Preparation method of electrolyte additive, high-voltage electrolyte containing the additive and lithium battery

Abstract

The application provides a preparation method of an electrolyte additive, a high-voltage electrolyte containing the additive and a lithium battery, and belongs to the technical field of lithium batteries. The electrolyte additive is lithium aromatic carboxylate containing fluorine (cyano, fluorosulfonyl). The method is simple, efficient, low in raw material cost and suitable for large-scale preparation based on a simple acid-base neutralization reaction and filtration purification. The electrolyte additive prepared by the method and the electrolyte containing the additive can effectively improve the high-voltage stability of the lithium battery, significantly improve the cycle stability of the lithium battery at a high charging voltage of 4.5 V or above, and further improve the specific capacity and specific energy density of the lithium battery, so that the application prospect is very good, and the electrolyte additive can be expected to be used in the field of high-voltage electrolyte additives for lithium batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, and relates to a method for preparing an electrolyte additive, a high-voltage electrolyte containing the additive, and a lithium battery. Background Technology

[0002] Lithium-ion batteries (LIBs) play a vital role in high-tech fields such as portable electronics, electric vehicles, and renewable energy, but currently the most advanced lithium-ion batteries only produce about 300 Wh / kg. -1 The specific energy density is insufficient to meet the growing demand for energy storage devices and other related products.

[0003] Improving battery energy density hinges on increasing the voltage difference between the positive and negative electrode materials and the battery's specific capacity. However, on the one hand, conventional carbonate electrolytes are prone to oxidative decomposition at high voltages (>4.3 V), and positive electrode materials (such as lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide) are also susceptible to structural damage such as transition metal dissolution and lattice oxygen loss, leading to capacity decay and increased interfacial impedance. On the other hand, lithium anodes with higher specific capacity are constrained by issues such as lithium dendrite formation and interfacial instability, hindering the further development of high-voltage lithium batteries.

[0004] Therefore, developing novel electrolyte systems that can simultaneously stabilize the positive (negative) electrode / electrolyte interface and have high voltage tolerance, especially highly efficient functional additives, has become the key to promoting the development of high energy density lithium batteries. Summary of the Invention

[0005] To address the lack of novel electrolyte systems in existing technologies that can simultaneously stabilize the positive (negative) electrode / electrolyte interface and possess high voltage tolerance, particularly efficient functional additives, this invention provides a method for preparing an electrolyte additive, a high-voltage electrolyte containing the additive, and a lithium battery. The electrolyte additive prepared by this invention, and the electrolyte containing the additive, can effectively improve the high-voltage stability of lithium batteries, significantly enhance the cycle stability of lithium batteries at high charging voltages above 4.5V, thereby increasing the specific capacity and specific energy density of lithium batteries. It has excellent application prospects and is expected to be used in the field of high-voltage electrolyte additives for lithium batteries.

[0006] One object of the present invention is to provide an electrolyte additive that improves the performance of lithium batteries under high voltage.

[0007] Another object of the present invention is to provide a high-voltage electrolyte containing the additive.

[0008] Another object of the present invention is to provide a lithium battery containing the high-voltage electrolyte.

[0009] The technical solution of the present invention is as follows:

[0010] This invention provides an electrolyte additive and its preparation method, as well as a high-voltage electrolyte and a lithium battery containing the additive. The electrolyte additive is a fluorine-containing (cyano, fluorosulfonyl) aromatic carboxylic acid lithium, having the chemical structure shown in Formula I:

[0011] Where R1~R5 are one or more of fluorine, cyano, fluoroalkyl, and fluorosulfonyl groups, R n The alkyl or carboxylic acid lithium group with 1 to 8 carbon atoms is directly attached to the benzene ring. In compounds containing more than one carboxylic acid lithium group, the position of the carboxylic acid lithium group on the benzene ring is ortho, meta, or para. The preparation method of this electrolyte additive includes: (1) adding a fluorine-containing (cyano, fluoroalkyl, fluorosulfonyl) aromatic carboxylic acid to a reaction vessel and adding ethanol and stirring to dissolve it, adding a lithium-containing inorganic base, stirring the reaction at room temperature until the lithium-containing inorganic base is completely dissolved, filtering to remove insoluble impurities, and then placing it in a vacuum drying oven to dry; (2) dissolving the dried powder with acetone, washing the insoluble precipitate with acetone, and drying it under vacuum to obtain a fluorine-containing (cyano, fluoroalkyl, fluorosulfonyl) aromatic carboxylic acid lithium compound. This method is based on a simple acid-base neutralization reaction and filtration purification, which is simple and efficient, has low raw material cost, and is suitable for large-scale preparation. A high-voltage electrolyte includes an electrolyte salt, an organic solvent, and the electrolyte additives described above; a lithium battery includes a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0012] The objective of this invention is achieved through the following technical solution: An electrolyte additive is used in high-voltage electrolytes for lithium batteries with charging voltages higher than 4.5V. This electrolyte additive is a lithium aromatic carboxylic acid compound containing fluorine (cyano, fluoroalkyl, or fluorosulfonyl), and the general formula of the lithium aromatic carboxylic acid compound containing fluorine (cyano, fluoroalkyl, or fluorosulfonyl) is shown in structural formula I.

[0013] Among them, R1, R2, R3, R4, and R5 are each independently selected from one or more of fluorine, cyano, fluoroalkyl, and fluorosulfonyl groups, R n An alkyl or carboxylic acid lithium group with 1 to 8 carbon atoms is directly attached to a benzene ring. In compounds containing more than one carboxylic acid lithium group, the position of the carboxylic acid lithium group on the benzene ring is ortho, meta, or para.

[0014] The preparation method of the above-mentioned electrolyte additive includes the following steps: S1. Add aromatic carboxylic acid to the reaction vessel and pour in organic solvent I and stir to dissolve. Add lithium-containing inorganic base and dissolve completely. Stir the reaction until the lithium-containing inorganic base is completely dissolved. Filter to remove insoluble impurities and then put it in a vacuum drying oven to dry. The molar ratio of the aromatic carboxylic acid to the lithium-containing inorganic base is (2~4):1. S2. The powder obtained after drying S1 is dissolved in organic solvent II, filtered and washed to remove the insoluble precipitate, and the precipitate is dried in a vacuum drying oven to obtain an aromatic carboxylic acid lithium compound.

[0015] Furthermore, the aromatic carboxylic acid described in S1 has a structure as shown in Formula II:

[0016] R1, R2, R3, R4, and R5 are each independently selected from one or more of the following groups: fluorine, cyano, fluoroalkyl, and fluorosulfonyl. n An alkyl or carboxyl group with 1 to 8 carbon atoms is directly attached to a benzene ring. In compounds containing more than one carboxyl group, the carboxyl group is positioned ortho, meta, or para on the benzene ring.

[0017] Furthermore, the organic solvent I mentioned in S1 is one of ethanol, methanol, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP).

[0018] Furthermore, the lithium-containing inorganic base mentioned in S1 is one or more of lithium hydroxide (LiOH), lithium oxide (Li2O), lithium carbonate (Li2CO3), and lithium phosphate (Li3PO4).

[0019] Furthermore, the stirring reaction described in S1 is carried out at a temperature of 10°C to 50°C for a time of 10 to 60 minutes.

[0020] Furthermore, the organic solvent II mentioned in S2 is one of acetone, tetrahydrofuran, and ethyl acetate.

[0021] Furthermore, the drying process described in S2 involves a temperature of 30°C to 180°C and a pressure of -0.01 MPa to -1.0 MPa.

[0022] The present invention also relates to a high-voltage electrolyte for use in lithium batteries with a charging voltage higher than 4.5V. The high-voltage electrolyte uses a carbonate organic solvent and includes a carbonate organic solvent, a lithium salt, and the above-mentioned electrolyte additive, wherein the content of the additive in the high-voltage electrolyte is 0.1wt%≤10wt%.

[0023] Furthermore, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate-borate), lithium methanesulfonate, and lithium bis(trifluoromethanesulfonylimide).

[0024] Furthermore, the concentration of the lithium salt is 0.5M to 2M.

[0025] Furthermore, the carbonate organic solvent is selected from one or more combinations of linear carbonates such as ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate, and cyclic carbonates such as fluoroethylene carbonate, propylene carbonate, and butene carbonate.

[0026] Furthermore, the carbonate organic solvent is composed of fluoroethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7.

[0027] The present invention also relates to a lithium battery, comprising a positive electrode, a negative electrode, a separator, and the aforementioned high-voltage electrolyte.

[0028] Furthermore, the lithium battery is one of lithium-ion batteries or lithium metal batteries.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. The electrolyte additive of the present invention is a high-voltage electrolyte additive. Due to the conjugated electron effect of the aromatic group itself and the electron-withdrawing effect of the fluorine, cyano, fluoroalkyl, and fluorosulfonyl groups on the aromatic group, the electrolyte containing this additive can preferentially form a thin and dense positive electrode-electrolyte interface film (CEI) rich in inorganic substances such as LiF, Li3N, and Li2S on the positive electrode surface. This avoids continuous contact between the positive electrode material and the electrolyte, thereby inhibiting the continuous oxidative decomposition of the electrolyte. At the same time, it protects the crystal structure of the electrode material and effectively reduces the loss of reversible capacity during cycling, thus significantly improving the cycle stability of the positive material at ultra-high charging voltages greater than 4.5V.

[0030] 2. The high-voltage electrolyte of the present invention can generate a thin and dense electrode-electrolyte interface film (SEI) rich in inorganic substances such as LiF, Li3N, and Li2S on the surface of the negative electrode. The formation of this interface film can inhibit the growth of lithium dendrites, thereby significantly improving the cycle stability of lithium batteries at ultra-high charging voltages greater than 4.5V.

[0031] 3. The high-voltage electrolyte additive provided by this invention can improve the charging voltage, energy density and cycle stability of lithium batteries. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the specific embodiments of this disclosure or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 The infrared spectrum of the fluorinated aromatic carboxylic acid lithium compound P1 synthesized in Example 1 of this invention; Figure 2 The XRD pattern of the lithium fluorinated aromatic carboxylic acid compound P1 synthesized in Example 1 of this invention; Figure 3 The image shows a SEM image of the fluorinated aromatic carboxylic acid lithium compound P1 synthesized in Example 1 of this invention, where a is a 100 μm magnified image and b is a 5 μm magnified image. Figure 4 The graph shows the cycle performance of lithium metal batteries prepared with the base electrolyte of Comparative Example 1 and the high-voltage electrolyte of Example 1 after 400 cycles, with a charge-discharge range of 3.0V-4.6V. Figure 5 The graph shows the cycle performance of lithium metal batteries prepared with the base electrolyte of Comparative Example 1 and the high-voltage electrolyte of Example 1 after 100 cycles, with a charge-discharge range of 3.0V-4.7V. Figure 6 The graph shows the cycle performance of lithium metal batteries prepared with the basic electrolyte of Comparative Example 1 and the high-voltage electrolyte of Example 1 after 100 cycles, with a charge-discharge range of 3.0V-4.8V. Figure 7 The graph shows the cycle performance of lithium metal batteries prepared with the electrolyte of Comparative Example 2 and the high-voltage electrolyte of Example 1, with a charge-discharge range of 3.0V-4.7V. Figure 8 This is a charge-discharge curve of the lithium metal battery prepared with the high-voltage electrolyte in Example 1 for the first three cycles. The positive electrode is a nickel-cobalt-manganese positive electrode, and the negative electrode is a lithium metal sheet. The voltage window is 3.0V-4.7V. Figure 9 This is a cycle performance diagram of a lithium metal battery prepared with the high-voltage electrolyte of Example 1 after 100 cycles. The positive electrode is a nickel-cobalt-manganese positive electrode, and the negative electrode is a lithium metal sheet. The voltage windows are 3.0V-4.5V and 3.0V-4.7V. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] This invention discloses an electrolyte additive, which is a lithium aromatic carboxylic acid compound containing fluorine (cyano, fluoroalkyl, fluorosulfonyl) for use in high-voltage electrolytes of lithium batteries with charging voltages higher than 4.5V. The additive is characterized in that the general formula of the lithium aromatic carboxylic acid compound containing fluorine (cyano, fluoroalkyl, fluorosulfonyl) is shown in structural formula I.

[0036] Among them, R1, R2, R3, R4, and R5 are each independently selected from one or more of fluorine, cyano, fluoroalkyl, and fluorosulfonyl groups, R n An alkyl or carboxylic acid lithium group with 1 to 8 carbon atoms is directly attached to a benzene ring. In compounds containing more than one carboxylic acid lithium group, the position of the carboxylic acid lithium group on the benzene ring is ortho, meta, or para. The present invention also discloses a high-voltage electrolyte for lithium batteries with a charging voltage higher than 4.5V, comprising a carbonate organic solvent and a lithium salt, and further comprising the aforementioned additives, wherein the content of the additives is ≥0.1wt% and ≤10wt%; in some embodiments, the amount of additives added is 0.5% or 1.0% of the total mass of the electrolyte; The lithium salt in the high-voltage electrolyte is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), and lithium perchlorate (LiClO4); the concentration of the lithium salt is 0.5M to 1.5M. The carbonate organic solvent is selected from one or more combinations of linear carbonates such as ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) and cyclic carbonates such as fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), and butene carbonate (BC). In some embodiments, the carbonate organic solvent is a mixture of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC); The present invention also discloses a lithium battery, comprising a positive electrode, a negative electrode, a separator, and the aforementioned high-voltage electrolyte; the lithium battery is either a lithium-ion battery or a lithium metal battery.

[0037] The following examples demonstrate the testing of different high-voltage electrolytes and compare them with comparative examples. The procedures are as follows: Step 1: In a fume hood, synthesize fluorine-containing (cyano, fluoroalkyl, fluorosulfonyl) aromatic carboxylic acid lithium compounds as additives for high-voltage electrolytes; Step 2: Characterize the structure of the above-synthesized additives; Step 3: In an argon-filled glove box, different concentrations of the above-mentioned additives were added to a conventional carbonate electrolyte and stirred thoroughly to obtain a series of modified high-voltage electrolytes. Step 4: Assemble the lithium battery and conduct electrochemical performance testing.

[0038] Example 1: A method for preparing an electrolyte additive includes the following steps: Synthesis of P1, a lithium compound containing fluorinated aromatic carboxylic acids

[0039] S1. Add fluorinated aromatic carboxylic acid S1 (1.59g) to the reaction vessel and pour in ethanol (20ml) as an organic solvent. After stirring and dissolving thoroughly, add lithium-containing inorganic base S2 (0.19g) and stir at room temperature for 30 minutes. Filter to remove insoluble impurities and dry the solution under vacuum at 50°C for 6 hours. S2. Then, acetone (20 ml) was added to the dried powder as an organic solvent. The insoluble precipitate was filtered out with filter paper, and 3 ml of acetone was added to it. The precipitate was gently stirred and the process was repeated three times after the acetone flowed down to achieve thorough washing. Then, the powder was vacuum dried at 160°C for 8 hours to obtain the product, a lithium fluorinated aromatic carboxylic acid compound P1.

[0040] Figure 1 This is the infrared characterization spectrum of P1, a lithium compound containing fluorinated aromatic carboxylic acids synthesized in Example 1. Figure 1 It can be seen at 1603cm -1 991cm -1 519cm -1 Obvious absorption peaks were generated at locations such as C=O, CF, and O-Li chemical bonds in the lithium pentafluorobenzoate prepared in Example 1; Figure 2 This is the XRD pattern of the fluorinated aromatic carboxylic acid lithium compound P1 synthesized in Example 1. Figure 2 As can be seen, the lithium pentafluorobenzoate prepared in Example 1 has obvious crystal characteristics; Figure 3 This is a SEM image of P1, a lithium compound containing fluorinated aromatic carboxylic acids synthesized in Example 1. Figure 3It can be seen that secondary structures with different characteristics are observed in different magnified images at 100 μm and 5 μm, which are derived from the crystallization process from the solution during preparation.

[0041] In an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), a fluorinated aromatic carboxylic acid lithium compound additive P1 was added to a 1 M LiPF6 in FEC:EMC = 3:7 vol% base electrolyte. The amount of additive added was 0.5% of the total mass of the electrolyte. After stirring for 4 hours, a high-voltage electrolyte was obtained.

[0042] Assemble a lithium metal battery with LCO, NCM811 or high-nickel cathode and lithium sheet as a cathode. The electrolyte in the battery is 70uL.

[0043] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0044] Example 2: A method for preparing a high-voltage electrolyte includes the following steps: In an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), a fluorinated aromatic carboxylic acid lithium compound additive P1 was added to a 1 M LiPF6 in FEC:EMC = 3:7 vol% base electrolyte. The amount of additive added was 1.0% of the total mass of the electrolyte. After stirring for 4 hours, a high-voltage electrolyte was obtained.

[0045] Assemble a lithium metal battery with LCO, NCM811 or high-nickel cathode and lithium sheet as a cathode. The electrolyte in the battery is 70uL.

[0046] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0047] Example 3: A method for preparing an electrolyte additive includes the following steps: S1. Add fluorinated aromatic carboxylic acid S1 (1.59g) to the reaction vessel and pour in DMF (20ml) as an organic solvent. After stirring and dissolving thoroughly, add lithium-containing inorganic base S2 (0.19g) and stir at room temperature for 30 minutes. Filter to remove insoluble impurities and dry the solution under vacuum at 50°C for 6 hours. S2. Then, ethyl acetate (20 ml) was added to the dried powder as an organic solvent. The insoluble precipitate was filtered out with filter paper, and 3 ml of ethyl acetate was added to it. The precipitate was gently stirred and the mixture was allowed to flow down. This process was repeated three times to achieve thorough washing. The powder was then vacuum dried at 160 °C for 8 hours to obtain the product, a lithium fluorinated aromatic carboxylic acid compound P1.

[0048] In an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), a fluorinated aromatic carboxylic acid lithium compound additive P1 was added to a 1M LiPF6 in FEC:EMC = 3:7 vol% basic electrolyte. The amount of additive added was 0.5% of the total mass of the electrolyte. After stirring for 4 hours, a high-voltage electrolyte was obtained.

[0049] Assemble a lithium metal battery with LCO, NCM811 or high-nickel cathode and lithium sheet as a cathode. The electrolyte in the battery is 70uL.

[0050] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0051] Example 4: A method for preparing an electrolyte additive includes the following steps:

[0052] S1. Add fluorinated aromatic carboxylic acid S1 (1.59g) to the reaction vessel and pour in ethanol (20ml) as an organic solvent. After stirring and dissolving thoroughly, add lithium-containing inorganic base S2 (0.12g) and stir at room temperature for 30 minutes. Filter to remove insoluble impurities and dry the solution under vacuum at 50°C for 6 hours. S2. Then, acetone (20 ml) was added to the dried powder as an organic solvent. The insoluble precipitate was filtered out with filter paper, and 3 ml of acetone was added to it. The precipitate was gently stirred and the process was repeated three times after the acetone flowed down to achieve thorough washing. Then, the powder was vacuum dried at 160°C for 8 hours to obtain the product, a lithium fluorinated aromatic carboxylic acid compound P1.

[0053] In an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), a fluorinated aromatic carboxylic acid lithium compound additive P1 was added to a 1 M LiPF6 in FEC:EMC = 3:7 vol% base electrolyte. The amount of additive added was 0.5% of the total mass of the electrolyte. After stirring for 4 hours, a high-voltage electrolyte was obtained.

[0054] Assemble a lithium metal battery with LCO, NCM811 or high-nickel cathode and lithium sheet as a cathode. The electrolyte in the battery is 70uL.

[0055] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0056] Example 5: A method for preparing an electrolyte additive includes the following steps: Synthesis of lithium compounds P2 containing fluorine (cyano) aromatic carboxylic acids

[0057] S1. Add fluorinated aromatic carboxylic acid S1 (1.24g) to the reaction vessel and pour in ethanol (20ml) as an organic solvent. After stirring and dissolving thoroughly, add lithium-containing inorganic base S2 (0.12g). Stir the reaction at room temperature for 30 minutes, filter to remove insoluble impurities, and dry the solution under vacuum at 50°C for 6 hours. S2. Then, acetone (20 ml) was added to the dried powder as an organic solvent. The insoluble precipitate was filtered out with filter paper, and 3 ml of acetone was added to it. The precipitate was gently stirred and the process was repeated three times after the acetone flowed down to achieve thorough washing. Then, the powder was vacuum dried at 160°C for 8 hours to obtain the product, a lithium fluorinated aromatic carboxylic acid compound P2.

[0058] In an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), a fluorinated aromatic carboxylic acid lithium compound additive P1 was added to a 1 M LiPF6 in FEC:EMC = 3:7 vol% base electrolyte. The amount of additive added was 0.5% of the total mass of the electrolyte. After stirring for 4 hours, a high-voltage electrolyte was obtained.

[0059] Assemble a lithium metal battery with LCO, NCM811 or high-nickel cathode and lithium sheet as a cathode. The electrolyte in the battery is 70uL.

[0060] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0061] Example 6: A method for preparing an electrolyte additive includes the following steps: Synthesis of P3, a lithium compound containing fluorinated aromatic carboxylic acids

[0062] S1. Add fluorinated aromatic carboxylic acid S1 (1.32g) to the reaction vessel and pour in ethanol (20ml) as an organic solvent. After stirring and dissolving thoroughly, add lithium-containing inorganic base S2 (0.12g). Stir the reaction at room temperature for 30 minutes, filter to remove insoluble impurities, and dry the solution under vacuum at 50°C for 6 hours. S2. Then, acetone (20 ml) was added to the dried powder as an organic solvent. The insoluble precipitate was filtered out with filter paper, and 3 ml of acetone was added to it. The precipitate was gently stirred and the process was repeated three times after the acetone flowed down to achieve thorough washing. Then, the powder was vacuum dried at 160°C for 8 hours to obtain the product, a lithium fluorinated aromatic carboxylic acid compound P2.

[0063] In an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), a fluorinated aromatic carboxylic acid lithium compound additive P1 was added to a 1M LiPF6 in FEC:EMC = 3:7 vol% basic electrolyte. The amount of additive added was 0.5% of the total mass of the electrolyte. After stirring for 4 hours, a high-voltage electrolyte was obtained.

[0064] Assemble a lithium metal battery with LCO, NCM811 or high-nickel cathode and lithium sheet as a cathode. The electrolyte in the battery is 70uL.

[0065] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0066] Example 7: A method for preparing an electrolyte additive includes the following steps: Synthesis of P4, a lithium compound containing fluorinated aromatic carboxylic acids

[0067] S1. Add 1.70 g of fluorinated aromatic carboxylic acid S1 to the reaction vessel and pour in 20 ml of ethanol as an organic solvent. After stirring thoroughly to dissolve, add 0.19 g of lithium-containing inorganic base S2 and stir the reaction at room temperature for 30 minutes. Filter to remove insoluble impurities and dry the solution under vacuum at 50 °C for 6 hours. S2. Then, acetone (20 ml) was added to the dried powder as an organic solvent. The insoluble precipitate was filtered out with filter paper, and 3 ml of acetone was added to it. The precipitate was gently stirred and the process was repeated three times after the acetone flowed down to achieve thorough washing. Then, the powder was vacuum dried at 160 °C for 8 hours to obtain the product, a lithium fluorinated aromatic carboxylic acid compound P4.

[0068] In an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), a fluorinated aromatic carboxylic acid lithium compound additive P4 was added to a 1 M LiPF6 in FEC:EMC = 3:7 vol% base electrolyte. The amount of additive added was 0.5% of the total mass of the electrolyte. After stirring for 2 hours, a high-voltage electrolyte was obtained.

[0069] Assemble a lithium metal battery with LCO, NCM811 or high-nickel cathode and lithium sheet as a cathode. The electrolyte in the battery is 70uL.

[0070] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0071] Comparative Example 1: In an argon-filled glove box (moisture content < 0.01 ppm, oxygen content < 0.01 ppm), lithium metal batteries were assembled using 1 M LiPF6 in FEC:EMC = 3:7 vol% as the base electrolyte. The positive electrode was LCO, NCM811 or high nickel, and the negative electrode was a lithium sheet. The electrolyte volume of the battery was 70 μL.

[0072] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0073] Comparative Example 2: Fluorinated aromatic carboxylic acid S1 (1.59 g) was added to the reaction vessel and ethanol (20 ml) was poured in as an organic solvent. After stirring and dissolving thoroughly, lithium-containing inorganic base S2 (0.19 g) was added and the reaction was stirred at room temperature for 30 minutes. The insoluble impurities were removed by filtration, and the solution was dried under vacuum at 50 °C for 6 hours to obtain lithium fluorinated aromatic carboxylic acid compound P1 containing excess fluorinated aromatic carboxylic acid.

[0074] The above product was added to a 1M LiPF6in FEC:EMC=3:7 vol% base electrolyte in an argon-filled glove box (moisture content <0.01ppm, oxygen content <0.01ppm). The amount added was 0.5% of the total mass of the electrolyte. The electrolyte was obtained after stirring for 4 hours.

[0075] Assemble a lithium metal battery with LCO, NCM811 or high-nickel cathode and lithium sheet as a cathode. The electrolyte in the battery is 70uL.

[0076] Cyclic performance tests were conducted on the above-mentioned lithium metal batteries: activation was performed by cycling once at a current density of 0.1C, followed by cycling at 0.5C charging and 1.0C discharging, with voltage windows of 3.0V-4.6V, 3.0V-4.7V, or 3.0V-4.8V.

[0077] Results and Discussion: Table 1: Test results of specific capacity and capacity retention of lithium batteries in comparative and example cases:

[0078] Table 2: Test results of specific capacity and capacity retention of lithium batteries in comparative and example cases:

[0079] Table 3: Test results of specific capacity and capacity retention of lithium batteries in comparative and example cases:

[0080] Figure 4 The graph shows the cycle performance of lithium metal batteries prepared with the base electrolyte of Comparative Example 1 (1M LiPF6-FEC:EMC = 3:7) and the high-voltage electrolyte of Example 1 (1M LiPF6-FEC:EMC = 3:7 with high-voltage electrolyte additives) after 400 cycles. Figure 4 The cycling stability of the high-voltage lithium metal batteries assembled in Example 1 and Comparative Example 1 at a charging voltage of 4.6V is shown. Figure 4 The data in Table 1 show that the addition of an appropriate amount of lithium pentafluorobenzoate additive can improve the cycle performance of lithium metal batteries at a high charging voltage of 4.6V, and greatly improve the capacity retention rate of the battery. The capacity of lithium metal batteries using the basic electrolyte shows significant decay after 250 charge-discharge cycles, while the lithium metal batteries using the high-voltage electrolyte of this invention can cycle stably for more than 400 cycles.

[0081] Figure 5 and Figure 6 The figures show the cycle performance of lithium metal batteries prepared with the base electrolyte of Comparative Example 1 (1M LiPF6-FEC:EMC = 3:7) and the high-voltage electrolyte of Example 1 (1M LiPF6-FEC:EMC = 3:7 with added high-voltage electrolyte additives) after 100 cycles (positive electrode LCO, negative electrode lithium metal sheet, voltage windows 3.0V-4.7V and 3.0V-4.8V, respectively). Figure 5 and Figure 6The cycling stability of the high-voltage lithium metal batteries assembled in Example 1 and Comparative Example 1 at charging voltages of 4.7V and 4.8V can be observed. Figure 5 The data in Table 1 show that lithium metal batteries using the basic electrolyte experience significant capacity decay after 40 charge-discharge cycles. However, the addition of an appropriate amount of lithium pentafluorobenzoate additive enables stable charge-discharge cycling at high charging voltages of 4.7V and 4.8V, significantly improving battery capacity retention. Furthermore, compared to cycles at a charging voltage of 4.6V, the increased charging voltage results in higher specific capacity and energy density for the lithium metal batteries.

[0082] Figure 7 The graph shows the cycle performance of lithium metal batteries prepared with the electrolyte of Comparative Example 2 and the high-voltage electrolyte of Example 1 (1M LiPF6-FEC:EMC = 3:7 with high-voltage electrolyte additives) (positive electrode is LCO, negative electrode is lithium metal sheet, voltage window is 3.0V-4.7V). Figure 6 The cycling stability of the high-voltage lithium metal batteries assembled in Example 1 and Comparative Example 2 at a charging voltage of 4.7V is shown. Figure 6 The data in Table 1 show that the addition of an appropriate amount of lithium pentafluorobenzoate additive enables the lithium metal battery to exhibit good cycle stability at a high charging voltage of 4.7V. However, since the impurity removal process described in step II of the preparation was not carried out in Comparative Example 2, the synthesized additive still contains excessive aromatic carboxylic acids and other trace impurities. When this impure additive is used in the high-voltage electrolyte, the capacity of the prepared lithium metal battery decays rapidly in the first 10 cycles, and it cannot play a role in improving the cycle performance at high charging voltage.

[0083] Figure 8 The graph shows the charge-discharge curves of the first three cycles of a lithium metal battery prepared with the high-voltage electrolyte of Example 1 (1M LiPF6-FEC:EMC = 3:7 with added high-voltage electrolyte additives) (the positive electrode is a high-nickel positive electrode, the negative electrode is a lithium metal sheet, and the voltage window is 3.0V-4.7V). It can be seen that the positive electrode adapted to the high-voltage electrolyte in this invention is not limited to lithium cobalt oxide. Lithium metal batteries using high-nickel positive electrodes also exhibit excellent high-voltage stability. That is, the general principle of this invention is universally applicable to different lithium battery systems.

[0084] Figure 9 This is a cycle performance diagram of a lithium metal battery prepared with the high-voltage electrolyte of Example 1 (1M LiPF6 in FEC:EMC = 3:7 with added high-voltage electrolyte additives) after 100 cycles (the positive electrode is a nickel-cobalt-manganese positive electrode, the negative electrode is a lithium metal sheet, and the voltage windows are 3.0V-4.5V and 3.0V-4.7V). Figure 9The data shows that the addition of an appropriate amount of lithium pentafluorobenzoate additive enables lithium metal batteries to exhibit good cycle performance at high charging voltages. Moreover, compared to the 4.5V charging voltage cycle, when the charging voltage is increased to 4.7V, the lithium metal battery with nickel cobalt manganese cathode exhibits higher specific capacity and energy density.

[0085] As can be seen from Examples 5, 6, and 7, the high-voltage electrolyte additive of the present invention is not limited to a single fluorinated (cyano, fluoroalkyl, fluorosulfonyl) aromatic carboxylic acid lithium compound, and the process method is not limited to a single fluorinated (cyano, fluoroalkyl, fluorosulfonyl) aromatic carboxylic acid and lithium-containing basic compound. Other similar additives synthesized also have excellent modification effects on the cycle stability of lithium batteries under high charging voltage. That is, the general principle of the present invention is universally applicable to different fluorinated (cyano, fluoroalkyl, fluorosulfonyl) aromatic carboxylic acid lithium compounds.

[0086] As can be seen from the above embodiments: (1) The high-voltage electrolyte additive provided by the present invention, due to the conjugated electronic effect of the aromatic group itself and the electron-withdrawing effect of the fluorine, cyano, fluoroalkyl, and fluorosulfonyl groups on the aromatic group, can form a thin and dense positive electrode-electrolyte interface film (CEI) rich in inorganic substances such as LiF, Li3N, and Li2S on the positive electrode surface. The formation of this interface film can avoid continuous contact between the electrode material and the electrolyte, inhibit the continuous oxidative decomposition of the electrolyte and the phase change of the crystal structure of the positive electrode material, thereby effectively reducing the loss of reversible capacity during cycling and improving the cycle stability of the battery; (2) The high-voltage electrolyte provided by the present invention can form a thin and dense negative electrode-electrolyte interface film (SEI) rich in inorganic substances such as LiF, Li3N, and Li2S on the surface of the lithium metal negative electrode. The formation of this interface film can inhibit the growth of lithium dendrites and improve the stability of the lithium metal negative electrode; (3) The high-voltage electrolyte additive provided by the present invention can improve the charging voltage, energy density, and cycle stability of lithium metal batteries.

[0087] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An electrolyte additive, characterized in that, In high-voltage electrolytes for lithium batteries with charging voltages higher than 4.5V, the electrolyte additive is a fluorine-containing (cyano, fluorosulfonyl) aromatic carboxylic acid lithium compound, the general formula of which is shown in structural formula I: Among them, R1, R2, R3, R4, and R5 are each independently selected from one or more of fluorine, cyano, fluoroalkyl, and fluorosulfonyl groups, R n An alkyl or carboxylic acid lithium group with 1 to 8 carbon atoms is directly attached to a benzene ring. In compounds containing more than one carboxylic acid lithium group, the position of the carboxylic acid lithium group on the benzene ring is ortho, meta, or para.

2. The method for preparing an electrolyte additive according to claim 1, characterized in that, Includes the following steps: S1. Add aromatic carboxylic acid to the reaction vessel and pour in organic solvent I and stir to dissolve. Add lithium-containing inorganic base and stir until the lithium-containing inorganic base is completely dissolved. Filter to remove insoluble impurities and then put it in a vacuum drying oven to dry. The molar ratio of the aromatic carboxylic acid to the lithium-containing inorganic base is (2~4):

1. S2. The powder obtained after drying S1 is dissolved in organic solvent II, filtered and washed to remove the insoluble precipitate, and the precipitate is dried in a vacuum drying oven to obtain an aromatic carboxylic acid lithium compound.

3. The method for preparing an electrolyte additive according to claim 2, characterized in that, Furthermore, the aromatic carboxylic acid described in S1 has a structure as shown in Formula II: R1, R2, R3, R4, and R5 are each independently selected from one or more of the following groups: fluorine, cyano, fluoroalkyl, and fluorosulfonyl. n An alkyl or carboxyl group with 1 to 8 carbon atoms is directly attached to a benzene ring. In compounds containing more than one carboxyl group, the carboxyl group is positioned ortho, meta, or para on the benzene ring.

4. The method for preparing an electrolyte additive according to claim 2, characterized in that, The organic solvent I mentioned in S1 is one of ethanol, methanol, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone; The lithium-containing inorganic base mentioned in S1 is one or more of lithium hydroxide, lithium oxide, lithium carbonate, and lithium phosphate. The stirring reaction described in S1 is carried out at a temperature of 10℃~50℃ for a time of 10 minutes~60 minutes.

5. The method for preparing an electrolyte additive according to claim 2, characterized in that, The organic solvent II mentioned in S2 is one of acetone, tetrahydrofuran, and ethyl acetate; The drying process described in S2 involves a temperature of 30℃ to 180℃ and a pressure of -0.01 MPa to -1.0 MPa.

6. A high-voltage electrolyte, characterized in that, For use in lithium batteries with a charging voltage higher than 4.5V, the high-voltage electrolyte comprises a carbonate organic solvent and a lithium salt, as well as an electrolyte additive as described in claim 1, wherein the content of the additive in the high-voltage electrolyte is 0.1wt%≤10wt%.

7. The high-voltage electrolyte according to claim 6, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalato)borate, lithium methanesulfonate, and lithium bis(trifluoromethanesulfonyl)imide; the concentration of the lithium salt is 0.5M to 2M.

8. The high-voltage electrolyte according to claim 6, characterized in that, The carbonate organic solvent is selected from one or more combinations of linear carbonates such as ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate, and cyclic carbonates such as fluoroethylene carbonate, propylene carbonate, and butene carbonate.

9. A high-voltage electrolyte according to claim 8, characterized in that, The carbonate organic solvent is composed of fluoroethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:

7.

10. A lithium battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and a high-voltage electrolyte as described in any one of claims 6-9.

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