Non-aqueous electrolyte and sodium-ion battery

Abstract

This invention provides a non-aqueous electrolyte and a sodium-ion battery. The non-aqueous electrolyte comprises a non-aqueous organic solvent, a sodium salt, and an additive, including compound I. Compound I contains a hydroxyl-containing cyclic ether bond. This structure is unstable and readily undergoes ring-opening reactions, enabling it to form a stable and uniform interfacial protective film on the surface of the cathode material at a relatively low oxidation potential. This suppresses the reaction between the electrolyte and the cathode material at high voltages, thereby improving the gas expansion problem of sodium-ion batteries and maintaining the stability of the electrode / electrolyte interface. Furthermore, this structure contains an imidazole-based nitrogen heterocycle. On one hand, the imidazole cation has high coulombic force, which is beneficial for improving the ion conduction performance of the interfacial protective film and increasing rate performance. On the other hand, it can complex with the sodium salt in the electrolyte, stabilizing its storage and reducing side reactions caused by electrolyte decomposition, thus improving the stability of the electrolyte itself.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a non-aqueous electrolyte and a sodium-ion battery. Background Technology

[0002] With the explosive growth of new energy vehicles, lithium prices have skyrocketed. The significant increase in the cost of lithium battery materials has put considerable pressure on the industry chain, ultimately limiting the development potential of lithium-ion batteries. From a resource perspective, lithium resources are becoming increasingly scarce, while sodium resources in the Earth's crust are 1353 times more abundant than lithium resources. Both belong to the same group and share similar physicochemical properties. Due to its abundant resources, low price, and environmental friendliness, sodium has broad application prospects in large-scale energy storage, electric vehicles, electric ships, and special engineering vehicles. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, mainly relying on the intercalation and deintercalation of sodium ions between the positive and negative electrodes. However, because sodium ions have a larger ionic radius than lithium ions, and the commonly used negative electrode material, hard carbon, has a large specific surface area and small interlayer spacing, sodium ions are difficult to deintercalate after insertion. Therefore, sodium ions are irreversibly consumed, leading to problems such as low initial efficiency and poor high-temperature storage performance in sodium-ion batteries.

[0003] Furthermore, the ideal SEI film formed by additives in the electrolyte should be electronically insulating and ionicly conductive, and should be insoluble and inert relative to the electrolyte to avoid irreversible capacity loss due to side reactions. Compared to lithium-ion batteries, the alkyl sodium and alkyl carbonate components in the SEI film formed in sodium-ion batteries typically have a solubility in carbonates that is 70 to 80 times higher than that of inorganic components such as NaF and Na2CO3. Moreover, the inorganic components NaF and Na2CO3 in Na-SEI films have a solubility that is 30 to 40 times higher than that in Li-SEI films. This leads to instability in the Na-SEI film, increased side reactions with the electrolyte, and consequently, reduced high-temperature storage and cycle performance degradation in sodium-ion batteries.

[0004] Therefore, improving the stability of sodium-ion batteries is a problem that the industry urgently needs to solve. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a non-aqueous electrolyte and a sodium-ion battery. The non-aqueous electrolyte contains additive compound I, which can form a stable and uniform interfacial protective film on the surface of the positive electrode material, thereby improving the stability of the electrode / electrolyte interface and reducing the occurrence of side reactions. It also has good interfacial reaction kinetics and better rate performance. In addition, it has flame retardant properties, which can further improve the safety performance of the electrolyte.

[0006] To achieve the above objectives, the first aspect of the present invention provides a non-aqueous electrolyte comprising a non-aqueous organic solvent, a sodium salt, and an additive, wherein the additive comprises compound I.

[0007]

[0008] The electrolyte additive used in this invention includes compound I, which contains a hydroxyl-containing cyclic ether bond. This structure is unstable and prone to ring-opening reactions, allowing it to form a stable and uniform interfacial protective film on the surface of the positive electrode material at a low oxidation potential. This suppresses the reaction between the electrolyte and the positive electrode material at high voltages, thereby improving the gas expansion problem of sodium-ion batteries and maintaining the stability of the electrode / electrolyte interface. Furthermore, this structure contains an imidazole-based nitrogen heterocycle. On one hand, the imidazole cation has high coulombic force, which is beneficial for improving the ion conduction performance of the interfacial protective film and increasing rate performance. On the other hand, it can complex with sodium salts in the electrolyte, stabilizing their storage and reducing side reactions caused by electrolyte decomposition, thus improving the stability of the electrolyte itself. Simultaneously, compound I contains a phosphate ester structure. Phosphorus can release phosphorus-containing free radicals, which can combine with hydrogen free radicals generated in the electrolyte, thereby blocking the chain reaction of free radicals. This makes the combustion process of the electrolyte impossible or difficult to occur, improving the flame retardant properties of the additive and further improving the safety performance of the electrolyte.

[0009] As one technical solution of the present invention, the sum of the masses of the non-aqueous organic solvent, the sodium salt and the additive is m, the mass of compound I is n, and n / m is 0.01 to 0.50%.

[0010] As one technical solution of the present invention, the sodium salt accounts for 6.5 to 15.5% of the total mass of the non-aqueous organic solvent, the sodium salt and the additive.

[0011] As a technical solution of the present invention, the sodium salt is a sodium salt selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalate-borate), sodium difluorophosphate, sodium di(oxalate-borate), sodium di(oxalate-difluorophosphate), and sodium bis(oxalate-imide).

[0012] As a technical solution of the present invention, the non-aqueous organic solvent is at least one of chain carbonate, cyclic carbonate and carboxylic acid ester.

[0013] As a technical solution of the present invention, the non-aqueous organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

[0014] A second aspect of this invention provides a sodium-ion battery, comprising a positive electrode material, a negative electrode material, and a non-aqueous electrolyte. This sodium-ion battery exhibits superior cycle life and high-temperature storage performance, which is beneficial for the further industrialization of sodium-ion batteries.

[0015] As a technical solution of the present invention, the positive electrode material is a layered oxide, and the chemical formula of the layered oxide is Na x M (1-y-z) Fe y Mn z O2, where M is 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, and y + z ≤ 1.

[0016] As a technical solution of the present invention, the negative electrode material is selected from at least one of carbon-based negative electrode materials, titanium-based oxide negative electrode materials, and alloy-based negative electrode materials. Detailed implementation manners

[0017] The present invention mainly provides a non-aqueous electrolyte for a sodium-ion battery. Of course, in addition to the non-aqueous electrolyte in the sodium-ion battery, it may also include a positive electrode material and a negative electrode material.

[0018] The positive electrode material can be a layered oxide, and the chemical formula of the layered oxide is Na x M (1-y-z) Fe y Mn z O2, where M is 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, and y + z ≤ 1. Of course, the positive electrode material can also be other materials that can undergo ion intercalation and deintercalation with sodium ions. The negative electrode material is selected from at least one of carbon-based negative electrode materials, titanium-based oxide negative electrode materials, and alloy-based negative electrode materials. Further, the negative electrode material can be selected from hard carbon, soft carbon, sodium titanate, Sb alloy, Sn alloy, potassium alloy, aluminum alloy, copper alloy, molybdenum alloy, etc. Among them, soft carbon can be graphitized into amorphous carbon at a high temperature above 2500 °C, and hard carbon is difficult to be graphitized even after high-temperature treatment, showing stronger sodium storage capacity and lower working potential.

[0019] The non-aqueous electrolyte of the present invention may include sodium salts, non-aqueous organic solvents, and additives.

[0020] The sodium salt comprises 6.5% to 15.5% of the sum of the non-aqueous organic solvent, sodium salt, and additives. Preferably, the sodium salt comprises 8.5% to 15.0%. As an example, the sodium salt proportion may be, but is not limited to, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, 13.0%, 13.5%, 14.0%, 14.5%, 15.0%, or 15.5%. The sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(trifluoromethanesulfonyl)imide (NaN(CF3SO2)2), sodium bis(oxalate)borate (C4BLiO8), sodium difluorophosphate (NaPO2F2), sodium di(oxalate)borate (C2BF2NaO4), sodium di(oxalate)phosphate (NaDFBP), and sodium bis(oxalate)imide (NaFSI).

[0021] The non-aqueous organic solvent accounts for more than 80%, preferably more than 85%, of the total mass of the non-aqueous organic solvent, sodium salt, and additives. The non-aqueous organic solvent is at least one selected from chain carbonates, cyclic carbonates, and carboxylic acid esters. Preferably, the non-aqueous organic solvent is a mixture of chain carbonates and cyclic carbonates. As an example, the non-aqueous organic solvent is selected from at least one selected from 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 is a combination of ethylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) to achieve more stable cycling performance.

[0022] Additives may include compound I.

[0023]

[0024]

[0025] CAS: 14999-52-1

[0026] Compound I comprises 0.01 to 0.50% of the total mass of the non-aqueous organic solvent, sodium salt, and additives. Preferably, compound I comprises 0.02 to 0.10% of the total mass of the non-aqueous organic solvent, sodium salt, and additives. As examples, the proportion of compound I may be, but is not limited to, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.08%, 0.10%, 0.20%, 0.30%, 0.40%, and 0.50%.

[0027] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0028] Where specific conditions are not specified in the examples, they can be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available standard products.

[0029] Example 1

[0030] (1) Preparation of non-aqueous electrolyte: The electrolyte was prepared in a vacuum glove box with a moisture content of <1ppm under an argon atmosphere. In a dry argon atmosphere glove box, propylene carbonate PC, ethyl methyl carbonate EMC and diethyl carbonate DEC were mixed in a weight ratio of PC:EMC:DEC = 4:4:2. Then, compound I was added, dissolved and stirred thoroughly, and sodium hexafluorophosphate was added. After mixing evenly, the electrolyte was obtained.

[0031] (2) Preparation of the positive electrode: The ternary material NaNi cobalt aluminate is prepared by... 1 / 3 Fe 1. / 3 Mn 1 / 3 O2, binder PVDF and conductive agent SuperP are mixed evenly in a mass ratio of 95:1:4 to prepare a sodium-ion battery positive electrode slurry of a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried and rolled to obtain the positive electrode sheet.

[0032] (3) Preparation of negative electrode: Hard carbon, conductive agent SuperP, thickener CMC and binder SBR (styrene-butadiene rubber emulsion) are mixed in a mass ratio of 95:1.5:1.0:2.5 to make a slurry. After mixing evenly, the mixed slurry is coated on both sides of copper foil, dried and rolled to obtain negative electrode sheet.

[0033] (4) Preparation of sodium-ion battery: The positive electrode, separator and negative electrode are stacked to form a square cell, which is packaged with polymer and filled with the sodium-ion battery non-aqueous electrolyte prepared above. After formation, capacity testing and other processes, a sodium-ion battery with a capacity of 1000mAh is made.

[0034] The electrolyte formulations of Examples 1-7 and Comparative Example 1 are shown in Table 1. The steps for preparing the electrolyte and manufacturing the battery in Examples 2-7 and Comparative Example 1 are the same as in Example 1.

[0035] Table 1 Electrolyte components of each embodiment and comparative example

[0036]

[0037] The sodium-ion batteries prepared in Examples 1-7 and Comparative Example 1 were subjected to rate performance tests, high-temperature cycle tests, and safety tests, respectively. The specific test conditions are as follows, and the test results are shown in Table 2.

[0038] (1) Rate performance test of sodium-ion batteries

[0039] At room temperature (25℃), the sodium-ion battery was charged at a constant current of 0.5C to 4.0V and discharged at a constant current of 0.5C to 2.0V, for 5 cycles. After the cycle, the sodium-ion battery was allowed to rest for 10 minutes. Then, the sodium-ion battery was charged at a constant current of 1C to 4.0V and discharged at a constant current of 1C to 2.0V, for 5 cycles. After the cycle, the sodium-ion battery was allowed to rest for 10 minutes, and then charged at a constant current of 3C to 4.0V and discharged at a constant current of 3C to 2.0V, for 5 cycles.

[0040] (2) High-temperature cycling test of sodium-ion battery

[0041] The sodium-ion battery was placed in a 45°C constant temperature chamber and allowed to stand for 30 minutes to reach a constant temperature. It was then charged at a constant current of 1C until the voltage reached 4.0V, followed by a constant voltage charge of 4.0V until the current reached 0.05C. Finally, it was discharged at a constant current of 1C until the voltage reached 2.0V. The first discharge capacity was recorded. This constitutes one charge-discharge cycle. This cycle was repeated 400 times, recording the discharge capacity of the first and last cycles. The capacity retention rate was calculated using the following formula.

[0042] Capacity retention rate = (Discharge capacity in the last cycle / Discharge capacity in the first cycle) × 100%

[0043] (3) Safety performance test of sodium-ion batteries

[0044] Place the sodium-ion battery in a 60°C oven and heat it to 60°C at a heating rate of 5°C / min. Maintain the temperature at 60°C for 30 minutes. Charge the sodium-ion battery with a 1C constant current and constant voltage, with an upper limit voltage of 10V. Observe whether the battery exhibits severe bulging, smoke, fire, or explosion.

[0045] Table 2 Performance test results of sodium-ion batteries

[0046]

[0047] As shown in Table 2, based on Comparative Example 1, the sodium-ion batteries in Examples 1-7 exhibit better rate performance. This is because the electrolytes in Examples 1-7 contain Compound I as an additive. Compound I contains an imidazole nitrogen heterocycle in its structure. The imidazole cation has high coulombic force, which is beneficial for improving the ion conduction performance of the interfacial protective film, thereby improving the rate performance of the sodium-ion battery.

[0048] Similarly, based on the results in Table 2, the sodium-ion batteries in Examples 1-7 exhibit better high-temperature cycling performance than Comparative Example 1. This is because Compound I in the sodium-ion batteries of Examples 1-7 contains a hydroxyl-containing cyclic ether bond. This structure is unstable and prone to ring-opening reactions, allowing it to form a stable and uniform interfacial protective film on the surface of the cathode material at a lower oxidation potential. This suppresses the reaction between the electrolyte and the cathode material at high voltage, maintaining the stability of the electrode / electrolyte interface. Simultaneously, the imidazole cation can complex with commonly used sodium salts in the electrolyte, stabilizing its storage and reducing battery side reactions caused by electrolyte decomposition, thus improving the stability of the electrolyte itself. Therefore, it can still maintain better cycling performance under high-temperature cycling.

[0049] Based on the results in Table 2, the sodium-ion batteries in Examples 1-7 exhibit better safety performance than Comparative Example 1. This is because Compound I in the sodium-ion batteries of Examples 1-7 contains a phosphate ester structure. Phosphorus can release phosphorus-containing free radicals, which can combine with hydrogen free radicals generated by the electrolyte, thereby blocking the chain reaction of free radicals. This makes the combustion process of the electrolyte impossible or difficult to occur, improving the flame retardant properties of the additives and further enhancing the safety performance of the electrolyte.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A non-aqueous electrolyte, comprising a non-aqueous organic solvent, a sodium salt, and an additive, characterized in that, The additive includes compound I.

2. The non-aqueous electrolyte according to claim 1, characterized in that, The sum of the masses of the non-aqueous organic solvent, the sodium salt, and the additive is m, the mass of compound I is n, and n / m is 0.01 to 0.50%.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The sodium salt accounts for 6.5 to 15.5% of the total mass of the non-aqueous organic solvent, the sodium salt, and the additive.

4. The non-aqueous electrolyte according to claim 3, characterized in that, The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalate-borate), sodium difluorophosphate, sodium di(oxalate-borate), sodium di(oxalate-difluorophosphate), and sodium bis(oxalate-imide).

5. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is at least one of chain carbonates, cyclic carbonates, and carboxylic acid esters.

6. The non-aqueous electrolyte according to claim 5, characterized in that, The non-aqueous organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

7. A sodium-ion battery, comprising a positive electrode material, a negative electrode material, and a non-aqueous electrolyte according to any one of claims 1 to 6.

8. The sodium-ion battery according to claim 7, characterized in that, The positive electrode material 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 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。 9. The sodium-ion battery according to claim 7, characterized in that, The negative electrode material is selected from at least one of carbon-based negative electrode materials, titanium-based oxide negative electrode materials, and alloy-based negative electrode materials.

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