Additive, method for preparing the same, electrolyte, and secondary battery

Abstract

The application relates to the field of secondary batteries, and discloses an additive, a preparation method, an electrolyte, and a secondary battery. The electrolyte additive disclosed by the application comprises a compound with a structure shown in formula A, wherein R1-R4 are independently selected from any one of -CH3, -C2H5, -CH2CF3, -CHC2F6, -Ph, -C(CH3)3, and -Si(CH3)3; R5 and R6 are independently selected from any one of C1-C20 alkylene or -R7-O-R8-; R7 is selected from a phenyl group or C1-C20 alkyl; and R8 is selected from C1-C20 alkyl. The additive disclosed by the application can reduce the deposition of negative electrode Mn, reduce impedance, and help form a stable interface film on the surface of the negative electrode. The additive contains a P-O bond, trivalent P is easy to be oxidized, thereby consuming oxygen generated from the positive electrode interface, free radicals generated by the breakage of the P-O bond diffuse to the surface of the positive electrode to form a CEI film, the dissolution of Mn on the positive electrode interface can be inhibited, the initial internal resistance of the battery and the internal resistance growth during storage can be reduced, and the high-temperature storage and cycle performance of the battery can be improved.

Description

Technical Field

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

[0002] With the rapid development of electric vehicles, the requirements for energy density, cycle life, and safety of lithium-ion batteries are constantly increasing. However, in traditional electrolyte systems, ternary cathode materials undergo drastic structural changes and interfacial side reactions under high pressure and high temperature, posing significant challenges to practical applications, especially for the cycle life and safety of high-nickel ternary materials. Developing suitable electrolyte additives is one of the most economical and effective methods to improve the electrochemical performance of lithium-ion batteries. Therefore, designing a class of film-forming additives to improve the cathode interfacial film is crucial for further enhancing the overall performance of high-power battery systems.

[0003] In addition, the SEI film formed on the graphite anode for the first time plays an important role in battery performance. If the impedance of the formed SEI film is too high, it will intensify battery polarization and easily lead to lithium plating on the anode surface, which will significantly reduce the reversible capacity of the battery.

[0004] Therefore, it is necessary to develop a novel positive and negative electrode film-forming additive and an electrolyte containing the additive, which can simultaneously form a low-impedance and stable passivation film at both the positive and negative electrode interfaces. This film can not only protect the positive electrode and suppress capacity loss and storage gas problems caused by excessive side reactions between the positive electrode and the electrolyte, but also protect the negative electrode and form a low-impedance SEI film, allowing lithium ions to pass through quickly, reducing polarization and improving the lithium plating window. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide an additive that can reduce the initial internal resistance of the battery and the increase in internal resistance during storage, thereby improving the capacity retention rate during high-temperature cycling and high-temperature storage.

[0006] To achieve the above objectives, as a first aspect of this application, an electrolyte additive is provided, said additive comprising a compound with the structure shown in Formula A:

[0007]

[0008] Among them, R1 to R4 are each individually selected from any one of -CH3, -C2H5, -CH2CF3, -CHC2F6, -Ph, -C(CH3)3, and -Si(CH3)3;

[0009] R5 and R6 are each independently selected from any one of C1 to C20 alkylene groups or -R7-O-R8-; R7 is selected from phenyl or C1 to C20 alkyl groups; R8 is selected from C1 to C20 alkyl groups.

[0010] Furthermore, R1 to R4 are selected from any one of -CH3, -C2H5, -CH2CF3, -CHC2F6, -Ph, -C(CH3)3 and -Si(CH3)3;

[0011] R5 and R6 are each independently selected from any one of C1 to C10 alkylene groups or -R7-O-R8-; R7 is selected from phenyl or C1 to C5 alkyl groups; R8 is selected from C1 to C5 alkyl groups.

[0012] Furthermore, the -R7-O-R8- includes any one of the following substituents:

[0013] , , .

[0014] Furthermore, the compound with the structure shown in Formula A comprises at least one of the following compounds:

[0015]

[0016] As a second aspect of this application, a method for preparing the additive is provided, comprising:

[0017] The compound with the structure shown in Formula II reacts with formic acid to generate intermediate II-1;

[0018] The intermediate product II-1 reacts with hydrochloric acid to generate intermediate product II-2;

[0019] The intermediate product II-2 reacts with phosphorus trichloride to generate intermediate product II-3, or the intermediate product II-2 reacts with Cl-R7-OH to generate intermediate product II-4;

[0020] The intermediate product II-3 reacts with X-OH (X is at least one of R1 to R4) to generate the compound with the structure shown in formula A, or the intermediate product II-4 reacts with phosphorus trichloride to generate intermediate product II-5, and intermediate product II-5 reacts with X-OH (X is at least one of R1 to R4) to generate the compound with the structure shown in formula A.

[0021]

[0022]

[0023] Where n is an integer from 1 to 20.

[0024] As a third aspect of this application, an electrolyte is provided, comprising an electrolyte lithium salt, an organic solvent, and the electrolyte additives described in this application.

[0025] Furthermore, the electrolyte additive accounts for 0.1% to 5% of the total mass of the electrolyte.

[0026] Furthermore, the mass of the additive accounts for 0.5% to 2% of the total mass of the electrolyte.

[0027] As a fourth aspect of this application, a secondary battery is provided, comprising the electrolyte described in this application.

[0028] Compared with previous technologies, the beneficial effects of the present invention are as follows:

[0029] The electrolyte additive of this application, as a novel additive, can reduce the deposition of Mn on the negative electrode, lower impedance, and help form a stable interfacial film on the negative electrode surface. The additive contains PO bonds, and the trivalent P is easily oxidized, thereby consuming oxygen generated from the positive electrode interface. The free radicals generated by the breaking of PO bonds diffuse to the positive electrode surface to form a CEI film, which can inhibit the dissolution of Mn at the positive electrode interface, reduce the initial internal resistance of the battery and the increase in internal resistance during storage, and improve the battery's high-temperature storage and cycle performance. Detailed Implementation

[0030] This application discloses an electrolyte additive and its preparation method, as well as an electrolyte, a secondary battery, and an electrical device. Those skilled in the art can refer to this document and appropriately modify the process parameters to achieve the desired results. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The products and processes described in this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the products and processes described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0031] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0032] In a first aspect of this application, an additive is provided, said additive comprising a compound with the structure shown in Formula A:

[0033]

[0034] Among them, R1 to R4 are each individually selected from any one of -CH3, -C2H5, -CH2CF3, -CHC2F6, -Ph, -C(CH3)3, and -Si(CH3)3;

[0035] R5 and R6 are each independently selected from any one of C1 to C20 alkylene groups or -R7-O-R8-; R7 is selected from phenyl or C1 to C20 alkyl groups; R8 is selected from C1 to C20 alkyl groups.

[0036] In some embodiments of this application, R1 to R4 are selected from any one of -CH3, -C2H5, -CH2CF3, -CHC2F6, -Ph, -C(CH3)3 and -Si(CH3)3;

[0037] R5 and R6 are each independently selected from any one of C1 to C5 alkylene groups or -R7-O-R8-; R7 is selected from phenyl or C1 to C5 alkyl groups; R8 is selected from C1 to C5 alkyl groups.

[0038] In some embodiments of this application, -R7-O-R8- contains any one of the following substituents:

[0039] , , .

[0040] In some embodiments of this application, the compound with the structure shown in Formula A comprises at least one of the following compounds:

[0041]

[0042] In a second aspect of this application, a method for preparing the additive is provided, comprising:

[0043] The compound with the structure shown in Formula II reacts with formic acid to generate intermediate II-1;

[0044] The intermediate product II-1 reacts with hydrochloric acid to generate intermediate product II-2;

[0045] The intermediate II-2 reacts with phosphorus trichloride to generate intermediate II-3 (with R5 and R6 selected from the alkylidene route with 1 to 20 carbon atoms), or the intermediate II-2 reacts with Cl-R7-OH to generate intermediate II-4 (with R5 and R6 selected from the R7-O-R8 substituent route).

[0046] The intermediate product II-3 reacts with X-OH (X is at least one of R1 to R4) to produce the electrolyte additive of this application, or the intermediate product II-4 reacts with phosphorus trichloride to produce intermediate product II-5, and intermediate product II-5 reacts with X-OH (X is at least one of R1 to R4) to produce the electrolyte additive of this application.

[0047]

[0048] Where n is an integer from 1 to 20, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. The reaction conditions, such as the amount of reactants and the reaction temperature, can be optimized experimentally to obtain the optimal reaction conditions. The compound with the structure shown in Formula II can be obtained by using 4,5-dimethyl-1,3-dioxacyclopenten-2-one (DMDO) as a starting material, through bromination and substitution reactions.

[0049] In some embodiments of this application, organic solvents such as acetonitrile, methanol, DMF, and dichloromethane can be selected to provide the reaction environment during the preparation process, depending on the actual situation. In other embodiments of this application, K2CO3, Na2CO3, or triethylamine can be selected as the base catalyst to improve the reaction efficiency, depending on the actual situation.

[0050] In some embodiments of this application, the preparation process is further described using additive compounds A1-A9 as examples:

[0051] (1) Formula A1 additive

[0052] Using 4-(bromomethyl)-5-(hydroxymethyl)-1,3-dioxanecyclopenten-2-one as the compound with the structure shown in Formula II (i.e., n=1), in a reaction environment provided by acetonitrile, with triethylamine as a catalyst, formic acid was reacted at room temperature, and the reaction was monitored until the reaction was complete. The mixture was then washed with water, the organic phases were combined and dried to give intermediate II-1 (n=1).

[0053] Intermediate II-1 (n=1) reacted with concentrated hydrochloric acid at room temperature in a methanol-provided reaction environment, while the reaction was monitored until it was complete. The mixture was then washed with water, the organic phases were combined and dried to give intermediate II-2 (n=1).

[0054] Intermediate II-2 (n=1) was reacted in a reaction environment provided by dichloromethane with triethylamine as a catalyst by adding phosphorus trichloride dropwise in an ice bath, and then naturally heated to room temperature while monitoring the reaction until it was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain intermediate II-3 (n=1).

[0055] In a protective gas atmosphere (such as inert gases like argon, the same below), intermediate product II-3 (n=1) and trimethylhydroxysilane (X-OH, where X is -Si(CH3)3) react at 50°C in a reaction environment provided by DMF with K2CO3 as a catalyst. The reaction is monitored until it is complete. The mixture is then washed with water, the organic phases are combined and dried to obtain the final product, additive A1.

[0056]

[0057] (2) Formula A2 additive

[0058] In a protective gas atmosphere, intermediate product II-3 (n=1), 1,1,1,3,3,3-hexafluoro-2-propanol (X-OH, X is -CHC2F6), reacted at 50°C in a reaction environment provided by DMF with K2CO3 as catalyst, while the reaction was monitored until the reaction was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain the final product, additive A2.

[0059]

[0060] (3) Formula A3 additive

[0061] In a protective gas atmosphere, intermediate product II-3 (n=1) and methanol (X-OH, X is -CH3) react at 50°C in a reaction environment provided by DMF with K2CO3 as catalyst. The reaction is monitored until the reaction is complete. The mixture is then washed with water, the organic phases are combined and dried to obtain the final product A3 electrolyte additive.

[0062]

[0063] (4) Formula A4 additive

[0064] In a protective gas atmosphere, intermediate product II-3 (n=1) and ethanol (X-OH, X is -C2H5) react at 50°C in a reaction environment provided by DMF with K2CO3 as catalyst, while monitoring the reaction until the reaction is complete. Then, the mixture is washed with water, the organic phases are combined and dried to obtain the final product A4 additive.

[0065]

[0066] (5) Formula A5 additive

[0067] In a protective gas atmosphere, intermediate product II-3 (n=1) and tert-butanol (X-OH, X is -C(CH3)3) reacted at 50°C in the reaction environment provided by DMF with K2CO3 as catalyst. The reaction was monitored until the reaction was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain the final product, additive A5.

[0068]

[0069] (6) Formula A6 additive

[0070] In a protective gas atmosphere, intermediate product II-3 (n=1) and phenol (X-OH, X is -Ph) react at 50°C in a reaction environment provided by DMF with K2CO3 as a catalyst, while monitoring the reaction until the reaction is complete. Then, the mixture is washed with water, the organic phases are combined and dried to obtain the final product A6 additive.

[0071]

[0072] (7) Formula A7 additive

[0073] Intermediate II-2 (n=1) reacted with chloroethanol (Cl-R7-OH, R7 being -CH2-CH2-) in a reaction environment provided by DMF with K2CO3 as a catalyst at 80°C. The reaction was monitored until it was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain intermediate II-4 (n=1).

[0074] Intermediate II-4 (n=1) was reacted in a reaction environment provided by dichloromethane with triethylamine as a catalyst by adding phosphorus trichloride dropwise in an ice bath, and then naturally heated to room temperature while monitoring the reaction until it was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain intermediate II-5 (n=1).

[0075] In a protective gas atmosphere, intermediate product II-5 (n=1) and trimethylhydroxysilane (X-OH, X is -Si(CH3)3) reacted at 50°C in a reaction environment provided by DMF with K2CO3 as catalyst, while the reaction was monitored until the reaction was complete. Then, the mixture was washed with water, the organic phases were combined and dried to obtain the final product A7 additive.

[0076]

[0077] (8) Formula A8 additive

[0078] Intermediate II-2 (n=1) reacted with 4-chlorocyclohexanol (Cl-R7-OH, R7 being a para-cyclohexane alkyl group) in a reaction environment provided by DMF with K2CO3 as a catalyst at 80 °C. The reaction was monitored until it was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain intermediate II-4 (n=1).

[0079] Intermediate II-4 (n=1) was reacted in a reaction environment provided by dichloromethane with triethylamine as a catalyst by adding phosphorus trichloride dropwise in an ice bath, and then naturally heated to room temperature while monitoring the reaction until it was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain intermediate II-5 (n=1).

[0080] In a protective gas atmosphere, intermediate product II-5 (n=1) and trimethylhydroxysilane (X-OH, X is -Si(CH3)3) reacted at 50°C in a reaction environment provided by DMF with K2CO3 as catalyst, while the reaction was monitored until the reaction was complete. Then the mixture was washed with water, the organic phases were combined and dried to obtain the final product A8 additive.

[0081]

[0082] (9) Formula A9 additive

[0083] Intermediate II-2 (n=1) reacted with 4-chlorophenol (Cl-R7-OH, R7 being a para-phenylene group) in a reaction environment provided by DMF with K2CO3 as a catalyst at 80°C. The reaction was monitored until it was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain intermediate II-4 (n=1).

[0084] Intermediate II-4 (n=1) was reacted in a reaction environment provided by dichloromethane with triethylamine as a catalyst by adding phosphorus trichloride dropwise in an ice bath, and then naturally heated to room temperature while monitoring the reaction until it was complete. The mixture was then washed with water, the organic phases were combined and dried to obtain intermediate II-5 (n=1).

[0085] In a protective gas atmosphere, intermediate product II-5 (n=1) and trimethylhydroxysilane (X-OH, X is -Si(CH3)3) reacted at 50°C in a reaction environment provided by DMF with K2CO3 as catalyst, while the reaction was monitored until the reaction was complete. Then, the mixture was washed with water, the organic phases were combined and dried to obtain the final product A9 additive.

[0086]

[0087] In a third aspect of this application, an electrolyte is provided, comprising a lithium salt, an organic solvent, and the additives described in this application.

[0088] In some embodiments of this application, the additive accounts for 0.1% to 5% of the total mass of the electrolyte. The electrolyte additive accounts for 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5% of the total mass of the electrolyte, or any combination thereof. Within the range of this application, the mass of the additive is beneficial for forming a passivation film of suitable thickness on the positive and negative electrode surfaces, reducing the battery impedance. More preferably, the additive accounts for 0.5% to 2% of the total mass of the electrolyte.

[0089] In some embodiments of this application, the lithium salt accounts for 10% to 15% of the total mass of the electrolyte. Too low a lithium salt concentration affects the conductivity of the electrolyte, while too high a concentration increases the viscosity. In other embodiments of this application, the lithium salt accounts for 12% to 13% of the total mass of the electrolyte, more specifically, 10%, 11%, 12%, 12.5%, 13%, 14%, or 15%. In still other embodiments of this application, the lithium salt is at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorodioxalatophosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0090] In some embodiments of this application, the organic solvent accounts for 80% to 90% of the total mass of the electrolyte, and more specifically, it can be selected from the range of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, or any combination thereof. The organic solvent can be selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl methyl carbonate (MPC), diphenyl carbonate (DPhC), methyl formate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN), and sulfolane (TMS).

[0091] In one embodiment of this application, the organic solvent is a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of (2-4):(5-8).

[0092] In a fourth aspect of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, and the electrolyte described in this application.

[0093] In some embodiments of this application, the positive electrode sheet includes a positive active material, a conductive agent, a binder, and a metal foil, and the negative electrode sheet includes a negative active material, a conductive agent, a binder, and a metal foil. In other embodiments of this application, the mass ratio of the positive / negative active material: conductive agent: binder is (90-95):(1-5):(1-5), and can be specifically selected as 94:3:3. In other embodiments of this application, the positive active material is Li(Ni) 0.8 Mn 0.1 Co 0.1 The negative electrode active material is graphite, the conductive agent is acetylene black (Super P), the binder is polyvinylidene fluoride (PVDF) or styrene-butadiene rubber (SBR), and the metal foil is copper foil or aluminum foil.

[0094] In some embodiments of this application, the positive electrode active material comprises Li a Ni x Co y Mn z M eO2, wherein 0.9≤a≤1.1, 0≤e≤0.1, 0.3≤x<1.0, 0<y<0.4, 0.1<z<0.4, x+y+z=1.0, and M contains at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, and Ce.

[0095] In some embodiments of this application, the secondary battery is a pouch battery. The preparation process is as follows: the prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding, hot pressing and shaping, and electrode tab welding, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film, baked, and then injected with the electrolyte described in this application. After standing, formation, and capacity testing, the preparation of the lithium-ion pouch battery is completed.

[0096] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials remain consistent to ensure comparability. Furthermore, all materials used in this application are commercially available.

[0097] The following provides further details regarding an additive, its preparation method, electrolyte, and secondary battery provided in this application.

[0098] Preparation of additive A1

[0099] 0.208 g of 4-(bromomethyl)-5-(hydroxymethyl)-1,3-dioxanecyclopenten-2-one, 0.101 g of triethylamine, and 100 ml of acetonitrile were placed in a 100 ml three-necked flask. 0.046 g of formic acid was slowly added dropwise using a syringe. After the addition was complete, the system was reacted at room temperature for 12 hours. After the reaction was stopped, the mixture was allowed to stand for 10 min, washed with water until neutral, and the organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=1) to obtain intermediate product II-1.

[0100] Intermediate II-1 and 20 ml of methanol were added sequentially to a 100 ml round-bottom flask. 0.05 g of concentrated hydrochloric acid was then slowly injected using a syringe. After the addition was complete, the reaction was allowed to proceed at room temperature, with TLC monitoring until the reaction was complete. The mixture was then washed with water, and the organic phases were combined and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA = 0.5) to obtain intermediate II-2.

[0101] In a 250 mL round-bottom flask, intermediate II-2, 100 mL of dichloromethane, and 0.21 g of triethylamine were added sequentially. The system was placed in an ice bath, and 0.3 g of phosphorus trichloride was slowly injected dropwise using a syringe. After the addition was complete, the mixture was allowed to warm to room temperature, and the reaction was monitored by TLC until it was complete. The mixture was then washed with water, and the organic phases were combined and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=5) to obtain intermediate II-3.

[0102] Under an argon atmosphere, intermediate II-3, 0.36 g of trimethylhydroxysilane, 0.552 g of K₂CO₃, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask, and the mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA=6) to give 0.10 g of final product A1 (overall yield of 19% across the four steps).

[0103] The NMR results were as expected: 1 H NMR (DMSO,300MHZ) δ(ppm): 4.20(d,4H), 0.21(s,36H), 13 C NMR (CDCl3,100MHZ) δ(ppm): 147.5, 121.0, 61.6, 6.6.

[0104] Preparation of additive A2

[0105] Under an argon atmosphere, 0.34 g of intermediate II-3, 0.67 g of 1,1,1,3,3,3-hexafluoro-2-propanol, 0.552 g of K₂CO₃, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask. The mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, and the organic phases were combined and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA=6) to give 0.37 g of final product A₂ (yield 43%).

[0106] The NMR results were as expected: 1 H NMR (DMSO,300MHZ) δ(ppm): 7.80(m,4H), 4.20(d,4H), 13 C NMR(CDCl3,100MHZ) δ(ppm): 147.5,120.8, 121.0,74.2, 62.6.

[0107] Preparation of Formula A3 additive

[0108] Under an argon atmosphere, 0.34 g of intermediate II-3, 0.13 g of methanol, 0.552 g of K2CO3, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask, and the mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA=4) to give 0.18 g of the final product A3 (yield 54%).

[0109] The NMR results were as expected: 1 H NMR (DMSO,300MHZ) δ(ppm): 4.20(d,4H), 3.51(d,12H), 13 C NMR(CDCl3,100MHZ) δ(ppm): 147.5,121.0, 62.2,49.3

[0110] Preparation of Formula A4 additives

[0111] Under an argon atmosphere, 0.34 g of intermediate II-3, 0.18 g of ethanol, 0.552 g of K₂CO₃, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask, and the mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA=3) to give 0.22 g of the final product A₄ (yield 58%).

[0112] The NMR results were as expected: 1 H NMR(DMSO,300MHZ) δ(ppm):4.20(d,4H),3.85(m,8H),1.25(m,12H) 13 CNMR(CDCl3,100MHZ) δ(ppm): 147.5,121.0, 62.2,57.4,16.6.

[0113] Preparation of Formula A5 additive

[0114] Under an argon atmosphere, 0.34 g of intermediate II-3, 0.3 g of tert-butanol, 0.552 g of K₂CO₃, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask, and the mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA = 3.5) to give 0.25 g of the final product A5 (yield 51%).

[0115] The NMR results were as expected: 1H NMR (DMSO,300MHZ) δ(ppm): 4.20(d,4H),1.20(d,12H), 13 C NMR(CDCl3,100MHZ) δ(ppm): 147.5,121.0,65.7, 62.2,31.2.

[0116] Preparation of Formula A6 additive

[0117] Under an argon atmosphere, 0.34 g of intermediate II-3, 0.38 g of phenol, 0.552 g of K₂CO₃, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask, and the mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA=2) to give 0.31 g of final product A6 (yield 53%).

[0118] The NMR results were as expected: 1 HNMR(DMSO,300MHZ) δ(ppm):7.22(m,8H),6.90(m,4H),6.81(m,8H)4.20(d,4H), 13 CNMR(CDCl3,100MHZ) δ(ppm): 152.7,147.5,124.9, 121.5,121.3,121.0,62.2.

[0119] Preparation of Formula A7 additive

[0120] 0.146 g of intermediate II-2, 0.276 g of K2CO3 and 100 ml of DMF were placed in a 250 ml three-necked flask. 0.16 g of 2-chloroethanol was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was placed in an oil bath at 80 °C and reacted for 12 hours. After the reaction was stopped, the mixture was allowed to stand for 10 min and washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=1.5) to obtain intermediate II-4.

[0121] In a 250 mL round-bottom flask, intermediate II-4, 100 mL of dichloromethane, and 0.21 g of triethylamine were added sequentially. The system was placed in an ice bath, and 0.3 g of phosphorus trichloride was slowly injected dropwise using a syringe. After the addition was complete, the mixture was allowed to warm to room temperature, and the reaction was monitored by TLC until the reaction was complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=5) to obtain intermediate II-5.

[0122] Under an argon atmosphere, intermediate II-5, 0.36 g of trimethylhydroxysilane, 0.552 g of K₂CO₃, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask, and the mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA=7) to give 0.14 g of the final product A7 (overall yield of 22% for the three steps).

[0123] The NMR results were as expected: 1 H NMR (DMSO,300MHZ) δ(ppm): 4.04(s,4H),3.70(m,4H),3.54(m,4H),0.21(s,36H), 13 CNMR(CDCl3,100MHZ) δ(ppm): 147.5,118.5, 71.9,67.5,62.3,6.6.

[0124] Preparation of Formula A8 additive

[0125] 0.146 g of intermediate II-2, 0.276 g of K2CO3 and 100 ml of DMF were placed in a 250 ml three-necked flask. 0.27 g of 4-chlorocyclohexanol was slowly added dropwise through a constant pressure dropping funnel. After the addition was complete, the system was placed in an oil bath at 80 °C and reacted for 12 hours. After the reaction was stopped, the mixture was allowed to stand for 10 min and washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=2) to obtain intermediate II-4.

[0126] In a 250 mL round-bottom flask, intermediate II-4, 100 mL of dichloromethane, and 0.21 g of triethylamine were added sequentially. The system was placed in an ice bath, and 0.3 g of phosphorus trichloride was slowly injected using a syringe. After the addition was complete, the mixture was allowed to warm to room temperature, and the reaction was monitored by TLC until it was complete. The mixture was then washed with water, and the organic phases were combined and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=5.5) to obtain intermediate II-5.

[0127] Under an argon atmosphere, intermediate II-5, 0.36 g of trimethylhydroxysilane, 0.552 g of K₂CO₃, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask, and the mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA = 7.5) to give 0.23 g of the final product A8 (overall yield of 31% for the three steps).

[0128] The NMR results were as expected: 1H NMR (DMSO,300MHZ) δ(ppm): 4.20(d,4H),3.54(m,2H),3.24(m,2H),1.72-1.70(m,8H),1.47-1.45(m,8H),0.21(d,36H), 13 CNMR(CDCl3,100MHZ)δ(ppm): 147.5,118.5, 86.4,64.6,30.4,29.8,6.6.

[0129] Preparation of Formula A9 additive

[0130] 0.146 g of intermediate II-2, 0.276 g of K2CO3 and 100 ml of DMF were placed in a 250 ml three-necked flask. 0.26 g of 4-chlorophenol was slowly added to the system. The system was then placed in an oil bath at 80 °C and reacted for 12 hours. After the reaction was stopped, the mixture was allowed to stand for 10 min. The mixture was washed with water until neutral. The organic layer was dried with anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=3) to obtain intermediate II-4.

[0131] In a 250 mL round-bottom flask, intermediate II-4, 100 mL of dichloromethane, and 0.21 g of triethylamine were added sequentially. The system was placed in an ice bath, and 0.3 g of phosphorus trichloride was slowly injected dropwise using a syringe. After the addition was complete, the mixture was allowed to warm to room temperature, and the reaction was monitored by TLC until the reaction was complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. Finally, the crude product was subjected to column chromatography (PE:EA=5) to obtain intermediate II-5.

[0132] Under an argon atmosphere, intermediate II-5, 0.36 g of trimethylhydroxysilane, 0.552 g of K₂CO₃, and 50 ml of DMF were added sequentially to a 250 ml round-bottom flask, and the mixture was stirred at 50 °C for 12 hours. The reaction was monitored by TLC until complete. The mixture was then washed with water, the organic phases were combined, and dried over anhydrous sodium sulfate. The crude product was finally purified by column chromatography (PE:EA=7) to give 0.21 g of the final product A9 (overall yield of 28% for the three steps).

[0133] The NMR results were as expected: 1 HNMR (DMSO,300MHZ) δ(ppm): 6.75(d,4H),6.68(d,4H),4.61(s,4H),0.21(s,36H), 13 CNMR(CDCl3,100MHZ) δ(ppm): 150.7,147.5,145.0,121.0,116.9,115.7,6.6.

[0134] Preparation of electrolyte

[0135] At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), organic solvents EC and EMC are mixed evenly at a mass ratio of 3:7 to obtain a mixed solvent. LiPF6 is added to the obtained mixed solvent one by one while stirring, and the mass fraction of LiPF6 in the electrolyte is controlled to be 12.5%. Then, 0.1% to 5.0% of the electrolyte additive of this application is added and stirred evenly to obtain the electrolyte.

[0136] Secondary battery preparation

[0137] Positive electrode: The positive electrode active material Li(Ni) 0.8 Mn 0.1 Co 0.1 O2 (NMC811), conductive agent acetylene black (SuperP), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of NMC811:Super P:PVDF=94:3:3, and then evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. The mixed black slurry is coated on both sides of aluminum foil, and then baked, rolled, and cut into sheets to obtain the positive electrode sheet.

[0138] Negative electrode sheet: The negative electrode active material graphite, the conductive agent acetylene black (Super P) and the binder styrene-butadiene rubber (SBR) are mixed evenly in a mass ratio of graphite:Super P:SBR=94:3:3, and then evenly dispersed in deionized water to form a uniform black slurry. The mixed slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0139] Soft-pack battery: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding, hot pressing and shaping, and welding of the tabs, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte is injected into the dried battery, and the battery is allowed to stand, form, and be capacity tested to complete the preparation of the lithium-ion soft-pack battery.

[0140] Battery performance test

[0141] Room temperature DCR test: At 25±2℃, the soft-pack battery was charged to 4.4V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, it was pulsed discharged at 10C constant current for 10 seconds. The SOC was then adjusted to 50% using the same method, and charged for another 10 seconds. The DCR was calculated as follows: DCR = (Voltage before pulse discharge - Voltage after pulse discharge) / Discharge current. 100%. After 30 days of storage at 60℃, and once the battery has completely cooled to 25±2℃, the DCR is tested again. The DCR change rate = (DCR after 30 days - DCR before 30 days) / DCR before 30 days. 100%;

[0142] High-temperature cycle performance test: At 25±2℃, the pouch battery was subjected to charge-discharge cycle tests at a charge / discharge rate of 1C / 1C within the range of 2.8~4.4V. The discharge specific capacity of the battery in the first cycle and the discharge specific capacity after 500 cycles were recorded. Capacity retention after 500 cycles = discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle. 100%;

[0143] High-temperature storage performance: The pouch battery was placed at 60±2℃ and charged / discharged at a 1C / 1C rate within the range of 2.8~4.4V. The discharge specific capacity of the battery in the first week was recorded. Afterwards, the battery was stored at 60±2℃ for 30 days, and the charge / discharge test was performed again, with the discharge specific capacity recorded. High-temperature storage capacity retention rate = discharge specific capacity after 7 days / discharge specific capacity in the first week. 100%;

[0144] High-temperature gas generation test: The soft-pack battery was charged at 25±2℃ with a constant current rate of 1C to 4.4V, and then charged at 4.4V with a constant voltage until the current dropped below 0.05C, bringing it to a fully charged state at 4.4V. The volume of the fully charged battery before storage was measured and recorded as V0. The fully charged battery was then placed in a 60±2℃ oven for 7 days. After 7 days, the battery was removed, and its volume after storage was immediately measured and recorded as V1. Volume expansion rate = (V1-V0) / V0 100%;

[0145] According to the above-described preparation methods for electrolyte and secondary battery, the examples and comparative examples respectively provide an electrolyte and a secondary battery containing the electrolyte. The composition of the electrolyte and the performance of the battery are shown in Table 1.

[0146] Table 1

[0147]

[0148] VC: vinylene carbonate; TMSP: tris(trimethylsilane)phosphate

[0149] Comparing the experimental results of Examples 1-5 and Comparative Example 1, it can be seen that adding the electrolyte additive A1 of this application can reduce the initial internal resistance of the battery and the increase in internal resistance during storage, and improve the capacity retention rate during high-temperature cycling and high-temperature storage. It can also be seen that as the content of additive A1 increases, the initial internal resistance increases accordingly. This is because the generated interfacial film becomes increasingly dense, increasing the interfacial film impedance, which has a beneficial effect on suppressing the increasing trend of battery internal resistance and volume expansion rate during high-temperature storage, reducing irreversible losses during storage. However, excessive additive usage leads to a significant increase in initial impedance, which is detrimental to the battery's kinetic performance. Considering all performance factors, the preferred electrolyte additive content is 0.5-2%, and the optimal content can be determined according to specific requirements.

[0150] The experimental results from Examples 3 and Comparative Examples 2-4 show that, compared to additives containing only a single functional group, the combination of the two, namely additive A1, exhibits better performance. Its VC structure makes it an excellent negative electrode film-forming additive, reducing Mn deposition on the negative electrode, lowering impedance, and facilitating the formation of a stable interface film on the negative electrode surface. The additive contains PO bonds; trivalent P is easily oxidized, thus consuming oxygen generated from the positive electrode interface. The free radicals generated by the breaking of PO bonds diffuse to the positive electrode surface to form a CEI film, which can inhibit the dissolution of Mn at the positive electrode interface. Furthermore, the silyl ether (O-Si-C) in A1 can react with HF, inhibiting its corrosion of transition metals. Through cross-linking coupling, these structures further stabilize the positive and negative electrode interface film, comprehensively enhancing its film-forming effect and improving the high-temperature storage gas generation and cycle performance of the battery cell.

[0151] In summary, electrolytes containing the electrolyte additives of this application can better improve the high-temperature storage gas generation and high-temperature cycle performance of batteries. The specific application can be adjusted according to the application scenario.

[0152] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. An additive, characterized in that, Compounds including those with the structure shown in Formula A: Among them, R1 to R4 are each individually selected from any one of -CH3, -C2H5, -CH2CF3, -CHC2F6, -Ph, -C(CH3)3, and -Si(CH3)3; R5 and R6 are each independently selected from any one of C1 to C20 alkylene groups or -R7-O-R8-; R7 is selected from phenyl or C1 to C20 alkyl groups; R8 is selected from C1 to C20 alkyl groups.

2. The additive according to claim 1, characterized in that, R1 to R4 are selected from any one of -CH3, -C2H5, -CH2CF3, -CHC2F6, -Ph, -C(CH3)3 and -Si(CH3)3; R5 and R6 are each independently selected from any one of C1 to C5 alkylene groups or -R7-O-R8-; R7 is selected from phenyl or C1 to C5 alkyl groups; R8 is selected from C1 to C5 alkyl groups.

3. The additive according to claim 1, characterized in that, The -R7-O-R8- contains any one of the following substituents: 、 、 。 4. The additive according to claim 1, characterized in that, The compound with the structure shown in Formula A contains at least one of the following compounds: 。 5. The method for preparing the additive according to claim 1, characterized in that, include: The compound with the structure shown in Formula II reacts with formic acid to generate intermediate II-1; The intermediate product II-1 reacts with hydrochloric acid to generate intermediate product II-2; The intermediate product II-2 reacts with phosphorus trichloride to generate intermediate product II-3, or the intermediate product II-2 reacts with Cl-R7-OH to generate intermediate product II-4; The intermediate product II-3 reacts with X-OH to generate the compound with the structure shown in Formula A of claim 1, or the intermediate product II-4 reacts with phosphorus trichloride to generate intermediate product II-5, and intermediate product II-5 reacts with X-OH to generate the compound with the structure shown in Formula A of claim 1. Where X is at least one of R1 to R4; II II-1 II-2 II-3 II-4 II-5 Where n is an integer from 1 to 20.

6. An electrolyte, characterized in that, It includes lithium salt, organic solvent and additives as described in any one of claims 1 to 5, wherein the mass of the additives accounts for 0.1% to 5% of the total mass of the electrolyte.

7. The electrolyte according to claim 6, characterized in that, The additive accounts for 0.5% to 2% of the total mass of the electrolyte.

8. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and the electrolyte as described in claim 6 or 7.

9. The secondary battery according to claim 8, characterized in that, The positive electrode sheet includes a positive electrode active material, which contains a chemical formula of Li. a Ni x Co y Mn z M e O2, wherein 0.9≤a≤1.1, 0≤e≤0.1, 0.3≤x<1.0, 0<y<0.4, 0.1<z<0.4, x+y+z=1.0, and M contains at least one of Al, Zr, Sr, Ti, B, Mg, Sn, W, Y, Ba, Nb, Mo, Ta, Si, La, Er, Nd, Gd, and Ce.

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