Sodium ion battery electrolyte additive, electrolyte and sodium ion battery

Abstract

The present invention discloses a sodium ion battery electrolyte additive comprising a compound represented by Formula I and a compound represented by Formula II. The present invention also discloses a sodium ion battery electrolyte and a sodium ion battery containing the additive. The electrolyte additive of the present invention can effectively improve the high-temperature stability and high-temperature cycle retention of sodium ion batteries, thereby improving the high-temperature shelf and cycle performance of sodium ion batteries.

Description

Technical Field

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

[0002] As lithium-ion batteries are used in numerous fields, resource scarcity is becoming increasingly prominent. Fluctuations in lithium resource prices have also significantly impacted their application. To overcome this constraint, the development of new metal-ion batteries is urgently needed. Sodium ions have a similar radius and chemical properties to lithium ions in the periodic table, yet sodium resources are far more abundant than lithium. Therefore, sodium-ion batteries hold great promise as a next-generation alternative to lithium-ion batteries.

[0003] The electrolyte, the lifeblood of power batteries, plays a crucial role in battery performance. Additives are crucial for influencing electrical performance. However, existing electrolytes in sodium-ion batteries suffer from poor stability and cycle performance. Therefore, there is a need to develop electrolyte additives and electrolytes that effectively improve the high-temperature stability and cycle performance of sodium-ion batteries. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a sodium ion battery electrolyte additive, an electrolyte and a sodium ion battery.

[0005] The present invention provides a sodium ion battery electrolyte additive, wherein the electrolyte additive comprises a compound represented by formula I and a compound represented by formula II:

[0006]

[0007] In formula I, R1 is a halogen atom, a C1-6 alkyl group or a C1-6 haloalkyl group, and R2-R4 are C1-6 alkyl groups;

[0008]

[0009] In formula II, R5 to R7 are independently selected from C1 to 6 alkyl, C6 to 12 an aryl or cyclic sulfate group.

[0010] The present invention uses a combination additive of compound A shown in formula I and compound B shown in formula II. When the two additives are used together, the silicon-oxygen bond in compound A is preferentially broken, and the generated alkyl silicon can remove HF and H2O in the electrolyte, which on the one hand avoids the corrosion of the positive electrode material and inhibits the dissolution of metal ions. On the other hand, it also removes LiF on the positive electrode surface, reducing the interface impedance of the positive electrode. At the same time, since the sulfonyl group has good film-forming properties, compound A participates in the film formation on the positive electrode surface, generating a solid interface film rich in F, S, and Si, increasing the ionic conductivity and improving the interface transport performance; compound B mainly forms a film at the negative electrode, and cooperates with compound A to construct a high-sulfur organic sodium sulfate-sodium sulfonate cross-linked structure at the negative electrode interface. This cross-linked structure interface film greatly stabilizes the structure of the hard carbon of the negative electrode material and improves the stability of the battery at high temperature and during the cycle. In summary, the combined electrolyte additive used in the present invention can protect the positive and negative electrode structures of sodium ion batteries and improve high-temperature shelf and high-temperature cycle performance.

[0011] Preferably, the compound represented by formula I is selected from at least one of the following compounds A-1 to A-4:

[0012]

[0013]

[0014] The compound represented by formula II is selected from at least one of the following compounds B-1 to B-4:

[0015]

[0016] By optimizing the selection of the compound represented by the above formula I and the compound represented by the above formula II, the synergistic effect of formula I and formula II can be further exerted, thereby further improving the high-temperature performance of the sodium-ion battery.

[0017] Preferably, the compound represented by formula I is The compound represented by formula II is The present invention has found that the electrolyte additive obtained by combining the above two specific components has the best synergistic effect and has the best improvement effect on the high-temperature cycle performance and high-temperature shelf performance of the battery.

[0018] Preferably, in the electrolyte additive, the mass ratio of compound A represented by formula I and compound B represented by formula II is in the range of 1:5 to 5:1, which can make the organic sodium sulfate-sodium sulfonate cross-linked structure formed at the negative electrode interface more stable and the phase state more uniform, thereby having better high-temperature cycle stability.

[0019] The present invention also provides a sodium ion battery electrolyte, comprising the electrolyte additive.

[0020] Preferably, the electrolyte additive accounts for 0.1-5% of the total mass of the electrolyte. Controlling the amount of the electrolyte additive of the present invention in the sodium ion electrolyte within the range of 0.1-5% can achieve better protection of the positive and negative electrodes and complete consumption of the additive, thereby achieving better cycle performance of the battery.

[0021] Preferably, the components of the sodium ion battery electrolyte include, by mass percentage, 6-20% of sodium salt, 0.1-5% of the electrolyte additive, 0.5-10% of other functional additives, and the balance being an organic solvent.

[0022] Preferably, the sodium salt is selected from one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate, sodium perchlorate, sodium bis(oxalatoborate), sodium difluorooxalatoborate (NaODFB), sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0023] Preferably, the other functional additives are selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate, styrene carbonate, tris(trimethylsilyl)phosphoric acid, benzoic anhydride, and sulfolane. By properly selecting or combining the above functional additives, the battery can have high capacity and high rate performance while ensuring high-temperature shelf and high-temperature cycling performance, and even further have excellent low-temperature performance, high-voltage performance, and other characteristics.

[0024] Preferably, the organic solvent is selected from one or more of cyclic or chain carbonate organic solvents, cyclic or linear carboxylate organic solvents, and cyclic or linear ether organic solvents.

[0025] Preferably, the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, ethyl propionate, methyl butyrate, butyl acetate, methyl propionate, propyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0026] The present invention also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte is the sodium ion battery electrolyte.

[0027] The beneficial effects of the present invention are as follows:

[0028] The invention uses a combination additive of compound A shown in formula I and compound B shown in formula II. When the two additives are used together, the silicon-oxygen bond in compound A is preferentially broken, and the generated alkyl silicon can remove HF and H2O in the electrolyte. On the one hand, it avoids the corrosion of the positive electrode material and inhibits the dissolution of metal ions. On the other hand, it also removes LiF on the surface of the positive electrode, reducing the interface impedance of the positive electrode. At the same time, because the sulfonyl group has good film-forming properties, compound A participates in the film formation on the positive electrode surface, generating a solid interface film rich in F, S, and Si, increasing the ionic conductivity and improving the interface transport performance; compound B mainly forms a film at the negative electrode, and cooperates with compound A to construct a high-sulfur organic sodium sulfate-sodium sulfonate cross-linked structure at the negative electrode interface. This cross-linked structure interface film greatly stabilizes the structure of the hard carbon of the negative electrode material and improves the stability of the battery at high temperature and during the cycle. In summary, the combined electrolyte additive used in the present invention can protect the positive and negative electrode structures of sodium ion batteries and improve high-temperature shelf and high-temperature cycle performance. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is described in detail below through specific embodiments.

[0030] Example 1

[0031] Preparation of sodium ion battery electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=3:2:5, and then NaPF6 and vinylene carbonate (VC) are added. After the sodium salt is completely dissolved, compound A-1 and compound B-4 are added, and the mixture is stirred and mixed evenly to obtain the electrolyte; the components of the above electrolyte are as follows: NaPF6 12wt%, VC 1wt%, compound A-10.5wt%, compound B-40.5wt%, and the balance is organic solvent.

[0032] Preparation of negative electrode sheet: Add appropriate amount of deionized water to the negative electrode material hard carbon, conductive agent SP, binder CMC, and dispersant SBR in a mass ratio of 94.5:1.5:2:2, mix well, and evenly apply the obtained negative electrode slurry on the negative electrode collector copper foil. Bake at 100°C for 12h to obtain the negative electrode sheet.

[0033] Preparation of positive electrode sheet: Add an appropriate amount of NMP solvent to the positive electrode material Na[Ni 1 / 3Fe 1 / 3Mn 1 / 3]O2, conductive agent SP, and binder PVDF in a mass ratio of 95:2:2.5, mix well, and evenly apply the obtained positive electrode slurry on the positive electrode current collector aluminum foil. Bake at 110°C for 12h to obtain the positive electrode sheet.

[0034] Preparation of a sodium ion battery: The positive electrode sheet, the separator, and the negative electrode sheet prepared above are stacked in sequence to obtain a sodium ion battery cell, and the cell is dried and injected with the sodium ion battery electrolyte prepared above to obtain a 1.8Ah soft-pack battery.

[0035] In Examples 2 to 14 and Comparative Examples 1 to 10, only the formula of the electrolyte was changed, and sodium ion batteries were obtained by referring to the preparation method of Example 1. The electrolyte formula is shown in Table 1 below.

[0036] Table 1 Electrolyte formula

[0037]

[0038]

[0039] The batteries prepared in the above examples and comparative examples were subjected to high temperature cycle tests and high temperature shelf performance tests, respectively. The test results are shown in Table 1 below.

[0040] The test method is as follows:

[0041] (1) 45℃ high temperature cycle test

[0042] The battery volume in the empty state is tested and recorded as V1. At 45°C, the sodium ion batteries of Examples 1-8 and Comparative Examples 1-3 are respectively charged to 3.9V with a constant current and constant voltage of 0.5C and a cut-off current of 0.05C; then discharged to 2.0V with a constant current of 0.5C, and the discharge capacity Q0 is recorded as the initial discharge capacity. After 500 cycles according to the same charge and discharge mode while keeping the ambient temperature unchanged, record the 500th discharge capacity Q500, and the room temperature discharge capacity retention rate = Q500 / Q0*100%. After 500 cycles, the battery is taken out of the cabinet with no electricity, and the battery volume is tested again, recorded as V2. The formula for calculating the battery volume expansion rate after 500 cycles of charge and discharge is: W = (V2-V1) / V1*100%.

[0043] (2) 45℃ high temperature shelf performance test

[0044] At 25°C, the sodium ion batteries of Examples 1-8 and Comparative Examples 1-3 were respectively charged to 3.9V using a constant current and constant voltage charge of 0.2C, with a cutoff current of 0.05C; then discharged to 2.0V using a constant current of 0.2C, and the discharge capacity Q0 was recorded as the initial discharge capacity. Subsequently, the fully charged experimental battery was charged to 3.9V using a constant current and constant voltage charge of 0.2C, with a cutoff current of 0.05C. The fully charged experimental battery was then placed in a 60°C oven for 28 days. The experimental battery cell after high-temperature storage was removed and first discharged to 2.0V using a constant current of 0.2C, and the discharge capacity Q1 was recorded. The three experimental batteries were tested in parallel and the average value was taken. The high-temperature storage capacity retention rate = Q1 / Q0*100%.

[0045] Table 2 Battery sample test results

[0046]

[0047] From the comparison between the above embodiments and the comparative examples, it can be seen that, compared with the traditional additive PS, the combined additive of the present invention can greatly improve the high-temperature cycling and shelf performance, and inhibit the volume expansion during the high-temperature cycling process.

[0048] Combined with the data of Comparative Examples 3-6 and Comparative Examples 1-2, it is shown that the addition of component A alone can significantly inhibit volume expansion, and the effect is better than that of conventional additive PS, and the effect of additive A-1 is the most obvious; Combined with the data of Comparative Examples 7-10 and Comparative Examples 1-2, it is shown that the addition of component B alone can significantly improve the high cycle retention rate and high shelf retention rate and recovery rate, and additive B-4 has the best improvement effect; Combined with the data of Comparative Examples 3-6 and Examples 2 and 12-14, it is shown that the addition of component A and component B at the same time can not only further improve the high cycle and high shelf performance, but also inhibit the degree of battery volume expansion. It is also enhanced compared to adding component A alone; combined with the data of comparative examples 7-10 and embodiments 2, 9-11, it is shown that after adding component A on the basis of adding component B, not only the volume expansion of the battery is significantly suppressed, but the high cycle and high shelf performance are also improved, which proves that component A and component B synergistically stabilize the positive and negative electrode structures, participate in the formation of CEI film rich in S, Si, and F and construct a SEI film with an organic sodium sulfate-sodium sulfonate cross-linked structure, which not only suppresses the dissolution of positive electrode metal ions, but also reduces the interfacial impedance of the positive and negative electrodes, and improves the gas production and electrical performance of the battery in a high temperature environment.

[0049] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A sodium ion battery electrolyte additive, characterized in that The electrolyte additive includes a compound represented by Formula I and a compound represented by Formula II: ； Formula I In Formula I, R1 is a halogen atom, a C1~6 alkyl group or a C1~6 haloalkyl group, and R2~R4 are C1~6 alkyl groups; ； Formula II In formula II, R5 to R7 are independently selected from C1 to 6 alkyl, C6 to 12 an aryl or cyclic sulfate group; In the electrolyte additive, the mass ratio of the compound represented by Formula I to the compound represented by Formula II is 1:5 to 5:

1.

2. The sodium ion battery electrolyte additive according to claim 1, characterized in that The compound represented by formula I is selected from at least one of the following compounds A-1 to A-4: ； Compound A-1 Compound A-2 Compound A-3 Compound A-4; The compound represented by Formula II is selected from at least one of the following compounds B-1 to B-4: ； Compound B-1 Compound B-2 Compound B-3 Compound B-4.

3. The sodium ion battery electrolyte additive according to claim 1, characterized in that The compound represented by formula I is , the compound represented by formula II is .

4. A sodium ion battery electrolyte, characterized in that The electrolyte additive comprises the electrolyte additive according to any one of claims 1 to 3.

5. The sodium ion battery electrolyte according to claim 4, characterized in that The electrolyte additive accounts for 0.1-5% of the total mass of the electrolyte.

6. The sodium ion battery electrolyte according to claim 4, characterized in that Calculated by mass percentage, the components of the electrolyte include: 6-20% sodium salt, 0.1-5% of the electrolyte additive, 0.5-10% of other functional additives, and the balance being organic solvent.

7. The sodium ion battery electrolyte according to claim 6, characterized in that The other functional additives are selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, styrene carbonate, tris(trimethylsilyl)phosphoric acid, benzoic anhydride, and sulfolane.

8. A sodium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The electrolyte is the sodium ion battery electrolyte according to any one of claims 4 to 7.

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