Non-aqueous electrolyte and sodium ion battery

Abstract

The invention discloses a non-aqueous electrolyte and a sodium ion battery, the non-aqueous electrolyte comprises a sodium salt, a non-aqueous organic solvent and an additive, the additive comprises a compound A as shown in a structural formula 1: # imgabs0 #, and R1-R6 are respectively and independently selected from hydrogen, alkyl or aryl. The non-aqueous electrolyte disclosed by the invention can keep the stability of a negative solid electrolyte membrane (SEI) and a positive solid electrolyte membrane (CEI) at high temperature and high pressure, and also can optimize the interface contact between the electrolyte and an electrode and improve the oxidation resistance of the electrolyte at the membrane; therefore, the sodium ion battery provided by the invention has good high-temperature cycle performance and safety performance under high voltage of 4.2 V.

Description

Technical Field

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

[0002] At present, sodium-ion secondary battery technology is experiencing a rapid development momentum. It has not only achieved a series of important breakthroughs in technological innovation, but also achieved a significant expansion in the scope of application, which has effectively promoted its transformation from theoretical research to commercial practice and has become a highly competitive alternative in the field of lithium-ion batteries. At the technical level, sodium-ion batteries have made significant progress in positive and negative electrode materials, electrolytes, and battery structures. The research on positive electrode materials has gradually expanded from early sodium metal oxides to multi-composite materials and nanostructured materials, effectively improving the energy density and cycle life of batteries; at the same time, the optimization of electrolytes has also provided strong support for the performance improvement of sodium-ion batteries; at the application level, sodium-ion batteries have gradually expanded from energy storage systems to diversified fields such as electric vehicles, power tools, and mobile devices, showing broad market prospects.

[0003] However, sodium-ion batteries still face many technical challenges under high-temperature cycling and storage conditions. On the one hand, high temperature environments accelerate the rate of chemical reactions inside the battery, which may lead to structural changes and capacity loss of electrode materials, thus affecting the cycle stability and service life of sodium-ion batteries; on the other hand, the performance of the electrolyte will also change under high temperature environments, such as volatilization, decomposition, or reduced conductivity, which will affect the safety and cycle performance of the battery.

[0004] Therefore, it is urgent to develop non-aqueous electrolytes suitable for sodium-ion batteries. Summary of the invention

[0005] In view of the above problems, an object of the present invention is to provide a non-aqueous electrolyte and a sodium ion battery, wherein the non-aqueous electrolyte can improve the high temperature cycle performance and safety performance of the sodium ion battery.

[0006] To achieve the above objectives, the first aspect of the present invention provides a non-aqueous electrolyte, comprising a sodium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises a compound A shown in structural formula 1:

[0007]

[0008] Wherein, R1 to R6 are each independently selected from hydrogen, alkyl or aryl.

[0009] Compared with the prior art, the non-aqueous electrolyte of the present invention uses compound A shown in structural formula 1 as an additive. Compound A shown in structural formula 1 has relatively high stability under high temperature and high pressure, so that it can effectively inhibit the continuous decomposition of the negative electrode solid electrolyte membrane (SEI) under high temperature and high pressure, thereby significantly reducing the gas production problem caused by repeated loss of the solid electrolyte membrane, thereby ensuring the high temperature cycle performance and safety performance of the sodium ion battery; at the same time, the azo structure in compound A can be preferentially reduced to form a thin and dense positive electrode solid electrolyte interface film (CEI), improve the stability of CEI, and can more effectively isolate the electrolyte from the active material, prevent unnecessary side reactions, and further ensure the high temperature cycle performance of the sodium ion battery; and the sulfonyl group in compound A can be relatively neatly arranged between the electrolyte and the electrode under the effect of affinity difference, optimize the interface contact between the electrolyte and the electrode and improve the antioxidant performance of the electrolyte at the membrane, thereby further ensuring the high temperature cycle performance and safety performance of the sodium ion battery. Therefore, the non-aqueous electrolyte of the present invention can improve the high temperature cycle performance and safety performance of the sodium ion battery.

[0010] Furthermore, R1 to R6 of the present invention are each independently selected from hydrogen, C1 to C5 alkyl or phenyl.

[0011] Further, the compound A of the present invention is selected from at least one of compound 1, compound 2 and compound 3:

[0012]

[0013] Specifically, the CAS number of compound 1 is: 554-73-4; the CAS number of compound 2 is: 547-58-0; and the CAS number of compound 3 is: 2491-71-6.

[0014] Further, the mass percentage of the additive of the present invention in the non-aqueous electrolyte is 0.01-0.5%. Preferably, the mass percentage of the additive of the present invention in the non-aqueous electrolyte is 0.05-0.5%. Specifically, the mass percentage of the additive in the non-aqueous electrolyte may be, but is not limited to, 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, 0.33%, 0.36%, 0.38%, 0.41%, 0.44%, 0.46%, 0.48%, 0.5%.

[0015] Further, the mass percentage of the sodium salt of the present invention in the non-aqueous electrolyte is 6.5-15.5%. Preferably, the mass percentage of the sodium salt in the non-aqueous electrolyte is 9-15.5%. Specifically, the mass percentage of the sodium salt in the non-aqueous electrolyte may be, but is not limited to, 6.5%, 6.8%, 7%, 7.5%, 7.7%, 7.9%, 8%, 8.4%, 8.8%, 9.3%, 9.7%, 9.9%, 10%, 10.4%, 10.7%, 10.9%, 11.1%, 11.4%, 11.7%, 11.9%, 12.2%, 12.4%, 12.7%, 12.9%, 13%, 13.4%, 13.7%, 13.9%, 14.2%, 14.4%, 14.8%, 15.1%, 15.5%.

[0016] Further, the sodium salt of the present invention is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium bistrifluoromethanesulfonyl imide (NaN(CF3SO2)2), sodium bisoxalate borate (C4BNaO8), sodium difluorophosphate (NaPO2F2), sodium difluorooxalate borate (C2BF2NaO4), sodium difluorobisoxalate phosphate (NaDFBP) and sodium bisfluorosulfonyl imide (NaFSI). Preferably, the sodium salt of the present invention is selected from sodium hexafluorophosphate (NaPF6) or sodium bisfluorosulfonyl imide (NaFSI).

[0017] Further, the non-aqueous organic solvent of the present invention is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), propyl propionate (n-Pp), ethyl propionate (EP) and ethyl butyrate (Eb). Preferably, the non-aqueous organic solvent includes a combination of propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) to achieve a more stable cycle performance. Specifically, the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolyte is 80% or more, preferably 85% or more.

[0018] Correspondingly, the second aspect of the present invention also provides a sodium ion battery, comprising a positive electrode and a negative electrode, and also comprising the non-aqueous electrolyte mentioned above, and the maximum charging voltage is 4.2V.

[0019] Compared with the prior art, the non-aqueous electrolyte is combined with the positive electrode and the negative electrode to form a battery. The non-aqueous electrolyte can maintain the stability of the negative electrode solid electrolyte membrane (SEI) and the positive electrode solid electrolyte interface membrane (CEI) under high temperature and high pressure, and can also optimize the interface contact between the electrolyte and the electrode and improve the antioxidant performance of the electrolyte at the membrane. Therefore, the sodium ion battery of the present invention has good high-temperature cycle performance and safety performance at a high voltage of 4.2V.

[0020] Furthermore, the active material of the positive electrode of the present invention is a layered oxide, and the chemical formula of the layered oxide is Na x M 1-y-z Fe y Mn z O2, wherein M is independently selected from at least one of Co, Ni, Cu, Mg, Zn, Al, Sn, Ga, Cr, Sr, V and Ti, 0 <x≤1,0≤y≤1,0≤z≤1,y+z≤1。

[0021] Furthermore, the active material of the negative electrode of the present invention is selected from soft carbon, hard carbon, sodium titanate, FeS x , Cu x O, MoS2, Sn x O. CoS x At least one of Fe2O3, Fe3O4, ZnS, Sb, and SbSn. Soft carbon is an amorphous carbon that can be graphitized at a high temperature of more than 2500°C. In contrast, hard carbon is difficult to graphitize even under similar high temperature conditions, thereby showing a stronger sodium storage capacity and a lower working potential. Therefore, the negative electrode material is preferably hard carbon. DETAILED DESCRIPTION

[0022] The purpose, technical scheme and beneficial effects of the present invention are further illustrated by specific examples below, but do not constitute any limitation to the present invention. If specific conditions are not specified in the examples, they can be carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products available on the market.

[0023] Example 1

[0024] Preparation of non-aqueous electrolyte:

[0025] A non-aqueous electrolyte was prepared in a vacuum glove box with an argon atmosphere and a moisture content of <1ppm. In a dry argon atmosphere glove box, propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a weight ratio of PC:EC:EMC:DEC=4:2:3:1 to obtain 87g of a non-aqueous organic solvent, followed by adding 0.05g of compound 1, dissolving and stirring thoroughly, then adding 12.95g of sodium salt, and mixing well to obtain a non-aqueous electrolyte.

[0026] Preparation of positive electrode:

[0027] The ternary material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:1:4 to form a sodium ion battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0028] Preparation of negative electrode:

[0029] Hard carbon, conductive agent SuperP, thickener CMC, and adhesive SBR (styrene-butadiene rubber latex) are made into slurry in a mass ratio of 95:1.5:1.0:2.5, mixed evenly, and the mixed slurry is coated on both sides of the copper foil, and then dried and rolled to obtain a negative electrode sheet.

[0030] Preparation of sodium ion batteries:

[0031] The positive electrode sheet, the separator and the negative electrode sheet are stacked to form a square battery cell, which is packaged with a polymer and filled with the prepared sodium ion battery non-aqueous electrolyte. After the processes of formation and capacity division, a sodium ion battery with a capacity of 1000 mAh is manufactured.

[0032] The components and contents of the non-aqueous electrolytes of Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 1, wherein the preparation processes of the non-aqueous electrolytes, positive electrode sheets, negative electrode sheets, and sodium ion batteries of Examples 2 to 6 and Comparative Examples 1 to 2 are the same as those of Example 1.

[0033] Table 1 Non-aqueous electrolyte components of Examples and Comparative Examples

[0034] Group Non-aqueous organic solvent / mass (g) Sodium salt / mass (g) Additives(g) Example 1 PC / EC / EMC / DEC=4:2:3:1(87g) <![CDATA[NaPF6(12.95g)]]> Compound 1 (0.05 g) Example 2 PC / EC / EMC / DEC=4:2:3:1(87g) <![CDATA[NaPF6(12.95g)]]> Compound 2 (0.05 g) Example 3 PC / EC / EMC / DEC=4:2:3:1(87g) <![CDATA[NaPF6(12.95g)]]> Compound 3 (0.05 g) Example 4 PC / EC / EMC / DEC=4:2:3:1(87g) <![CDATA[NaPF6(12.9g)]]> Compound 3 (0.1 g) Example 5 PC / EC / EMC / DEC=4:2:3:1(87g) <![CDATA[NaPF6(12.5g)]]> Compound 3 (0.5 g) Example 6 EP / EC / EMC / DEC=5:2:3:1(86g) NaFSI (13.8 g) Compound 1 (0.2 g) Comparative Example 1 PC / EC / EMC / DEC=4:2:3:1(87g) <![CDATA[NaPF6(13g)]]> / Comparative Example 2 PC / EC / EMC / DEC=4:2:3:1(87g) <![CDATA[NaPF6(12.95g)]]> Compound 4 (0.05 g)

[0035] The structure of compound 4 (CAS: 1936-15-8) is shown below:

[0036]

[0037] The sodium ion batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were subjected to high temperature cycle tests, high temperature storage performance tests, and safety performance tests, respectively. The test results are shown in Table 2.

[0038] High temperature cycle performance test:

[0039] Place the sodium ion battery in a 45℃ constant temperature box and let it stand for 30 minutes to allow the sodium ion battery to reach a constant temperature. Charge at a constant current of 1C to a voltage of 4.2V, then charge at a constant voltage of 4.2V to a current of 0.05C, then discharge at a constant current of 1C to a voltage of 2.5V, and record the first cycle discharge capacity of the battery. This is a charge and discharge cycle. Repeat this cycle for 400 weeks, record the discharge capacity of the first cycle and the discharge capacity of the last cycle, and calculate the capacity retention rate according to the following formula.

[0040] Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%

[0041] High temperature storage performance test:

[0042] At room temperature (25°C), the sodium ion battery was charged and discharged at 0.5C / 0.5C (the battery discharge capacity was recorded as C0), and the upper limit voltage was 4.20V; the battery was placed in a 60°C oven for 30 days, the battery was taken out, and the battery was placed in a 25°C environment for 0.5C discharge, and the discharge capacity was recorded as C1; then the sodium ion battery was charged and discharged at 0.5C / 0.5C (the battery discharge capacity was recorded as C2), and the capacity retention rate and capacity recovery rate of the sodium ion battery were calculated using the following formula.

[0043] Capacity retention rate = (C1 / C0) · 100%

[0044] Capacity recovery rate = (C2 / C0) · 100%

[0045] Safety performance test:

[0046] Place the sodium ion battery in a 60°C oven, heat to 60°C at a heating rate of 5°C / min, and maintain at 60°C for 30 minutes. Perform 1C constant current and constant voltage charging on the sodium ion battery with an upper limit voltage of 10V, and observe whether the battery has serious bulging, smoking, fire, explosion, etc.

[0047] Table 2 Sodium ion battery performance test results

[0048]

[0049] It can be seen from the results in Table 2 that, compared with Comparative Example 1, the sodium ion batteries of Examples 1 to 6 have better high-temperature storage, high-temperature cycle performance and safety performance. This is because the non-aqueous electrolyte of the present invention uses compound A shown in structural formula 1 as an additive, and compound A shown in structural formula 1 has relatively high stability under high temperature and high pressure, so that it can effectively inhibit the continuous decomposition of the negative electrode solid electrolyte membrane (SEI) under high temperature and high pressure, thereby significantly reducing the gas production problem caused by repeated loss of the solid electrolyte membrane, thereby ensuring the high temperature cycle performance and safety performance of the sodium ion battery; at the same time, the azo structure in compound A can be preferentially reduced to form a thin and dense positive electrode solid electrolyte interface film (CEI), improve the stability of CEI, and can more effectively isolate the electrolyte from the active material, prevent unnecessary side reactions, and further ensure the high temperature cycle performance of the sodium ion battery; and the sulfonyl group in compound A can be relatively neatly arranged between the electrolyte and the electrode under the action of affinity difference, optimize the interface contact between the electrolyte and the electrode and improve the antioxidant performance of the electrolyte at the membrane, thereby further ensuring the high temperature cycle performance and safety performance of the sodium ion battery.

[0050] Comparing Examples 1 to 3 with Comparative Example 2, it can be seen that although Compound 4 also contains a sulfonyl group and an azo structure, it cannot significantly improve the high temperature cycle performance and safety performance of the sodium ion battery. This is because Compound 4 is not very stable under high temperature and high pressure, and the solid electrolyte membrane formed by it is prone to multiple decomposition and consumption, thereby affecting the high temperature cycle performance and safety performance of the sodium ion battery.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A non-aqueous electrolyte comprising a sodium salt, a non-aqueous organic solvent and an additive, characterized in that: The additive includes compound A shown in structural formula 1: Wherein, R1 to R6 are each independently selected from hydrogen, alkyl or aryl.

2. The non-aqueous electrolyte according to claim 1, characterized in that R1 to R6 are each independently selected from hydrogen, C1 to C5 alkyl or phenyl.

3. The non-aqueous electrolyte according to claim 1, characterized in that The compound A is selected from at least one of compound 1, compound 2 and compound 3:

4. The non-aqueous electrolyte according to claim 1, characterized in that The mass percentage of the additive in the non-aqueous electrolyte is 0.01-0.5%.

5. The non-aqueous electrolyte according to claim 1, characterized in that The mass percentage of the sodium salt in the non-aqueous electrolyte is 6.5-15.5%.

6. The non-aqueous electrolyte according to claim 1, characterized in that The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium bistrifluoromethanesulfonyl imide, sodium bisoxalatoborate, sodium difluorophosphate, sodium difluorooxalatoborate, sodium difluorobisoxalatophosphate and sodium bisfluorosulfonyl imide.

7. The non-aqueous electrolyte according to claim 1, characterized in that The non-aqueous organic solvent is at least one selected from ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate and ethyl butyrate.

8. A sodium ion battery comprising a positive electrode and a negative electrode, characterized in that: It also includes the non-aqueous electrolyte as claimed in any one of claims 1 to 7, and the maximum charging voltage is 4.2V.

9. The sodium ion battery according to claim 8, characterized in that The active material of the positive electrode is a layered oxide, and the chemical formula of the layered oxide is Na x M 1-y-z Fe y Mn z O2, wherein M is independently selected from at least one of Co, Ni, Cu, Mg, Zn, Al, Sn, Ga, Cr, Sr, V and Ti, 0 <x≤1,0≤y≤1,0≤z≤1,y+z≤1。 10. The sodium ion battery according to claim 8, characterized in that The active material of the negative electrode is selected from soft carbon, hard carbon, sodium titanate, FeS x , Cu x O, MoS2, Sn x O. CoS x , Fe2O3, Fe3O4, ZnS, Sb, and SbSn.

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