A long-life sodium ion battery electrolyte and its preparation method and application

Abstract

The present invention discloses an electrolyte for a long-life sodium ion battery, a preparation method and an application thereof, and relates to the technical field of sodium ion battery electrolytes. In the present invention, the performance of the sodium ion electrolyte is significantly improved by adding piperidinyl and phosphite tetrafluoroborate ionic liquids. First, these additives improve the thermal stability and chemical stability of the electrolyte, which is particularly important during the long-term operation of the battery, and can effectively prevent the decomposition of the electrolyte under high temperature or extreme operating conditions. Secondly, since the ionic liquids themselves have excellent electrochemical stability, their presence enhances the electrochemical window of the electrolyte, that is, the electrolyte can withstand a wider voltage range without electrochemical reactions. This is very beneficial for improving the energy density and power output of the battery. Finally, the introduction of ionic liquids can also increase the ionic conductivity of the electrolyte and reduce the internal impedance of the battery, thereby improving the charge and discharge efficiency and cycle life of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery electrolyte, in particular to an electrolyte for a long-life sodium ion battery and a preparation method and application thereof. Background Art

[0002] With the growth of global energy demand and increasingly severe environmental problems, the development of renewable energy and the improvement of energy efficiency have become the focus of attention of countries around the world. As a high-energy-density energy storage device, lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and grid energy storage. However, the scarcity of lithium resources and the negative impact of its mining and processing on the environment have prompted the scientific and industrial communities to seek more environmentally friendly and lower-cost alternative energy storage technologies. In this context, sodium-ion batteries are considered to be a strong competitor for the next generation of energy storage technology because of their abundant resources, low cost, and working principles similar to lithium-ion batteries.

[0003] However, despite the significant advantages of sodium-ion batteries in terms of resources and cost, they still face many challenges in practical applications, especially their cycle life and capacity retention rate need to be further improved. Compared with lithium-ion batteries, sodium-ion batteries have poor cycle performance, mainly due to the large radius of sodium ions, insufficient stability of the electrolyte, and interface problems.

[0004] Patent application with publication number CN116344933A discloses a sodium ion battery electrolyte and a sodium ion battery, wherein the sodium ion battery electrolyte comprises a non-aqueous organic solvent, a sodium salt and an additive, wherein the additive comprises a nitrate and vinyl sulfate, wherein the mass percentage of the nitrate in the sodium ion battery electrolyte is 0.01% to 1%, and the mass percentage of the vinyl sulfate in the sodium ion battery electrolyte is 0.1% to 2%.

[0005] The patent application with publication number CN115275206A discloses a sodium ion battery negative electrode and a sodium ion battery. The sodium ion battery negative electrode of the invention includes a negative electrode collector and a negative electrode active material layer coated on the negative electrode collector. The negative electrode active material layer includes a sodium ion battery negative electrode main material, a conductive agent, a binder, and a weak alkaline alkali metal salt; the mass ratio of the sodium ion battery negative electrode main material, the conductive agent, the binder, and the weak alkaline alkali metal salt is 90~98:1~9:1~9:0.5~2.

[0006] Although these methods have improved the cycle performance of sodium-ion batteries to a certain extent, there are still many difficulties in achieving commercial application. Among them, the electrolyte is an important component of sodium-ion batteries, and its formula design directly affects the cycle life, energy density and safety of the battery. Therefore, the development of a sodium-ion battery electrolyte with excellent performance has important scientific research value and application prospects. Summary of the invention

[0007] In view of this, the present application provides an electrolyte for a long-life sodium ion battery, a preparation method and an application thereof, which significantly improves the cycle performance of the sodium ion battery and extends the service life of the battery by optimizing the solvent system and introducing functional additives, providing strong support for the practical application of sodium ion batteries.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The invention provides an electrolyte for a long-life sodium ion battery, comprising a sodium salt, an organic solvent and a functional additive. The functional additive contains a piperidinyl and a phosphite tetrafluoroborate ion liquid, which is obtained by esterifying phosphorous trichloride with 4-hydroxy-2-piperidinylcarboxylic acid and 1-hydroxyethyl-3-methylimidazole tetrafluoroborate.

[0010] Preferably, the preparation method of the functional additive is as follows: by weight, 18-36 parts of phosphorous trichloride, 100-150 parts of toluene, 0.2-2 parts of tetrabutylammonium bromide, 14-28 parts of 4-hydroxy-2-piperidinic acid and 0.05-0.42 parts of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate are mixed, an inert gas is introduced, and the mixture is stirred at 70-120° C. for 150-180 minutes, and the toluene is removed by distillation to obtain a functional additive containing a piperidinyl and phosphite-containing tetrafluoroborate ion liquid.

[0011] The functional additive preparation mechanism:

[0012] Phosphorous trichloride is subjected to esterification reaction with 4-hydroxy-2-piperidinic acid and 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate respectively to obtain the stabilizing additive of the tetrafluoroborate ionic liquid containing piperidinyl and phosphite. This reaction is mainly carried out through esterification reaction. The specific mechanism is that phosphorous trichloride reacts with the hydroxyl groups in 4-hydroxy-2-piperidinic acid and 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate to form phosphate ester bonds. In this process, the chlorine atom of phosphorous trichloride is replaced by a hydroxyl group to form a phosphite group. Subsequently, tetrafluoroborate, as part of the ionic liquid, stabilizes the entire structure through ion exchange or interaction. This structure provides better thermal stability and electrochemical stability in sodium ion batteries.

[0013] In some embodiments of the present invention, the electrolyte for long-life sodium ion battery comprises, by weight, 10-20 parts of sodium salt, 70-90 parts of organic solvent and 0.1-5 parts of functional additives.

[0014] In some embodiments of the present invention, the sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(oxalatoborate) (NaBOB), sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0015] Preferably, the concentration of the sodium salt is 0.6-1.2 mol / L.

[0016] In some embodiments of the present invention, the organic solvent is at least one of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate.

[0017] Preferably, the organic solvent is dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate.

[0018] The mass percentages of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate are (30-35) %: (25-30) %: (35-40) %.

[0019] The present invention also provides a method for preparing the electrolyte for the long-life sodium ion battery, comprising the following steps:

[0020] (1) In an argon-filled glove box, weigh an organic solvent, stir to obtain a mixed solution 1, and treat with molecular sieves to control the water content of the mixed solution 1 to be no higher than 1 ppm;

[0021] (2) dissolving the sodium salt in the mixed solution 1 of step (1) to obtain a mixed solution 2;

[0022] (3) Dissolving the functional additive in the mixed solution 2 of step (2), stirring evenly at room temperature to obtain the electrolyte for the long-life sodium ion battery.

[0023] The present invention also provides a long-life sodium ion battery, comprising a positive electrode material, an electrolyte, a diaphragm and a negative electrode material, wherein the electrolyte is the electrolyte for the long-life sodium ion battery.

[0024] In some embodiments of the present invention, the positive electrode material is a metallic sodium sheet, the negative electrode material is hard carbon, and the diaphragm is at least one of a polypropylene diaphragm, a polyethylene diaphragm, a composite diaphragm of polypropylene and polyethylene, an Al2O3 coated diaphragm, a glass fiber diaphragm, a polytetrafluoroethylene diaphragm, a cellulose diaphragm and an aramid diaphragm.

[0025] Beneficial effects of the present invention:

[0026] In the present invention, the performance of the sodium ion electrolyte is significantly improved by adding piperidinyl and phosphite tetrafluoroborate ionic liquids. First, these additives improve the thermal stability and chemical stability of the electrolyte, which is particularly important during the long-term operation of the battery, and can effectively prevent the decomposition of the electrolyte under high temperature or extreme operating conditions. Secondly, since the ionic liquid itself has excellent electrochemical stability, their presence enhances the electrochemical window of the electrolyte, that is, the electrolyte can withstand a wider voltage range without electrochemical reaction. This is very beneficial for improving the energy density and power output of the battery. Finally, the introduction of ionic liquids can also increase the ionic conductivity of the electrolyte, reduce the internal impedance of the battery, thereby improving the charge and discharge efficiency and cycle life of the battery. DETAILED DESCRIPTION

[0027] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0028] The following are typical but non-limiting embodiments of the present invention:

[0029] Example 1

[0030] The preparation method of the functional additive in this embodiment is:

[0031] 18 g of phosphorous trichloride, 100 g of toluene, 0.2 g of tetrabutylammonium bromide, 14 g of 4-hydroxy-2-piperidinic acid and 0.05 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (CAS: 374564-83-7) were added into a closed stirred reactor, nitrogen was introduced, and the reaction was stirred at 70° C. for 150 minutes. The toluene was removed by distillation to obtain a stable additive of tetrafluoroborate ionic liquid containing piperidinyl and phosphite groups.

[0032] The electrolyte for long-life sodium ion batteries in this embodiment comprises the following components:

[0033] It contains 10g of 0.6 mol / L NaPF6, 70g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage is 30%:30%:40%) and 0.1g of functional additives.

[0034] The preparation method of the electrolyte for long-life sodium ion battery in this embodiment is as follows:

[0035] (1) In an argon-filled glove box, 70 g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage: 30%: 30%: 40%) were stirred to obtain a mixed solution, and the solution was treated with molecular sieves to control the water content of the solution to be no more than 1 ppm;

[0036] (2) Dissolve 10 g of 0.6 mol / L NaPF6 in the mixed solution of step (1);

[0037] (3) Dissolve 0.1 g of the functional additive in the mixed solution of step (2), and stir evenly at room temperature to obtain the electrolyte.

[0038] The long-life sodium ion battery in this embodiment comprises a positive electrode material, an electrolyte, a separator and a negative electrode material. The positive electrode material is a composite metal sodium sheet, the negative electrode material is hard carbon, and the separator is a polypropylene separator.

[0039] Example 2

[0040] The preparation method of the functional additive in this embodiment is:

[0041] 24 g of phosphorous trichloride, 115 g of toluene, 1 g of tetrabutylammonium bromide, 18 g of 4-hydroxy-2-piperidinic acid and 0.18 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (CAS: 374564-83-7) were added into a closed stirred reactor, nitrogen was introduced, and the reaction was stirred at 85° C. for 160 minutes. The toluene was removed by distillation to obtain a stable additive of tetrafluoroborate ionic liquid containing piperidinyl and phosphite groups.

[0042] The electrolyte for long-life sodium ion batteries in this embodiment comprises the following components:

[0043] It contains 15g of 0.8 mol / L NaCF3SO3, 80g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage is 35%:25%:40%) and 2g of functional additives.

[0044] The preparation method of the electrolyte for long-life sodium ion battery in this embodiment is as follows:

[0045] (1) In an argon-filled glove box, 80 g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage: 35%: 25%: 40%) were stirred to obtain a mixed solution, which was treated with molecular sieves to control the water content of the solution to be no higher than 1 ppm;

[0046] (2) Dissolve 15 g of 0.8 mol / L NaCF3SO3 in the mixed solution of step (1);

[0047] (3) Dissolve 2 g of the functional additive in the mixed solution of step (2), and stir evenly at room temperature to obtain the electrolyte.

[0048] The long-life sodium ion battery in this embodiment comprises a positive electrode material, an electrolyte, a separator and a negative electrode material. The positive electrode material is a composite metal sodium sheet, the negative electrode material is hard carbon, and the separator is a polyethylene separator.

[0049] Example 3

[0050] The preparation method of the functional additive in this embodiment is:

[0051] 32 g of phosphorous trichloride, 140 g of toluene, 1.6 g of tetrabutylammonium bromide, 22 g of 4-hydroxy-2-piperidinic acid and 0.30 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (CAS: 374564-83-7) were added into a closed stirred reactor, nitrogen was introduced, and the reaction was stirred at 100° C. for 170 minutes. The toluene was removed by distillation to obtain a stable additive of tetrafluoroborate ionic liquid containing piperidinyl and phosphite groups.

[0052] The electrolyte for long-life sodium ion batteries in this embodiment comprises the following components:

[0053] The invention comprises 15 g of 1 mol / L NaBOB, 80 g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (the mass percentage is 32%:28%:40%) and 4 g of functional additives.

[0054] The preparation method of the electrolyte for long-life sodium ion battery in this embodiment is as follows:

[0055] (1) In an argon-filled glove box, 80 g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage: 32%: 28%: 40%) were stirred to obtain a mixed solution, which was treated with molecular sieves to control the water content of the solution to be no higher than 1 ppm;

[0056] (2) Dissolve 15 g of 1 mol / L NaBOB in the mixed solution of step (1);

[0057] (3) Dissolve 4 g of the functional additive in the mixed solution of step (2), and stir evenly at room temperature to obtain the electrolyte.

[0058] The long-life sodium ion battery in this embodiment comprises a positive electrode material, an electrolyte, a separator and a negative electrode material. The positive electrode material is a composite metal sodium sheet, the negative electrode material is hard carbon, and the separator is Al2O3.

[0059] Example 4

[0060] The preparation method of the functional additive in this embodiment is:

[0061] 36 g of phosphorous trichloride, 150 g of toluene, 2 g of tetrabutylammonium bromide, 28 g of 4-hydroxy-2-piperidinic acid and 0.42 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (CAS: 374564-83-7) were added into a closed stirred reactor, nitrogen was introduced, and the reaction was stirred at 120° C. for 180 minutes. The toluene was removed by distillation to obtain a stable additive of tetrafluoroborate ionic liquid containing piperidinyl and phosphite groups.

[0062] The electrolyte for long-life sodium ion batteries in this embodiment comprises the following components:

[0063] The invention comprises 20 g of 1.2 mol / L NaFSI, 90 g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (the mass percentage is 35%:30%:35%) and 5 g of functional additives.

[0064] The preparation method of the electrolyte for long-life sodium ion battery in this embodiment is as follows:

[0065] (1) In an argon-filled glove box, 90 g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage: 35%:30%:35%) were stirred to obtain a mixed solution, which was treated with molecular sieves to control the water content of the solution to be no higher than 1 ppm;

[0066] (2) Dissolve 20 g of 1.2 mol / L NaFSI in the mixed solution of step (1);

[0067] (3) Dissolve 5 g of the functional additive in the mixed solution of step (2), and stir evenly at room temperature to obtain the electrolyte.

[0068] The long-life sodium ion battery in this embodiment comprises a positive electrode material, an electrolyte, a separator and a negative electrode material. The positive electrode material is a composite metal sodium sheet, the negative electrode material is hard carbon, and the separator is a polytetrafluoroethylene separator.

[0069] Comparative Example 1

[0070] The preparation method of the functional additive in this comparative example is:

[0071] 18 g of phosphorous trichloride, 100 g of toluene, 0.2 g of tetrabutylammonium bromide and 14 g of 4-hydroxy-2-piperidinic acid were added to a closed stirred reactor, nitrogen was introduced, and the reaction was stirred at 70° C. for 150 minutes. The toluene was distilled off to obtain a stable additive containing piperidinyl and phosphite groups.

[0072] The electrolyte for sodium ion battery in this comparative example comprises the following components:

[0073] It contains 10g of 0.6 mol / L NaPF6, 70g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage is 30%:30%:40%) and 0.1g of functional additives.

[0074] Preparation method of electrolyte for sodium ion battery in this comparative example:

[0075] (1) In an argon-filled glove box, 70 g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage: 30%: 30%: 40%) were stirred to obtain a mixed solution, which was treated with molecular sieves to control the water content of the solution to be no higher than 1 ppm;

[0076] (2) Dissolve 10 g of 0.6 mol / L NaPF6 in the mixed solution of step (1);

[0077] (3) Dissolve 0.1 g of the functional additive in the mixed solution of step (2), and stir evenly at room temperature to obtain the electrolyte.

[0078] The sodium ion battery in this comparative example comprises a positive electrode material, an electrolyte, a separator and a negative electrode material. The positive electrode material is a composite metal sodium sheet, the negative electrode material is hard carbon, and the separator is a polypropylene separator.

[0079] Comparative Example 2

[0080] The preparation method of the functional additive in this comparative example is:

[0081] 18 g of phosphorous trichloride, 100 g of toluene, 0.2 g of tetrabutylammonium bromide and 0.05 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (CAS: 374564-83-7) were added into a closed stirred reactor, nitrogen was introduced, and the reaction was stirred at 70° C. for 150 minutes. The toluene was removed by distillation to obtain a stabilizing additive for a phosphite-based tetrafluoroborate ionic liquid.

[0082] The electrolyte for long-life sodium ion batteries in this comparative example comprises the following components:

[0083] It contains 10g of 0.6 mol / L NaPF6, 70g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage is 30%:30%:40%) and 0.1g of functional additives.

[0084] Preparation method of electrolyte for sodium ion battery in this comparative example:

[0085] (1) In an argon-filled glove box, 70 g of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate (mass percentage: 30%: 30%: 40%) were stirred to obtain a mixed solution, which was treated with molecular sieves to control the water content of the solution to be no higher than 1 ppm;

[0086] (2) Dissolve 10 g of 0.6 mol / L NaPF6 in the mixed solution of step (1);

[0087] (3) Dissolve 0.1 g of the functional additive in the mixed solution of step (2), and stir evenly at room temperature to obtain the electrolyte.

[0088] The sodium ion battery in this comparative example comprises a positive electrode material, an electrolyte, a separator and a negative electrode material. The positive electrode material is a composite metal sodium sheet, the negative electrode material is hard carbon, and the separator is a polypropylene separator.

[0089] Test Example 1

[0090] The button cell was packaged under inert gas protection according to the method described in the embodiment and the comparative example, and a CR2032 button cell was used as a test platform, and the amount of electrolyte was 100 μL.

[0091] 1) Cycle performance test

[0092] Test conditions: Charge and discharge cycles were performed in a voltage window between 2.0 V and 4.0 V at a constant temperature (25°C).

[0093] Current density: 0.1 C charge / discharge cycle 300 times for capacity retention evaluation.

[0094] Test equipment: Neware battery test system.

[0095] 2) Rate performance test

[0096] Test conditions: At a constant temperature of 25°C, charge and discharge cycles were performed at rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 5 C, and the corresponding discharge capacities were calculated.

[0097] The test results are shown in Table 1.

[0098] Table 1

[0099]

[0100] The test results in Table 1 show that after the electrolyte prepared by the present invention is assembled into a battery, the capacity retention rate remains above 90% after 300 charge / discharge cycles at 0.1 C; in terms of rate performance, especially after 5 C rate charge / discharge cycles, the discharge capacity can reach up to 126 mAh / g, which is more than 28% higher than the discharge capacity of the comparative example. This proves that the electrolyte provided by the present invention has significant technical effects in extending the life of sodium ion batteries, improving capacity retention and improving electrochemical performance.

[0101] The above is only a preferred embodiment of the present invention, and does not limit the technical solution of the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An electrolyte for a long-life sodium ion battery, comprising a sodium salt and an organic solvent, characterized in that: The invention also comprises a functional additive, wherein the functional additive contains a piperidinyl and a phosphite tetrafluoroborate ion liquid, which is obtained by esterifying phosphorous trichloride with 4-hydroxy-2-piperidinic acid and 1-hydroxyethyl-3-methylimidazole tetrafluoroborate.

2. The electrolyte for long-life sodium ion batteries according to claim 1, characterized in that: By weight, 18-36 parts of phosphorous trichloride, 100-150 parts of toluene, 0.2-2 parts of tetrabutylammonium bromide, 14-28 parts of 4-hydroxy-2-piperidinic acid and 0.05-0.42 parts of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate are mixed, an inert gas is introduced, the mixture is stirred at 70-120° C. for 150-180 minutes, and the toluene is removed by distillation to obtain a functional additive of tetrafluoroborate ion liquid containing piperidinyl and phosphite groups.

3. The electrolyte for long-life sodium ion batteries according to claim 1, characterized in that: In parts by weight, the electrolyte for the long-life sodium ion battery comprises 10-20 parts of sodium salt, 70-90 parts of organic solvent and 0.1-5 parts of functional additives.

4. The electrolyte for long-life sodium ion batteries according to claim 1, characterized in that: The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium bis(oxalatoborate), sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

5. The electrolyte for long-life sodium ion batteries according to claim 4, characterized in that: The concentration of the sodium salt is 0.6-1.2 mol / L.

6. The electrolyte for long-life sodium ion battery according to claim 1, characterized in that: The organic solvent is at least one of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate.

7. The electrolyte for long-life sodium ion battery according to claim 6, characterized in that: The organic solvent is dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate. The mass percentages of dimethyl carbonate, ethylene carbonate and ethyl methyl carbonate are (30-35) %: (25-30) %: (35-40) %.

8. The method for preparing the electrolyte for a long-life sodium ion battery according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) In an argon-filled glove box, weigh an organic solvent, stir to obtain a mixed solution 1, and treat with molecular sieves to control the water content of the mixed solution 1 to be no higher than 1 ppm; (2) dissolving the sodium salt in the mixed solution 1 of step (1) to obtain a mixed solution 2; (3) Dissolving the functional additive in the mixed solution 2 of step (2), stirring evenly at room temperature to obtain the electrolyte for the long-life sodium ion battery.

9. A long-life sodium ion battery, comprising a positive electrode material, an electrolyte, a separator and a negative electrode material, characterized in that: The electrolyte is the electrolyte for a long-life sodium ion battery according to any one of claims 1 to 7.

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