An electrolyte for improving high-rate discharge performance of lithium battery and lithium battery

Abstract

The present invention provides an electrolyte and a lithium battery for electrically improving the high-rate discharge performance of a lithium battery, relating to the technical field of lithium-ion battery materials. The electrolyte comprises a lithium salt, a non-aqueous solvent, and an additive, wherein the non-aqueous solvent comprises fluoroacetonitrile and the additive comprises lithium tetrafluorooxalophosphate. The addition of the fluoroacetonitrile solvent to the electrolyte significantly improves the conductivity of the electrolyte and the high-rate discharge performance of the battery. Furthermore, the addition of lithium tetrafluorooxalophosphate to the electrolyte suppresses the negative effects of fluoroacetonitrile on the negative electrode, thereby improving the battery's cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery materials, and in particular to an electrolyte and a lithium battery for improving the high-rate discharge performance of a lithium battery. Background Art

[0002] Lithium-ion batteries, due to their high energy density, long lifespan, and lack of memory effect, have established a dominant position in many sectors, including the consumer electronics, power battery, and energy storage markets. With the development of the low-altitude economy, demand for high-rate lithium-ion batteries is increasing. Conventional electrolytes, using carbonate or carboxylate solvents, have conductivity levels ranging from approximately 7-13 mS / cm, and their conductivity decreases significantly at low temperatures, failing to meet the growing consumer demand for high-energy-density, high-rate lithium-ion batteries.

[0003] Patent CN117996181A discloses a locally high-concentration flame-retardant electrolyte that uses 2%-10% fluoroacetonitrile as a diluent to reduce the viscosity of the electrolyte. However, the conductivity of this locally high-concentration flame-retardant electrolyte is low and cannot meet the battery's high-rate discharge requirements. Patent CN117317372B discloses a fluorinated additive electrolyte. The patent claims involve the use of fluoroacetonitrile as a co-solvent, but the patent does not disclose technical data on the impact of fluoroacetonitrile on battery performance. In fact, due to its small molecular weight, fluoroacetonitrile easily undergoes a reduction reaction with the negative electrode, resulting in a serious degradation of the battery's cycle performance. The existing technology using fluoroacetonitrile as a co-solvent is obviously difficult to meet the requirements of high-rate discharge and long-cycle performance. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an electrolyte and a lithium battery for improving the high-rate discharge performance of a lithium battery.

[0005] The present invention solves the technical problem by adopting the following technical solutions.

[0006] A first aspect of the present invention provides an electrolyte for improving the high-rate discharge performance of a lithium battery, comprising: a lithium salt, a non-aqueous solvent and an additive, wherein the non-aqueous solvent comprises fluoroacetonitrile and the additive comprises lithium tetrafluorooxalophosphate.

[0007] Furthermore, in a preferred embodiment of the present invention, the mass percentage of fluoroacetonitrile (FAN) in the electrolyte is 10% to 70%. More preferably, the mass percentage of fluoroacetonitrile in the electrolyte is 20% to 60%, for example, 20% or 30%. A higher fluoroacetonitrile content increases the conductivity of the electrolyte and improves the high-rate discharge performance of the battery.

[0008] Furthermore, in a preferred embodiment of the present invention, the mass percentage of the lithium tetrafluorooxalophosphate (LiOTFP) in the electrolyte is 2% to 5%, for example, 2%, 3%, 4%, etc.

[0009] Furthermore, in a preferred embodiment of the present invention, the additive further includes fluorinated polyetheramine (F-PEA) and R-fluorosulfonamide (RCONHSO2F).

[0010] Specifically, the fluorinated polyetheramine can be prepared as follows: 1.5 mol of hexafluoroisopropanol, 5 mol of ethylene glycol dimethyl ether, and 0.5 g of BF3 are added to a reactor. 10 mol of propylene oxide is slowly added dropwise at a pressure of 0.10 MPa and a temperature of 45°C. After the addition is complete, the mixture is reacted at 70°C for 10 hours, and then vacuumed to remove impurities to obtain a reaction product. The reaction product, a precious metal catalyst, 5 mol of liquid ammonia, and hydrogen are introduced into a reaction apparatus. The reaction apparatus is controlled at a temperature of 120°C and a pressure of 2 MPa. After reacting for 24 hours, the mixture is cooled and filtered to obtain the fluorinated polyetheramine.

[0011] Specifically, R-fluorosulfonamide can be selected from one or more of the following:

[0012]

[0013] Furthermore, the preparation steps of R-fluorosulfonamide may be: placing carboxylic acid (such as benzoic acid) and fluorosulfonyl isocyanate in acetonitrile, and reacting at room temperature for 5 to 10 hours to obtain R-fluorosulfonamide.

[0014] Furthermore, in a preferred embodiment of the present invention, the mass fraction of the fluorinated polyetheramine in the electrolyte is 0.3% to 2%, and the mass fraction of the R-fluorosulfonamide in the electrolyte is 0.5% to 6%. By adding fluorinated polyetheramine and R-fluorosulfonamide to the electrolyte, a synergistic effect can be achieved with fluoroacetonitrile to further improve the high-rate discharge performance of the electrolyte. The fluorinated polyetheramine and fluorosulfonyl groups can reduce the occurrence of negative electrode side reactions, improve the low-temperature storage performance of the electrolyte, reduce the negative electrode film formation resistance, and improve low-temperature cycle performance.

[0015] Furthermore, in a preferred embodiment of the present invention, the electrolyte also includes an organic solvent, and the organic solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propyl acetate (PA) and ethyl propionate (EP).

[0016] Furthermore, in a preferred embodiment of the present invention, the additive also includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), vinyl sulfate (DTD) and propenyl-1,3-sultone (PST).

[0017] Furthermore, in a preferred embodiment of the present invention, the lithium salt is selected from one or both of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0018] Furthermore, in a preferred embodiment of the present invention, the mass fraction of the lithium salt in the electrolyte is 12% to 20%. For example, the lithium salt content is 12%, 15%, 18%, etc. More preferably, the mass fraction of the lithium salt in the electrolyte is 15% to 17%. Increasing the lithium salt content can improve rate performance, but too high a lithium salt content can lead to excessively high electrolyte costs.

[0019] A second aspect of the present invention provides a lithium battery comprising the electrolyte described in any one of the above items, wherein the discharge rate of the lithium battery is greater than 15C.

[0020] The electrolyte and lithium battery for improving the high-rate discharge performance of lithium batteries according to the embodiments of the present invention have the following beneficial effects:

[0021] The present invention uses fluoroacetonitrile as an electrolyte additive, effectively increasing the electrolyte conductivity and thus significantly improving the high-rate discharge performance of the battery. Furthermore, by combining fluoroacetonitrile with lithium tetrafluorooxalophosphate, the negative effects of fluoroacetonitrile on the negative electrode are suppressed, thereby effectively improving the battery's cycle performance.

[0022] Furthermore, the additives also include fluorinated polyetheramine (F-PEA) and R-fluorosulfonamide (RCONHSO2F). By adding fluorinated polyetheramine and R-fluorosulfonamide, they can play a synergistic role with fluoroacetonitrile to improve the high-rate discharge performance and low-temperature performance of the battery. DETAILED DESCRIPTION

[0023] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0024] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0025] Example 1

[0026] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 22 g EMC, 18 g EP, 10 g FAN, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA01.

[0027] Example 2

[0028] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 17 g EMC, 18 g EP, 15 g FAN, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA02.

[0029] Example 3

[0030] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 12 g EMC, 18 g EP, 20 g FAN, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA03.

[0031] Example 4

[0032] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 7 g EMC, 18 g EP, 25 g FAN, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA04.

[0033] Example 5

[0034] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 20 g EC, 2 g EMC, 18 g EP, 30 g FAN, 1 g F-PEA, 4 g RCONHSO2F, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA05.

[0035] The preparation method of F-PEA is as follows: 1.5 mol of hexafluoroisopropanol, 5 mol of ethylene glycol dimethyl ether, and 0.5 g of BF3 are added to a reactor. Under the conditions of a pressure of 0.10 MPa and a temperature of 45°C, 10 mol of propylene oxide is slowly added dropwise. After the addition is complete, the reaction is carried out at 70°C for 10 hours, and then the impurities are removed by vacuum to obtain a reaction product. The reaction product, a precious metal catalyst, 5 mol of liquid ammonia, and hydrogen are introduced into a reaction apparatus. The temperature of the reaction apparatus is controlled to 120°C and the pressure is maintained at 2 MPa. After the reaction is carried out for 24 hours, the temperature is lowered and the fluorinated polyetheramine is obtained after filtration.

[0036] The structural formula of RCONHSO2F is:

[0037]

[0038] Example 6

[0039] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 20 g EC, 2 g EMC, 18 g EP, 30 g FAN, 5 g RCONHSO2F (same as in Example 5), 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA06.

[0040] Example 7

[0041] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 2 g EMC, 17 g EP, 30 g FAN, 1 g F-PEA (same as in Example 5), 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA07.

[0042] Example 8

[0043] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 10 g EP, 40 g FAN, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD. The above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA08.

[0044] Example 9

[0045] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 50 g FAN, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD. The above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA09.

[0046] Example 10

[0047] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 15 g EC, 60 g FAN, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD. The above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA10.

[0048] Example 11

[0049] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 5 g EC, 70 g FAN, 3 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g VC, and 1 g DTD. The above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA11.

[0050] Example 12

[0051] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 20 g EC, 17 g EMC, 18 g EP, 15 g FAN, 1.5 g F-PEA (same as in Example 5), 4.5 g RCONHSO2F (same as in Example 5), 3 g LiOTFP, 1 g LiDFOB, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA12.

[0052] Example 13

[0053] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 18 g EMC, 18 g EP, 15 g FAN, 2 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g FEC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA13.

[0054] Example 14

[0055] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 25 g EC, 16 g EMC, 18 g EP, 15 g FAN, 4 g LiOTFP, 1 g LiPO2F2, 1.5 g PST, 1.5 g FEC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA14.

[0056] Example 15

[0057] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 7 g LiFSI, 20 g EC, 5 g PC, 15 g EMC, 18 g EP, 15 g FAN, 5 g LiOTFP, 1 g LiPO2F2, 1.5 g PS, 1.5 g FEC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA15.

[0058] Example 16

[0059] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 2 g LiFSI, 25 g EC, 5 g PC, 17 g EMC, 18 g EP, 15 g FAN, 3 g LiOTFP, 1 g LiDFOB, 1.5 g PS, 1.5 g VC, and 1 g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA16.

[0060] Example 17

[0061] This embodiment provides an electrolyte having the following formula: 10 g LiPF6, 10 g LiFSI, 22 g EC, 17 g EMC, 18 g EP, 15 g FAN, 3 g LiOTFP, 1 g LiDFOB, 1.5 g PS, 1.5 g VC, and 1 g DTD. The above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNA17.

[0062] Comparative Example 1

[0063] This comparative example provides an electrolyte with the following formula: 10g LiPF6, 7g LiFSI, 25g EC, 25g EMC, 28g EP, 1g LiPO2F2, 1.5g PS, 1.5g VC, and 1g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNB01.

[0064] Comparative Example 2

[0065] This comparative example provides an electrolyte with the following formula: 10g LiPF6, 7g LiFSI, 25g EC, 25g EMC, 18g EP, 10g FAN, 1g LiPO2F2, 1.5g PS, 1.5g VC, and 1g DTD; the above components are mixed evenly to obtain a lithium-ion battery electrolyte, which is named SNB02.

[0066] Test Example 1

[0067] Electrolyte performance tests were conducted using high-rate lithium cobalt oxide cells for consumer drones. Specifically, the electrolyte samples prepared in Examples 1 to 17, Comparative Examples 1, and 2 were first tested for conductivity and then injected into unfilled dry cells. After sealing, formation, and volume separation, rate performance and low-temperature performance tests were performed. Three dry cells were injected with each electrolyte solution, and the test results were averaged across the three cells.

[0068] The prepared battery was subjected to a 30C high-rate discharge test, and the discharge retention ratio was calculated. The charge cutoff voltage was 4.2V, and the discharge cutoff voltage was 2.7V. The 30C discharge retention ratio = 30C discharge capacity / 1C discharge capacity * 100%. The results are shown in Table 1.

[0069] Table 1

[0070]

[0071]

[0072] As can be seen from Table 1, as the amount of fluoroacetonitrile added continues to increase, the conductivity of the electrolyte also continues to increase, and the high-rate discharge performance of the battery also continues to improve. However, the cost of fluoroacetonitrile is high, so different amounts of fluoroacetonitrile can be added according to the customer's performance and price balance requirements. In addition, the additional addition of fluorinated polyamide and R-fluorosulfonamide can further improve the high-rate discharge performance and low-temperature performance of the electrolyte. From the comparison of Examples 16 and 17, when the lithium salt content (the total content of LiFP6 plus LiFSI) is 12%, the rate performance of the battery will decrease, but it is still better than the performance without fluoroacetonitrile; when the lithium salt content is 20%, the rate performance of the battery will be improved, but a high content of lithium salt will increase the cost of the electrolyte, so an appropriate content of lithium salt (such as 15%-17%) has a higher cost performance.

[0073] Test Example 2

[0074] The batteries made using the electrolytes obtained in Examples 1, 4 and 5 and Comparative Examples 1 and 2 were subjected to a cycle test, and the discharge retention rate after 300 cycles was calculated. The charge cut-off voltage was 4.2V, and the discharge cut-off voltage was 2.7V. The charge rate was 1C, and the discharge rate was 15C. The cycle retention rate after 300 cycles = 300th discharge capacity / first discharge capacity * 100%, and the results are shown in Table 2. The prepared batteries were subjected to a 15C high-rate discharge test, and the 15C discharge capacity retention rate was calculated. The 15C discharge capacity retention rate = 15C discharge capacity / 1C discharge capacity * 100%, and the results are shown in Table 2.

[0075] Table 2

[0076]

[0077] As shown in Table 2, lithium tetrafluorooxalophosphate can significantly improve the high-rate discharge and low-temperature performance of lithium-ion batteries. Fluoroacetonitrile also significantly improves the battery's high-rate discharge and low-temperature performance in discharge tests using a 15C rate. The high-rate discharge performance of the battery is particularly enhanced when fluoroacetonitrile is combined with fluorinated polyamide and R-fluorosulfonamide.

[0078] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. An electrolyte for improving the high-rate discharge performance of a lithium battery, characterized in that: include: A lithium salt, a non-aqueous solvent, and an additive, wherein the non-aqueous solvent includes fluoroacetonitrile, and the mass percentage of the fluoroacetonitrile in the electrolyte is 10% to 70%; the additive includes lithium tetrafluorooxalate phosphate, and the mass percentage of the lithium tetrafluorooxalate phosphate in the electrolyte is 2% to 5%; the additive further includes a fluorinated polyetheramine and R-fluorosulfonamide, the mass fraction of the fluorinated polyetheramine in the electrolyte is 0.3% to 2%, and the mass fraction of the R-fluorosulfonamide in the electrolyte is 0.5% to 6%, and the R-fluorosulfonamide is selected from one or more of the following: 、 、 。 2. The electrolyte for improving the high-rate discharge performance of a lithium battery according to claim 1, characterized in that: The electrolyte further includes an organic solvent, and the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, propyl acetate and ethyl propionate.

3. The electrolyte for improving the high-rate discharge performance of a lithium battery according to claim 1, characterized in that: The additive further comprises one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, lithium difluorophosphate, lithium difluorooxalatoborate, vinyl sulfate and propenyl-1,3-sultone.

4. The electrolyte for improving the high-rate discharge performance of a lithium battery according to claim 1, characterized in that: The lithium salt is selected from one or both of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

5. The electrolyte for improving the high-rate discharge performance of a lithium battery according to claim 1, characterized in that: The mass fraction of the lithium salt in the electrolyte is 12% to 20%.

6. A lithium battery, characterized in that: Comprising the electrolyte according to any one of claims 1 to 5, the discharge rate of the lithium battery is greater than 15C.

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