Electrolyte additive and preparation method, electrolyte, secondary battery and electric device

Abstract

The application provides an electrolyte additive and a preparation method thereof, an electrolyte, a secondary battery and an electric device. The electrolyte additive can improve the wettability of the electrolyte to the electrode plate and can reduce the impedance at the negative electrode interface, thereby improving the cycle performance of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to electrolyte additives and their preparation methods, electrolytes, secondary batteries, and electrical equipment. Background Technology

[0002] For secondary batteries using liquid electrolytes, the electrolyte is one of the key materials. It provides a transport channel for electrons and active ions during the charge-discharge cycle to maintain the normal operation of the battery. In addition, the components in the electrolyte can also participate in the solid electrolyte interface (SEI) film on the surface of the negative electrode. Therefore, the electrolyte components can also affect the interfacial characteristics of the battery.

[0003] As market demands for higher battery energy density increase, the industry often chooses to increase the thickness of the electrode active material layer to improve battery energy density. One technical approach is to increase the coating thickness and / or compaction density of the electrode active material. However, increasing the thickness or compaction density of the electrode active material increases the difficulty of electrolyte wetting. Insufficient electrolyte wetting can lead to localized inhomogeneities in the electrode properties. During subsequent cycles, these conditions gradually worsen, exacerbating battery polarization and severely impacting the battery's cycle performance.

[0004] To address the aforementioned technical issues, some literature reports the use of low-viscosity solvents, such as carboxylic acid esters or ethers, as co-solvents to reduce the overall viscosity of the electrolyte, thereby improving the wetting of the electrodes and enhancing kinetics, thus improving battery performance. However, carboxylic acid ester solvents often have low boiling points, resulting in poor high-temperature performance of the formulated electrolyte, and they are generally used in large quantities, which is detrimental to battery cost control. Alternatively, some patents and literature suggest adding surfactants as additives to improve the wetting of the electrolyte and electrodes. However, existing surfactants are not specifically developed for battery systems, and their electrochemical stability is poor, which may lead to battery performance degradation. Summary of the Invention

[0005] Therefore, embodiments of this application provide an electrolyte additive and its preparation method, an electrolyte, a secondary battery, and an electrical device. This electrolyte additive can improve the wettability of the electrolyte to the electrode plates and reduce the impedance at the negative electrode interface, thereby improving the cycle performance of the battery.

[0006] The first aspect of this application provides an electrolyte additive, comprising a general structural formula as shown in Formula I. Formula I,

[0007] Z is selected from , , and any one of them;

[0008] R1 is selected from any one of fluorine, chlorine, bromine, iodine and substituted or unsubstituted alkyl groups.

[0009] The aforementioned electrolyte additive possesses both hydrophilic and hydrophobic ends. Therefore, it can function as a surfactant, enhancing the wetting performance of the electrolyte on the electrode active material layer. This is particularly beneficial for improving the wetting effect on electrode active material layers with high compaction density or significant thickness, thereby improving battery cycle performance. Furthermore, the aforementioned electrolyte additive contains -Z1N. - SO3 - This allows it to participate in the formation of the SEI film on the negative electrode surface during battery formation, which can improve the stability of the SEI film while also helping to reduce its thickness. Furthermore, each 1 mol of electrolyte additive molecules can dissociate up to 2 mol of Li. + Therefore, the interface impedance of the battery can be reduced, which can further optimize the cycle performance of the battery.

[0010] The second aspect of this application provides a method for preparing an electrolyte additive, comprising: (1) Under conditions of ≤15℃, chlorosulfonic acid, raw material a, and a first solvent are mixed to carry out a first reaction to obtain an intermediate; the raw material a is ;

[0011] Wherein, R1 is selected from any one of fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, and substituted or unsubstituted alkyl groups, and Z is selected from... , , , any one of them;

[0012] (2) Under conditions of ≤25°C, the lithium salt is added to a second solvent containing the intermediate to carry out a second reaction; wherein the lithium salt includes lithium carbonate; (3) After evaporating the material obtained after the second reaction, a third solvent is added, and the mixture is allowed to stand, filtered, and dried in sequence to obtain the electrolyte additive provided in the first aspect of the present application.

[0013] The above preparation method has simple steps, reliable process, and can realize large-scale industrial production.

[0014] A third aspect of this application provides an electrolyte comprising an electrolyte, a non-aqueous solvent, and an electrolyte additive provided in the first aspect of this application. Because it contains the electrolyte additive provided in the first aspect of this application, the electrolyte exhibits good wettability on the electrode sheets, and the electrolyte additive can be completely or partially decomposed during the formation process to participate in the formation of the SEI film on the negative electrode surface, reducing the interfacial impedance of the negative electrode surface, thereby providing a secondary battery with good cycle performance.

[0015] A fourth aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte provided in the third aspect of this application located between the positive electrode and the negative electrode. Due to the use of the electrolyte provided in this application, the secondary battery exhibits good cycle performance.

[0016] The fifth aspect of this application provides an electrical device, including the secondary battery provided in the fourth aspect of this application. Because it uses the secondary battery provided in this application for power supply, this electrical device has good market prospects. Attached Figure Description

[0017] Figure 1A The NMR fluorine spectrum of the electrolyte additive provided in Example 1 of this application; Figure 1B The lithium NMR spectrum of the electrolyte additive provided in Example 1 of this application; Figure 2 The infrared spectrum of the electrolyte additive provided in Example 1 of this application. Detailed Implementation

[0018] To meet market demand for devices with long battery life, battery manufacturers are dedicated to developing batteries with higher energy density. One technological approach involves increasing the coating thickness and / or compaction density of the electrode active materials. However, increasing the thickness or compaction density of the electrode active materials increases the difficulty of electrolyte wetting. Insufficient electrolyte wetting can lead to localized inhomogeneities in the electrodes. During subsequent cycles, this situation gradually worsens, exacerbating battery polarization and severely impacting battery cycle performance. To improve electrolyte wetting, manufacturers typically choose to reduce electrolyte viscosity or add surfactants. However, existing surfactants are not specifically designed for battery systems, resulting in poor electrochemical stability and also contributing to battery performance degradation.

[0019] To address the aforementioned technical problems, embodiments of this application provide an electrolyte additive, comprising a general structural formula as shown in Formula I. Formula I,

[0020] Z is selected from , , and any one of them;

[0021] R1 is selected from any one of fluorine, chlorine, bromine, iodine and substituted or unsubstituted alkyl groups.

[0022] One end of the above-mentioned electrolyte additive is a hydrophilic -SO3 group. - One end of the additive is a hydrophobic group –R1 (halogen atoms, carbon chains, and other groups have a certain degree of hydrophobicity). Therefore, this electrolyte additive can act as a surfactant, improving the wetting performance of the electrolyte on the electrode active material layer. It is particularly beneficial for improving the wetting effect of the electrolyte on electrode active material layers with high compaction density or large thickness, thereby improving the battery's cycle performance. Furthermore, the above-mentioned electrolyte additive contains –Z1N. - SO3 - This allows it to participate in the formation of the SEI film on the negative electrode surface during battery formation. Because it contains sulfonic acid groups, it can improve the stability of the SEI film while also helping to reduce its thickness. Furthermore, each 1 mol of electrolyte additive molecules can dissociate up to 2 mol of Li. + Therefore, the interface impedance of the battery can be reduced, which can further optimize the cycle performance of the battery.

[0023] In addition, improving the wetting performance of the electrolyte on the electrode active material layer is beneficial for the electrolyte to better wet the active particles in the high-pressure dense electrode, thereby improving the rate performance and discharge capacity of the battery.

[0024] In some embodiments of this application, the number of carbon atoms in the substituted or unsubstituted alkyl group is ≤10. Specifically, when R1 is a substituted or unsubstituted alkyl group, the number of carbon atoms can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. Controlling the number of carbon atoms in R1 within the above range can reduce the steric hindrance of the electrolyte additive molecules and minimize its impact on the electrolyte viscosity when applied to the electrolyte, thus facilitating the application of the electrolyte.

[0025] In some embodiments of this application, when R1 is a substituent alkyl group, the substituent includes, but is not limited to, a halogen atom, specifically trifluoromethyl, but is not limited thereto. In other embodiments, R1 can be methyl, ethyl, propyl, isopropyl, vinyl, etc., but is not limited thereto. All of the above groups have good hydrophobicity and react with -SO3. - The synergistic effect of these factors helps to improve the wettability of the electrolyte to the electrode active material layer.

[0026] In some embodiments of this application, the electrolyte additive comprises any compound as shown in formulas A-F:

[0027] Wherein, the compound represented by formula A is lithium sulfonate (2,2,2-trifluoroacetyl)imide; the compound represented by formula B is lithium sulfonate (2,2,2-trifluoromethanesulfonyl)imide; the compound represented by formula C is lithium sulfonate fluorinated carbon imide; the compound represented by formula D is lithium sulfonate fluorinated sulfonyl imide; the compound represented by formula E is lithium sulfonate (2,2,2-trifluorosulfinyl)imide; and the compound represented by formula F is lithium sulfonate (sulfinyl fluoride)imide.

[0028] In lithium sulfonic acid (2,2,2-trifluoroacetyl)imine and lithium sulfonic acid (2,2,2-trifluoromethanesulfonyl)imine, one end of the strongly electronegative N atom is successively connected to a strongly electron-withdrawing S atom and a trifluoromethyl group, making the Li in the compound... + It is easier to dissociate, which can significantly improve its ionic conductivity and benefit the battery performance.

[0029] This application also provides a method for preparing an electrolyte additive, which can be used to prepare the aforementioned electrolyte additive. The preparation method includes: (1) Under conditions of ≤15℃, chlorosulfonic acid, raw material a and first solvent are mixed and a first reaction is carried out to obtain an intermediate; The raw material a is ;

[0030] Wherein, R1 is selected from any one of fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, and substituted or unsubstituted alkyl groups, and Z is selected from... , , , any one of them;

[0031] (2) Under conditions of ≤25°C, lithium salt is added to a second solvent containing the intermediate to carry out a second reaction; wherein, the lithium salt includes lithium carbonate; in order to improve the yield of electrolyte additives, sufficient or excessive amounts of lithium salt are generally added. Excess lithium carbonate is easy to remove from the system, thereby helping to ensure the purity of electrolyte additives.

[0032] (3) After evaporating the material obtained after the second reaction, a third solvent is added. The evaporation process is to remove some of the solvent (including the first solvent, the second solvent, and some byproducts generated by the reaction, such as hydrochloric acid). The first solvent is added again to provide a suitable crystallization environment for the electrolyte additive. The electrolyte additive is allowed to crystallize and precipitate, filtered, and dried in sequence to obtain the electrolyte additive provided in the embodiments of this application.

[0033] The above preparation method has simple steps, high process reliability, high production efficiency, and can realize large-scale industrial production.

[0034] In step (1), the temperature at which chlorosulfonic acid, raw material a, and the first solvent are mixed can be 15°C, 10°C, 5°C, etc. This allows chlorosulfonic acid and raw material a to react fully in the first solvent, reduces side reactions, and improves the yield and purity of the intermediate. In step (2), the temperature is controlled to ≤25°C when the lithium salt is added to the second solvent containing the intermediate. This is also to ensure that the two react fully and reduce the generation of by-products (impurities), which is beneficial to the yield and purity of the final electrolyte additive. Specifically, the above temperatures can be 25°C, 20°C, 15°C, 10°C, 5°C, etc.

[0035] In some embodiments of this application, in step (1), raw material a is dissolved in a first solvent and cooled to 0°C~10°C in an ice-water bath. Chlorosulfonic acid is then added dropwise to the first solvent containing raw material a, ensuring that the temperature of the system does not exceed 15°C during the addition of chlorosulfonic acid. In some specific embodiments of this application, the process further includes dissolving chlorosulfonic acid in a first solvent and then adding the resulting solution dropwise to the first solvent containing raw material a. The first solvent used to dissolve the chlorosulfonic acid can be the same as or different from the first solvent used to dissolve the trifluoroacetamide.

[0036] In some embodiments of this application, in step (1), the first solvent mentioned above includes, but is not limited to, at least one of dichloromethane, dichloroethane, trichloromethane, carbon tetrachloride, benzene, toluene, p-xylene, petroleum ether, and n-hexane.

[0037] In some embodiments of this application, the above-mentioned raw material a is trifluoroacetamide, which can be used to prepare lithium sulfonic acid (2,2,2-trifluoroacetyl)imine, and the synthetic route is as follows: .

[0038] In some embodiments of this application, the above-mentioned raw material a is trifluoromethanesulfonamide, which can be used to prepare lithium sulfonic acid (2,2,2-trifluoromethanesulfonyl)imide, and its synthetic route is as follows: .

[0039] In some specific embodiments, during the synthesis of lithium sulfonic acid (2,2,2-trifluoroacetyl)imine, the molar ratio of trifluoroacetamide to chlorosulfonic acid is (0.95~1.1):1. This is beneficial for improving the conversion rate of trifluoroacetamide and chlorosulfonic acid. Specifically, the molar ratio of trifluoroacetamide to chlorosulfonic acid can be, but is not limited to, 0.95:1, 0.98:1, 1.00:1, 1.02:1, 1.05:1, 1.08:1, 1.10:1, etc.

[0040] In some embodiments of this application, in step (1), the temperature of the first reaction is 15°C to 35°C. Controlling the temperature of the first reaction within the above range can suppress the occurrence of side reactions and improve the purity and yield of the product. Specifically, the temperature of the first reaction can be, but is not limited to, 15°C, 20°C, 25°C, 30°C, 35°C, etc.

[0041] In some embodiments of this application, in step (1), the duration of the first reaction is 2h to 8h. This allows for a more complete reaction between the raw materials in the first reaction, resulting in a higher conversion rate. It also reduces the risk of intermediates being decomposed and destroyed, as well as the increase in byproducts, thereby improving the yield and purity of the intermediates in the first reaction. Specifically, the duration of the first reaction can be, but is not limited to, 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, 5.5h, 6.0h, 6.5h, 7.0h, 7.5h, 8.0h, etc.

[0042] In some specific embodiments, the materials may also be stirred during the first reaction process described above.

[0043] In some embodiments of this application, in step (2), the material obtained after the first reaction is allowed to stand to separate into layers, and the lower layer liquid (containing an intermediate) is taken. The obtained lower layer liquid is dissolved in a second solvent and placed in an ice-water bath to cool to 0°C~10°C. Lithium salt is then added to it, and the temperature is ensured not to exceed 25°C during the addition process.

[0044] In some embodiments of this application, in step (2), the lithium salt is added at a molar ratio of Li to raw material a of (2~2.2):1. Taking lithium carbonate as an example, the molar ratio of lithium carbonate added in step (2) to the molar ratio of raw material a is (1~1.1):1. This allows the intermediate to react fully with the lithium salt, improving the yield of the electrolyte additive.

[0045] In some embodiments of this application, the temperature of the second reaction is 15°C to 35°C. Specifically, the temperature of the first reaction can be, but is not limited to, 15°C, 20°C, 25°C, 30°C, 35°C, etc. This facilitates the second reaction and reduces side reactions, thereby ensuring high purity and yield of the electrolyte additive.

[0046] In some embodiments of this application, the second reaction time is 3h to 24h. Specifically, the second reaction time can be, but is not limited to, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 22h, and 24h. Controlling the second reaction time is more suitable and helps to improve the conversion rate of the intermediate.

[0047] In some specific embodiments of this application, the materials also need to be stirred during the second reaction process described above.

[0048] In some embodiments of this application, the second solvent includes, but is not limited to, at least one of acetonitrile, propionitrile, ethyl acetate, propyl acetate, acetone, dimethyl sulfoxide, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0049] In some embodiments of this application, in step (3), the third solvent mentioned above includes, but is not limited to, at least one of dichloromethane, dichloroethane, trichloromethane, carbon tetrachloride, benzene, toluene, p-xylene, petroleum ether, and n-hexane. The first solvent in step (1) and the third solvent used in step (3) may be the same or different, as can be determined by those skilled in the art based on actual production needs.

[0050] In some embodiments of this application, in step (3), the material obtained from the second reaction is evaporated to remove 65wt.%~75wt.% of solvent, yielding a residual liquid. This significantly reduces the risk of impurities in the residual liquid and during subsequent settling adhering to the electrolyte additive, thereby improving the purity of the electrolyte additive. In some specific embodiments, the evaporation is performed under reduced pressure, with the temperature ranging from 30°C to 50°C. Specifically, the temperature during reduced pressure evaporation can be, but is not limited to, 30°C, 35°C, 40°C, 45°C, 50°C, etc.

[0051] In some specific embodiments of this application, the material obtained after the second reaction is first subjected to solid-liquid separation, and the liquid obtained after separation is taken and evaporated.

[0052] In some embodiments of this application, in step (3), after the obtained residual liquid is naturally cooled to room temperature, a third solvent is added to the residual liquid, and the mixture is left to stand at -25°C to 5°C for 6 hours to 36 hours. As mentioned above, during the standing process in step (3), the electrolyte additive crystallizes. Controlling the standing temperature to no more than 5°C is to balance the crystallization rate and product quality. Controlling the standing temperature to no less than -25°C is to avoid solvent solidification that could damage the product purity. In addition, controlling the standing time to be between 6 hours and 36 hours under the above temperature conditions is also to improve the purity and yield of the electrolyte additive. Specifically, the standing temperature can be -25°C, -20°C, -15°C, -10°C, -5°C, etc., and the standing time can be 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, 25 hours, 28 hours, 30 hours, 32 hours, 36 hours, etc.

[0053] This application provides a method for preparing electrolyte additives. The raw materials are simple and readily available, the reaction conditions are mild, there are few side reactions, and the reaction cycle is short, making it suitable for large-scale industrial production.

[0054] This application also provides an electrolyte comprising an electrolyte, a non-aqueous solvent, and an electrolyte additive provided in this application embodiment. Due to the presence of the electrolyte additive provided in this application embodiment, the electrolyte exhibits good wettability of the electrode sheets, and the electrolyte additive can be completely or partially decomposed during the formation process to participate in the formation of the SEI film on the negative electrode surface, reducing the interfacial impedance of the negative electrode surface, thereby providing a secondary battery with good cycle performance.

[0055] In some embodiments of this application, the electrolyte additive accounts for 0.01% to 5% of the electrolyte by mass. A small amount of electrolyte additive can effectively improve the battery's cycle performance and reduce battery costs. Controlling the electrolyte content to less than or equal to 5% can significantly reduce the risk of electrolyte corrosion of the electrode current collector and help control the electrolyte viscosity within a suitable range. In some specific embodiments, the electrolyte additive accounts for 0.05% to 1.5% of the electrolyte by mass. This is more conducive to balancing battery cycle performance and battery production costs, and can further reduce the risk of electrolyte corrosion of the electrode current collector. Specifically, the mass percentage of the electrolyte additive in the electrolyte can be 0.01%, 0.02%, 0.05%, 0.08%, 0.10%, 0.50%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00%, 4.50%, 5.00%, etc.

[0056] In some embodiments of this application, the electrolyte salt can be any electrolyte known in the art. Specifically, the electrolyte includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium bis(oxalateborate)borate (LiBOB), lithium difluorooxalateborate (LiODFB), and lithium perchlorate (LiClO4).

[0057] In some embodiments of this application, the molar concentration of the electrolyte in the electrolyte solution is 0.7 mol / L to 1.5 mol / L. Exemplarily, the molar concentration of the electrolyte in the electrolyte solution can be 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc.

[0058] In some embodiments of this application, the non-aqueous solvent can be any non-aqueous solvent known in the art. Specifically, the aforementioned non-aqueous solvents include, but are not limited to, at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate. All of the above-mentioned non-aqueous solvents are good solvents for electrolytes and electrolyte additives, and their viscosity, wettability, and other parameters are suitable.

[0059] In some embodiments of this application, the electrolyte further includes a second additive; the second additive includes, but is not limited to, at least one of fluoroethylene carbonate, vinylene carbonate, lithium monofluorophosphate, ethylene sulfate, and tris(trimethylsilane)borate. The aforementioned second additive is beneficial for improving the overall performance of the SEI film and / or for improving the ionic conductivity of the electrolyte. Combined with electrolyte additives, it further enhances the overall performance of the battery.

[0060] In some embodiments of this application, the mass percentage of the second additive in the electrolyte is 0.5% to 5%. This allows for improved overall battery performance while maintaining a low electrolyte cost. Specifically, the mass percentage of the second additive in the electrolyte can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, etc.

[0061] In some embodiments of this application, the mass ratio of the electrolyte additive to the second additive in the electrolyte is 2:8. This helps to ensure better overall battery performance.

[0062] This application also provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte provided in this application, located between the positive and negative electrodes. Due to the use of the electrolyte provided in this application, the secondary battery exhibits good cycle performance.

[0063] In some embodiments of this application, the secondary battery is a lithium-ion battery.

[0064] This application also provides an electrical device, including the secondary battery provided in this application embodiment. Because it uses the secondary battery provided in this application embodiment for power supply, this electrical device has good market prospects.

[0065] In some embodiments of this application, the aforementioned electrical equipment includes, but is not limited to, new energy vehicles, consumer electronics products, and electric bicycles.

[0066] The technical solution of this application will be further described in detail below with reference to several embodiments.

[0067] Example 1 (1) Add 113g of raw material a (specifically trifluoroacetamide) to a three-necked flask equipped with a thermometer, a constant pressure dropping funnel, and a glass stopper. Weigh 200g of the first solvent (specifically dichloromethane), stir and mix thoroughly, and place in an ice-water bath to cool to 10°C. Dissolve 116.5g of chlorosulfonic acid in 100g of the first solvent (dichloromethane) to prepare a solution. Transfer the above solution to a constant pressure dropping funnel and add it dropwise to the trifluoroacetamide dichloromethane solution. During the dropwise addition, control the system temperature at 12°C. After the addition is complete, control the temperature at 25°C and stir the reaction for 6 hours (i.e., carry out the first reaction).

[0068] (2) After the first reaction is completed, stop stirring. The solution will separate into layers. Use a separatory funnel to separate the lower layer and transfer it to a three-necked flask. Add 300g of the second solvent (specifically acetonitrile) to dilute the solvent. Place the resulting solution in an ice-water bath to cool to 10°C. Weigh 75g (slight excess) of lithium salt (specifically lithium carbonate) and add it slowly in batches to the solution, ensuring the temperature is 23°C during the addition. After the addition is completed, control the temperature at 23°C and stir the reaction for 16 hours (to carry out the second reaction). (3) After the second reaction is completed, a white solid is produced in the system. The white solid is filtered and the filtrate is collected. The filtrate is heated to 35°C and evaporated under reduced pressure. After about 210g of filtrate is removed, evaporation is stopped and the mixture is allowed to cool naturally to room temperature. 80g of the first solvent (specifically dichloromethane) is added to the residue. The resulting solution is transferred to a low-temperature chamber and allowed to stand at -10°C for 24 hours to allow the electrolyte additive to crystallize, resulting in a large amount of white solid. The solid is filtered, collected, and dried to obtain the electrolyte additive of Example 1 - lithium sulfonic acid (2,2,2-trifluoroacetyl)imine. Based on chlorosulfonic acid, the yield of Example 1 is 71.2%, and the product purity is 99.7%. In the examples of this application, the purity of the product is determined by nuclear magnetic resonance.

[0069] Example 2 The only difference from Example 1 is that the first solvent used in steps (1) and (3) is replaced with dichloroethane instead of dichloromethane. Based on chlorosulfonic acid, the yield of Example 2 is 71.1%; the product purity is greater than 99.6%.

[0070] Example 3 The only difference from Example 1 is that the first solvent used in steps (1) and (3) is replaced with toluene instead of dichloromethane. Based on chlorosulfonic acid, the yield of Example 3 is 71.7%; the product purity is 99.7%.

[0071] Example 4 The only difference from Example 1 is that the first solvent used in steps (1) and (3) is replaced with petroleum ether instead of dichloromethane. Based on chlorosulfonic acid, the yield of Example 4 is 70.5%; the product purity is 99.5%.

[0072] Example 5 The only difference from Example 1 is that the second solvent used in step (2) is replaced with ethyl acetate instead of acetonitrile. Based on chlorosulfonic acid, the yield of Example 5 is 72.5%; the product purity is 99.8%.

[0073] Example 6 The only difference from Example 1 is that the second solvent used in step (2) is replaced with acetone instead of acetonitrile. Based on chlorosulfonic acid, the yield of Example 6 is 72.1%; the product purity is 99.7%.

[0074] Example 7 The only difference from Example 1 is that the second solvent used in step (2) is replaced with dimethyl carbonate instead of acetonitrile. Based on chlorosulfonic acid, the yield of Example 7 is 71.7%; the product purity is 99.7%.

[0075] Example 8 The only difference from Example 1 is that in steps (1) and (2), the temperature of both the first and second reactions is 35°C. Based on chlorosulfonic acid, the yield of Example 8 is 72.2%; the product purity is 99.7%.

[0076] Example 9 The only difference from Example 1 is that the temperatures of both the first and second reactions in steps (1) and (2) are 15°C. Based on chlorosulfonic acid, the yield of Example 9 is 71.6%; the product purity is 99.7%.

[0077] Example 10 The only difference from Example 1 is that the reaction time of the first reaction in step (1) is 4 hours. Based on chlorosulfonic acid, the yield of Example 10 is 70.5%; the product purity is 99.7%.

[0078] Example 11 The only difference from Example 1 is that the reaction time of the first reaction in step (1) is 8 hours. Based on chlorosulfonic acid, the yield of Example 11 is 71.2%; the product purity is 99.7%.

[0079] Example 12 (1) Add 192.18g of raw material a (specifically trifluoromethanesulfonamide) to a three-necked flask equipped with a thermometer, a constant pressure dropping funnel, and a glass stopper. Weigh 400g of the first solvent (specifically dichloromethane), stir and mix thoroughly, and place in an ice-water bath to cool to 0°C. Dissolve 116.5g of chlorosulfonic acid in 100g of the first solvent (dichloromethane) to prepare a solution. Transfer the above solution to a constant pressure dropping funnel and add it dropwise to the dichloromethane solution of trifluoroacetamide. During the addition, control the system temperature at 12°C. After the addition is complete, control the temperature at 25°C and stir the reaction for 4 hours (i.e., carry out the first reaction).

[0080] (2) After the first reaction is completed, stop stirring. The solution will separate into layers. Use a separatory funnel to separate the lower layer and transfer it to a three-necked flask. Add 350g of the second solvent (specifically acetonitrile) to dilute the solvent. Place the resulting solution in an ice-water bath to cool to 0°C. Weigh 75g of lithium salt (specifically lithium carbonate) and add it slowly in batches to the solution, ensuring the temperature is 23°C during the addition. After the addition is complete, control the temperature at 23°C and stir the reaction for 16 hours (to carry out the second reaction). (3) After the second reaction is completed, a white solid is produced in the system. The white solid is filtered and the filtrate is collected. The filtrate is heated to 50°C and evaporated under reduced pressure. After about 210g of filtrate is removed, the evaporation is stopped and the system is allowed to cool naturally to room temperature. 80g of the first solvent (specifically dichloromethane) is added to the residue. The resulting solution is transferred to a low-temperature chamber and allowed to stand at -10°C for 24h to allow the electrolyte additive to crystallize, resulting in a large amount of white solid. The solid is filtered, collected, and dried to obtain the electrolyte additive of Example 12 - lithium sulfonic acid (2,2,2-trifluoromethanesulfonyl)imide.

[0081] Structural characterization of electrolyte additives The electrolyte additives prepared in Examples 1-12 were subjected to NMR and infrared spectroscopy tests. For the NMR and infrared spectra of the electrolyte additive in Example 1, please refer to [link to relevant documentation]. Figure 1A-Figure 2 . Figure 1A The NMR fluorine spectrum of the electrolyte additive in Example 1 shows that the peak with a shift of -77 ppm is the peak of trifluoromethyl. Figure 1B The lithium NMR spectrum of the electrolyte additive in Example 1 shows the peaks shifted by 0-2 ppm in the fluorine spectrum, which represent Li₂ released from the electrolyte additive in Example 1 in the solvent. + The peak; Figure 2 This is the infrared spectrum of the electrolyte additive in Example 1, where 1000 cm⁻¹... -1 Below (approximately 800 cm) -1 The trifluoromethyl peak at 1100 cm⁻¹ -1 The sulfonyl peak shifted to the right, at 1712 cm⁻¹ -1It is a carbonyl amide (C=O), 3300 cm -1 The peak is the Li-active bond peak. Combining the NMR and IR spectra, it can be confirmed that the product obtained in Example 1 is lithium sulfonic acid (2,2,2-trifluoroacetyl)imine, and no other peaks were observed in the NMR spectrum, indicating that the product has high purity.

[0082] Electrolyte Examples Electrolyte Example 1 In an argon atmosphere glove box with a moisture content ≤1ppm, 25g of ethylene carbonate (EC), 5g of polycarbonate (PC), 30g of dimethyl carbonate (DMC), and 40g of ethyl methyl carbonate (EMC) were mixed. Then, 13.9g of dry electrolyte (specifically, solid lithium hexafluorophosphate) was added to the mixed solvent. After the lithium hexafluorophosphate was completely dissolved, 1.15g of electrolyte additive (specifically, lithium (2,2,2-trifluoroacetyl)imine sulfonate) was added. Then, a second additive was added, specifically consisting of 2.3g of ethylene carbonate, 1.15g of tris(trimethylsilane)borate, and 2.3g of ethylene sulfate. After mixing thoroughly, the electrolyte was obtained.

[0083] In the above electrolyte, the molar concentration of the electrolyte is 1 mol / L, and the mass percentage of the electrolyte additive in the electrolyte is 1%.

[0084] Electrolyte Example 2 The only difference from the electrolyte in Example 1 is that the lithium sulfonic acid (2,2,2-trifluoroacetyl)imine has a mass percentage of 0.1% in the electrolyte.

[0085] Electrolyte Example 3 The only difference from the electrolyte in Example 1 is that the lithium sulfonic acid (2,2,2-trifluoroacetyl)imine has a mass percentage of 0.2% in the electrolyte.

[0086] Electrolyte Example 4 The only difference from the electrolyte in Example 1 is that the lithium sulfonic acid (2,2,2-trifluoroacetyl)imine has a mass percentage of 0.5% in the electrolyte.

[0087] Electrolyte Example 5 The only difference from the electrolyte in Example 1 is that the mass percentage of lithium sulfonic acid (2,2,2-trifluoroacetyl)imine in the electrolyte is 0.01%.

[0088] Electrolyte Example 6 The only difference from the electrolyte in Example 1 is that the lithium sulfonate (2,2,2-trifluoroacetyl)imine has a mass percentage of 2% in the electrolyte.

[0089] Electrolyte Example 7 The only difference from the electrolyte in Example 1 is that lithium sulfonic acid (2,2,2-trifluoroacetyl)imine is replaced with... .

[0090] To highlight the beneficial effects of the electrolyte embodiments of this application, the following comparative examples are provided.

[0091] Electrolyte Comparative Example 1 The difference from electrolyte example 1 is that this electrolyte does not contain electrolyte additives.

[0092] Electrolyte Comparative Example 2 The difference from electrolyte example 4 is that the electrolyte additive is replaced with P127 (brand: SIGMA-ALDRICHSUK: P2443-250G).

[0093] Electrochemical performance testing (1) Preparation of test batteries: 12.0g of each electrolyte prepared in Examples 1-7 and the electrolytes of Comparative Examples 1-2 were injected into each unfilled pouch cell. After formation, test batteries with a designed capacity of 3Ah were obtained. The positive electrode active material layer of the battery was lithium iron phosphate: conductive agent: binder in a mass ratio of 97:1:2; the negative electrode active material layer of the battery was graphite: conductive agent: binder in a mass ratio of 96:2:2. Test batteries with electrolytes from Examples 1-7 were obtained and were designated as S1-S7; batteries with comparative electrolytes were designated as DS1-DS2.

[0094] (2) Cyclic performance test: The batteries S1-S7 and DS1-DS2 were connected to a charge / discharge apparatus for charge / discharge cycles. The test temperature was -20℃, the cycle rate was 1C, and the charging voltage was 3.0V~4.0V. The capacity retention rate after 500 cycles was calculated, and the results are summarized in Table 1. The formula for calculating the capacity retention rate is: Capacity retention rate after 500 cycles = (Discharge capacity after 500 cycles / Discharge capacity of the first cycle) × 100%.

[0095] Table 1

[0096] As can be seen from the parameters in Table 1, the electrolyte additive provided in this application embodiment can significantly improve the cycle performance of the battery. Furthermore, Table 1 shows that when the electrolyte additive content is 0.01% of the electrolyte mass, it can effectively improve the battery's cycle performance. Comparing the data between the embodiments reveals that when the amount of electrolyte additive is within the range recommended in this application embodiment (0.05 wt.%-1.5 wt.%), it is more conducive to the battery's performance.

[0097] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. An electrolyte additive, characterized in that, Electrolytes used in secondary batteries, wherein the electrolyte additives include those with a general structural formula as shown in Formula I. Formula I, Z is selected from , , , any one of them; R1 is selected from any one of fluorine, chlorine, bromine, iodine and substituted or unsubstituted alkyl groups.

2. The electrolyte additive according to claim 1, characterized in that, The number of carbon atoms in the substituted or unsubstituted alkyl group is ≤10.

3. The electrolyte additive according to claim 1 or 2, characterized in that, The substituted alkyl group includes haloalkyl groups.

4. The electrolyte additive according to claim 1, characterized in that, The electrolyte additive includes any compound as shown in formulas A-F:

5. A method for preparing an electrolyte additive, characterized in that, include: (1) Under conditions of ≤15℃, chlorosulfonic acid, raw material a and the first solvent are mixed and the first reaction is carried out to obtain the intermediate; The raw material a is ; Wherein, R1 is selected from any one of fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, and substituted or unsubstituted alkyl groups, and Z is selected from... , , , any one of them; (2) Under conditions of ≤25°C, the lithium salt is added to a second solvent containing the intermediate to carry out a second reaction; wherein the lithium salt includes lithium carbonate; (3) After evaporating the material obtained after the second reaction, a third solvent is added, and the mixture is allowed to stand, filtered, and dried in sequence to obtain the electrolyte additive as described in claim 1.

6. The preparation method according to claim 5, characterized in that, In step (1), the temperature of the first reaction is 15℃~35℃, and the duration of the first reaction is 2h~8h; In step (2), the temperature of the second reaction is 15℃~35℃, and the duration of the second reaction is 3h-24h; In step (3), the temperature for standing is -25℃ to 5℃, and the duration of standing is 6h to 36h.

7. The preparation method according to claim 5, characterized in that, In step (2), the lithium salt is added according to the molar ratio of Li to the raw material a of (2.0~2.2):

1.

8. The preparation method according to claim 5, characterized in that, The first solvent and the third solvent are each independently selected from at least one of dichloromethane, dichloroethane, trichloromethane, carbon tetrachloride, benzene, toluene, p-xylene, petroleum ether, and n-hexane; The second solvent includes at least one of acetonitrile, propionitrile, ethyl acetate, propyl acetate, acetone, dimethyl sulfoxide, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

9. An electrolyte, characterized in that, The electrolyte comprises an electrolyte, a non-aqueous solvent, and at least one electrolyte additive as described in any one of claims 1-4; the electrolyte additive accounts for 0.01% to 5% of the electrolyte by mass.

10. The electrolyte according to claim 9, characterized in that, The electrolyte also includes a second additive, wherein the second additive accounts for 0.5% to 5% of the mass of the electrolyte; The second additive includes at least one of fluoroethylene carbonate, vinylene carbonate, lithium monofluorophosphate, ethylene sulfate, and tris(trimethylsilane)borate.

11. A secondary battery, characterized in that, The secondary battery includes a positive electrode, a negative electrode, and an electrolyte as described in any one of claims 9-10, located between the positive electrode and the negative electrode.

12. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in claim 11.

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