Electrolyte with wide temperature range and high voltage resistance as well as preparation and application methods thereof

Abstract

The invention relates to the technical field of electrolytes, in particular to a wide-temperature-range and high-voltage-resistant electrolyte and a preparation and application method thereof. The electrolyte is composed of a lithium salt, a non-aqueous organic solvent and a functional additive, the mass content of the functional additive in the electrolyte is 0.25%-1%, and the functional additive is 2-propoxy-5-pyridine borate and / or triethanolamine borate. The existence of the boron-containing, nitrogen-containing and propoxy-containing functional additive is beneficial to rapid removal of Li < + > from a solvated shell, accelerates the dynamic characteristics of lithium deposition / stripping, inhibits the formation of lithium dendrites, and is beneficial to reduction of interface impedance and polarization. Besides, by inhibiting generation of HF, reducing decomposition and gas production of the electrolyte and inhibiting dissolution of transition metal, a compact and stable CEI film is formed on the surface of the positive electrode material, the interface stability of the positive electrode-electrolyte is improved, and the capacity retention ratio, the cycling stability and the safety of the battery at high and low temperatures are comprehensively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and in particular to an electrolyte with wide temperature range and high voltage resistance, and a preparation and application method thereof. Background Art

[0002] The electrolyte is known as the "blood" of the battery. It plays the role of a bridge for transporting current between the positive and negative electrodes and is an important component of the battery. The choice of electrolyte greatly affects the capacity, cycle life, safety performance and operating temperature of the battery. The electrolyte used in commercial lithium-ion batteries is composed of lithium hexafluorophosphate (LiPF6) and organic carbonate solvents. Traditional commercial carbonate electrolytes will undergo severe oxidative decomposition when the operating voltage exceeds 4.3V, resulting in the production of adverse byproducts such as hydrofluoric acid (HF), and increasing the interface impedance between the electrode / electrolyte, thereby causing the battery performance to deteriorate.

[0003] Electrolyte additives can improve battery performance and stability, extend battery life, and improve safety, playing a vital role in lithium-ion batteries. However, some electrolyte additives are unstable under high temperature or high pressure conditions, which leads to a decrease in the battery's cycle performance and safety performance. In addition, under low temperature conditions, some electrolyte additives have a high melting point and will directly solidify into a solid state at low temperatures, resulting in extremely poor battery cycle performance at low temperatures or even the battery being unable to discharge electricity.

[0004] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art known to those skilled in the art. Summary of the invention

[0005] The first purpose of the present invention is to provide an electrolyte with a wide temperature range and high voltage resistance, so as to improve the capacity retention rate, cycle stability and safety of the battery under high voltage and high and low temperature conditions and extend the battery life. The present invention also provides a preparation method thereof and its mechanism of action and application in lithium-ion batteries.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] A wide temperature range and high voltage resistant electrolyte comprises a lithium salt, a non-aqueous organic solvent and a boron electron-deficient compound functional additive. The mass content of the functional additive is 0.25% to 1% based on the total mass of the high voltage resistant electrolyte as 100%, and the functional additive is 2-propoxy-5-pyridine borate and / or triethanolamine borate.

[0008] Preferably, the lithium salt is lithium hexafluorophosphate.

[0009] The functional additive is preferably a binary electrolyte additive composed of 2-propoxy-5-pyridine borate and triethanolamine borate in a ratio of 1:1, and the electrolyte contains BO groups, propoxy groups and pyridine groups at the same time. It can improve the ion conductivity of the electrolyte at low temperatures and ensure that the battery can still work normally in a cold environment. Under high temperature conditions, it can also maintain the chemical stability of the electrolyte, reduce the decomposition of the electrolyte and gas generation at high temperatures, and improve the safety of the battery. Among them, the introduction of the propoxy group can effectively improve the stability and uniformity of the electrolyte and inhibit the growth of lithium dendrites through its hydrophobicity, polarity regulation and steric hindrance effect, thereby reducing the occurrence of side reactions and improving the performance and life of lithium-ion batteries; at the same time, the triethanolamine group can react with acidic substances (such as HF) to play a buffering role, reduce the acidic environment in the electrolyte, and prevent corrosion of electrode materials; in addition, the pyridine group can decompose to generate CN-, BO group, CN- and the hydroxyl group (-OH) and nitrogen atom of triethanolamine participate in the coordination of Li+ to form CEI containing LiBO2 and Li3N, so that the electrolyte has the effect of resisting high voltage, high temperature and low temperature.

[0010] Among them, the molecule of 2-propoxy-5-pyridine borate contains BO group, pyridyl group and propoxy group at the same time, and the pyridyl group can decompose to generate CN - BO groups and CN- participate in Li + The coordination of LiBO2 and Li3N forms a CEI containing LiBO2 and Li3N, which makes the electrolyte resistant to high voltage, high temperature and low temperature. It enables good electronic matching with nickel cobalt manganese oxide or lithium iron phosphate at the molecular level, which helps to form a stable passivation film on the electrode surface, thereby reducing the occurrence of side reactions without affecting the migration of ions. 2-Propoxy-5-pyridine borate has the following structural formula:

[0011]

[0012] 2-Propoxy-5-pyridine borate introduces a propoxy group into the molecular structure. The presence of the propoxy functional group increases the hydrophobicity and steric hindrance of the molecule, making the solubility and distribution of the compound in the electrolyte more uniform, thereby improving its stability and effectiveness in the electrolyte. The pyridine ring at the 5-position can form a specific interaction with the electrode surface, which helps to form a stable passivation film on the electrode interface. It has good chemical inertness and allows lithium ions to pass freely, effectively improving the cycle life and electrochemical performance of the battery. Due to the presence of the propoxy group, the electronic distribution of 2-propoxy-5-pyridine borate in the electrolyte is more stable, making it more tolerant under high voltage, helping to inhibit the decomposition of the electrolyte and reduce the internal resistance of the battery, thereby improving the overall electrochemical performance.

[0013] Specifically, the inventors found that electron-deficient bodies can use valence orbitals to more easily coordinate with electrons, thereby enhancing the stability of the electrolyte system and making the electrolyte more solvated. The advantages of 2-propoxy-5-pyridine borate and triethanolamine borate as electrolyte additives are that the boron atom in the molecule exists in a trivalent form, has strong electrophilicity, and is easy to react with Li + The stable compound formed by the combination participates in the formation of the negative electrode-electrolyte interface film (SEI), thereby protecting the negative electrode material; at the same time, the boron atoms can interact with F- to inhibit the generation of HF, thereby inhibiting the dissolution of positive electrode metal ions and stabilizing the positive electrode-electrolyte interface (CEI).

[0014] The present invention uses boron atoms to cooperate with propoxy groups and groups containing N elements and being weakly alkaline. The introduction of propoxy groups has a significant effect on improving battery performance. It increases the hydrophobicity of the entire molecule, thereby effectively inhibiting the direct contact between the highly polar substances in the electrolyte and the active lithium surface, reducing certain side reactions in the electrolyte, and thus extending the life of the battery; and the oxygen atoms in the propoxy group have a certain electronegativity, which makes the propoxy group itself have a certain polarity. By adjusting the polarity of the molecule, the propoxy group can affect the solubility of the electrolyte, making it more compatible with other electrolyte components. Not only that, the presence of the propoxy group can improve the distribution of the components in the electrolyte, reduce the phase separation phenomenon in the electrolyte, and thus improve the battery performance; on this basis, the propoxy group, as a larger substituent, will increase the steric hindrance of the molecule. This steric hindrance effect helps to prevent excessive aggregation between molecules and avoid certain unfavorable interface reactions. Due to the steric hindrance effect of the propoxy group, it can form a "barrier" effect in the electrolyte, inhibit the growth of lithium dendrites, and thus reduce the risk of dendrite short circuit.

[0015] At the same time, triethanolamine is an alkaline group that can achieve the effect of removing HF, and the CN- generated by the decomposition of the pyridine group in 2-propoxy-5-pyridine borate can be complexed with transition metal ions (Ni, Co, Mn) to inhibit the dissolution of positive electrode metal ions; at the same time, N atoms can form hydrogen bonds with hydrogen atoms in solvent molecules, thereby improving the stability of the electrolyte, and N atoms participate in the coordination of Li+, thereby reducing the generation of LiF to achieve the effect of reducing interface impedance, and at the same time forming CEI containing Li3N, so that the electrolyte has the effect of high voltage, high temperature and low temperature resistance. The mechanism of action of 2-propoxy-5-pyridine borate and triethanolamine borate is as follows:

[0016] 1. Reaction of removing HF

[0017]

[0018] 2. With Li + Nucleophilic reaction

[0019]

[0020] 3. Reaction of removing H2O

[0021]

[0022] Preferably, the non-aqueous organic solvent is a mixture of one or more of ethylene carbonate, diethyl carbonate, fluoroethylene carbonate, dimethyl carbonate or propylene carbonate.

[0023] Further preferably, the non-aqueous organic solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC). Among them, the mass ratio of ethylene carbonate and diethyl carbonate is 3:7, and fluoroethylene carbonate accounts for 1.5-4.5wt% of the total mass of the mixed solution of EC and DEC. Ethylene carbonate is a solvent with a high dielectric constant that can effectively dissolve lithium salts, provide higher ionic conductivity, and help form a stable solid electrolyte interface (SEI) film on the electrode surface. Diethyl carbonate is a low viscosity solvent that can reduce the overall viscosity of the electrolyte, thereby improving the ionic conductivity and low temperature performance of the battery. Fluoroethylene carbonate is a modified ethylene carbonate with enhanced electrochemical stability and better interface properties, especially in high voltage environments, it can effectively inhibit the decomposition of the electrolyte and improve the quality of the SEI film.

[0024] The most preferred non-aqueous organic solvent is: the mass ratio of ethylene carbonate and diethyl carbonate is 3:7. A higher proportion of DEC can reduce the viscosity of the solvent and improve the conductivity at low temperatures, while EC provides sufficient dielectric constant and film forming ability. The mass ratio of ethylene carbonate and diethyl carbonate is 3:7, which can optimize the comprehensive performance of the electrolyte under low temperature and high voltage conditions. Fluorinated ethylene carbonate accounts for 3wt% of the total mass of the mixed solution of EC and DEC. A lower FEC content can inhibit the decomposition reaction under high voltage, while a higher content further enhances the stability and uniformity of the SEI film. The 3wt% content allows FEC to provide effective electrochemical protection without affecting the basic properties of the electrolyte.

[0025] The second object of the present invention is to provide a method for preparing an electrolyte with a wide temperature range and high voltage resistance, which has the same technical effect.

[0026] The above technical objectives of the present invention are achieved through the following technical solutions:

[0027] A method for preparing an electrolyte with a wide temperature range and high voltage resistance, characterized in that, in a reaction container filled with inert gas, a lithium salt is first dissolved in a non-aqueous organic solvent, and the solution is stirred on a stirrer to serve as a basic electrolyte; and then a boron-based electron-deficient compound functional additive is added to the basic electrolyte to obtain an electrolyte with a wide temperature range and high voltage resistance.

[0028] In the wide temperature range and high voltage resistant lithium ion battery electrolyte of the present invention, the presence of the electron-deficient compound additive containing boron, nitrogen and propoxy groups is conducive to the rapid release of Li+ from the solvation shell, accelerates the kinetic characteristics of lithium deposition / stripping, inhibits the formation of lithium dendrites, and helps to reduce interface impedance and polarization. In addition, by inhibiting the generation of HF, reducing the decomposition and gas production of the electrolyte, inhibiting the dissolution of transition metals, and forming a dense and stable CEI film on the surface of the positive electrode material, the crystal structure of the positive electrode material is protected, the interface stability of the positive electrode-electrolyte is improved, and the increase of the interface impedance is reduced, thereby improving the capacity retention rate, cycle stability and safety of the battery at high and low temperatures.

[0029] The third object of the present invention is to provide an application method of an electrolyte with a wide temperature range and high voltage resistance, and to use the above-mentioned electrolyte with a wide temperature range and high voltage resistance as the electrolyte of a lithium-ion battery with a nine-series high-nickel ternary as the positive electrode material, which has the same technical effect.

[0030] The above technical objectives of the present invention are achieved through the following technical solutions:

[0031] The present invention also provides a lithium-ion battery, comprising a positive electrode material and an electrolyte, wherein the electrolyte is the above-mentioned wide temperature range and high voltage resistant electrolyte, the positive electrode material is a nine-series high nickel ternary material, and the negative electrode material is a conventional negative electrode material. Preferably, the lithium-ion battery is LiNi 0.90 Co 0.05 Mn 0.05 O2||Li, referred to as NCM9055||Li. The nine-series high-nickel ternary materials are prone to side reactions under high voltage, leading to problems such as electrolyte decomposition and transition metal ion dissolution. CN generated by the decomposition of the pyridine group in 2-propoxy-5-pyridine borate - It can complex with dissolved transition metal ions and inhibit their diffusion in the electrolyte, thereby reducing the dissolution and failure of positive electrode materials. Boric acid triethanolamine reduces the acidity of the electrolyte by reacting with acidic substances such as HF, thereby preventing the dissolution of metal ions in the positive electrode material. The steric hindrance effect of the propoxy group forms a physical "barrier" on the surface of the negative electrode, inhibiting the growth of lithium dendrites, thereby reducing the risk of short circuit caused by dendrites.

[0032] In summary, the present invention has the following beneficial effects:

[0033] The present invention combines the film-forming ability of triethanolamine borate with the steric hindrance of 2-propoxy-5-pyridine borate, triethanolamine borate can form a more stable SEI film, while inhibiting the growth of lithium dendrites, and 2-propoxy-5-pyridine borate enhances the anti-lithium dendrite ability of this film through the steric hindrance effect. At the same time, the triethanolamine group of triethanolamine borate can play a buffering role by reacting with an acidic substance (such as HF) to maintain the stability of the electrolyte, while 2-propoxy-5-pyridine borate further enhances the dispersibility and uniformity of the electrolyte by adjusting the polarity. The two work together to prevent local unevenness and acid corrosion of the electrolyte. Triethanolamine borate coordinates with lithium ions to help stabilize the concentration and balance of lithium ions, while the structure of 2-propoxy-5-pyridine borate helps to optimize the transmission path of lithium ions. The combination of the two can improve the conductivity of lithium ions and the conductivity of the electrolyte, and make the electrolyte have the effect of high voltage, high temperature and low temperature resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments described in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 This is a normal temperature cycle performance diagram of the NCM9055||Li battery prepared in Example 1 and Comparative Example 1.

[0036] Figure 2 This is a high temperature cycle performance diagram of the NCM9055||Li battery prepared in Example 1 and Comparative Example 1.

[0037] Figure 3 This is a low temperature cycle performance diagram of the NCM9055||Li battery prepared in Example 1 and Comparative Example 1.

[0038] Figure 4 This is a rate performance diagram of the NCM9055||Li battery prepared in Example 1 and Comparative Example 1.

[0039] Figure 5 These are the EIS graphs of the NCM9055||Li batteries prepared in Example 1 and Comparative Example 1.

[0040] Figure 6 TEM images of the NCM9055 pole pieces after cycling of the NCM9055||Li batteries prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0041] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, a wide temperature range and high voltage resistant electrolyte and its preparation and application method proposed by the present invention, its specific implementation method, characteristics and effects are described in detail as follows.

[0042] Sources of raw materials used in the embodiments and comparative examples:

[0043]

[0044]

[0045] Example 1

[0046] In a glove box filled with high-purity argon, 1.0 mol of LiPF6 was dissolved in a mixed solution of ethylene carbonate (EC) / diethyl carbonate (DEC) with a mass ratio of 3:7 and containing 3wt% of fluoroethylene carbonate (FEC) (the total mass of the configured mixed solution was 2g) to form a basic electrolyte (Blank), and then 0.5wt% of a functional additive was added to the basic electrolyte, the functional additive being a mixture of 2-propoxy-5-pyridine borate (PMBP) and triethanolamine borate (TEB) in a mass ratio of 1:1 to obtain an electrolyte (i.e., PMBP and TEB were first mixed in a 1:1 ratio, and the mixture accounted for 0.5% of the total mass of the high-voltage resistant electrolyte, referred to as 0.5-MIX), and assembled into an NCM9055||Li half-cell.

[0047] Comparative Example 1

[0048] This comparative example is basically the same as Example 1, except that it does not contain a functional additive (ie, the electrolyte is the basic electrolyte).

[0049] Figure 1-3 To conduct constant current charge and discharge test in the voltage range of 2.75-4.6V. Figure 1 It can be seen that at room temperature, the capacity of the battery in the basic electrolyte decays very quickly, and the addition of the functional additive prepared by the present invention can significantly improve the cycle performance of the battery. After 100 charge and discharge cycles, the battery discharge capacity of the 0.5wt% MIX electrolyte is 186.44mAh g -1 The capacity retention rate was as high as 89.88%. The half-cell assembled with the basic electrolyte increased from an initial capacity of 202.45 mAh g -1 Rapidly decays to 139.81 mAh g -1 , the capacity retention rate is only 69.06%. Figure 2 and Figure 3It can be seen that the addition of the composite functional additives (2-propoxy-5-pyridine borate and triethanolamine borate) of the present invention also improves the cycle life of the battery at high and low temperatures.

[0050] The functional additive prepared by the composite method of the present invention improves the cycle life of the battery and also improves the rate performance of the battery. Figure 4 It is the rate diagram of NCM9055||Li battery in basic electrolyte (Comparative Example 1) and containing 0.5-MIX electrolyte (Example 1); Figure 4 It can be seen that when cycling under 0.1-5C conditions, the discharge specific capacity of the battery containing 0.5-MIX is higher than that of the base sample.

[0051] Figure 5 The impedance diagram of NCM9055||Li battery after cycling in the basic electrolyte (Comparative Example 1) and the 0.5-MIX electrolyte (Example 1). EIS analysis further proves that the 0.5-MIX electrolyte can effectively improve the electrode interface stability. Figure 5 As shown, after 100 cycles, the basic electrolyte continued to oxidize and decompose under high voltage, and the inorganic salts and organic matter produced continued to accumulate on the surface of the positive electrode material, resulting in an increase in the polarization of the battery and a significant increase in resistance. On the contrary, the impedance of the battery using 0.5-MIX electrolyte is significantly lower than that of the basic sample. This shows that the functional additives (2-propoxy-5-pyridine borate and triethanolamine borate) prepared by the present invention form a stable interface film on NCM9055, inhibiting the decomposition of the electrolyte.

[0052] Figure 6 This is the TEM image of NCM9055||Li after cycling in the basic electrolyte and the 0.5-MIX electrolyte. TEM can further analyze the oxidation film of the electrolyte on the electrode surface. Figure 6 It can be seen that after cycling in the basic electrolyte, an unevenly distributed and thick interface film is formed on the surface of the electrode, which will hinder the deintercalation of lithium ions and thus affect the cycling performance of the battery. However, the surface of the NCM9055 electrode cycling in the 0.5-MIX electrolyte is coated with a dense and thin passivation layer. This interface film separates the positive electrode from the electrolyte, which not only protects the positive electrode structure from collapse during the cycle, but also prevents the electrolyte from continuous oxidation and decomposition.

[0053] Example 2

[0054] This embodiment is basically the same as the embodiment 1, except that: 0.25 wt % of a mixture of 2-propoxy-5-pyridine borate (PMBP) and triethanolamine borate (TEB) in a mass ratio of 1:1 is added to the base electrolyte as the electrolyte.

[0055] Example 3

[0056] This embodiment provides a high-voltage resistant electrolyte and a lithium-ion battery based thereon, which is basically the same as that in Embodiment 1, except that a mixture of 1 wt % of 2-propoxy-5-pyridine borate (PMBP) and triethanolamine borate (TEB) in a mass ratio of 1:1 is added to the base electrolyte as the electrolyte.

[0057] Example 4

[0058] This embodiment is basically the same as that in Embodiment 1, except that: 0.5 wt % of a mixture of 2-propoxy-5-pyridine borate (PMBP) and triethanolamine borate (TEB) in a mass ratio of 2:1 is added to the base electrolyte as the electrolyte.

[0059] Example 5

[0060] This embodiment is basically the same as that in Embodiment 1, except that: 0.5 wt % of a mixture of 2-propoxy-5-pyridine borate (PMBP) and triethanolamine borate (TEB) in a mass ratio of 1:2 is added to the base electrolyte as the electrolyte.

[0061] Example 6

[0062] This embodiment is basically the same as that in Embodiment 1, except that 0.25 wt % of 2-propoxy-5-pyridine borate is added to the basic electrolyte as the electrolyte.

[0063] Example 7

[0064] This embodiment is basically the same as that in Embodiment 1, except that 0.5 wt % of 2-propoxy-5-pyridine borate is added to the basic electrolyte as the electrolyte.

[0065] Example 8

[0066] This embodiment is basically the same as that in Embodiment 1, except that 1 wt % of 2-propoxy-5-pyridine borate is added to the basic electrolyte as the electrolyte.

[0067] Example 9

[0068] This embodiment is basically the same as the embodiment 1, except that: 0.25 wt % of a functional additive is added to the basic electrolyte as the electrolyte, wherein the functional additive is triethanolamine borate as the electrolyte.

[0069] Example 10

[0070] This embodiment is basically the same as the embodiment 1, except that 0.5 wt % of a functional additive is added to the basic electrolyte as the electrolyte, wherein the functional additive is triethanolamine borate as the electrolyte.

[0071] Embodiment 11

[0072] This embodiment is basically the same as the embodiment 1, except that 1 wt % of a functional additive is added to the basic electrolyte as the electrolyte, wherein the functional additive is triethanolamine borate as the electrolyte.

[0073] Comparative Example 2

[0074] 1.0 mol of LiPF6 was dissolved in ethylene carbonate (EC) / diethyl carbonate (DEC) with a mass ratio of 3:7 to form a mixed solution (the total mass of the mixed solution was 2 g) to form a basic electrolyte solution free of fluoroethylene carbonate.

[0075] The rest is the same as in Example 1.

[0076] Comparative Example 3

[0077] This embodiment is basically the same as Embodiment 1, except that 1.0 mol of LiPF6 is dissolved in a mixed solution of ethylene carbonate (EC) / diethyl carbonate (DEC) in a mass ratio of 3:7 and containing 1.5 wt% of fluoroethylene carbonate (the total mass of the mixed solution is 2 g) to form basic electrolytes with different contents of fluoroethylene carbonate.

[0078] Comparative Example 4

[0079] This embodiment is basically the same as Embodiment 1, except that 1.0 mol of LiPF6 is dissolved in a mixed solution of ethylene carbonate (EC) / diethyl carbonate (DEC) in a mass ratio of 3:7 and containing 4.5 wt% of fluoroethylene carbonate (the total mass of the mixed solution is 2 g) to form basic electrolytes with different contents of fluoroethylene carbonate.

[0080] Comparative Example 5

[0081] 1.0 mol of LiPF6 was dissolved in a mixed solution of propylene carbonate / dimethyl carbonate in a mass ratio of 3:7 and containing 3 wt% of fluoroethylene carbonate (the total mass of the mixed solution was 2 g) to form a basic electrolyte with different solvents.

[0082] The rest is the same as in Example 1.

[0083] Comparative Example 6

[0084] This embodiment is basically the same as Embodiment 1, except that 1.0 mol of LiPF6 is dissolved in a propylene carbonate / dimethyl carbonate mixed solution (the total mass of the mixed solution is 2 g) in a mass ratio of 3:7 to form a basic electrolyte that does not contain fluoroethylene carbonate.

[0085] Comparative Example 7

[0086] This comparative example is basically the same as the example, except that 0.5 wt % of triethyl diphosphate is added to the basic electrolyte as the electrolyte.

[0087] Comparative Example 8

[0088] This comparative example is basically the same as Example 1, except that 0.5 wt % of tetrabutyl silicate is added to the basic electrolyte as the electrolyte.

[0089] Comparative Example 9

[0090] This comparative example is basically the same as that in Example 1, except that 0.5 wt % of tris(hexafluoroisopropyl) borate is added to the base electrolyte as the electrolyte.

[0091] The test results of assembling NCM9055||Li half-cells with the electrolytes of Examples 1-11 and Comparative Examples 1-9 are shown in Table 1.

[0092] Table 1

[0093]

[0094] The experimental results show that although the initial specific capacity of the battery is not much different when added alone, the retention rate of the single addition decreases significantly with the increase in the number of cycles. This shows that although both additives can provide good electrochemical performance in the early stage, the limitations of the two additives used alone will appear in long-term cycles. Specifically, 2-propoxy-5-pyridine borate can provide good interface protection at high voltage and inhibit the growth of lithium dendrites by virtue of its excellent polarity adjustment ability and steric hindrance effect. However, when used alone, its chemical stability and thermal stability in long-term cycles are relatively weak, which can easily lead to aggravated interfacial reactions, thereby affecting the retention rate of the battery. On the other hand, triethanolamine borate performs well in chemical stability and thermal stability, and can reduce the generation of LiF through hydrogen bonding and coordination, thereby reducing interfacial impedance. However, its interface protection effect under high voltage conditions is relatively insufficient, which can easily lead to faster specific capacity decay, especially in long-term cycles. Therefore, the present invention uses the two in a 1:1 composite to give full play to the advantages of the two and make up for their respective shortcomings. The use of composite additives can not only maintain a good initial specific capacity, but also significantly improve the cycle retention rate of the battery, especially under high voltage and long-term cycle conditions. The combination of 2-propoxy-5-pyridine borate and triethanolamine borate can effectively complement their respective deficiencies. The former mainly provides interface protection under high voltage, while the latter excels in chemical stability and thermal stability. This complementary effect makes the electrolyte more durable as a whole and can maintain stable electrochemical properties during long-term use.

[0095] From the above data, it can be seen that the electrolyte composed of 1.0 mol of LiPF6 dissolved in a mixed solution of ethylene carbonate (EC) / diethyl carbonate (DEC) with a mass ratio of 3:7 and containing 3wt% fluoroethylene carbonate (FEC) is the most preferred basic electrolyte and compared with the addition of additives of phosphate, silicate and borate containing only fluorine groups, the addition of nitrogen-containing and propoxy-containing boron-based electron-deficient compounds to the basic electrolyte can significantly improve the cycle retention rate of lithium ions at high operating voltage and extreme temperature (-20°C).

[0096] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An electrolyte having a wide temperature range and high voltage resistance, characterized in that: The wide temperature range and high voltage resistant electrolyte comprises a lithium salt, a non-aqueous organic solvent and a boron electron-deficient compound functional additive, wherein the mass content of the boron electron-deficient compound functional additive in the electrolyte is 0.25% to 1%, and the boron electron-deficient compound functional additive is 2-propoxy-5-pyridine borate and / or triethanolamine borate.

2. The wide temperature range and high voltage resistant electrolyte according to claim 1, characterized in that: Wherein 2-propoxy-5-pyridine borate has the following structural formula: The functional additive is a binary electrolyte additive composed of 2-propoxy-5-pyridine borate and triethanolamine borate in a ratio of 1:

1.

3. The wide temperature range and high voltage resistant electrolyte according to claim 1, characterized in that: The lithium salt is lithium hexafluorophosphate.

4. The wide temperature range and high voltage resistant electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent is a mixture of ethylene carbonate, diethyl carbonate and fluoroethylene carbonate.

5. The wide temperature range and high voltage resistant electrolyte according to claim 3, characterized in that: The mass ratio of ethylene carbonate to diethyl carbonate is 3:7, and the fluoroethylene carbonate accounts for 1.5-4.5wt% of the total mass of the mixed solution of ethylene carbonate and diethyl carbonate.

6. The wide temperature range and high voltage resistant electrolyte according to claim 1 has an operating voltage range of 2.75 V to 4.6 V, and a capacity retention rate of 89.88% after 100 charge and discharge cycles.

7. The method for preparing a wide temperature range and high voltage resistant electrolyte according to any one of claims 1 to 6, characterized in that: In a reaction container filled with inert gas, lithium salt is first dissolved in a non-aqueous organic solvent, and then stirred on a stirrer as a basic electrolyte; then boron-based electron-deficient compound functional additives are added to the basic electrolyte to obtain an electrolyte with a wide temperature range and high voltage.

8. The method for preparing a wide temperature range and high voltage resistant electrolyte according to claim 7, characterized in that: In an inert gas environment, the lithium salt is dissolved in a non-aqueous organic solvent at a constant temperature of 30° C., with a stirring speed of 300 rpm for 30 minutes, and then the boron electron-deficient compound functional additive is added and stirring is continued for 20 minutes.

9. Use of the wide temperature range and high voltage resistant electrolyte according to any one of claims 1 to 6, characterized in that: The wide temperature range and high voltage resistant electrolyte is an electrolyte for lithium ion batteries using high nickel ternary materials as positive electrode materials.

10. The use of the wide temperature range and high voltage resistant electrolyte according to claim 9, characterized in that: The lithium ion battery is LiNi 0.90 Co 0.05 Mn 0.05 O2||Li.

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