Electrolyte additive as well as preparation method and application thereof

Abstract

The invention provides an electrolyte additive as well as a preparation method and application thereof, and relates to the technical field of secondary batteries. Specifically, the invention provides a novel electrolyte additive with a specific structure, and the novel electrolyte additive is used for a sodium-ion battery electrolyte and has wide-temperature-range electrochemical performance. The additive contains sulfonate functional groups, conjugated aromatic rings and silicon-oxygen bonds, and due to the unique structure and functional group characteristics, when the additive is applied to the electrolyte, the low-temperature cycling stability, mechanical performance and safety performance of the battery can be improved, and the additive has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and more specifically, to an electrolyte additive, its preparation method, and its application. Background Technology

[0002] With the increasing popularity of electric vehicles, global demand for lithium-ion batteries has surged. However, the limited supply, uneven geographical distribution, and high price of lithium have raised concerns about its sustainable supply. Sodium-ion batteries (SIBs) have emerged as a promising alternative due to the abundance and low cost of sodium resources. Sodium ions typically have a lower desolvation energy than lithium ions, thus reducing the activation barrier for their participation in electrochemical reactions. Furthermore, sodium salts generally exhibit better thermal stability than lithium salts, giving sodium-ion batteries the potential to operate over a wide temperature range. In recent years, although progress has been made in electrode materials for sodium-ion batteries, the development of electrolytes still falls short of meeting the demands of large-scale energy storage. Achieving long cycle life, high rate capability, and ensuring wide temperature range compatibility remain technical challenges. To ensure efficient operation over a wide temperature range, sodium-ion battery electrolytes must possess fundamental characteristics such as high conductivity, low viscosity, and high electrochemical stability over a broad temperature range.

[0003] It is known in the art that excessively low and high temperatures reduce ion transport rates and interfacial stability, thereby degrading electrochemical performance. At low temperatures, delayed ion transport in the electrolyte, increased desolvation barriers, and increased charge transfer resistance at the interface lead to slow kinetics, further resulting in severe electrochemical polarization and a significant reduction in capacity. In contrast, as the temperature increases, the kinetic problems disappear, replaced by electrolyte deterioration and numerous side reactions at the electrode or electrolyte interface, leading to rapid performance degradation, and even thermal runaway and subsequent safety issues. Therefore, to meet the requirements of a wide operating temperature range, in addition to selecting suitable solvents with high dielectric constants, low viscosity, low melting points, and high boiling points, as well as highly soluble salts with sufficient stability to ensure the electrolyte's liquefaction temperature range and sufficient ionic conductivity, it is also necessary to design and reconstruct an electrode / electrolyte interface with rapid sodium ion transport capabilities, compatibility with both positive and negative electrodes, and thermal stability.

[0004] In traditional electrolytes, high-dielectric-constant electrolytes such as ethylene carbonate (EC) facilitate sodium salt dissociation and migration. However, the sodium ion solvation layer contains more solvent molecules, leading to high desolvation energy and the easy formation of organic-rich solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), which affect sodium ion transfer kinetics and battery electrochemical performance. Although high-concentration electrolytes and locally high-concentration electrolytes have improved these problems to some extent, their high cost and poor performance at high and low temperatures have hindered further development. Conversely, in weakly solvated electrolytes (WSE), the weak interaction between sodium ions and solvent molecules lowers the energy barrier for sodium ion desolvation, which is beneficial for improving sodium ion transport kinetics. Furthermore, its solvation layer is rich in anions, which is conducive to the formation of inorganic-rich SEI. However, WSE has certain limitations in application due to its low dielectric constant and insufficient sodium salt dissolution. Therefore, balancing the sodium ion solvation and desolvation processes and developing electrolytes with high ionic conductivity, low desolvation energy barrier, and stable electrode / electrolyte interface is crucial for realizing high-performance sodium-ion batteries over a wide temperature range. Achieving sodium-ion batteries that operate over a wide temperature range remains a challenge due to the poor conductivity of the electrolyte and the instability of the electrode interface under extreme temperatures.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide an electrolyte additive, primarily for use in sodium-ion battery electrolytes, to address the shortcomings of conventional electrolytes in achieving both high and low temperature performance.

[0007] The second objective of this invention is to provide a method for preparing the electrolyte additive described above, which is simple, easy to implement, and can be widely applied.

[0008] A third objective of this invention is to provide an electrolyte that improves the full-temperature performance of sodium-ion batteries by introducing the electrolyte additives of this invention into carbonate solvents. The introduction of the additives optimizes the solvation structure, accelerates reaction kinetics, removes residual H2O / HF in the electrolyte, and promotes the formation of a high-quality interfacial film, thereby greatly improving the performance of sodium-ion batteries in complex environments.

[0009] The fourth objective of this invention is to provide a secondary battery.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: An electrolyte additive comprising compounds represented by structural formula (I) and / or structural formula (II); (I), (II).

[0011] A method for preparing the electrolyte additive includes the following steps: A first reaction system containing reactants, a first catalyst and a nucleophile was prepared and stirred at 60℃~120℃ for 4h~8h to obtain a phenolic hydroxyl-substituted intermediate product. A second reaction system comprising the intermediate product, the second catalyst and trimethylchlorosilane was prepared and reacted under microwave conditions for 1 min to 4 min to obtain a compound as shown in structural formula (I) or structural formula (II); Wherein, when the product is a compound represented by structural formula (I), the reactants include compounds represented by structural formula (III); when the product is a compound represented by structural formula (II), the reactants include compounds represented by structural formula (IV). (III) (IV); The R group is a halogen atom Br.

[0012] Preferably, the first catalyst comprises cuprous iodide, and the nucleophile comprises at least one of sodium hydroxide, potassium hydroxide, potassium tert-butoxide, and sodium carbonate.

[0013] Preferably, the solvent of the first reaction system includes polyethylene glycol and water, and the volume ratio is (2~6):1.

[0014] Preferably, the molar ratio of the reactant to the first catalyst is 1:(0.1~0.2), and the molar ratio of the reactant to the nucleophile is 1:(4~8).

[0015] Preferably, the second catalyst comprises elemental iodine.

[0016] Preferably, the solvent of the second reaction system includes at least one of tetrahydrofuran, N,N-dimethylformamide, dichloromethane, dichloroethane, and 1,4-dioxane.

[0017] Preferably, the molar ratio of the intermediate product to trimethylchlorosilane is 1:(1.1~1.5), and the molar ratio of the intermediate product to the second catalyst is 1:(0.1~0.3).

[0018] An electrolyte comprising the electrolyte additives.

[0019] Preferably, the mass ratio of the electrolyte additive to the electrolyte is 1% to 5%.

[0020] Preferably, the electrolyte further includes a non-aqueous organic solvent and a sodium salt; The mass ratio of the non-aqueous organic solvent to the electrolyte is 60% to 90%, and the mass ratio of the sodium salt to the electrolyte is 8% to 25%.

[0021] A secondary battery comprising either the electrolyte additive or the electrolyte.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention designs and provides a novel type of electrolyte additive, which is specifically designed for use in sodium-ion battery electrolytes and is a wide-temperature-range stable additive.

[0023] (2) Because the fluorine electrolyte additive can reduce the side reaction caused by fluorine to generate HF substances that are easy to corrode electrode materials; and the additive of the present invention contains sulfonate functional groups, which improves the temperature adaptability range of the electrolyte. The sodium alkyl sulfonate generated by decomposition can form a composite interface film with NaF, which has both mechanical strength and toughness. It will optimize the performance of the battery interface film during battery cycling; effectively inhibit the dissolution of transition metals and sodium deposition on the negative electrode, and significantly improve the overall cell performance and stability.

[0024] (3) The additive of the present invention contains a conjugated aromatic ring, which can react with hexafluorophosphate (PF6) through π-π conjugation. - Combined with additives, it promotes PF6 - Entering the solvation shell of sodium ions weakens the coordination between sodium and solvent molecules, forming a weak solvation structure, lowering the desolvation energy barrier of sodium, and further improving the ion migration efficiency inside the electrolyte.

[0025] (4) The additive structure of the present invention is stable, and the Si-O bond therein has the effect of inhibiting and isolating the trace amounts of H2O and HF in the electrolyte, thereby improving the cycle stability and safety performance of the battery. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 A synthetic route diagram of Embodiment 1 of the present invention is provided; Figure 2 A synthesis route diagram for Embodiment 2 of the present invention is provided. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0029] The performance of wide-temperature-range electrolytes is mainly related to the ion transport capabilities of the internal electrodes, electrolyte, and interface of the secondary battery. Modification of electrode materials has limited impact on low-temperature performance. Optimization of both the electrolyte and the battery interface relies on electrolyte modification; however, current electrolyte optimization primarily focuses on solvent optimization. Using low-melting-point solvents maintains lower viscosity at low temperatures, increasing ion transport rates. However, the sodium ion desolventizing barrier and increased interfacial impedance still exist at low temperatures, resulting in limited performance improvement. Simultaneously, while the internal kinetics of the electrolyte, i.e., ion transport performance, improve at high temperatures, the electrolyte is highly susceptible to deterioration at high temperatures, leading to increased interfacial side reactions between the electrodes and electrolyte. This could potentially cause thermal runaway during charge and discharge, resulting in safety issues.

[0030] Current research on electrolyte modification mainly focuses on the ionic conductivity and ion transport kinetics of electrolytes. Therefore, the primary modification targets are solvents and salts, with limited research and development on additives. The main improvement directions are increasing the viscosity of the solvent system to improve interfacial properties, as interfacial stability can improve the low-temperature performance of batteries to some extent. However, research on the effects of additives on the overall stability of electrolytes, improving the dielectric constant of the electrolyte system, the solvent-desolventization process capability, and the interfacial repair capability is limited.

[0031] A first aspect of the present invention is to provide an electrolyte additive, comprising compounds represented by the following structural formulas (I) and / or (II); (I), (II).

[0032] It is understood that the electrolyte additive of the present invention may be composed independently of the compound shown in structural formula (I), or independently of the compound shown in structural formula (II), or composed of the compounds shown in structural formulas (I) and (II) together; in addition, other components may be additionally included in addition to the compounds shown in structural formulas (I) and / or (II), without strict limitation in this regard.

[0033] A second aspect of the present invention is to provide a method for preparing an electrolyte additive as described in the first aspect, which mainly includes the following steps: A first reaction system containing reactants, a first catalyst and a nucleophile was prepared and stirred at 60℃~120℃ for 4h~8h to obtain a phenolic hydroxyl-substituted intermediate product. A second reaction system comprising the intermediate product, the second catalyst and trimethylchlorosilane was prepared and reacted under microwave conditions for 1 min to 4 min to obtain a compound as shown in structural formula (I) or structural formula (II); Wherein, when the product is a compound represented by structural formula (I), the reactants include compounds represented by structural formula (III); when the product is a compound represented by structural formula (II), the reactants include compounds represented by structural formula (IV). (III) (IV); The R group independently includes one of F, Cl, Br, and I; in some preferred embodiments, the R group is entirely composed of halogen atoms Br.

[0034] In a preferred embodiment, the temperature of the stirring reaction is 80℃~100℃, and the duration is 5h~6h.

[0035] In a preferred embodiment, the first catalyst comprises cuprous iodide, and the nucleophile comprises at least one of sodium hydroxide, potassium hydroxide, potassium tert-butoxide, and sodium carbonate; in some more preferred embodiments, the nucleophile comprises one or both of sodium tert-butoxide and potassium hydroxide.

[0036] In a preferred embodiment, the solvent of the first reaction system comprises polyethylene glycol and water, and the volume ratio of the two is (2~6):1. In some more preferred embodiments, the molar ratio of the reactants to the solvent of the first reaction system is 1:(3~8).

[0037] In a preferred embodiment, the molar ratio of the reactant to the first catalyst is 1:(0.1~0.2), and the molar ratio of the reactant to the nucleophile is 1:(4~8).

[0038] In a preferred embodiment, the reactants obtained by the stirring reaction are extracted to obtain an organic phase, and then the organic phase is purified and separated by a chromatography column to obtain the intermediate.

[0039] In a preferred embodiment, the reaction is carried out under microwave conditions for 2 to 3 minutes.

[0040] In a preferred embodiment, the power of the microwave conditions is 80W to 100W. In some more preferred embodiments, the temperature of the reaction system obtained based on the microwave conditions is 40°C to 60°C, and more preferably 45°C to 55°C.

[0041] In a preferred embodiment, the second catalyst comprises elemental iodine.

[0042] In a preferred embodiment, the solvent of the second reaction system includes at least one selected from tetrahydrofuran, N,N-dimethylformamide, dichloromethane, dichloroethane, and 1,4-dioxane, more preferably dichloromethane and / or dichloroethane. In some more preferred embodiments, the molar ratio of the intermediate product to the solvent of the second reaction system is 1:(3~8).

[0043] In a preferred embodiment, when the reactant is a compound as shown in structural formula (III), the intermediate product corresponds to a compound as shown in structure (V); when the reactant is a compound as shown in structural formula (IV), the intermediate product corresponds to a compound as shown in structure (VI). (V), (VI).

[0044] In a preferred embodiment, the molar ratio of the intermediate product to trimethylchlorosilane is 1:(1.1~1.5), more preferably 1:(1.2~1.4), and the molar ratio of the intermediate product to the second catalyst is 1:(0.1~0.3), more preferably 1:(0.1~0.2).

[0045] In a preferred embodiment, the solvents of the first reaction system and the second reaction system are purified before use, and the purification process includes either redistillation or molecular sieve dehydration.

[0046] In a more preferred embodiment, the anhydrous indicator for the molecular sieve dewatering treatment is benzophenone and sodium filament, and the molecular sieve includes one of 4A, 5A, and 13X type molecular sieves, requiring that the water content in the reaction dispersion medium is <1ppm; more preferably, the molecular sieve is at least one of 5A or 13X.

[0047] In a preferred embodiment, after the reaction under microwave conditions is completed, the mixture is cooled to room temperature, diluted with a solvent, washed with a dilute sodium thiosulfate solution, and then extracted and washed several times with water to collect the organic phase. The organic phase is dried, the solvent is removed by vacuum distillation, and then purified by column chromatography to obtain the product.

[0048] A third aspect of the present invention is to provide an electrolyte comprising the electrolyte additives described in the first aspect.

[0049] In a preferred embodiment, the mass ratio of the electrolyte additive to the electrolyte is 1% to 5%, including but not limited to any one or any two of the following: 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%.

[0050] In a preferred embodiment, the electrolyte further includes a non-aqueous organic solvent and a sodium salt; it is understood that the electrolyte may also include other functional components, which are not strictly limited in this invention.

[0051] In a more preferred embodiment, the non-aqueous organic solvent includes one or more of organic esters, C1-C10 alkyl ethers, cyclic ethers, sulfones, and dinitriles.

[0052] As a further preferred embodiment, the organic esters include ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and 1,4-ethylhexyl carbonate. At least one of butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and ethyl butyrate; the C1-C10 alkyl ethers include at least one of dimethyl ether, diethyl ether, and methyl ethyl ether; the cyclic ethers include at least one of tetrahydrofuran, 1,3-dioxolane, and 2-methyltetrahydrofuran; the dinitrile includes at least one of adiponitrile, succinic anion, and glutaronitrile; and the sulfones include at least one of dimethyl sulfoxide and sulfolane.

[0053] In a more preferred embodiment, the sodium salt includes at least one of sodium hexafluorophosphate (NaPF6), sodium difluorosulfonamide (NaFSI), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium difluorophosphate (NaPO2F2), and sodium difluorooxalate borate (NaODFB).

[0054] In a more preferred embodiment, the mass ratio of the non-aqueous organic solvent to the electrolyte is 60% to 90%, more preferably 74% to 90%.

[0055] In a more preferred embodiment, the mass ratio of the sodium salt to the electrolyte is 8% to 25%, more preferably 13% to 15%.

[0056] In a preferred embodiment, the preparation method of the electrolyte includes: fully mixing the raw material components of the electrolyte. The full mixing can be assisted by means of oscillation, stirring, shaking, centrifugation, ultrasound, heating, etc., which helps to accelerate dispersion and obtain a relatively uniform dispersion system.

[0057] A fourth aspect of the present invention is to provide a secondary battery comprising an electrolyte additive as described in the first aspect, or comprising an electrolyte as described in the third aspect. It is understood that, based on the background and technical features of the present invention, the secondary battery is typically a sodium-ion secondary battery.

[0058] It is understood that, apart from the electrolyte containing the electrolyte additive, the secondary battery includes a positive electrode, a negative electrode, a separator, and other necessary or non-essential functional components or packaging components, which can be arbitrarily selected and combined by those skilled in the art; when the secondary battery contains the electrolyte additive of the present invention, it can be considered as an embodiment of the present invention regardless of whether the secondary battery also uses electrolyte components.

[0059] In a preferred embodiment, the positive electrode active material includes at least one of sodium manganate, sodium copper iron manganate, sodium nickel iron manganate, sodium copper nickel iron manganate, sodium iron phosphate, sodium vanadium phosphate, and composite sodium iron phosphate, with sodium nickel iron manganate being more preferred.

[0060] In a preferred embodiment, the negative electrode active material includes at least one of hard carbon, soft carbon, artificial graphite, natural graphite, metallic sodium, silicon-carbon composite material, and silicon suboxide, with hard carbon being more preferred.

[0061] In a preferred embodiment, the diaphragm includes at least one of a polypropylene membrane, a polyethylene membrane, and a glass fiber diaphragm.

[0062] Example 1 like Figure 1 A synthesis roadmap for this embodiment is provided.

[0063] S1. Add 10g (1 eq, 0.0305 mol) of 99% pure benzo[a]propanesulfonyl 5,7-dibromo ...

[0064] The mass spectrometry results are as follows: TOF-MS (ESI) m / z calcd for C7H6O5S: 201.99; [M+H]+found: 202.81.

[0065] S2. Add 10g (1 eq, 0.0495 mol) of substance B1 prepared in the previous step to an Erlenmeyer flask, then add 50 mL of dichloroethane after dehydration using 5A molecular sieve. After thorough stirring and dissolution, weigh out 6.45g (1.2 eq, 0.0594 mol) of trimethylchlorosilane and 1.25g (0.1 eq, 0.005 mol) of elemental iodine catalyst and add them to the reaction system. Place the Erlenmeyer flask in a microwave oven at 90W power for 2 min. The system temperature after the reaction is 50℃. Cool the system temperature to room temperature, dilute the reaction solution with dichloroethane, wash with dilute sodium thiosulfate solution, and wash three times with extraction water. Collect the organic phase, dry it with anhydrous sodium sulfate, filter it, and distill the remaining solvent under reduced pressure to obtain the organic phase. The organic phase is separated by dry loading onto a silica gel column using ethyl acetate and methanol (volume ratio 2:3) as eluents. Finally, substance M1 is obtained with a yield of 67% (11.5g) and a purity of 99%.

[0066] The mass spectrometry results are as follows: TOF-MS (ESI) m / z calcd for C 13 H 22 O5SSi2: 346.54; [M+H]+ found: 347.48.

[0067] Example 2 like Figure 2 A synthesis roadmap for this embodiment is provided.

[0068] S1. Add 10g (1 eq, 0.04 mol) of 99% pure benzo[a]propanesulfonyl 5-bromosulfonyl ester to a reaction flask equipped with a thermometer, then add 100mL of pure water and heated and melted polyethylene glycol (v:v=1:4). After stirring and dissolving thoroughly, weigh out 0.76g (0.1 eq, 0.004 mol) of cuprous iodide and 23g (6 eq, 0.24 mol) of sodium tert-butoxide and add them to the reaction system. Control the temperature of the reaction system at 100℃ and stir for 6h. Then, return the system temperature to room temperature, acidify with dilute hydrochloric acid solution, and adjust the pH value to 2.5±0.5. Extract the organic phase three times with ethyl acetate. After dry loading of the organic phase, separate it on a silica gel column using ethyl acetate and methanol (volume ratio 1:3). The final product is substance B2 with a yield of 87% (6.47g) and a purity of 99%.

[0069] The mass spectrometry results are as follows: TOF-MS (ESI) m / z calcd for C7H6O4S: 186; [M+H]+found: 186.99.

[0070] S2. Add 10g (1 eq, 0.0538 mol) of substance B2 prepared in the previous step to an Erlenmeyer flask, then add 50 mL of dichloromethane after water removal using 5A molecular sieve. After thorough stirring and dissolution, weigh out 8.18g (1.4 eq, 0.0753 mol) of trimethylchlorosilane and 2.73g (0.2 eq, 0.011 mol) of elemental iodine catalyst and add them to the reaction system. Place the Erlenmeyer flask in a microwave oven at 100W power for 3 min. After the reaction, the system temperature is 54℃. Cool the system temperature to room temperature, dilute the reaction solution with dichloroethane, wash with dilute sodium thiosulfate solution, and wash three times with extraction water. Collect the organic phase and dry it with anhydrous sodium sulfate. After filtration, distill the remaining solvent under reduced pressure to obtain the organic phase. The organic phase is then separated on a silica gel column using a dry loading method. The eluent used is ethyl acetate and methanol (volume ratio 2:3). Finally, substance M2 is obtained with a yield of 75% (10.4g) and a purity of 99%.

[0071] The mass spectrometry results are as follows: TOF-MS (ESI) m / z calcd for C 10 H 14 O4SSi: 258.36; [M+H]+ found: 259.24.

[0072] Electrolytes for sodium-ion batteries were prepared using substances M1 or M2 obtained in Examples 1 or 2, as shown in the following examples. First, in a nitrogen-filled glove box, propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of PC:EMC:DEC = 3:5:2. Sodium hexafluorophosphate was slowly added to the mixed solution until the molar concentration of NaPF6 reached 1 mol / L, thus obtaining a standard electrolyte.

[0073] Example 3 The electrolyte of this example was obtained by adding 1 wt.% of M1 from Example 1 to the standard electrolyte.

[0074] Example 4 The electrolyte of this example was obtained by adding 3 wt.% of M1 from Example 1 to the standard electrolyte.

[0075] Example 5 The electrolyte of this example was obtained by adding 5 wt.% of M1 from Example 1 to the standard electrolyte.

[0076] Example 6 The electrolyte of this example was obtained by adding 1 wt.% of M2 from Example 2 to the standard electrolyte.

[0077] Example 7 The electrolyte of this example was obtained by adding 3 wt.% of M2 from Example 2 to the standard electrolyte.

[0078] Example 8 The electrolyte of this example was obtained by adding 5 wt.% of M2 from Example 2 to the standard electrolyte.

[0079] Comparative Example 1: Standard Electrolyte Comparative Example 2 To the standard electrolyte, 1 wt.% of unsaturated carbonate additive vinylene carbonate (VC) was added to obtain the electrolyte of this comparative example.

[0080] Comparative Example 3 The electrolyte of this comparative example was obtained by adding 1 wt.% of fluorocarbonate additive fluoroethylene carbonate (FEC) to the standard electrolyte.

[0081] Comparative Example 4 The electrolyte of this comparative example was obtained by adding 1 wt.% of sulfolane, a sulfone additive, to the standard electrolyte.

[0082] Comparative Example 5 The electrolyte of this comparative example was obtained by adding 1 wt.% of the ether additive 18-crown ether-6 to the standard electrolyte.

[0083] Experimental Example 1 After preparing the electrolytes of Examples 3-8 and Comparative Examples 1-5, their viscosity, moisture content after standing for 48 hours, and electrolyte state after being placed in a high temperature environment of 60°C for 7 days were tested. The results are summarized in Table 1 below.

[0084] Table 1

[0085] Experimental Example 2 The method for preparing a sodium-ion battery 2032 for testing is as follows: Weigh out the active material Na... 0.9 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, carbon black, and PVDF binder solution (5 wt.% PVDF solution prepared with NMP as solvent) in a mass ratio of 8:1:1 were dissolved in NMP, mixed and stirred for 5 h, and then evenly coated onto the current collector. The mixture was then vacuum dried for 12 h and pressed into a positive electrode sheet using a die-cutting machine. The positive electrode sheet was then brought into a glove box for battery assembly. The negative electrode of the battery used a sodium sheet, the separator used a PE film, and the electrolyte was prepared according to the electrolytes prepared in Examples 3-8 and Comparative Examples 1-5. Each electrolyte was used to prepare a button cell for testing.

[0086] The button batteries used for testing were tested for 1000 cycles at room temperature (25℃), discharge performance at the first low temperature (-20℃), discharge performance at the second low temperature (-40℃), and 150 cycles at high temperature (60℃). The results of the tests in sequence are shown in Table 2 below.

[0087] Table 2

[0088] The data above clearly shows that: a) The addition of the novel additive of this invention can effectively reduce the viscosity of the existing basic electrolyte formulation system. Furthermore, monitoring of the water content in the electrolyte under air conditions shows that the addition of the additive of this invention can significantly inhibit the rise of trace water in the electrolyte, further protecting the battery electrolyte from deterioration due to increased water content, inhibiting the generation of HF after further side reactions, and significantly improving the overall stability of the electrolyte under high temperature conditions, thereby improving the subsequent cycle stability and safety of the battery.

[0089] (b) In sodium-ion batteries, after 1000 cycles at room temperature, the capacity retention rate is above 91.4%; after 150 cycles at high temperature, the capacity retention rate is above 95.5%; the discharge retention rate at low temperature (-20℃) is above 93.3%, and at low temperature (-40℃) it is above 83.3%, with a high capacity retention rate after cycling. It can be seen that the multiple synergistic effects of the additives in this invention contribute to the battery's excellent discharge performance and capacity retention rate over a wide temperature range. This provides a framework for the subsequent development of wide-temperature-range electrolyte formulations. In contrast, batteries prepared using existing positive and negative electrode film-forming additives exhibit significantly lower battery performance under harsh conditions such as high and low temperatures compared to those prepared with the additives of this invention.

[0090] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. An electrolyte additive, characterized in that, Including compounds represented by the following structural formulas (I) and / or (II); (AND), (II)。 2. The method for preparing the electrolyte additive as described in claim 1, characterized in that, Includes the following steps: A first reaction system containing reactants, a first catalyst and a nucleophile was prepared and stirred at 60℃~120℃ for 4h~8h to obtain a phenolic hydroxyl-substituted intermediate product. A second reaction system comprising the intermediate product, the second catalyst and trimethylchlorosilane was prepared and reacted under microwave conditions for 1 min to 4 min to obtain a compound as shown in structural formula (I) or structural formula (II); Wherein, when the product is a compound represented by structural formula (I), the reactants include compounds represented by structural formula (III); when the product is a compound represented by structural formula (II), the reactants include compounds represented by structural formula (IV). (III), (IV)) The R group is a halogen atom Br.

3. The preparation method according to claim 2, characterized in that, The first catalyst comprises cuprous iodide, and the nucleophile comprises at least one of sodium hydroxide, potassium hydroxide, potassium tert-butoxide, and sodium carbonate; And / or, the solvent of the first reaction system includes polyethylene glycol and water, and the volume ratio is (2~6):

1.

4. The preparation method according to claim 2, characterized in that, The molar ratio of the reactant to the first catalyst is 1:(0.1~0.2), and the molar ratio of the reactant to the nucleophile is 1:(4~8).

5. The preparation method according to claim 2, characterized in that, The second catalyst comprises elemental iodine; And / or, the solvent of the second reaction system includes at least one of tetrahydrofuran, N,N-dimethylformamide, dichloromethane, dichloroethane, and 1,4-dioxane.

6. The preparation method according to claim 2, characterized in that, The molar ratio of the intermediate product to trimethylchlorosilane is 1:(1.1~1.5), and the molar ratio of the intermediate product to the second catalyst is 1:(0.1~0.3).

7. An electrolyte, characterized in that, Includes the electrolyte additive as described in claim 1.

8. The electrolyte according to claim 7, characterized in that, The mass ratio of the electrolyte additive to the electrolyte is 1% to 5%.

9. The electrolyte according to claim 7, characterized in that, The electrolyte also includes a non-aqueous organic solvent and a sodium salt; The mass ratio of the non-aqueous organic solvent to the electrolyte is 60% to 90%, and the mass ratio of the sodium salt to the electrolyte is 8% to 25%.

10. A secondary battery, characterized in that, Includes the electrolyte additive as described in claim 1 or the electrolyte as described in claim 7.

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