Lithium ion battery electrolyte, lithium ion battery and electrical equipment

Abstract

The present application provides a lithium-ion battery electrolyte, a lithium-ion battery, and electrical equipment, belonging to the field of lithium-ion battery manufacturing technology. The lithium-ion battery electrolyte comprises an organic solvent, a lithium salt, and an additive, the structural formula of the additive being as shown in Formula I: wherein R1 is selected from any one of a substituted or unsubstituted alkyl group and a substituted or unsubstituted phenyl group, and R2 and R3 are independently selected from any one of a substituted or unsubstituted alkyl group and a substituted or unsubstituted silyl group. The electrolyte enables the corresponding battery to have a high initial efficiency when used at high voltage while also having relatively excellent high and low temperature performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion battery manufacturing, and in particular to a lithium-ion battery electrolyte, a lithium-ion battery, and electrical equipment. Background Art

[0002] In the existing technology, lithium-ion batteries are widely used in digital 3C, power tools, and electric vehicles due to their advantages such as high energy density and good cycle performance. As the energy density of lithium-ion batteries increases, the battery operating voltage gradually increases from 4.2V to above 4.5V (correspondingly, the battery's operating temperature also increases). When the existing electrolyte system is used under high voltage conditions, the strong oxidizing property of the battery's positive electrode causes the battery to produce more gas, which also causes the battery's cycle life to decay rapidly. In order to suppress the gas production when the battery is used under high voltage conditions, the current main method is to add additives such as 1,3-propylene sultone (PST) and maleic anhydride to the electrolyte. However, the use of these additives leads to problems such as increased interfacial impedance, decreased initial efficiency, and poor low-temperature performance. Summary of the Invention

[0003] The purpose of the present application is to provide a lithium-ion battery electrolyte, a lithium-ion battery and an electrical device, wherein the electrolyte enables the corresponding battery to have a higher initial efficiency when used at a high voltage and also has relatively excellent high and low temperature performance.

[0004] The embodiment of the present application is implemented as follows:

[0005] In a first aspect, an embodiment of the present application provides a lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt, and an additive, wherein the additive has a structural formula as shown in Formula I:

[0006]

[0007] Wherein, R1 is selected from any one of substituted or unsubstituted alkyl and substituted or unsubstituted phenyl, and R2 and R3 are independently selected from any one of substituted or unsubstituted alkyl and substituted or unsubstituted silyl.

[0008] In the above technical solution, the additive component with the above specific structure in the lithium-ion battery electrolyte, on the one hand, the additive can form a stable interface film on the surface of both the positive and negative electrodes, wherein the lithium ions contained in the additive itself will spontaneously participate in the interface film formation, which can reduce the loss of active lithium in the first charge, thereby improving the initial efficiency of the battery when used at high voltage; at the same time, the interface film formed contains a composite lithium phosphate salt with good lithium conductivity and thermal stability, which can passivate the positive and negative electrode interfaces, reduce the decomposition of the electrolyte at the positive and negative electrodes, and also inhibit the increase in the battery interface impedance, thereby improving the low-temperature performance of the battery when used at high voltage (such as low-temperature discharge retention rate). On the other hand, the phosphorus-nitrogen structure contained in the additive has a strong coordination ability, which can complex the metal ions dissolved from the positive electrode of the battery (such as Ni 2+ and Mn 2+ ) to reduce the risk of metal ion accumulation and damage to the battery's negative electrode, thereby improving the battery's high-temperature performance (such as high-temperature cycling performance) when used at high voltage. In this application, an additive having the above-mentioned specific structure is used as an additional component of the electrolyte. Through the combined effect of two aspects, the battery corresponding to this electrolyte has a high initial efficiency when used at high voltage and also has relatively excellent high and low temperature performance.

[0009] In some optional embodiments, R1 is selected from any one of substituted or unsubstituted C1-C3 alkyl and unsubstituted phenyl, and R2 and R3 are independently selected from any one of substituted or unsubstituted C1-C3 alkyl and substituted silyl.

[0010] In some optional embodiments, R1 is selected from any one of methyl, ethyl, propyl, trifluoromethyl and unsubstituted phenyl, and R2 and R3 are independently selected from any one of methyl, ethyl, propyl, trifluoromethyl and trimethyl-substituted silyl.

[0011] In the above technical solution, the structural selection of additives is limited to a specific range step by step, which helps to further improve the initial efficiency and high and low temperature performance of the battery corresponding to the electrolyte when used at high voltage.

[0012] In some optional embodiments, R1 is selected from unsubstituted phenyl, and R2 and R3 are independently selected from any one of methyl, ethyl, propyl, trifluoromethyl and trimethyl-substituted silyl.

[0013] In the above technical solution, R1 selects an unsubstituted phenyl group because within the limited preferred range of R1, the phenyl group has a relatively large steric hindrance, and this property helps the dissociation of lithium ions in the additive, which is more conducive to the participation of lithium ions in the formation of the positive and negative electrode interface film, and thus helps to improve the initial efficiency and low-temperature performance of the corresponding battery when used at high voltage.

[0014] In some optional embodiments, R1 is selected from unsubstituted phenyl, and R2 and R3 are each independently selected from trimethyl-substituted silyl.

[0015] In the above technical solution, R2 and R3 are independently selected as trimethyl-substituted silyl groups because the trimethyl-substituted silyl group itself can also participate in the formation of the interface film, which can assist lithium ions in forming the interface film, so as to further improve the initial efficiency and low-temperature performance of the corresponding battery when used at high voltage.

[0016] In some optional embodiments, the mass percentage of the additive in the electrolyte is 0.1-3%.

[0017] In the above technical solution, the amount of the additive is limited to a specific range, so that the battery corresponding to the electrolyte has a higher initial efficiency when used at high voltage and can also take into account relatively excellent high and low temperature performance.

[0018] In some optional embodiments, the electrolyte further includes an auxiliary additive, the auxiliary additive including at least one of vinyl sulfate, vinyl ethylene carbonate, 1,3-propane sultone, methylene disulfonate, 2-fluoropyridine, allyl isocyanate, triallyl isocyanurate, 2(5H)-furanone, tris(trimethylsilyl)phosphite and tripropylene phosphate.

[0019] Optionally, the mass percentage of the auxiliary additive in the electrolyte is 0.5-5%.

[0020] In the above technical solution, adding specific types of auxiliary additives to the electrolyte can give the electrolyte more functions, thereby more comprehensively improving the comprehensive electrical performance of the corresponding battery (such as safety performance and high and low temperature performance, etc.).

[0021] Furthermore, the composition of the auxiliary additive is limited to a specific range so that the auxiliary additive has an appropriate dosage, thereby better improving the comprehensive electrical performance of the corresponding battery.

[0022] In some optional embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bisfluorosulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisoxalatoborate.

[0023] Optionally, the mass percentage of lithium salt in the electrolyte is 10-20%.

[0024] Among the above technical solutions, the technical solutions provided in the embodiments of the present application are applicable to a wide variety of lithium salts and can provide a wide variety of feasible implementation plans, thereby facilitating the promotion and application of the technical solutions provided in the present application.

[0025] Furthermore, limiting the amount of lithium salt to the above range can ensure that the lithium salt has an appropriate amount, thereby better improving the comprehensive electrical performance of the corresponding battery.

[0026] In some optional embodiments, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, methyl trifluoroethyl carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0027] Among the above technical solutions, the technical solutions provided in the embodiments of the present application are applicable to a wide variety of organic solvents and can provide a wide variety of feasible implementation plans, thereby facilitating the promotion and application of the technical solutions provided in the present application.

[0028] In a second aspect, an embodiment of the present application provides a lithium-ion battery comprising a housing, an electrode assembly, and an electrolyte as provided in the embodiment of the first aspect. The electrode assembly is housed in the housing; and the electrolyte is housed in the housing.

[0029] In the above technical solution, the lithium-ion battery includes the electrolyte provided in the embodiment of the first aspect. By taking advantage of the unique advantages of the electrolyte, the battery has a higher initial efficiency when used at high voltage and can also take into account relatively excellent high and low temperature performance.

[0030] In some optional embodiments, in the electrode assembly, the positive electrode active material satisfies A and / or B of the following conditions:

[0031] A positive electrode active material includes LiNi x Co y Mn z O2, where x+y+z=1, 0<x<1, 0<y<1, 0<z<1.

[0032] B positive electrode active material includes LiNi 0.5 Mn 1.5 O4.

[0033] Among the above technical solutions, the technical solution provided in the embodiment of the present application can be applied to the above-mentioned multiple positive electrode active material systems, providing more feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application; in addition, the use of the above-mentioned type of positive electrode active material has the advantage of being more resistant to high pressure compared to the use of other types of positive electrode active materials.

[0034] In some optional embodiments, in the electrode assembly, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, silicon, silicon oxides, and silicon-carbon composites.

[0035] Among the above technical solutions, the technical solution provided in the embodiment of the present application can be applied to the above-mentioned multiple negative electrode active material systems, providing more feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application.

[0036] In a third aspect, an embodiment of the present application provides an electrical device, comprising a lithium-ion battery as provided in the embodiment of the second aspect. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0038] It should be noted that “and / or” in this application, such as “Feature 1 and / or Feature 2”, refers to three situations: “Feature 1” alone, “Feature 2” alone, or “Feature 1” plus “Feature 2”.

[0039] In addition, in the description of this application, unless otherwise specified, the meaning of "multiple" in "one or more" refers to two or more; the range of "value a to value b" includes the two end values ​​"a" and "b", and the "unit of measurement" in "value a to value b+unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0040] In the existing technology, high-voltage-resistant electrolyte additives usually use some organic substances, such as 1,3-propylene sultone and maleic anhydride. Although these additives can solve the problem of gas production when the battery is used at high voltage to a certain extent, they will bring about problems such as increased battery interface impedance, decreased initial efficiency and poor low-temperature performance.

[0041] The inventors have discovered that by using an organic lithium salt containing lithium ions and having a specific skeleton as an additive, with the help of the lithium ions and specific skeleton structure, the corresponding battery can have a higher initial efficiency when used at high voltage while also having relatively excellent high and low temperature performance.

[0042] The lithium-ion battery electrolyte, lithium-ion battery, and electrical equipment of the embodiments of the present application are described in detail below.

[0043] In a first aspect, an embodiment of the present application provides a lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt, and an additive, wherein the additive has a structural formula as shown in Formula I:

[0044]

[0045] Wherein, R1 is selected from any one of substituted or unsubstituted alkyl and substituted or unsubstituted phenyl, and R2 and R3 are independently selected from any one of substituted or unsubstituted alkyl and substituted or unsubstituted silyl.

[0046] In the present application, the additive component with the above-mentioned specific structure in the lithium-ion battery electrolyte, on the one hand, the additive can form a stable interface film on the surface of both the positive and negative electrodes, wherein the lithium ions contained in the additive itself will spontaneously participate in the interface film formation, which can reduce the loss of active lithium in the first charge, thereby improving the initial efficiency of the battery when used at high voltage; at the same time, the interface film formed contains a composite lithium phosphate salt with good lithium conductivity and thermal stability, which can passivate the positive and negative electrode interfaces, reduce the decomposition of the electrolyte at the positive and negative electrodes, and also inhibit the increase in the battery interface impedance, thereby improving the low-temperature performance of the battery when used at high voltage (such as low-temperature discharge retention rate). On the other hand, the phosphorus-nitrogen structure contained in the additive has a strong coordination ability, which can complex the metal ions dissolved from the positive electrode of the battery (such as Ni 2+ and Mn 2+ ) to reduce the risk of metal ion accumulation and damage to the battery's negative electrode, thereby improving the battery's high-temperature performance (such as high-temperature cycling performance) when used at high voltage. In this application, an additive having the above-mentioned specific structure is used as an additional component of the electrolyte. Through the combined effect of two aspects, the battery corresponding to this electrolyte has a high initial efficiency when used at high voltage and also has relatively excellent high and low temperature performance.

[0047] As an example, R1 is selected from any one of substituted or unsubstituted C1-C3 alkyl and unsubstituted phenyl, and R2 and R3 are independently selected from any one of substituted or unsubstituted C1-C3 alkyl and substituted silyl.

[0048] As an example, R1 is selected from any one of methyl, ethyl, propyl, trifluoromethyl and unsubstituted phenyl, and R2 and R3 are independently selected from any one of methyl, ethyl, propyl, trifluoromethyl and trimethyl-substituted silyl.

[0049] In this embodiment, the structural selection of the additive is limited within a specific range step by step, which helps to further improve the initial efficiency and high and low temperature performance of the battery corresponding to the electrolyte when used at high voltage.

[0050] As an example, R1 is selected from unsubstituted phenyl, and R2 and R3 are independently selected from any one of methyl, ethyl, propyl, trifluoromethyl and trimethyl-substituted silyl.

[0051] In this embodiment, R1 selects an unsubstituted phenyl group because within the limited preferred range of R1, the phenyl group has a relatively large steric hindrance, and this property helps the dissociation of lithium ions in the additive, which is more conducive to the participation of lithium ions in the formation of the positive and negative electrode interface film, and further helps to improve the initial efficiency and low-temperature performance of the corresponding battery when used at high voltage.

[0052] As an example, R1 is selected from unsubstituted phenyl, and R2 and R3 are each independently selected from trimethyl-substituted silyl.

[0053] In this embodiment, R2 and R3 are independently selected as trimethyl-substituted silyl groups because the trimethyl-substituted silyl group itself can also participate in the formation of the interface film, which can assist lithium ions in forming the interface film, so as to further improve the initial efficiency and low-temperature performance of the corresponding battery when used at high voltage.

[0054] In order to better understand the technical solution, the specific compound structures of some additives are used as examples below.

[0055]

[0056]

[0057]

[0058] It should be noted that the effectiveness of additives is closely related to their dosage. Specifically, if the dosage is too low, the performance of the corresponding battery will not be effectively improved; if the dosage is too high, the interface film will be too thick, which will also affect the performance of the corresponding battery. Based on this, considering the ultimate performance of the corresponding battery, the dosage of the additive can be limited.

[0059] As an example, the mass percentage of the additive in the electrolyte is 0.1-3%, such as but not limited to any one of 0.1%, 0.5%, 1%, 2% and 3% by mass, or a range between any two of them.

[0060] In this embodiment, the amount of the additive is limited to a specific range, so that the battery corresponding to the electrolyte has a higher initial efficiency when used at a high voltage and can also take into account relatively excellent high and low temperature performance.

[0061] As an example, the electrolyte further includes auxiliary additives, which include at least one of vinyl sulfate, vinyl ethylene carbonate, 1,3-propane sultone, methylene disulfonate, 2-fluoropyridine, allyl isocyanate, triallyl isocyanurate, 2(5H)-furanone, tris(trimethylsilyl)phosphite and tripropylene phosphate.

[0062] In this embodiment, adding specific types of auxiliary additives to the electrolyte can give the electrolyte more functions, thereby more comprehensively improving the comprehensive electrical performance of the corresponding battery (such as safety performance and high and low temperature performance, etc.).

[0063] As an example, the mass percentage of the auxiliary additive in the electrolyte is 0.5-5%, for example, but not limited to, any one of 0.5%, 1%, 2%, 3%, 4% and 5% by mass, or a range between any two of them.

[0064] In this embodiment, the composition of the auxiliary additive is further limited to a specific range so that the auxiliary additive has an appropriate dosage, thereby better improving the comprehensive electrical performance of the corresponding battery.

[0065] As an example, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bisfluorosulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisoxalatoborate.

[0066] In this embodiment, the technical solution provided in the embodiment of the present application is applicable to a wide variety of lithium salts and can provide a wide variety of feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the present application.

[0067] As an example, the mass percentage of lithium salt in the electrolyte is 10-20%, for example, but not limited to, any one of 10%, 12%, 14%, 16%, 18% and 20% by mass, or a range between any two of them.

[0068] In this embodiment, the amount of lithium salt is further limited to the above range, so that the lithium salt has an appropriate amount, thereby better improving the comprehensive electrical performance of the corresponding battery.

[0069] As an example, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, methyl trifluoroethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0070] In this embodiment, the technical solution provided in the embodiment of the present application is applicable to a wide variety of organic solvents and can provide a wide variety of feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the present application.

[0071] It should be noted that the components and amounts in the electrolyte that are not specifically described or limited can be set according to conventional selection in the art.

[0072] In a second aspect, an embodiment of the present application provides a lithium-ion battery comprising a housing, an electrode assembly, and an electrolyte as provided in the embodiment of the first aspect. The electrode assembly is housed in the housing; and the electrolyte is housed in the housing.

[0073] In the present application, the lithium-ion battery includes the electrolyte provided in the first embodiment. By taking advantage of the unique advantages of the electrolyte, the battery has a higher initial efficiency when used at high voltage and can also take into account relatively excellent high and low temperature performance.

[0074] As an example, in the electrode assembly, the positive electrode active material satisfies A and / or B of the following conditions:

[0075] A positive electrode active material includes LiNi x Co y Mn z O2, where x+y+z=1, 0<x<1, 0<y<1, 0<z<1.

[0076] B positive electrode active material includes LiNi 0.5 Mn 1.5 O4.

[0077] In this embodiment, the technical solution provided in the embodiment of the present application can be applied to the above-mentioned multiple positive electrode active material systems, providing more feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application; in addition, the use of the above-mentioned type of positive electrode active material has the advantage of being more resistant to high pressure compared to the use of other types of positive electrode active materials.

[0078] As an example, in the electrode assembly, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, silicon, silicon oxides, and silicon-carbon composites.

[0079] In this embodiment, the technical solution provided in the embodiment of the present application can be applied to the above-mentioned multiple negative electrode active material systems, providing more feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application.

[0080] It should be noted that any structure not specifically described in the battery may be configured according to conventional options in the art.

[0081] In a third aspect, an embodiment of the present application provides an electrical device, comprising a lithium-ion battery as provided in the embodiment of the second aspect.

[0082] It should be noted that there is no limitation on the types of electrical equipment, such as mobile phones, portable devices, laptops, electric vehicles, electric cars, ships, electric aircraft, spacecraft, electric toys, energy storage devices and power tools.

[0083] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0084] Example 1

[0085] The present invention provides a method for preparing an electrolyte, comprising the following steps:

[0086] Ethylene carbonate (EC), diethyl carbonate (DEC) and methyl trifluoroethyl carbonate (FEMC) are mixed in a mass ratio of 3:4:3 to obtain a mixed organic solvent; then, lithium hexafluorophosphate (LiPF6) and compound 1 are added to the mixed organic solvent and mixed evenly to obtain a lithium-ion battery electrolyte; wherein, in terms of mass percentage, the mixed organic solvent: lithium hexafluorophosphate: compound 1 = 89.9:10:0.1.

[0087] The preparation methods of the subsequent embodiments and comparative examples can all refer to Example 1. In order to better understand the differences between the various embodiments and comparative examples, they are summarized in the form of a table below.

[0088] Table 1 Summary of electrolyte formulations for various embodiments and comparative examples

[0089]

[0090]

[0091] Here, “—” indicates that the component is not contained, and the amount of the organic solvent is equal to 100 minus the remainder of the sum of the amounts of the other components.

[0092] Specifically, the preparation method of compound 1 is as follows:

[0093] 1. Dissolve dimethyl chlorophosphate in n-butanol solvent (the volume ratio of the two is 1:2), then add methanol solution containing KOH dropwise and react at room temperature (25°C) for 5 hours (the molar ratio of dimethyl chlorophosphate and KOH is 1:1). After the reaction is completed, add water to separate the layers, remove the upper organic layer (containing unreacted dimethyl chlorophosphate), add dilute hydrochloric acid to the remaining aqueous layer to adjust the pH to 7, and precipitate monomethyl chlorophosphate with a yield of 81.3%.

[0094] 2. Using dichloromethane as a solvent, the above-mentioned monomethyl chlorophosphate and hexamethyldisiloxane (the molar ratio of monomethyl chlorophosphate to hexamethyldisiloxane is 2:1) were added, the reaction temperature was controlled to 10°C and the reaction was carried out for 5 hours to prepare intermediate product A and trimethylchlorosilane. The yield of intermediate product A was 72.5%.

[0095] The structural formula of intermediate product A is as follows:

[0096]

[0097] 3. Using tetrahydrofuran (THF) as a solvent, intermediate product A was added to react with n-butyl lithium to prepare compound 1 (the molar ratio of intermediate product A to n-butyl lithium was 1:1, and the concentration of both in THF was 1 mol / L). The yield of compound 1 was 91.2%.

[0098] Specifically, the preparation method of compound 2 is as follows:

[0099] 1. Dissolve di(trifluoromethyl)chlorophosphate in n-butanol solvent (the volume ratio of the two is 1:2), then add methanol solution containing KOH dropwise and react at room temperature (25°C) for 5h (the molar ratio of di(trifluoromethyl)chlorophosphate and KOH is 1:1). After the reaction is complete, add water to separate the layers, remove the upper organic layer (containing unreacted di(trifluoromethyl)chlorophosphate), and add dilute hydrochloric acid to the remaining aqueous layer to adjust the pH to 7, thereby precipitating mono(trifluoromethyl)chlorophosphate with a yield of 81.2%.

[0100] 2. Using dichloromethane as a solvent, the above-mentioned trifluoromethyl chlorophosphate and hexamethyldisiloxane (the molar ratio of trifluoromethyl chlorophosphate to hexamethyldisiloxane is 2:1) were added, the reaction temperature was controlled to 10°C and the reaction was carried out for 5 hours to prepare intermediate product B and trimethylchlorosilane. The yield of intermediate product B was 68.3%.

[0101] The structural formula of intermediate product B is as follows:

[0102]

[0103] 3. Using tetrahydrofuran (THF) as a solvent, the intermediate product B was added to react with n-butyl lithium to prepare compound 2 (the molar ratio of intermediate product B to n-butyl lithium was 1:1, and the concentration of both in THF was 1 mol / L). The yield of compound 2 was 90.6%.

[0104] Specifically, the preparation method of compound 3 is as follows:

[0105] 1. Dissolve diethyl chlorophosphate in n-butanol solvent (the volume ratio of the two is 1:2), then add methanol solution containing KOH dropwise and react at room temperature (25°C) for 5 hours (the molar ratio of diethyl chlorophosphate and KOH is 1:1). After the reaction is complete, add water to separate the layers, remove the upper organic layer (containing unreacted diethyl chlorophosphate), add dilute hydrochloric acid to the remaining aqueous layer to adjust the pH to 7, and precipitate monoethyl chlorophosphate with a yield of 81.6%.

[0106] 2. Using dichloromethane as a solvent, monoethyl chlorophosphate and hexamethyldisiloxane-trifluoromethylamine (the molar ratio of monoethyl chlorophosphate to hexamethyldisiloxane-trifluoromethylamine is 2:1) were added, the reaction temperature was controlled at 20°C and the reaction was carried out for 5 hours to prepare intermediate product C and trimethylchlorosilane. The yield of intermediate product C was 66.5%.

[0107] The structural formula of intermediate product C is as follows:

[0108]

[0109] 3. Using tetrahydrofuran (THF) as a solvent, intermediate product C was added and reacted with n-butyl lithium to prepare compound 3 (the molar ratio of intermediate product C to n-butyl lithium was 1:1, and the concentrations of both in THF were 1 mol / L). The yield of compound 3 was 89.4%.

[0110] Specifically, the preparation method of compound 4 is as follows:

[0111] 1. Dissolve dimethyl chlorophosphate in n-butanol solvent (the volume ratio of the two is 1:2), then add KOH methanol solution dropwise and react at room temperature (25°C) for 5 hours (the molar ratio of dimethyl chlorophosphate and KOH is 1:1). After the reaction is completed, add water to separate the layers, remove the upper organic layer (containing unreacted dimethyl chlorophosphate), add dilute hydrochloric acid to the remaining aqueous layer to adjust the pH to 7, and precipitate monomethyl chlorophosphate with a yield of 81.5%.

[0112] 2. Using dichloromethane as a solvent, monomethyl chlorophosphate and hexamethyldisiloxane (the molar ratio of monomethyl chlorophosphate to hexamethyldisiloxane is 2:1) were added, the reaction temperature was controlled at 10°C and the reaction was carried out for 5 hours to prepare intermediate product A and trimethylchlorosilane. The yield of intermediate product A was 72.5%.

[0113] 3. Using tetrahydrofuran (THF) as a solvent and sodium methoxide as a catalyst, the intermediate product A and trimethylsilanol (the molar ratio of the intermediate product A to trimethylsilanol is 1:2) are added to carry out an ester exchange reaction to prepare an intermediate product D and methanol.

[0114] The structural formula of intermediate product D is as follows:

[0115]

[0116] 4. Using tetrahydrofuran (THF) as a solvent, the intermediate product D was reacted with n-butyl lithium to prepare compound 4 (the molar ratio of the intermediate product D to n-butyl lithium was 1:1, and the concentrations of both in THF were 1 mol / L). The yield of compound 4 was 80.7%.

[0117] Specifically, the preparation method of compound 5 is as follows:

[0118] 1. Dissolve dimethyl chlorophosphate in n-butanol solvent (the volume ratio of the two is 1:2), then add KOH methanol solution dropwise and react at room temperature (25°C) for 5 hours (the molar ratio of dimethyl chlorophosphate and KOH is 1:1). After the reaction is complete, add water to separate the layers, remove the upper organic layer (containing unreacted dimethyl chlorophosphate), add dilute hydrochloric acid to the remaining aqueous layer to adjust the pH to 7, and precipitate monomethyl chlorophosphate with a yield of 81.1%.

[0119] 2. Using dichloromethane as a solvent, monomethyl chlorophosphate, monopropyl chlorophosphate and hexamethyldisiloxane-trifluoromethylamine (the molar ratio of monomethyl chlorophosphate, monopropyl chlorophosphate and hexamethyldisiloxane-trifluoromethylamine is 1:1:1, respectively) were added, the reaction temperature was controlled at 20°C and the reaction was carried out for 5 hours to prepare intermediate product E and trimethylchlorosilane. The yield of intermediate product E was 74.3%.

[0120] The structural formula of intermediate product E is as follows:

[0121]

[0122] 3. Using tetrahydrofuran (THF) as a solvent, intermediate product E was added to react with n-butyl lithium to prepare compound 5 (the molar ratio of intermediate product E to n-butyl lithium was 1:1, and the concentration in THF was 1 mol / L). The yield of compound 5 was 88.2%.

[0123] Specifically, the preparation method of compound 6 is as follows:

[0124] 1. Dissolve dimethyl chlorophosphate in n-butanol solvent, then add methanol solution of KOH dropwise and react at room temperature (25°C) for 5 hours (the molar ratio of dimethyl chlorophosphate to KOH is 1:1). After the reaction is complete, add water to separate the layers, remove the upper organic layer (containing unreacted dimethyl chlorophosphate), add dilute hydrochloric acid to the remaining aqueous layer to adjust the pH to 7, and precipitate monomethyl chlorophosphate with a yield of 81.3%.

[0125] 2. Using dichloromethane as a solvent, add monomethyl chlorophosphate and hexamethyldisiloxane-phenylamine (the molar ratio of the two is 2:1), control the reaction temperature to 20°C and react for 5 hours to prepare intermediate product F and trimethylchlorosilane.

[0126] The structural formula of intermediate product F is as follows:

[0127]

[0128] 3. Using tetrahydrofuran (THF) as solvent, the intermediate product F was added and reacted with n-butyl lithium to prepare compound 6 (the molar ratio of the intermediate product F to n-butyl lithium was 1:1, and the concentration in THF was 1 mol / L), with a yield of 85.7%.

[0129] Specifically, the preparation method of compound 7 is as follows:

[0130] 1. Dissolve dimethyl chlorophosphate in n-butanol solvent (the volume ratio of the two is 1:2), then add KOH methanol solution dropwise and react at room temperature (25°C) for 5 hours (the molar ratio of dimethyl chlorophosphate and KOH is 1:1). After the reaction is complete, add water to separate the layers, remove the upper organic layer (containing unreacted dimethyl chlorophosphate), add dilute hydrochloric acid to the remaining aqueous layer to adjust the pH to 7, and precipitate monomethyl chlorophosphate with a yield of 81.4%.

[0131] 2. Using dichloromethane as a solvent, add monomethyl chlorophosphate and hexamethyldisiloxane (the molar ratio of the two is 2:1), control the reaction temperature to 10°C and react for 5 hours to prepare intermediate product F and trimethylchlorosilane with a yield of 72.5%.

[0132] 3. Using tetrahydrofuran (THF) as a solvent and sodium methoxide as a catalyst, the intermediate product F and trimethylsilanol were added to carry out an ester exchange reaction (the molar ratio of the intermediate product F to the trimethylsilanol was 1:2) to prepare the intermediate product G and methanol with a yield of 62.1%.

[0133] The structural formula of intermediate product G is as follows:

[0134]

[0135] 4. Using tetrahydrofuran (THF) as a solvent, the intermediate product G was added and reacted with n-butyl lithium to prepare compound 7 (the molar ratio of the intermediate product G to n-butyl lithium was 1:1, and the concentration in THF was 1 mol / L). The yield of compound 7 was 78.3%.

[0136] Test Example 1

[0137] Electrical performance test

[0138] Test method:

[0139] The lithium-ion battery electrolytes prepared in Examples 1 to 19 and Comparative Example 1 were assembled into batteries and numbered accordingly. Then, the batteries were tested for their initial efficiency at 25°C, capacity retention after 100 cycles at 25°C, capacity retention after 100 cycles at 45°C, and discharge retention at -20°C.

[0140] The battery is assembled as follows:

[0141] S1 is mixed with LiNi in a mass ratio of 96:2:2 0.5 Mn 1.5O4 (positive electrode active material), conductive carbon black (conductive agent) and polyvinylidene fluoride (binder) are dispersed in N-methyl-2-pyrrolidone to obtain positive electrode slurry; then, the positive electrode slurry is evenly coated on both sides of the aluminum foil; then, after drying, calendering and vacuum drying in sequence, an aluminum lead wire is welded with an ultrasonic welder to obtain a positive electrode sheet with a thickness of 125μm.

[0142] S2 is mixed with graphite (negative electrode active material), conductive carbon black (conductive agent), styrene-butadiene rubber and carboxymethyl cellulose (binder) in a mass ratio of 95:1.5:1.5:2, and dispersed in deionized water to obtain a negative electrode slurry; then, the negative electrode slurry is coated on both sides of the copper foil; then, after drying, calendering and vacuum drying in sequence, a nickel lead wire is welded with an ultrasonic welder to obtain a negative electrode sheet with a thickness of 125μm.

[0143] S3: The prepared positive electrode sheet, negative electrode sheet and ion separator (PP / PE / PP three-layer composite separator) are wound to prepare a bare battery cell. Then, the bare battery cell and the shell, as well as the high-voltage electrolyte group prepared in Examples 1 to 19 and Comparative Example 1, are injected into the dried battery. After packaging, standing, formation, shaping and capacity testing, the battery is assembled.

[0144] The test of the battery's electrical parameters and the corresponding calculation formulas are as follows:

[0145] (1) First efficiency test of battery:

[0146] Place the battery that has not been charged and activated after filling with liquid at 25℃, charge and discharge the battery once with a current of 0.1C in the charge and discharge voltage range of 3.5~4.85V, and record its charge and discharge capacity.

[0147] (2) Battery capacity retention test after 100 cycles at 25°C:

[0148] The battery was placed at 25°C and cycled at a current of 0.5C in the charge and discharge voltage range of 3.5 to 4.85V, and the discharge retention capacity at the 100th cycle was recorded.

[0149] (3) Battery capacity retention test after 100 cycles at 45°C:

[0150] The battery was placed at 45°C and cycled at a current of 0.5C in the charge and discharge voltage range of 3.5 to 4.85V, and the discharge retention capacity at the 100th cycle was recorded.

[0151] (4) Battery low temperature discharge test at -20℃:

[0152] The battery was charged and discharged three times at room temperature (25°C) with a current of 0.33C in the charge and discharge voltage range of 3.5 to 4.85V. The last discharge capacity was taken as the initial capacity at room temperature. The battery was then fully charged with 0.33C. The battery was then placed at low temperature (-20°C) for 4 hours and then discharged at a constant current of 0.33C to 3.0V to obtain the low-temperature discharge capacity.

[0153] The calculation formula is as follows:

[0154] First efficiency (%) = (first discharge capacity / first charge capacity) × 100%.

[0155] 100-cycle capacity retention rate (%) = (100th discharge retention capacity / 1st cycle discharge capacity) × 100%.

[0156] Low-temperature discharge capacity retention rate (%) = low-temperature initial discharge capacity / room-temperature initial discharge capacity × 100%.

[0157] Table 2 Battery performance test results

[0158]

[0159]

[0160] Referring to Table 2, it can be seen from the performance test results of Examples 1 to 19 and Comparative Example 1 that the additives provided in the embodiments of the present application (specifically, one or more) have better initial efficiency and high and low temperature performance than the conventional electrolyte additives used in Comparative Example 1.

[0161] From the performance test results of Examples 2 and 4 to 9, it can be seen that when R1 is selected as an unsubstituted phenyl group and / or when R2 and R3 are both trimethyl-substituted silyl groups, the corresponding lithium-ion batteries have better initial efficiency and high and low temperature performance.

[0162] It can be seen from the performance test results of Examples 12 to 15 that limiting the amount of electrolyte additives to the range of 0.1 to 3% provided in the embodiments of this application, compared to not being within the set range, the lithium-ion battery corresponding to the former has better initial efficiency and high and low temperature performance.

[0163] It can be seen from the performance test results of Examples 2 and 16 to 17 that, on the basis of the electrolyte containing the additives provided in the examples of the present application, further adding the auxiliary additives (FEC or DMMA) provided in the examples of the present application can further improve the initial efficiency and high and low temperature performance of the corresponding battery.

[0164] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A lithium ion battery electrolyte, characterized in that It includes an organic solvent, a lithium salt and an additive, wherein the structural formula of the additive is as shown in Formula I: wherein R1 is selected from any one of substituted or unsubstituted alkyl and substituted or unsubstituted phenyl, and R2 and R3 are independently selected from any one of substituted or unsubstituted alkyl and substituted or unsubstituted silyl; The mass percentage of the additive in the electrolyte is 0.1-3%.

2. The electrolyte according to claim 1, characterized in that The R1 is selected from any one of a substituted or unsubstituted C1-C3 alkyl group and an unsubstituted phenyl group, and R2 and R3 are independently selected from any one of a substituted or unsubstituted C1-C3 alkyl group and a substituted silyl group.

3. The electrolyte according to claim 2, characterized in that The R1 is selected from any one of methyl, ethyl, propyl, trifluoromethyl and unsubstituted phenyl, and the R2 and R3 are independently selected from any one of methyl, ethyl, propyl, trifluoromethyl and trimethyl-substituted silyl.

4. The electrolyte according to claim 3, characterized in that The R1 is selected from an unsubstituted phenyl group, and the R2 and R3 are independently selected from any one of a methyl group, an ethyl group, a propyl group, a trifluoromethyl group, and a trimethyl-substituted silyl group.

5. The electrolyte according to claim 4, characterized in that The R1 is selected from an unsubstituted phenyl group, and the R2 and R3 are independently selected from a trimethyl-substituted silyl group.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The electrolyte further includes an auxiliary additive, which includes at least one of vinyl sulfate, vinyl ethylene carbonate, 1,3-propane sultone, methylene disulfonate, 2-fluoropyridine, allyl isocyanate, triallyl isocyanurate, 2(5H)-furanone, tris(trimethylsilyl)phosphite and tripropylene phosphate.

7. The electrolyte according to claim 6, characterized in that The mass percentage of the auxiliary additive in the electrolyte is 0.5-5%.

8. The electrolyte according to any one of claims 1 to 5, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalatophosphate), lithium tetrafluorooxalatophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(oxalatoborate).

9. The electrolyte according to claim 8, characterized in that The mass percentage of the lithium salt in the electrolyte is 10-20%.

10. The electrolyte according to any one of claims 1 to 5, characterized in that The organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, methyl trifluoroethyl carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

11. A lithium-ion battery, characterized in that: include: case; an electrode assembly, the electrode assembly being accommodated in the housing; as well as The electrolyte according to any one of claims 1 to 10, wherein the electrolyte is contained in the housing.

12. The lithium-ion battery according to claim 11, wherein In the electrode assembly, the positive electrode active material satisfies A and / or B of the following conditions: A positive electrode active material includes LiNi x Co y Mn z O2, where, x+y+z=1, 0<x<1, 0<y<1, 0<z<1; B The positive electrode active material includes LiNi 0.5 Mn 1.5 O4.

13. The lithium-ion battery according to claim 11, characterized in that In the electrode assembly, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, silicon, silicon oxides, and silicon-carbon composites.

14. An electrical device, characterized in that: The electrical device includes the lithium-ion battery according to any one of claims 11 to 13.

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