Electrolyte, secondary battery and electrical equipment

Abstract

The present invention belongs to the technical field of secondary battery electrolytes, and specifically relates to an electrolyte, a secondary battery and an electrical device. The electrolyte provided by the present invention includes a lithium salt, a solvent and an additive, wherein the additive includes a compound having a structure shown in formula (I), wherein the molecular structure contains a cyclic sulfonate functional group, which can help the electrolyte form a stable interface film on the positive and negative electrode surfaces, and also contains an isocyanate group. The S=O in the sulfonate structure can increase the degree of delocalization of the nitrogen nucleus in the isocyanate structure, and as a weak base point, inhibit the reaction of PF5, thereby inhibiting the formation of HF and LiF, and in the film-forming reaction process, after the two types of functional groups gain or lose electrons, each molecular fragment will produce a strong mutual cross-linking effect, so the above two functional groups work together, through cross-linking coupling, to further stabilize the interface film, improve the film-forming effect of the electrolyte, thereby reducing the high-temperature storage gas production of the battery and improving the high-temperature cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary battery electrolytes, and in particular relates to an electrolyte, a secondary battery and an electrical device. Background Art

[0002] Driven by environmental pressure and carbon emissions, research into alternative energy sources is in full swing. Secondary batteries, with their high specific energy, long cycle life, low self-discharge, and excellent safety, are attracting significant attention in both the energy storage and power sectors. As market demands become increasingly stringent and diverse, secondary batteries must meet diverse application scenarios while maintaining excellent performance. This places higher demands on secondary battery technology R&D capabilities, requiring them to simultaneously possess the following properties: high power performance, long cycle life, and long storage life.

[0003] In order to obtain higher energy density and reduce cost, the content of Ni in ternary cathode materials has been continuously increased, and the oxidation of the material in the delithiation state has been significantly enhanced. 3+ / Ni 4+ The side reactions such as accelerated decomposition of the electrolyte lead to increased positive electrode interface impedance and capacity loss. Therefore, it is crucial to form a uniform and dense positive electrode interface film (CEI) at the positive electrode to inhibit the interface side reactions between the high-nickel positive electrode material and the electrolyte, which is crucial to improving the performance of high-nickel materials. On the other hand, the solid electrolyte interface film (SEI) generated by the initial formation of the graphite negative electrode also plays an important role in battery performance. If the impedance of the formed SEI film is too large, the initial polarization of the battery will be aggravated. At this time, it is easy to cause the precipitation of metallic lithium on the surface of the negative electrode, which consumes the active lithium in the battery and greatly reduces the reversible capacity of the battery.

[0004] Therefore, there is an urgent need to develop a new type of electrolyte additive and an electrolyte containing the additive, which can simultaneously form a low-impedance and stable passivation film at the interface between the positive and negative electrodes. On the one hand, it protects the positive electrode and inhibits the capacity loss and storage flatulence problems caused by excessive reaction between the positive electrode and the electrolyte. On the other hand, it also protects the negative electrode and forms a low-impedance SEI film, so that lithium ions can pass through quickly, reduce polarization, and improve the lithium precipitation window. Summary of the Invention

[0005] In view of this, the primary purpose of the present invention is to provide an electrolyte that can simultaneously form a low-impedance and stable passivation film at both the positive and negative electrode interfaces, thereby reducing the high-temperature storage gas production of the battery and improving the high-temperature cycle performance.

[0006] Another object of the present invention is to provide a secondary battery and an electric device including the secondary battery.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a compound having a structure represented by formula (I):

[0009]

[0010] Wherein, R1, R2, and R3 are independently selected from H, halogen, amino, carboxyl, C1-C 20 Any of a hydrocarbon group, a halogenated hydrocarbon group, and a heterocyclic group.

[0011] In some embodiments of the present invention, the additive includes a compound represented by formula (IA) and / or formula (IB):

[0012]

[0013] In some embodiments of the present invention, the amount of the additive added is 0.1 to 5.0% of the total mass of the electrolyte. Too little additive may form a passivation film on the surface of the positive and negative electrodes that is too thin and easy to break, and cannot play the role of blocking the positive and negative electrodes and the electrolyte. Too much additive may form a passivation film on the surface of the positive and negative electrodes that is too thick, increasing the impedance of the battery. The inventors have found that when the amount of additive added is 0.5 to 1.5% of the total mass of the lithium-ion battery electrolyte, a stable passivation film can be formed on the surface of the positive and negative electrodes without increasing the battery impedance, achieving a better effect.

[0014] In some embodiments of the present invention, the lithium salt content is 10-15% of the total mass of the electrolyte. A lithium salt concentration that is too low can affect the electrolyte's conductivity, while a high concentration can increase the electrolyte's viscosity. The inventors have found that a lithium salt content of 12-13% of the total mass of the lithium-ion battery electrolyte achieves optimal results.

[0015] Optionally, the lithium salt is one or more of lithium hexafluorophosphate (abbreviated as LiPF6), lithium tetrafluoroborate (abbreviated as LiBF4), lithium bis(oxalatoborate) (abbreviated as LiBOB), lithium difluorooxalatoborate (abbreviated as LiDFOB), lithium difluorobis(oxalatophosphate) (abbreviated as LiDFOP), lithium bis(fluorosulfonyl)imide (abbreviated as LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (abbreviated as LiTFSI). Considering the comprehensive performance and cost, the preferred lithium salt of the present invention is lithium hexafluorophosphate.

[0016] Optionally, the organic solvent is at least one of ethylene carbonate (abbreviated as EC), propylene carbonate (abbreviated as PC), butylene carbonate (abbreviated as BC), fluoroethylene carbonate (abbreviated as FEC), dimethyl carbonate (abbreviated as DMC), ethyl methyl carbonate (abbreviated as EMC), diethyl carbonate (abbreviated as DEC), methylpropyl carbonate (abbreviated as MPC), diphenyl carbonate (abbreviated as DPhC), ethyl acetate (abbreviated as EA), propyl acetate (abbreviated as PA), methyl propionate (abbreviated as MP), ethyl propionate (abbreviated as EP), propyl propionate (abbreviated as PP), methyl butyrate (abbreviated as MB), ethyl butyrate (abbreviated as EB), γ-butyrolactone (abbreviated as γ-GBL), and sulfolane (abbreviated as TMS).

[0017] In some embodiments of the present invention, the organic solvent includes ethylene carbonate (abbreviated as EC) and ethyl methyl carbonate (abbreviated as EMC), and the mass ratio of ethylene carbonate to ethyl methyl carbonate is (2-4): (6-8).

[0018] In a second aspect, the present invention provides a method for preparing the additive, comprising the following steps:

[0019] Under acidic conditions, compound (a) reacts with a sulfonating agent to obtain compound (b);

[0020] Under heating conditions, compound (b) undergoes dehydration and cyclization to obtain compound (c);

[0021] Under low temperature conditions, compound (c) reacts with phosgene for 1 to 1.5 hours, and then the temperature is raised to 70 to 80° C. to continue the reaction to obtain a compound with the structure represented by formula (I);

[0022] The reaction route is as follows:

[0023]

[0024] In some embodiments of the present invention, the molar ratio of the sulfonating agent to the compound (a) is (1.1-1.2):1, and the sulfonating agent is NaHSO3.

[0025] In some embodiments of the present invention, the dehydration cyclization reaction conditions are 120-160° C. and 260-530 Pa.

[0026] In some embodiments of the present invention, the low temperature condition refers to 0°C to 5°C.

[0027] The additive provided by the present invention contains a cyclic sulfonate functional group in its molecular structure, which can help the electrolyte form a stable interfacial film on the positive and negative electrode surfaces. At the same time, the molecular structure of the cyclic sulfonate compound also contains an isocyanate group. The S=O in the sulfonate structure can increase the degree of delocalization of the nitrogen nucleus in the isocyanate structure, acting as a weak base point to inhibit the reaction of PF5, thereby inhibiting the formation of HF and LiF. In addition, during the film-forming reaction, after the two types of functional groups gain or lose electrons, each molecular fragment will produce a strong mutual cross-linking effect. Therefore, the above two functional groups work together to further stabilize the interfacial film through cross-linking coupling, improve the film-forming effect of the electrolyte, and thus reduce the high-temperature storage gas production of the battery and improve the high-temperature cycle performance.

[0028] In a third aspect, the present invention provides a method for preparing the above-mentioned electrolyte, comprising the following steps:

[0029] Under the protection of an inert atmosphere, the lithium salt and the organic solvent are mixed to obtain a mixed liquid, and the additive is mixed with the mixed liquid.

[0030] In some embodiments of the present invention, during the mixing process of the lithium salt and the organic solvent, the temperature of the mixed solution is controlled to not exceed 2°C. Since the addition of lithium salt will cause the electrolyte temperature to rise, resulting in a certain degree of thermal decomposition of the lithium salt, the electrolyte temperature should be controlled during the addition of lithium salt. When the electrolyte temperature rises by more than 2°C, the addition of lithium salt is stopped. When the electrolyte temperature is below 2°C, the addition of lithium salt can continue. The above-mentioned electrolyte temperature can be controlled using temperature control methods commonly used in the art, such as ice bath, dry ice circulation cooling, liquid nitrogen cooling, etc.

[0031] In some embodiments of the present invention, the water content of the organic solvent is no more than 20 ppm. Since lithium salts are easily hydrolyzed in water, the water content of the organic solvent needs to be strictly controlled. For example, the organic solvent can be dehydrated by molecular sieve adsorption, and the dried organic solvent is then mixed with the lithium salt.

[0032] In a fourth aspect, the present invention further provides a secondary battery comprising a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte. The secondary battery comprising the electrolyte provided by the present invention has good high-temperature performance.

[0033] In some embodiments of the present invention, the positive electrode comprises a ternary positive electrode material, and the general structural formula of the ternary positive electrode material comprises Li a Ni x Co y Mn z A bO2, wherein 0.9≤a≤1.1, 0.8≤x<1, x+y+z=1, 0≤b≤0.1, and A comprises at least one of Al, Mg, Ti, Zr, Zn, W, Nb, Mo, B or F.

[0034] In a fifth aspect, the present invention further provides an electrical device comprising the above-mentioned secondary battery.

[0035] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0036] 1. The electrolyte provided by the present invention uses a cyclic sulfonate compound as an additive. Since the molecular structure of the additive contains a cyclic sulfonate functional group, it can help the electrolyte form a stable interface film on the surface of the positive and negative electrodes. At the same time, the molecular structure of the additive also contains an isocyanate group. The S=O in the sulfonate structure can increase the degree of delocalization of the nitrogen nucleus in the isocyanate structure, acting as a weak base point to inhibit the reaction of PF5, thereby inhibiting the formation of HF and LiF. In addition, during the film-forming reaction, after these two types of functional groups gain or lose electrons, each molecular fragment will produce a strong mutual cross-linking effect. Therefore, the above two functional groups work together to further stabilize the interface film through cross-linking coupling, improve the film-forming effect of the electrolyte, and thus reduce the high-temperature storage gas production of the battery and improve the high-temperature cycle performance.

[0037] 2. The lithium-ion battery provided in the embodiment of the present invention comprises the above-mentioned electrolyte provided in the embodiment of the present invention, and thus has good high-temperature cycle performance. DETAILED DESCRIPTION

[0038] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0039] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0040] In a first aspect, the present invention provides an electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises a compound having a structure represented by formula (I):

[0041]

[0042] Wherein, R1, R2, and R3 are independently selected from H, halogen, amino, carboxyl, C1-C 20Any of a hydrocarbon group, a halogenated hydrocarbon group, and a heterocyclic group.

[0043] In some embodiments of the present invention, the additive includes a compound represented by formula (IA) and / or formula (IB):

[0044]

[0045] In some embodiments of the present invention, the amount of the additive added is 0.1 to 5.0% of the total mass of the electrolyte. Too little additive may form a passivation film on the surface of the positive and negative electrodes that is too thin and easy to break, and cannot play the role of blocking the positive and negative electrodes and the electrolyte. Too much additive may form a passivation film on the surface of the positive and negative electrodes that is too thick, increasing the impedance of the battery. The inventors have found that when the amount of additive added is 0.5 to 1.5% of the total mass of the lithium-ion battery electrolyte, a stable passivation film can be formed on the surface of the positive and negative electrodes without increasing the battery impedance, achieving a better effect.

[0046] In some embodiments of the present invention, the lithium salt content is 10-15% of the total mass of the electrolyte. A lithium salt concentration that is too low can affect the electrolyte's conductivity, while a high concentration can increase the electrolyte's viscosity. The inventors have found that a lithium salt content of 12-13% of the total mass of the lithium-ion battery electrolyte achieves optimal results.

[0047] Optionally, the lithium salt is one or more of lithium hexafluorophosphate (abbreviated as LiPF6), lithium tetrafluoroborate (abbreviated as LiBF4), lithium bis(oxalatoborate) (abbreviated as LiBOB), lithium difluorooxalatoborate (abbreviated as LiDFOB), lithium difluorobis(oxalatophosphate) (abbreviated as LiDFOP), lithium bis(fluorosulfonyl)imide (abbreviated as LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (abbreviated as LiTFSI). Considering the comprehensive performance and cost, the preferred lithium salt of the present invention is lithium hexafluorophosphate.

[0048] Optionally, the organic solvent is at least one of ethylene carbonate (abbreviated as EC), propylene carbonate (abbreviated as PC), butylene carbonate (abbreviated as BC), fluoroethylene carbonate (abbreviated as FEC), dimethyl carbonate (abbreviated as DMC), ethyl methyl carbonate (abbreviated as EMC), diethyl carbonate (abbreviated as DEC), methylpropyl carbonate (abbreviated as MPC), diphenyl carbonate (abbreviated as DPhC), ethyl acetate (abbreviated as EA), propyl acetate (abbreviated as PA), methyl propionate (abbreviated as MP), ethyl propionate (abbreviated as EP), propyl propionate (abbreviated as PP), methyl butyrate (abbreviated as MB), ethyl butyrate (abbreviated as EB), γ-butyrolactone (abbreviated as γ-GBL), and sulfolane (abbreviated as TMS).

[0049] In some embodiments of the present invention, the organic solvent includes ethylene carbonate (abbreviated as EC) and ethyl methyl carbonate (abbreviated as EMC), and the mass ratio of ethylene carbonate to ethyl methyl carbonate is (2-4): (6-8). Specifically, the mass ratio of ethylene carbonate to ethyl methyl carbonate can be (2-3): (7-8), (3-4): (6-7), 2:8, 3:7, and 4:6.

[0050] In a second aspect, the present invention provides a method for preparing the additive, comprising the following steps:

[0051] Under acidic conditions, compound (a) reacts with a sulfonating agent to obtain compound (b);

[0052] Under heating conditions, compound (b) undergoes dehydration and cyclization to obtain compound (c);

[0053] Under low temperature conditions, compound (c) reacts with phosgene for 1 to 1.5 hours, and then the temperature is raised to 70 to 80° C. to continue the reaction to obtain a compound with the structure represented by formula (I);

[0054] The reaction route is as follows:

[0055]

[0056] In some embodiments of the present invention, the method for preparing the above-mentioned additive provided by the present invention comprises the following steps:

[0057] Compound a and a sulfonating agent are added to ethanol at a molar ratio of 1: (1.1-1.2), and a sulfonation reaction occurs under stirring. After the reaction is completed, a solid precipitate is filtered to obtain a solid precipitate. A strong acid is added, stirred, and filtered to obtain a filtrate containing compound b. The filtrate is placed under high temperature (120-160° C.) and reduced pressure (260-530 Pa) for dehydration and cyclization to obtain compound c. Compound c is added to a cold phosgene solution, and the reaction is carried out at low temperature (0-5° C.) for 1 hour. Subsequently, phosgene is introduced and the temperature is gradually raised to 70-80° C. The reactants are separated and purified to obtain a compound with a structure represented by formula (I).

[0058] The additive provided by the present invention contains a cyclic sulfonate functional group in its molecular structure, which can help the electrolyte form a stable interfacial film on the positive and negative electrode surfaces. At the same time, the molecular structure of the cyclic sulfonate compound also contains an isocyanate group. The S=O in the sulfonate structure can increase the degree of delocalization of the nitrogen nucleus in the isocyanate structure, acting as a weak base point to inhibit the reaction of PF5, thereby inhibiting the formation of HF and LiF. In addition, during the film-forming reaction, after the two types of functional groups gain or lose electrons, each molecular fragment will produce a strong mutual cross-linking effect. Therefore, the above two functional groups work together to further stabilize the interfacial film through cross-linking coupling, improve the film-forming effect of the electrolyte, and thus reduce the high-temperature storage gas production of the battery and improve the high-temperature cycle performance.

[0059] In a third aspect, the present invention provides a method for preparing the above-mentioned electrolyte, comprising the following steps:

[0060] Under the protection of an inert atmosphere, the lithium salt and the organic solvent are mixed to obtain a mixed liquid, and the additive is mixed with the mixed liquid.

[0061] In some embodiments of the present invention, during the mixing process of the lithium salt and the organic solvent, the temperature of the mixed solution is controlled to not exceed 2°C. Since the addition of lithium salt will cause the electrolyte temperature to rise, resulting in a certain degree of thermal decomposition of the lithium salt, the electrolyte temperature should be controlled during the addition of lithium salt. When the electrolyte temperature rises by more than 2°C, the addition of lithium salt is stopped. When the electrolyte temperature is below 2°C, the addition of lithium salt can continue. The above-mentioned electrolyte temperature can be controlled using temperature control methods commonly used in the art, such as ice bath, dry ice circulation cooling, liquid nitrogen cooling, etc.

[0062] In some embodiments of the present invention, the water content of the organic solvent is no more than 20 ppm. Since lithium salts are easily hydrolyzed in water, the water content of the organic solvent needs to be strictly controlled. For example, the organic solvent can be dehydrated by molecular sieve adsorption, and the dried organic solvent is then mixed with the lithium salt.

[0063] In a fourth aspect, the present invention further provides a secondary battery comprising the above electrolyte. The secondary battery comprising the electrolyte provided by the present invention has good high-temperature performance.

[0064] In some embodiments of the present invention, the positive electrode comprises a ternary positive electrode material, and the general structural formula of the ternary positive electrode material comprises Li a Ni x Co y Mn z A b O2, wherein 0.9≤a≤1.1, 0.8≤x<1, x+y+z=1, 0≤b≤0.1, and A comprises at least one of Al, Mg, Ti, Zr, Zn, W, Nb, Mo, B or F.

[0065] In a fifth aspect, the present invention further provides an electrical device comprising the above-mentioned secondary battery.

[0066] The electrolyte and battery provided by the present invention are described in detail below with reference to specific embodiments.

[0067] Example 1

[0068] This embodiment provides a method for preparing a lithium-ion battery, which specifically includes the following steps:

[0069] (1) Preparation of electrolyte

[0070] At room temperature, in a glove box filled with argon (H2O <1ppm, O2 <1ppm), EC and EMC were mixed in a mass ratio of 3:7. Molecular sieves were used to remove water to obtain a mixed solvent with a water content of less than 20 ppm. LiPF6 was added to the mixed solvent in batches while stirring continuously and cooling with dry ice. LiPF6 could be added only when the solution temperature did not rise by more than 2°C. Finally, a colorless, transparent liquid was obtained in which the mass fraction of LiPF6 was 12.5%. Compound IA was then added in an amount equivalent to 0.1% of the total mass of the electrolyte and stirred evenly to obtain the electrolyte.

[0071] Among them, the preparation method of compound IA is as follows:

[0072]

[0073] Compound a1 and sodium sulfonate were added to ethanol at a molar ratio of 1:1.1, and a sulfonation reaction occurred with stirring. After completion of the reaction, a solid precipitate was filtered to obtain a solid precipitate. 2.0 M hydrochloric acid was added to the solid precipitate, stirred for 1.5 hours, and filtered to obtain a filtrate containing compound b1. This filtrate was then subjected to dehydration and cyclization at 120°C and 300 Pa to obtain compound c1. Compound c1 was reacted in a cold phosgene solution (0°C) for approximately 1 hour, followed by the addition of phosgene and a gradual increase in temperature to 70°C. The reactant was isolated and purified to obtain compound IA. According to the above preparation method, the total yield of compound IA was 87.5%, and the purity was 99.75%.

[0074] (2) Preparation of positive electrode sheet

[0075] The positive electrode active material Li(Ni 0.8 Mn 0.1 Co 0.1)O2 (NMC811), conductive agent acetylene black (SuperP) and binder polyvinylidene fluoride (PVDF) are mixed evenly in the mass ratio of NMC811:SuperP:PVDF=94:3:3, and evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black slurry. After the black slurry is coated on both sides of the aluminum foil, it is baked, rolled and cut into pieces to obtain the positive electrode sheet.

[0076] (3) Preparation of negative electrode sheet

[0077] The negative electrode active material graphite, the conductive agent acetylene black (SuperP) and the binder SBR are mixed evenly in a mass ratio of graphite:SuperP:SBR=94:3:3, and evenly dispersed in deionized water to form a uniform black slurry. The slurry is coated on both sides of the copper foil, and then baked, rolled and cut into pieces to obtain the negative electrode sheet.

[0078] (4) Production of soft pack batteries

[0079] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets. After winding, hot pressing and shaping, and tab welding, a bare battery cell is obtained. The bare battery cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10°C for 24 hours. The electrolyte prepared in the above step (1) is injected into the dried battery, allowed to stand, formed, and divided into different volumes to complete the preparation of the lithium-ion soft-pack battery.

[0080] Examples 2 to 6 are based on Example 1, with the addition amount of Compound IA increasing in sequence, as shown in Table 1.

[0081] Table 1

[0082]

[0083] Example 7 is based on Example 3, using compound IB instead of compound IA, wherein the synthetic route of compound IB is as follows:

[0084]

[0085] The preparation method of the compound IB is as follows:

[0086] Compound d is sequentially subjected to elimination, halogen addition, hydroxyl substitution, elimination, addition, and elimination to obtain compound a2. Compound a2 and sodium sulfonate are then added to ethanol at a molar ratio of 1:1.1, and a sulfonation reaction occurs with stirring. After completion of the reaction, a solid precipitate is filtered to obtain a solid precipitate. 2.0 M hydrochloric acid is added to the solid precipitate, stirred for 1.5 hours, and filtered to obtain a filtrate containing compound b2. This filtrate is dehydrated and cyclized at 120°C and 300 Pa to obtain compound c2. Compound c2 is reacted in a cold phosgene solution (0°C) for approximately 1.5 hours, followed by the addition of phosgene and a gradual increase in temperature to 90°C. The reactant is separated and purified to obtain compound IB. According to the above preparation method, the total yield of compound IB is 81% and the purity is 99.5%.

[0087] In Examples 8 and 9, the amount of LiPF6 used is adjusted based on Example 3.

[0088] In Example 10, the type of organic solvent was adjusted based on Example 3, and a mixed solvent of EC / EMC / DEC was used instead of EC / EMC.

[0089] Example 11 is based on Example 3, and the type of positive electrode active material is adjusted. Li(Ni 0.5 Mn 0.3 Co 0.2 )O2(NMC532) instead of Li(Ni 0.8 Mn 0.1 Co 0.1 )O2(NMC811).

[0090] Example 12 is based on Example 3 to adjust the type of positive electrode active material, using Li (Ni 0.6 Mn 0.2 Co 0.2 )O2(NMC622) instead of Li(Ni 0.8 Mn 0.1 Co 0.1 )O2(NMC811).

[0091] Example 13 is based on Example 7, and the type of positive electrode active material is adjusted, using Li(Ni 0.5 Mn 0.3 Co 0.2 )O2(NMC532) instead of Li(Ni 0.8 Mn 0.1 Co 0.1 )O2(NMC811).

[0092] Example 14 is based on Example 7, and the type of positive electrode active material is adjusted, using Li(Ni 0.6 Mn0.2 Co 0.2 )O2(NMC622) instead of Li(Ni 0.8 Mn 0.1 Co 0.1 )O2(NMC811).

[0093] Example 15 is based on Example 3, and the type of positive electrode active material is adjusted to use Li(Ni 0.9 Mn 0.05 Co 0.05 )O2 instead of Li(Ni 0.8 Mn 0.1 Co 0.1 )O2(NMC811).

[0094] Example 16 is based on Example 3, except that the mass ratio of EC to EMC in the mixed solvent is adjusted to 2:8.

[0095] Example 17 is based on Example 3, except that the mass ratio of EC to EMC in the mixed solvent is adjusted to 4:6.

[0096] Comparative Example 1 is based on Example 3 without using any electrolyte additives.

[0097] Comparative Example 2 is based on Example 3, using benzyl isocyanate instead of Compound IA as the electrolyte additive.

[0098] Comparative Example 3 is based on Example 3 and uses 1,4-butane sultone instead of Compound IA as the electrolyte additive.

[0099] Comparative Example 4 is based on Example 3, but benzyl isocyanate and 1,4-butane sultone in a mass ratio of 1:1 are used instead of Compound IA as the electrolyte additive.

[0100] Comparative Examples 5 to 7 are based on Examples 11, 12, and 15, respectively, without using any electrolyte additives.

[0101] Battery performance test

[0102] 1. Room Temperature DCR Test: At 25±2°C, the soft-pack batteries obtained in each Example and Comparative Example were charged to 4.4V at 1C, then discharged at 1C for 30 minutes. After adjusting to 50% SOC, they were pulse-discharged at 10C for 10 seconds. The SOC was then adjusted to 50% using the above SOC adjustment method, and charged for another 10 seconds. The DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current * 100%. After 30 days of high-temperature storage at 60°C, the DCR was retested when the battery was completely cooled to 25±2°C. The DCR change rate = (DCR after 30 days - DCR before 30 days) / DCR before 30 days * 100%. The results are shown in Table 2.

[0103] 2. High-Temperature Cycling Performance Test: The soft-pack batteries obtained from each Example and Comparative Example were subjected to charge-discharge cycling at a charge-discharge rate of 1C / 1C within the voltage range of 2.8-4.4V at 25±2°C. The battery's first-cycle discharge capacity and the discharge capacity after 500 cycles were recorded. The 500-cycle capacity retention ratio = 500-cycle discharge capacity / first-cycle discharge capacity * 100%. The recorded data are shown in Table 2.

[0104] 3. High-Temperature Storage Performance: The soft-pack batteries obtained from each Example and Comparative Example were charged and discharged at a charge / discharge rate of 1C / 1C in the range of 2.8-4.4V at 60±2°C. The first-week discharge capacity was recorded. The batteries were then stored at 60±2°C for 30 days, and the charge / discharge test was repeated, with the discharge capacity recorded. High-Temperature Storage Capacity Retention = Discharge Capacity after 7 Days / Discharge Capacity in the First Week * 100%. The recorded data are shown in Table 2.

[0105] 4. High-Temperature Gas Generation Test: The soft-pack batteries obtained from each Example and Comparative Example were charged at 25±2°C at a constant current rate of 1C to 4.4V. They were then charged at a constant voltage rate of 4.4V until the current dropped below 0.05C, bringing the battery to a fully charged state at 4.4V. The volume of the fully charged battery before storage was measured and recorded as V0. The fully charged battery was then placed in an oven at 60±2°C for 7 days. The battery was removed and its post-storage volume was immediately measured and recorded as V1. Volume expansion ratio = (V1-V0) / V0*100%. The results are shown in Table 2.

[0106] Table 2

[0107]

[0108]

[0109] Analysis of experimental results:

[0110] Comparing the experimental results of Examples 1-6 and Comparative Example 1, it can be seen that the addition of Compound IA can reduce the initial internal resistance of the battery, as well as the internal resistance growth and volume expansion during storage, and improve the capacity retention rate during high-temperature cycling and high-temperature storage. It can also be seen that as the content of Compound IA increases, the initial internal resistance increases accordingly. This is because the resulting interfacial film becomes increasingly dense, increasing the impedance of the interfacial film. This has a beneficial effect on suppressing the increasing trend of the battery's internal resistance and volume expansion rate during high-temperature storage, reducing irreversible losses during storage. However, excessive use of the additive significantly increases the initial impedance, which is detrimental to the battery's dynamic performance. Therefore, based on comprehensive performance, the content of Additive IA is preferably 0.5-1.5%, and the optimal content can be determined based on specific needs.

[0111] The experimental results of Example 7 and Comparative Example 1 show that the addition of Compound IB can also reduce the battery's initial internal resistance, as well as its internal resistance growth and volume expansion during storage, and improve the capacity retention during high-temperature cycling and high-temperature storage. This demonstrates that the additive provided by the present invention can help the electrolyte form a stable interfacial film, improving the electrolyte's film-forming effect, thereby reducing the battery's gas production during high-temperature storage and improving high-temperature cycling performance.

[0112] The experimental results of Examples 3 and 7 show that the addition of 1 wt% of Compounds IA or IB results in some performance differences between the cells. This is primarily due to the -CF3 substituents, which lead to differences in film formation mechanisms and, consequently, film composition and mechanical strength. The -CF3 group in Additive IB enhances its antioxidant capacity and increases the LiF content in the SEI film, which in turn increases interfacial impedance. However, significant improvements are still achieved compared to Comparative Example 1.

[0113] It can be seen from the experimental results of Example 3 and Examples 8 and 9 that too high or too low a lithium salt content will cause poor performance. If the lithium salt content is too low, the electrolyte conductivity is low, and if the lithium salt content is too high, the electrolyte viscosity increases. In addition, changes in the lithium salt content will also cause differences in the solvation structure, affecting the solvation energy barrier, and affecting the film formation during the desolvation process, thereby changing the interface film components. Therefore, it is necessary to optimize the lithium salt content. The present invention preferably uses a lithium salt content of 12 to 13 wt% in the electrolyte.

[0114] It can be seen from the experimental results of Example 3 and Example 10 that using DEC instead of EMC increases the initial DCR. This is mainly because the viscosity of DEC is greater, which slows down the lithium ion migration rate and increases polarization, while slightly deteriorating the high-temperature performance.

[0115] The experimental results of Example 3 and Comparative Examples 2 to 4 show that compared with additives containing only a single functional group, the battery containing Additive IA has better performance. This can be attributed to the fact that the structure of Additive IA contains both cyclic sulfonate and isocyanate functional groups. The S=O in the sulfonate structure can increase the degree of delocalization of the nitrogen nucleus, acting as a weak base point to inhibit the reaction of PF5, thereby hindering the formation of HF and LiF. In addition, during the film-forming reaction, after these two types of functional groups gain or lose electrons, the molecular fragments will produce strong mutual cross-linking, which can exert a stronger synergistic effect, thereby enabling the electrolyte to better improve the high-temperature storage gas production and high-temperature cycling performance of the battery.

[0116] The experimental results of Examples 11 to 15 and Comparative Examples 5 to 7 show that the performance improvement of the additives in the high-nickel system is more significant than that in the medium-nickel system. This is because, when no additives are added, as the Ni content increases, the side reactions at the interface between the positive electrode material and the electrolyte become more severe, causing the performance of the high-nickel system to deteriorate more significantly. The excellent film-forming effect of Additives IA and IB can inhibit the occurrence of side reactions, thereby significantly improving battery performance. Even when applied to positive electrode materials with higher nickel contents, the performance does not show significant degradation.

[0117] The experimental results of Examples 16-17 and Example 3 show that, based on the solvent ratio of Example 3, Example 16 reduces the EC content, which can reduce the initial DCR, but the cycling and storage performance will deteriorate slightly. This is mainly due to the fact that reducing the EC content can reduce the viscosity of the electrolyte and improve the kinetic performance. At the same time, EC can preferentially participate in solvation compared to EMC. During the first charge and discharge process, it is closer to the material interface and preferentially forms a film. Its film stability is better than EMC. Therefore, ensuring a certain content of EC can stabilize the interface film and inhibit solvent decomposition, thereby improving long-term performance. Increasing the EC content in Example 17 increases the electrolyte viscosity, deteriorates the battery kinetic performance, increases the initial DCR, and increases polarization, resulting in performance deterioration.

[0118] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. An electrolyte comprising a lithium salt, an organic solvent and an additive, characterized in that: The additive includes a compound having a structure shown in formula (I): Wherein, R1, R2, and R3 are independently selected from H, halogen, amino, carboxyl, C1-C 20 Any of a hydrocarbon group, a halogenated hydrocarbon group, and a heterocyclic group; The amount of the additive added is 0.1 to 5.0% of the total mass of the electrolyte; The content of the lithium salt is 10-15% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that The additives include compounds represented by formula (IA) and / or formula (IB):

3. The electrolyte according to claim 1, characterized in that The additive is added in an amount of 0.5 to 1.5% of the total mass of the electrolyte.

4. The electrolyte according to claim 1, characterized in that The content of the lithium salt is 12-13% of the total mass of the electrolyte.

5. The electrolyte according to claim 1, characterized in that The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; The organic solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, and sulfolane.

6. A secondary battery, characterized in that: The electrolyte comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 5.

7. The secondary battery according to claim 6, characterized in that: The positive electrode includes a ternary positive electrode material, and the general structural formula of the ternary positive electrode material includes Li a Ni x Co y Mn z A b O2, wherein 0.9≤a≤1.1, 0.8≤x<1, x+y+z=1, 0≤b≤0.1, and A comprises at least one of Al, Mg, Ti, Zr, Zn, W, Nb, Mo, B or F.

8. An electrical device, characterized in that: Comprising the secondary battery according to claim 6 or 7.

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