Application of bis (trimethylsilyl) vinyl phosphonate as lithium battery electrolyte additive, electrolyte and lithium battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses application of bis (trimethylsilyl) vinyl phosphonate as a lithium battery electrolyte additive, an electrolyte and a lithium battery. The electrolyte comprises a lithium salt, a non-aqueous organic solvent, a film-forming additive and an electrolyte additive, wherein the electrolyte additive is bis (trimethylsilyl) vinyl phosphonate. The electrolyte additive has good chemical stability, the double-bond structure helps to form SEI at the negative electrode of the battery, inhibit the growth of lithium dendrites and reduce the decomposition of the electrolyte, the silicon-oxygen group can be used as an acid-binding agent to remove trace HF reaction in the electrolyte, meanwhile, oxidative decomposition reaction can be preferentially carried out at the positive electrode side to form a Si-O-R interface, and the electrolyte additive has good electrochemical performance. A positive electrode solid electrolyte interface layer on the positive electrode side is more stable, interface impedance is reduced, and dissolution of metal ions is inhibited. The coulombic efficiency and the cycling stability of the battery are improved. And meanwhile, phosphorus and silicon have certain flame retardance, so that the safety of the battery is improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to the application of bis(trimethylsilyl)vinylphosphonate as an electrolyte additive for lithium batteries, and to electrolytes and lithium batteries. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles, hybrid vehicles, energy storage systems, portable electronic devices and many other fields due to their high energy density, long cycle life, high charge and discharge efficiency, low self-discharge, no memory effect, wide operating temperature range, high average output voltage, environmental friendliness, safety and reliability. With economic development and the advancement of science and technology, the requirements for the energy density and safety of lithium-ion batteries are becoming higher and higher. Adding different additives to the electrolyte is the most effective and economical way to solve this problem. Electrolyte additives can significantly improve certain battery properties with a tiny content, so that the production cost is almost not increased. Generally speaking, adding an additive of no more than 5% by mass or volume can significantly improve the cycle performance and cycle life of lithium-ion batteries.

[0003] Lithium-ion battery electrolyte additives can be divided into two categories, one is organic additives and the other is inorganic additives. Organic additives have attracted great attention and developed rapidly due to their multiple advantages such as good solubility with lithium-ion battery electrolytes, excellent optimization effects and convenient use. The action mechanism of additives is diverse, which can be roughly summarized as solid electrolyte interface (SEI) film-forming additives, additives for controlling the HF and water content in the electrolyte, flame retardant additives, overcharge protection additives and multifunctional additives.

[0004] The additive forms a protective film by preferentially undergoing redox reactions, reduces electrolyte side reactions, protects the electrode structure, and improves battery cycle performance; trace water and HF are produced during the battery cycle, causing lithium salt decomposition and electrode structure damage. Additives that react with HF can remove HF to improve battery performance. In addition, flame retardant additives containing elements such as P, N, and F can improve battery safety. The above additives can provide more options for improving battery performance and safety, but few single additives can achieve the above functions at the same time. The application of bis(trimethylsilyl)vinylphosphonate as a lithium battery electrolyte additive has not been reported yet. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide the application of di(trimethylsilyl)vinylphosphonate as a lithium battery electrolyte additive, electrolyte, and lithium battery. The electrolyte additive of the present invention has good chemical stability, the double bond structure helps to form SEI at the negative electrode of the battery, inhibits the growth of lithium dendrites, and reduces the decomposition of the electrolyte. The silicon-oxygen group can be used as an acid binding agent to remove trace HF reactions in the electrolyte. At the same time, an oxidative decomposition reaction can also occur preferentially on the positive electrode side to form a Si-OR interface, making the positive electrode solid electrolyte interface (CEI) layer on the positive electrode side more stable, reducing the interface impedance, and inhibiting the dissolution of metal ions. Improve the coulombic efficiency and cycle stability of the battery. At the same time, phosphorus and silicon have certain flame retardancy, which improves battery safety.

[0006] In order to achieve the above object, the technical solution of the present invention is: use of bis(trimethylsilyl)vinylphosphonate as an additive for lithium battery electrolyte.

[0007] Another technical solution of the present invention is: a lithium battery electrolyte, comprising a lithium salt, a non-aqueous organic solvent, a film-forming additive and an electrolyte additive, wherein the electrolyte additive is bis(trimethylsilyl)vinylphosphonate, the structural formula of which is shown in formula (I),

[0008]

[0009] Further, the lithium salt is selected from at least one of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium oxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(difluorosulfonyl imide) and lithium bis(trifluorosulfonyl imide), and the mass of the lithium salt accounts for 0.1-25.0wt% of the total mass of the lithium battery electrolyte.

[0010] Further; the non-aqueous organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl butyrate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, dioxolane, dimethyl sulfoxide, dimethyl sulfone, acetone, and N,N-dimethylformamide, and the mass of the non-aqueous organic solvent accounts for 20.0-70.0wt% of the total mass of the lithium battery electrolyte.

[0011] Furthermore, the film-forming additive is selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, methylene disulfonate, propene sultone, citraconic anhydride, succinonitrile, adiponitrile, ethylene glycol diether and hexane trinitrile, and the mass of the film-forming additive accounts for 0-20.0wt% of the total mass of the lithium battery electrolyte.

[0012] Furthermore, the mass of the electrolyte additive accounts for 0.1%-10wt% of the total mass of the lithium battery electrolyte.

[0013] Another technical solution of the present invention is: a lithium battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte sealed in a battery housing, wherein the electrolyte is the lithium battery electrolyte.

[0014] Further; the positive electrode material is selected from Li 1+a (Ni x Co y M 1-x-y )O2、Li(Ni n Mn m Co 2-n-m )O4、LiM p (PO4) q Any one of; wherein 0≤a≤0.3, 0≤x≤1, 0≤y≤1, 0≤x+y≤1, 0≤n≤2, 0≤m≤2, 0≤n+m≤2, M is selected from any one of Al, Fe, Ni, Co, Mn, V, and 0<p<5, 0<q<5;

[0015] The negative electrode material is any one of graphite, lithium metal, lithium alloy, silicon, silicon oxide, tin, tin oxide, and lithium titanate.

[0016] Beneficial effects of the present invention: The present invention uses di(trimethylsilyl)vinylphosphonate as an electrolyte additive for lithium batteries. The olefin group in the structural formula can undergo polymerization reaction on the surface of the negative electrode and participate in the film-forming process of the solid electrolyte interface film of the negative electrode, thereby forming a stable, low-impedance solid electrolyte interface film with an outer layer rich in polymer and an inner layer rich in inorganic matter at the contact interface between the electrode and the electrolyte; the Si-O group can remove H2O and HF, thereby improving the moisture resistance of the electrolyte and helping to maintain the stability of the positive electrode. The electrolyte additive has a lower LUMO energy level and a higher HOMO energy level, so the redox reaction occurs preferentially, thereby achieving excellent electrochemical performance and improving the overall coulomb efficiency and cycle stability. In addition, it also has excellent flame retardant elements phosphorus and silicon, which make the electrolyte have flame retardant properties, thereby improving the safety performance of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 11 is a comparison chart of the cycle capacity retention rates of lithium / lithium iron phosphate batteries of Example 2, Example 4 and Comparative Example 1;

[0018] Figure 2 It is a comparison chart of the cycle capacity retention rate of lithium / nickel cobalt manganese 622 batteries of Example 3, Example 5 and Comparative Example 2;

[0019] Figure 3 It is the rate diagram of lithium / lithium iron phosphate battery of Example 6 and Comparative Example 3;

[0020] Figure 4 It is the rate diagram of lithium / nickel cobalt manganese 622 battery of Example 7 and Comparative Example 4;

[0021] Figure 5 is the impedance change diagram of Example 2;

[0022] Figure 6 This is the impedance change diagram of comparative example 1;

[0023] Figure 7 is the CV curve diagram of Example 8;

[0024] Figure 8 is the CV curve diagram of Example 9;

[0025] Fig. 9 It is the CV curve diagram of comparative example 5;

[0026] Fig.10 It is the CV curve diagram of Comparative Example 6;

[0027] Fig.11 is the surface morphology of lithium metal after cycling in Example 2;

[0028] Fig.12 This is the surface morphology of lithium metal after cycling in Comparative Example 1;

[0029] Fig.13 is the flame retardant condition of Example 10;

[0030] Fig.14 This is the flame retardant condition of Comparative Example 7;

[0031] Fig.15 is the nuclear magnetic resonance fluorine spectrum of Example 11;

[0032] Fig.16 It is the nuclear magnetic resonance fluorine spectrum of Comparative Example 8. DETAILED DESCRIPTION

[0033] The following examples are intended to further illustrate the present invention. The following examples are only used to illustrate the present invention, but the present invention is not limited to these examples. All equivalent changes and modifications made within the scope of the present invention should fall within the scope of the present invention.

[0034] All raw materials mentioned in the specification were purchased from the market. The sources and purity of some reagents and the models of instruments used are shown in Tables 1 and 2.

[0035] Table 1 Source and purity of reagents

[0036]

[0037] Table 2 Instruments and equipment

[0038]

[0039]

[0040] The present invention will be further described below in conjunction with embodiments:

[0041] The original electrolyte was prepared in an argon glove box (water <0.01ppm, oxygen <0.01ppm), by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1 to obtain an organic solvent; then fully dried lithium salt LiPF6 was added to the solvent to prepare an original electrolyte with a LiPF6 concentration of 1 mol / L.

[0042] Example 1

[0043] The synthesis method of bis(trimethylsilyl)vinylphosphonate is referred to Chemical Research in Chinese Universities, 2019, 35(2): 340-344. The specific synthesis method is as follows: add diethyl vinyl phosphate (0.75 mL, 48 mmol) to a flask dried under an argon atmosphere, add 6 mL of dichloromethane, add trimethylsilyl bromide (2.45 mL, 192 mmol) dropwise to the flask, and keep the reaction at room temperature under an argon atmosphere for 24 hours. After the reaction is completed, trimethylsilyl bromide and dichloromethane are removed by rotary evaporation, and bis(trimethylsilyl)vinylphosphonate is obtained after reduced pressure distillation, which is used as an electrolyte additive.

[0044] Example 2

[0045] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 1% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. According to the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-lithium iron phosphate positive electrode sheet-gasket-spring-positive electrode shell", CR 2032 button batteries are assembled. After standing and formation, the battery circulation system is used to test the cycle performance of the battery at 1C current. The cycle results are shown in Figure 1 , the impedance changes after cycling as Figure 5 The morphology of lithium metal anode after cycling is as follows Fig.11 .

[0046] Example 3

[0047] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 1% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. According to the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-nickel-cobalt-manganese 622 positive electrode sheet-gasket-spring-positive electrode shell", CR 2032 button batteries are assembled. After standing and formation, the battery circulation system is used to test the cycle performance of the battery at 1C current. The cycle results are shown in Figure 2 .

[0048] Example 4

[0049] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 2% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. According to the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-lithium iron phosphate positive electrode sheet-gasket-spring-positive electrode shell", CR 2032 button batteries are assembled. After standing and formation, the battery circulation system is used to test the cycle performance of the battery at 1C current. The cycle results are shown in Figure 1 .

[0050] Example 5

[0051] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 2% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. According to the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-nickel-cobalt-manganese 622 positive electrode sheet-gasket-spring-positive electrode shell", CR 2032 button batteries are assembled. After standing and formation, the battery circulation system is used to test the cycle performance of the battery at 1C current. The cycle results are shown in Figure 2 .

[0052] Example 6

[0053] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 1% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. According to the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-lithium iron phosphate positive electrode sheet-gasket-spring-positive electrode shell", CR 2032 button batteries are assembled. After standing and formation, the battery cycle system is used to test the rate performance of the battery at different currents. The rate results are shown in Figure 3 .

[0054] Example 7

[0055] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 1% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. According to the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-nickel-cobalt-manganese 622 positive electrode sheet-gasket-spring-positive electrode shell", CR 2032 button batteries are assembled. After standing and formation, the battery cycle system is used to test the rate performance of the battery at different currents. The rate results are shown in Figure 4 .

[0056] Example 8

[0057] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 1% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. According to the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-lithium iron phosphate positive electrode sheet-gasket-spring-positive electrode shell", CR 2032 button cells are assembled. The cyclic voltammetry (CV) curve of the battery is tested by an electrochemical workstation. The CV results are shown in Figure 7 .

[0058] Example 9

[0059] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 1% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. According to the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-nickel cobalt manganese 622 positive electrode sheet-gasket-spring-positive electrode shell", CR 2032 button cells are assembled. The battery CV is tested by an electrochemical workstation. The CV results are as follows: Figure 8 .

[0060] Example 10

[0061] Add the electrolyte additive prepared in Example 1 to the prepared original electrolyte, the mass of the electrolyte additive is 1% of the total mass of the electrolyte, and stir evenly to obtain the electrolyte. Soak the cellulose diaphragm in the electrolyte until it is completely soaked, take it out and ignite it, leave the flame immediately after ignition, and observe the combustion condition. Flame retardancy is as follows Fig.13 .

[0062] Embodiment 11

[0063] The electrolyte additive prepared in Example 1 was added to the prepared original electrolyte, the mass of the electrolyte additive being 1% of the total mass of the electrolyte, and the electrolyte was obtained by stirring evenly. 1% volume fraction of water was added to the electrolyte, and the electrolyte was left to stand for 7 days before fluorine spectrum detection. The results are as follows Fig.15 , verify the effect of additive water application.

[0064] Comparative Example 1

[0065] Using the original electrolyte, the CR 2032 button cell was assembled in the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-lithium iron phosphate positive electrode sheet-gasket-spring-positive electrode shell". After standing and forming, the battery cycle system was used to test the cycle performance of the battery at 1C current. The cycle results are as follows: Figure 1 , the impedance changes after the cycle are as follows Figure 6 The morphology of lithium metal anode after cycling is as follows Fig.12 .

[0066] Comparative Example 2

[0067] Using the original electrolyte, the CR 2032 button cell was assembled in the order of "negative electrode shell - lithium sheet - electrolyte - diaphragm - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring - positive electrode shell". After standing and forming, the battery cycle system was used to test the cycle performance of the battery at 1C current. The cycle results are as follows: Figure 2 .

[0068] Comparative Example 3

[0069] Using the original electrolyte, the CR 2032 button cell was assembled in the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-lithium iron phosphate positive electrode sheet-gasket-spring-positive electrode shell". After standing and forming, the battery cycle system was used to test the rate performance of the battery at different currents. The cycle results are as follows: Figure 3 .

[0070] Comparative Example 4

[0071] Using the original electrolyte, the CR 2032 button cell was assembled in the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-NiCoMn 622 positive electrode sheet-gasket-spring-positive electrode shell". After standing and forming, the battery cycle system was used to test the rate performance of the battery at different currents. The cycle results are as follows: Figure 4 .

[0072] Comparative Example 5

[0073] Using the original electrolyte, the CR 2032 button cell was assembled in the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-lithium iron phosphate positive electrode sheet-gasket-spring-positive electrode shell". The battery's CV was tested using an electrochemical workstation. The CV results are shown in Figure 2. Fig. 9 .

[0074] Comparative Example 6

[0075] Using the original electrolyte, the CR 2032 button cell was assembled in the order of "negative electrode shell-lithium sheet-electrolyte-diaphragm-electrolyte-NiCoMn 622 positive electrode sheet-gasket-spring-positive electrode shell". The CV of the battery was tested by an electrochemical workstation. The CV results are shown in Fig.10 .

[0076] Comparative Example 7

[0077] Soak the cellulose diaphragm in the original electrolyte until it is completely soaked, take it out and ignite it, leave the flame immediately after ignition, and observe the burning condition of the diaphragm. Fig.14 .

[0078] Comparative Example 8

[0079] Add 1v% water to the original electrolyte, let it stand for 7 days and then do a fluorine spectrum test. The results are as follows: Fig.16 , measure HF content.

[0080] The composition ratios of the electrolyte additives of Examples 2-11 and Comparative Examples 1-8 are shown in Table 3 below.

[0081] Table 3 Details of Examples and Comparative Examples

[0082] Test content Cathode Materials Electrolyte Additives Example 2 1C Cycle Lithium Iron Phosphate 1wt% Example 3 1C Cycle NCM622 1wt% Example 4 1C Cycle Lithium Iron Phosphate 2wt% Example 5 1C Cycle NCM622 2wt% Example 6 magnification Lithium Iron Phosphate 1wt% Example 7 magnification NCM622 1wt% Example 8 CV Lithium Iron Phosphate 1wt% Example 9 CV NCM622 1wt% Example 10 Flame retardant none 1wt% Embodiment 11 Water Binding none 1wt% Comparative Example 1 1C Cycle Lithium Iron Phosphate none Comparative Example 2 1C Cycle NCM622 none Comparative Example 3 magnification Lithium Iron Phosphate none Comparative Example 4 magnification NCM622 none Comparative Example 5 CV Lithium Iron Phosphate none Comparative Example 6 CV Lithium Iron Phosphate none Comparative Example 7 Flame retardant none none

[0083] The batteries prepared in Examples 2-11 and Comparative Examples 1-6 were subjected to relevant performance tests.

[0084] Cycle performance test: At 30°C, charge the battery to a specific voltage with constant current, then discharge it to a specific voltage with constant current (charge lithium iron phosphate battery to 4V, charge NCM622 battery to 4.3V), and repeat this cycle. The positive voltage range of lithium iron phosphate is 2.5-4.0V, and the positive voltage range of NCM622 is 3.0-4.3V.

[0085] The Xth cycle capacity retention rate (%) = (Xth cycle discharge capacity / 5th cycle discharge capacity) × 100%.

[0086] Rate performance test: At 30°C, charge the battery at 0.1C to a specific voltage (lithium iron phosphate battery is charged to 4V, NCM622 battery is charged to 4.3V), then discharge it to a specific voltage at 0.1C, and repeat this cycle 5 times; then adjust the current to 0.2C, 0.5C, 1C, 2C, 3C, 4C, 5C, and repeat 5 times respectively, and finally restore the current to 1C, 0.5C, 0.2C, and 0.1C, and repeat in sequence. The capacity retention rate is based on the initial 0.1C fifth cycle capacity.

[0087] Impedance and CV were measured by electrochemical workstation.

[0088] Flame retardant test: Soak the cellulose diaphragm in electrolyte, take it out and ignite it after it is soaked, leave the flame immediately after ignition, observe the burning condition of the diaphragm and take pictures.

[0089] Water binding test: Add 1% volume fraction of water to equal amounts of electrolyte containing electrolyte additives and original electrolyte. After standing for seven days, take equal amounts of electrolyte and add equal amounts of deuterated chloroform to perform nuclear magnetic resonance fluorine spectrum to compare the changes in HF content.

[0090] The test results of the lithium battery and electrolyte cycle performance of Examples 2-5 and Comparative Examples 1-2 are shown in Table 4 below:

[0091] Table 4 Cycle capacity retention rate

[0092]

[0093] The rate performance tests of the lithium batteries and electrolytes of Examples 6-7 and Comparative Examples 3-4 are shown in Table 5 below:

[0094] Table 5 Rate performance

[0095]

[0096]

[0097] According to the above experimental data results, we can know that:

[0098] (1) It can be seen from the cycle data of Examples 2-5 and Comparative Examples 1-2 that the electrolyte additive of the present invention maintains the stability of the electrode material and the electrolyte during the cycle, and exhibits high cycle stability in battery performance. The capacity retention rate of Example 2 after 300 cycles is 87.85%, and the capacity retention rate of Example 4 after 300 cycles is 84.58%, both higher than 74.15% of Comparative Example 1. At the same time, the capacity retention rates of Example 3 and Example 5 after 300 cycles are 68.68% and 63.61%, respectively, which are significantly higher than 54.05% of Comparative Example 2. It can be seen that the electrolyte of the present invention can perform well in different positive electrode material systems, indicating that it has a certain versatility. The double bond structure gives it a lower LUMO energy level, preferentially undergoes redox reactions, improves the stability of the electrolyte, and can form a dense and uniform SEI layer, inhibit the growth of lithium dendrites, and improve the cycle performance of the battery. It can be seen from the overall impedance levels of the batteries of Example 2 and Comparative Example 1 that the impedances of both batteries first decrease and then increase; the initial impedances are not much different, both are about 40Ω, but the impedance of Example 2 added with the electrolyte additive of the present invention is smaller after the cycle; after 50 cycles, the impedance of Example 2 is 60Ω, which is much smaller than the impedance of Comparative Example 1 of 120Ω, indicating that the SEI formed by the battery containing the electrolyte additive of the present invention has greater conductivity to lithium ions.

[0099] (2) It can be seen from the cycle data of Examples 6-7 and Comparative Examples 3-4 that the capacity recovery rate of the electrolyte additive of the present invention is better in rate performance. The capacity recovery rates of Example 6 and Example 7 at 0.5C are 99.86% and 90.69%, which are better than 95.27% and 83.85% of Comparative Example 3 and Comparative Example 4. And the specific capacity is significantly improved during 5C charge and discharge. The capacity retention rates of Example 6 and Example 7 during 5C charge and discharge are 53.86% and 70.18%, far exceeding 19.34% and 10.12% of Comparative Example 3 and Comparative Example 4. This is because it forms a stable SEI layer on the electrode surface, which prevents the solvent molecules from continuing to react, inhibits the growth of lithium dendrites, and ensures the normal transport of lithium ions.

[0100] (3) From the scanning electron microscope images of Example 2 and Comparative Example 1, it can be seen that the surface of the lithium sheet in Comparative Example 1 (the electrolyte additive of the present invention is not added to the electrolyte) is rough. The surface of the lithium sheet in Example 2 (the electrolyte additive of the present invention is added to the electrolyte) is dense and smooth, which shows that the electrolyte additive of the present invention forms a protective film on the electrode surface.

[0101] (4) It can be seen from Examples 8-9 and Comparative Examples 5-6 that the embodiment (see Figure 7 and Figure 8 ) and the comparative example (see Fig. 9 and Fig.10 ) have only one pair of redox peaks, and the two peaks represent the two electrochemical reaction stages of lithium removal and lithium insertion. The redox peaks of the first cycle are slightly different, and the electrolyte additive of the present invention participates in film formation; the second and third cycles containing the electrolyte additive of the present invention have a higher degree of overlap, indicating that the reversibility of the battery is stronger after adding the electrolyte additive of the present invention.

[0102] (5) It can be seen from Example 10 and Comparative Example 7 that the cellulose diaphragm soaked in the electrolyte containing the electrolyte additive of the present invention extinguishes itself after ignition and is completely extinguished within 0.9 seconds, while the cellulose diaphragm soaked in the electrolyte without the electrolyte additive of the present invention burns completely after ignition. It can be seen that the electrolyte additive of the present invention has excellent flame retardant properties.

[0103] (6) It can be seen from the fluorine spectra of Example 11 and Comparative Example 8 that the HF content of the electrolyte containing the electrolyte additive of the present invention after being added with water and left to stand for seven days is 0.00295, which is less than 0.00452 of Comparative Example 8. It can be seen that the electrolyte additive of the present invention has a certain water-binding property.

[0104] In summary, the present invention prepares a new type of electrolyte by using electrolyte additives in combination with relevant lithium salts and organic solvents. This electrolyte is applied to lithium batteries and can regulate SEI to form components with high lithium ion conductivity, improve the migration rate of lithium ions, perform well in high-rate charge and discharge performance, and can significantly improve the cycle stability and rate performance. At the same time, it has excellent flame retardant properties and can remove trace water and HF in the battery to protect the battery positive electrode.

[0105] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. Application of bis(trimethylsilyl)vinylphosphonate as an electrolyte additive for lithium batteries.

2. A lithium battery electrolyte, characterized in that: The invention comprises a lithium salt, a non-aqueous organic solvent, a film-forming additive and an electrolyte additive. The electrolyte additive is di(trimethylsilyl)vinylphosphonate, and the structural formula is shown in formula (I).

3. The lithium battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from at least one of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium oxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(difluorosulfonyl imide) and lithium bis(trifluorosulfonyl imide), and the mass of the lithium salt accounts for 0.1-25.0wt% of the total mass of the lithium battery electrolyte.

4. The lithium battery electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl butyrate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, dioxolane, dimethyl sulfoxide, dimethyl sulfone, acetone, and N,N-dimethylformamide, and the mass of the non-aqueous organic solvent accounts for 20.0-70.0wt% of the total mass of the lithium battery electrolyte.

5. The lithium battery electrolyte according to claim 1, characterized in that: The film-forming additive is selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, methylene disulfonate, propene sultone, citraconic anhydride, succinonitrile, adiponitrile, ethylene glycol diether and hexane trinitrile, and the mass of the film-forming additive accounts for 0-20.0wt% of the total mass of the lithium battery electrolyte.

6. The lithium battery electrolyte according to claim 1, characterized in that: The mass of the electrolyte additive accounts for 0.1%-10wt% of the total mass of the lithium battery electrolyte.

7. A lithium battery comprising a positive electrode, a negative electrode, a separator and an electrolyte sealed in a battery housing, characterized in that: The electrolyte is the lithium battery electrolyte according to any one of claims 2 to 6.

8. The lithium battery according to claim 7, characterized in that: The positive electrode material is selected from Li 1+a (Ni x Co y M 1-x-y )O2、Li(Ni n Mn m Co 2-n-m )O4、LiM p (PO4) q Any one of; wherein 0≤a≤0.3, 0≤x≤1, 0≤y≤1, 0≤x+y≤1, 0≤n≤2, 0≤m≤2, 0≤n+m≤2, M is selected from any one of Al, Fe, Ni, Co, Mn, V, and 0<p<5, 0<q<5; The negative electrode material is any one of graphite, lithium metal, lithium alloy, silicon, silicon oxide, tin, tin oxide, and lithium titanate.

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