Flame-retardant electrolyte and application thereof in long-life sodium ion total battery

Abstract

The invention belongs to the technical field of total batteries, and discloses a flame-retardant electrolyte and an application thereof in a long-life sodium ion total battery. The flame-retardant electrolyte comprises a sodium salt, a phosphate solvent, a carbonate solvent and an additive, the total battery comprises a Prussian blue positive electrode and a hard carbon negative electrode. According to the electrolyte, the sodium ion total battery can stably work under the condition of 1.5-3.7 V, meanwhile, the problem of flame retardance of the battery is solved, and the high-performance sodium ion battery is obtained. According to the invention, the solvation structure of the electrolyte system is finely regulated and controlled through a carbonate cosolvent strategy, so that the stability of the electrolyte, the intercalation / deintercalation kinetics of sodium ions in the Prussian blue positive electrode and the passivation layer stability of the Prussian blue and hard carbon electrode / electrolyte interface are improved. The Prussian blue-hard carbon total battery using the flame-retardant electrolyte provided by the invention not only has excellent flame-retardant performance, but also has good cycle performance.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a flame retardant electrolyte and application thereof in a long-life sodium ion full battery. Background Art

[0002] As the demand for environmentally friendly energy storage devices continues to grow, sodium-ion batteries are gaining increasing attention as a powerful alternative to lithium-ion batteries. With their long cycle life, abundant sodium resources, and excellent electrochemical performance, sodium-ion batteries show broad application prospects. In particular, rechargeable energy storage devices based on sodium electrochemistry are expected to be an ideal choice for regulating the output of large-scale power grids with intermittent solar and wind power.

[0003] However, over the past decade, a series of safety incidents have raised concerns about battery safety. Safety incidents are often caused by the instability of the electrolyte. Common liquid electrolytes (LE), such as ethylene carbonate (EC), are highly volatile and flammable, making them more susceptible to thermal runaway. Compared with typical carbonate solvents, phosphate-based solvents reduce the possibility of thermal runaway due to their high thermal stability. In addition, the advantages of phosphate-based solvents also include a large electrochemical stability window and low cost. However, since phosphate solvents cannot establish a strong solid electrolyte interface (SEI) layer between the hard carbon anode and the electrolyte, this will impair the cycling performance of sodium-ion batteries.

[0004] So far, research on flame-retardant electrolytes for sodium-ion full batteries is still in its early stages, specifically including several strategies such as high-concentration electrolytes (HCEs), locally high-concentration electrolytes (LHCEs), optimized salts and co-solvents. However, HCEs, salts and LHCEs are not cost-effective. Co-solvents such as dimethyl carbonate (DMC) can improve the cycle stability of the battery and extend the cycle life of the battery. It can reduce the number of phosphates participating in the first solvation shell, thereby forming a more stable SEI and giving the battery a longer service life. Therefore, co-solvents are one of the best choices to improve the cycling performance of flame-retardant solvents. There are other patents related to flame retardant electrolytes, for example: the invention patent with application publication number CN 116072975B discloses a local high-concentration flame retardant electrolyte and a lithium metal battery containing the electrolyte, which mainly provides a lithium metal battery assembled by a local high-concentration flame retardant electrolyte, various lithium battery positive electrodes, lithium negative electrodes, and diaphragms, but the design salt is expensive, cumbersome to prepare, and the cost is high. In addition, the manufacturing cost of the battery system is high, the operating requirements are strict, and it is difficult to achieve large-scale industrial production. The invention patent with authorization announcement number CN 118213627A announces an ionic liquid solvent, a flame retardant electrolyte, and a sodium metal battery, which ensures the flame retardancy and capacity retention rate of the sodium metal battery, but its cost is still very high. The battery system provided by the present invention is a full battery system, which is a battery system closer to industrialization, and the cost of the flame retardant electrolyte is much lower than that of the above-mentioned electrolyte.

[0005] Therefore, the development of low-cost flame-retardant electrolytes and long-life sodium-ion full battery systems is crucial for the future commercialization of sodium-ion full batteries. Summary of the invention

[0006] The purpose of the present invention is to solve the technical problem of poor compatibility of phosphate-based electrolyte negative electrodes in the prior art, and to provide a flame retardant electrolyte and its application in a long-life sodium ion full battery.

[0007] To achieve the above objectives, the present invention adopts the following technical scheme: a flame retardant electrolyte and a long-life sodium ion full battery, wherein the flame retardant electrolyte comprises a sodium salt, a phosphate solvent, a carbonate solvent and an additive.

[0008] Preferably, the sodium salt is any one of NaPF6, NaPF2O2, NaClO4, C2F6NNaO4S2, CF3SO3Na, F2NNaO4S2, NaBF4 or a mixture of at least two of them in any proportion. Among them, NaClO4 is the most preferred.

[0009] The phosphate solvent is any one of TEP and TMP or a mixture of the two in any proportion, wherein TEP is the most preferred.

[0010] The carbonate solvent is any one of PC, EC, EMC, DMC, and DEC, or a mixture of at least two of them in any proportion, among which EMC is the most preferred.

[0011] The additives are VC, FEC, ES and DTD.

[0012] Preferably, the sodium ion concentration of the sodium salt dissolved in the carbonate solvent is 0.5-2.0 mol / L, and the weight percentage of the fluorine-containing additive in the electrolyte is 0-10%.

[0013] Preferably, the phosphate, carbonate and additive are all dehydrated through a 4-Å molecular sieve before use, and the electrolyte preparation operation is carried out in a glove box filled with argon, and the water and oxygen content in the glove box is less than 0.01 ppm.

[0014] The present invention uses the flame retardant electrolyte to prepare a long-life sodium ion full battery. Preferably, the sodium ion full battery includes a Prussian blue positive electrode, a hard carbon negative electrode, a separator and any one of the flame retardant electrolytes described above.

[0015] Preferably, the positive electrode comprises Prussian blue powder, sodium alginate, Ketjen black and an aluminum current collector, the negative electrode comprises hard carbon powder, Ketjen black, sodium alginate and an aluminum current collector, and the separator is a cellulose separator.

[0016] Preferably, the weight percentages of the positive electrode are as follows: 80-98% Prussian blue powder, 1-10% sodium alginate, and 1-10% Ketjen black; the weight percentages of the negative electrode are as follows: 80-98% hard carbon powder, 1-10% Ketjen black, and 1-10% sodium alginate.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The carbonate in the solvent has a certain polarity and forms competitive coordination with the phosphate molecules, changing the solvation structure of the electrolyte. The addition of co-solvent reduces the number of phosphate molecules in the first solvation shell, ensuring the formation of a stable SEI film.

[0018] (2) Due to the synergistic effect of the components in the flame-retardant electrolyte, a stable SEI film is formed, thereby extending the cycle life of the battery. At the same time, the appropriate ratio between the components also enhances the insertion / extraction kinetics of sodium ions in the Prussian blue positive electrode, thereby improving the ion conductivity of the electrolyte, thereby solving the problem of low capacity and low coulombic efficiency of the phosphate-based electrolyte full battery.

[0019] (3) The full battery system is closer to industrialization than other systems. The application of this flame-retardant electrolyte in this system promotes the development of sodium-ion battery industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The coordination numbers of the first solvation shell sodium ions and various solvents obtained based on molecular dynamics simulation in Example 1 and Comparative Example 1.

[0021] Figure 2 This is the cycle performance test of the Prussian blue / / hard carbon full battery of Example 1 and Comparative Example 1.

[0022] Figure 3This is the rate performance test of the Prussian blue / / hard carbon full cell of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0023] The present invention will be specifically described below in conjunction with the embodiments and comparative examples, which are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. It should be understood that after reading the content of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

[0024] Example 1

[0025] The flame retardant electrolyte provided by the present invention includes NaClO4, TEP, EMC and VC, wherein the mixing ratio of TEP to EMC is 8:2, the sodium ion concentration of NaClO4 dissolved in TEP is 1 mol / L, and the weight percentage of VC in the electrolyte is 3%, which is recorded as 1MNaClO4-TEP-EMC+3% VC. The above TEP, EMC and VC are all used after dehydration through 4-Å molecular sieves, and the configuration operation of the electrolyte is carried out in a glove box filled with argon, and the water and oxygen content in the glove box is less than 0.01 ppm.

[0026] The present invention uses the flame-retardant electrolyte to prepare a long-life sodium ion full battery. The preparation method of the positive electrode, negative electrode and separator of the battery and the battery assembly are as follows: (1) Preparation of positive electrode: The active material of the positive electrode is composed of 93% Prussian blue powder, 3% sodium alginate and 4% Ketjen black in a weight ratio. After high-energy mechanical grinding, the active material is coated on the aluminum current collector with an appropriate amount of deionized water. After drying in a vacuum oven at 120°C for 12 h, it is pressed into a sheet to prepare the positive electrode of the sodium-ion full battery.

[0027] (2) Preparation of the negative electrode: The active material of the negative electrode is composed of 70% hard carbon powder, 15% Ketjen black and 15% sodium alginate in a weight ratio. After high-energy mechanical grinding, the active material is coated on the aluminum current collector with an appropriate amount of deionized water, and then dried in a vacuum oven at 80 °C for 12 h and pressed into a sheet to prepare the negative electrode of the sodium ion full battery.

[0028] (3) Preparation of diaphragm: Press the cellulose diaphragm into sheets and set them aside as diaphragms.

[0029] (4) Battery assembly: In an argon-protected glove box, the water and oxygen content in the glove box is less than 0.01 ppm. The prepared negative electrode, separator, and positive electrode are stacked tightly in sequence, and the electrolyte is dripped to completely soak the separator. Then, the stacked part is encapsulated into a button-type shell to complete the assembly of the sodium ion full battery.

[0030] (5) Battery cycle test: stand at room temperature for 6 h, then cycle at 75 mA g -1 The cycle was carried out by constant current charge and discharge, with the voltage upper and lower limits being 1.5-3.7 V. The test results are shown in Table 2 and Appendix Figure 2 shown.

[0031] (6) Battery rate test: stand at room temperature for 6 h, then test at 0.15-150 mA g -1 The test adopts constant current charging and discharging mode, and the voltage upper and lower limits are 1.5-3.7V. The test results are as attached. Figure 3 shown.

[0032] Example 2

[0033] A flame retardant electrolyte and a long-life sodium ion full battery are provided, wherein the content ratio of each component in the electrolyte is shown in Table 1, and the other steps are the same as those in Example 1.

[0034] Example 3

[0035] A flame retardant electrolyte and a long-life sodium ion full battery are provided, wherein the content ratio of each component in the electrolyte is shown in Table 1, and the other steps are the same as those in Example 1.

[0036] Example 4

[0037] A flame retardant electrolyte and a long-life sodium ion full battery are provided, wherein the content ratio of each component in the electrolyte is shown in Table 1, and the other steps are the same as those in Example 1.

[0038] Comparative Example 1 A flame retardant electrolyte and a long-life sodium ion full battery are provided, wherein the content ratio of each component in the electrolyte is shown in Table 1, and the other steps are the same as those in Example 1, and Comparative Example 1 is recorded as 1M NaClO4-TEP+3% VC.

[0039] Comparative Example 2 A flame retardant electrolyte and a long-life sodium ion full battery are provided, wherein the content ratio of each component in the electrolyte is shown in Table 1, and the other steps are the same as those in Example 1.

[0040] Comparative Example 3 A flame retardant electrolyte and a long-life sodium ion full battery are provided, wherein the content ratio of each component in the electrolyte is shown in Table 1, and the other steps are the same as those in Example 1.

[0041] Comparative Example 4 A flame retardant electrolyte and a long-life sodium ion full battery are provided, wherein the content ratio of each component in the electrolyte is shown in Table 1, and the other steps are the same as those in Example 1.

[0042] Comparative Example 5 A flame retardant electrolyte and a long-life sodium ion full battery are provided, wherein the content ratio of each component in the electrolyte is shown in Table 1, and the other steps are the same as those in Example 1.

[0043] Table 1 Electrolyte content ratio of Examples 1-4 and Comparative Examples 1-5

[0044] Table 2 Performance test results of sodium ion full batteries of Examples 1-4 and Comparative Examples 1-5

[0045] Figure 1 The coordination numbers of sodium ions in the first solvation shell and each solvent obtained based on molecular dynamics simulation in Example 1 and Comparative Example 1. The carbonate ester in the solvent forms competitive coordination with the phosphate ester molecules, which changes the solvation structure of the electrolyte. The addition of the co-solvent reduces the coordination number of the phosphate ester in the first solvation shell. Figure 2 The Prussian blue / / hard carbon full battery cycle performance test of Example 1 and Comparative Example 1. The Prussian blue / / hard carbon full battery containing the electrolyte of Example 1 has a higher capacity retention rate and coulombic efficiency. In addition, it can be seen from the comparison of the data in the above table that the use of the electrolyte provided by the present invention greatly improves the cycle performance of the sodium ion full battery.

[0046] Figure 3 The rate performance test of the Prussian blue / / hard carbon full battery of Example 1 and Comparative Example 1. The Prussian blue / / hard carbon full battery containing the electrolyte of Example 1 has better rate performance.

Claims

1. A flame retardant electrolyte, characterized in that: The flame retardant electrolyte includes sodium salt, phosphate ester solvent, carbonate solvent and additives, and the volume proportion of the phosphate ester solvent is greater than or equal to 60%.

2. A flame retardant electrolyte according to claim 1, characterized in that: The sodium ion concentration of the sodium salt dissolved in the mixed solvent of phosphate ester and carbonate ester is 0.5-2.0 mol / L, the weight percentage of the additive in the electrolyte is 0-10%, and the ratio of the mixed solvent of phosphate ester and carbonate ester is 6:4-9:

1.

3. A flame retardant electrolyte according to claim 2, characterized in that: The sodium salt is any one of sodium hexafluorophosphate (NaPF6), sodium difluorophosphate (NaPF2O2), sodium perchlorate (NaClO4), sodium bis(trifluoromethylsulfonyl)imide (C2F6NNaO4S2), sodium trifluoromethylsulfonate (CF3SO3Na), sodium bis(fluorosulfonyl)imide (F2NNaO4S2), sodium tetrafluoroborate (NaBF4), or a mixture of at least two of them in any proportion; the phosphate solvent is any one of trimethyl phosphate (TMP) and triethyl phosphate (TEP), or a mixture of at least two of them in any proportion; the carbonate solvent is any one of propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), or a mixture of at least two of them in any proportion; the additive is any one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), and vinyl sulfate (DTD), or a mixture of at least two of them in any proportion.

4. A flame retardant electrolyte according to claim 3, characterized in that: Phosphates, carbonates, and additives were all dehydrated through 4-Å molecular sieves before use. The electrolyte preparation operation was carried out in a glove box filled with argon. The water and oxygen content in the glove box was less than 0.01 ppm.

5. A long-life sodium-ion full battery, characterized in that: The sodium ion full battery comprises a Prussian blue positive electrode, a hard carbon negative electrode, a separator and the flame retardant electrolyte according to any one of claims 1 to 4.

6. A long-life sodium-ion full battery according to claim 5, characterized in that: The Prussian blue positive electrode includes Prussian blue powder, sodium alginate, Ketjen black and aluminum current collector, the hard carbon negative electrode includes hard carbon powder, Ketjen black, sodium alginate and aluminum current collector, and the separator is a cellulose separator.

7. A long-life sodium-ion full battery according to claim 6, characterized in that: The weight percentages of the Prussian blue positive electrode are as follows: Prussian blue powder 80-98%, sodium alginate 1-10%, Ketjen black 1-10%; the weight percentages of the hard carbon negative electrode are as follows: hard carbon powder 80-98%, Ketjen black 1-10%, sodium alginate 1-10%.

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