Preparation method of high-flame-retardant two-component functional additive for enhancing ion transport and interface stability, liquid electrolyte and electrochemical battery

Abstract

The invention discloses a preparation method of a high-flame-retardant two-component functional additive for enhancing ion transport and interface stability, a liquid electrolyte and an electrochemical battery, and belongs to the technical field of electrochemical batteries. According to the invention, two additives of 3-(diphenylphosphine) propionitrile and diphenylphosphine oxyethyl phenyl sulfone are firstly designed and prepared, and due to the synergistic effect of phosphorus groups, cyano groups and phenyl sulfone groups, the flame retardance and ionic conductivity of the electrolyte can be remarkably enhanced, the generation of CEI and SEI layers on the surfaces of positive and negative electrodes is promoted, and the cycle stability of the battery is improved. The liquid electrolyte has excellent flame retardant property, and the self-extinguishing time is 12.68 s g <-1 >. And the assembled lithium-lithium symmetrical battery realizes remarkable long-term cycle stability exceeding 1000 hours under the current density of 1 mA cm <-2 >. The capacity retention rate of the Li | | LiFePO4 half cell is up to 98.4% after 800 times of circulation under the 1C multiplying power. The first specific discharge capacity can be kept at 114 mAh g <-1 > even under the large multiplying power of 6 C, and the capacity retention rate is still 94% after 1000 times of circulation.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical battery technology, specifically relating to a method for preparing a highly flame-retardant two-component functional additive that enhances ion transport and interface stability, a liquid electrolyte, and an electrochemical battery. Background Technology

[0002] Electrolyte safety is a key factor limiting the commercial application of liquid lithium metal batteries, and flame-retardant additives can effectively address the safety hazards associated with liquid batteries. However, while traditional single flame-retardant additives can improve the flame-retardant properties of electrolytes to some extent, their functions are relatively limited and cannot meet the demands for improved overall battery performance. Against this backdrop, multifunctional additives based on flame-retardant properties have emerged. These additives not only possess flame-retardant properties but also offer multiple benefits such as enhancing ionic conductivity and electrode interface stability. They hold the promise of fundamentally solving the safety hazards of electrochemical batteries and comprehensively improving their overall performance, thus paving a new path for the development of electrochemical batteries.

[0003] Commonly used flame retardant additives include trimethyl phosphate (TMP) (ACS Applied Energy Materials, 2019, 2(2): 1363-1370), triethyl phosphate (TEP) (International Journal of Electrochemical Science, 2020, 15(11): 11265-11274), triphenyl phosphate (TPP) (Journal of Power Sources, 2014, 256: 430-43), and tributyl phosphate (TBP) (Journal of Power Sources, 2003, 119: 383-387). However, adding these flame retardants significantly increases viscosity and reduces ionic conductivity. Therefore, it is urgent to develop novel flame retardant additives that enhance ionic conductivity. In 2016, Tang et al. (Journal of Physical Chemistry Letters, 2016, 7(22): 4795-4801) determined a novel and faster "solvent-assisted lithium-ion diffusion" mechanism in electrolytes containing C≡N through theoretical calculations, which improved the ionic conductivity of electrolyte systems with this mechanism.

[0004] C≡N and Li + There is a strong ion-dipole interaction between them, which can promote the dissociation process of lithium salts and accelerate the Li... +The migration speed is increased, thereby improving ionic conductivity. The highly redox-active sulfone group allows DPVS to preferentially form CEI and SEI layers on the positive and negative electrode surfaces, respectively, improving battery cycle stability. Introducing C≡N and sulfone groups into the electrolyte additive simultaneously provides high flame retardancy, high ionic conductivity, and high cycle stability. Due to the synergistic effect of phosphorus, cyanide, and sulfone groups, this additive significantly enhances the flame retardancy and ionic conductivity of the electrolyte and effectively promotes the formation of CEI and SEI layers on the positive and negative electrode surfaces, improving battery cycle stability.

[0005] Based on the above reasons, this application is hereby submitted. Summary of the Invention

[0006] Based on the above reasons, and in view of the problems or defects existing in the prior art, the purpose of this invention is to provide a method for preparing a high flame-retardant two-component functional additive that enhances ion transport and interface stability, and an electrochemical battery, thereby solving or at least partially solving the above-mentioned technical defects existing in the prior art.

[0007] To achieve the above-mentioned objectives of the present invention, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a highly flame-retardant two-component functional additive that enhances ion transport and interfacial stability, the method specifically comprising the following steps:

[0009] (1) Preparation of additive 3-(diphenylphosphine)propionitrile (DA)

[0010] Equimolar amounts of diphenylphosphine oxide and acrylonitrile were added to a flask. The flask was evacuated and purged three times to create a vacuum, and then argon (Ar) gas was introduced. Under the Ar atmosphere, the temperature was kept constant, and the reaction was stirred to obtain a transparent gel-like solution. The product was poured into a watch glass while still hot. After cooling to room temperature, the gel-like solution turned into a white waxy solid. The product was placed in a vacuum oven and dried at a certain temperature. Then, it was ground into powder and dried again in a vacuum oven.

[0011] (2) Preparation of additive diphenylphosphoxyethyl sulfone (DPPVS)

[0012] Equimolar amounts of diphenylphosphine oxide and phenylvinyl sulfone nitrile were added to a flask. The flask was evacuated to a vacuum by repeated evacuation and purging three times, and then argon (Ar) gas was introduced. Under the Ar atmosphere, the temperature was kept constant, and the reaction was stirred to obtain a transparent gel-like solution. The product was poured into a watch glass while hot, and after cooling to room temperature, the gel-like solution turned into a white waxy solid. The product was placed in a vacuum oven and dried at a certain temperature, then ground into powder and dried again in a vacuum oven.

[0013] (3) Preparation of two-component additive liquid electrolyte

[0014] A two-component additive liquid electrolyte can be prepared by adding a certain amount of DA and DPPVS to a commercial electrolyte and stirring to dissolve them at room temperature.

[0015] Furthermore, in the above technical solution, the reaction temperature in step (1) is 50-120°C. In a preferred embodiment of the present invention, the reaction temperature is 80°C.

[0016] Furthermore, in the above technical solution, the reaction time in step (1) is 2-48 hours. In a preferred embodiment of the present invention, the reaction time is 12 hours.

[0017] Furthermore, in the above technical solution, the two vacuum drying temperatures in step (1) are room temperature - 120°C. In a preferred embodiment of the present invention, the two vacuum drying temperatures are 80°C.

[0018] Furthermore, in the above technical solution, the two vacuum drying times in step (1) are 2-48 hours. In a preferred embodiment of the present invention, the two vacuum drying times are 12 hours.

[0019] Furthermore, in the above technical solution, the reaction temperature in step (2) is 50-120°C. In a preferred embodiment of the present invention, the reaction temperature is 80°C.

[0020] Furthermore, in the above technical solution, the reaction time in step (2) is 2-48 hours. In a preferred embodiment of the present invention, the reaction time is 12 hours.

[0021] Furthermore, in the above technical solution, the two vacuum drying temperatures in step (2) are room temperature - 120°C. In a preferred embodiment of the present invention, the two vacuum drying temperatures are 80°C.

[0022] Furthermore, in the above technical solution, the two vacuum drying times in step (2) are 2-48 hours. In a preferred embodiment of the present invention, the two vacuum drying times are 12 hours.

[0023] Furthermore, in the above technical solution, the commercial liquid electrolyte in step (3) comprises a commercially available organic liquid electrolyte formulation. In a preferred embodiment of the present invention, the commercial electrolyte (CE) is 1M LiPF6 / EC / DMC.

[0024] Furthermore, in the above technical solution, the content of DA in step (3) is 0%-20 wt.%. In a preferred embodiment of the present invention, the content of DA is 10 wt.%.

[0025] Furthermore, in the above technical solution, the content of DPPVS in step (3) is 0%-20 wt.%. In a preferred embodiment of the present invention, the content of DPPVS is 1 wt.%.

[0026] Furthermore, in the above technical solution, the stirring time in step (3) depends on the stirring efficiency; generally, it is 0.5h-2h at room temperature. In a preferred embodiment of the present invention, the stirring time is 1h.

[0027] Furthermore, the application fields of a method for preparing a highly flame-retardant two-component functional additive that enhances ion transport and interfacial stability include electrochemical batteries such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, and sodium-sulfur batteries. In a preferred embodiment of the present invention, the electrochemical battery is a lithium-ion battery.

[0028] The second objective of this invention is to provide a liquid electrolyte prepared by the method described above, containing a highly flame-retardant two-component functional additive that enhances ion transport and interfacial stability.

[0029] A third objective of this invention is to provide the application of a liquid electrolyte containing a highly flame-retardant two-component functional additive that enhances ion transport and interfacial stability, prepared by the method described above, in an electrochemical battery.

[0030] An electrochemical battery includes a positive electrode, a negative electrode, a separator, and a liquid electrolyte, wherein the liquid electrolyte is the liquid electrolyte of the present invention described above containing a dual-component functional additive that enhances high flame retardancy, high ion transport, and high interface stability.

[0031] Furthermore, in the above technical solution, the positive electrode sheet includes a positive electrode active material, a conductive material, and a binder. The positive electrode active material is lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), or lithium nickel cobalt manganese oxide (LiNi). x Co y Mn z Any one of O2, lithium manganese oxide (LiMn2O4), and S.

[0032] Preferably, in the above technical solution, the preparation method of the positive electrode sheet includes the following steps: mixing the positive electrode active material, conductive material, and binder at a mass ratio of 8:1:1, using N,N-dimethylpyrrolidone as a solvent, thoroughly grinding to form a slurry, then coating it onto aluminum foil using a wet film preparation device, and vacuum drying at 80°C for 12 hours. After drying, using a cutting tool, cutting the aluminum foil coated with the sample into ready-made electrode sheets.

[0033] Furthermore, in the above technical solution, the negative electrode is a lithium metal disc or a sodium metal disc.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] This invention first uses a one-step synthesis method to prepare DA and DPPVS, wherein DA contains both a phosphorus-oxygen double bond and a cyano group, and DPPVS contains both a phosphorus-oxygen double bond and a sulfone group. Then, DA and DPPVS are dissolved in CE to prepare a liquid electrolyte containing DA and DPPVS additives.

[0036] The liquid electrolyte containing 10% DA and 1% DPPVS exhibits excellent flame retardant properties, with a self-extinguishing time of 12.68 sg. -1 This is significantly lower than the self-extinguishing time of commercial liquid electrolytes (83.30 sg). -1 The ionic conductivity of this liquid electrolyte is 0.522 mS / cm at 25℃ and 80℃, respectively. -1 and 0.960mS cm -1 This is far higher than the ionic conductivity of commercial liquid electrolytes (0.112 mS / cm). -1 and 0.269mS cm -1 The assembled lithium-ion symmetric battery operates at 1 mA cm⁻¹. -2 Significant long-term cycling stability exceeding 1000 hours was achieved at the specified current density. The Li‖LiFePO4 half-cell exhibited an initial discharge specific capacity of 134.6 mAh g⁻¹ at 1C rate. -1 The highest capacity reached 144.5 mAh g -1 After 800 cycles, it still maintains 142.1 mAh g. -1 The discharge specific capacity retains a high efficiency of 98.4%. Even at a high rate of 6C, the initial discharge specific capacity remains at 114 mAh g. -1 After 1000 cycles, it still has 110.3 mAh g. -1 The discharge specific capacity has a capacity retention rate of approximately 94%. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 (a) is the synthetic roadmap for DA; (b) is the synthetic roadmap for DPVS.

[0039] Figure 2(a) 1H NMR spectrum of DPOP; (b) 1H NMR spectrum of AN; (c) 1H NMR spectrum of DA.

[0040] Figure 3 (a) 1H NMR spectrum of DPOP; (b) 1H NMR spectrum of PVS; (c) 1H NMR spectrum of DPPVS.

[0041] Figure 4 (a) Combustion states of CE and DA-10%+DPPVS-1% electrolytes at different times; (b) SET and C SET value.

[0042] Figure 5 Ionic conductivity of CE and DA-10%+DPPVS-1% electrolytes.

[0043] Figure 6 (a) Rate performance of Li‖LiFePO4 batteries assembled with CE-based and DA-10%+DPPVS-1% based electrolytes at room temperature; (b) Charge-discharge curves at different rates; (c) Long-term cycle performance at 1C; (d) Long-term cycle performance at 6C.

[0044] Figure 7 Electrochemical impedance spectroscopy (EIS) of Li‖LiFePO4 batteries assembled with CE-based and DA-10%+DPPVS-1% based electrolytes: (a) before cycling; (b) after 50 cycles at 6C.

[0045] Figure 8 After 100 cycles at 6C, the following images were obtained from the CE-based electrolyte battery: (a, b) SEM images of the lithium anode at 100 μm and 10 μm; (c) TEM image of the LiFePO4 cathode at 10 nm; After 100 cycles at 6C, the following images were obtained from the DA-10%+DPPVS-1% based electrolyte battery: (d, e) SEM images of the lithium anode at 100 μm and 10 μm; (f) TEM image of the LiFePO4 cathode at 10 nm.

[0046] Figure 9 XPS spectra of lithium foil anodes after cycling in different electrolytes. CE electrolyte: (a), (c), and (e); DA-10% + DPPVS-1% electrolyte: (b), (d), and (f). Detailed Implementation

[0047] The present invention will be further described in detail below through implementation examples. These implementation examples are carried out based on the technology of the present invention. Detailed implementation methods and specific operating procedures are provided to illustrate the inventiveness of the present invention, but the scope of protection of the present invention is not limited to the following implementation examples.

[0048] Based on the information contained in this application, various modifications to the precise description of the invention can be readily made by those skilled in the art. It should be understood that the scope of the invention is not limited to the defined processes, properties, or components, as these embodiments and other descriptions are merely illustrative of specific aspects of the invention.

[0049] To better understand the invention and not to limit its scope, all figures indicating amounts, percentages, and other numerical values ​​used in this application should, in all cases, be understood to be modified by the word "approximately." Therefore, unless otherwise stated, the numerical parameters listed in the specification are approximate values ​​and may vary depending on the desired properties being sought. Each numerical parameter should at least be considered as obtained based on reported significant figures and through conventional rounding methods.

[0050] The equipment and raw materials used in this invention are all commercially available or commonly used in the field. Unless otherwise specified, the methods in the following embodiments are conventional methods in the field.

[0051] Example 1

[0052] This embodiment describes a method for preparing a liquid electrolyte with a high flame-retardant two-component functional additive that enhances ion transport and interfacial stability. The method specifically includes the following steps:

[0053] (1) Preparation of DA

[0054] like Figure 1 As shown in Figure a, DPOP and AN were added to a flask in equal molar ratios. The flask was evacuated to a vacuum by repeated evacuation and purging three times, and then argon (Ar) gas was introduced. Under the Ar atmosphere, the temperature was kept constant at 80°C, and the reaction was stirred for 12 hours to obtain a transparent gel-like solution. The product was poured into a watch glass while hot, and after cooling to room temperature, the gel-like solution turned into a white waxy solid. The product was placed in a vacuum oven at 80°C and dried for 24 hours, then ground into powder, and dried again in a vacuum oven at 80°C for 24 hours. Finally, it was stored in a glove box for later use.

[0055] (2) Preparation of DPVS

[0056] like Figure 1As shown in b, DPOP and PVS were added to the flask in equal molar ratios. The flask was evacuated to a vacuum by repeated evacuation and purging three times, and then argon (Ar) gas was introduced. Under the Ar atmosphere, the temperature was kept constant at 80°C, and the reaction was stirred for 12 hours to obtain a transparent gel-like solution. The product was poured into a watch glass while hot, and after cooling to room temperature, the gel-like solution turned into a white waxy solid. The product was placed in a vacuum oven at 80°C and dried for 24 hours, then ground into powder, and dried again in a vacuum oven at 80°C for 24 hours. Finally, it was stored in a glove box for later use.

[0057] (3) Preparation of DA-10% + DPPVS-1% liquid electrolyte

[0058] Add 10 wt% DA and 1 wt% DPPVS to CE and name it DA-10%+DPPVS-1%.

[0059] Structural characterization of additives

[0060] Further research was conducted on the chemical structure of the prepared DA. Figure 2 Images (a), (b), and (c) show the 1H NMR spectra of DPOP, AN, and DA, respectively. The peak at 2.5 ppm is the solvent peak, and the peak at 3.3 ppm is the residual water peak. In the 1H NMR spectrum of DPOP, peak a is the characteristic peak of hydrogen atoms on the benzene ring, and peak b is the characteristic peak of PH (8.70 ppm). In the 1H NMR spectrum of AN, peak a is the characteristic peak of unsaturated C=C hydrogen atoms (5.90-6.37 ppm). For the 1H NMR spectrum of DA, the disappearance of the characteristic peaks of PH in DPOP and C=C hydrogen atoms in AN, and the appearance of two peaks at 2.62 ppm and 2.85 ppm (peaks b and c), indicate that the reaction proceeded successfully.

[0061] Further research was conducted on the chemical structure of the prepared DPPVS. Figure 3 Images (a), (b), and (c) show the 1H NMR spectra of DPOP, PVS, and DPPVS, respectively. The peak at 2.5 ppm is the solvent peak, and the peak at 3.3 ppm is the residual water peak. In the DPOP 1H NMR spectrum, peak a is the characteristic peak of hydrogen atoms on the benzene ring, and peak b is the characteristic peak of PH (8.70 ppm). In the PVS 1H NMR spectrum, peaks a and b are characteristic peaks of unsaturated C=C hydrogen atoms (6.2 ppm-6.4 ppm and 7.2 ppm, respectively). For the DPPVS 1H NMR spectrum, the disappearance of the characteristic peaks of PH in DPOP and C=C hydrogen atoms in PVS, and the appearance of two peaks at 2.71 ppm and 3.90 ppm (peaks b and c), indicate that the reaction proceeded successfully.

[0062] Electrolyte flame retardant performance test

[0063] Figure 4 The image shows the combustion state and self-extinguishing time of CE and DA-10%+DPPVS-1% electrolytes over a certain period of time. CE is highly flammable, with a tall flame column and a very bright flame; its SET value is 83.30 sg. -1 The DA-10% + DPPVS-1% electrolyte is difficult to ignite, producing a low flame column and a noticeably dim flame; its SET value is 12.68 sg. -1 The CSET value is 15.22%. It can be seen that the DA-10%+DPPVS-1% electrolyte has extremely high flame retardancy.

[0064] Ionic conductivity performance

[0065] like Figure 5 As shown, the ionic conductivity of CE at room temperature is 0.112 mS / cm. -1 The ionic conductivity of the DA-10%+DPPVS-1% electrolyte is 0.522 mS / cm. -1 As temperature increases, ion transport speed accelerates, and ionic conductivity increases. When the temperature rises to 80℃, the ionic conductivity of both electrolytes increases, with the DA-10% + DPPVS-1% electrolyte exhibiting an ionic conductivity of 0.960 mS / cm. -1 The ionic conductivity is much higher than that of CE (0.269 mS / cm). -1 The high ionic conductivity of the DA-10%+DPPVS-1% electrolyte is mainly attributed to the interaction of C≡N in DA and Li in LiPF6. + The strong coordination of DPVS accelerates the migration rate of Li+, and the CEI and SEI layers formed by the oxidation of the positive electrode and the reduction of the negative electrode, respectively, promote better interfacial contact during battery cycling, thereby enhancing the Li+ at the interface. + Both transport and transport work together to improve the ionic conductivity of the electrolyte.

[0066] Battery charge / discharge and interface performance

[0067] Testing Li‖LiFePO4 batteries can evaluate the rate capability and cycle performance of the electrolyte. Figure 6 Figures (a) and (b) show the rate performance and charge-discharge curves at different rates of Li||LiFePO4 batteries assembled with CE-based and DA-10%+DPPVS-1% based electrolytes at room temperature. The CE-based electrolyte battery showed a capacity of 149.7 mAh g at 0.5C, 1C, and 6C. -1 140.1mAh g -1 and 86.2mAh g -1The reversible discharge capability of the DA-10%+DPPVS-1% based electrolyte battery was observed, while the DA-10%+DPPVS-1% based electrolyte battery exhibited 150.7 mAh g⁻¹ at 0.5C, 1C, and 6C. -1 144.5mAh g -1 and 117.3mAh g -1 Its reversible discharge capability is superior to that of CE-based electrolyte batteries. Figure 6 (c) and (d) show the long-term cycling performance of CE-based and DA-10%+DPPVS-1% based electrolyte batteries at room temperature at 1C and 6C rates, respectively. After 800 cycles at 1C rate, the discharge specific capacity of the CE-based electrolyte battery increased from 140.1 mAh g⁻¹. -1 It dropped to 104.2 mAh g. -1 The degradation rate is as high as 25.7%. However, the initial discharge specific capacity of the DA-10%+DPPVS-1% based electrolyte battery is 134.6 mAh g⁻¹. -1 As cycling progresses, the battery discharge specific capacity shows an increasing trend. This is mainly due to the participation of the DA-10% + DPPVS-1% electrolyte in the film-forming reaction, which forms a uniform SEI layer on the negative electrode surface, improving the Li-10% discharge capacity. + Migration. The highest discharge specific capacity of the DA-10%+DPPVS-1% based electrolyte battery reached 144.5 mAh g. -1 The discharge specific capacity after 800 cycles (142.1 mAh g) -1 Compared to [previous model], the capacity retention rate is approximately 98.4%. After 1000 cycles at a high rate of 6C, the discharge specific capacity of the CE-based electrolyte battery increased from 86.2 mAh g⁻¹. -1 It dropped to 55.4 mAh g. -1 The capacity retention rate is approximately 64.2%. The initial discharge specific capacity of the DA-10%+DPPVS-1% based electrolyte battery is 114 mAh g. -1 The highest capacity is 117.3 mAh g. -1 After 1000 cycles, the discharge specific capacity is 110.3 mAh g. -1 The capacity retention rate is as high as 94.0%. The excellent discharge capability and cycle stability of the DA-10%+DPPVS-1% based electrolyte battery are mainly attributed to the C≡N in the DA-10%+DPPVS-1% electrolyte and the Li in LiPF6. +Strong coordination promotes the dissociation process of lithium salt and accelerates the migration rate of Li+, resulting in high ionic conductivity of the electrolyte and improving battery discharge capability. Simultaneously, the DPVS in the DA-10%+DPPVS-1% electrolyte possesses a high HOMO energy level and reduction potential, and a low LUMO energy level and oxidation potential. This allows DPVS to preferentially participate in film formation reactions on the electrode surface, forming uniform CEI and SEI layers. This promotes better interfacial contact during battery cycling, thereby enhancing Li+ ionization at the interface. + The improved transmission enhances the protection of the electrodes and improves the cycle stability of the battery.

[0068] To analyze the effect of DA-10% + DPVS-1% electrolyte on Li‖LiFePO4 batteries, the electrochemical impedance spectroscopy (EIS) of Li‖LiFePO4 batteries assembled with CE-based and DA-10% + DPVS-1% based electrolytes was measured before cycling and after 50 cycles at 6C. The fitted EIS spectra are shown below. Figure 7 As shown, before cycling, the Li||LiFePO4 battery assembled with CE-based electrolyte exhibited an interface resistance as high as 146 Ω. In contrast, the Li||LiFePO4 battery assembled with DA-10%+DPPVS-1% based electrolyte showed a lower interface resistance of 109 Ω. After 50 cycles at 6C, the CE-based electrolyte battery exhibited an interface resistance as high as 300 Ω, while the DA-10%+DPPVS-1% based electrolyte battery showed a lower interface resistance of 71 Ω. This is likely due to the uniform SEI layer formed by DPPVS in DA-10%+DPPVS-1% on the electrode surface, allowing Li+ to pass through the SEI film more easily, thereby reducing the battery resistance.

[0069] Peeling / plating performance and lithium electrode morphology

[0070] To investigate the effects of DA-10%+DPPVS-1% electrolyte on the lithium anode and LiFePO4 cathode, scanning electron microscopy (SEM) was performed on the lithium anode of Li‖LiFePO4 batteries assembled with CE-based and DA-10%+DPPVS-1% based electrolytes after 100 cycles at 6C, and transmission electron microscopy (TEM) was performed on the LiFePO4 cathode. Figure 8 (a) and Figure 8(b) shows SEM images of the lithium anode at 100 μm and 10 μm after 100 cycles at 6C for the CE-based electrolyte battery. Numerous cracks and granular protrusions are visible on the surface after cycling, while the surface of the DA-10%+DPPVS-1% based electrolyte battery is relatively smooth. This is mainly attributed to the fact that DPVS in the DA-10%+DPPVS-1% additive has a lower LUMO energy level than the electrolyte components (EC, DMC), enhancing its electron attraction and thus preferentially reducing it at the anode to form a uniform SEI layer, thereby enhancing the electrode's protection. Figure 8 (d) and Figure 8 (e)). Figure 8 (c) shows a TEM image of the LiFePO4 cathode after 100 cycles at 6C in a CE-based electrolyte battery. It can be seen that an uneven CEI layer formed on the surface after cycling, indicating significant electrolyte decomposition and severe side reactions on the electrode surface. In contrast, the DA-10%+DPPVS-1% based electrolyte battery formed a CEI layer of approximately 21.36 nm with relatively uniform thickness after cycling. This is mainly attributed to the fact that DPVS in the DA-10%+DPPVS-1% additive has a higher HOMO energy level than the electrolyte components (EC, DMC), enhancing its electron attraction and thus preferentially oxidizing at the cathode to form a uniform CEI layer. Figure 8 (f)). The uniform CEI layer formed by the DA-10% + DPPVS-1% additive effectively inhibits the occurrence of side reactions, thereby reducing electrolyte decomposition and improving the cycle stability of the battery.

[0071] To investigate the compositional changes of the SEI layer on the surface of the lithium anode after cycling with different electrolytes, XPS analysis was performed on lithium sheets after 50 cycles in CE and DA-10%+DPPVS-1% electrolyte batteries. The results are as follows: Figure 9 As shown. Figure 9 (a) and (b) are the C1s spectra of DPPVS-0% and DA-10%+DPPVS-1% electrolytes. The C=O peak (288.8 eV) mainly originates from the decomposition products of alkyl lithium carbonate (RCO2Li) in the electrolyte. The peak at 290.2 eV represents LiCO3, corresponding to Li2CO3 in the SEI membrane. Li2CO3 is one of the main components of lithium salts in the SEI membrane, originating from the irreversible decomposition of LiPF6 and carbonate solvents in the electrolyte. The relatively low peaks of C=O and Li2CO3 in the DA-10%+DPPVS-1% electrolyte indicate that the addition of DA-10%+DPPVS-1% inhibits the decomposition of the electrolyte. Figure 9 (c) and (d) are the F1s spectra of CE and DA-10%+DPPVS-1% electrolytes. Li was detected in the F1s spectra.x PO y F z LiP x F y The signal peaks for LiP, LiF, and LiF are 688.2 eV, 686.3 eV, and 684.2 eV, respectively. x F y Li x PO y F z The LiF peak intensity increased after the addition of additives, indicating that more LiF participated in the construction of the interface layer, making the interface layer more stable. Therefore, Li... x PO y F z The peak intensity also increases. Furthermore, the presence of C≡N in DA-10%+DPPVS-1% increases the degree of dissociation of the lithium salt, thus increasing the peak intensity of LiP. x F y The peak is enhanced. Figure 9 (e) and (f) are S of CE and DA-10% + DPPPVS-1% electrolytes. 2p Spectrum, in S 2p The spectrum showed three signal peaks (170 eV, 168.8 eV, and 166.4 eV) for Li2SO4, ROSO2Li, and Li2SO3, indicating that DPPPVS was involved in the construction of the SEI film. These S-containing components can passivate the electrode-electrolyte interface and reduce the generation of electrode cracks.

Claims

1. A method for preparing a highly flame-retardant two-component functional additive that enhances ion transport and interfacial stability, comprising a liquid electrolyte and an electrochemical battery, characterized in that: The method specifically includes the following steps: (1) Preparation of additive 3-(diphenylphosphine)propionitrile (DA) Equimolar amounts of diphenylphosphine oxide and acrylonitrile were added to a flask. The flask was evacuated and purged three times to create a vacuum, and then argon (Ar) gas was introduced. Under the Ar atmosphere, the temperature was kept constant, and the reaction was stirred to obtain a transparent gel-like solution. The product was poured into a watch glass while hot. After cooling to room temperature, the gel-like solution turned into a white waxy solid. The product was placed in a vacuum oven and dried at a certain temperature. Then it was ground into powder and dried again in a vacuum oven. (2) Preparation of additive diphenylphosphoxyethyl sulfone (DPPVS) Equimolar amounts of diphenylphosphine oxide and phenylvinyl sulfone nitrile were added to a flask. The flask was evacuated and purged three times to create a vacuum, and then argon (Ar) gas was introduced. Under the Ar atmosphere, the temperature was kept constant, and the reaction was stirred to obtain a transparent gel-like solution. The product was poured into a watch glass while hot. After cooling to room temperature, the gel-like solution turned into a white waxy solid. The product was placed in a vacuum oven and dried at a certain temperature. Then it was ground into powder and dried again in a vacuum oven. (3) Preparation of two-component additive liquid electrolyte By adding a certain amount of DA and DPPVS to a commercial electrolyte and stirring to dissolve them at room temperature, a two-component additive liquid electrolyte can be prepared.

2. The method according to claim 1, characterized in that: The reaction temperature in step (1) is 50-120℃, the reaction time is 2-48 h, and the two vacuum drying temperatures are room temperature-120℃, with a drying time of 2-48 h.

3. The method according to claim 1, characterized in that: The reaction temperature in step (2) is 50-120℃, the reaction time is 2-48 h, and the two vacuum drying temperatures are room temperature-120℃, with a drying time of 2-48 h.

4. The method according to claim 1, characterized in that: The commercial electrolyte mentioned in step (3) includes commercially available organic liquid electrolyte formulations, including but not limited to 1M LiPF6 / EC / DMC commercial electrolyte.

5. The method according to claim 1, characterized in that: The content of 3-(diphenylphosphine)propionitrile in step (3) is 0%-20 wt.%.

6. The method according to claim 1, characterized in that: The content of diphenylphosphoxyethyl sulfone in step (3) is 0%-20 wt.%.

7. The method according to claim 1, characterized in that: The stirring time mentioned in step (3) depends on the stirring efficiency. Generally, it is 0.5h-2h at room temperature.

8. The application fields of a two-component functional additive with high flame retardancy, high ion transport and high interface stability enhancement include electrochemical batteries such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries and sodium-sulfur batteries.

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