Electrolyte, secondary battery, and electric device

Abstract

The embodiment of the present application provides an electrolyte, a secondary battery and an electric device, wherein the electrolyte provided by the embodiment of the present application comprises a sodium salt, an organic solvent and an additive, the additive at least simultaneously comprises a B-O bond, a C=C bond and a C=O bond, wherein B in the B-O bond is in an electron-deficient state, so that the additive is acidic, can complex with an acid radical ion of the sodium salt, thereby improving the dissociation degree of the sodium salt and the migration number of sodium ions, and reducing the bulk phase and electrode interface impedance; and the C=C bond and the C=O bond in the additive can effectively reduce the deposition of transition metals such as Mn of the negative electrode, reduce the impedance, can form a highly stable electrode-electrolyte interface structure, can stabilize the positive and negative electrode interface film, and improve the high-temperature storage and cycle performance of the battery, thereby solving the problems that the electrode / electrolyte interface of the existing sodium ion battery is unstable, and is easy to cause the battery to deform and the performance to decay.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an electrolyte, a secondary battery, and an electrical device. Background Technology

[0002] Currently, sodium-ion batteries are receiving widespread attention due to their advantages such as high theoretical capacity, abundant sodium resources, excellent high and low temperature performance, and high safety.

[0003] The electrochemical performance and safety of sodium-ion batteries are both affected by the electrolyte. The electrolyte not only determines the battery's electrochemical window and energy density but also controls the properties of the electrode / electrolyte interface. However, the electrode / electrolyte interface in existing sodium-ion batteries is unstable, which can easily lead to battery deformation and performance degradation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an electrolyte, a secondary battery and an electrical device to solve the problem of unstable electrode / electrolyte interface in existing sodium-ion batteries, which easily leads to battery deformation and performance degradation.

[0005] To solve the above problems, the present invention is achieved through the following technical solution:

[0006] The present invention provides an electrolyte comprising a sodium salt, an organic solvent, and an additive, wherein the additive comprises at least BO bonds, C=C bonds, and C=O bonds.

[0007] Furthermore, in the electrolyte, the additive has a structural formula of at least one of formulas (A) and (B):

[0008]

[0009] Wherein, R1 is independently selected from one of methylene, C1-C10 straight-chain alkylene group, cycloalkylene group, phenylene group, alkoxyene group, cycloalkoxyene group, and phenoxyene group; R 21 R1 is independently selected from methyl, C1-C10 straight-chain alkyl, cycloalkyl, and phenyl; R2 is independently selected from methylene, C1-C10 straight-chain alkylene, cycloalkylene, phenylene, alkoxyene, cycloalkoxyene, and phenoxyene.

[0010] R3, R4, R5, and R6 are each independently selected from one of the following C1-C10 alkyl, phenyl, haloalkyl, and C1-C10 halophenyl groups.

[0011] Furthermore, in the electrolyte, R3, R4, R5, and R6 are each independently selected from one of -CH3, -C2H5, -CH2CF3, -CHC2F6, and -C(CH3)3.

[0012] Furthermore, in the electrolyte, the additive has a structural formula of at least one of formulas (A1) to (A4) and (B1) to (B4):

[0013]

[0014]

[0015] Furthermore, in the electrolyte, R3, R4, R5, and R6 are selected from trimethylsilyl groups.

[0016] Furthermore, in the electrolyte, the additive has a structural formula of at least one of formulas (A5) to (A8) and (B5) to (B8):

[0017]

[0018]

[0019] Furthermore, in the electrolyte, the content of additives is 0.1wt% to 5.0wt%, the content of sodium salt is 8wt% to 15wt%, and the content of organic solvent is 80wt% to 90wt%.

[0020] Furthermore, in the electrolyte, the sodium salt is one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(oxalato)borate, sodium difluorooxalatoborate, sodium difluorodi(oxalato)phosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

[0021] Furthermore, in the electrolyte, the organic solvent is at least two of the following: ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, acetonitrile, and sulfolane.

[0022] The present invention also proposes a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte as described above, wherein the positive electrode comprises a positive active material, and the positive active material comprises a sodium-containing compound.

[0023] The present invention also proposes an electrical device, wherein the aforementioned secondary battery is provided as the power supply for the electrical device.

[0024] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0025] In this embodiment of the invention, the electrolyte provided includes a sodium salt, an organic solvent, and an additive. The additive includes at least three BO bonds, C=C bonds, and C=O bonds. In the BO bond, the B atoms are in an electron-deficient state, making the additive acidic. This allows the additive to complex the anions of the sodium salt, thereby increasing the degree of dissociation of the sodium salt and the migration number of sodium ions, and reducing the bulk and electrode interface impedance. The C=C and C=O bonds in the additive can effectively reduce the deposition of Mn on the negative electrode and reduce impedance, forming a highly stable electrode-electrolyte interface structure. This stabilizes the positive and negative electrode interface films and improves the high-temperature storage and cycle performance of the battery. Therefore, it solves the problem of unstable electrode / electrolyte interface in existing sodium-ion batteries, which easily leads to battery deformation and performance degradation.

[0026] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0028] The applicant of this invention has discovered that although sodium-ion batteries have advantages such as high theoretical capacity, abundant sodium resources, excellent high and low temperature performance, and high safety, the electrode / electrolyte interface of existing sodium-ion batteries is unstable, which can easily lead to battery deformation and performance degradation.

[0029] To address the aforementioned problems, this invention provides an electrolyte comprising a sodium salt, an organic solvent, and additives, wherein the additives simultaneously comprise at least BO bonds, C=C bonds, and C=O bonds.

[0030] The electrolyte provided by this invention contains additives that simultaneously include at least BO bonds, C=C bonds, and C=O bonds. In the BO bonds, the B atoms are in an electron-deficient state, making the additive acidic. This allows the additive to complex sodium salt anions, thereby increasing the degree of dissociation of the sodium salt and the migration number of sodium ions, and reducing the bulk and electrode interface impedance. Meanwhile, the C=C and C=O bonds in the additive can effectively reduce the deposition of Mn on the negative electrode and reduce impedance, forming a highly stable electrode-electrolyte interface structure. This stabilizes the positive and negative electrode interface films, improves the high-temperature storage and cycle performance of the battery, and thus solves the problem of unstable electrode / electrolyte interfaces in existing sodium-ion batteries, which easily leads to battery deformation and performance degradation.

[0031] Optionally, in one embodiment, the structural formula of the above-mentioned additive is at least one of formula (A) and formula (B):

[0032]

[0033] Wherein, R1 is independently selected from one of methylene, C1-C10 straight-chain alkylene group, cycloalkylene group, phenylene group, alkoxyene group, cycloalkoxyene group, and phenoxyene group; R 21 R1 is independently selected from methyl, C1-C10 straight-chain alkyl, cycloalkyl, and phenyl; R2 is independently selected from methylene, C1-C10 straight-chain alkylene, cycloalkylene, phenylene, alkoxyene, cycloalkoxyene, and phenoxyene.

[0034] R3, R4, R5, and R6 are each independently selected from one of the following C1-C10 alkyl, phenyl, haloalkyl, and C1-C10 halophenyl groups.

[0035] In this embodiment of the invention, the additive's structural formula includes a borate ester bond and a dioxanepentenone group. The borate ester bond has a boron group in an electron-deficient state, making the additive acidic and allowing it to complex PF6 in the sodium salt. - F - The presence of anions increases the dissociation degree of sodium salt and the migration number of sodium ions, thereby reducing the bulk phase and electrode interface impedance. Meanwhile, the dioxanepentenone group can effectively reduce the deposition of Mn on the negative electrode and reduce impedance, forming a highly stable electrode-electrolyte interface structure. This can stabilize the positive and negative electrode interface film and improve the high-temperature storage and cycle performance of the battery.

[0036] When at least one of R3, R4, R5, and R6 is selected from C1 to C10 alkyl or phenyl halogroups, the halogen group -X can react with sodium salt in the electrolyte to form NaX, which, in synergy with dioxanepentenone, forms a highly stable electrode-electrolyte interface structure. This allows the various groups and structures mentioned above to further stabilize the positive and negative electrode interface films through cross-linking coupling, thereby improving the high-temperature storage and cycle performance of the battery cell by combining their film-forming effects.

[0037] The structure of the above-mentioned additive may include one or two borate ester groups, and the dioxacyclopentenone group may specifically be 1,3-dioxacyclopenten-2-one.

[0038] Optionally, in one specific embodiment, in the structural formula of the above-mentioned additive, R3, R4, R5, and R6 are each independently selected from one of -CH3, -C2H5, -CH2CF3, -CHC2F6, and -C(CH3)3.

[0039] Optionally, in one specific embodiment, the structural formula of the above-mentioned additive is at least one of formulas (A1) to (A4) and formulas (B1) to (B4):

[0040]

[0041] In the above embodiments, when the additive has the structural formulas (A1) and (B1), the CF bond can react with the sodium salt in the electrolyte to generate NaF, which works synergistically with the 1,3-dioxane-2-one group to form a highly stable electrode-electrolyte interface structure. This can effectively delay the deformation and performance degradation of sodium-ion batteries caused by the instability of the electrode / electrolyte interface.

[0042] In one embodiment, appropriate amounts of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one (VC-1), 2,2,2-trifluoroethanol, and acetonitrile are mixed, and boric acid solution is slowly added dropwise to the above system. The mixture is heated to reflux, and after the dehydration reaction, it is cooled to room temperature. The solvent is removed under reduced pressure, and finally, the crude product is subjected to column chromatography to obtain additive A1.

[0043] The chemical reaction formulas for the above preparation process are as follows:

[0044]

[0045] For example, 0.13 g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, 0.138 g of K2CO3, 0.20 g of 2,2,2-trifluoroethanol, and 100 mL of acetonitrile were placed in a 100 mL three-necked flask. Then, 0.06 g of boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 4) to obtain 0.15 g of product P1, with a yield of 46.1%.

[0046] The proton NMR spectrum of the above product P1 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 4.53 (s, 2H), 4.38 (s, 4H), 2.26 (s, 3H), ¹³C NMR spectrum: 13 CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 125.8, 121.8, 116.2, 67.5, 60.0, 16.5, indicating that the above product P1 is additive A1.

[0047] In one embodiment, an appropriate amount of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, K2CO3, methanol, and acetonitrile are mixed, and boric acid solution is slowly added dropwise to the above system. The mixture is heated to reflux, and after the dehydration reaction, the reaction is cooled to room temperature. The solvent is removed under reduced pressure, and finally, the crude product is subjected to column chromatography to obtain additive A2.

[0048] The chemical reaction formulas for the above preparation process are as follows:

[0049]

[0050] For example, 0.13 g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, 0.138 g of K2CO3, 0.064 g of methanol, and 100 mV of acetonitrile were placed in a 100 mL three-necked flask. Then, 0.06 g of boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.08 g of product P2 (yield 41.2%).

[0051] The proton NMR spectrum of the above product P2 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 4.53 (s, 2H), 3.39 (s, 6H), 2.26 (s, 3H), ¹³C NMR spectrum: 13 CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 121.8, 116.2, 60.0, 51.3, 16.5, indicating that the above product P2 is additive A2.

[0052] In one embodiment, 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, K2CO3, ethanol, and acetonitrile are mixed, and boric acid solution is slowly added dropwise to the above system. The mixture is heated to reflux, and after the dehydration reaction, the reaction is cooled to room temperature. The solvent is removed under reduced pressure, and finally, the crude product is subjected to column chromatography to obtain additive A3.

[0053] The chemical reaction formulas for the above preparation process are as follows:

[0054]

[0055] For example, 0.13 g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, 0.138 g of K2CO3, 0.092 g of ethanol, and 100 mL of acetonitrile were placed in a 100 mL three-necked flask. Then, 0.06 g of boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.11 g of product P3, with a yield of 47.5%.

[0056] The proton NMR spectrum of the above product P3 is as follows: 1 H NMR (DMSO, 300MHZ) δ (ppm): 4.53 (s, 2H), 3.90 (m, 4H), 2.26 (s, 3H), 1.10 (t, 6H);

[0057] The carbon NMR spectrum of the above product P3 is as follows: 13CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 121.8, 116.2, 60.0, 57.3, 18.2, 16.5; indicating that the above product is additive A3.

[0058] In one embodiment, 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, K2CO3, phenol, and acetonitrile are mixed, and boric acid solution is slowly added dropwise to the above system. The mixture is heated to reflux, and after the dehydration reaction, it is cooled to room temperature. The solvent is removed under reduced pressure, and finally, the crude product is subjected to column chromatography to obtain additive A4.

[0059] The chemical reaction formulas for the above preparation process are as follows:

[0060]

[0061] For example, 0.13 g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, 0.138 g of K2CO3, 0.188 g of phenol, and 100 mL of acetonitrile were placed in a 100 mL three-necked flask. Then, 0.06 g of boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 4) to obtain 0.18 g of product P4, with a yield of 56.2%.

[0062] The proton NMR spectrum of the above product P4 is as follows: 1 H NMR (DMSO, 300MHZ) δ (ppm): 7.22-6.81 (m, 10H), 4.53 (s, 2H), 2.26 (s, 3H);

[0063] The proton NMR spectrum of the above product P4 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 156.9, 147.5, 130.1, 121.3, 121.8, 121.1, 116.2, 60.0, 16.5; indicating that the above product is additive A4.

[0064] In one embodiment, 4-(bromomethyl)-5-(hydroxymethyl)-1,3-dioxanecyclopenten-2-one (VC-5), triethylamine and acetonitrile were mixed and formic acid was slowly added dropwise. After the addition was complete, the system was reacted at room temperature and then cooled to room temperature. The mixture was washed with water until neutral, and the organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography to obtain the intermediate product VC-6.

[0065] After mixing the above intermediate product VC-6 and methanol, concentrated hydrochloric acid was slowly injected and the reaction was carried out at room temperature until the reaction was complete. The mixture was washed with water, the organic phases were combined and dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography to obtain intermediate product VC-7.

[0066] After mixing the above intermediate products VC-7, K2CO3, 2,2,2-trifluoroethanol and acetonitrile, boric acid solution was slowly added dropwise to the above system, heated to reflux, and after the dehydration reaction, the reaction was cooled to room temperature. The solvent was removed under reduced pressure, and finally, the crude product was subjected to column chromatography to obtain additive B1.

[0067] The chemical reaction formulas for the above preparation process are as follows:

[0068]

[0069] For example, 0.208 g of 4-(bromomethyl)-5-(hydroxymethyl)-1,3-dioxanecyclopenten-2-one, 0.101 g of triethylamine and 100 mL of acetonitrile were placed in a 100 mL three-necked flask. 0.046 g of formic acid was slowly added dropwise using a syringe. After the addition was complete, the system was reacted at room temperature for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 1) to obtain the intermediate product VC-6.

[0070] The above intermediate product VC-6 and 20 mL of methanol were added sequentially to a 100 mL round-bottom flask. 0.05 g of concentrated hydrochloric acid was slowly injected with a syringe. After the addition was complete, the reaction was carried out at room temperature, and the reaction was monitored by TLC until the reaction was complete. The mixture was then washed with water, the organic phases were combined and dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 0.5) to obtain the intermediate product VC-7.

[0071] The above intermediate product VC-7, 0.276 g K2CO3, 0.40 g 2,2,2-trifluoroethanol, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.12 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and allowed to undergo dehydration reaction for 6 h. The reaction was then cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 4) to obtain 0.315 g of product Q1. The overall yield of the reaction was 56.1%.

[0072] The proton NMR spectrum of the above product Q1 is as follows: 1 H NMR (DMSO, 300MHZ) δ (ppm): 4.53 (s, 4H), 4.38 (s, 8H);

[0073] The carbon NMR spectrum of the above product Q1 is as follows: 13 C NMR (DMSO, 100MHZ) δ (ppm): 147.5, 125.8, 121.0, 67.5, 60.3; indicating that the above product is additive B1.

[0074] In one embodiment, VC-7, K2CO3, methanol, and acetonitrile are mixed, and boric acid solution is slowly added dropwise to the above system. The mixture is heated to reflux, dehydrated, cooled to room temperature, and the solvent is removed under reduced pressure. Finally, the crude product is subjected to column chromatography to obtain additive B2.

[0075] The chemical reaction formulas for the above preparation process are as follows:

[0076]

[0077] For example, 0.146 g VC-7, 0.276 g K2CO3, 0.128 g methanol, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.12 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and allowed to dehydrate for 6 h. The reaction was then cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.13 g of product Q2, with a yield of 45.2%.

[0078] The proton NMR spectrum of the above product Q2 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 4.53 (s, 4H), 3.39 (s, 12H); The carbon NMR spectrum of the above product Q2 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 121.0, 60.3, 51.3; indicating that the above product is additive B2.

[0079] In one embodiment, VC-7, K2CO3, ethanol, and acetonitrile are mixed, and boric acid solution is slowly added dropwise to the above system. The mixture is heated to reflux, and after the dehydration reaction, the reaction is cooled to room temperature. The solvent is removed under reduced pressure, and finally, the crude product is subjected to column chromatography to obtain additive B3.

[0080] The chemical reaction formulas for the above preparation process are as follows:

[0081]

[0082] For example, 0.146 g VC-7, 0.276 g K2CO3, 0.184 g ethanol, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.12 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and allowed to dehydrate for 6 h. The mixture was then cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.19 g of product Q3, with a yield of 55.1%.

[0083] The proton NMR spectrum of the above product Q3 is as follows: 1¹H NMR (DMSO, 300 MHz) δ (ppm): 4.53 (s, 4H), 3.90 (m, 8H), 1.10 (t, 12H); The carbon NMR spectrum of the above product Q3 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 121.0, 60.3, 57.3, 18.2; indicating that the above product is additive B3.

[0084] In one embodiment, VC-7, K2CO3, phenol, and acetonitrile are mixed, and boric acid solution is slowly added dropwise to the above system. The mixture is heated to reflux, and after the dehydration reaction, the reaction is cooled to room temperature. The solvent is removed under reduced pressure, and finally, the crude product is subjected to column chromatography to obtain additive B4.

[0085] The chemical reaction formulas for the above preparation process are as follows:

[0086]

[0087] For example, 0.146 g VC-7, 0.276 g K2CO3, 0.376 g phenol, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.12 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and allowed to dehydrate for 6 h. The reaction was then cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 4) to obtain 0.28 g of product Q4, with a yield of 53.1%.

[0088] The proton NMR spectrum of the above product Q4 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 7.22-6.81 (m, 20H), 4.53 (s, 4H); The carbon NMR spectrum of the above product Q4 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 156.9, 147.5, 130.1, 121.3, 121.1, 121.0, 60.3; indicating that the above product is additive B4.

[0089] Optionally, in one embodiment, R3, R4, R5, and R6 in the above electrolyte structural formula are selected from trimethylsilyl groups. In one embodiment, the trimethylsilyl group can react with HF in the electrolyte to inhibit its corrosion of transition metals in the electrode, thereby further improving the stability of the electrode-electrolyte interface structure.

[0090] Optionally, in one specific embodiment, the structural formula of the above-mentioned additive is at least one of formulas (A5) to (A8) and formulas (B5) to (B8):

[0091]

[0092]

[0093] In one embodiment, 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, K2CO3, trimethylhydroxysilane, and acetonitrile are mixed, and boric acid solution is slowly added dropwise to the above system. The mixture is heated to reflux, and after the dehydration reaction, it is cooled to room temperature. The solvent is removed under reduced pressure, and the crude product is finally obtained by column chromatography as additive A5.

[0094] The chemical reaction formulas for the above preparation process are as follows:

[0095]

[0096] For example, 0.13 g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, 0.138 g of K2CO3, 0.18 g of trimethylhydroxysilane, and 100 mL of acetonitrile were placed in a 100 mL three-necked flask. Then, 0.06 g of boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.16 g of product P5, with a yield of 52.1%.

[0097] The proton NMR spectrum of the above product P5 is as follows: 1 H NMR (DMSO, 300MHZ) δ (ppm): 4.53 (s, 2H), 2.26 (s, 3H), 0.21 (s, 18H);

[0098] The carbon NMR spectrum of the above product P5 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 121.8, 116.2, 59.4, 16.5, 4.8; indicating that the above product is additive A5.

[0099] In one embodiment, 4-(hydroxymethyl)-5-methyl-[1,3]dioxacyclopenten-2-one, K2CO3 and DMF are mixed, and 2-chloroethanol is slowly added dropwise. After the addition is complete, the system is placed in an oil bath and reacted, then cooled to room temperature, washed with water until neutral, the organic layer is dried with anhydrous sodium sulfate, and finally the crude product is subjected to column chromatography (to obtain the intermediate product VC-2).

[0100] After mixing the above intermediate products VC-2, K2CO3, trimethylhydroxysilane, and acetonitrile, boric acid solution was slowly added dropwise to the above system, heated to reflux, and after the dehydration reaction was carried out, the mixture was cooled to room temperature, the solvent was removed under reduced pressure, and finally the crude product was subjected to column chromatography to obtain additive A6.

[0101] The chemical reaction formulas for the above preparation process are as follows:

[0102]

[0103] For example, 0.13 g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, 0.138 g of K2CO3 and 100 mL of LDMF were placed in a 250 mL three-necked flask. 0.08 g of 2-chloroethanol was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was placed in an oil bath at 80 °C and reacted for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 1.5) to obtain the intermediate product VC-2.

[0104] The above intermediate product VC-2, 0.138 g K2CO3, 0.18 g trimethylhydroxysilane, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.06 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.12 g of product P6. The overall yield of the two-step reaction was 34.2%.

[0105] The proton NMR spectrum of the above product P6 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 4.04–4.03 (m, 4H), 3.56 (m, 2H), 2.26 (s, 3H), 0.21 (s, 18H); The carbon NMR spectrum of the above product P6 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 119.9, 115.6, 73.5, 67.2, 57.5, 16.5, 4.8; indicating that the above product is additive A6.

[0106] In one embodiment, 4-(hydroxymethyl)-5-methyl-[1,3]dioxacyclopenten-2-one, K2CO3 and DMF were mixed and 4-chlorocyclohexanol was slowly added dropwise. After the addition was complete, the system was placed in an oil bath and reacted, then cooled to room temperature, washed with water until neutral, the organic layer was dried with anhydrous sodium sulfate, and finally the crude product was subjected to column chromatography to obtain the intermediate product VC-3.

[0107] After mixing the above intermediate products VC-3, K2CO3, trimethylhydroxysilane, and acetonitrile, boric acid solution was slowly added dropwise to the above system, heated to reflux, and after the dehydration reaction, cooled to room temperature. The solvent was removed under reduced pressure, and finally, the crude product was subjected to column chromatography to obtain additive A7.

[0108] The chemical reaction formulas for the above preparation process are as follows:

[0109]

[0110] For example, 0.13 g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, 0.138 g of K2CO3 and 100 mL of DMF were placed in a 250 mL three-necked flask. 0.13 g of 4-chlorocyclohexanol was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was placed in an oil bath at 80 °C and reacted for 12 hours. After the reaction was stopped, the mixture was cooled to room temperature, washed with water until neutral, and the organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 1.5) to obtain the intermediate product VC-3.

[0111] The above intermediate product VC-3, 0.138 g K2CO3, 0.18 g trimethylhydroxysilane, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.06 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.13 g of product P7. The overall yield of the two-step reaction was 32.2%.

[0112] The proton NMR spectrum of the above product P7 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 4.04 (m, 2H), 3.54 (m, 1H), 3.24 (m, 1H), 2.26 (s, 3H), 1.74–1.45 (m, 8H), 0.21 (s, 18H); The ¹H NMR spectrum of the above product P7 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 119.9, 115.6, 86.4, 65.0, 62.7, 31.4, 30.5, 16.5, 4.8; indicating that the above product is additive A7.

[0113] In one embodiment, 4-(hydroxymethyl)-5-methyl-[1,3]dioxanepenten-2-one, K2CO3 and DMF were mixed and 4-chlorophenol was slowly added dropwise. After the addition was complete, the system was placed in an oil bath for reaction. After the reaction was stopped, it was cooled to room temperature, washed with water until neutral, and the organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography to obtain the intermediate product VC-4.

[0114] After mixing the above intermediate products VC-4, K2CO3, trimethylhydroxysilane, and acetonitrile, boric acid solution was slowly added dropwise to the above system, heated to reflux, and after the dehydration reaction, cooled to room temperature. The solvent was removed under reduced pressure, and finally, the crude product was subjected to column chromatography to obtain additive A8.

[0115] The chemical reaction formulas for the above preparation process are as follows:

[0116]

[0117] For example, 0.13 g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one, 0.138 g of K2CO3 and 100 mL of DMF were placed in a 250 mL three-necked flask. 0.13 g of 4-chlorophenol was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was placed in an oil bath at 80 °C and reacted for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 1.5) to obtain the intermediate product VC-4.

[0118] The intermediate product VC-4, 0.138 g K2CO3, 0.18 g trimethylhydroxysilane, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.06 g boric acid solution was slowly added dropwise to the system. The mixture was heated to reflux and allowed to undergo dehydration for 6 h. After cooling to room temperature, the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.11 g of product P8. The overall yield of the two-step reaction was 28.3%.

[0119] The proton NMR spectrum of the above product P8 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 6.68–6.75 (m, 4H), 4.61 (m, 2H), 2.26 (s, 3H), 0.21 (s, 18H); The carbon NMR spectrum of the above product P8 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 150.7, 149.2, 147.5, 121.8, 116.9, 116.2, 115.7, 75.0, 16.5, 4.8; indicating that the above product is additive A8.

[0120] In one embodiment, 4-(bromomethyl)-5-(hydroxymethyl)-1,3-dioxanecyclopenten-2-one (VC-5), triethylamine and acetonitrile were mixed and formic acid was slowly added dropwise. After the addition was complete, the system was reacted at room temperature and then cooled to room temperature. The mixture was washed with water until neutral, and the organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography to obtain the intermediate product VC-6.

[0121] After mixing the above intermediate product VC-6 and methanol, concentrated hydrochloric acid was slowly injected and the reaction was carried out at room temperature until the reaction was complete. The mixture was washed with water, the organic phases were combined and dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography to obtain intermediate product VC-7.

[0122] After mixing the above intermediate products VC-7, K2CO3, trimethylhydroxysilane, and acetonitrile, boric acid solution was slowly added dropwise to the above system, heated to reflux, and after the dehydration reaction, the reaction was cooled to room temperature. The solvent was removed under reduced pressure, and finally, the crude product was subjected to column chromatography to obtain additive B5.

[0123] The chemical reaction formulas for the above preparation process are as follows:

[0124]

[0125] For example, 0.208 g of 4-(bromomethyl)-5-(hydroxymethyl)-1,3-dioxanecyclopenten-2-one, 0.101 g of triethylamine and 100 mL of acetonitrile were placed in a 100 mL three-necked flask. 0.046 g of formic acid was slowly added dropwise using a syringe. After the addition was complete, the system was reacted at room temperature for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 1) to obtain the intermediate product VC-6.

[0126] The above intermediate product VC-6 and 20 mL of methanol were added sequentially to a 100 mL round-bottom flask. 0.05 g of concentrated hydrochloric acid was slowly injected with a syringe. After the addition was complete, the reaction was carried out at room temperature, and the reaction was monitored by TLC until the reaction was complete. The mixture was then washed with water, the organic phases were combined and dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 0.5) to obtain the intermediate product VC-7.

[0127] The above intermediate product VC-7, 0.276 g K2CO3, 0.36 g trimethylhydroxysilane, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.12 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and allowed to undergo dehydration reaction for 6 h. The reaction was then cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.18 g of product Q5. The overall yield of the reaction was 34.1%.

[0128] The proton NMR spectrum of the above product Q5 is as follows: 1 H NMR (DMSO, 300MHZ) δ (ppm): 4.53 (s, 4H), 0.21 (s, 36H);

[0129] The carbon NMR spectrum of the above product Q5 is as follows: 13 C NMR (DMSO, 100MHZ) δ (ppm): 147.5, 121.0, 59.7, 4.8; indicating that the above product is additive B5.

[0130] In one embodiment, VC-7, K2CO3 and DMF are mixed, and 2-chloroethanol is slowly added dropwise to the above system. After the addition is complete, the system is placed in an oil bath for reaction and then cooled to room temperature. The system is washed with water until neutral, the organic layer is dried with anhydrous sodium sulfate, and finally the crude product is subjected to column chromatography to obtain the intermediate product VC-8.

[0131] After mixing the above intermediate products VC-8, K2CO3, trimethylhydroxysilane, and acetonitrile, boric acid solution was slowly added dropwise to the above system, heated to reflux, and after the dehydration reaction, the reaction was cooled to room temperature. The solvent was removed under reduced pressure, and finally, the crude product was subjected to column chromatography to obtain additive B6.

[0132] The chemical reaction formulas for the above preparation process are as follows:

[0133]

[0134] For example, 0.146 g of VC-7, 0.276 g of K2CO3 and 100 mL of LDMF were placed in a 250 mL three-necked flask. 0.16 g of 2-chloroethanol was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was placed in an oil bath at 80 °C and reacted for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 1.5) to obtain the intermediate product VC-8.

[0135] The above intermediate product VC-8, 0.276 g K2CO3, 0.36 g trimethylhydroxysilane, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.12 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.19 g of product Q6. The overall yield of the reaction was 31.9%.

[0136] The proton NMR spectrum of the above product Q6 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 4.04–4.03 (m, 8H), 3.56 (m, 4H), 0.21 (s, 36H); The carbon NMR spectrum of the above product Q7 is as follows: 13 C NMR (DMSO, 100MHZ) δ (ppm): 147.5, 118.5, 73.5, 67.5, 57.5, 4.8; indicating that the above product is additive B6.

[0137] In one embodiment, VC-7, K2CO3 and DMF are mixed, and 4-chlorocyclohexanol is slowly added dropwise to the above system. After the addition is complete, the system is placed in an oil bath for reaction. After the reaction is stopped, it is cooled to room temperature, washed with water until neutral, the organic layer is dried with anhydrous sodium sulfate, and finally the crude product is subjected to column chromatography to obtain the intermediate product VC-9.

[0138] After mixing the above intermediate products VC-9, K2CO3, trimethylhydroxysilane, and acetonitrile, boric acid solution was slowly added dropwise to the above system, heated to reflux, and after the dehydration reaction, the reaction was cooled to room temperature. The solvent was removed under reduced pressure, and finally, the crude product was subjected to column chromatography to obtain additive B7.

[0139] The chemical reaction formulas for the above preparation process are as follows:

[0140]

[0141] For example, 0.146 g of VC-7, 0.276 g of K2CO3 and 100 mL of LDMF were placed in a 250 mL three-necked flask. 0.26 g of 4-chlorocyclohexanol was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was placed in an oil bath at 80 °C and reacted for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 1.5) to obtain the intermediate product VC-9.

[0142] The above intermediate product VC-9, 0.276 g K2CO3, 0.36 g trimethylhydroxysilane, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.12 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and dehydrated for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.27 g of product Q7. The overall yield of the reaction was 38.1%.

[0143] The proton NMR spectrum of the above product Q7 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 4.04 (m, 4H), 3.54 (m, 2H), 3.24 (m, 2H), 1.74–1.45 (m, 16H), 0.21 (s, 36H); The carbon NMR spectrum of the above product Q7 is as follows: 13 CNMR (DMSO, 100MHZ) δ (ppm): 147.5, 118.5, 86.4, 65.3, 62.7, 31.4, 30.5, 4.8; indicating that the above product is additive B7.

[0144] In one embodiment, VC-7, K2CO3 and DMF are mixed, and 4-chlorophenol is slowly added dropwise to the above system. After the addition is complete, the system is placed in an oil bath for reaction. After the reaction is stopped, it is cooled to room temperature, washed with water until neutral, and the organic layer is dried with anhydrous sodium sulfate. Finally, the crude product is subjected to column chromatography to obtain the intermediate product VC-10.

[0145] After mixing the above intermediate products VC-10, K2CO3, trimethylhydroxysilane, and acetonitrile, boric acid solution was slowly added dropwise to the above system, heated to reflux, and after the dehydration reaction, the reaction was cooled to room temperature. The solvent was removed under reduced pressure, and finally, the crude product was subjected to column chromatography to obtain additive B8.

[0146] The chemical reaction formulas for the above preparation process are as follows:

[0147]

[0148] For example, 0.146 g of VC-7, 0.276 g of K2CO3 and 100 mL of LDMF were placed in a 250 mL three-necked flask. 0.26 g of 4-chlorophenol was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was placed in an oil bath at 80 °C and reacted for 12 hours. The reaction was stopped and cooled to room temperature. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 1.5) to obtain the intermediate product VC-10.

[0149] The above intermediate product VC-10, 0.276 g K2CO3, 0.36 g trimethylhydroxysilane, and 100 mL acetonitrile were placed in a 100 mL three-necked flask. Then, 0.12 g boric acid solution was slowly added dropwise to the above system. The mixture was heated to reflux and the dehydration reaction was carried out for 6 h. The reaction was cooled to room temperature, and the solvent was removed under reduced pressure. Finally, the crude product was subjected to column chromatography (PE:EA = 5) to obtain 0.19 g of product Q8 (total yield 26.9%).

[0150] The proton NMR spectrum of the above product Q8 is as follows: 1 ¹H NMR (DMSO, 300 MHz) δ (ppm): 6.68-6.75 (m, 8H), 4.61 (m, 4H), 0.21 (s, 36H); The carbon NMR spectrum of the above product Q8 is as follows: 13 C NMR (DMSO, 100MHZ) δ (ppm): 150.7, 149.2, 147.5, 121.0, 116.9, 116.2, 115.7, 75.3, 4.8; indicating that the above product is additive B8.

[0151] In the electrolyte provided in this embodiment of the invention, the content of additives is 0.1wt% to 5.0wt%, the content of sodium salt is 8wt% to 15wt%, and the content of organic solvent is 80wt% to 90wt%. This can generate a passivation film of moderate thickness that is not easily broken, effectively blocking the interaction between the positive and negative electrodes and the electrolyte, while avoiding the passivation film formed by the additives on the surface of the positive and negative electrodes being too thick and increasing the impedance of the battery.

[0152] In some embodiments, the content of additives in the electrolyte can be 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%, 1.2 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.5 wt%, 5 wt%, or any combination thereof; optionally, the content of additives in the electrolyte is 0.1 wt% to 1.5 wt%, 0.5 wt% to 4.5 wt%, or 2 wt% to 3 wt%.

[0153] In the electrolyte provided by the embodiments of the present invention, the sodium salt content is in the range of 8% to 15% of the total mass, which makes the electrolyte have excellent conductivity and moderate viscosity, that is, it can effectively balance the conductivity and viscosity of the electrolyte. More preferably, the sodium salt content in the electrolyte is 12% to 13% of the total mass, for example 12 wt%, 12.5 wt%, or 13 wt%.

[0154] In the electrolyte provided in this embodiment of the invention, the sodium salt can be one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (BF4Na), sodium bis(oxaloyl)borate (NaBOB), sodium difluorooxaloylborate (NaDFOB), sodium difluorodioxaloyl phosphate (NaDFOP), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).

[0155] In the electrolyte provided in this embodiment of the invention, the organic solvent may be two or more of the following: ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN), and sulfolane (TMS).

[0156] This invention provides a method for preparing an electrolyte, the method comprising: mixing a sodium salt and an organic solvent under an inert gas atmosphere, wherein the temperature rise during the mixing process does not exceed 2°C, to obtain a colorless and transparent liquid; and mixing the above-mentioned additive with the above-mentioned colorless and transparent liquid to obtain an electrolyte.

[0157] During the mixing of sodium salt and organic solvent, the addition of sodium salt will cause the electrolyte temperature to rise, resulting in a certain degree of thermal decomposition of the sodium salt. Therefore, when adding sodium salt, the electrolyte temperature should be controlled. When the electrolyte temperature rises above 2°C, the addition of sodium salt should be stopped, and when the electrolyte temperature is below 2°C, the addition of sodium salt should continue.

[0158] The temperature of the electrolyte can be controlled using common temperature control methods in the field, such as ice bath, dry ice circulation cooling, and liquid nitrogen cooling.

[0159] Optionally, in some embodiments, the organic solvent includes multiple solvents. These solvents are pre-mixed and dehydrated. Then, under inert gas protection, the sodium salt and the organic solvent are mixed to obtain the colorless and transparent liquid. The additive is then mixed with the colorless and transparent liquid to obtain the electrolyte. Molecular sieve adsorption can be used to dehydrate the organic solvent.

[0160] The present invention also proposes a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte as described above.

[0161] In this process, the electrolyte in the electrolyte solution plays a role in conducting ions between the positive and negative electrode plates.

[0162] The aforementioned positive electrode sheet includes a positive current collector and a positive active material layer disposed on the aforementioned positive current collector. The aforementioned positive active material layer includes a positive active material, and the aforementioned positive active material includes a sodium-containing compound, wherein the sodium-containing compound includes at least one of sodium ion transition metal oxide, sodium ion transition metal phosphate, sodium ion transition metal sulfate, sodium ion transition metal Prussian blue compound, and sodium ion transition metal Prussian blue compound.

[0163] Optionally, in one embodiment, the positive electrode sheet further includes an adhesive, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0164] In some embodiments, the positive electrode sheet is prepared as follows: the components used to prepare the positive electrode sheet, such as the positive active material, binder and any other components, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on both sides of a positive electrode current collector such as an aluminum foil; after baking, rolling, cutting and other processes, the positive electrode sheet can be obtained.

[0165] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer can be a negative active material for batteries known in the art, such as at least one of carbon, alloy, transition metal oxide, and sodium ion transition metal phosphate. Carbon includes artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, etc.

[0166] In some embodiments, the negative electrode sheet is prepared as follows: the components used to prepare the negative electrode sheet, such as the negative electrode active material, binder and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as copper foil; after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0167] Understandably, the secondary battery provided in the embodiments of the present invention also includes a separator.

[0168] The secondary battery provided in this embodiment of the invention has a charging cutoff voltage of 3.6V to 4.2V.

[0169] The present invention also proposes an electrical device, wherein the aforementioned secondary battery is provided as the power supply for the electrical device.

[0170] The above-described secondary battery embodiments and electrical device embodiments include the electrolyte described above and can achieve the same technical effect. To avoid repetition, they will not be repeated here. For relevant details, please refer to the description of the positive electrode material embodiments.

[0171] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0172] The present invention will be described in detail below through embodiments.

[0173] Performance testing methods

[0174] (1) Room temperature DCR test: At 25±2℃, the battery is charged to 3.9V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, it is pulsed discharged at 10C constant current for 10 seconds. The SOC is then adjusted to 50% using the same method as above, and then charged for 10 seconds. The DCR is calculated as follows: DCR = (Voltage before pulse discharge - Voltage after pulse discharge) / Discharge current * 100%. After 30 days of high-temperature storage at 60℃, the DCR is tested again when the battery has completely cooled to 25±2℃. The DCR change rate is calculated as follows: DCR = (DCR after 30 days - DCR before 30 days) / DCR before 30 days * 100%.

[0175] (2) Room temperature cycle performance test: At 25±2℃, the battery was charged and discharged at a rate of 1C / 1C within the range of 2.0~3.9V. The discharge specific capacity of the battery in the first cycle and the discharge specific capacity after 500 cycles were recorded. The capacity retention rate after 500 cycles was calculated as: discharge specific capacity of 500 cycles / discharge specific capacity in the first cycle * 100%.

[0176] (3) High temperature storage performance: The battery was placed at 60±2℃ and charged and discharged at a rate of 1C / 1C within the range of 2.0 to 3.9V. The discharge specific capacity of the battery in the first week was recorded. After that, the battery was stored at 60±2℃ for 30 days. The charge and discharge test was carried out again and the discharge specific capacity was recorded. The high temperature storage capacity retention rate was calculated as: discharge specific capacity after 7 days / discharge specific capacity in the first week * 100%.

[0177] (4) High-temperature gas generation test: The battery was charged at 25±2℃ with a constant current of 1C to 3.9V, and then charged at 3.9V with a constant voltage until the current was lower than 0.05C, so that it was in a fully charged state of 3.9V; the volume of the fully charged battery before storage was measured and recorded as V0; the fully charged battery was then placed in an oven at 60±2℃. After 7 days, the battery was taken out and its volume after storage was measured immediately and recorded as V1. The volume expansion rate was calculated as (V1-V0) / V0*100%.

[0178] Example 1

[0179] (1) Preparation of electrolyte:

[0180] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), EC, PC, and EMC were mixed thoroughly in a 1:1:1 mass ratio. Molecular sieves are used to remove water, resulting in a mixed solvent. NaPF6 is added to the mixed solvent in batches while continuously stirring and cooling with dry ice. NaPF6 can be added as long as the electrolyte temperature rise does not exceed 2°C. The mass fraction of NaPF6 in the electrolyte is controlled at 12.5%. Finally, a colorless and transparent liquid is obtained. Additive A5, equivalent to 0.1% of the total mass of the electrolyte, is added and stirred evenly to obtain the electrolyte.

[0181] (2) Preparation of positive electrode sheet

[0182] The positive electrode active material Na3V2(PO4)3, the conductive agent acetylene black (Super P), and the binder polyvinylidene fluoride (PVDF) were mixed evenly in a mass ratio of Na3V2(PO4)3:Super P:PVDF = 90:6:4, and then uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to prepare a uniform black slurry. The mixed black slurry was coated on both sides of aluminum foil, and after baking, rolling, and cutting, the positive electrode sheet was obtained.

[0183] (3) Preparation of negative electrode sheet

[0184] The negative electrode active material hard carbon, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in a mass ratio of 97:1:2 and evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0185] (4) Preparation of sodium-ion batteries

[0186] The prepared positive electrode sheet, separator (PP separator), and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding, hot pressing and shaping, and welding of the tabs, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery, and the battery is allowed to stand, form, and be capacity tested to complete the preparation of the sodium-ion soft pack battery.

[0187] Example 2

[0188] The difference between Example 2 and Example 1 is that, in the preparation of the electrolyte, the mass percentage of additive A5 in the electrolyte is adjusted to 0.5%.

[0189] Example 3

[0190] The difference between Example 3 and Example 1 is that, in the preparation of the electrolyte, the mass percentage of additive A5 in the electrolyte is adjusted to 1.0%.

[0191] Example 4

[0192] The difference between Example 4 and Example 1 is that, in the preparation of the electrolyte, the mass percentage of additive A5 in the electrolyte is adjusted to 1.5%.

[0193] Example 5

[0194] The difference between Example 5 and Example 1 is that, during the preparation of the electrolyte, the mass percentage of additive A5 in the electrolyte is adjusted to 5%.

[0195] Example 6

[0196] The difference between Example 6 and Example 3 is that the additive is changed to A1 during the preparation of the electrolyte.

[0197] Example 7

[0198] The difference between Example 7 and Example 3 is that the additive was changed to A2 during the preparation of the electrolyte.

[0199] Example 8

[0200] The difference between Example 8 and Example 3 is that the additive was changed to A3 during the preparation of the electrolyte.

[0201] Example 9

[0202] The difference between Example 9 and Example 3 is that the additive was changed to A4 during the preparation of the electrolyte.

[0203] Example 10

[0204] The difference between Example 10 and Example 3 is that the additive was changed to A6 during the preparation of the electrolyte.

[0205] Example 11

[0206] The difference between Example 11 and Example 3 is that the additive was changed to A7 during the preparation of the electrolyte.

[0207] Example 12

[0208] The difference between Example 12 and Example 3 is that the additive was changed to A8 during the preparation of the electrolyte.

[0209] Example 13

[0210] The difference between Example 13 and Example 3 is that the additive was changed to B5 during the preparation of the electrolyte.

[0211] Example 14

[0212] The difference between Example 14 and Example 3 is that the additive was changed to B1 during the preparation of the electrolyte.

[0213] Example 15

[0214] The difference between Example 15 and Example 3 is that the additive was changed to B2 during the preparation of the electrolyte.

[0215] Example 16

[0216] The difference between Example 16 and Example 3 is that the additive was changed to B3 during the preparation of the electrolyte.

[0217] Example 17

[0218] The difference between Example 17 and Example 3 is that the additive was changed to B4 during the preparation of the electrolyte.

[0219] Example 18

[0220] The difference between Example 18 and Example 3 is that the additive was changed to B6 during the preparation of the electrolyte.

[0221] Example 19

[0222] The difference between Example 19 and Example 3 is that the additive was changed to B7 during the preparation of the electrolyte.

[0223] Example 20

[0224] The difference between Example 20 and Example 3 is that the additive was changed to B8 during the preparation of the electrolyte.

[0225] Examples 21-23

[0226] The difference between Examples 21-23 and Example 3 is that the type and proportion of sodium salt were adjusted during the preparation of the electrolyte, as shown in Table 1.

[0227] Comparative Example 1

[0228] The difference between Example 1 and Example 3 is that no additive A5 is added during the preparation of the electrolyte.

[0229] Comparative Example 2

[0230] The difference between Comparative Example 2 and Example 3 is that, in the preparation of the electrolyte, additive A5 was changed to vinylene carbonate (VC).

[0231] Comparative Example 3

[0232] The difference between Comparative Example 3 and Example 3 is that, in the preparation of the electrolyte, additive A5 was changed to tris(trimethylsilane)borate (TMSB).

[0233] Comparative Example 4

[0234] The difference between Comparative Example 4 and Example 3 is that, in the preparation of the electrolyte, additive A5 was adjusted to vinylene carbonate (VC) and tris(trimethylsilane)borate (TMSB), and the mass percentage of each in the electrolyte was 0.5%.

[0235] The process parameters for each embodiment and comparative example are shown in Table 1.

[0236] The batteries prepared in each embodiment and comparative example were subjected to room temperature DCR test, room temperature cycle performance test, high temperature storage performance test and high temperature gas generation test. The test data are shown in Table 1.

[0237] Table 1

[0238]

[0239]

[0240] The experimental results from Examples 1-5 and Comparative Example 1 show that adding additive A5 can reduce the initial internal resistance of the battery and the increase in internal resistance during storage, and improve the capacity retention rate during room temperature cycling and high temperature storage. At the same time, as the content of additive A5 in the electrolyte increases, the resulting interfacial film becomes denser, which has a beneficial effect on suppressing the increasing trend of battery internal resistance and volume expansion rate during high temperature storage, and reducing irreversible losses during storage. However, excessive additive usage can significantly increase the initial impedance, which is not conducive to the dynamic performance of the cell. Therefore, the preferred mass percentage of A5 in the electrolyte is 0.5-1.5%.

[0241] The experimental results of Examples 3, 6-20 and Comparative Example 1 show that the addition of additives A1-A8 and B1-B8 can reduce the initial internal resistance of the battery, as well as the increase in internal resistance and volume expansion during storage, and improve the capacity retention rate during room temperature cycling and high temperature storage.

[0242] The experimental results from Example 3 and Comparative Cases 2-4 show that, compared to additives containing only a single functional group, the combination of the two, namely additive A5, exhibits better performance. It contains a 1,3-dioxanepenten-2-one structure, which can reduce the deposition of transition metals such as Mn on the negative electrode, lower impedance, and facilitate the formation of a stable interfacial film on the negative electrode surface. Furthermore, additive A5 contains a BO bond, with the central atom B in an electron-deficient state, making additive A5 acidic and capable of complexing PF6. - or F -This increases the degree of dissociation of sodium salt and the migration number of sodium ions, thereby reducing the impedance of the bulk phase and electrode interface. At the same time, the silyl ether (O-Si-C) in A5 can react with HF to inhibit its corrosion of transition metals. In addition, the above-mentioned 1,3-dioxacyclopenten-2-one structure, BO bond and silyl ether structure further stabilize the positive and negative electrode interface film through cross-linking coupling. Combined with its film-forming effect, it improves the high-temperature storage gas generation and cycle performance of the battery cell.

[0243] In summary, in this embodiment, the electrolyte includes sodium salt, organic solvent, and additives. The additives include at least BO bonds, C=C bonds, and C=O bonds. In the BO bonds, the B atoms are in an electron-deficient state, making the additive acidic. This allows the additive to complex the anions of the sodium salt, thereby increasing the degree of dissociation of the sodium salt and the migration number of sodium ions, and reducing the bulk and electrode interface impedance. The C=C and C=O bonds in the additives can effectively reduce the deposition of transition metals such as Mn on the negative electrode, reduce impedance, and form a highly stable electrode-electrolyte interface structure. This stabilizes the positive and negative electrode interface films, improves the high-temperature storage and cycle performance of the battery, and thus solves the problem of unstable electrode / electrolyte interface in existing sodium-ion batteries, which easily leads to battery deformation and performance degradation.

[0244] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present invention.

[0245] The electrolyte, secondary battery, and electrical device provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An electrolyte, characterized in that, It includes sodium salts, organic solvents, and additives, wherein the additives simultaneously include at least BO bonds, C=C bonds, and C=O bonds; In the electrolyte, the content of the additive is 0.1wt% to 5.0wt%, the content of the sodium salt is 8wt% to 15wt%, and the content of the organic solvent is 80wt% to 90wt%. The additive has a structural formula of at least one of formulas (A) and (B): Wherein, R1 is independently selected from one of methylene, C1-C10 straight-chain alkylene group, cycloalkylene group, phenylene group, alkoxyene group, cycloalkoxyene group, and phenoxyene group; R 21 R1 is independently selected from methyl, C1-C10 straight-chain alkyl, cycloalkyl, and phenyl; R2 is independently selected from methylene, C1-C10 straight-chain alkylene, cycloalkylene, phenylene, alkoxyene, cycloalkoxyene, and phenoxyene; R3, R4, R5, and R6 are each independently selected from C1-C10 alkyl, phenyl, C1-C10 haloalkyl, halophenyl, and trimethylsilyl.

2. The electrolyte according to claim 1, characterized in that, R3, R4, R5, and R6 are each independently selected from one of -CH3, -C2H5, -CH2CF3, -CHC2F6, and -C(CH3)3.

3. The electrolyte according to claim 1, characterized in that, The additive has a structural formula of at least one of formulas (A1) to (A4) and (B1) to (B4):

4. The electrolyte according to claim 1, characterized in that, R3, R4, R5, and R6 are selected from trimethylsilyl groups.

5. The electrolyte according to claim 4, characterized in that, The additive has a structural formula of at least one of formulas (A5) to (A8) and (B5) to (B8):

6. The electrolyte according to claim 1, characterized in that, The sodium salt is one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(oxalato)borate, sodium difluorooxalatoborate, sodium difluorodi(oxalato)phosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

7. The electrolyte according to claim 1, characterized in that, The organic solvent is at least two of the following: ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, acetonitrile, and sulfolane.

8. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte as described in any one of claims 1 to 7, wherein the positive electrode includes a positive active material, and the positive active material includes a sodium-containing compound.

9. An electrical appliance, characterized in that, The device includes the secondary battery as described in claim 8, wherein the secondary battery serves as the power supply for the electrical equipment.

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