Sodium-ion battery electrolyte

Abstract

The invention relates to a sodium-ion battery electrolyte, and belongs to the technical field of sodium-ion batteries. The electrolyte comprises the following components: a sodium salt, a non-aqueous organic solvent and an additive, and the additive comprises 4, 4 '-bis (pinacol) borate diphenyl sulfone, bipyridine carbonate and sodium difluorophosphate; the preparation method comprises the following steps: adding 4, 4 '-dipinacol borate diphenyl sulfone, bipyridine carbonate and sodium difluorophosphate; the three additives have a synergistic effect, so that the components of the SEI membrane and the CEI membrane are effectively optimized, the membrane components have relatively good sodium conduction performance and thermal stability, the impedance of the sodium-ion battery is remarkably reduced, the power performance of the sodium-ion battery is improved, meanwhile, gas production in the circulation and storage processes of the sodium-ion battery can be remarkably inhibited, and the service life of the sodium-ion battery is prolonged. Therefore, the cycle performance, the high-temperature storage performance and the safety performance of the sodium-ion battery are well improved.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery electrolyte. Background Art

[0002] In recent years, with the rapid development of electronic devices, power tools, and low-power electric vehicles, research on energy storage materials with high energy efficiency, abundant resources, and environmental friendliness is a necessary condition for the sustainable development of human society. In order to meet the huge market demand, it is far from enough to measure battery materials only by performance such as energy density and charge and discharge rate. Whether the manufacturing cost and energy consumption of the battery cause pollution to the environment and the recycling rate of resources will also become important indicators for evaluating battery materials. Sodium is one of the most abundant elements on the earth, and its chemical properties are similar to those of sodium, so it can also be applied to lithium-ion battery systems. Sodium-ion batteries have many advantages over lithium-ion batteries, such as low cost and good safety. With the deepening of research, sodium-ion batteries will become more and more cost-effective and are expected to replace lithium-ion batteries in the future and be widely used. As a new type of energy storage battery, sodium-ion batteries need to meet performance requirements at different temperatures and high cycle requirements.

[0003] The layered positive electrode active materials of existing sodium ion batteries have poor stability in the air, especially in humid air, the impact will be further aggravated. This is mainly because the unstable positive electrode active materials will undergo Na-H exchange reaction with water to generate more NaOH, and react with CO2 in the air to generate electrochemically inert Na2CO3. The generated alkaline impurities (NaOH and Na2CO3) will cause the slurry to gel during the processing, making it difficult to coat. Subsequently, in the electrochemical reaction process, the alkaline impurities will react with the electrolyte to increase gas production, seriously affecting the cycle performance and safety performance.

[0004] Therefore, there is an urgent need to provide an electrolyte material with good stability to improve its processing performance and enhance the cycle performance of sodium ion batteries. Summary of the invention

[0005] The present application provides a sodium ion battery electrolyte to improve the cycle performance of the sodium ion battery.

[0006] The present application provides a sodium ion battery electrolyte, the components of the electrolyte include: sodium salt, non-aqueous organic solvent and additives, wherein the additives include: 4,4'-dipinacol borate diphenyl sulfone, dipyridyl carbonate and sodium difluorophosphate.

[0007] As an optional implementation, the mass proportion of the 4,4'-dipinacol borate diphenyl sulfone in the electrolyte is 0.5% to 1.5%.

[0008] As an optional implementation, the mass proportion of the bipyridyl carbonate in the electrolyte is 0.5% to 1.5%.

[0009] As an optional implementation manner, the mass proportion of the sodium difluorophosphate in the electrolyte is 0.5% to 1.5%.

[0010] As an optional embodiment, the sodium salt includes NaPF6, NaClO4, NaAlCl4, NaFeCl4, NaSO3CF3, NaBCl4, NaNO3, NaPOF4, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH 3) At least one of C6H4SO3, NaHSO4 and NaB(C6H5)4.

[0011] As an optional embodiment, the molar concentration of the sodium salt is 0.5-2.0M;

[0012] As an optional embodiment, the non-aqueous organic solvent includes at least two of ethylene carbonate, propylene carbonate, butylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, cyclopentane sulfone, dimethyl sulfone, ethyl methyl sulfone and diethyl sulfone.

[0013] As an optional embodiment, the non-aqueous organic solvent is two of ethylene carbonate, propylene carbonate, butylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, cyclopentane sulfone, dimethyl sulfone, ethyl methyl sulfone and diethyl sulfone.

[0014] As an optional implementation manner, the volume ratio of the two non-aqueous organic solvents is (3:7) to (7:3).

[0015] As an optional embodiment, the electrolyte further includes: at least one of vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, succinonitrile, adiponitrile, 1,3-propylene sultone, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

[0016] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0017] The electrolyte provided by the embodiment of the present application is prepared by adding 4,4'-dipinacol borate diphenyl sulfone, bipyridinium carbonate and sodium difluorophosphate; the HOMO energy level of 4,4'-dipinacol borate diphenyl sulfone is relatively high, and it has a lower oxidation potential than the positive electrode, and it can form a thinner CEI film at the positive electrode; the CS bond connected to the benzene ring is easily broken to participate in the formation of the CEI film, and the film contains sulfur components that are beneficial to ionic conductivity, thereby improving the ability of sodium ion insertion and extraction; and the 4,4'-dipinacol borate diphenyl sulfone can combine with the sodium salt anion in the electrolyte to inhibit solvent decomposition and improve the interface impedance; bipyridinium carbonate has two pyridine functional groups directly connected to the carbonate functional group, and the carbonate functional group and the two adjacent pyridine functional groups have a common spatial effect and charge effect, so that bipyridinium carbonate can be used as a substrate. The ester exhibits a strong complexing effect in the electrolyte, can effectively complex metal ions, and can stabilize the sodium salt in the electrolyte; and the bipyridinium carbonate ester also exhibits a good film-forming effect, and can form a good passivation film on the surface of the battery negative electrode; sodium difluorophosphate participates in the formation of SEI and CEI films, reduces the content of LiF in the interface film, further reduces the interface impedance, and improves the electrochemical properties of the electrolyte; the three additives play a synergistic role, effectively optimizes the composition of the SEI film and the CEI film, so that the film composition has both good sodium conductivity and thermal stability, and significantly reduces the impedance of the sodium ion battery, improves the power performance of the sodium ion battery, and can significantly inhibit the gas production during the circulation and storage of the sodium ion battery, thereby greatly improving the circulation performance, high-temperature storage performance and safety performance of the sodium ion battery. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0019] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0020] An embodiment of the present application provides an electrolyte for a sodium ion battery, wherein the components of the electrolyte include: a sodium salt, a non-aqueous organic solvent, and an additive, wherein the additive includes: 4,4'-dipinacol borate diphenyl sulfone, bipyridyl carbonate, and sodium difluorophosphate.

[0021] In some embodiments, the mass proportion of the 4,4'-dipinacol borate diphenyl sulfone in the electrolyte is 0.5% to 1.5%. The mass proportion of the bipyridyl carbonate in the electrolyte is 0.5% to 1.5%. The mass proportion of the sodium difluorophosphate in the electrolyte is 0.5% to 1.5%.

[0022] In some embodiments, the sodium salt includes NaPF6, NaClO4, NaAlCl4, NaFeCl4, NaSO3CF3, NaBCl4, NaNO3, NaPOF4, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH 3) At least one of C6H4SO3, NaHSO4 and NaB(C6H5)4; preferably, the sodium salt includes at least one of NaPF6, NaClO4, NaSO3CF3 and Na(CH3)C6H4SO3, and more preferably, the sodium salt includes NaClO4. The concentration of the sodium salt can be the conventional concentration of the sodium salt in the sodium ion battery electrolyte in the art. In this embodiment, the molar concentration of the sodium salt is 0.5-2.0M, and more preferably the molar concentration is 0.8-1.2M, such as 1M.

[0023] In some embodiments, the non-aqueous organic solvent includes at least two of ethylene carbonate, propylene carbonate, butylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone; when the non-aqueous organic solvent is two of ethylene carbonate, propylene carbonate, butylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone, the volume ratio of the two non-aqueous organic solvents is (3:7) to (7:3). The preferred volume ratio of the two non-aqueous organic solvents is (3:2) to (2:3).

[0024] In some embodiments, the electrolyte further includes: at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinonitrile (SN), adiponitrile (ADN), 1,3-propylene sultone (PST), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0025] The electrolyte is prepared by adding 4,4'-dipinacol borate diphenyl sulfone, bipyridinium carbonate and sodium difluorophosphate; 4,4'-dipinacol borate diphenyl sulfone has a higher HOMO energy level and a lower oxidation potential than the positive electrode, and can form a thinner CEI film at the positive electrode; the CS bond connected to the benzene ring is easily broken to participate in the formation of the CEI film, and the film contains sulfur components that are beneficial to ion conductivity and improve the ability of sodium ion insertion and extraction; and 4,4'-dipinacol borate diphenyl sulfone can combine with sodium salt anions in the electrolyte to inhibit solvent decomposition and improve interface impedance; bipyridinium carbonate has two pyridine functional groups directly connected to the carbonate functional group, and the carbonate functional group and the two adjacent pyridine functional groups have a common spatial effect and charge effect, so that bipyridinium carbonate can be used in the electrolyte. It exhibits a strong complexing effect, can effectively complex metal ions, and can stabilize the sodium salt in the electrolyte; and bipyridinium carbonate also exhibits a good film-forming effect, and can form a good passivation film on the surface of the battery negative electrode; sodium difluorophosphate participates in the formation of SEI and CEI films, reduces the content of LiF in the interface film, further reduces the interface impedance, and improves the electrochemical properties of the electrolyte; the three additives play a synergistic role, effectively optimizes the composition of the SEI film and the CEI film, so that the film composition has good sodium conductivity and thermal stability, and significantly reduces the impedance of the sodium ion battery, improves the power performance of the sodium ion battery, and can significantly inhibit the gas production during the cycle and storage of the sodium ion battery, thereby greatly improving the cycle performance, high temperature storage performance and safety performance of the sodium ion battery.

[0026] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0027] Example 1

[0028] A sodium ion battery electrolyte, the composition of the electrolyte is shown in the following table:

[0029]

[0030] Comparative Example 1

[0031] A sodium ion battery electrolyte, the composition of the electrolyte is shown in the following table:

[0032]

[0033] The electrolyte provided by Example 1-x and Comparative Example 1-x was applied to a sodium ion battery, the positive electrode of which was a layered oxide and the negative electrode was hard carbon. After the sodium ion battery was stored at a high temperature of 45°C for 15 days, the performance was compared, and the results are shown in the following table:

[0034]

[0035] It can be seen from the above table that the use of the electrolyte provided in the embodiments of the present application can effectively improve the cycle performance of the sodium ion battery and reduce the high-temperature storage gas production of the sodium ion battery.

[0036] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0037] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0038] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A sodium ion battery electrolyte, characterized in that: The electrolyte comprises sodium salt, non-aqueous organic solvent and additives, wherein the additives comprise 4,4'-dipinacol borate diphenyl sulfone, dipyridyl carbonate and sodium difluorophosphate.

2. The sodium ion battery electrolyte according to claim 1, characterized in that The mass proportion of the 4,4'-dipinacol borate diphenyl sulfone in the electrolyte is 0.5% to 1.5%.

3. The sodium ion battery electrolyte according to claim 1, characterized in that The mass proportion of the bipyridyl carbonate in the electrolyte is 0.5% to 1.5%.

4. The sodium ion battery electrolyte according to claim 1, characterized in that The mass proportion of the sodium difluorophosphate in the electrolyte is 0.5% to 1.5%.

5. The sodium ion battery electrolyte according to claim 1, characterized in that The sodium salts include NaPF6, NaClO4, NaAlCl4, NaFeCl4, NaSO3CF3, NaBCl4, NaNO3, NaPOF4, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH 3) At least one of C6H4SO3, NaHSO4 and NaB(C6H5)4.

6. The sodium ion battery electrolyte according to claim 1 or 5, characterized in that: The molar concentration of the sodium salt is 0.5-2.0M.

7. The sodium ion battery electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent includes at least two of ethylene carbonate, propylene carbonate, butylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, sulfolane, dimethyl sulfone, ethyl methyl sulfone and diethyl sulfone.

8. The sodium ion battery electrolyte according to claim 1 or 7, characterized in that: The non-aqueous organic solvent is two of ethylene carbonate, propylene carbonate, butylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

9. The sodium ion battery electrolyte according to claim 8, characterized in that: The volume ratio of the two non-aqueous organic solvents is (3:7) to (7:3).

10. The sodium ion battery electrolyte according to claim 1, characterized in that: The electrolyte further comprises: at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, succinonitrile, adiponitrile, 1,3-propylene sultone, tris(trimethylsilane)phosphate, and tris(trimethylsilane)borate.

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