Electrolyte additive and preparation method thereof, electrolyte containing additive and lithium ion battery thereof

Abstract

The invention relates to the technical field of lithium ion battery electrolytes, in particular to an electrolyte additive and a preparation method thereof, an electrolyte containing the electrolyte additive, a lithium ion battery containing the electrolyte additive and an electrolyte additive bicyclic carbonate, and the structural general formula of the electrolyte additive is a structural formula I; wherein R1 is independently selected from one of hydrogen, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl and substituted or unsubstituted heteroatom-containing groups; during substitution, the substituent is selected from halogen; the heteroatoms comprise at least one of B, N, O, Si, P and S. Bicyclic carbonate has good chemical stability, and a cyclic carbonate structure can be subjected to electrochemical reaction in the battery to form a layer of compact inorganic salt structure on the surface of an electrode, so that the growth of lithium dendrites is inhibited, the stability of the battery is effectively improved, the overall coulombic efficiency and cycling stability of the battery are improved, and the interface impedance is reduced; and the safety of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery electrolytes, and specifically relates to an electrolyte additive, a preparation method thereof, an electrolyte containing the additive, and a lithium-ion battery containing the electrolyte. Background Art

[0002] With the rapid development of technology and the continuous progress of society, new energy vehicles, mobile communications, wearable devices and other fields have been widely applied. As a key technical support for these fields, lithium-ion batteries, as important energy storage devices, their performance and safety have increasingly become the focus of public attention.

[0003] Lithium-ion batteries play a crucial role in various electronic devices due to their many advantages such as high energy density, long cycle life, and low self-discharge rate. However, during use, lithium-ion batteries have also exposed some problems and challenges, such as the attenuation of battery capacity and insufficient battery safety performance. These problems need to be solved through technological improvements. Lithium-ion battery additives, as an important part of lithium-ion batteries, play a crucial role in improving battery performance, extending battery life, and enhancing battery safety.

[0004] At present, although lithium-ion batteries have been widely used in many fields, the problem of their relatively short cycle life cannot be ignored. As the number of charge and discharge cycles increases, the capacity of lithium-ion batteries gradually decays, mainly because during the process of multiple lithium insertion and extraction in the electrode material, the electrode structure may change, resulting in material deterioration. Among them, during the battery cycle, the solid electrolyte interface membrane (SEI membrane, full name: Solid Electrolyte Interface) formed by the reaction of the electrolyte with the anode is an important factor affecting the battery cycle life.

[0005] The SEI membrane is a passivation layer formed on the surface of the electrode material by the reaction of the electrode material and the electrolyte at the solid-liquid phase interface during the first charge and discharge process of the lithium-ion battery. As a physical barrier, it can prevent side reactions between the electrode material and the electrolyte, thereby delaying the degradation process of the electrode and improving the battery cycle life. The SEI membrane remains stable during charging and discharging, which helps to reduce the internal resistance of the battery and improve the overall performance of the battery. However, the thickness and composition of the SEI membrane will directly affect the power, energy density, and temperature adaptability of the battery, and thus affect the working efficiency of the battery. Therefore, how to form a high-performance SEI membrane has become the key to improving the cycle life of lithium-ion batteries.

[0006] Carbonate compound additives play a crucial role in the formation process of the SEI film in lithium batteries. By optimizing the film formation process, improving conductivity, increasing mechanical stability, etc., these additives can significantly enhance the performance and lifespan of lithium batteries. With the development of materials science, using these additives to continue optimizing the performance of the SEI film will be a key area for improving lithium battery technology. Summary of the Invention

[0007] The object of the present invention is to provide an electrolyte additive, its preparation method, an electrolyte containing this additive, and a lithium ion battery, to solve the problems of poor cycling performance and low safety performance of the above-mentioned battery. This additive can participate in the film formation on the positive and negative electrodes, thereby enhancing the stability of the electrolyte, reducing the interfacial transfer impedance of lithium ions, increasing the charge mobility, and significantly improving the comprehensive performance of the battery.

[0008] To achieve the above object, the technical solution of the present invention is: an electrolyte additive, and the structural general formula of the electrolyte additive is Structural Formula I;

[0009]

[0010] Wherein, R1 is independently selected from one of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, and a substituted or unsubstituted heteroatom-containing group;

[0011] Wherein, when being substituted, the substituent is selected from a halogen; the heteroatom includes at least one of B, N, O, Si, P, and S; the number of carbon atoms in the alkyl group is less than or equal to 10; the number of carbon atoms in the alkenyl group is less than or equal to 10; the number of carbon atoms in the alkynyl group is less than or equal to 10.

[0012] Further, the Structural Formula I includes at least one of the following compounds:

[0013]

[0014]

[0015] Wherein, n≥22.

[0016] Further, the preparation method of Compounds 1 to 7 in the Structural Formula I includes the following steps:

[0017] (1) Under an argon atmosphere, add TMPIC (imidazole-1-carboxylic acid-(5-ethyl-2-oxo-1,3-dioxolan-5-yl)methyl ester), diol, cesium fluoride, and acetone into a reactor dried by Schlenk technology, and react at 26 - 30 °C for 20 - 24 h. The molar ratio of TMPIC to diol is 2 - 4:1;

[0018] (2) The reacted mixture was passed through a short silica gel column to remove cesium fluoride, and the solvent was removed by distillation under reduced pressure to separate the crude product, obtaining the compounds 1 to 7.

[0019] The preparation method of TMPIC is as follows: Referring to the method of Olsson et al. for preparing imidazole-1-carboxylic acid-(5-ethyl-2-oxo-1,3-dioxolan-5-yl)methyl ester (TMPIC), this method is prior art and will not be elaborated here.

[0020] The chemical formula of TMPIC is as shown in compound 9.

[0021]

[0022] The synthesis method of compound 8 was prepared with reference to Matsukizono et al., and the preparation method of compound 8 is prior art and will not be elaborated here.

[0023] Further, the diol is one of 1,4-butanediol, 1,6-hexanediol, 1,4-benzenedimethanol, polyethylene glycol, 2-hydroxyethyl disulfide, o-nitro-p-benzenedimethanol, 2-({2-[(2-hydroxyethyl)oxy]propan-2-yl}oxy)ethan-1-ol.

[0024] A lithium-ion battery electrolyte includes a lithium salt, a non-aqueous organic solvent, an additive, and the electrolyte additive described in any one of the above.

[0025] Further, the lithium salt is at least one of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium oxalato(phosphate), lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(difluoromethanesulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and the content of the lithium salt accounts for 0.1 to 25.0 wt% of the total mass of the lithium-ion battery electrolyte.

[0026] Further, the non-aqueous organic solvent is 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, methyl propyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, dioxolane, dimethyl sulfoxide, dimethyl sulfone, acetone, N,N-dimethylformamide, and the content of the non-aqueous organic solvent accounts for 20.0 to 70.0 wt% of the total mass of the lithium-ion battery electrolyte.

[0027] Further, the additive is at least one of fluoroethylene carbonate, vinylene carbonate, 1,3 - propane sultone, ethylene sulfate, methylene methanedisulfonate, propene sultone, citraconic anhydride, succinonitrile, adiponitrile, ethylene glycol diether, and hexane trinitrile, and the content of the additive accounts for 0.1 - 20.0 wt% of the total mass of the lithium - ion battery electrolyte.

[0028] Further, the content of the electrolyte additive accounts for 0.1 - 10.0 wt% of the total mass of the lithium - ion battery electrolyte.

[0029] A lithium - ion battery, which includes a positive electrode, a negative electrode, a separator, and a lithium - ion battery electrolyte sealed in a battery casing, and the lithium - ion battery electrolyte is the lithium - ion battery electrolyte described in any one of the above;

[0030] The positive electrode material is 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 them; where 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 any one of Al, Fe, Ni, Co, Mn, V, and 0 < p < 5, 0 < q < 5;

[0031] The negative electrode material is any one of graphite, lithium metal, lithium alloy, silicon, silicon oxide, tin, tin oxide, and lithium titanate.

[0032] The beneficial effects achieved by the present invention are as follows:

[0033] In the structural formula of the present invention, the carbonate can undergo a polymerization reaction on the surface of the negative electrode and participate in the formation process of the solid electrolyte interface film on the negative electrode, thereby forming a stable and low - impedance solid electrolyte interface film with a polymer - rich outer layer and an inorganic - rich inner layer at the contact interface between the electrode and the electrolyte. The introduction of the ester bond makes the polymer in the outer layer of the formed SEI film have a certain flexibility, and the polymer containing the ester bond itself has a certain ionic conductivity. This structure does not hinder the shuttling of lithium ions, but can effectively hinder the transmission of electrons and the entry of solvent molecules into the electrode. Therefore, it reduces the damage to the electrode structure, improves the stability of the negative electrode, and is beneficial to improving the overall Coulomb efficiency and cycle stability of the battery; and the inorganic - rich interface film in the inner layer effectively inhibits the growth of dendritic lithium, prevents dendritic lithium from piercing the SEI film and causing internal short - circuit of the battery, reduces the interface impedance, and improves the safety of the battery. Description of the Drawings

[0034] Figure 1 is the 1H NMR spectrum of Compound 1;

[0035] Figure 2 is the 1H NMR spectrum of Compound 2;

[0036] Figure 3 is the 1H NMR spectrum of Compound 3;

[0037] Figure 4 is the 1H NMR spectrum of Compound 4;

[0038] Figure 5 is the 1H NMR spectrum of Compound 5;

[0039] Figure 6 is the 1H NMR spectrum of Compound 6;

[0040] Figure 7 is the 1H NMR spectrum of Compound 7;

[0041] Figure 8 is the 1C cycle capacity retention rate of the lithium / nickel cobalt manganese 622 battery in Example 8;

[0042] Figure 9 is the 1C cycle capacity retention rate of the lithium / nickel cobalt manganese 622 battery in Example 9;

[0043] Figure 10 is the 1C cycle capacity retention rate of the lithium / nickel cobalt manganese 622 battery in Example 10;

[0044] Figure 11 is the 1C cycle capacity retention rate of the lithium / nickel cobalt manganese 622 battery in Example 11;

[0045] Figure 12 is the 1C cycle capacity retention rate of the lithium / nickel cobalt manganese 622 battery in Example 12;

[0046] Figure 13 is the 1C cycle capacity retention rate of the lithium / nickel cobalt manganese 622 battery in Comparative Example 1;

[0047] Figure 14 is the rate performance of the lithium / nickel cobalt manganese 622 battery in Example 13;

[0048] Figure 15 is the rate performance of the lithium / nickel cobalt manganese 622 battery in Example 14;

[0049] Figure 16 is the rate performance of the lithium / nickel cobalt manganese 622 battery in Example 15;

[0050] Figure 17 is the rate performance of the lithium / nickel cobalt manganese 622 battery in Comparative Example 2;

[0051] Figure 18 is the cyclic voltammogram of the lithium / nickel cobalt manganese 622 battery in Example 16;

[0052] Figure 19 is the cyclic voltammogram of the lithium / nickel cobalt manganese 622 battery in Comparative Example 3;

[0053] Figure 20 is the impedance change in Example 11;

[0054] Figure 21 is the impedance change in Comparative Example 1;

[0055] Figure 22 is the surface morphology of the lithium metal electrode after cycling in Example 11;

[0056] Figure 23 is the surface morphology of the lithium metal electrode after cycling in Comparative Example 1. Detailed Embodiments

[0057] The present invention discloses an electrolyte additive, a preparation method thereof, an electrolyte containing the additive, and a lithium ion battery. Those skilled in the art can draw on the content of this article and appropriately modify the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make changes or appropriate modifications and combinations to the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0058] 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 shall fall within the scope of the present invention. All kinds of raw materials involved in the specification are purchased from the market, and the sources, purities, and models of some reagents and instruments are shown in Tables 1 and 2.

[0059] Table 1 Reagent Sources and Purities

[0060]

[0061]

[0062] Table 2 Instruments and Equipment

[0063]

[0064] The preparation of the electrolyte was carried out in an argon glove box (with moisture < 0.01 ppm and oxygen < 0.01 ppm). Ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1:1 to obtain an organic solvent. Then, the fully dried lithium salt LiPF6 was added to this solvent to prepare a raw electrolyte with a LiPF6 concentration of 1 mol / L.

[0065] The present invention will be further described below in conjunction with embodiments:

[0066] Example 1

[0067] TMPIC (6 g, 23.4 mmol), 1,4-butanediol (702 mg, 7.8 mmol), cesium fluoride (468 mg, 3.1 mmol), and 135 mL of acetone were added to a round-bottom flask that had been dried by Schlenk technology. The reaction was carried out at 30 °C under an argon atmosphere for 24 h. The mixture was passed through a short silica gel column to remove cesium fluoride. After removing the solvent by vacuum distillation, the crude product was separated by passing through a liquid chromatography column with an eluent of ethyl acetate:n-hexane = 4:1. Then, it was stirred and precipitated in a mixed solvent of ethyl acetate:n-hexane = 1:1 at 65 °C for 10 min and then left in the refrigerator overnight to obtain a white solid product. The 1H NMR spectrum of Compound 1 is as Figure 1 shown.

[0068] Example 2

[0069] TMPIC (6.5 g, 25.5 mmol), 1,6-hexanediol (1 g, 8.5 mmol), cesium fluoride (511 mg, 3.4 mmol), and 150 mL of acetone were added to a round-bottom flask that had been dried by Schlenk technology. The reaction was carried out at 30 °C under an argon atmosphere for 20 h. The mixture was passed through a short silica gel column to remove cesium fluoride. After removing the solvent by vacuum distillation, the crude product was separated by passing through a liquid chromatography column with an eluent of ethyl acetate:n-hexane:acetic acid = 4.5:3:0.02 to obtain a colorless transparent oily product. The 1H NMR spectrum of Compound 2 is as Figure 2 shown.

[0070] Example 3

[0071] TMPIC (4.6 g, 18 mmol), 1,4-benzenedimethanol (1.1 g, 7.6 mmol), cesium fluoride (76 mg, 0.5 mmol), and 77 mL of acetone were added to a round-bottom flask dried by the Schlenk technique, and the reaction was carried out at 30 °C under an argon atmosphere for 24 h. The mixture was passed through a short silica gel column to remove cesium fluoride. After removing the solvent by distillation under reduced pressure, the crude product was separated by a liquid chromatography column using an eluent of ethyl acetate:n-hexane:acetic acid = 4.5:3:0.02. After removing the solvent by rotary evaporation, the residue was dissolved in dichloromethane, and then washed three times with 50% saturated sodium bicarbonate and sodium chloride solutions respectively. The organic phase was collected, anhydrous magnesium sulfate was added, and the mixture was stirred at room temperature for 30 min for drying and then filtered. After removing the solvent by distillation under reduced pressure, a white solid product was obtained. The 1H NMR spectrum of compound 3 is as shown in Figure 3 shown.

[0072] Example 4

[0073] TMPIC (4.48 g, 17.6 mmol), polyethylene glycol (1000 Da, PEG-1000) (5.6 g, 5.6 mmol), cesium fluoride (56 mg, 0.37 mmol), and 86 mL of acetone were added to a round-bottom flask dried by the Schlenk technique, and the reaction was carried out at 30 °C under an argon atmosphere for 24 h. The mixture was passed through a short silica gel column to remove cesium fluoride. After removing the solvent by distillation under reduced pressure, the product was precipitated 5 times in diethyl ether to obtain the product. The 1H NMR spectrum of compound 4 is as shown in Figure 4 shown.

[0074] Example 5

[0075] TMPIC (4 g, 15.7 mmol), dihydroxydisulfide (1 g, 6.5 mmol), cesium fluoride (76 mg, 0.5 mmol), and 77 mL of acetone were added to a round-bottom flask dried by the Schlenk technique, and the reaction was carried out at 30 °C under an argon atmosphere for 24 h. The mixture was passed through a short silica gel column to remove cesium fluoride. After removing the solvent by distillation under reduced pressure, the product was separated by a liquid chromatography column using an eluent of ethyl acetate:n-hexane = 4:1 to obtain a pale yellow oily product. The 1H NMR spectrum of compound 5 is as shown in Figure 5 shown.

[0076] Example 6

[0077] TMPIC (2.9 g, 11.5 mmol), 2-(hydroxymethyl)-5-nitrophenol (0.9 g, 4.8 mmol), cesium fluoride (76 mg, 0.5 mmol), and 77 mL of acetone were added to a round-bottom flask dried by Schlenk technique, and the reaction was carried out at 30 °C under an argon atmosphere for 24 h. The mixture was passed through a short silica gel column to remove cesium fluoride. After removing the solvent by distillation under reduced pressure, the product was separated by liquid chromatography using an eluent of ethyl acetate:n-hexane = 4:1 to obtain a pale yellow oily product. The 1H NMR spectrum of compound 6 is shown as Figure 6 shown below.

[0078] Example 7

[0079] Refer to Shenoi et al. to prepare 2-({2-[(2-hydroxyethyl)oxy]propan-2-yl}oxy)ethanol. The preparation method of 2-({2-[(2-hydroxyethyl)oxy]propan-2-yl}oxy)ethanol is prior art and will not be discussed here.

[0080] TMPIC (4 g, 15.7 mmol), 2-({2-[(2-hydroxyethyl)oxy]propan-2-yl}oxy)ethanol (1.1 g, 6.54 mmol), cesium fluoride (390 mg, 2.58 mmol), and 92 mL of acetone were added to a round-bottom flask dried by Schlenk technique, and the reaction was carried out at 26 °C under an argon atmosphere for 24 h. The mixture was passed through a short silica gel column to remove cesium fluoride. After removing the solvent by distillation under reduced pressure, the product was separated by liquid chromatography using an eluent of ethyl acetate:n-hexane = 7:1 to obtain a pale yellow oily product. The 1H NMR spectrum of compound 7 is shown as Figure 7 shown below.

[0081] Example 8

[0082] The above-mentioned compound 1 was added to the prepared original electrolyte, and the mass of the additive was 1% of the mass of the electrolyte. After stirring evenly, the electrolyte was obtained. According to the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case", a CR 2032 type button cell was assembled. After standing and formation, the cycle performance of the battery at a current of 1C was tested by a battery cycle system. The cycle results are shown as Figure 8 .

[0083] Example 9

[0084] Add the above compound 3 to the prepared original electrolyte, with the mass of the additive being 1% of the mass of the electrolyte, and stir evenly to obtain the electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the cycle performance of the battery at 1C current through the battery cycle system. The cycle results are as Figure 9 .

[0085] Example 10

[0086] Add the above compound 8 to the prepared original electrolyte, with the mass of the additive being 0.5% of the mass of the electrolyte, and stir evenly to obtain the electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the cycle performance of the battery at 1C current through the battery cycle system. The cycle results are as Figure 10 .

[0087] Example 11

[0088] Add the above compound 8 to the prepared original electrolyte, with the mass of the additive being 1% of the mass of the electrolyte, and stir evenly to obtain the electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the cycle performance of the battery at 1C current through the battery cycle system. The cycle results are as Figure 11 , and the impedance change results during the cycle are as Figure 20 , and the morphology of the lithium metal negative electrode after the cycle is as Figure 22 .

[0089] Example 12

[0090] Add the above compound 8 to the prepared original electrolyte, with the mass of the additive being 2% of the mass of the electrolyte, and stir evenly to obtain the electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the cycle performance of the battery at 1C current through the battery cycle system. The cycle results are as Figure 12 .

[0091] Example 13

[0092] Add the above compound 1 to the prepared original electrolyte. The mass of the additive is 1% of the mass of the electrolyte. Stir evenly to obtain the electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the rate performance of the battery at different currents through the battery cycling system. The rate results are as Figure 14 。

[0093] Example 14

[0094] Add the above compound 3 to the prepared original electrolyte. The mass of the additive is 1% of the mass of the electrolyte. Stir evenly to obtain the electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the rate performance of the battery at different currents through the battery cycling system. The rate results are as Figure 15 。

[0095] Example 15

[0096] Add the above compound 8 to the prepared original electrolyte. The mass of the additive is 1% of the mass of the electrolyte. Stir evenly to obtain the electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the rate performance of the battery at different currents through the battery cycling system. The rate results are as Figure 16 。

[0097] Example 16

[0098] Add the above compound 8 to the prepared original electrolyte. The mass of the additive is 1% of the mass of the electrolyte. Stir evenly to obtain the electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the cyclic voltammetry performance of the battery through the battery cycling system. The results are as Figure 18 。

[0099] Comparative Example 1

[0100] Use the original electrolyte. Assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring piece - positive electrode case". After standing and formation, test the cycling performance of the battery at 1C current through the battery cycling system. The cycling results are as Figure 13 ,and the impedance change results during the cycling process are asFigure 21 , the morphology of the lithium metal anode after cycling is as shown in Figure 23 .

[0101] Comparative Example 2

[0102] Using the original electrolyte, assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring sheet - positive electrode case". After standing and formation, test the rate performance of the battery at different currents through the battery cycling system. The rate results are as shown in Figure 17 .

[0103] Comparative Example 3

[0104] Using the original electrolyte, assemble a CR 2032 type button cell in the order of "negative electrode case - lithium sheet - electrolyte - separator - electrolyte - nickel cobalt manganese 622 positive electrode sheet - gasket - spring sheet - positive electrode case". After standing and formation, test the cyclic voltammetry performance of the battery through the battery cycling system. The cycling results are as shown in Figure 19 .

[0105] The component compositions of the electrolytes in Examples 8 to 20 and Comparative Examples 1 to 3 are shown in Table 3 below

[0106] Table 3 Component Compositions and Performance Tests of Examples and Comparative Examples

[0107] Test content Cathode material Additive Example 8 1C cycle NCM622 Compound 1: 1 wt% Example 9 1C cycle NCM622 Compound 3: 1 wt% Example 10 1C cycle NCM622 Compound 8: 0.5 wt% Example 11 1C cycle NCM622 Compound 8: 1 wt% Example 12 1C cycle NCM622 Compound 8: 2 wt% Example 13 Rate NCM622 Compound 1: 1 wt% Example 14 Rate NCM622 Compound 3: 1 wt% Example 15 Rate NCM622 Compound 8: 1 wt% Example 16 CV NCM622 Compound 8: 1 wt% Comparative Example 1 1C cycle NCM622 None Comparative Example 2 Rate NCM622 None Comparative Example 3 CV NCM622 None

[0108] Perform relevant performance tests on the batteries prepared in Examples 8 to 16 and Comparative Examples 1 to 3.

[0109] Cycling performance test: At 30 °C, charge the battery at a constant current to a specific voltage, and then discharge it at a constant current to a specific voltage, and cycle accordingly. The voltage range of the NCM622 positive electrode is 3.0 - 4.3 V.

[0110] Cycling capacity retention rate (%) in the Xth week = (discharge capacity in the Xth week of cycling / discharge capacity in the 4th week of cycling) × 100%.

[0111] Rate performance test: At 25 °C, charge the battery at 0.05C to a specific voltage, and then discharge it at 0.05C to a specific voltage, and cycle 5 times accordingly; then adjust the current to 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 4C respectively and cycle 5 times each according to this procedure, and finally restore the current to 1C and cycle successively. The capacity retention rate is based on the capacity of the fifth cycle at the initial 0.05C.

[0112] The test results of the cycling performance of the lithium-ion batteries and electrolytes in Examples 8 to 12 and Comparative Example 1 are shown in Table 4 below:

[0113] Table 4 Cycling Capacity Retention Rate

[0114]

[0115] The test results of the lithium ion batteries and electrolyte rate performance of Examples 13 to 15 and Comparative Example 2 are shown in Table 5 below:

[0116] Table 5 Rate performance

[0117]

[0118]

[0119] According to the above experimental data results, we can know that:

[0120] 1. It can be seen from the cycle data of Examples 8 to 15 and Comparative Examples 1 to 2 that the additives involved in the article maintain the stability of the electrode material and the electrolyte during the cycle, and show high cycle stability in battery performance. In the cycle performance data of Examples 8, 9, and 11, this type of structural electrolyte additive shows high cycle stability in battery performance. In the cycle performance data of Examples 10, 11, and 12, the 1% concentration electrolyte additive performs best in battery performance. From the overall impedance level of the battery in Example 11 and Comparative Example 1, it can be seen that the impedance of Example 11 with additives first decreases and then increases, which is slower and has a lower impedance value than the comparative example 1 without additives; the change in its impedance corresponds to the film formation process of the additive and the deterioration of the electrode interface. The impedance of Example 11 containing additives during the film formation process is less than that of Comparative Example 2. After the film formation is completed, the interfaces of the two begin to deteriorate as the cycle proceeds, so the impedance continues to increase.

[0121] 2. From the cycle data of Examples 13 to 15 and Comparative Example 2, it can be seen that the additives involved in the article have better capacity recovery rate in rate performance, and the specific capacity of high-rate charge and discharge is significantly improved, far exceeding the comparative example. This is due to the special structure of the SEI film formed on the electrode surface. The outer side is a flexible polymer that can prevent solvent molecules from continuing to react, and the inner side is a hard inorganic substance that can inhibit dendrite lithium while ensuring the normal transmission of lithium ions. This special structure is crucial in the high current density charge and discharge process and is an important factor that distinguishes it from other additives.

[0122] 3. From the scanning electron micrographs of Example 11 and Comparative Example 1, it can be seen that the surface of the lithium sheet of the electrolyte in Comparative Example 1 without any additives is the roughest; on the surface of the lithium sheet of Example 11 with the addition of Compound 8 after cycling, not only a dense structure similar to that of the surface of Comparative Example 1 is observed, but also obvious polymer morphology is observed, indicating that Compound 8 forms a layer of polymer as a protective film on the surface of the electrode.

[0123] In summary, the present invention prepares a novel electrolyte through electrolyte additives in combination with relevant lithium salts and organic solvents. When applied to lithium batteries, this electrolyte can regulate the components forming SEI with high lithium-ion conductivity, enhance the migration rate of lithium ions, and exhibit excellent performance in high-rate charge and discharge. Due to its special structure, it can significantly improve the cycling stability and rate performance.

[0124] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that, without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. An electrolyte additive, characterized in that, The general structural formula of the electrolyte additive is Structural Formula I; wherein, R1 is independently selected from one of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, and a substituted or unsubstituted heteroatom-containing group; wherein, when being substituted, the substituent is selected from a halogen; the heteroatom includes at least one of B, N, O, Si, P, and S; the number of carbon atoms in the alkyl group is less than or equal to 10; the number of carbon atoms in the alkenyl group is less than or equal to 10; the number of carbon atoms in the alkynyl group is less than or equal to 10.

2. An electrolyte additive according to claim 1, characterized in that, The Structural Formula I includes at least one of the following compounds: wherein, n≥22.

3. An electrolyte additive according to claim 2, characterized in that, The preparation method of Compounds 1 to 7 in the Structural Formula I includes the following steps: (1) Under an argon atmosphere, add TMPIC (imidazole-1-carboxylic acid-(5-ethyl-2-oxo-1,3-dioxolan-5-yl)methyl ester), diol, cesium fluoride, and acetone into a reactor dried by Schlenk technology, and react at 26-30 °C for 20-24 h. The molar ratio of TMPIC to diol is 2-4:1; (2) Remove cesium fluoride from the reaction mixture through a short silica gel column, remove the solvent by vacuum distillation, and separate the crude product to obtain Compounds 1 to 7.

4. An electrolyte additive according to claim 3, characterized in that, The diol is one of 1,4-butanediol, 1,6-hexanediol, 1,4-benzenedimethanol, polyethylene glycol, 2-hydroxyethyl disulfide, o-nitro-p-benzenedimethanol, 2-({2-[(2-hydroxyethyl)oxy]propan-2-yl}oxy)ethan-1-ol.

5. A lithium-ion battery electrolyte, characterized in that, It includes a lithium salt, a non-aqueous organic solvent, an additive, and the electrolyte additive according to any one of Claims 1 to 4.

6. The electrolyte for a lithium-ion battery according to claim 5, wherein, The lithium salt is at least one of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium oxalato(phosphate), lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(difluoromethanesulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. The content of the lithium salt accounts for 0.1-25.0 wt% of the total mass of the lithium-ion battery electrolyte.

7. The electrolyte for a lithium-ion battery according to claim 5, wherein The non-aqueous organic solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, n-butyl acetate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, dioxolane, dimethyl sulfoxide, dimethyl sulfone, acetone, N,N-dimethylformamide. The content of the non-aqueous organic solvent accounts for 20.0-70.0 wt% of the total mass of the lithium-ion battery electrolyte.

8. The electrolyte for a lithium-ion battery according to claim 5, wherein The additive is at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, ethylene sulfate, methylene methanedisulfonate, propene sultone, citraconic anhydride, succinonitrile, adiponitrile, ethylene glycol diether, and hexane trinitrile. The content of the additive accounts for 0.1-20.0 wt% of the total mass of the lithium-ion battery electrolyte.

9. The electrolyte for a lithium-ion battery according to claim 5, characterized in that, The content of the electrolyte additive accounts for 0.1 to 10.0 wt% of the total mass of the lithium-ion battery electrolyte.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a lithium-ion battery electrolyte sealed in a battery casing, and the lithium-ion battery electrolyte is the lithium-ion battery electrolyte according to any one of claims 5 to 9; The positive electrode material is 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 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 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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