Acetonitrile electrolyte and sodium-ion battery and soft package battery thereof

Abstract

The application discloses an acetonitrile electrolyte and a sodium ion battery thereof, and aims to provide an electrolyte which can not only retain the high conductivity advantage of acetonitrile and widen the electrochemical window of the electrolyte, but also be compatible with positive and negative electrodes and form a stable interface, and a sodium ion battery which can improve the rate performance of the acetonitrile electrolyte and realize super-fast charging; the acetonitrile electrolyte comprises a solvent acetonitrile, and a composite film forming agent, NaPF6 and NaClO4 are added into the acetonitrile; the mass ratio of the acetonitrile, the composite film forming agent, NaPF6 and NaClO4 is 100:2-5:17.1-20.3:0.78-3.11; the composite film forming agent is composed of vinylene carbonate and ethylene sulfate; and the application belongs to the technical field of sodium ion batteries.

Description

Technical Field

[0001] This invention relates to an electrolyte, specifically an acetonitrile electrolyte, and also to a sodium-ion battery, belonging to the field of sodium-ion battery technology. Background Technology

[0002] The fast charging capability of sodium-ion batteries is one of the important indicators for measuring their performance, especially in fields such as electric vehicles and portable electronic devices, where there are extremely high requirements for the fast charging capability of sodium-ion batteries.

[0003] Currently, sodium-ion batteries generally use carbonate-based electrolytes, but their inherent high viscosity and relatively low ionic conductivity can lead to severe polarization during high-current fast charging, hindering the rapid migration of sodium ions and easily causing problems such as sodium dendrite growth on the negative electrode and interface instability, posing safety hazards and failing to meet fast charging requirements.

[0004] Acetonitrile (AN) solvent has the advantages of low viscosity and high dielectric constant, which can be used to formulate electrolytes with extremely high ionic conductivity, theoretically making it very suitable for fast charging. However, the direct application of acetonitrile faces two major challenges: First, it has poor compatibility with the hard carbon anode commonly used in sodium-ion batteries, making it difficult to form a stable and dense solid electrolyte interphase (SEI) film, resulting in low coulombic efficiency and poor cycle life; second, its electrochemical stability window is narrow, especially at high voltages it is prone to oxidative decomposition, and its compatibility with high-voltage cathode materials is insufficient.

[0005] Peng Z, Cao X, Gao P, et al. High-power lithium metal batteries enabled by high-concentration acetonitrile-based electrolytes with vinylenecarbonate additive[J]. Advanced Functional Materials, 2020, 30(24): 2001285. This study developed a high-concentration acetonitrile-based electrolyte by adding vinylcarbonate (VC) to acetonitrile and significantly increasing the lithium salt concentration (typically exceeding 3.0 M). The core change lies in the fact that the extremely high salt concentration promotes the formation of special "solvated clusters" between the anions and cations and acetonitrile molecules, thereby eliminating highly reactive free acetonitrile molecules. This change does indeed enhance the stability of the electrode / electrolyte interface and suppress side reactions. However, the large amount of expensive lithium salt (such as lithium bisfluorosulfonylimide, LiFSI) added to achieve this state has led to a sharp increase in the cost of electrolyte raw materials. Meanwhile, high salt concentration directly leads to a significant increase in the overall viscosity of the electrolyte, which hinders ion migration and largely negates the advantages of acetonitrile itself, such as low viscosity and high conductivity, ultimately hindering the full realization of fast charging performance.

[0006] Another common approach is to use acetonitrile as a co-solvent, mixing it with traditional solvents such as ethylene carbonate (EC) and dimethyl carbonate (DMC). This method attempts to balance the negative effects of acetonitrile by adding a large amount of other solvents to "dilute" the negative effects of acetonitrile. However, this change directly reduces the actual proportion of high-conductivity acetonitrile in the system, resulting in the overall ionic conductivity of the electrolyte not reaching its optimal level, and the fast-charging potential not being fully realized.

[0007] To circumvent the high viscosity problem, recent research has proposed a "locally high-concentration electrolyte" approach. This involves introducing expensive fluorinated ethers (such as TTE or BTFE) as inert diluents into the aforementioned high-concentration AN-based electrolyte. This change reduces the system viscosity without disrupting the original solvation structure. However, this approach incurs the dual costs of high-cost lithium salts and high-cost diluents. Furthermore, the fluorinated diluents themselves are extremely sensitive to moisture and require stringent preparation conditions, further increasing the barriers to industrial production and its costs.

[0008] In summary, existing improvement schemes all modify the solvation environment or interfacial reactivity of acetonitrile by adding excess lithium salts, other solvents, or special diluents. However, these modifications invariably come at the cost of sacrificing cost, viscosity, or the intrinsic advantages of acetonitrile, making it difficult to achieve a balance between meeting fast-charging requirements, cycle stability, and industrial economics. Therefore, developing a novel strategy that directly optimizes the compatibility between acetonitrile and the electrode interface without relying on ultra-high concentrations or expensive additives has indeed become crucial for driving technological development. This stands in stark contrast to the "medium-to-low concentration dual salts" and "directional composite film-forming agents" technical approach adopted in this invention. Summary of the Invention

[0009] To address the aforementioned problems, the first objective of this invention is to provide an electrolyte that retains the high conductivity of acetonitrile, broadens the electrochemical window, and simultaneously achieves good compatibility with both positive and negative electrodes, forming a stable interface.

[0010] The second objective of this invention is to provide a sodium-ion battery that can improve the rate performance of acetonitrile electrolyte and enable sodium-ion batteries to complete ultra-fast charging.

[0011] Therefore, the first technical solution provided by the present invention is as follows:

[0012] An acetonitrile electrolyte includes acetonitrile as a solvent, wherein a composite film-forming agent, NaPF6, and NaClO4 are added to the acetonitrile.

[0013] The mass ratio of acetonitrile, composite film-forming agent, NaPF6, and NaClO4 is 100 : 2~5 : 17.1~20.3 : 0.78~3.11;

[0014] The composite film-forming agent is composed of vinylene carbonate and vinyl sulfate.

[0015] Furthermore, in the aforementioned acetonitrile electrolyte, the mass ratio of vinylene carbonate to vinyl sulfate is 1-4:1.

[0016] The second technical solution of the present invention is to provide a sodium-ion battery, comprising the acetonitrile electrolyte described in the first technical solution.

[0017] Furthermore, the aforementioned sodium-ion battery also includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode is primarily a layered oxide NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2; the negative electrode is mainly hard carbon; the separator is GF / A.

[0018] The third technical solution of the present invention is to provide a soft-pack battery, including the acetonitrile electrolyte described in the first technical solution.

[0019] Furthermore, the aforementioned pouch cell also includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode is primarily a layered oxide NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2; the negative electrode is mainly hard carbon; the separator is Celgard 2400.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The acetonitrile electrolyte provided by this invention uses vinylene carbonate and vinyl sulfate as film-forming agents, and introduces perchlorate anions (ClO4) with a high donor number. - The ion was activated in a sodium-ion battery system using acetonitrile as the pure solvent. ClO4 was used as the solvent. - Furthermore, the VC synergy successfully broadened the acetonitrile electrolyte window, enabling it to operate at high voltages; the introduction of DTD successfully restored the high-rate performance of acetonitrile, thereby improving the rate performance of the acetonitrile electrolyte and enabling sodium-ion batteries to complete ultra-fast charging.

[0022] 2. The acetonitrile electrolyte provided by this invention reduces usage costs and is easy to mass-produce.

[0023] 3. When the acetonitrile electrolyte provided by this invention is used as an electrolyte for sodium-ion batteries, it exhibits good rate performance and excellent high-rate long-cycle stability. Attached Figure Description

[0024] Figure 1 These are rate performance test charts for R2032 coin sodium-ion batteries with different electrolytes.

[0025] Figure 2 These are 5C long-cycle test results of R2032 coin sodium-ion batteries with different electrolytes.

[0026] Figure 3 These are 10C long-cycle test results for R2032 coin sodium-ion batteries with different electrolytes.

[0027] Figure 4 This is a rate performance test chart of the 1Ah soft-pack sodium-ion battery in Example 1.

[0028] Figure 5 This is a test graph of the 2C long-cycle performance of the 1Ah soft-pack sodium-ion battery in Example 1. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, preferred embodiments are selected below to further describe the present invention in detail. However, the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0030] The sources of some of the materials used in this application are as follows:

[0031] Positive electrode layered oxide NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was purchased from Shenzhen Kejing Zhida Technology Co., Ltd.

[0032] The negative hard carbon was purchased from Shenzhen Kejing Zhida Technology Co., Ltd.

[0033] Super P carbon black was sourced from Huipu Industrial Chemicals Co., Ltd.

[0034] The membranes were glass cellulose membranes GF / A and Celgard 2400, purchased from MapleBio Biomembrane Technology Co., Ltd. and Celgard Corporation of the United States, respectively.

[0035] Example 1

[0036] This embodiment provides an acetonitrile electrolyte by dissolving 151.1 mg (0.900 mmol) NaPF6 and 12.2 mg (0.100 mmol) NaClO4 in 1 ml of anhydrous acetonitrile. After the solutes are completely dissolved, a mixed solution is obtained. 2 wt% vinylene carbonate (18.986 mg) and 1 wt% vinyl sulfate (9.493 mg) of the mixed solution are added to the solution, and the mixture is stirred on a stirring table for 30 min to obtain the acetonitrile electrolyte.

[0037] Example 2

[0038] The acetonitrile electrolyte provided in this embodiment has parameters that are basically the same as those in Example 1, except that the amount of NaPF6 is 0.800 mmol and the amount of NaClO4 is 0.200 mmol.

[0039] Example 3

[0040] The acetonitrile electrolyte provided in this embodiment has parameters that are basically the same as those in Example 1, except that the amount of NaPF6 is 0.9500 mmol and the amount of NaClO4 is 0.050 mmol.

[0041] Example 4

[0042] The acetonitrile electrolyte provided in this embodiment has parameters that are basically the same as those in Example 1, with the only difference being that the amount of vinylene carbonate is 2 wt% of the mixed solution and the amount of vinyl sulfate is 2 wt% of the mixed solution.

[0043] Example 5

[0044] The acetonitrile electrolyte provided in this embodiment has parameters that are basically the same as those in Example 1, with the only difference being that the amount of vinylene carbonate is 2 wt% of the mixed solution and the amount of vinyl sulfate is 0.5 wt% of the mixed solution.

[0045] Example 6

[0046] The acetonitrile electrolyte provided in this embodiment has parameters that are basically the same as those in Example 1, with the only difference being that the amount of vinylene carbonate is 1 wt% of the mixed solution and the amount of vinyl sulfate is 1 wt% of the mixed solution.

[0047] Example 7

[0048] The acetonitrile electrolyte provided in this embodiment has parameters that are basically the same as those in Example 1, with the only difference being that the amount of vinylene carbonate is 4 wt% of the mixed solution and the amount of vinyl sulfate is 1 wt% of the mixed solution.

[0049] Comparative Example 1

[0050] The acetonitrile electrolyte provided in this comparative example has parameters for each substance that are basically the same as those in Example 1. The only difference is that equimolar amounts of propylene sulfite are used instead of vinyl sulfate.

[0051] Comparative Example 2

[0052] The acetonitrile electrolyte provided in this comparative example has parameters for each substance that are basically the same as those in Example 1. The only difference is that equimolar amounts of 1,4-butanesulfonyl lactone are used instead of vinyl sulfate.

[0053] Comparative Example 3

[0054] The acetonitrile electrolyte provided in this comparative example has parameters for each substance that are basically the same as those in Example 1. The only difference is that equimolar amounts of ethylene sulfite are used instead of ethylene sulfate.

[0055] Comparative Example 4

[0056] The acetonitrile electrolyte provided in this comparative example has parameters for each substance that are basically the same as those in Example 1. The only difference is that an equimolar amount of methylene disulfonate is used instead of vinyl sulfate.

[0057] Comparative Example 5

[0058] The acetonitrile electrolyte provided in this comparative example was prepared by dissolving 122 mg (1.00 mmol) NaClO4 in 1 ml of anhydrous acetonitrile. After the solute was completely dissolved, a mixed solution was obtained. 2 wt% vinylene carbonate (18.986 mg) of the mixed solution was added to the solution and stirred on a stirring table for 30 min to obtain the acetonitrile electrolyte.

[0059] Comparative Example 6

[0060] The acetonitrile electrolyte provided in this comparative example is prepared by dissolving 122 mg (1.00 mmol) NaClO4 in 1 ml of anhydrous acetonitrile. After the solute is completely dissolved, a mixed solution is obtained. 2 wt% vinylene carbonate (18.986 mg) and 1 wt% vinyl sulfate (9.493 mg) of the mixed solution are added to the solution, and the mixture is stirred on a stirring table for 30 min to obtain the acetonitrile electrolyte.

[0061] Comparative Example 7

[0062] The acetonitrile electrolyte provided in this comparative example is prepared by dissolving 151.1 mg (0.900 mmol) NaPF6 and 12.2 mg (0.100 mmol) NaClO4 in 1 ml of anhydrous acetonitrile. After the solutes are completely dissolved, a mixed solution is obtained. 2 wt% vinylene carbonate (18.986 mg) of the mixed solution is added to the solution, and the mixture is stirred on a stirring table for 30 min to obtain the acetonitrile electrolyte.

[0063] Comparative Example 8

[0064] The acetonitrile electrolyte provided in this comparative example is prepared by dissolving 151.1 mg (0.900 mmol) NaPF6 and 12.2 mg (0.100 mmol) NaClO4 in 1 ml of anhydrous acetonitrile. After the solutes are completely dissolved, a mixed solution is obtained. 1 wt% vinyl sulfate (9.493 mg) of the mixed solution is added to the solution, and the mixture is stirred on a stirring table for 30 min to obtain the acetonitrile electrolyte.

[0065] Comparative Example 9

[0066] This comparative example provides an electrolyte in which 168 mg (0.100 mmol) of NaPF6 is dissolved in a mixed solution of 0.5 ml ethylene carbonate and 0.5 ml dimethyl carbonate. The electrolyte is obtained after the solutes are completely dissolved.

[0067] Comparative Example 10

[0068] The electrolyte provided in this comparative example is prepared by dissolving 168 mg (0.100 mmol) NaPF6 in 1 ml of diethylene glycol dimethyl ether. The electrolyte is obtained after the solute has completely dissolved.

[0069] Comparative Example 11

[0070] The electrolyte provided in this comparative example is prepared by dissolving 168 mg (0.100 mmol) NaPF6 in 1 ml of propylene carbonate, and obtaining the electrolyte after the solute has completely dissolved.

[0071] Application Example 1

[0072] This application example provides an R2032 type coin cell sodium-ion battery, denoted as R2032 type coin cell sodium-ion battery-1, and its preparation method is as follows:

[0073] First, place the negative electrode shell flat on an insulating platform and center the negative electrode sheet. Next, smoothly cover the negative electrode sheet with the GF / A separator, whose diameter is typically slightly larger than the negative electrode sheet. Then, using a pipette, precisely inject 100 μL of the electrolyte described in any of Examples 1-7 and Comparative Examples 1-11 onto the separator. Next, use insulating tweezers to pick up the positive electrode sheet, ensuring that the side coated with the active material faces the separator and is aligned with the negative electrode sheet. Place the spacer and spring sheet sequentially on top of the positive electrode sheet. Finally, cover with the positive electrode shell, completing the stacking of all components. Transfer the assembled battery assembly to a button cell sealing machine for sealing, ensuring a tight seal.

[0074] The negative electrode / positive electrode capacity ratio (N / P ratio) is set to 1.1:1.

[0075] The positive electrode used in the aforementioned R2032 coin cell sodium-ion battery is prepared through the following steps:

[0076] 94.5g of NFM (NaNi) 1 / 3 Fe 1 / 3 Mn 1 / 3 A slurry was prepared using O2 (an active material), 1.5g of polyvinylidene fluoride (PVDF), and 5g of super P carbon black. This slurry was coated onto aluminum foil, with a compaction density of 3.4 g·cm³. -3 The surface density is 33 g·cm³. -2 After being vacuum dried at 105℃ for 24 hours, it is rolled into a positive electrode sheet.

[0077] The negative electrode used in the aforementioned R2032 coin cell sodium-ion battery is prepared through the following steps:

[0078] A slurry consisting of 95g of hard carbon, 1.5g of carboxymethyl cellulose, 2.0g of styrene-butadiene rubber, and 1.5g of super P conductive carbon was coated onto aluminum foil to achieve an areal density of 20.1 g·cm³. -2 Compacted density 1.6 g·cm³ -3 After being vacuum dried at 100℃ for 24 hours, it is rolled into a negative electrode sheet.

[0079] Application Example 2

[0080] This application example provides an R2032 type coin cell sodium-ion battery, referred to as R2032 type coin cell sodium-ion battery-2. Its preparation method and the positive electrode, negative electrode and GF / A separator used are completely the same as those in application example 1. The only difference is that the acetonitrile electrolyte prepared in example 2 is used instead of the acetonitrile electrolyte prepared in example 1.

[0081] Application Example 3

[0082] This application example provides an R2032 type coin cell sodium-ion battery, referred to as R2032 type coin cell sodium-ion battery-3. Its preparation method and the positive electrode, negative electrode and GF / A separator used are completely the same as those in application example 1. The only difference is that the acetonitrile electrolyte prepared in example 3 is used instead of the acetonitrile electrolyte prepared in example 1.

[0083] Application Example 4

[0084] This application example provides an R2032 type coin cell sodium-ion battery, denoted as R2032 type coin cell sodium-ion battery-4. Its preparation method and the positive electrode, negative electrode, and GF / A separator used are completely the same as those in application example 1. The only difference is that the acetonitrile electrolyte prepared in example 4 is used instead of the acetonitrile electrolyte prepared in example 1.

[0085] Application Example 5

[0086] This application example provides an R2032 type coin cell sodium-ion battery, denoted as R2032 type coin cell sodium-ion battery-5. Its preparation method and the positive electrode, negative electrode, and GF / A separator used are completely the same as those in application example 1. The only difference is that the acetonitrile electrolyte prepared in example 5 is used instead of the acetonitrile electrolyte prepared in example 1.

[0087] Application Example 6

[0088] This application example provides an R2032 type coin cell sodium-ion battery, denoted as R2032 type coin cell sodium-ion battery-6. Its preparation method and the positive electrode, negative electrode, and GF / A separator used are completely the same as those in application example 1. The only difference is that the acetonitrile electrolyte prepared in example 6 is used instead of the acetonitrile electrolyte prepared in example 1.

[0089] Application Example 7

[0090] This application example provides an R2032 type coin cell sodium-ion battery, referred to as R2032 type coin cell sodium-ion battery-7. Its preparation method and the positive electrode, negative electrode and GF / A separator used are completely the same as those in application example 1. The only difference is that the acetonitrile electrolyte prepared in example 7 is used instead of the acetonitrile electrolyte prepared in example 1.

[0091] Comparative application example 1-11

[0092] The R2032 coin cell sodium-ion battery provided in Comparative Examples 1-11 is prepared in the same way as Example 1, using the same positive electrode, negative electrode, and GF / A separator. The only difference is the electrolyte used. See Table 1 for the specific correspondence.

[0093] Table 1

[0094] Comparative Application Examples R2032 type coin cell sodium-ion battery electrolyte Comparative Application 1 R2032 type coin sodium-ion battery - 8 Acetonitrile electrolyte prepared in Comparative Example 1 Comparative application 2 R2032 type coin sodium-ion battery - 9 Acetonitrile electrolyte prepared in Comparative Example 2 Comparative application 3 R2032 type button sodium-ion battery-10 Acetonitrile electrolyte prepared in Comparative Example 3 Comparative application 4 R2032 type button sodium-ion battery-11 Acetonitrile electrolyte prepared in Comparative Example 4 Comparative application 5 R2032 type button sodium-ion battery-12 Acetonitrile electrolyte prepared in Comparative Example 5 Comparative application 6 R2032 type coin sodium-ion battery-13 Acetonitrile electrolyte prepared in Comparative Example 6 Comparative application 7 R2032 type coin sodium-ion battery-14 Acetonitrile electrolyte prepared in Comparative Example 7 Comparative application 8 R2032 type button sodium-ion battery - 15 Acetonitrile electrolyte prepared in Comparative Example 8 Comparative application 9 R2032 type coin sodium-ion battery - 16 Electrolyte prepared in Comparative Example 9 Comparative application 10 R2032 type button sodium-ion battery-17 Electrolyte prepared in Comparative Example 10 Comparative application 11 R2032 type button sodium-ion battery - 18 Electrolyte prepared in Comparative Example 11

[0095] To verify the performance of the sodium-ion battery provided in this application, electrochemical tests were conducted on R2032 coin sodium-ion batteries-1 to R2032 coin sodium-ion batteries-18 after they were left to stand for 5 hours. The rate performance (0.1, 0.5, 1, 3, 5, 7, 10C) and long-cycle stability (10C) were tested using constant current charging technology. The results are shown in Table 2.

[0096] Table 2

[0097] <![CDATA[0.1 C capacity (mAhg -1 )]]> <![CDATA[0.5 C capacity (mAhg -1 )]]> <![CDATA[1 C capacity (mAhg -1 )]]> <![CDATA[3 C capacity (mAhg -1 )]]> <![CDATA[5 C capacity (mAhg -1 )]]> <![CDATA[7 C capacity (mAhg -1 )]]> <![CDATA[10 C capacity (mAhg -1 )]]> Capacity retention rate after 500 cycles at 30°C and 10°C Capacity retention rate after 500 cycles at 30°C and 10°C R2032 type button sodium-ion battery-1 103.8 98.3 94.5 87.1 80.3 74.1 65.4 85.3% 80.1% R2032 type button sodium-ion battery-2 99.6 93.1 90.3 81.5 75.5 67.1 56.3 74.1% 72.3% R2032 type coin sodium-ion battery - 3 104.1 98.2 93.8 84.6 78.4 70.8 61.6 79.3% 78.4% R2032 type coin sodium-ion battery - 4 103.2 97.2 93.7 85.4 77.8 70.7 59.1 75.8% 73.4% R2032 type button sodium-ion battery - 5 104.1 96.7 91.4 80.7 71.3 62.1 45.8 78.7% 76.5% R2032 type coin sodium-ion battery - 6 104.4 98.9 94.8 87.3 79.9 73.8 62.9 81.1% 78.6% R2032 type button sodium-ion battery - 7 105.6 100.1 95.8 85.8 77.8 69.1 55.5 78.1% 77.4% R2032 type coin sodium-ion battery - 8 102.3 98.5 94.3 82.1 65.3 45.1 21.2 / / R2032 type coin sodium-ion battery - 9 103.1 97.1 94.6 83.4 71.1 51.2 30.1 / / R2032 type button sodium-ion battery-10 93.9 98.3 94.5 87.1 80.3 74.1 15.4 / / R2032 type button sodium-ion battery-11 103.8 82.4 78.6 50.2 25.6 11.2 6.8 / / R2032 type button sodium-ion battery-12 95.5 89.7 86.3 77.6 70.1 59.4 47.3 63.1% 61.4% R2032 type coin sodium-ion battery-13 95.7 90.1 86.5 77.4 70.3 61.1 49.5 73.2% 71.3% R2032 type coin sodium-ion battery-14 102.5 97.5 94.6 84.6 70.1 54.5 38.0 62.01% 12.6% R2032 type button sodium-ion battery - 15 98.5 93.4 89.9 79.5 68.7 55.3 41.5 63.2% 15.4% R2032 type coin sodium-ion battery - 16 95.5 89.7 86.3 77.6 70.1 59.4 47.3 65.2% 61.4% R2032 type button sodium-ion battery-17 95.7 90.1 86.5 77.4 70.3 61.1 49.5 69.9% 71.3% R2032 type button sodium-ion battery - 18 102.5 97.5 94.6 84.6 70.1 54.5 38.0 43.3% 12.6%

[0098] Through Table 2, Figures 1-3 It can be seen that the acetonitrile electrolyte provided in this application, through the synergistic system of "dual salt (NaPF6 / NaClO4)" and "composite film-forming agent (ethylene carbonate VC / ethylene sulfate DTD)," effectively solves the core problem of poor compatibility between pure acetonitrile electrolyte and high-voltage positive electrode and hard carbon negative electrode, achieving the dual goals of broadening the electrochemical window and restoring high-rate performance. The best-performing R2032 coin cell sodium-ion battery-1 (NaPF6:NaClO4 molar ratio 9:1, VC:DTD mass ratio 2:1) can still provide a capacity of 65.4 mAh / g at an ultra-high rate of 10C, and the capacity retention rate is as high as 80.1% after 500 cycles under these harsh conditions, proving that the technical solution provided in this application not only achieves ultra-fast charging, but also has excellent high-voltage long-cycle stability.

[0099] The R2032 coin cell sodium-ion battery-14 of this application, which uses an electrolyte containing only VC and lacking DTD, has a 10C capacity of only 38.0 mAh / g and a cycle retention rate of only 12.6%. The R2032 coin cell sodium-ion battery-15, which uses an electrolyte containing only DTD and lacking VC, has a 10C capacity of only 41.5 mAh / g and a cycle retention rate of only 15.4%. This confirms the irreplaceable synergistic effect of the two in constructing a dense and stable interfacial film: VC tends to form an organic layer, while the introduction of DTD can increase the inorganic components and toughness of the interfacial film, thereby enhancing the interfacial stability while ensuring high-speed ion transport.

[0100] In Comparative Examples 8 to 11, the R2032 coin sodium-ion batteries prepared by replacing DTD with propylene sulfite (PS), 1,4-butanesulfonyl lactone (BMS), ethylene sulfite (ES), and methylene disulfonate (MMDS), respectively, showed a significant decrease in capacity at 15-18 cycles. Particularly at 10C rate, the capacities of 21.2 mAh / g, 30.1 mAh / g, 15.4 mAh / g, and 6.8 mAh / g were significantly lower than the 65.4 mAh / g capacity of R2032 coin sodium-ion battery 1, and neither battery successfully completed effective long-cycle testing. This demonstrates that the specific sulfonate structure (-SO3-) in the DTD molecule of the technical solution provided in this application can form an inorganic component with good ion conductivity and mechanical stability in the interfacial film.

[0101] The R2032 coin sodium-ion battery prepared in the embodiments of this application also has significantly better performance than the R2032 coin sodium-ion battery prepared with traditional carbonate-based electrolyte. For example, the 10C capacity of the R2032 coin sodium-ion battery-16 prepared using Comparative Example 9 of this application is only 47.3 mAh / g.

[0102] To further verify the advantages of the electrolyte provided in this application, a pouch cell prepared using the electrolyte provided in this application is presented below.

[0103] Application Example 8

[0104] This application example provides a pouch cell with the same positive electrode, negative electrode, and separator as the application example. It uses a winding process to assemble an NFM||HC pouch cell, which has a theoretical design capacity of 1 Ah. 7 ml of the electrolyte from Example 1 is added to it, and this is designated as a 1 Ah pouch sodium-ion battery.

[0105] To verify the performance of the 1 Ah soft-pack sodium-ion battery provided in this application, electrochemical tests were performed on the 1 Ah soft-pack sodium-ion battery after it was left to stand for 5 hours. The rate performance (0.1, 0.5, 1, 3, 5, 7, 10C) and long-cycle stability (10C) were tested using constant current charging technology. The results are shown in Table 3.

[0106] Table 3

[0107] 0.1 C capacity (mAh) 0.5 C capacity (mAh) 1 C capacity (mAh) 3C capacity (mAh) 5 C capacity (mAh) Capacity retention rate after 400 cycles at 30°C (2 C cycles) 1 Ah soft-pack sodium-ion battery 882.1 822.5 777.5 697.9 633.3 80.1%

[0108] pass Figure 4 , 5As shown in Table 3, when the electrolyte of Example 1 is applied to a 1Ah soft-pack sodium-ion battery, the battery can still release a high capacity of 633.3 mAh at a 5C rate, and the capacity retention rate remains stable at 80.1% after 400 cycles at a 2C rate. This result successfully replicates the excellent performance of coin cell batteries to a soft-pack battery system that is closer to practical applications, strongly demonstrating that the electrolyte formulation of this invention has good process adaptability and potential for large-scale application.

[0109] In summary, the technical solution provided in this application optimizes interfacial chemistry at the molecular level through the synergy of "dual salts" and "composite film-forming agents," thereby simultaneously achieving a broadening of the electrochemical window of sodium-ion batteries, maximizing rate performance, and significantly improving cycle life.

Claims

1. An acetonitrile electrolyte, comprising the solvent acetonitrile, characterized in that, The acetonitrile contains a composite film-forming agent, NaPF6, and NaClO4. The mass ratio of acetonitrile, composite film-forming agent, NaPF6, and NaClO4 is 100 : 2~5 : 17.1~20.3 : 0.78~3.11; The composite film-forming agent is composed of vinylene carbonate and vinyl sulfate.

2. The acetonitrile electrolyte according to claim 1, characterized in that, The mass ratio of vinylene carbonate to vinyl sulfate is 1-4:

1.

3. A sodium-ion battery, characterized in that, Includes any acetonitrile electrolyte according to claims 1-2.

4. The sodium-ion battery according to claim 3, characterized in that, The sodium-ion battery further includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode is mainly a layered oxide NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2; the negative electrode is mainly hard carbon; the separator is GF / A.

5. A pouch battery, characterized in that, Includes the acetonitrile electrolyte according to any one of claims 1-2.

6. The soft-pack battery according to claim 5, characterized in that, The pouch cell also includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode is mainly a layered oxide NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2; the negative electrode is mainly hard carbon; the separator is GF / A.

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