A sodium ion secondary battery non-aqueous electrolyte and preparation method thereof

Abstract

The invention discloses a sodium ion secondary battery non-aqueous electrolyte and a preparation method thereof, and relates to the technical field of sodium ion secondary batteries; including a basic electrolyte and an additive, the basic electrolyte including a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 0.5-2.2 mol / L; the mass ratio of the additive to the basic electrolyte is (0.3-5.5):100. The additive includes the following components: fluoroethylene carbonate, 4,5-dicyanoimidazole, cyclopentyl-N-succinimidyl carbonate, 1H-imidazole-4,5-dimethyl dicarboxylate, hexahydrophthalic anhydride, 4-toluenesulfonic anhydride and 2,3-pyridinedicarboxylic anhydride. The sodium ion secondary battery non-aqueous electrolyte disclosed in the invention is non-flammable and has good thermal stability, can form a stable SEI film, has good discharge efficiency and battery cycle performance, and is safe to use.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion secondary batteries, and in particular to a sodium ion secondary battery non-aqueous electrolyte and a preparation method thereof. Background Art

[0002] Secondary batteries, also known as rechargeable batteries, are batteries that can be repeatedly charged and discharged and used multiple times. Compared with non-reusable primary batteries, secondary batteries have the advantages of low cost and less environmental pollution. Among the main secondary battery technologies currently, lithium-ion secondary batteries are the most widely used. Due to their high energy density, they are widely used in transportation equipment such as electric vehicles and electric motorcycles, as well as large-scale household and commercial power storage equipment. However, lithium is a rare metal and there is a problem of low output. It is in this situation that sodium-ion secondary batteries came into being. Sodium-ion secondary batteries have attracted people's attention due to their abundant resources, high safety, environmental friendliness, and high energy density, and are considered to be the next generation of clean energy materials.

[0003] The electrolyte is an important component of sodium-ion secondary batteries. It plays the role of transporting ions in sodium-ion secondary batteries. Its physical and chemical properties and chemical composition not only determine the kinetic properties of sodium ions in the electrolyte, but also determine the composition and structure of the solid electrolyte interface (SEI) film on the electrode surface, which has an important influence on the rate performance of sodium-ion batteries, the stability of the electrode structure and the cycle life. The ideal electrolyte for sodium-ion secondary batteries needs to have the advantages of being non-toxic, safe and applicable, high ionic conductivity, wide electrochemical window, good thermal stability and good chemical stability.

[0004] The electrolyte of the existing sodium ion secondary battery has poor thermal stability and non-flammability, unsatisfactory discharge efficiency and battery cycle performance, high viscosity and cost, excessive corrosiveness and oxidizability, and environmental protection and safety of use due to the unreasonable composition formula design of solvents, salts and additives. For example, Chinese invention patent CN106797054B discloses an electrolyte for sodium ion secondary battery and a sodium ion secondary battery containing it, wherein the electrolyte has sodium ion conductivity and contains sodium salt and non-aqueous solvent, wherein the non-aqueous solvent contains fluorophosphate and propylene carbonate, and the content of the fluorophosphate in the non-aqueous solvent is 5% to 50% by mass. However, its electrochemical performance, discharge efficiency and battery cycle performance need to be further improved. Summary of the invention

[0005] The main purpose of the present invention is to solve the above technical problems and provide a non-aqueous electrolyte for sodium ion secondary batteries and a preparation method thereof, which has good non-flammability and thermal stability, can form a stable SEI film, has good discharge efficiency and battery cycle performance, and is safe to use.

[0006] To achieve the above object, the present invention provides a sodium ion secondary battery non-aqueous electrolyte, comprising a basic electrolyte and an additive, wherein the basic electrolyte comprises a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 0.5 to 2.2 mol / L; the mass ratio of the additive to the basic electrolyte is (0.3-5.5):100; the non-aqueous solvent is at least two of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, and diethyl carbonate.

[0007] Preferably, the sodium salt is at least one of sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium hexafluorophosphate, and sodium bis(fluorosulfonyl)imide.

[0008] Preferably, the additive is fluoroethylene carbonate.

[0009] Preferably, the additive comprises the following components in parts by weight: 8-10 parts of fluoroethylene carbonate, 1-2 parts of 4,5-dicyanoimidazole, 0.8-1.2 parts of cyclopentyl-N-succinimidyl carbonate, 0.1-0.5 parts of 1H-imidazole-4,5-dicarboxylic acid dimethyl ester, 0.05-0.1 parts of hexahydrophthalic anhydride, 0.05-0.1 parts of 4-toluenesulfonic anhydride, and 0.05-0.1 parts of 2,3-pyridinedicarboxylic anhydride.

[0010] Another object of the present invention is to provide a method for preparing the sodium ion secondary battery non-aqueous electrolyte, comprising the following steps: mixing a sodium salt, a non-aqueous solvent and an additive in proportion, stirring evenly, to obtain a sodium ion secondary battery non-aqueous electrolyte.

[0011] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0012] (1) The method for preparing the non-aqueous electrolyte for sodium ion secondary batteries disclosed in the present invention has a simple preparation process, convenient operation and control, high preparation efficiency and finished product qualification rate, low energy consumption, low dependence on equipment, and is suitable for industrial production.

[0013] (2) The sodium ion secondary battery non-aqueous electrolyte disclosed in the present invention comprises a basic electrolyte and an additive, wherein the basic electrolyte comprises a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 0.5 to 2.2 mol / L; the mass ratio of the additive to the basic electrolyte is (0.3-5.5):100; through the reasonable selection of the chemical composition and formula of each component, they can cooperate with each other to give the product the advantages of non-flammability and good thermal stability, forming a stable SEI film, good discharge efficiency and battery cycle performance, and sufficient safety in use. Compared with traditional electrolytes, this electrolyte exhibits higher ionic conductivity, excellent high-power performance, and can effectively improve the cycle life of sodium ion batteries.

[0014] (3) The non-aqueous electrolyte for sodium ion secondary batteries disclosed in the present invention, wherein the non-aqueous solvent is at least two of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, and diethyl carbonate; the compounding of the non-aqueous solvent can further improve the working voltage window of the electrolyte; and the combination with the sodium salt and the additive can keep the viscosity of the electrolyte within a more reasonable range, thereby improving the conductivity of the electrolyte; at the same time, the product matching performance can be better, the temperature range can be wider, and the stability can be higher; and the sodium ion secondary battery using the electrolyte can exhibit excellent coulombic efficiency and cycle life.

[0015] (4) The sodium ion secondary battery non-aqueous electrolyte disclosed in the present invention, wherein the additive comprises the following components in parts by weight: 8-10 parts of fluoroethylene carbonate, 1-2 parts of 4,5-dicyanoimidazole, 0.8-1.2 parts of cyclopentyl-N-succinimidyl carbonate, 0.1-0.5 parts of 1H-imidazole-4,5-dicarboxylic acid dimethyl ester, 0.05-0.1 parts of hexahydrophthalic anhydride, 0.05-0.1 parts of 4-toluenesulfonic anhydride, and 0.05-0.1 parts of 2,3-pyridinedicarboxylic anhydride. 1 part; through the cooperation between the components, the alkalinity on the surface of the positive electrode material can be effectively neutralized, the decomposition effect of the alkalinity of the metal oxide on the carbonate can be inhibited, and the cycle performance of the sodium ion battery can be improved; the addition of 4,5-dicyanoimidazole and 1H-imidazole-4,5-dicarboxylic acid dimethyl ester can also improve the flame retardancy of the electrolyte; the synergistic effect with other components makes the sodium ion secondary battery using this electrolyte not only have good electrochemical properties, but also greatly improve the safety and show excellent capacity retention rate. DETAILED DESCRIPTION

[0016] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art may think of other obvious variations. Example 1

[0017] A sodium ion secondary battery non-aqueous electrolyte comprises a basic electrolyte and an additive, wherein the basic electrolyte comprises a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 1 mol / L; the mass ratio of the additive to the basic electrolyte is 1:100; and the non-aqueous solvent is a mixture of propylene carbonate and diethyl carbonate in a volume ratio of 2:3.

[0018] The sodium salt is sodium hexafluorophosphate; the additive includes the following components in parts by weight: 8 parts of fluoroethylene carbonate, 1 part of 4,5-dicyanoimidazole, 0.8 parts of cyclopentyl-N-succinimidyl carbonate, 0.1 parts of 1H-imidazole-4,5-dicarboxylic acid dimethyl ester, 0.05 parts of hexahydrophthalic anhydride, 0.05 parts of 4-toluenesulfonic anhydride, and 0.05 parts of 2,3-pyridinedicarboxylic anhydride.

[0019] A method for preparing the sodium ion secondary battery non-aqueous electrolyte comprises the following steps: mixing sodium salt, non-aqueous solvent and additive in proportion, stirring evenly, and obtaining the sodium ion secondary battery non-aqueous electrolyte. Example 2

[0020] A sodium ion secondary battery non-aqueous electrolyte comprises a basic electrolyte and an additive, wherein the basic electrolyte comprises a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 1.2 mol / L; the mass ratio of the additive to the basic electrolyte is 2:100; and the non-aqueous solvent is a mixture of propylene carbonate and ethyl methyl carbonate in a volume ratio of 2:3.

[0021] The sodium salt is sodium trifluoromethanesulfonate; the additive includes the following components in parts by weight: 8.5 parts of fluoroethylene carbonate, 1.2 parts of 4,5-dicyanoimidazole, 0.9 parts of cyclopentyl-N-succinimidyl carbonate, 0.2 parts of 1H-imidazole-4,5-dicarboxylic acid dimethyl ester, 0.07 parts of hexahydrophthalic anhydride, 0.07 parts of 4-toluenesulfonic anhydride, and 0.06 parts of 2,3-pyridinedicarboxylic anhydride.

[0022] A method for preparing the sodium ion secondary battery non-aqueous electrolyte comprises the following steps: mixing sodium salt, non-aqueous solvent and additive in proportion, stirring evenly, and obtaining the sodium ion secondary battery non-aqueous electrolyte. Example 3

[0023] A sodium ion secondary battery non-aqueous electrolyte comprises a basic electrolyte and an additive, wherein the basic electrolyte comprises a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 1.6 mol / L; the mass ratio of the additive to the basic electrolyte is 3:100; and the non-aqueous solvent is a mixture of propylene carbonate and dimethyl carbonate in a volume ratio of 2:3.

[0024] The sodium salt is sodium tetrafluoroborate; the additive includes the following components in parts by weight: 9 parts of fluoroethylene carbonate, 1.5 parts of 4,5-dicyanoimidazole, 1 part of cyclopentyl-N-succinimidyl carbonate, 0.3 parts of 1H-imidazole-4,5-dicarboxylic acid dimethyl ester, 0.09 parts of hexahydrophthalic anhydride, 0.08 parts of 4-toluenesulfonic anhydride, and 0.08 parts of 2,3-pyridinedicarboxylic anhydride.

[0025] A method for preparing the sodium ion secondary battery non-aqueous electrolyte comprises the following steps: mixing sodium salt, non-aqueous solvent and additive in proportion, stirring evenly, and obtaining the sodium ion secondary battery non-aqueous electrolyte. Example 4

[0026] A sodium ion secondary battery non-aqueous electrolyte comprises a basic electrolyte and an additive, wherein the basic electrolyte comprises a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 1.8 mol / L; the mass ratio of the additive to the basic electrolyte is 4.5:100; and the non-aqueous solvent is a mixture of propylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:2:1.

[0027] The sodium salt is a mixture of sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium hexafluorophosphate, and sodium bis(fluorosulfonyl)imide in a mass ratio of 1:3:1:2; the additive includes the following components in parts by weight: 9.5 parts of fluoroethylene carbonate, 1.8 parts of 4,5-dicyanoimidazole, 1.1 parts of cyclopentyl-N-succinimidyl carbonate, 0.4 parts of 1H-imidazole-4,5-dicarboxylic acid dimethyl ester, 0.09 parts of hexahydrophthalic anhydride, 0.09 parts of 4-toluenesulfonic anhydride, and 0.08 parts of 2,3-pyridinedicarboxylic anhydride.

[0028] A method for preparing the sodium ion secondary battery non-aqueous electrolyte comprises the following steps: mixing sodium salt, non-aqueous solvent and additive in proportion, stirring evenly, and obtaining the sodium ion secondary battery non-aqueous electrolyte. Example 5

[0029] A sodium ion secondary battery non-aqueous electrolyte comprises a basic electrolyte and an additive, wherein the basic electrolyte comprises a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 2.2 mol / L; the mass ratio of the additive to the basic electrolyte is 5.5:100; and the non-aqueous solvent is a mixture of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, and diethyl carbonate in a volume ratio of 2:1:2:3:5.

[0030] The sodium salt is sodium hexafluorophosphate; the additive includes the following components in parts by weight: 10 parts of fluoroethylene carbonate, 2 parts of 4,5-dicyanoimidazole, 1.2 parts of cyclopentyl-N-succinimidyl carbonate, 0.5 parts of 1H-imidazole-4,5-dicarboxylic acid dimethyl ester, 0.1 parts of hexahydrophthalic anhydride, 0.1 parts of 4-toluenesulfonic anhydride, and 0.1 parts of 2,3-pyridinedicarboxylic anhydride.

[0031] A method for preparing the sodium ion secondary battery non-aqueous electrolyte comprises the following steps: mixing sodium salt, non-aqueous solvent and additive in proportion, stirring evenly, and obtaining the sodium ion secondary battery non-aqueous electrolyte.

[0032] Comparative Example 1

[0033] The present invention provides a sodium ion secondary battery non-aqueous electrolyte, the formula and preparation method of which are similar to those of Example 1, except that 4,5-dicyanoimidazole and cyclopentyl-N-succinimidyl carbonate are not added.

[0034] Comparative Example 2

[0035] The present invention provides a sodium ion secondary battery non-aqueous electrolyte, the formula and preparation method of which are similar to those of Example 1, except that 2,3-pyridinedicarboxylic anhydride and 1H-imidazole-4,5-dicarboxylic acid dimethyl ester are not added.

[0036] In order to further illustrate the beneficial technical effects of the non-aqueous electrolyte of the sodium ion secondary battery prepared in each embodiment of the present invention, the non-aqueous electrolyte of the sodium ion secondary battery prepared in each example is used as the electrolyte, the XN33S sodium positive electrode produced by Jiangsu Xiangying New Energy Technology Co., Ltd. is used as the positive electrode, and the 16mm diameter sodium sheet is used as the negative electrode. The battery is assembled and charged, left to stand for 8 hours, and the battery performance test is performed respectively. At a voltage range of 1.0-4.2V and a current density of 0.1C, room temperature charging and discharging are performed, and the first charging and discharging efficiency is recorded. Under 45°C conditions, the battery is charged to 4.0 volts with a current of 0.5C, and then left for 5 minutes; the battery is discharged to 1.5 volts with a current of 0.5C and left for 5 minutes. Repeat the above steps 200 times to obtain the capacity of the battery after 200 cycles with a current of 0.1C to 1.5 volts. The capacity maintenance rate before and after the cycle is calculated by the following formula: Capacity maintenance rate = (200th cycle discharge efficiency / first cycle discharge efficiency) × 100%, and the test results are shown in Table 1.

[0037] Table 1

[0038] project First charge and discharge efficiency (%) Capacity retention after 200 cycles (%) Example 1 95.25 94.3 Example 2 95.40 94.8 Example 3 95.62 95.6 Example 4 95.96 96.0 Example 5 96.17 96.5 Comparative Example 1 88.06 90.7 Comparative Example 2 92.28 92.4

[0039] As can be seen from Table 1, the sodium ion battery using the sodium ion secondary battery non-aqueous electrolyte disclosed in the embodiment of the present invention has better electrochemical performance and cycle performance than the comparative example product; the addition of 4,5-dicyanoimidazole, cyclopentyl-N-succinimidyl carbonate, 2,3-pyridinedicarboxylic anhydride and 1H-imidazole-4,5-dicarboxylic acid dimethyl ester is beneficial to improving the above performance.

[0040] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A non-aqueous electrolyte for a sodium ion secondary battery, It is characterized in that The invention comprises a basic electrolyte and an additive, wherein the basic electrolyte comprises a sodium salt and a non-aqueous solvent; the concentration of the sodium salt relative to the basic electrolyte is 0.5 to 2.2 mol / L; the mass ratio of the additive to the basic electrolyte is (0.3-5.5):100; the additive comprises the following components in parts by weight: 8-10 parts of fluoroethylene carbonate, 1-2 parts of 4,5-dicyanoimidazole, 0.8-1.2 parts of cyclopentyl-N-succinimidyl carbonate, 0.1-0.5 parts of 1H-imidazole-4,5-dicarboxylic acid dimethyl ester, 0.05-0.1 parts of hexahydrophthalic anhydride, 0.05-0.1 parts of 4-toluenesulfonic anhydride, and 0.05-0.1 parts of 2,3-pyridinedicarboxylic anhydride.

2. The sodium ion secondary battery nonaqueous electrolyte according to claim 1, It is characterized in that The non-aqueous solvent is at least two of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, and diethyl carbonate.

3. The sodium ion secondary battery nonaqueous electrolyte according to claim 1, It is characterized in that The sodium salt is at least one of sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium hexafluorophosphate, and sodium bis(fluorosulfonyl)imide.

4. A method for preparing the non-aqueous electrolyte for sodium ion secondary batteries according to any one of claims 1 to 3, It is characterized in that The method comprises the following steps: mixing sodium salt, non-aqueous solvent and additive in proportion, and stirring evenly to obtain non-aqueous electrolyte for sodium ion secondary battery.