Non-aqueous electrolyte and sodium-ion battery

Abstract

The application provides a nonaqueous electrolyte and a sodium ion battery. The nonaqueous electrolyte comprises a nonaqueous organic solvent, a sodium salt and an additive, and the additive comprises compound 1. Compound 1 is a sodium phosphate salt compound, contains a structure of three carbon-nitrogen single bonds, has strong alkalinity and is easy to hydrolyze to generate an organic amine compound by reacting with water, and the organic amine can continue to react with free acid in the nonaqueous electrolyte to generate a neutral inorganic salt, so that more effective water removal and acid removal effects are achieved, thereby reducing the side reaction of the nonaqueous electrolyte and protecting the positive electrode material of the sodium ion battery, and the stability of the whole battery system is improved. The sodium phosphate salt compound supplements the sodium ions consumed in the step of the first formation process to form a solid electrolyte membrane, and the invalid sodium ions that are embedded in the negative electrode and cannot be removed in the subsequent cycle process, so that the energy density and the first coulomb efficiency of the sodium ion battery are significantly improved.

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] In the periodic table, sodium and lithium belong to the same group and have very similar physicochemical properties. Furthermore, their battery operating principles are similar; sodium-ion batteries primarily rely on the insertion and extraction of sodium ions between the positive and negative electrodes. During charging, Na... + It deintercalates from the positive electrode and enters the negative electrode; during discharge, Na... + From the negative electrode back to the positive electrode, electrons in the external circuit move from the negative electrode to the positive electrode, carrying Na... + It is reduced to Na.

[0003] Meanwhile, compared to lithium-ion batteries, sodium ions have a lower solvation energy, better interfacial ion diffusion, and a smaller Stokes diameter. Sodium ions also exhibit higher ionic conductivity than lithium salt electrolytes at the same concentration. This allows for the use of lower concentration electrolytes (sodium salt electrolytes have approximately 20% higher conductivity than lithium electrolytes at the same concentration) to reduce costs. Sodium-ion batteries also offer superior high and low temperature performance and better safety. While their internal resistance is slightly higher than lithium-ion batteries, they generate less heat and experience a lower temperature rise during short circuits. Furthermore, lithium resources are becoming increasingly scarce, while sodium resources are 1353 times more abundant in the Earth's crust than lithium resources.

[0004] Therefore, as the new energy vehicle market entered a period of explosive growth, lithium ore prices skyrocketed. The significant increase in the cost of lithium battery materials put considerable pressure on the industry chain, ultimately limiting the development potential of lithium-ion batteries. In contrast, sodium, with its abundant resources, low price, and environmental friendliness, has broad application prospects in large-scale energy storage, electric vehicles, electric ships, and special engineering vehicles.

[0005] However, due to the larger ionic radius of sodium ions compared to lithium ions, and the large specific surface area and small interlayer spacing of commonly used anode materials like hard carbon, sodium ions are difficult to detach after insertion, resulting in irreversible consumption and consequently, low initial coulombic efficiency in sodium-ion batteries. Furthermore, compared to lithium-ion batteries, the solubility of alkyl sodium and alkyl carbonates in the SE1 film formed in sodium-ion batteries in carbonates is typically 70-80 times higher than that of inorganic components such as NaF and Na2CO3. Moreover, the solubility of inorganic components NaF and Na2CO3 in the Na-SE1 film is 30-40 times higher than that of inorganic components L1F and L12CO3 in the L1-SE1 film. This leads to instability in the Na-SE1 film and increased side reactions with the electrolyte, resulting in poor high-temperature storage and reduced cycle performance of sodium-ion batteries.

[0006] Therefore, improving the initial coulombic efficiency and reducing side reactions of sodium-ion batteries are urgent problems that the industry needs to solve. Summary of the Invention

[0007] In view of the above problems, the purpose of the present invention is to provide a non-aqueous electrolyte and a sodium-ion battery. The non-aqueous electrolyte contains an additive compound 1 that can be used as an additive to supplement sodium ions to compensate for the initial capacity loss of the battery. This can effectively solve the problem of low initial coulombic efficiency, improve the capacity and stability of the battery, and also improve the safety performance of the sodium-ion battery.

[0008] 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 1.

[0009]

[0010] The electrolyte additive used in this invention includes Compound 1, a sodium phosphate salt compound containing three carbon-nitrogen single bonds. It exhibits strong alkalinity and readily undergoes hydrolysis with water to generate organic amine compounds. These organic amines can further react with free acids in the non-aqueous electrolyte to form neutral inorganic salts, thus achieving more effective dehydration and deacidification. This reduces side reactions in the non-aqueous electrolyte, protects the positive electrode material of the sodium-ion battery, and improves the overall stability of the battery system, contributing to enhanced cycle performance. This sodium phosphate salt compound replenishes the sodium ions consumed in the initial formation process during solid electrolyte membrane formation, as well as the sodium ions that are embedded in the negative electrode and cannot be extracted during subsequent cycles, significantly improving the energy density and initial coulombic efficiency of the sodium-ion battery. Furthermore, the introduction of phosphate groups into Compound 1 gives it excellent flame-retardant properties, improving the safety performance of the sodium-ion battery.

[0011] 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 1 is n, and n / m is 0.01% to 1.00%. As examples, n / m 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%, 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, or 1.00%.

[0012] As a technical solution of the present invention, the sodium salt accounts for 6-15% of the sum of the mass of the non-aqueous organic solvent, the sodium salt, and the additive. Preferably, the sodium salt accounts for 8-15%. As an example, the sodium salt percentage may be, but is not limited to, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. The sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium difluorophosphate (NaPO2F2), sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(trifluoromethanesulfonyl)imide (NaN(CF3SO2)2), sodium bis(oxalateborate)borate (C4BL1O8), sodium difluorooxalateborate (C2BF2NaO4), sodium difluorodioxalate phosphate (NaDFBP), and sodium bis(oxalateborate)imide (NaFS1).

[0013] As a technical solution of the present invention, 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). The non-aqueous organic solvent accounts for more than 80% of the total mass of the non-aqueous organic solvent, sodium salt, and additives, preferably more than 85%. As an example, the non-aqueous organic solvent may, but is not limited to, account for more than 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90% of the total mass of the non-aqueous organic solvent, sodium salt, and additives.

[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 one 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, 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。

[0016] As one 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-type negative electrode materials.

[0017] As one technical solution of the present invention, the negative electrode material can be selected from at least one of hard carbon, soft carbon, sodium titanate, Sb alloy, Sn alloy, potassium alloy, aluminum alloy, copper alloy and molybdenum alloy. Detailed Implementation

[0018] 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.

[0019] 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.

[0020] Example 1

[0021] (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, ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) were mixed in a weight ratio of EC:DEC:PC = 1:1:1. Then, compound 1 was added, dissolved, and stirred thoroughly. Sodium hexafluorophosphate was then added and mixed evenly to obtain the electrolyte.

[0022] (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 96:2:3 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.

[0023] (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 96:1:1:2 to form a slurry. The mixture is then coated on both sides of copper foil, dried and rolled to obtain the negative electrode sheet.

[0024] (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 1400mAh is made.

[0025] The electrolyte formulations of Examples 1-6 and Comparative Example 1 are shown in Table 1. The steps for preparing the electrolyte and manufacturing the battery in Examples 2-6 and Comparative Example 1 are the same as in Example 1.

[0026] Table 1 Electrolyte components of each embodiment and comparative example

[0027] Group Non-aqueous organic solvents / mass (g) Sodium salt / mass (g) <![CDATA[ Additives (g) ]]> Example 1 EC:DEC:PC = 1:1:1 (87.49g) <![CDATA[NaPF6(12.5g)]]> Compound 1 (0.01g) Example 2 EC:DEC:PC = 1:1:1 (87.45g) <![CDATA[NaPF6(12.5g)]]> Compound 1 (0.05g) Example 3 EC:DEC:PC = 1:1:1 (87.4g) <![CDATA[NaPF6(12.5g)]]> Compound 1 (0.1g) Example 4 EC:DEC:PC = 1:1:1 (87.0g) <![CDATA[NaPF6(12.5g)]]> Compound 1 (0.5g) Example 5 EC:DEC:PC = 1:1:1 (86.5g) <![CDATA[NaPF6(12.5g)]]> Compound 1 (1.0g) Example 6 PC / EMC / DEC = 1:2:1 (87.0g) <![CDATA[NaPF6(7.7g)+NaFSI(4.3g)]]> Compound 1 (1.0g) Comparative Example 1 EC:DEC:PC = 1:1:1 (87.5g) <![CDATA[NaPF6(12.5g)]]> /

[0028] The sodium-ion batteries prepared in Examples 1-6 and Comparative Example 1 were subjected to initial efficiency 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.

[0029] (1) Initial efficiency test of sodium-ion battery

[0030] At room temperature (25℃), the sodium-ion battery was charged to 3.2V with a constant current of 0.1C for 60 minutes, then charged to 3.2V with a constant current of 0.2C for 120 minutes, with a charging capacity of C1+C2. After the formation was completed, the battery was sealed again. Then it was charged to 4.0V with a constant current of 0.5C, with a charging capacity of C3. Finally, it was discharged to 2.0V with a constant current of 0.5C, with a discharge capacity of C4. This process was repeated for 3 cycles. After the cycle, the sodium-ion battery was left to stand for 10 minutes.

[0031] First-time efficiency = C4 / (C1+C2+C3)×100%

[0032] (2) High-temperature cycling test of sodium-ion battery

[0033] 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.

[0034] Capacity retention rate = (Discharge capacity in the last cycle / Discharge capacity in the first cycle) × 100%

[0035] (3) Safety performance test of sodium-ion batteries

[0036] 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.

[0037] Table 2 Performance test results of sodium-ion batteries

[0038]

[0039] As shown in Table 2, based on Comparative Example 1, the sodium-ion batteries in Examples 1-6 exhibited higher initial coulombic efficiency. This is because the electrolytes in Examples 1-6 included Compound 1 as an additive. Compound 1 replenished the sodium ions consumed in forming the solid electrolyte membrane during the initial formation process, thus improving the initial coulombic efficiency of the sodium-ion batteries.

[0040] Similarly, based on the results in Table 2, the sodium-ion batteries in Examples 1-6 exhibited higher capacity retention after 400 cycles at 45°C and 1C, and their high-temperature cycling performance was superior to that of Comparative Example 1. This is because Compound 1 contained in the sodium-ion batteries in Examples 1-6 has a structure with three carbon-nitrogen single bonds, exhibits strong alkalinity, and readily undergoes hydrolysis with water to generate organic amine compounds. These organic amines can further react with free acids in the non-aqueous electrolyte to generate neutral inorganic salts, thereby achieving more effective dehydration and deacidification. This reduces side reactions in the non-aqueous electrolyte, protects the positive electrode material of the sodium-ion battery, and improves the stability of the entire battery system, thus contributing to improved cycle performance.

[0041] Based on the results in Table 2, the sodium-ion batteries in Examples 1-6 exhibit better safety performance than Comparative Example 1. This is because the sodium-ion batteries in Examples 1-6 contain compound 1, which incorporates phosphate groups, giving it excellent flame-retardant properties and improving the safety performance of the sodium-ion batteries.

[0042] 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 1.

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 1 is n, and n / m is 0.01 to 1.00%.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The sodium salt accounts for 6 to 15% 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 tetrafluoroborate, sodium difluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalate-borate), sodium di(fluorooxalate-borate), sodium di(fluorodi(oxalate-phosphate)) phosphate, and sodium bis(fluorosulfonyl)imide.

5. The non-aqueous electrolyte according to claim 1, 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.

6. 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 5.

7. The sodium-ion battery according to claim 6, 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。 8. The sodium-ion battery according to claim 6, 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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