Sodium-ion battery electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a sodium-ion battery electrolyte as well as a preparation method and application thereof, and belongs to the technical field of battery electrolytes. According to the preparation method disclosed by the invention, the boric acid ester additive is added into the basic electrolyte, and the boric acid ester is preferentially decomposed in the battery circulation process, so that the generated boron-containing substance can inhibit the side reaction of the electrolyte and increase the stability of the electrolyte; the boric acid ester preferably participates in the formation of electrode / electrolyte interface layers on the two sides of the positive electrode and the negative electrode, and the boric acid ester assists in dissolving NaF with low ionic conductivity at the electrode / electrolyte interface and promotes dissociation of sodium salt in the electrolyte to increase free sodium ions, so that the diffusion rate of the sodium ions is improved, and the performance of the sodium-based half cell and the sodium-based total cell is improved; and the capacity retention ratio and the rate capability of the sodium-nickel iron sodium manganate battery at room temperature or low temperature can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery electrolytes, and in particular relates to a sodium ion battery electrolyte and a preparation method and application thereof. Background Art

[0002] As an important energy storage technology, lithium-ion batteries are widely used in portable electronic devices, new energy vehicles, military and aviation fields. However, the scarcity and high cost of lithium have become bottlenecks for its large-scale application in the field of energy storage. In order to help achieve my country's dual carbon goals, researchers have been committed to developing sodium-based batteries with cheaper and more accessible materials. As alkali metal elements of the same main group, sodium and lithium have certain similarities in chemical properties. At the same time, sodium is abundant, widely distributed, and low in cost. Because of its similar physical and chemical properties to lithium, it is considered to be an ideal substitute for lithium-ion batteries and has received widespread attention from researchers. In addition, the existing lithium-ion battery material production equipment and battery assembly production lines are fully suitable for the production of sodium-ion batteries, with broad industrial prospects, significant economic advantages, and great significance for energy strategic deployment.

[0003] Service life and safety are the core technologies and issues of power secondary batteries. Regardless of whether it is a lithium-ion battery, a sodium-ion battery or other types of batteries, considering the capacity retention rate of the battery in extreme geographical environments, low-temperature performance and cycle performance are technical issues that require special attention.

[0004] Fluorinated esters, such as fluoroethylene carbonate (FEC), have a good effect on improving the low-temperature performance of batteries. They can also increase the flash point and thermal stability of the electrolyte, and reduce volatility, which effectively improves the flame retardant performance of the electrolyte. The SEI film formed by FEC in the electrolyte is uniform, dense, low-impedance, and highly elastic, and can effectively inhibit the growth of sodium dendrites. However, FEC is expensive and causes serious environmental damage. It will cause an increase in overpotential between charging and discharging, thereby affecting the cycle life of the battery.

[0005] Therefore, it is necessary to find an electrolyte additive that can improve both the low temperature performance and cycle performance of the battery. Summary of the invention

[0006] The object of the present invention is to provide a sodium ion battery electrolyte and a preparation method and application thereof, so as to solve the technical problem that the existing electrolyte is difficult to simultaneously improve the low temperature performance and cycle performance of the battery.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: The invention discloses a method for preparing a sodium ion battery electrolyte, comprising the following steps: In an inert environment, an organic solvent and a sodium salt are mixed to obtain a basic electrolyte; then a borate ester additive is added to the basic electrolyte to obtain a sodium ion battery electrolyte; Wherein, the borate ester additive is one or more of tributyl borate, trimethyl borate, triethyl borate, triisopropyl borate, tri-tert-butyl borate, tri(pentafluorophenyl)borane and triphenyl borate.

[0008] Furthermore, the structural formula of the borate ester additive is: , , , , or .

[0009] Furthermore, the mass concentration of the basic electrolyte is 0.5~3M.

[0010] Furthermore, the organic solvent is one or more of tetrahydrofuran, dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, trimethyl borate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl carbonate or ethylene carbonate; the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethylsulfonyl)imide.

[0011] Furthermore, in the sodium ion battery electrolyte, the mass fraction of the borate ester additive is 0.1% to 5%.

[0012] The invention also discloses a sodium ion battery electrolyte prepared by the preparation method.

[0013] The invention also discloses application of the sodium ion battery electrolyte in a sodium ion battery.

[0014] Furthermore, the type of the sodium ion battery is a sodium ion symmetric battery, a sodium ion half-cell or a sodium ion full battery.

[0015] Furthermore, the positive electrode active material of the sodium ion battery is a Prussian blue analogue, a sodium vanadium phosphate material, a sodium nickel iron manganate material or a sodium iron phosphate material.

[0016] Furthermore, the negative electrode active material of the sodium ion battery is a hard carbon material.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The invention discloses a method for preparing a sodium ion battery electrolyte. A borate additive is added to a basic electrolyte. Since the borate is preferentially decomposed during the battery cycle, the generated boron-containing substance can inhibit the side reaction of the electrolyte and increase the stability of the electrolyte. In addition, a dense SEI / CEI film can be formed on the surface of the negative electrode or the positive electrode to prevent the oxidation or reduction of the solvent or the sodium salt during the charge and discharge process, thereby widening the electrochemical window of the electrolyte. Compared with the traditional ether-based electrolyte, the electrolyte proposed by the invention can increase the voltage window of the battery. Since the borate ester is preferentially oxidized on the electrode surface, a more uniform, more stable, and lower resistance cathode solid electrolyte interface is generated, thereby improving the cycle stability of the battery and reducing the internal impedance of the battery. According to the results of relevant experiments, compared with the traditional ether-based electrolyte, the electrolyte proposed by the present invention can increase the cycle life of the symmetrical battery by more than 4 times and has a smaller polarization voltage. By introducing borate esters as additives, a strong borate and boron-rich electrode / electrolyte interface layer is constructed to alleviate the performance degradation of sodium metal; borate esters participate in the passivation process of the electrolyte-electrode interface through redox formation of B−O, effectively inhibiting the growth of sodium dendrites, the decomposition of the electrolyte and the dissolution of transition metal ions; compared with traditional ether-based electrolytes, the use of the electrolyte proposed by the present invention can improve the cycle stability of sodium ion batteries; As a film-forming additive, borate ester preferentially participates in the formation of the electrode / electrolyte interface layer on both sides of the positive and negative electrodes. The borate ester assists in dissolving NaF with low ionic conductivity at the electrode / electrolyte interface and promotes the dissociation of sodium salt in the electrolyte to increase free sodium ions, successfully constructing a self-optimizing interface layer; the interface can effectively alleviate the side reactions and decomposition of the electrolyte on the positive electrode surface, inhibit the dissolution of transition metals and the degradation of the electrode surface, enhance the reaction kinetics of sodium nickel iron manganese oxide, and comprehensively improve the cycle stability and rate performance of the sodium nickel iron manganese oxide positive electrode material; compared with the traditional ether-based electrolyte, the use of the electrolyte proposed by the present invention can improve the capacity retention rate and rate performance of the sodium ion battery at room temperature or low temperature; Since borate ester is a film-forming additive and preferentially participates in the formation of the electrode / electrolyte interface layer on both sides of the positive and negative electrodes, borate ester assists in dissolving NaF with low ionic conductivity at the electrode / electrolyte interface and promotes the dissociation of sodium salt in the electrolyte to increase free sodium ions, thereby increasing the diffusion rate of sodium ions and improving the performance of sodium-based half-cells and full cells. Compared with traditional ether-based electrolytes, the use of the electrolyte proposed in the present invention can improve the cycle stability and rate performance of sodium-hard carbon batteries, the use of the electrolyte proposed in the present invention can improve the cycle stability of hard carbon-sodium nickel iron manganese oxide batteries, and the use of the electrolyte proposed in the present invention can improve the cycle performance of sodium ion batteries at room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1LSV curves of traditional ether-based electrolyte and electrolyte containing 1% TB; Figure 2 This is a comparison chart of the cycling stability of traditional ether-based electrolytes and electrolytes containing different proportions of TB; Figure 3 The cycling performance of sodium metal batteries with different electrolytes based on ether-based solvents at a cut-off voltage of 3.7V with sodium iron phosphate as the positive electrode; Figure 4 The cycling stability, rate performance and low temperature performance of sodium metal batteries with different electrolytes based on ether-based solvents at a cut-off voltage of 4V using sodium nickel iron manganese oxide as the positive electrode; Wherein: a-cycle performance at room temperature at a current density of 100 mA / g; b-rate performance at room temperature; c-cycle performance at different temperatures at a current density of 100 mA / g; Figure 5 The cycling performance and rate performance of sodium metal batteries with different electrolytes based on ether-based solvents and hard carbon as negative electrode; Where: a-cycle performance; b-rate performance; Figure 6 To study the cycling performance of sodium metal batteries with different electrolytes based on ether-based solvents using hard carbon as negative electrode and sodium nickel iron manganese oxide as positive electrode. Figure 7 To study the cycling performance of sodium metal batteries with different electrolytes based on ester-based solvents using sodium nickel iron manganese oxide as the positive electrode; Among them: a-cycling performance compared with traditional single-solvent ester-based electrolytes; b-cycling performance compared with traditional dual-solvent ester-based electrolytes. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0021] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0022] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0023] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0024] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0025] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0026] Example 1 A method for preparing a sodium ion battery electrolyte comprises the following steps: In a glove box filled with argon (water < 0.1 ppm, oxygen < 0.1 ppm), add 0.3359 g of sodium hexafluorophosphate (NaPF6) into a 2 mL constant volume bottle, and add tetrahydrofuran solvent (THF) to the 2 mL mark to obtain a 1 M NaPF6 in THF electrolyte (basic electrolyte); A sodium ion battery electrolyte (TH+%1TB) was obtained by adding 1% TB (tributyl borate) by mass into the base electrolyte.

[0027] Example 2 A method for preparing a sodium ion battery electrolyte comprises the following steps: In a glove box filled with argon (water < 0.1 ppm, oxygen < 0.1 ppm), add 0.3359 g of sodium hexafluorophosphate (NaPF6) into a 2 mL constant volume bottle, and add tetrahydrofuran solvent (THF) to the 2 mL mark to obtain a 1 M NaPF6 in THF electrolyte (basic electrolyte); By adding 3% by mass of TB (tributyl borate) to the base electrolyte, a sodium ion battery electrolyte (TH+% 3TB) was obtained.

[0028] Example 3 A method for preparing a sodium ion battery electrolyte comprises the following steps: In a glove box filled with argon (water < 0.1 ppm, oxygen < 0.1 ppm), add 0.3359 g of sodium hexafluorophosphate (NaPF6) into a 2 mL constant volume bottle, and add tetrahydrofuran solvent (THF) to the 2 mL mark to obtain a 1 M NaPF6 in THF electrolyte (basic electrolyte); A sodium ion battery electrolyte (TH+%5TB) was obtained by adding 5% TB (tributyl borate) by mass into the base electrolyte.

[0029] Example 4 A method for preparing a sodium ion battery electrolyte comprises the following steps: In a glove box filled with argon (water < 0.1 ppm, oxygen < 0.1 ppm), add 0.3359 g of sodium hexafluorophosphate (NaPF6) into a 2 mL constant volume bottle, and add propylene carbonate (PC) to the 2 mL mark to obtain a 1 M NaPF6 in PC electrolyte (basic electrolyte); A sodium ion battery electrolyte (PC+%1TB) was obtained by adding 1% TB (tributyl borate) by mass into the base electrolyte.

[0030] Example 5 A method for preparing a sodium ion battery electrolyte comprises the following steps: In a glove box filled with argon (water < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC) and propylene carbonate (PC) were uniformly mixed at a volume ratio of EC: PC = 1:1, 0.3359 g of sodium hexafluorophosphate (NaPF6) was added to a 2 mL constant volume bottle, and EC: PC = 1:1 mixed solvent was added to the 2 mL mark to obtain a concentration of 1 M NaPF6 in EC: PC = 1:1 electrolyte (basic electrolyte); A sodium ion battery electrolyte (EP+%1TB) was obtained by adding 1% TB (tributyl borate) by mass into the base electrolyte.

[0031] Comparative Example 1 In a glove box filled with argon (water content <0.1ppm, oxygen content <0.1ppm), 0.3359 g of sodium hexafluorophosphate (NaPF6) was added to a 2 mL constant volume bottle, and tetrahydrofuran solvent (THF) was added to the 2 mL mark to obtain a 1 M NaPF6 in THF electrolyte (basic electrolyte).

[0032] Comparative Example 2 In a glove box filled with argon (water content <0.1ppm, oxygen content <0.1ppm), 0.3359 g of sodium hexafluorophosphate (NaPF6) was added to a 2 mL constant volume bottle, and propylene carbonate (PC) was added to the 2 mL mark to obtain a 1 M NaPF6 in PC electrolyte (basic electrolyte).

[0033] Comparative Example 3 In a glove box filled with argon (water content <0.1ppm, oxygen content <0.1ppm), ethylene carbonate (EC) and propylene carbonate (PC) were uniformly mixed at a volume ratio of EC:PC = 1:1, 0.3359 g of sodium hexafluorophosphate (NaPF6) was added to a 2 mL constant volume bottle, and EC:PC = 1:1 mixed solvent was added to the 2 mL mark to obtain an electrolyte (basic electrolyte) with a concentration of 1 M NaPF6 in EC:PC = 1:1.

[0034] Application Examples The electrolytes obtained in the above-mentioned embodiments and comparative examples are respectively mixed with a metal sodium sheet, a positive electrode sheet, a negative electrode sheet, a separator and battery auxiliary materials, wherein the positive electrode active material is a sodium nickel iron manganate material or a sodium iron phosphate material; and the negative electrode active material is a hard carbon material. The preparation process is as follows: the positive electrode sheet, the separator and the negative electrode sheet are stacked together in a symmetrical battery, a half-battery or a full battery of a size of CR2032. The obtained symmetrical battery is subjected to a performance test, and the test results are shown in Table 1 below. It can be seen from Table 1 that compared with Comparative Example 1, the electrolyte prepared using Example 1 can increase the cycle life of the symmetrical battery by more than 4 times and has a smaller overpotential.

[0035] Table 1 Symmetrical battery performance test results

[0036] The prepared half-cells were subjected to performance tests, and the test results are shown in Table 2 below. It can be seen from Table 2 that the half-cells with borate ester additives are superior to the corresponding comparative electrolytes and have better cycle stability and capacity retention.

[0037] Table 2 Half-cell performance test results

[0038] The capacity retention rate of the sodium ion battery with Example 1 as the electrolyte, sodium nickel iron manganese oxide as the positive electrode and hard carbon as the negative electrode after running 80 cycles is 72.2%, while the capacity retention rate of the sodium ion battery with Comparative Example 1 as the electrolyte after 80 cycles is only 13.2%. It can be clearly seen from the above data that the boron-containing electrolyte additive can significantly improve the cycle performance, rate performance and low-temperature cycle performance of the sodium ion battery, mainly in terms of improving the cycle stability and capacity retention rate of the battery. In addition, the data show that increasing the amount of additive added further improves the low-temperature performance of the battery.

[0039] Figure 1 Figure 3 is the LSV curve of the traditional ether-based electrolyte and the electrolyte with 1% TB added to the traditional ether-based electrolyte. It can be seen from the figure that compared with the traditional ether-based electrolyte, the electrolyte proposed by the present invention effectively suppresses the side reactions generated by the traditional ether-based electrolyte at around 2.6 V, and expands the voltage window of the battery to around 4.5 V.

[0040] Figure 2 The figure is a comparison chart of the cycle stability of the traditional ether-based electrolyte and the electrolyte containing different proportions of TB. It can be seen from the figure that compared with the traditional ether-based electrolyte, the use of the electrolyte proposed in the present invention can increase the cycle life of the symmetrical battery by more than 4 times (1100 h) and has a smaller polarization voltage (about 8 mV).

[0041] Figure 3 The figure shows the cycle performance of sodium metal batteries with different electrolytes based on ether-based solvents at a cut-off voltage of 3.7 V using sodium iron phosphate as the positive electrode. It can be seen from the figure that the use of the electrolyte proposed in the present invention can improve the cycle life (500 h) of the sodium-sodium iron phosphate battery.

[0042] Figure 4 The figure shows the cycle stability, rate performance and low temperature performance of sodium metal batteries with different electrolytes based on ether-based solvents at a cut-off voltage of 4 V with sodium nickel iron manganese oxide as the positive electrode. It can be seen from the figure that the use of the electrolyte proposed in the present invention can improve the capacity retention rate and rate performance of sodium-sodium nickel iron manganese oxide batteries at room temperature, and the traditional ether-based electrolyte cannot operate stably at 0 ℃, but the electrolyte after adding borate ester can still operate stably when the temperature drops to -30 ℃.

[0043] Figure 5The cycle performance and rate performance of sodium metal batteries with different electrolytes based on ether-based solvents and hard carbon as the negative electrode. It can be seen from the figure that the traditional ether-based electrolyte can only maintain 40 h at a current density of 500 mA / g, while the electrolyte proposed in the present invention can be cycled for more than 800 h, greatly improving the cycle stability of the sodium-hard carbon battery, and its rate performance is also better than that of the traditional ether-based electrolyte.

[0044] Figure 6 The figure shows the cycle performance of sodium ion batteries with different electrolytes based on ether-based solvents and hard carbon as the negative electrode and sodium nickel iron manganese oxide as the positive electrode. It can be seen from the figure that the use of the electrolyte proposed in the present invention can improve the cycle stability of the hard carbon-sodium nickel iron manganese oxide battery, and the capacity retention rate is 68.5% after running 100 cycles.

[0045] Figure 7 The figure shows the cycling performance of sodium metal batteries with different electrolytes based on ester-based solvents and sodium nickel iron manganese oxide as the positive electrode. It can be seen from the figure that the use of the electrolyte proposed in the present invention greatly improves the capacity retention rate of the ester-based electrolyte. The use of borate as an electrolyte additive not only improves the battery performance in the ether-based electrolyte, but also can produce an effect in the ester-based electrolyte.

[0046] The borate ester additives in the sodium ion battery electrolyte disclosed in the present invention can participate in the chemical and electrochemical reactions at the interface between the electrode (especially the negative electrode) and the electrolyte to form a layer of solid electrolyte interface (SEI). This interface film can selectively transmit sodium ions and prevent solvent molecules from embedding into the negative electrode, thereby protecting the negative electrode material. For the positive electrode, the borate ester additives may also be oxidized and decomposed on the surface of the positive electrode material to generate a similar solid electrolyte interface (CEI), protect the internal positive electrode material, reduce cation dissolution, and improve the sodium ion transmission performance.

[0047] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a sodium ion battery electrolyte, characterized in that: The following steps are involved: In an inert environment, an organic solvent and a sodium salt are mixed to obtain a basic electrolyte; Subsequently, a borate ester additive is added to the basic electrolyte to obtain a sodium ion battery electrolyte; Wherein, the borate ester additive is one or more of tributyl borate, trimethyl borate, triethyl borate, triisopropyl borate, tri-tert-butyl borate, tri(pentafluorophenyl)borane and triphenyl borate.

2. The method for preparing a sodium ion battery electrolyte according to claim 1, characterized in that: The structural formula of the borate ester additive is: 、 、 、 , or .

3. The method for preparing a sodium ion battery electrolyte according to claim 1, characterized in that: The mass concentration of the basic electrolyte is 0.5~3M.

4. The method for preparing a sodium ion battery electrolyte according to claim 1, characterized in that: The organic solvent is one or more of tetrahydrofuran, dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxyalkane, trimethyl borate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl carbonate or ethylene carbonate; the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethylsulfonyl)imide.

5. The method for preparing a sodium ion battery electrolyte according to claim 1, characterized in that: In the sodium ion battery electrolyte, the mass fraction of the borate ester additive is 0.1% to 5%.

6. A sodium ion battery electrolyte, characterized in that: The method is prepared by any one of claims 1 to 5.

7. Use of the sodium ion battery electrolyte according to claim 6 in a sodium ion battery.

8. The use of a sodium ion battery electrolyte in a sodium ion battery according to claim 7, characterized in that: The sodium ion battery is a sodium ion symmetrical battery, a sodium ion half battery or a sodium ion full battery.

9. The use of a sodium ion battery electrolyte in a sodium ion battery according to claim 7, characterized in that: The positive electrode active material of the sodium ion battery is a Prussian blue analog, a sodium vanadium phosphate material, a sodium nickel iron manganate material or a sodium iron phosphate material.

10. The use of a sodium ion battery electrolyte in a sodium ion battery according to claim 7, characterized in that: The negative electrode active material of the sodium ion battery is a hard carbon material.

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