Electrolyte, positive electrode, lithium-ion battery, and vehicle

Abstract

The application discloses an electrolyte, a positive electrode, a lithium ion battery and a vehicle. The electrolyte comprises a lithium salt, an organic solvent and an additive, and the additive comprises a first additive, the first additive is a dicyano cyclic ether compound, and a structural formula of the dicyano cyclic ether compound is as follows: wherein n, x, y and z are each independent positive integers, and 1<=n<=3, 0<=x<=5, 0<=y<=5 and 0<=z<=5; R1 is selected from one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, a C2-C5 unsaturated alkyl group, a C6-C 10 aryl group or a C7-C 10 alkylaryl group; and the hydrogen atom in the C1-C5 alkyl group, the C2-C5 unsaturated alkyl group, the C6-C 10 aryl group or the C7-C 10 alkylaryl group can be partially or totally substituted by a substituent. The electrolyte disclosed by the application has a small impedance growth at low temperature, is beneficial to improve the low-temperature discharge performance of the lithium ion battery, can preferentially form a stable interface protection film on the surface of the positive electrode, and improves the battery capacity, cycle life and the like of the battery at high voltage.

Description

Technical Field

[0001] This invention generally relates to the field of new energy, and specifically to an electrolyte, a positive electrode, a lithium-ion battery, and a vehicle. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the demand for long-range power batteries is increasing. Increasing the operating voltage of lithium-ion batteries (>4.2V) can effectively increase the battery's energy density. However, under high voltage, the electrolyte in existing lithium-ion batteries is prone to oxidation at the positive electrode material interface, resulting in side reactions and poor cycle and storage stability under high voltage conditions. Current technologies improve lithium-ion battery performance by adding additives to the electrolyte to promote the formation of an interfacial protective film at the positive electrode interface.

[0003] Currently, existing additives still cannot guarantee that lithium-ion batteries will have excellent charge and discharge performance at both high and low temperatures, which greatly limits the application of high-voltage lithium-ion batteries. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide an electrolyte, a positive electrode, a lithium-ion battery, and a vehicle.

[0005] In a first aspect, the present invention provides an electrolyte comprising: a lithium salt, an organic solvent, and additives;

[0006] Additives include: primary additive; The first additive is a dicyanocyclic ether compound, the structural formula of which is as follows:

[0007] Where n, x, y and z are all independent positive integers, and 1≤n≤3, 0≤x≤5, 0≤y≤5, 0≤z≤5; R1 is selected from hydrogen atoms, halogen atoms, C1-C5 alkane groups, C2-C5 unsaturated hydrocarbon groups, C6-C5 alkane groups, and C6-C5 alkane groups. 10 aryl or C7~C 10 One of the alkylaryl groups; C1–C5 alkane groups, C2–C5 unsaturated hydrocarbon groups, C6–C 10 aryl or C7~C 10 The hydrogen atoms in the alkylaryl group can be partially or completely replaced by substituents.

[0008] As a preferred option, the substituent includes at least one of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group.

[0009] As a preferred option, the dicyanocyclic ether compound is selected from at least one of the following compounds: Compound I Compound II, Compound III Compound IV Compound V, Compound VI.

[0010] As a preferred embodiment, the additive further includes: a second additive, which is selected from at least one of vinylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, lithium difluorophosphate, and lithium difluorobis(oxalato)phosphate.

[0011] As a preferred embodiment, the mass fraction of the first additive is 0.1% to 15% based on the total mass of the electrolyte.

[0012] As a preferred option, the mass fraction of the first additive is 0.5% to 5% based on the total mass of the electrolyte.

[0013] As a preferred embodiment, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorosulfonylimide.

[0014] As a preferred embodiment, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, γ-butyrolactone, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.

[0015] In a second aspect, the present invention provides a positive electrode for a lithium-ion battery, comprising a positive electrode current collector and a positive electrode active material layer located on the surface of the positive electrode current collector, wherein the surface of the positive electrode active material layer has an interface protective film, which is formed according to the electrolyte as described in the first aspect.

[0016] Thirdly, the present invention provides a lithium-ion battery comprising: the electrolyte described in the first aspect.

[0017] Fourthly, the present invention provides a vehicle, characterized in that it includes: the lithium-ion battery described in the third aspect.

[0018] The electrolyte provided in this application includes a first additive, which is a dicyanocyclic ether compound. The dicyanocyclic ether compound has low impedance at low temperatures, thus improving the low-temperature discharge performance of lithium-ion batteries. Furthermore, the dicyanocyclic ether compound can preferentially form a stable and highly uniform interfacial protective film at the positive electrode at a low oxidation potential. The formation of the interfacial protective film reduces the occurrence of side reactions between the electrolyte and the positive electrode active material, maintains the stability of the electrode / electrolyte interface, and helps to suppress the growth of positive electrode film impedance and electrochemical reaction impedance during cycling, resulting in good high-temperature performance and cycle performance of the lithium-ion battery. In addition, the dicyanocyclic ether compound can complex with metal ions, inhibiting the dissolution of transition metal ions at the positive electrode. It can also absorb a small amount of H2O and HF, reducing the gas expansion caused by electrolyte decomposition, thereby improving the cycle performance of the battery at high voltage. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the embodiments. It is to be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0021] In a first aspect, embodiments of the present invention provide an electrolyte comprising: a lithium salt, an organic solvent, and an additive; Additives include: primary additive; The first additive is a dicyanocyclic ether compound, the structural formula of which is as follows:

[0022] Where n, x, y and z are all independent positive integers, and 1≤n≤3, 0≤x≤5, 0≤y≤5, 0≤z≤5; R1 is selected from hydrogen atoms, halogen atoms, C1-C5 alkane groups, C2-C5 unsaturated hydrocarbon groups, C6-C5 alkane groups, and C6-C5 alkane groups. 10 aryl or C7~C 10 One of the alkylaryl groups; C1–C5 alkane groups, C2–C5 unsaturated hydrocarbon groups, C6–C 10 aryl or C7~C 10 The hydrogen atoms in the alkylaryl group can be partially or completely replaced by substituents.

[0023] The dicyanocyclic ether compound of this invention exhibits minimal impedance growth at low temperatures, thus improving the low-temperature discharge performance of lithium-ion batteries. Furthermore, during lithium-ion battery formation, the dicyanocyclic ether compound preferentially forms a stable and highly uniform passivation film (also known as an interface protection film) at the positive electrode at a lower oxidation potential. This interface protection film suppresses side reactions between the electrolyte and the positive electrode active material, maintaining the stability of the electrode / electrolyte interface. This helps to suppress the growth of positive electrode film impedance and electrochemical reaction impedance during cycling, resulting in excellent high-temperature and cycle performance of the lithium-ion battery. Simultaneously, the stable interface protection film helps to alleviate the problem of gas accumulation in lithium-ion batteries. Therefore, the electrolyte of this invention is beneficial for improving battery cycle performance at high voltages while also maintaining good low-temperature performance.

[0024] The reason why the electrolyte of this invention can improve the performance of lithium-ion batteries, based on theoretical calculations and experimental results, is likely due to the presence of cyano and cyclic ether bonds in the dicyanocyclic ether compound. On the one hand, the ring-opening reaction of the cyclic ether allows it to form a stable and uniform interfacial protective film on the positive electrode surface at a lower oxidation potential, inhibiting the reaction between the electrolyte and the positive electrode active material at high voltages, while maintaining the stability of the electrode / electrolyte interface. This helps to suppress the increase in positive electrode film impedance and electrochemical reaction impedance during cycling, resulting in good high-temperature performance and cycle performance of the lithium-ion battery. On the other hand... The cyano functional group can absorb small amounts of H2O and HF to form amides, reducing the gas expansion problem caused by electrolyte decomposition catalyzed by HF and POF3. Simultaneously, the dicyano functional group exhibits high ionic conductivity in organic solvents, lowering the lower limit of electrolyte operating temperature and enhancing lithium-ion conductivity at low temperatures, thus improving the low-temperature charge-discharge performance of lithium-ion batteries. Furthermore, the dicyanocyclic ether compound can complex with transition metal ions, inhibiting the dissolution of transition metal ions from the positive electrode and preventing their migration to the negative electrode, which could damage the solid electrolyte interphase (SEI) film. The dicyanocyclic ether compound used in this invention contains both cyclic ether bonds and dicyano functional groups in its molecular structure. The synergistic effect of these two components produces superior technical effects without considering the impact of component ratios and system compatibility on battery performance when used individually, thereby increasing production efficiency.

[0025] Furthermore, the hydrogen atoms in the alkane group, unsaturated hydrocarbon group, aryl group, or alkylaryl group can be partially or completely replaced by one or more of the halogen group, cyano group, carboxyl group, and sulfonic acid group. In the embodiments of the present invention, the hydrogen atoms in the alkane group, unsaturated hydrocarbon group, aryl group, or alkylaryl group can be partially or completely replaced, increasing the reactivity of the alkane group, unsaturated hydrocarbon group, aryl group, or alkylaryl group. On the one hand, this is beneficial for the first additive to form an interfacial protective film at the positive electrode of the lithium-ion battery, thereby inhibiting the oxidative decomposition of the electrolyte under high voltage and avoiding the damage of the SEI film on the negative electrode surface caused by the dissolution of positive electrode metal ions; on the other hand, the halogen group, cyano group, carboxyl group, and sulfonic acid group have high bond energies and are not easily oxidized, exhibiting good stability on the positive electrode surface. At the same time, the cyano group also has a strong coordination ability and can combine with the active sites on the electrode surface (such as high-valence metal ions such as nickel / cobalt / manganese, etc.), thereby masking these active ions on the positive electrode surface and reducing the decomposition effect of the electrode on the electrolyte.

[0026] Preferably, the dicyanocyclic ether compound in the embodiments of the present invention is selected from at least one of the following compounds: Compound I Compound II, Compound III Compound IV Compound V, Compound VI.

[0027] As a possible implementation, the additive also includes: a second additive selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (1,3-PST), ethylene sulfate (VS), lithium difluorophosphate (LD), and lithium difluorobis(oxalate) phosphate (LDP).

[0028] The second additive in the electrolyte of the embodiments of the present invention is mainly used to improve the film formation of the negative electrode, which is beneficial for the lithium-ion battery to form a low impedance and high stability SEI film at the negative electrode. The SEI film is insoluble in organic solvents and can exist stably in organic electrolyte solutions. Solvent molecules cannot pass through the SEI film, thereby effectively preventing the co-intercalation of solvent molecules and avoiding damage to the electrode material caused by the co-intercalation of solvent molecules. Thus, the cycle performance and service life of the electrode are greatly improved.

[0029] As an feasible method, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorosulfonylimide. As a possible method, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, γ-butyrolactone, methyl formate, ethyl acetate, methyl acetate, propyl acetate (EP), butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.

[0030] In the electrolyte of the embodiments of the present invention, the first additive has low impedance at low temperature, which can improve the low-temperature charge and discharge performance of lithium-ion batteries; and the dicyanocyclic ether compound does not need to be combined with other additives, and will preferentially form a stable and highly uniform interface protective film at the positive electrode at a low oxidation potential, thereby effectively suppressing the growth of positive electrode film impedance and electrochemical reaction impedance during cycling, and improving the problem of gas expansion in lithium-ion batteries. The second additive is mainly used to improve the film formation of the negative electrode, which is beneficial for lithium-ion batteries to form a low-impedance and high-stability SEI film at the negative electrode. The SEI film is insoluble in organic solvents and can exist stably in organic electrolyte solutions. Solvent molecules cannot pass through the SEI film, thus effectively preventing the co-intercalation of solvent molecules and avoiding damage to the electrode material caused by the co-intercalation of solvent molecules. Therefore, it greatly improves the cycle performance and service life of the electrode.

[0031] In summary, the electrolyte of the present invention can generate an interfacial protective film at the positive and negative electrodes, thereby effectively improving the performance of lithium-ion batteries and meeting the requirements of high-voltage systems for cycle performance, high and low temperature performance, and storage performance.

[0032] Furthermore, based on the total mass of the electrolyte, the mass fraction of the first additive is 0.1% to 15%. Preferably, the mass fraction of the first additive is 0.5% to 5%. The mass fraction range of this embodiment is beneficial for forming a dense and stable interfacial protective film at the positive electrode, which can reduce the occurrence of side reactions between the electrolyte and the active material, while better preventing the dissolution of metal ions at the positive electrode, maintaining the stability of the electrode / electrolyte interface, and also improving the diffusion of lithium ions under low temperature conditions, thereby effectively improving the high and low temperature performance of the lithium-ion battery.

[0033] Secondly, embodiments of the present invention provide a positive electrode for a lithium-ion battery. The positive electrode includes a positive current collector and a positive active material layer located on the surface of the current collector. The surface of the positive active material layer has an interface protective film, which is formed using the electrolyte described in the first aspect. Therefore, this positive electrode possesses all the characteristics and advantages of the electrolyte described above, which will not be repeated here.

[0034] Thirdly, embodiments of the present invention provide a lithium-ion battery. This lithium-ion battery includes the electrolyte described in the first aspect and / or the positive electrode described in the second aspect. Thus, this lithium-ion battery possesses all the features and advantages of the electrolyte and / or the positive electrode described above, which will not be repeated here. In general, this lithium-ion battery has the characteristic of being able to form a stable and uniform interfacial protective film at both the positive and negative electrode interfaces, and exhibits good cycle performance, high and low temperature performance, and storage performance under high voltage systems. In particular, this lithium-ion battery demonstrates excellent discharge performance under low temperature conditions.

[0035] The positive electrode active material of this lithium-ion battery is selected from LiFe. x Mn y M z PO4 (0≤ x ≤1, 0≤ y ≤1, 0≤ z ≤1, x + y + z =1, where M is at least one of Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo), Li3V2(PO4)3, Li3V3(PO4)3, LiNi 0.5-x Mn 1.5-y M x+y O4 (-0.1≤ x ≤0.5, 0≤ y ≤1.5, M is at least one of Li, Co, Fe, Al, Mg, Ca, Ti, Mo, Cr, Cu, Zn), LiVPO4F, Li 1＋x L 1－y－z M y N z O2 (L, M, N can be at least one of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S, B, -0.1≤ x ≤0.2, 0≤ y ≤1, 0≤ z ≤1, 0≤ y+z One or more of the following: ≤1.0), Li2CuO2, and Li5FeO4, with a charging cut-off voltage ≥4.35V.

[0036] Fourthly, the present invention provides a vehicle that includes the lithium-ion battery described in the third aspect. For example, it may include a battery pack composed of multiple lithium-ion batteries as described above. Thus, the vehicle possesses all the features and advantages of the lithium-ion battery described above, which will not be repeated here.

[0037] The present invention will be described below through specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods that do not specifically describe the conditions or steps are conventional methods, and the reagents and materials used can be obtained commercially.

[0038] The preparation methods of the lithium-ion batteries in Examples 1-17 and Comparative Examples 1-5 are as follows: (1) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:EMC:DEC = 3:2:5 to form a mixed solvent. Lithium hexafluorophosphate (LiPF6) was added to the mixed solvent until the molar concentration reached 1.1 mol / L. Then, additives were added, and the mixture was stirred until homogeneous to obtain the electrolyte. The specific types and contents of the additives used in the electrolyte are shown in Table 1, where the proportion of the additives is the mass percentage of the total mass of the electrolyte.

[0039] (2) Preparation of the positive electrode: Ternary cathode material (NCM523), Super-P, CNT, and PVDF were mixed in a mass ratio of 95:2:1.5:1.5, and then dispersed in NMP. The mixture was stirred under vacuum until stable and homogeneous to obtain a cathode slurry. The cathode slurry was then uniformly coated onto an aluminum foil with a thickness of 15 μm. After the aluminum foil was dried at room temperature, it was transferred to a 120°C container. o The positive electrode sheet is dried in a forced-air oven for 2 hours, and then subjected to cold pressing and slitting processes.

[0040] (3) Preparation of negative electrode: Artificial graphite, Super-P, SBR, and CMC were mixed in a mass ratio of 95.5:1.5:1:2, and then dispersed in deionized water to obtain an 8µm negative electrode slurry on a copper foil. After drying the copper foil at room temperature, it was transferred to a 120°C container. o The cathode is dried in a forced-air oven for 2 hours, and then subjected to cold pressing and slitting processes to obtain the negative electrode sheet.

[0041] (4) Preparation of lithium-ion batteries: The positive electrode, negative electrode, and separator are wound together to form a bare cell. The cell is then packaged in an aluminum-plastic film shell, injected with electrolyte, and sealed in sequence. After processes such as settling, hot and cold pressing, formation, and capacity testing, a lithium-ion battery is produced.

[0042] Table 1. Specific types and contents of additives in Examples 1-17 and Comparative Examples 1-10

[0043] The structural formula of 1,3-dioxane in Comparative Example 4 is as follows:

[0044] The structural formula of 1,3-dioxane in Comparative Example 5 is as follows:

[0045] The structural formula of phosphonyl cyclic ether compound I in Comparative Example 8 is as follows:

[0046] The structural formula of phosphonyl cyclic ether compound II in Comparative Example 9 is as follows:

[0047] The structural formula of phosphonyl cyclic ether compound III in Comparative Example 10 is as follows:

[0048] The following describes the performance testing process and results for lithium-ion batteries: (1) Room temperature cycling test The lithium-ion battery was charged to 4.5V at 25℃ with a constant current of 1C, then charged to the cutoff current of 0.1C with a constant voltage, left to stand for 30 minutes, and then discharged to 2.5V with a constant current of 1C. This was recorded as one charge-discharge cycle. The battery was cycled for 800 cycles under the above conditions. The capacity retention rate (%) of the lithium-ion battery after 800 cycles = (discharge capacity of the 800th cycle / discharge capacity of the first cycle) × 100%.

[0049] (2) High-temperature cycling performance test The lithium-ion battery was charged to 4.5V at 45℃ with a constant current of 1C, then charged to the cutoff current of 0.1C with a constant voltage, left to stand for 30 minutes, and then discharged to 2.5V with a constant current of 1C. This was recorded as one charge-discharge cycle. Then, the battery was cycled for 400 cycles under the above conditions. The capacity retention rate (%) of the lithium-ion battery after 400 cycles = (discharge capacity of the 400th cycle / discharge capacity of the first cycle) × 100%. (3) High-temperature storage performance test The lithium-ion battery was charged at 25℃ with a constant current and constant voltage of 1C to 4.5V, cut off at 0.1C, and left to stand for 30 minutes. Then it was discharged at a constant current of 1C to 2.5V, and this discharge capacity was recorded as the initial capacity C0. The battery volume V0 before storage was measured by charging it to 4.5V with a constant current and constant voltage of 1C. The fully charged battery was then transferred to a high-temperature test chamber and stored at 60℃ for 15 days. After storage, the test battery was removed and left to stand at room temperature for 12 hours. The battery volume V1 after storage was measured. Then it was discharged at a constant current of 1C to 2.5V, and the discharge capacity C1 was recorded. After standing for 120 minutes, it was charged at a constant current and constant voltage of 1C to 4.5V, cut off at 0.1C, and left to stand for 30 minutes. Then it was discharged at a constant current of 1C to 2.5V, and the discharge capacity C2 was recorded. Capacity Remaining Rate (%) = C1 / C0 100%; Capacity recovery rate (%) = C2 / C0 100%; Battery volume expansion rate (%) = [(V1-V0) / V0] 100%.

[0050] (4) Low-temperature discharge capacity test The lithium-ion battery was charged at 25℃ with a constant current and constant voltage of 1C to 4.5V, cut off at 0.1C, and left to stand for 30 minutes. Then it was discharged at a constant current of 1C to 2.5V. This discharge capacity was recorded as the initial capacity C0. The battery was charged at a constant current and constant voltage of 1C to 4.5V. The fully charged battery was then transferred to an ambient temperature chamber at -20℃ and left to stand for 8 hours. Then it was discharged at a constant current of 1 / 3C to 2.5V. The discharge capacity C1 was recorded. -20℃ discharge capacity ratio (%) = C1 / C0 100%; The structures of the lithium-ion batteries of Examples 1-17 and Comparative Examples 1-10, tested according to the above process and method, are shown in Table 2: Table 2 Test results of Examples 1-17 and Comparative Examples 1-10

[0051] Based on the results shown in Table 2: Compared to Comparative Example 1, the lithium-ion batteries of Examples 1-17 showed significant improvements in room temperature cycling, high temperature cycling, and high temperature storage performance. Furthermore, the discharge capacity test results at low temperatures showed that the discharge capacity ratio of the batteries in Examples 1-17 was far superior to that of the batteries in Comparative Examples 1-10, indicating that the dicyanocyclic ether compound of the present application is beneficial for improving the low-temperature performance of lithium-ion batteries.

[0052] The electrolytes of Examples 16 and 17 contained only the first additive, while Comparative Example 1 contained only the second additive. According to the results shown in Table 2, the lithium-ion batteries of Examples 16 and 17 exhibited superior performance in terms of capacity retention after 800 cycles at 25°C, capacity retention after 400 cycles at 45°C, capacity retention after storage at 60°C, capacity recovery, and battery volume expansion compared to the lithium-ion battery of Comparative Example 1. This indicates that the first additive can improve the high-temperature performance of the battery. Furthermore, the lithium-ion batteries of Examples 16 and 17 showed significantly better discharge capacity ratios at -20°C than Comparative Example 1, demonstrating that the addition of the dicyanocyclic ether compound resulted in excellent low-temperature discharge performance of the lithium-ion battery.

[0053] Examples 1-8 illustrate the effect of dicyanocyclic ether compound I (structure I) on the performance of lithium-ion batteries. Battery test results show that the amount of dicyanocyclic ether compound has a significant impact on battery performance. An appropriate amount of dicyanocyclic ether compound can form an interfacial protective film on the positive electrode surface, preventing the electrolyte from being oxidized on the positive electrode surface, inhibiting the dissolution of transition metal ions, and efficiently removing HF and Lewis acids generated in the electrolyte. Examples 9 and 11-14 illustrate the effect of dicyanocyclic ether compounds with different structures on the performance of lithium-ion batteries. Test results show that the dicyanocyclic ether compounds in the embodiments of the present invention significantly improve the cycle performance, high-temperature performance, and low-temperature performance of lithium-ion batteries.

[0054] The battery test results of Examples 9, 10, 14, and 15 show that the combination of dicyanocyclic ether compounds with different negative electrode film-forming additives has a significant impact on the electrical performance of lithium-ion batteries, and a suitable additive combination scheme can play a certain role in further improving the electrical performance of lithium-ion batteries.

[0055] The battery test results of Comparative Examples 2-10 show that when dicyano compounds, phosphonyl cyclic ether compounds, cyclic ether compounds, or a mixture of dicyano compounds and cyclic ether compounds are used as additives, the low-temperature discharge capacity of lithium-ion batteries is significantly reduced. Although the compound shown in Example 10 also contains dicyano and cyclic ether groups, the interference of the phosphonyl group increases its impedance at low temperatures, resulting in poor low-temperature performance. This demonstrates that the synergistic effect of the dicyano and cyclic ether structures in the first additive of this invention can effectively improve the high-temperature and low-temperature performance of lithium-ion batteries.

[0056] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. An electrolyte, characterized in that, include: Lithium salts, organic solvents, and additives; The additive includes: a first additive; The first additive is a dicyanocyclic ether compound, and the structural formula of the dicyanocyclic ether compound is as follows: Where n, x, y and z are all independent positive integers, and 1≤n≤3, 0≤x≤5, 0≤y≤5, 0≤z≤5; R1 is selected from hydrogen atoms, halogen atoms, C1-C5 alkane groups, C2-C5 unsaturated hydrocarbon groups, C6-C5 alkane groups, and C6-C5 alkane groups. 10 aryl or C7~C 10 One of the alkylaryl groups; The C1-C5 alkane groups, the C2-C5 unsaturated hydrocarbon groups, and the C6-C5 alkane groups 10 aryl or C7-C 10 The hydrogen atoms in the alkylaryl group can be partially or completely replaced by substituents.

2. The electrolyte according to claim 1, wherein the substituent comprises at least one selected from halogen, cyano, carboxyl, and sulfonic acid groups.

3. The electrolyte according to claim 1, wherein the dicyanocyclic ether compound is selected from at least one of the following compounds: Compound I Compound II, Compound III Compound IV Compound V, Compound VI.

4. The electrolyte according to claim 1, characterized in that, The additive further includes: a second additive, wherein the second additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, 1,3-propane sulfonate lactone, 1,3-propene sulfonate lactone, ethylene sulfate, lithium difluorophosphate, and lithium difluorobis(oxalato) phosphate.

5. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass fraction of the first additive is 0.1% to 15%.

6. The electrolyte according to claim 5, characterized in that, Based on the total mass of the electrolyte, the mass fraction of the first additive is 0.5% to 5%.

7. The electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium di(trifluoromethanesulfonyl)imide, and lithium difluorosulfonylimide.

8. The electrolyte according to claim 1, characterized in that, The organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, γ-butyrolactone, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.

9. A positive electrode for a lithium-ion battery, characterized in that, include: A positive current collector and a positive active material layer located on the surface of the positive current collector, wherein the surface of the positive active material layer has an interface protective film, the interface protective film being formed by electrolyte liquefaction according to any one of claims 1-8.

10. A lithium-ion battery, characterized in that, include: The electrolyte according to any one of claims 1-8.

11. A vehicle, characterized in that, Including the lithium-ion battery as described in claim 10.

Images