High-voltage sodium-ion battery electrolyte for high-specific-energy O3 type layered oxide positive electrode

Abstract

The invention discloses a high-voltage sodium ion battery electrolyte for a high-specific-energy O3 type layered oxide positive electrode, and relates to the technical field of sodium ion battery electrolyte preparation. Comprising sodium salt, an organic solvent and an additive, the sodium salt is sodium hexafluorophosphate; the organic solvent is propylene carbonate, diethyl carbonate and ethyl methyl carbonate; the additive comprises a self-cleaning additive and a film-forming additive. The electrolyte is suitable for an O3 type layered oxide positive electrode system with the working voltage as high as 4.2 V. The system has good interface stability, oxidation inhibition capability and whole-process protection mechanism, so that side reaction and gas generation are effectively inhibited, the safety of the sodium ion battery under high voltage is improved, and the cycle life of the sodium ion battery under high voltage is prolonged. And meanwhile, the constructed electrolyte system is reasonable in formula, raw materials are easy to obtain, and good cost control and commercialization amplification prospects are achieved. The problem that an interface of an existing traditional electrolyte is unstable under the high-voltage condition is solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery electrolyte preparation, and particularly relates to a high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode. BACKGROUND

[0002] Sodium ion batteries are widely considered as an important supplement to lithium ion batteries in large-scale energy storage applications due to the advantages of abundant raw material resources, low cost, wide working temperature range, good safety performance and the like. However, there are still obvious deficiencies in key performances such as energy density and cycle life, which restrict the process of large-scale commercial application.

[0003] In recent years, O3-type layered oxide positive electrode materials have been widely concerned in the sodium ion battery system due to the advantages of high theoretical capacity, simple synthesis process and good compatibility with hard carbon negative electrodes. Among them, NaNi 0.4 Fe 0.2 Mn 0.4 O2 can realize a high specific capacity of about 160 mAh / g in the voltage window of 2.0-4.2V due to the high Ni content, and shows good application prospect.

[0004] However, the improvement of the working voltage puts forward more stringent requirements on the stability of the electrolyte system. Under the working voltage of 4.2V, the unstable positive electrode / electrolyte interface film formed in the conventional electrolyte system is easy to break, which causes the oxidation and decomposition reaction of the electrolyte on the surface of the positive electrode to produce gas and other by-products. At the same time, the irreversible release of lattice oxygen in the positive electrode material at high voltage will further aggravate the decomposition of the electrolyte and the generation of gas. The gas accumulation caused by the above-mentioned side reactions not only may cause the increase of the internal pressure of the battery, leading to the problems such as battery bulging and deformation, but also may cause cross-talk reactions between the positive electrode and the negative electrode, increasing the risk of thermal runaway, and seriously affecting the cycle stability and safety of the battery. In addition, the existing electrolyte design often only simply combines functional additives, and it is difficult to meet the multiple requirements of impurity removal, interface film formation and continuous protection, and there is a lack of reasonable functional division and reaction sequence control among the additives, resulting in problems such as unstable interface film and failure of additives at high voltage. Therefore, it is urgent to build a sodium ion battery electrolyte system suitable for high-voltage O3-type layered oxide positive electrodes. SUMMARY

[0005] In order to solve the above technical problems, the purpose of the present application is to provide a high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode, so as to solve the problem of unstable interface of the existing conventional electrolyte under high-voltage conditions.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: providing a high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode, comprising: a sodium salt, an organic solvent, and an additive; The sodium salt is sodium hexafluorophosphate; The organic solvents are propylene carbonate, diethyl carbonate and ethyl methyl carbonate; Additives include self-cleaning additives and film-forming additives.

[0007] On the basis of the above technical solution, the present invention can also be improved as follows: Furthermore, the concentration of the sodium salt in the organic solvent is 0.8-1.5 mol / L.

[0008] Furthermore, the concentration of the sodium salt in the organic solvent is 1 mol / L.

[0009] Furthermore, the volume ratio of propylene carbonate, diethyl carbonate and ethyl methyl carbonate is 1:1-3:1.

[0010] Furthermore, the volume ratio of propylene carbonate, diethyl carbonate and ethyl methyl carbonate is 1:2:1.

[0011] Furthermore, the self-cleaning additive is tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphite, diphenyldimethoxysilane or triethyl borate, or diphenyldimethoxysilane and triethyl borate.

[0012] Furthermore, the film-forming additive is a mixture of fluoroethylene carbonate and one of the following four, or fluoroethylene carbonate, vinyl sulfate and sodium difluorophosphate, or fluoroethylene carbonate; the following four are sodium difluorooxalatoborate, adiponitrile, vinyl sulfate, and sodium difluorophosphate.

[0013] Furthermore, the amount of the self-cleaning additive is 0.5-5 vol % of the organic solvent.

[0014] Furthermore, the amount of the self-cleaning additive is 1 vol % of the organic solvent.

[0015] Furthermore, the amount of fluoroethylene carbonate in the film-forming additive is 3-10 vol% of the organic solvent.

[0016] Furthermore, the amount of fluoroethylene carbonate in the film-forming additive is 5 vol % of the organic solvent.

[0017] Furthermore, when the film-forming additive is a mixture of fluoroethylene carbonate and one of the following four types, the amount of adiponitrile is 0.2-5 vol% of the organic solvent, and the amounts of sodium difluorooxalatoborate, vinyl sulfate, and sodium difluorophosphate are all 0.1-1.5 wt% of the high-voltage sodium ion battery electrolyte for high-energy O3 layered oxide positive electrode.

[0018] Furthermore, when the film-forming additive is a mixture of fluoroethylene carbonate and one of the following four, the amount of adiponitrile is 1 vol% of the organic solvent, and the amounts of sodium difluorooxalatoborate, vinyl sulfate, and sodium difluorophosphate are all 0.2-1 wt% of the high-voltage sodium ion battery electrolyte for high-energy O3 layered oxide positive electrode.

[0019] Furthermore, when the film-forming additives are fluoroethylene carbonate, vinyl sulfate and sodium difluorophosphate, the amounts of vinyl sulfate and sodium difluorophosphate are both 0.1-2 wt % of the high-voltage sodium ion battery electrolyte for high-energy O3 layered oxide positive electrode.

[0020] Furthermore, when the film-forming additives are fluoroethylene carbonate, vinyl sulfate and sodium difluorophosphate, the amounts of vinyl sulfate and sodium difluorophosphate are both 1 wt % of the high-voltage sodium ion battery electrolyte for the high-energy O3 layered oxide positive electrode.

[0021] The present invention also provides a method for preparing the high-voltage sodium ion battery electrolyte for the high-energy O3 layered oxide positive electrode, comprising removing water from the organic solvent and the additive, and then mixing the sodium salt, the organic solvent and the additive, and stirring at room temperature until the mixture is uniform and transparent, thereby preparing the high-voltage sodium ion battery electrolyte for the high-energy O3 layered oxide positive electrode.

[0022] The present invention also provides the use of the high-voltage sodium ion battery electrolyte for high-specific-energy O3-type layered oxide positive electrode in the preparation of sodium ion batteries.

[0023] The present invention has the following beneficial effects: 1. The present invention relates to a sodium-ion battery electrolyte, particularly suitable for use in O3-type layered oxide cathode systems operating at voltages up to 4.2V. This system should possess excellent interfacial stability, oxidation inhibition, and a full-process protection mechanism to effectively suppress side reactions and gas generation, thereby enhancing the safety and cycle life of sodium-ion batteries at high voltages. Furthermore, the constructed electrolyte system features a rational formulation and readily available raw materials, offering excellent cost control and promising prospects for commercial scale-up.

[0024] 2. The "self-cleaning" additives of the present invention, such as tris(trimethylsilyl)borate, preferentially react with trace water in the electrolyte in the early stages to form a -(Si-O)n- structure. This structure then reacts with HF generated by the decomposition of NaPF6 to form a stable Si-F bond, removing impurity molecules at the source and stabilizing the initial interface environment. Furthermore, the central boron atom in tris(trimethylsilyl)borate is electron-deficient, capable of capturing reactive oxygen species that may be released during operation of the layered oxygen cathode, further inhibiting the oxidative decomposition of the electrolyte and gas generation. Film-forming additives such as fluoroethylene carbonate, sodium difluorooxalatoborate, vinyl sulfate, sodium difluorophosphate, and adiponitrile construct a dense, multi-element composite interface film rich in B, F, and S on the cathode surface during charge and discharge, effectively inhibiting the dissolution of transition metals and enhancing the structural stability of the cathode interface. Furthermore, the "self-cleaning" additives are not limited to the initial stages of the battery; they continuously capture HF and reactive oxygen species that may be generated during subsequent operation, providing protection throughout the battery's operation and effectively preventing degradation of the interface film. The additive combination builds a multiple protection barrier for sodium-ion batteries under high-voltage conditions through reaction sequence and division of labor coordination mechanism, fundamentally solving problems such as electrolyte decomposition, gas by-product generation and interface film degradation.

[0025] 3. The sodium ion battery electrolyte of the present invention and NaNi 0.4 Fe 0.2 Mn 0.4 The O2 positive electrode assembled half-cell can provide a discharge specific capacity of nearly 160 mAh / g within the voltage range of 2-4.2V, and can still provide a reversible discharge capacity of more than 140 mAh / g when cycled at a 1 C rate. The capacity retention rate exceeds 80% after 400 cycles, showing excellent cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Fig. 1 This is the first cycle charge and discharge curve of the sodium ion battery in Example 1.

[0027] Fig. 2 Graph showing the cycling performance of the sodium ion batteries in Examples 1-2, Example 10, and Comparative Example 1 at a rate of 1 C. DETAILED DESCRIPTION

[0028] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are 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 that can be purchased commercially.

[0029] Example 1: A high-voltage sodium-ion battery electrolyte for high specific energy O3-type layered oxide cathodes, comprising a sodium salt, an organic solvent, and an additive; Among them, the sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the organic solvent is 1 mol / L. The organic solvent is propylene carbonate, diethyl carbonate, and methyl ethyl carbonate, with a volume ratio of 1:2:1. The additive is tris(trimethylsilyl) borate (self-cleaning additive, amounting to 1 vol% of the organic solvent), fluoroethylene carbonate (film-forming additive, amounting to 5 vol% of the organic solvent), and sodium difluoro(oxalato)borate (film-forming additive, amounting to 0.2 wt% of the electrolyte).

[0030] A preparation method of a high-voltage sodium-ion battery electrolyte for high specific energy O3-type layered oxide cathodes, comprising the following steps: first, using molecular sieves to remove water from the organic solvent and the additive, mixing propylene carbonate, diethyl carbonate, and methyl ethyl carbonate in a volume ratio of 1:2:1, and then adding sodium hexafluorophosphate to a salt concentration of 1 mol / L. Then, 1 vol% of tris(trimethylsilyl) borate, 5 vol% of fluoroethylene carbonate, and 0.2 wt% of sodium difluoro(oxalato)borate are added in sequence. At room temperature, a magnetic stirrer is used for continuous stirring for 4 h, so that the sodium salt is completely dissolved and the components are uniformly dispersed, to obtain a high-voltage sodium-ion battery electrolyte for high specific energy O3-type layered oxide cathodes.

[0031] Example 2: A high-voltage sodium-ion battery electrolyte for high specific energy O3-type layered oxide cathodes, in which the additive sodium difluoro(oxalato)borate is replaced by adiponitrile (film-forming additive, amounting to 1 vol% of the organic solvent), and the rest is the same as in Example 1.

[0032] Example 3: A high-voltage sodium-ion battery electrolyte for high specific energy O3-type layered oxide cathodes, in which the additive sodium difluoro(oxalato)borate is replaced by vinyl sulfate (film-forming additive, amounting to 1 wt% of the electrolyte), and the rest is the same as in Example 1.

[0033] Example 4: A high-voltage sodium-ion battery electrolyte for high specific energy O3-type layered oxide cathodes, in which the additive sodium difluoro(oxalato)borate is replaced by sodium difluorophosphate (film-forming additive, amounting to 1 wt% of the electrolyte), and the rest is the same as in Example 1.

[0034] Example 5: A high-voltage sodium-ion battery electrolyte for high specific energy O3-type layered oxide cathodes, in which the additive sodium difluoro(oxalato)borate is replaced by vinyl sulfate (film-forming additive, amounting to 1 wt% of the electrolyte) and sodium difluorophosphate (film-forming additive, amounting to 1 wt% of the electrolyte), and the rest is the same as in Example 1.

[0035] Example 6: A high-voltage sodium-ion battery electrolyte for a high-energy O3-type layered oxide positive electrode, comprising a sodium salt, an organic solvent, and an additive; The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the organic solvent is 0.8 mol / L. The organic solvent is propylene carbonate, diethyl carbonate, and methyl ethyl carbonate, with a volume ratio of 1:1:1. The additive is tris(trimethylsilyl) phosphite (self-cleaning additive, amounting to 0.5 vol% of the organic solvent), fluoroethylene carbonate (film-forming additive, amounting to 3 vol% of the organic solvent), and sodium difluoro(oxalato)borate (film-forming additive, amounting to 0.1 wt% of the electrolyte).

[0036] Example 7: A high-voltage sodium-ion battery electrolyte for a high-energy O3-type layered oxide positive electrode, comprising a sodium salt, an organic solvent, and an additive; The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the organic solvent is 1.5 mol / L. The organic solvent is propylene carbonate, diethyl carbonate, and methyl ethyl carbonate, with a volume ratio of 1:3:1. The additive is diphenyldimethoxysilane (self-cleaning additive, amounting to 5 vol% of the organic solvent), fluoroethylene carbonate (film-forming additive, amounting to 10 vol% of the organic solvent), and sodium difluoro(oxalato)borate (film-forming additive, amounting to 1.5 wt% of the electrolyte).

[0037] Example 8: A high-voltage sodium-ion battery electrolyte for a high-energy O3-type layered oxide positive electrode, The self-cleaning additive is triethyl borate, amounting to 1 vol% of the organic solvent, and the rest is the same as in Example 1.

[0038] Example 9: A high-voltage sodium-ion battery electrolyte for a high-energy O3-type layered oxide positive electrode, The self-cleaning additive is diphenyldimethoxysilane and triethyl borate, amounting to 1 vol% of the organic solvent, and the rest is the same as in Example 1.

[0039] Example 10: A high-voltage sodium-ion battery electrolyte for a high-energy O3-type layered oxide positive electrode, comprising a sodium salt, an organic solvent, and an additive; The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the organic solvent is 1 mol / L. The organic solvent is propylene carbonate, diethyl carbonate, and methyl ethyl carbonate, with a volume ratio of 1:2:1. The additive is tris(trimethylsilyl) borate (1 vol% of the organic solvent) and fluoroethylene carbonate (5 vol% of the organic solvent).

[0040] Comparative Example 1: A sodium ion battery electrolyte, comprising a sodium salt, an organic solvent and an additive; The sodium salt is sodium hexafluorophosphate, and the concentration of the sodium salt in the organic solvent is 1 mol / L. The organic solvent is propylene carbonate. The additive is fluoroethylene carbonate (5 vol% of the organic solvent).

[0041] To test the application effect of the sodium ion battery electrolyte proposed in the application in a sodium ion battery, it is compared with NaNi 0.4 Fe 0.2 Mn 0.4 O2 positive electrode to assemble a half-cell. The electrolyte and the half-cell are assembled in an argon glove box with a water content and oxygen content of less than 0.1 ppm, and the type is CR2032 button cell. After assembly, it is placed for 6-12 h, and then tested on a LAND battery test system provided by Wuhan LanDian Electronics Co., Ltd. The voltage range is 2-4.2 V, and the constant current charge and discharge test is carried out at a current density of 0.1 C and 1 C, respectively. The results are shown in Table 1 and Figs. 1-2 .

[0042] Table 1 is the performance test results of the sodium ion battery

[0043] As shown in Table 1 and Figs. 1-2 Compared with Comparative Example 1, the capacity retention rate of the sodium ion battery provided by the application is higher than 80% after 400 cycles at high voltage, which shows excellent cycle stability. This performance advantage is due to the interface stability strategy of reaction timing and division of labor, and the "self-cleaning" additive builds a stable initial interface environment for the additive film in the early stage, and continuously captures the possible generated adverse by-products during the battery operation. The film-forming additive builds a dense and stable interface film structure on the surface of the positive electrode, effectively blocking the direct contact of the electrolyte with the positive active material, and slowing down the occurrence of interface side reactions.

[0044] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A high-voltage sodium ion battery electrolyte for a high-energy O3-type layered oxide positive electrode, characterized in that: including sodium salts, organic solvents and additives; The sodium salt is sodium hexafluorophosphate; The organic solvents are propylene carbonate, diethyl carbonate and ethyl methyl carbonate; Additives include self-cleaning additives and film-forming additives.

2. The high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode according to claim 1, characterized in that: The concentration of the sodium salt in the organic solvent is 0.8-1.5 mol / L.

3. The high-voltage sodium ion battery electrolyte for a high-energy O3-type layered oxide positive electrode according to claim 1, characterized in that: The volume ratio of propylene carbonate, diethyl carbonate and ethyl methyl carbonate is 1:1-3:

1.

4. The high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode according to claim 1, characterized in that: The self-cleaning additive is tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphite, diphenyldimethoxysilane or triethyl borate, or diphenyldimethoxysilane and triethyl borate.

5. The high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode according to claim 1, characterized in that: The film-forming additive is a mixture of fluoroethylene carbonate and one of the following four, or fluoroethylene carbonate, vinyl sulfate and sodium difluorophosphate, or fluoroethylene carbonate; the following four are sodium difluorooxalatoborate, adiponitrile, vinyl sulfate and sodium difluorophosphate.

6. The high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode according to claim 1 or 4, characterized in that: The amount of the self-cleaning additive is 0.5-5 vol% of the organic solvent.

7. The high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode according to claim 5, characterized in that: The amount of fluoroethylene carbonate in the film-forming additive is 3-10 vol% of the organic solvent.

8. The high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode according to claim 5, characterized in that: The amount of fluoroethylene carbonate in the film-forming additive is 5 vol % of the organic solvent.

9. The method for preparing a high-voltage sodium ion battery electrolyte for a high-energy O3-type layered oxide positive electrode according to any one of claims 1 to 8, characterized in that: The organic solvent and the additive are dehydrated separately, and then the sodium salt, the organic solvent and the additive are mixed and stirred at room temperature until they are uniform and transparent to prepare a high-voltage sodium ion battery electrolyte for a high-energy O3 layered oxide positive electrode.

10. Use of the high-voltage sodium ion battery electrolyte for a high-specific-energy O3-type layered oxide positive electrode according to any one of claims 1 to 8 in the preparation of a sodium ion battery.

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