet the application requirements of high-working voltage electrodes. Therefore, the above-mentioned electrolyte system still has many shortcomings. For example, under high voltage and high temperature conditions, the cycle performance and storage performance of the above-mentioned electrolyte system need to be improved.

[0004] In summary, it is necessary to develop an electrolyte with good cycle stability at high voltage. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides an electrolyte having good cycle stability under high voltage.

[0006] The present invention also provides a method for preparing the electrolyte.

[0007] The present invention also provides application of the electrolyte in sodium ion batteries.

[0008] Specifically, the present invention provides an electrolyte comprising the following raw materials: 1-ethoxy-1-trimethylsilylcyclopropane (CAS No.: 98720-98-0).

[0009] According to one technical solution of the electrolyte technical solution of the present invention, at least the following beneficial effects are achieved:

[0010] The present invention uses 1-ethoxy-1-trimethylsilylcyclopropane as a high-voltage electrolyte additive. The Si-C contained in the 1-ethoxy-1-trimethylsilylcyclopropane can undergo an electron-loss oxidation reaction and combine with oxygen free radicals to form a new organosilicon compound and generate Si-O. The product participates in the formation of a stable CEI film, which covers the surface of the positive electrode material. This effectively inhibits the oxidative decomposition of the electrolyte at high voltage (above 4.5V) and prevents the dissolution of transition metal ions in the positive electrode material, thereby improving the stability of the positive electrode material, thereby enhancing the cycle performance of the battery.

[0011] The equation for the oxidation reaction is as follows:

[0012]

[0013] At the same time, through the reduction reaction, 1-ethoxy-1-trimethylsilylcyclopropane grows a protective layer on the surface of the negative electrode material (graphite negative electrode material, etc.), which resists the corrosion and damage of transition metal ions to the negative electrode active material during high-temperature storage, and inhibits the increase of negative electrode impedance during the cycle process; thereby improving the cycle stability.

[0014] According to some embodiments of the present invention, the structural formula of the 1-ethoxy-1-trimethylsilylcyclopropane is shown below:

[0015]

[0016] According to some embodiments of the present invention, the electrolyte further includes the following preparation raw materials: a film-forming additive, a sodium salt, and a solvent.

[0017] Film-forming additives promote the formation of solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), thereby giving the battery better thermal and electrochemical stability.

[0018] Sodium salt is Na + The main provider of calcium, acting as electrolytes.

[0019] The solvent serves to dissolve film-forming additives, sodium salts, and the like.

[0020] According to some embodiments of the present invention, the electrolyte comprises the following raw materials in weight percentage: 0.5% to 1% of the 1-ethoxy-1-trimethylsilylcyclopropane, 1% to 2% of the film-forming additive, and 10% to 15% of the sodium salt.

[0021] By controlling the mass fraction of each preparation raw material within the above range, the cycle performance and rate performance of the battery can be effectively improved.

[0022] According to some embodiments of the present invention, the electrolyte is composed of the following raw materials in weight percentage: 0.5% to 1% of the 1-ethoxy-1-trimethylsilylcyclopropane, 1% to 2% of the film-forming additive, 10% to 15% of the sodium salt, and the remainder of the solvent.

[0023] According to some embodiments of the present invention, the mass of the 1-ethoxy-1-trimethylsilylcyclopropane accounts for 0.5% of the mass of the electrolyte.

[0024] According to some embodiments of the present invention, the mass of the film-forming additive accounts for 1.5% of the mass of the electrolyte.

[0025] According to some embodiments of the present invention, the film-forming additive includes fluoroethylene carbonate.

[0026] The lowest unoccupied molecular orbital energy of fluoroethylene carbonate is low and it is easily reduced, making it a good negative electrode film-forming additive. At the same time, it can significantly inhibit the decomposition of the electrolyte solvent and form a NaF-rich protective layer on the positive electrode, thereby improving the stability of the positive electrode lattice structure during the cycle, thereby improving the cycle stability of the battery.

[0027] According to some embodiments of the invention, the sodium salt includes at least one of sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide.

[0028] The above sodium salt can have a high ionic conductivity, can increase the ion conduction rate, reduce the internal resistance of the battery, and is beneficial to improving the cycle performance of the sodium ion battery.

[0029] According to some embodiments of the invention, the sodium salt consists of sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide.

[0030] According to some embodiments of the present invention, the mass of the sodium hexafluorophosphate accounts for 10% of the mass of the electrolyte.

[0031] According to some embodiments of the present invention, the mass of the sodium bis(fluorosulfonyl)imide accounts for 2% of the mass of the electrolyte.

[0032] According to some embodiments of the present invention, the solvent includes at least one of propylene carbonate (PC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and ethylene glycol dimethyl ether (CAS No.: 110-71-4).

[0033] Among them, EC and PC solvents have the advantages of wide electrochemical window, large dielectric constant, and good chemical stability, making them very attractive organic solvents for sodium-ion batteries. EC solvents can also form a relatively stable passivation layer on the surface of carbon-based anodes during reduction, inhibiting the continued decomposition of the solvent at low potentials.

[0034] Ethylene glycol dimethyl ether has good anti-redox ability, and forms a thinner and more stable SEI film and a high first coulombic efficiency on the negative electrode surface.

[0035] Ethyl methyl carbonate can increase the energy density and discharge capacity of batteries; at the same time, it can improve the safety of batteries and extend their service life.

[0036] According to some embodiments of the present invention, the solvent consists of propylene carbonate, ethyl methyl carbonate, ethylene carbonate and ethylene glycol dimethyl ether.

[0037] The use of the above solvents can effectively increase the gram capacity of sodium ion batteries, reduce battery impedance, and inhibit battery gas production.

[0038] According to some embodiments of the present invention, the mass ratio of the propylene carbonate, the ethyl methyl carbonate, the ethylene carbonate and the ethylene glycol dimethyl ether is 35-42:20-25:5.5-8:11-16.

[0039] Controlling the mass ratio of each solvent within the above range can effectively increase the gram capacity of the sodium ion battery and reduce the battery impedance.

[0040] The second aspect of the present invention provides a method for preparing the above-mentioned electrolyte, comprising the following steps: mixing the preparation raw materials.

[0041] A third aspect of the present invention provides a sodium ion battery, the preparation raw materials of which include the above-mentioned electrolyte.

[0042] According to some embodiments of the present invention, the sodium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and the electrolyte.

[0043] According to some embodiments of the present invention, the positive electrode sheet comprises a positive electrode active material capable of extracting and inserting sodium ions.

[0044] According to some embodiments of the present invention, the positive electrode active material includes at least one of sodium-iron composite oxide, sodium-cobalt composite oxide, sodium-chromium composite oxide, sodium-manganese composite oxide, sodium-nickel composite oxide, sodium-nickel-titanium composite oxide, sodium-nickel-zinc-manganese-titanium oxide, sodium-nickel-manganese composite oxide, sodium-iron-manganese composite oxide, sodium-nickel-cobalt-manganese composite oxide, sodium-iron phosphate compound, sodium-manganese phosphate compound, and sodium-cobalt phosphate compound.

[0045] According to some embodiments of the present invention, the positive electrode active material is NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1 O2.

[0046] According to some embodiments of the present invention, the negative electrode plate comprises a negative electrode active material capable of inserting and extracting sodium ions.

[0047] According to some embodiments of the present invention, the negative electrode active material includes at least one of hard carbon, natural graphite, artificial graphite, soft carbon, carbon black, acetylene black, carbon nanotubes, graphene, and carbon nanofibers.

[0048] According to some embodiments of the present invention, the separator includes one of polyethylene, polypropylene, polyvinylidene fluoride, and a multilayer composite film thereof.

[0049] According to some embodiments of the present invention, the positive electrode sheet further includes a binder and a conductive agent.

[0050] According to some embodiments of the present invention, the method for preparing the positive electrode sheet includes the following steps: coating a positive electrode slurry containing a positive electrode active material, a binder and a conductive agent on a positive electrode current collector, and obtaining a positive electrode sheet after the positive electrode slurry is dried.

[0051] According to some embodiments of the present invention, the negative electrode sheet further includes a binder and a conductive agent.

[0052] According to some embodiments of the present invention, the method for preparing the negative electrode sheet includes the following steps: coating a negative electrode slurry containing a negative electrode active material, a binder and a conductive agent on a negative electrode current collector, and obtaining a negative electrode sheet after the negative electrode slurry is dried.

[0053] According to some embodiments of the present invention, the operating voltage of the sodium ion battery is 2.8V to 5.0V.

[0054] Under high voltage conditions, the higher the valence state of the transition metal on the surface of the positive electrode material, the stronger the Coulomb interaction with 1-ethoxy-1-trimethylsilylcyclopropane, which means that the additive can play a greater protective role.

[0055] According to some embodiments of the present invention, the operating temperature of the sodium ion battery is 0°C to 60°C.

[0056] The sodium ion battery of the present invention has a wide operating temperature range, which expands the application scenarios of the sodium ion battery.

[0057] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0059] Figure 1 1 and 2 are oxidation curves of the electrolytes in Comparative Example 1 and Example 1 of the present invention.

[0060] Figure 2 1 and 2 are the reduction curves of the electrolytes in Comparative Example 1 and Example 1 of the present invention.

[0061] Figure 3 These are the internal resistance test results of the soft-pack batteries corresponding to the electrolytes of Comparative Example 1 and Example 1 of the present invention after being stored at 60°C for 14 days.

[0062] Figure 4 These are the cycle performance test results of the soft-pack batteries corresponding to the electrolytes of Comparative Example 1 and Example 1 of the present invention.

[0063] Figure 5 This is an SEM image of the positive electrode of the soft-pack battery in Comparative Example 1 of the present invention after 100 cycles.

[0064] Figure 6 This is an SEM image of the positive electrode of the soft-pack battery in Example 1 of the present invention after 100 cycles. DETAILED DESCRIPTION

[0065] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0066] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0067] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0068] Specific embodiments of the present invention are described in detail below.

[0069] Example 1

[0070] This embodiment provides an electrolyte and a preparation method thereof.

[0071] In this embodiment, the electrolyte is prepared from the following raw materials in mass fractions:

[0072] 1-ethoxy-1-trimethylsilylcyclopropane 0.5%, film-forming additive (fluoroethylene carbonate (FEC)) 1.5%, sodium salt (sodium hexafluorophosphate 10% and sodium bis(fluorosulfonyl)imide 2% by mass of the electrolyte) 12% and solvent (propylene carbonate, ethyl methyl carbonate, ethylene carbonate and ethylene glycol dimethyl ether in a mass ratio of 35:20:8:16) as the balance.

[0073] The preparation method of the electrolyte in this embodiment consists of the following steps:

[0074] At 15° C., in an anhydrous and oxygen-free glove box, the solvent, sodium salt, 1-ethoxy-1-trimethylsilylcyclopropane and film-forming additive were mixed and stirred.

[0075] Comparative Example 1

[0076] This comparative example is an electrolyte and a preparation method thereof.

[0077] The electrolyte in this comparative example was prepared from the following raw materials in mass fractions:

[0078] The balance includes 1.5% film-forming additive (fluoroethylene carbonate), 12% sodium salt (10% sodium hexafluorophosphate and 2% sodium bis(fluorosulfonyl)imide by weight of the electrolyte) and the remainder is solvent (propylene carbonate, ethyl methyl carbonate, ethylene carbonate and ethylene glycol dimethyl ether in a mass ratio of 35:20:8:16).

[0079] The preparation method of the electrolyte in this comparative example is the same as that in Example 1.

[0080] Comparative Example 2

[0081] This comparative example is an electrolyte and a preparation method thereof.

[0082] The electrolyte in this comparative example was prepared from the following raw materials in mass fractions:

[0083] 1-ethoxy-1-trimethylsilylcyclopropane 0.1%, film-forming additive (fluoroethylene carbonate) 1.5%, sodium salt (sodium hexafluorophosphate 10% and sodium bis(fluorosulfonyl)imide 2% by mass of the electrolyte) 12% and solvent (propylene carbonate, ethyl methyl carbonate, ethylene carbonate and ethylene glycol dimethyl ether in a mass ratio of 35:20:8:16) as the balance.

[0084] The preparation method of the electrolyte in this comparative example is the same as that in Example 1.

[0085] Comparative Example 3

[0086] This comparative example is an electrolyte and a preparation method thereof.

[0087] The electrolyte in this comparative example was prepared from the following raw materials in mass fractions:

[0088] 1-ethoxy-1-trimethylsilylcyclopropane 0.2%, film-forming additive (fluoroethylene carbonate) 1.5%, sodium salt (sodium hexafluorophosphate 10% and sodium bis(fluorosulfonyl)imide 2% by mass of the electrolyte) 12% and solvent (propylene carbonate, ethyl methyl carbonate, ethylene carbonate and ethylene glycol dimethyl ether in a mass ratio of 35:20:8:16) as the balance.

[0089] The preparation method of the electrolyte in this comparative example is the same as that in Example 1.

[0090] Comparative Example 4

[0091] This comparative example is an electrolyte and a preparation method thereof.

[0092] The electrolyte in this comparative example was prepared from the following raw materials in mass fractions:

[0093] 1-ethoxy-1-trimethylsilylcyclopropane 0.3%, film-forming additive (fluoroethylene carbonate) 1.5%, sodium salt (sodium hexafluorophosphate 10% and sodium bis(fluorosulfonyl)imide 2% by mass of the electrolyte) 12% and solvent (propylene carbonate, ethyl methyl carbonate, ethylene carbonate and ethylene glycol dimethyl ether in a mass ratio of 35:20:8:16) as the balance.

[0094] The preparation method of the electrolyte in this comparative example is the same as that in Example 1.

[0095] Comparative Example 5

[0096] This comparative example is an electrolyte and a preparation method thereof.

[0097] The electrolyte in this comparative example was prepared from the following raw materials in mass fractions:

[0098] 1-ethoxy-1-trimethylsilylcyclopropane 0.4%, film-forming additive (fluoroethylene carbonate) 1.5%, sodium salt (sodium hexafluorophosphate 10% and sodium bis(fluorosulfonyl)imide 2% by mass of the electrolyte) 12% and solvent (propylene carbonate, ethyl methyl carbonate, ethylene carbonate and ethylene glycol dimethyl ether in a mass ratio of 35:20:8:16) as the balance.

[0099] The preparation method of the electrolyte in this comparative example is the same as that in Example 1. The electrolytes prepared in Example 1 and Comparative Example 1 were subjected to performance tests using the following method:

[0100] Soft pack battery: This test example uses Example 1 and Comparative Example 1 as the electrolyte, with NaNi 0.45 Zn 0.05 Mn 0.4 Ti 0.1 A soft-pack battery was prepared using O2 as the positive electrode material, artificial graphite as the negative electrode material, aluminum foil as the positive and negative electrode current collectors, and polyethylene film as the separator. After injection, the battery was left to stand at room temperature (25°C) for 24 hours and then tested. The ratio of the design capacity of the positive and negative electrodes of the battery was 1:1.08~1.1, and the electrolyte retention capacity was 4.5g / Ah±0.3g / Ah.

[0101] LSV test: perform multiple cyclic voltammetry scans at a scan rate of 50 mV per second to activate the catalyst, and select the maximum sensitivity of the scan rate test, 0.1 A / V.

[0102] Storage performance test at different voltages:

[0103] The electrolytes corresponding to Example 1 of the present invention and Comparative Example 1 were respectively assembled into 7 groups of batteries; these were charged to different cutoff voltages (4.2 V, 4.25 V, 4.3 V, 4.35 V, 4.4 V, 4.45 V, and 4.5 V) and then stored at 60°C for 14 days. The internal resistance of the batteries after storage was tested.

[0104] High temperature cycle performance test:

[0105] The soft-pack batteries prepared with the corresponding electrolytes in Example 1 and Comparative Example 1 were tested for cycle performance at 45° C., a rate of 1C, and a voltage of 2.8V to 4.4V.

[0106] Normal temperature cycle performance test:

[0107] The soft-pack batteries prepared with the corresponding electrolytes in Example 1 and Comparative Examples 1 to 5 were tested for cycle performance at 25° C., a rate of 1C, and a voltage of 2.8V to 4.4V.

[0108] The oxidation curves and reduction curves of the electrolytes corresponding to Example 1 and Comparative Example 1 after LSV testing are shown in Figures 1 and 2. Figure 1 and Figure 2 The electrolyte in Comparative Example 1 began to undergo oxidative decomposition at 5.0 V, while the electrolyte in Example 1 (1-ethoxy-1-trimethylsilylcyclopropane) decomposed preferentially over the solvent at around 4 V, confirming that 1-ethoxy-1-trimethylsilylcyclopropane participated in the positive electrode oxidation reaction.

[0109] According to the LSV test results, 1-ethoxy-1-trimethylsilylcyclopropane undergoes oxidation reaction before the solvent, participates in the positive electrode film formation, and helps to improve the electrode stability. Figure 2In the reduction curve with graphite as the working electrode, a reduction peak appears at 0.5 V in Comparative Example 1, corresponding to the reduction and decomposition of EC, while the current at 0.5 V in Example 1 shows a decreasing trend, indicating that 1-ethoxy-1-trimethylsilylcyclopropane can inhibit the reduction reaction of EC, improve the stability of the electrolyte, contribute to the formation of the negative electrode film, and extend the service life of the battery.

[0110] according to Figure 1 The oxidation curve of the electrolyte in Example 1 has oxidation peaks at 5.0 V and 5.5 V, indicating that 1-ethoxy-1-trimethylsilylcyclopropane decomposes before the solvent, that is, 1-ethoxy-1-trimethylsilylcyclopropane undergoes electron-loss oxidation reaction in the battery and combines with oxygen free radicals to form new organosilicon compounds.

[0111] The storage results at 60°C under different voltages in Example 1 of the present invention and Comparative Example 1 are shown in FIG. Figure 3 .from Figure 3 It is known that as the charge cut-off voltage increases, the high-temperature storage stability of the soft-pack battery corresponding to Comparative Example 1 gradually decreases. The internal resistance at different voltages is 19.2mΩ (4.2V), 21.8mΩ (4.25V), 23.2mΩ (4.3V), 24.1mΩ (4.35V), 25.7mΩ (4.4V), 26.8mΩ (4.45V), and 27.5mΩ (4.5V). That is, the charge cut-off voltage increases from 4.2V to 4.5V; the internal resistance increases from 19.2mΩ to 27.5mΩ. This shows that the increase in charge cut-off voltage causes the stability of the interface between the active material and the electrolyte to decrease. Compared with the soft-pack battery corresponding to Comparative Example 1, at a charging cut-off voltage of 4.2V to 4.5V, the internal resistance of the soft-pack battery corresponding to Example 1 was significantly improved after storage under the same conditions (the internal resistance at different voltages was 17.2mΩ (4.2V), 17.8mΩ (4.25V), 18.1mΩ (4.3V), 19.3mΩ (4.35V), 19.8mΩ (4.4V), 21.2mΩ (4.45V), and 22.1mΩ (4.5V)).

[0112] During storage at 60°C, the SEI film decomposes due to thermal decomposition due to poor stability, and the EC in the electrolyte decomposes on the surface of the negative electrode to produce gases such as C2H4, CO and CH4. On the one hand, the increase in the battery charging cut-off voltage exacerbates the precipitation of active oxygen at the positive electrode, causing EC to be oxidized and decomposed to produce CO2. On the other hand, it makes EC more likely to lose electrons and be oxidized on the surface of the positive electrode, and diffuse to the surface of the negative electrode to be reduced to H2. The gas composition and content of 6 groups of batteries (Example 1 and Comparative Example 1 were repeated three times) after storage were analyzed. Compared with the soft-pack batteries corresponding to Comparative Example 1, the gas of the soft-pack batteries corresponding to Example 1 decreased from 253.9μL, 354.2μL, and 223.7μL to 5.1μL, 7.3μL, and 5.8μL, respectively, indicating that the SEI film constructed with 1-ethoxy-1-trimethylsilylcyclopropane is more stable and inhibits the reduction and decomposition of EC at the negative electrode. The gas content was significantly reduced from 253.9 μL to 5.1 μL, indicating that 1-ethoxy-1-trimethylsilylcyclopropane enhanced the stability of the positive electrode CEI film and inhibited the oxidative decomposition of EC. The above test results confirm that 1-ethoxy-1-trimethylsilylcyclopropane as an electrolyte additive effectively improves the high temperature (60°C) storage performance of soft-pack batteries at a high voltage of 4.5V.

[0113] The cycle performance test results of Example 1 of the present invention and Comparative Example 1 are shown in Figure 4 ,from Figure 4 It is known that the capacity of the soft-pack battery corresponding to Comparative Example 1 decays rapidly, and the capacity retention rate is only about 82.7% after 200 cycles. However, when 0.5% by mass fraction of 1-ethoxy-1-trimethylsilylcyclopropane is added to the electrolyte, the battery capacity decay is significantly suppressed, and the capacity retention rate is increased to about 92.8% (soft-pack battery corresponding to Example 1). This shows that the 1-ethoxy-1-trimethylsilylcyclopropane additive is beneficial for constructing a stable electrode-electrolyte interface film, improving battery cycle stability, and reducing capacity loss.

[0114] The positive electrode morphology of the soft pack battery corresponding to Comparative Example 1 after 100 cycles is as follows: Figure 5 The positive electrode morphology of the soft pack battery corresponding to Example 1 after 100 cycles is shown in Figure 2. Figure 6 ; From the comparison of the test results of Comparative Example 1 and Example 1, it can be seen that after introducing 1-ethoxy-1-trimethylsilylcyclopropane into the electrolyte, the positive electrode surface of the corresponding soft-pack battery in Example 1 is still smooth and flat after 100 cycles, and there are no cracks in the positive electrode particles in the corresponding soft-pack battery in Comparative Example 1, indicating that 1-ethoxy-1-trimethylsilylcyclopropane can improve the stability of the positive electrode interface under high voltage and high temperature, inhibit the interfacial side reaction between the positive electrode material and the electrolyte, thereby slowing down the battery performance degradation.

[0115] Table 1 Normal temperature cycle performance data of Example 1 of the present invention and Comparative Examples 1 to 5

[0116]

[0117]

[0118] Within a certain range, when the addition amount of 1-ethoxy-1-trimethylsilylcyclopropane is low, it cannot form a dense CEI film and will also lead to an increase in the internal resistance of the battery, thereby having a certain adverse effect on the cycle performance.

[0119] When the addition amount of 1-ethoxy-1-trimethylsilylcyclopropane is 0.4% to 0.5%, it is beneficial to improve the capacity retention rate of the battery, and the higher the addition amount, the better the cycle performance.

[0120] A good CEI film can be formed when the addition amount of 1-ethoxy-1-trimethylsilylcyclopropane is 0.5%. When the addition amount continues to increase, 1-ethoxy-1-trimethylsilylcyclopropane will remain in the electrolyte, thereby increasing the internal resistance of the battery.

[0121] In summary, 1-ethoxy-1-trimethylsilylcyclopropane as an electrolyte additive significantly improves the high-temperature and high-voltage performance of sodium-ion batteries.

[0122] While the embodiments of the present invention have been described in detail above in conjunction with specific implementation methods, the present invention is not limited to the aforementioned embodiments. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. An electrolyte, characterized in that: The preparation method comprises the following raw materials: 1-ethoxy-1-trimethylsilylcyclopropane, a film-forming additive, a sodium salt and a solvent; calculated by weight percentage: 0.5% to 1% of the 1-ethoxy-1-trimethylsilylcyclopropane, 1% to 2% of the film-forming additive, and 10% to 15% of the sodium salt.

2. The electrolyte according to claim 1, wherein: The film-forming additive includes fluoroethylene carbonate.

3. The electrolyte according to claim 1, wherein: The sodium salt includes at least one of sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide.

4. The electrolyte according to claim 1, wherein: The solvent includes at least one of propylene carbonate, ethyl methyl carbonate, ethylene carbonate and ethylene glycol dimethyl ether.

5. A method for preparing the electrolyte according to any one of claims 1 to 4, characterized in that: The following steps are involved: The preparation raw materials are mixed to obtain the product.

6. A sodium ion battery, characterized in that: The electrolyte comprises the electrolyte according to any one of claims 1 to 4.

7. The sodium ion battery according to claim 6, characterized in that: The operating voltage is 2.8V~5.0V.

8. The sodium ion battery according to claim 6, wherein: The operating temperature is 0℃~60℃.

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