Electrolyte, lithium ion battery and electric equipment

Abstract

The invention provides an electrolyte, a lithium ion battery and electric equipment. The electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises a calcium salt. Therefore, due to the introduction of the calcium salt in the electrolyte, the solvation structure of the electrolyte can be effectively regulated and controlled, and the multivalent metal cation Ca < 2 + > can adsorb more anions to enter a solvation shell layer through strong electrostatic interaction; moreover, Ca < 2 + > has more positive charges and can enter a negative electrode interface double-electrode layer more easily, and an optimized electrolyte solvation structure is matched, so that decomposition of anions in the electrolyte can be well regulated and controlled to participate in negative electrode interface film formation (SEI), solvent decomposition is reduced, more inorganic SEI components are generated, interface stability is improved, interface impedance is reduced, and the service life of the electrolyte is prolonged. And the cycling stability, storage performance and safety performance of the battery are obviously improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and more specifically, to electrolytes, lithium-ion batteries and electrical equipment. Background Art

[0002] Lithium-ion batteries are widely used in mobile electronic devices, electric vehicles, electrochemical energy storage and other fields due to their advantages such as high energy density, long cycle life, portability and environmental protection. Nowadays, with the continuous expansion of application scenarios, higher requirements are placed on the performance of lithium-ion batteries. The electrolyte is called the blood of the battery. By adjusting and optimizing its formula, the performance of lithium-ion batteries can be effectively improved. Among them, electrolyte additives only need a small amount to play a significant role, which can specifically improve the cycle life and safety performance of the battery. However, the additives currently reported are mainly concentrated in various organic substances, which have complex structures, are difficult to synthesize, are easy to deteriorate, and have a relatively single optimization effect.

[0003] Therefore, the research on electrolytes of lithium-ion batteries needs to be further deepened. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one purpose of the present application is to provide an electrolyte in which the strong electrostatic adsorption of calcium ions in the electrolyte can effectively regulate the film formation at the negative electrode interface.

[0005] In one aspect of the present application, the present application provides an electrolyte. According to an embodiment of the present application, the electrolyte includes a lithium salt, an organic solvent and an additive, wherein the additive includes a calcium salt. Thus, the introduction of the calcium salt into the electrolyte can effectively regulate the solvation structure of the electrolyte, and the polyvalent metal cation Ca 2+ More anions can be adsorbed into the solvation shell through strong electrostatic interactions; moreover, due to the Ca 2+ It has more positive charges and is easier to enter the double electrical layer of the negative electrode interface. Combined with the optimized electrolyte solvation structure, it can well regulate the decomposition of anions in the electrolyte to participate in the negative electrode interface film formation (SEI), reduce the decomposition of the solvent, generate more inorganic SEI components, improve the interface stability, reduce the interface impedance, and significantly improve the battery cycle stability as well as storage and safety performance.

[0006] According to an embodiment of the present application, the anions in the calcium salt include fluorine-containing anions.

[0007] According to an embodiment of the present application, the calcium salt includes at least one of calcium bis(trifluoromethanesulfonyl imide), calcium bis(fluorosulfonyl)imide, calcium trifluoromethanesulfonate and calcium hexafluorophosphate.

[0008] According to an embodiment of the present application, based on the total weight of the electrolyte, the mass concentration of calcium ions in the electrolyte is 50-800 ppm.

[0009] According to an embodiment of the present application, based on the total weight of the electrolyte, the mass concentration of calcium ions in the electrolyte is 50-100 ppm.

[0010] According to an embodiment of the present application, the lithium salt satisfies at least one of the following conditions: the concentration of the lithium salt in the electrolyte is 0.6-1.5 mol / L; the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, lithium difluorobis(oxalatophosphate) and lithium tetrafluoroborate.

[0011] According to an embodiment of the present application, the organic solvent includes one or more of a carbonate solvent and / or a carboxylate solvent, and the organic solvent satisfies at least one of the following conditions: the carbonate solvent includes a cyclic carbonate and / or a chain carbonate, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate and trifluoropropylene carbonate, the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate; the mass ratio of the cyclic carbonate and the chain carbonate is (2-5): (5-8); the carboxylate solvent includes at least one of ethyl acetate, methyl acetate and ethyl propionate; the content of the organic solvent in the electrolyte is 70-90wt%.

[0012] According to an embodiment of the present application, the additive also includes an auxiliary additive, wherein the auxiliary additive includes at least one of vinylene carbonate, fluoroethylene carbonate, methylene disulfonate, vinyl sulfate, 1,3-propane sultone, and propenyl-1,3-sultone; and / or, the content of the auxiliary additive in the electrolyte is 0.5-5wt%.

[0013] In another aspect of the present application, the present application provides a lithium-ion battery. According to an embodiment of the present application, the lithium-ion battery comprises a positive electrode, a negative electrode, a separator and the electrolyte described above. As a result, the lithium-ion battery has better battery cycle stability and storage and safety performance. It can be understood by those skilled in the art that the lithium-ion battery has all the features and advantages of the electrolyte described above, and no further elaboration is given here.

[0014] In another aspect of the present application, the present application provides an electric device. According to an embodiment of the present application, the electric device includes the lithium-ion battery described above. Thus, the electric device has a longer battery life and safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0016] Figure 1 1 is a cycle curve diagram of the lithium ion battery in Example 1, Example 2 and Comparative Example 1 of the present application at room temperature;

[0017] Figure 2 It is a graph of ARC test data of the lithium-ion batteries in Example 1, Example 2 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0018] The scheme of the present application will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are indicated in the embodiments, the technology or conditions described in the literature in this area or the product specification are carried out. The reagents used or the instruments that do not indicate the manufacturer are all conventional products that can be obtained commercially.

[0019] The present application is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present application in any way.

[0020] In one aspect of the present application, the present application provides an electrolyte. According to an embodiment of the present application, the electrolyte includes a lithium salt, an organic solvent and an additive, wherein the additive includes a calcium salt. Thus, the introduction of the calcium salt into the electrolyte can effectively regulate the solvation structure of the electrolyte, and the polyvalent metal cation Ca 2+ More anions can be adsorbed into the solvation shell through strong electrostatic interactions; moreover, due to the Ca 2+ It has more positive charges and is easier to enter the double electrical layer of the negative electrode interface. Combined with the optimized electrolyte solvation structure, it can well regulate the decomposition of anions in the electrolyte to participate in the negative electrode interface film formation (SEI), reduce the decomposition of the solvent, generate more inorganic SEI components, improve the interface stability, reduce the interface impedance, and significantly improve the battery cycle stability as well as storage and safety performance.

[0021] According to some embodiments of the present application, the anion in the calcium salt includes a fluorine-containing anion, that is, the calcium salt is a fluorine-containing calcium salt. 2+ It has a strong electrostatic interaction adsorption with fluorine-containing anions, namely Ca 2+ It can better adsorb fluoride-containing anions and reduce and decompose them at the negative electrode to form more LiF-containing SEI, which is beneficial to improving battery performance.

[0022] According to some embodiments of the present application, the calcium salt includes at least one of calcium bis(trifluoromethanesulfonyl imide) (Ca(TFSI)2), calcium bis(fluorosulfonyl) imide, calcium trifluoromethanesulfonate and calcium hexafluorophosphate. The above-mentioned fluorine-containing calcium salt can be well mixed with other components in the electrolyte, and will not have side reactions with components such as lithium salts, organic solvents or other additives in the electrolyte. Moreover, there is a strong electrostatic adsorption effect between the calcium ions and anions in the above-mentioned calcium salts. Ca 2+ The above-mentioned fluorine-containing anions can be better adsorbed and reduced and decomposed at the negative electrode to form more LiF-containing SEI films, which is beneficial to improving battery performance.

[0023] According to some embodiments of the present application, based on the total weight of the electrolyte, the mass concentration of calcium ions in the electrolyte is 50-800ppm, such as 50ppm, 55ppm, 60ppm, 65ppm, 70ppm, 75ppm, 80ppm, 85ppm, 90ppm, 95ppm, 100ppm, 120ppm, 150ppm, 180ppm, 200ppm, 250ppm, 300ppm, 350ppm, 400ppm, 450ppm, 500ppm, 550ppm, 600ppm, 650ppm, 700ppm, 750ppm, 800ppm, etc. Therefore, the introduction of a very small amount of calcium ions into the electrolyte can effectively achieve the technical effects of regulating the film formation at the negative electrode interface, improving the interface stability during the battery cycle and reducing the interface impedance, thereby significantly improving the cycle life, storage and safety performance of the battery; moreover, since only a very small amount of calcium ions are introduced into the electrolyte, it is not easy to cause the undesirable phenomenon of reduction and formation of dendrites on the negative electrode side of the battery. Since the reduction potential of calcium ions is higher than that of Li + / Li, if the content of calcium ions is too high, it is possible to reduce and deposit on the negative electrode side to form dendrites, which deteriorates battery performance and brings safety problems. According to some specific embodiments of the present application, the mass concentration of calcium ions in the electrolyte is 50-100ppm based on the total weight of the electrolyte.

[0024] According to some embodiments of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethylsulfonyl imide), lithium difluorophosphate, lithium trifluoromethanesulfonate, lithium difluorobis(oxalatophosphate) and lithium tetrafluoroborate. Thus, all of the above lithium salts are lithium salts containing fluorine anions, so that calcium ions can adsorb more fluorine anions and reduce and decompose on the negative electrode side of the battery to form more LiF-containing SEI films, thereby improving interface stability, reducing interface impedance, and significantly improving battery cycle stability, storage and safety performance.

[0025] According to some embodiments of the present application, the concentration of lithium salt in the electrolyte is 0.6-1.5 mol / L, such as 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc. Thus, the electrolyte of the above concentration helps to improve the overall performance of the battery. In some specific embodiments, the concentration of lithium salt in the electrolyte is 0.8-1.2 mol / L.

[0026] According to some embodiments of the present application, the organic solvent includes one or more of carbonate solvents and / or carboxylate solvents. In some embodiments, the carbonate solvent includes cyclic carbonate and / or chain carbonate, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate and trifluoropropylene carbonate, and the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate; in some embodiments, the carboxylate solvent includes at least one of ethyl acetate, methyl acetate and ethyl propionate. The above-mentioned organic solvent has a suitable dielectric constant, which is conducive to the dissolution of the above-mentioned lithium salt and calcium salt; the above-mentioned organic solvent has a suitable viscosity, which is conducive to improving the migration rate of lithium ions; the above-mentioned organic solvent has the characteristics of high boiling point and low melting point, which can ensure the normal operation of the electrolyte in a wide temperature range; and the above-mentioned organic solvent has good electrochemical stability, which can effectively ensure that the battery is not easy to decompose during charging and discharging, and improve the safety of the battery.

[0027] In some embodiments, the carbonate solvent includes cyclic carbonate and chain carbonate, and the mass ratio of cyclic carbonate to chain carbonate is (2-5): (5-8). Thus, it is helpful to improve the solubility of lithium salt and calcium salt, improve the mobility of lithium ions and other properties, and further help to improve the overall performance of the electrolyte and the battery.

[0028] According to some embodiments of the present application, the content of organic solvent in the electrolyte is 70-90wt%, such as 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, etc. Thus, the electrolyte has a suitable viscosity, which is beneficial to improving the mobility of lithium ions.

[0029] According to some embodiments of the present application, the additives also include auxiliary additives. In some embodiments, the auxiliary additives include at least one of vinylene carbonate, fluoroethylene carbonate, methylene disulfonate, vinyl sulfate, 1,3-propane sultone, and propenyl-1,3-sultone. The selection of the above auxiliary additives can further contribute to the formation of the SEI film on the negative electrode side; in other embodiments, the content of the auxiliary additives in the electrolyte is 0.5-5wt%, such as 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, etc.

[0030] In another aspect of the present application, the present application provides a lithium-ion battery. According to an embodiment of the present application, the lithium-ion battery comprises a positive electrode, a negative electrode, a separator and the electrolyte described above. As a result, the lithium-ion battery has better battery cycle stability and storage and safety performance. It can be understood by those skilled in the art that the lithium-ion battery has all the features and advantages of the electrolyte described above, and no further elaboration is given here.

[0031] According to some embodiments of the present application, the positive electrode includes a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the current collector.

[0032] In some embodiments, the positive electrode current collector may be aluminum foil.

[0033] In some embodiments, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent, wherein, as an example, the positive electrode active material includes one or more combinations of a lithiated transition metal phosphate having an olivine structure, a lithium ion embedded transition metal oxide having a layered structure, and a lithiated transition metal mixed oxide having a spinel structure, and further, the lithiated transition metal phosphate includes but is not limited to lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate; the lithium transition metal oxide includes but is not limited to lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide. As an example, the binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, and polyvinyl alcohol. As an example, the conductive agent may include at least one of Super P, graphene, acetylene black, conductive carbon black, Ketjen black, and carbon nanotubes.

[0034] In some embodiments, in the positive electrode active material layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (94-98.5):(0.5-3):(1-3).

[0035] According to some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the current collector.

[0036] In some embodiments, copper foil is used as the negative electrode current collector.

[0037] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite materials, and silicon-oxygen-carbon materials; the conductive agent includes at least one of Super P, graphene, acetylene black, conductive carbon black, Ketjen black, and carbon nanotubes; and the binder includes at least one of styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, and sodium alginate.

[0038] In some embodiments, in the negative electrode active material layer, the ratio of the negative electrode active material, the conductive agent, and the binder is (94-98.5):(0.5-2.5):(1-3.5).

[0039] According to some embodiments of the present application, the diaphragm is selected from any one of polyethylene, polypropylene, and a surface-modified composite diaphragm.

[0040] In another aspect of the present application, the present application provides an electric device. According to an embodiment of the present application, the electric device includes the lithium-ion battery described above. Thus, the electric device has a longer battery life and safety performance.

[0041] According to some embodiments of the present application, electrical equipment may include but is not limited to mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains and other equipment.

[0042] Example

[0043] Example 1

[0044] Preparation of electrolyte:

[0045] Select Ca(TFSI)2 as the calcium salt additive for the electrolyte; select ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate as the organic solvent, and the water content of the solvent is less than 10ppm. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed in a mass ratio of 3:5:2 to obtain an organic solvent. Slowly add lithium hexafluorophosphate to the above organic solvent and stir well to obtain a 1 mol / L organic electrolyte. Based on the total weight of the electrolyte, add 100ppm of Ca 2+ (Ca 2+ Derived from calcium salt additive). Based on the total weight of the electrolyte, 2wt% of vinylene carbonate is added as an auxiliary additive.

[0046] Lithium-ion battery manufacturing includes the following steps:

[0047] (1) Positive electrode preparation: Using N-methylpyrrolidone (NMP) as solvent, lithium iron phosphate (positive electrode active material), binder (PVDF) and conductive agent (Super P) are mixed evenly at a mass ratio of 95:2.5:2.5 to prepare positive electrode slurry. Aluminum foil with a thickness of 13μm is selected as the current collector. After the prepared positive electrode slurry is coated on both sides of the aluminum foil, the final positive electrode sheet is obtained through drying, rolling, slitting and die cutting steps. The specific parameters of the positive electrode sheet are: double-sided coating surface density is 340g / m 2 , compacted density is 2.40g / cm 3 .

[0048] (2) Negative electrode preparation: Using deionized water as solvent, mix artificial graphite (negative electrode active material), binder (SBR), thickener (CMC) and conductive agent (Super P) in a mass ratio of 95:1.4:1.6:2 to form negative electrode slurry. Use copper foil with a thickness of 6μm as the current collector, coat the prepared negative electrode slurry on both sides of the aluminum foil, and then go through drying, rolling, slitting and die cutting steps to obtain the final negative electrode sheet. The specific parameters of the negative electrode sheet are: double-sided coating surface density is 165g / m 2 , compacted density is 1.35g / cm 3 .

[0049] (3) Select a PP separator, stack the positive electrode sheet, negative electrode sheet and separator in a conventional manner to obtain a dry cell, and bake at 95°C until the moisture content is less than 100 ppm. Then inject and package the electrolyte prepared above, and after aging, formation, aging and capacity separation processes, a lithium secondary battery is produced.

[0050] The aging process is to stand at 45°C for 24 hours to allow the electrolyte to fully infiltrate the electrode.

[0051] The formation process is: 0.05C charging for 4 hours, and 0.2C charging for 1.5 hours;

[0052] The aging process is: standing at 25°C for 48 hours to further stabilize the SEI film on the negative electrode side;

[0053] The capacity division process is: 0.5C constant current and constant voltage charging to 3.65V, the cut-off current is 0.02C, standby for 10 minutes, 0.5C discharge to 2V, and the discharge capacity is used as the nominal capacity of the battery for subsequent testing.

[0054] Example 2

[0055] Preparation of electrolyte:

[0056] Select Ca(TFSI)2 as the calcium salt additive for the electrolyte; select ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate as the organic solvent, and the water content of the solvent is less than 10ppm. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed in a mass ratio of 3:5:2 to obtain an organic solvent. Slowly add lithium hexafluorophosphate to the above organic solvent and stir well to obtain a 1 mol / L organic electrolyte. Based on the total weight of the electrolyte, add 800ppm of Ca 2+ (Ca 2+ Based on the total weight of the electrolyte, 2% of vinylene carbonate was added as the second additive.

[0057] The same battery manufacturing steps as in Example 1 were adopted, and the electrolyte prepared in Example 2 was injected to obtain the battery of Example 2 for subsequent testing.

[0058] Example 3

[0059] Preparation of electrolyte:

[0060] Ca(TFSI)2 was selected as the calcium salt additive for the electrolyte. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate were selected as the organic solvents. The water content of the solvents was less than 10 ppm. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate were mixed in a mass ratio of 3:5:2 to obtain an organic solvent. Lithium hexafluorophosphate was slowly added to the organic solvent and stirred thoroughly to obtain a 1 mol / L organic electrolyte. Based on the total weight of the electrolyte, 50 ppm of Ca(TFSI)2 was added. 2+ (Ca 2+ Based on the total weight of the electrolyte, 2% of vinylene carbonate was added as the second additive.

[0061] The same battery manufacturing steps as in Example 1 were adopted, and the electrolyte prepared in Example 2 was injected to obtain the battery of Example 2 for subsequent testing.

[0062] Example 4

[0063] Preparation of electrolyte:

[0064] Select Ca(TFSI)2 as the calcium salt additive for the electrolyte; select ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate as the organic solvent, and the water content of the solvent is less than 10ppm. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed in a mass ratio of 3:5:2 to obtain an organic solvent. Slowly add lithium hexafluorophosphate to the above organic solvent and stir well to obtain a 1 mol / L organic electrolyte. Based on the total weight of the electrolyte, add 300ppm of Ca 2+ (Ca 2+ Based on the total weight of the electrolyte, 2% of vinylene carbonate was added as the second additive.

[0065] The same battery manufacturing steps as in Example 1 were adopted, and the electrolyte prepared in Example 2 was injected to obtain the battery of Example 2 for subsequent testing.

[0066] Example 5

[0067] Preparation of electrolyte:

[0068] Select Ca(TFSI)2 as the calcium salt additive for the electrolyte; select ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate as the organic solvent, and the water content of the solvent is less than 10ppm. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed in a mass ratio of 3:5:2 to obtain an organic solvent. Slowly add lithium hexafluorophosphate to the above organic solvent and stir well to obtain a 1 mol / L organic electrolyte. Based on the total weight of the electrolyte, add 500ppm of Ca 2+ (Ca 2+ Based on the total weight of the electrolyte, 2% of vinylene carbonate was added as the second additive.

[0069] The same battery manufacturing steps as in Example 1 were adopted, and the electrolyte prepared in Example 2 was injected to obtain the battery of Example 2 for subsequent testing.

[0070] Example 6

[0071] Preparation of electrolyte:

[0072] Calcium bis(trifluoromethanesulfonyl imide) (Ca(TFSI)2) was selected as the calcium salt additive for the electrolyte. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate were selected as the organic solvents. The water content of the solvents was less than 10 ppm. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate were mixed in a mass ratio of 3:5:2 to obtain an organic solvent. Lithium hexafluorophosphate was slowly added to the organic solvent and stirred thoroughly to obtain a 1 mol / L organic electrolyte. Based on the total weight of the electrolyte, 40 ppm of Ca(TFSI)2 was added. 2+ (Ca 2+ Based on the total weight of the electrolyte, 2% of vinylene carbonate was added as the second additive.

[0073] The same battery manufacturing steps as in Example 1 were adopted, and the electrolyte prepared in Example 2 was injected to obtain the battery of Example 2 for subsequent testing.

[0074] Example 7

[0075] Preparation of electrolyte:

[0076] Select Ca(TFSI)2 as the calcium salt additive for the electrolyte; select ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate as the organic solvent, and the water content of the solvent is less than 10ppm. Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed in a mass ratio of 3:5:2 to obtain an organic solvent. Slowly add lithium hexafluorophosphate to the above organic solvent and stir well to obtain a 1 mol / L organic electrolyte. Based on the total weight of the electrolyte, add 900ppm of Ca 2+ (Ca 2+ Based on the total weight of the electrolyte, 2% of vinylene carbonate was added as the second additive.

[0077] The same battery manufacturing steps as in Example 1 were adopted, and the electrolyte prepared in Example 2 was injected to obtain the battery of Example 2 for subsequent testing.

[0078] Example 8

[0079] The difference from Example 1 is that the calcium salt additive is calcium bis(fluorosulfonyl)imide.

[0080] Example 9

[0081] The difference from Example 1 is that the calcium salt additive is calcium trifluoromethanesulfonate.

[0082] Example 10

[0083] The difference from Example 1 is that the calcium salt additive is calcium hexafluorophosphate.

[0084] Comparative Example 1

[0085] Preparation of electrolyte: Ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed in a mass ratio of 3:5:2 to obtain an organic solvent. Lithium hexafluorophosphate is slowly added to the organic solvent and stirred thoroughly to obtain a 1 mol / L organic electrolyte. Based on the total weight of the electrolyte, 2% vinylene carbonate is added as an additive.

[0086] The same battery manufacturing steps as in the embodiment were adopted, and the electrolyte prepared in this comparative example was injected to obtain a comparative example battery for subsequent testing.

[0087] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to normal temperature cycle test, high temperature storage test and safety test. The specific test conditions and test results are as follows:

[0088] Normal temperature cycle test

[0089] In a 45℃ constant temperature test cabinet, the lithium-ion battery was subjected to a 0.5CP / 0.5CP constant power charge / discharge test, with a test voltage range of 2.0-3.65V, and a 10-minute rest period between each charge and discharge. The first cycle discharge capacity of the lithium-ion battery is recorded as C0, and the nth cycle discharge capacity is recorded as C n. , calculate the capacity retention rate = (C n / C0)×100%.

[0090] The test results of the capacity retention rate of the lithium ion batteries in Examples 1 to 10 and Comparative Example 1 at room temperature can be found in Table 1, wherein the cycle curves of the lithium ion batteries in Examples 1, 2 and Comparative Example 1 at room temperature can be found in Table 1. Figure 1 .

[0091] Table 1

[0092] Calcium salt additives <![CDATA[Ca 2+ Add Amount]]> Capacity retention after 350 cycles Example 1 Calcium bis(trifluoromethanesulfonimide) 100ppm 89.30％ Example 2 Calcium bis(trifluoromethanesulfonimide) 800ppm 87.71％ Example 3 Calcium bis(trifluoromethanesulfonimide) 50ppm 88.09％ Example 4 Calcium bis(trifluoromethanesulfonimide) 300ppm 87.92％ Example 5 Calcium bis(trifluoromethanesulfonimide) 500ppm 87.84％ Example 6 Calcium bis(trifluoromethanesulfonimide) 40ppm 86.81％ Example 7 Calcium bis(trifluoromethanesulfonimide) 900ppm 86.45％ Example 8 Calcium bis(fluorosulfonyl)imide 100ppm 89.21％ Example 9 Calcium trifluoromethanesulfonate 100ppm 89.16％ Example 10 Calcium hexafluorophosphate 100ppm 89.18％ Comparative Example 1 none 0 86.73％

[0093] Depend on Figure 1 It can be seen from Table 1 that the addition amount of calcium salt in the electrolyte of the lithium ion battery of the present application has better cycle performance within 100-800ppm, with 100ppm being the best. Compared with Comparative Example 1, the capacity retention rate of the lithium ion battery in Example 1 can be increased by 2.6% after 350 cycles at room temperature. It can be seen from Examples 6 and 7 that the improvement effect is relatively poor when the content of calcium salt additive is too little, and excessive calcium ions may deteriorate the cycle performance of the battery when the content of calcium salt additive is too much.

[0094] High temperature storage test

[0095] The lithium-ion battery was subjected to a 0.5CP / 0.5CP constant power charge / discharge test, with a test voltage range of 2.0-3.65V and a charge / discharge time interval of 10min. The discharge capacity C0 and full charge thickness d0 before storage were recorded. After 30 days of storage in a 45°C constant temperature box, the lithium-ion battery was taken out and left to stand for 2 hours to record the cooling thickness d1 of the lithium-ion battery. The discharge capacity C1 was recorded for 0.5CP discharge, and the discharge capacity of the third cycle of 0.5CP charge and discharge was recorded as C2. The capacity remaining rate = C1 / C0×100%, and the capacity recovery rate = C2 / C0×100% were calculated.

[0096] The test data of the lithium-ion batteries in Examples 1 to 10 and Comparative Example 1 stored at high temperature for 30 days can be seen in Table 2.

[0097] Table 2

[0098]

[0099] The data in Table 2 show that compared with Comparative Example 1, the storage performance of the lithium-ion battery in the embodiment is also improved. After being stored at 45 degrees for 30 days, the thickness change rate of the battery is reduced, and the remaining capacity rate and recovery rate are increased.

[0100] Security Testing

[0101] Accelerating calorimetry (ARC) is used to test the thermal runaway behavior of lithium-ion batteries. After the lithium-ion battery is fully charged, it is placed in an insulated cavity and heated in steps of 5°C-10°C. After the sample temperature reaches stability, search for self-heating. If so, track the sample temperature change until the sample reaches a thermal runaway state. If there is no self-heating phenomenon, continue step heating until self-heating phenomenon occurs, and track the sample temperature change until the sample reaches a thermal runaway state.

[0102] The accelerated calorimetry (ARC) test results (battery self-heating starting temperature, thermal runaway starting temperature and thermal runaway maximum temperature) of the lithium ion batteries in Examples 1 to 10 and Comparative Example 1 can be found in Table 3, wherein the accelerated calorimetry (ARC) test data of the lithium ion batteries in Example 1, Example 2 and Comparative Example 1 can be found in Figure 2 .

[0103] Table 3

[0104]

[0105] From Table 3 and Figure 2 It can be seen from the test structure that the self-heating starting temperature and thermal runaway starting temperature of the lithium-ion battery in the embodiment are increased compared with the battery in comparative example 1, and the maximum thermal runaway temperature is reduced, thereby reducing the thermal runaway risk of the lithium-ion battery. That is, the lithium-ion battery of the present application has higher safety performance.

[0106] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0107] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. An electrolyte, characterized in that: The invention comprises a lithium salt, an organic solvent and an additive, wherein the additive comprises a calcium salt.

2. The electrolyte according to claim 1, characterized in that The anions in the calcium salt include fluoride-containing anions.

3. The electrolyte according to claim 2, characterized in that The calcium salt includes at least one of calcium bis(trifluoromethanesulfonyl imide), calcium bis(fluorosulfonyl)imide, calcium trifluoromethanesulfonate and calcium hexafluorophosphate.

4. The electrolyte according to any one of claims 1 to 3, characterized in that Based on the total weight of the electrolyte, the mass concentration of calcium ions in the electrolyte is 50-800 ppm.

5. The electrolyte according to claim 4, characterized in that The mass concentration of calcium ions in the electrolyte is 50-100 ppm based on the total weight of the electrolyte.

6. The electrolyte according to any one of claims 1 to 3, characterized in that The lithium salt satisfies at least one of the following conditions: The concentration of the lithium salt in the electrolyte is 0.6-1.5 mol / L; The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, lithium difluorobis(oxalato)phosphate and lithium tetrafluoroborate.

7. The electrolyte according to any one of claims 1 to 3, characterized in that The organic solvent includes one or more of a carbonate solvent and / or a carboxylate solvent, and the organic solvent satisfies at least one of the following conditions: The carbonate solvent includes cyclic carbonate and / or chain carbonate, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate and trifluoropropylene carbonate, and the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate; The mass ratio of the cyclic carbonate to the linear carbonate is (2-5):(5-8); The carboxylate solvent includes at least one of ethyl acetate, methyl acetate and ethyl propionate; The content of the organic solvent in the electrolyte is 70-90 wt %.

8. The electrolyte according to any one of claims 1 to 3, characterized in that The additives also include auxiliary additives, wherein: The auxiliary additive includes at least one of vinylene carbonate, fluoroethylene carbonate, methylene methanedisulfonate, vinyl sulfate, 1,3-propane sultone, and propenyl-1,3-sultone; And / or, the content of the auxiliary additive in the electrolyte is 0.5-5wt%.

9. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 8.

10. An electrical device, characterized in that: Includes the lithium ion battery as claimed in claim 9.

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