Carboxylate-based wide-temperature-range electrolyte and application thereof

Abstract

The invention relates to a carboxylic ester-based wide-temperature-range electrolyte and application thereof, and belongs to the technical field of secondary batteries, and the specific scheme is as follows: the carboxylic ester-based wide-temperature-range electrolyte comprises a lithium salt and a solvent, and the solvent comprises cyclic carbonate and carboxylic ester; the carboxylic ester comprises an ester group and an alkoxy functional group, and the number of atoms on a main chain of the carboxylic ester is 5-9; the carboxylic ester comprises one or a combination of more of methyl methoxyacetate, ethyl methoxyacetate, methyl ethoxyacetate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate and ethylene glycol monomethyl ether propionate. The alkoxy group of the carboxylic ester and oxygen on the ester group have high electron cloud density, dissolution of lithium salt can be promoted, meanwhile, the chain length of the carboxylic ester is increased along with introduction of the alkoxy group, the stability of the carboxylic ester is greatly improved, and the carboxylic ester integrates the advantages of linear carbonic ester and short-chain carboxylic ester.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a carboxylate-based wide-temperature range electrolyte and applications thereof. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles, portable electronic devices, energy storage systems and other fields due to their high energy density and long cycle life. As the application demand for lithium-ion batteries continues to expand, traditional lithium-ion batteries will face serious performance degradation and even safety risks under extreme temperature conditions, especially in low or high temperature environments. Under extremely low temperature conditions, the viscosity of the electrolyte increases and the mobility of lithium ions decreases, resulting in a significant decrease in the battery's charge and discharge efficiency, and even aggravates the growth of lithium dendrites, causing the dendrites to pierce the diaphragm. Under high temperature conditions, the stability of the electrolyte will be affected, and it is easy to decompose and produce gas and cause thermal runaway.

[0003] Although traditional linear carbonate solvents such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) have low viscosity, DMC, which has the highest dielectric constant, has a high freezing point and a low boiling point, and is not suitable for wide temperature working environments. DEC has the advantage of a wide liquid range, but the increase in chain length further reduces the ability of linear carbonates to dissolve lithium salts, making it unsuitable for large-scale addition.

[0004] Compared with carbonate solvents in traditional commercial electrolytes, short-chain carboxylic acid ester solvents have the advantages of low viscosity, low melting point, and moderate salt dissolving ability, becoming a potential low-temperature solvent and have been extensively studied. However, the commonly used short-chain carboxylates: methyl acetate, ethyl acetate, methyl propionate, etc., although they have a low melting point and strong salt dissolving ability, they react with Li at low temperatures. + The binding energy is high, which is not conducive to Li + It is dissolved and embedded in graphite from the solvated form. At the same time, short-chain carboxylates have low boiling points and flash points, and are easily decomposed and gasified at high temperatures (>50°C), affecting the normal use of the battery. Long-chain carboxylates such as methyl butyrate and ethyl butyrate have a wider liquid range (melting point <-85°C, boiling point >100°C), but the extension of the alkyl chain reduces the ability of carboxylates to dissolve lithium salts, reduces the conductivity of the electrolyte, and has an adverse effect on the rate performance of the electrolyte. By fluorinating the carboxylates, the Li + The desolvation energy of the electrolyte can be improved, and the low-temperature performance of the electrolyte can be improved. However, fluorination will increase the viscosity of the solvent to a certain extent, and at the same time reduce the solvent's ability to dissolve lithium salts, making it unsuitable as a main solvent. In addition, fluorinated solvents are expensive, have a high solvent density, and are highly toxic, which is not conducive to large-scale commercial applications. Although mixing carboxylates with carbonates can improve the wide-temperature performance of the electrolyte, the problem of slow lithium ion desolvation at low temperatures still occurs.

[0005] Therefore, combining the advantages and disadvantages of carbonates and carboxylates, developing electrolytes suitable for use in a wide temperature range is of great significance to broadening the application scenarios of lithium batteries. Summary of the invention

[0006] In order to solve the problems existing in the background technology, the present invention provides a carboxylate-based wide temperature range electrolyte and its application, which combines the advantages of long-chain carboxylates, short-chain carboxylates and linear carbonates, introduces alkoxy groups on the carboxylate carbon chain, and under the joint action of multiple oxygens with high electron cloud density, the ability of the carboxylate to dissolve lithium salts is improved. At the same time, the addition of alkoxy groups extends the length of the carbon chain and improves the stability of the carboxylate.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A carboxylate-based wide temperature range electrolyte, comprising a lithium salt and a solvent, wherein the solvent comprises a cyclic carbonate and a carboxylate; the carboxylate comprises an ester group and an alkoxy functional group, and the number of atoms on the main chain of the carboxylate is between 5 and 9, and the carboxylate comprises a combination of one or more of methyl methoxyacetate, ethyl methoxyacetate, methyl ethoxyacetate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, and ethylene glycol methyl ether propionate, and the structural formula is as follows: Figure 1 The carboxylic acid ester can significantly improve the low-temperature and high-temperature performance of lithium batteries when mixed with lithium salt to form an electrolyte.

[0009] Furthermore, the carboxylic acid ester accounts for 10%-95% of the total volume of the wide temperature range electrolyte, and the cyclic carbonate accounts for 5%-90% of the total volume of the wide temperature range electrolyte.

[0010] Furthermore, the solvent also includes linear carbonate, and the linear carbonate accounts for 0%-85% of the total volume of the wide temperature range electrolyte.

[0011] Further, the cyclic carbonate includes one or more combinations of ethylene carbonate (EC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), and propylene carbonate (PC); the linear carbonate includes one or more combinations of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl trifluoroethyl carbonate (FEMC), and bistrifluoroethyl carbonate (FDEC).

[0012] Furthermore, the lithium salt includes one or more combinations of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorophosphate, lithium hexafluoroarsenate, and lithium nitrate.

[0013] Furthermore, the concentration of lithium salt in the wide temperature range electrolyte is 0.2-4 mol / L.

[0014] Further, when the lithium salt comprises lithium hexafluorophosphate, the concentration of the lithium hexafluorophosphate is 0.1-1.5moL / L; when the lithium salt comprises lithium bis(fluorosulfonyl)imide, the concentration of the lithium bis(fluorosulfonyl)imide is 0.1-4moL / L; when the lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide, the concentration of the lithium bis(trifluoromethanesulfonyl)imide is 0.1-4moL / L; when the lithium salt comprises lithium difluorophosphate, the concentration of the lithium difluorophosphate is 0.02-0.2moL / L, and when the lithium salt comprises lithium difluorooxalatoborate, the concentration of the lithium difluorooxalatoborate is 0.05-0.3moL / L.

[0015] An application of the carboxylate-based wide-temperature range electrolyte, wherein the electrolyte is applied to a lithium battery.

[0016] Furthermore, the lithium battery includes a lithium metal battery or a lithium ion battery.

[0017] Furthermore, the wide temperature range electrolyte can be used in a temperature range of -60-60°C.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The electrolyte solution described in the present invention does not rely on a large amount of additives or fluorination of carboxylic acid esters to obtain better low-temperature performance. Instead, it uses the method of adjusting the molecular structure to regulate the functional groups on the carboxylic acid esters so that the groups inside the carboxylic acid esters can jointly react with Li + Interaction occurs. The oxygen on the alkoxy group and ester group of the carboxylic acid ester has a high electron cloud density, which can promote the dissolution of lithium salts. At the same time, the carboxylic acid ester chain length increases with the introduction of the alkoxy group, and the stability of the carboxylic acid ester is greatly improved, so that this type of carboxylic acid ester combines the advantages of linear carbonates and short-chain carboxylates. At the same time, the viscosity and freezing point of the electrolyte are reduced due to the addition of such carboxylates, so the low-temperature and high-temperature performance can be improved at the same time. Lithium batteries with such carboxylic acid ester electrolytes can be stably cycled at 60°C, cycled at 1C rate for 100 cycles, and the capacity retention rate can reach about 95%; and can be reversibly charged and discharged at -40°C, and the capacity is maintained at more than 80% of the capacity at room temperature. Even at -60°C, the discharge capacity of the battery can reach about 80%; in addition, at room temperature, lithium metal batteries can be cycled at 1C rate for 600 cycles, and the capacity retention rate is about 94%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 : Molecular structure diagram of carboxylic acid ester in the electrolyte of the present invention;

[0021] Figure 2 : Cycling performance diagram of lithium metal battery at room temperature 25°C in Example 1;

[0022] Figure 3 : The high temperature 60°C cycle performance diagram of the lithium metal battery in Example 1;

[0023] Figure 4 : The low temperature -30°C cycle performance diagram of the lithium metal battery in Example 1;

[0024] Figure 5 : The charge and discharge diagram of the lithium metal battery at low temperature of -30°C in Example 1;

[0025] Figure 6 : The high temperature 60°C cycle performance diagram of the lithium metal battery in Example 2;

[0026] Figure 7 : The charge and discharge diagram of the lithium metal battery at low temperature of -40°C in Example 2;

[0027] Figure 8 : The low temperature -60°C discharge diagram of the lithium ion battery in Example 2;

[0028] Fig. 9 : The high temperature 60°C cycle performance diagram of the lithium metal battery in Example 3;

[0029] Fig.10 : Discharge diagram of the lithium-ion battery at low temperature of -60°C in Example 3. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] A carboxylate-based wide temperature range electrolyte, the preparation method of which specifically comprises the following steps:

[0033] Lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide were used as lithium salts, the molar ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide was 1:5, fluoroethylene carbonate, ethyl methyl carbonate, methyl methoxyacetate and methyl 3-methoxypropionate were used as solvents, and the volume ratio was 1:3:3:3 to prepare a lithium salt concentration of 1.2 mol L -1 of electrolyte and stir until fully dissolved.

[0034] A wide-temperature lithium metal battery comprises a carboxylate-based wide-temperature range electrolyte prepared by the above method.

[0035] The prepared electrolyte was assembled into a half-cell with lithium cobalt oxide. After two 0.1C charge and discharge activations at room temperature, the capacity retention rate was 94.58% after 600 cycles at 1C at room temperature in the voltage range of 3-4.3V. Figure 2 As shown; at 60 ° C 1C cycle 100 times, the capacity retention rate is 95.48%, as shown Figure 3 As shown; 90 cycles at -30 °C and 0.1C, with 140 mAh g -1 The above reversible capacity is 93.33% of the capacity at room temperature. Figure 4 , Figure 5 shown.

[0036] Example 2

[0037] A carboxylate-based wide temperature range electrolyte, the preparation method of which specifically comprises the following steps:

[0038] Lithium bis(fluorosulfonyl)imide and lithium difluorooxalate borate were used as lithium salts, the molar ratio of lithium bis(fluorosulfonyl)imide and lithium difluorooxalate borate was 5:1, fluoroethylene carbonate, methyl 3-methoxypropionate and ethylene glycol ethyl ether acetate were used as solvents, and the lithium salt concentration was prepared in a volume ratio of 1:4:5 to obtain a lithium salt concentration of 1.2 mol L -1 of electrolyte and stir until fully dissolved.

[0039] A wide-temperature lithium metal battery comprises a carboxylate-based wide-temperature range electrolyte prepared by the above method.

[0040] The prepared electrolyte was assembled into a half-cell with lithium cobalt oxide. After two 0.1C charge and discharge activations at room temperature, it was cycled 100 times at 60°C in the voltage range of 3-4.3V at 1C, and the capacity retention rate was about 95.4%. Figure 6 As shown in the figure, in the voltage range of 3-4.3 V, the reversible capacity reaches 125 mAh g at 0.1C cycle at -40 °C. -1 Above, the capacity reaches more than 83.35% of the normal temperature capacity. Figure 7 shown.

[0041] A low-temperature lithium-ion soft-pack battery, the preparation method of which specifically comprises the following steps:

[0042] Lithium cobalt oxide and graphite were made into a 4Ah soft-pack battery, which was encapsulated and packaged with the prepared electrolyte. It was charged to 4.2V by CC-CV at room temperature and 0.2C, with a cut-off current of 0.05C. It was discharged to 2.0V at 0.5C at -60℃, with a discharge capacity of 3.317Ah and a release capacity of 81.12% of the room temperature capacity. Figure 8 shown.

[0043] Example 3

[0044] A carboxylate-based wide temperature range electrolyte, the preparation method of which specifically comprises the following steps:

[0045] Lithium bis(fluorosulfonyl)imide, lithium difluorophosphate and lithium difluorooxalate borate were used as lithium salts, the molar ratio of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate and lithium difluorooxalate borate was 10:0.5:0.5, fluoroethylene carbonate, methyl 3-methoxypropionate, ethylene glycol methyl ether acetate and ethylene glycol ethyl ether acetate were used as solvents, and the lithium salt concentration was prepared in a ratio of 1:3:3:3 by volume. -1 of electrolyte and stir until fully dissolved.

[0046] A wide temperature range lithium metal battery, the preparation method of which specifically comprises the following steps:

[0047] The prepared electrolyte was assembled into a half-cell with lithium cobalt oxide. After two 0.1C charge-discharge activations at room temperature, the capacity retention rate was 96.57% after 100 cycles at 60°C in the voltage range of 3-4.3V. Fig. 9 shown.

[0048] A low-temperature lithium-ion soft-pack battery, the preparation method of which specifically comprises the following steps:

[0049] Lithium cobalt oxide and graphite are made into a 4Ah soft-pack battery, which is encapsulated and packaged using the electrolyte. It is charged to 4.2V at 0.2C at room temperature by CC-CV, with a cut-off current of 0.05C, and discharged to 2.0V at 0.5C at -60°C. The discharge capacity is 3.639Ah, and the release capacity is 86.64% of the capacity at room temperature. Fig.10 shown.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the electrolyte solvents used are fluoroethylene carbonate and ethyl methyl carbonate, with a volume ratio of 1:9, and the other conditions are the same. The prepared electrolyte and lithium cobalt oxide are assembled into a half-cell. After two 0.1C charge and discharge activations at room temperature, the capacity retention rate is 67.82% after 100 cycles at 60°C and 0.1C at a voltage range of 3-4.3V. The capacity retention rate is only 65mAh g after 60 cycles at -30°C and 0.1C. -1 reversible capacity.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 2 is that the electrolyte solvents used are fluoroethylene carbonate and ethyl acetate, with a volume ratio of 1:9, and the other conditions are the same. The prepared electrolyte and lithium cobalt oxide are assembled into a half-cell. After two 0.1C charge and discharge activations at room temperature, the capacity retention rate is 56.98% after 100 cycles at 60°C at a voltage range of 3-4.3V; the reversible capacity is 78mAh g after 0.1C cycles at -40°C. -1 The prepared electrolyte was used to carry out liquid injection packaging test on a 4Ah soft-pack battery. The battery was charged to 4.2V by CC-CV at room temperature and 0.2C, with a cut-off current of 0.05C. It was discharged to 2.0V at 0.5C at -60℃, with a discharge capacity of 2.144Ah, which was 51.04% of the capacity at room temperature.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 3 is that the electrolyte solvents used are fluoroethylene carbonate and ethyl acetate, with a volume ratio of 1:9, and the other conditions are the same. The prepared electrolyte is assembled into a half-cell with lithium cobalt oxide. After two 0.1C charge and discharge activations at room temperature, the capacity retention rate is 45.76% after 100 cycles at 1C at 60°C in the voltage range of 3-4.3V; the prepared electrolyte is used to perform a liquid injection packaging test on a 4Ah soft-pack battery, and the CC-CV is charged to 4.2V at room temperature 0.2C, the cut-off current is 0.05C, and the discharge capacity is 2.284Ah at 0.5C at -60°C, which is 54.38% of the capacity at room temperature.

[0056] The above examples and comparative examples compare the optimized carboxylic acid esters with the traditional linear carbonates and short-chain carboxylic acid esters. It can be concluded that the carboxylic acid ester solvents with rationally designed molecular structures have more advantages than the traditional carbonates and carboxylic acid ester solvents, which not only maintain the stability of the long-chain molecules, but also make the electrolyte less prone to side reactions under high temperature conditions; and the carboxylic acid ester solvents can also participate in the solvation structure, and at the same time have lower viscosity and binding energy, can be quickly desolvated at low temperatures, and obtain better wide temperature performance.

[0057] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A carboxylate-based wide temperature range electrolyte, comprising a lithium salt and a solvent, wherein the solvent comprises a cyclic carbonate and a carboxylate; characterized in that: The carboxylate comprises an ester group and an alkoxy functional group, and the number of atoms on the main chain of the carboxylate is between 5 and 9. The carboxylate comprises a combination of one or more of methyl methoxyacetate, ethyl methoxyacetate, methyl ethoxyacetate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, and ethylene glycol methyl ether propionate.

2. The carboxylate-based wide temperature range electrolyte according to claim 1, characterized in that: The carboxylic acid ester accounts for 10%-95% of the total volume of the wide temperature range electrolyte, and the cyclic carbonate accounts for 5%-90% of the total volume of the wide temperature range electrolyte.

3. The carboxylate-based wide temperature range electrolyte according to claim 1, characterized in that: The solvent also includes linear carbonate, and the linear carbonate accounts for 0%-85% of the total volume of the wide temperature range electrolyte.

4. The carboxylate-based wide temperature range electrolyte according to claim 3, characterized in that: The cyclic carbonate includes one or more combinations of ethylene carbonate, vinylene carbonate, fluoroethylene carbonate, and propylene carbonate; the linear carbonate includes one or more combinations of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl trifluoroethyl carbonate, and bistrifluoroethyl carbonate.

5. The carboxylate-based wide temperature range electrolyte according to claim 1, characterized in that: The lithium salt includes one or more combinations of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorophosphate, lithium hexafluoroarsenate, and lithium nitrate.

6. The carboxylate-based wide temperature range electrolyte according to claim 1, characterized in that: The concentration of lithium salt in the wide temperature range electrolyte is 0.2-4 mol / L.

7. The carboxylate-based wide temperature range electrolyte according to claim 5, characterized in that: When the lithium salt comprises lithium hexafluorophosphate, the concentration of the lithium hexafluorophosphate is 0.1-1.5moL / L; when the lithium salt comprises lithium bisfluorosulfonyl imide, the concentration of the lithium bisfluorosulfonyl imide is 0.1-4moL / L; when the lithium salt comprises lithium bistrifluoromethanesulfonyl imide, the concentration of the lithium bistrifluoromethanesulfonyl imide is 0.1-4moL / L; when the lithium salt comprises lithium difluorophosphate, the concentration of the lithium difluorophosphate is 0.02-0.2moL / L, and when the lithium salt comprises lithium difluorooxalatoborate, the concentration of the lithium difluorooxalatoborate is 0.05-0.3moL / L.

8. An application of the carboxylate-based wide temperature range electrolyte according to any one of claims 1 to 7, characterized in that: The electrolyte is applied in lithium batteries.

9. The use according to claim 8, characterized in that: The lithium battery includes a lithium metal battery or a lithium ion battery.

10. The use according to claim 8, characterized in that: The wide temperature range electrolyte is applied in a temperature range of -60-60°C.

Images