Electrolyte, battery and electric system

Abstract

The present application relates to the field of batteries, and specifically discloses an electrolyte, a battery, and an electric system. The electrolyte comprises an electrolyte salt, an organic solvent, and additives. The additives comprise a first additive and a second additive, the first additive comprising at least one of compounds represented by formula I, and the second additive comprising at least one of compounds represented by formula II, wherein R1, R2, R3 and R4 are each independently selected from at least one of hydrogen, fluorine, vinyl, and methyl, R5 and R6 are each independently selected from at least one of methyl, ethyl, propyl, vinyl, propenyl, and (triethoxysilyl)propyl, and n is an integer from 3 to 6.

Description

Electrolyte, battery and power utilization system

[0001] Priority information

[0002] The present application claims priority to and the benefit of Chinese Patent Application No. 2024110881146, filed on August 8, 2024, entitled "Electrolyte, battery and power utilization system", the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application belongs to the field of batteries, and specifically relates to an electrolyte, a battery and a power utilization system. BACKGROUND

[0004] With the development of the energy storage industry, lithium ion battery technology is continuously developed and widely applied in the fields of electric vehicles, mobile devices and energy storage systems. However, the lithium ion cell has a problem of electrolyte instability under high temperature environment, which not only affects the performance and life of the cell, but also may cause safety hazards. However, with the increasing energy density and the increasing integration of cells, it is more and more difficult to maintain the safety line for the current large-scale energy storage batteries.

[0005] In order to improve the energy density of energy storage cells and reduce the manufacturing cost, higher electrode coating and higher compaction density are generally used, and the single cell capacity is also increasing. On the basis of the same active material capacity, the use amount of current collector and electrolyte needs to be reduced. These strategies not only bring high energy density and reduce cost, but also lead to the increasingly prominent stability problem of the cell under high temperature conditions. In large-capacity cells, the cell generates a lot of heat and has poor heat dissipation. During operation, heat is easily accumulated, which leads to the decomposition and evaporation of electrolyte, resulting in the increase of internal pressure of the cell, and even may cause the cell to catch fire, explode, etc. SUMMARY

[0006] The present application aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present application is to provide an electrolyte, a battery and a power utilization system. The present application simultaneously adds a first additive and a second additive in the electrolyte, which can effectively improve the high-temperature stability and high-temperature cycle performance of the battery, thereby effectively improving the cycle life and safety performance of the battery under high temperature environment.

[0007] The first aspect of the present application provides an electrolyte. According to the embodiments of the present application, the electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a first additive and a second additive, the first additive comprises at least one of the compounds as shown in formula I, and the second additive comprises at least one of the compounds as shown in formula II;

[0008] wherein R1, R2, R3and R4are each independently selected from at least one of hydrogen, fluorine, vinyl, methyl, R5, R6are each independently selected from at least one of methyl, ethyl, propyl, vinyl, propenyl, (triethoxysilyl)propyl, and n is an integer from 3 to 6.

[0009] According to the electrolyte of the above-mentioned embodiments of the present application, the first additive and the second additive are simultaneously added in the electrolyte. During the battery cycle process, the first additive can effectively improve the high-temperature stability of the battery cell, and the second additive can effectively improve the ionic conductivity of the SEI film at the interface, thereby reducing the charge transfer impedance of the battery cell. In addition, the combined use of the first additive and the second additive can increase the inorganic components in the SEI interface layer, which are mainly lithium sulfide and lithium sulfonate. The interface layer rich in inorganic matter can comprehensively improve the high-temperature stability of sulfonate and the rapid active ion (such as lithium ion) transmission characteristics of sulfide, effectively improving the high-temperature stability and high-temperature cycle performance of the battery, thereby effectively improving the cycle life and safety performance of the battery in a high-temperature environment.

[0010] The second aspect of the present application proposes a battery. According to the embodiments of the present application, the battery comprises the electrolyte of the first aspect. Therefore, the high-temperature stability and high-temperature cycle performance of the battery are effectively improved, thereby effectively improving the cycle life and safety performance of the battery in a high-temperature environment.

[0011] The third aspect of the present application proposes a power utilization system. According to the embodiments of the present application, the power utilization system comprises: a power utilization device, and an energy storage device for supplying power to the power utilization device, wherein the energy storage device comprises the electrolyte of the above-mentioned embodiments or the lithium ion battery of the above-mentioned embodiments. Therefore, the energy storage device of the power utilization system has excellent high-temperature cycle performance, service life and safety performance. It should be noted that the features and advantages described above for the battery also apply to the power utilization device, which will not be described here.

[0012] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION

[0013] The embodiments of the present application are described in detail below, which are intended to explain the present application and cannot be understood as a limitation of the present application.

[0014] The first aspect of the present application provides an electrolyte. According to the embodiments of the present application, the electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a first additive and a second additive, the electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a first additive and a second additive, the first additive comprises at least one of the compounds as shown in Formula I, and the second additive comprises at least one of the compounds as shown in Formula II.

[0015] wherein R1, R2, R3 and R4 are each independently selected from at least one of hydrogen, fluorine, vinyl, methyl, R5 and R6 are each independently selected from at least one of methyl, ethyl, propyl, vinyl, propenyl, (triethoxysilyl)propyl, n is an integer of 3-6, and n represents the number of S.

[0016] The beneficial effects of the electrolyte proposed in the present application are described in detail as follows:

[0017] In order to solve the problem of electrolyte failure in high temperature environment, the first additive and the second additive are simultaneously added to the electrolyte. In the battery cycle process, the first additive can generate a flexible polysulfonate SEI film on the negative electrode surface through reduction reaction. The polysulfonate SEI film has excellent high temperature stability, thereby effectively improving the chemical stability of the interface layer. However, the ion conductivity of the polysulfonate SEI film at the interface is low, which leads to rapid increase of the initial impedance of the battery cell and causes degradation of the normal temperature performance. In order to solve this problem, the second additive is also added to the electrolyte. The S-S bond of the second additive is homolytically cleaved during the reduction process, and the polysulfide anion produced has a strong interaction with the active ion (such as lithium ion), and at the same time, has a low solubility in the electrolyte, thereby being deposited on the graphite surface. Therefore, the second additive can preferentially adsorb on the damaged interface and promote the desolvation process of the active ion (such as lithium ion) at the interface, thereby improving the ion conductivity of the SEI film at the interface and reducing the charge transfer impedance of the battery cell. In addition, the first additive and the second additive are used in combination. The polysulfide formed by the homolytic cleavage of the S-S bond of the second additive can increase the concentration of the active ion (such as lithium ion) at the interface, thereby promoting the degradation of the cyclic sulfate of the first additive, and thus increasing the inorganic components, mainly lithium sulfide and lithium sulfonate, in the SEI interface layer. The interface layer rich in inorganic matter can combine the high temperature stability of sulfonate and the rapid active ion (such as lithium ion) transport characteristics of sulfide, effectively improving the high temperature stability and high temperature cycle performance of the battery, thereby effectively improving the cycle life and safety performance of the battery in high temperature environment.

[0018] In embodiments of the present application, n is an integer from 3 to 6, the inventors have found that n should not be too large, because when the S-S bond in the long polysulfide chain homolytically cleaves, more short-chain lithium sulfide products of Li2S4 to Li4S4 are produced, which are slightly soluble in the electrolyte and shuttle between the positive and negative electrodes, which can significantly deteriorate the electrical performance. Preferably, n is 3 or 4.

[0019] In embodiments of the present application, R5, R6 are each independently selected from at least one of methyl, ethyl, propyl, ethenyl, propenyl, (triethoxysilyl)propyl, preferably R5 and R6 are the same.

[0020] According to some specific embodiments of the present application, the first additive comprises at least one of the following compounds:

[0021] Thus, the first additive of the above structure can generate a flexible polysulfonate SEI film on the surface of the negative electrode by reduction reaction, thereby further effectively improving the chemical stability of the interface layer, and the first additive of the above structure can be effectively used in combination with the second additive, further effectively improving the high-temperature stability and high-temperature cycle performance of the battery.

[0022] According to still some specific embodiments of the present application, the second additive comprises at least one of the following compounds:

[0023] Thus, the second additive of the above structure can generate polysulfide anions by homolytic cleavage of S-S bonds during reduction, which have a strong interaction with active ions (such as lithium ions), and can further promote the desolvation process of active ions (such as lithium ions) at the interface, improve the ionic conductivity of the SEI film at the interface, and thus reduce the charge transfer resistance of the battery. And the second additive of the above structure can be effectively used in combination with the first additive, further effectively improving the high-temperature stability and high-temperature cycle performance of the battery.

[0024] The first additive as shown in formula I-1 and the second additive as shown in formula II-2 will undergo the following reactions during battery cycling:

[0025] According to some specific embodiments of the present application, the mass percentage of the first additive in the electrolyte is a, which satisfies 0.2%≤a≤5%, and can be 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. By limiting the mass percentage of the first additive in the electrolyte within the above range, the chemical stability of the interface layer can be further improved, and meanwhile, the first additive can be used in combination with the second additive, thereby further improving the high-temperature stability and high-temperature cycle performance of the battery.

[0026] According to some specific embodiments of the present application, the mass percentage of the second additive in the electrolyte is b, which satisfies 0.2%≤b≤5%, and can be 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. By limiting the mass percentage of the second additive in the electrolyte within the above range, the desolvation process of active ions (e.g., lithium ions) at the interface can be further promoted, the ionic conductivity of the SEI film at the interface can be improved, thereby reducing the charge transfer resistance of the battery cell, and meanwhile, the second additive can be used in combination with the first additive, thereby further improving the high-temperature stability and high-temperature cycle performance of the battery.

[0027] According to some specific embodiments of the present application, the ratio of a to b is 1:(0.5-1.5), and can be 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, etc. By limiting the ratio of a to b within the above range, the first additive and the second additive can be used in combination, the chemical stability of the interface layer can be improved, the ionic conductivity of the SEI film at the interface can be improved, thereby reducing the charge transfer resistance of the battery cell, and meanwhile, the high-temperature stability and high-temperature cycle performance of the battery can be further improved.

[0028] According to some specific embodiments of the present application, the additive comprises a third additive, and the third additive comprises a fluorine-containing additive. After the fluorine-containing additive is introduced into the SEI layer in an appropriate amount, the cycle performance of the battery cell is further improved. This is because the fluorine-containing additive can generate an interface layer rich in lithium fluoride (lithium fluoride has high voltage stability and thermal stability) at the interface in the early stage of film formation, and the interface layer has good electrochemical stability, thereby further improving the high-temperature cycle performance and high-temperature storage performance of the battery cell.

[0029] In the embodiments of the present application, the specific type of the above-mentioned fluorine-containing additive is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some preferred embodiments, the third additive includes at least one of fluoroethylene carbonate (FEC), 2-fluoro-pyridine (2FP), and 2-fluoro-5-amino-pyridine (5A-2FP). Preferably, 2-fluoro-5-amino-pyridine (5A-2FP) is used. The 5A-2FP additive can improve the content of interfacial lithium fluoride and thus improve the effect, because the defluorination reaction is promoted by the aminoization at the para position of fluorine.

[0030] According to still some specific embodiments of the present application, the mass percentage of the third additive in the electrolyte is c, which satisfies 0.2%≤c≤3%. For example, c can be 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. By limiting the mass percentage of the third additive in the electrolyte to the above range, the cycle performance and high-temperature storage performance of the battery cell can be further improved.

[0031] In the embodiments of the present application, the specific type of the above-mentioned electrolyte salt is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some specific examples, the above-mentioned electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonylimide (LiFSI), lithium difluorophosphate (LiDFP), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Preferably, at least one of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) is used.

[0032] According to still some specific embodiments of the present application, the mass percentage of the electrolyte salt in the electrolyte is 5% to 20%, which can be 5%, 8%, 10%, 12%, 15%, 17%, 20%, etc. Preferably, the mass percentage is 6% to 15%.

[0033] In the embodiments of the present application, the above-mentioned organic solvent is a non-aqueous organic solvent. The non-aqueous organic solvent is a main component of the electrolyte and should have a high solubility of the electrolyte salt, so that the electrolyte has a high ionic conductivity. The specific type of the non-aqueous organic solvent is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some preferred embodiments, the above-mentioned organic solvent includes a cyclic carbonate and a chain carbonate. The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate, and the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. More preferably, the above-mentioned organic solvent includes a mixed solvent of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate.

[0034] The second aspect of the present application provides a battery. According to embodiments of the present application, the battery comprises the electrolyte of the first aspect. In this way, the high-temperature stability and the high-temperature cycle performance of the battery are effectively improved, thereby effectively improving the cycle life and safety performance of the battery in a high-temperature environment.

[0035] In embodiments of the present application, the above-mentioned electrolyte can be used in both lithium-ion batteries and sodium-ion batteries. Hereinafter, lithium-ion batteries are taken as examples for illustration:

[0036] Generally, a lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, lithium ions are inserted into and extracted from the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive electrode and the negative electrode, while allowing lithium ions to pass through.

[0037] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material. The specific type of the positive electrode active material is not particularly limited, and as some specific embodiments, the positive electrode active material comprises at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobaltate, lithium nickelate, lithium cobalt phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium manganate, binary material, and ternary material.

[0038] In some embodiments of the present application, the positive electrode current collector can comprise a metal foil or a composite positive electrode current collector. For example, the metal foil can be an aluminum foil. The composite positive electrode current collector can comprise a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer, for example, the composite negative electrode current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. base material).

[0039] In some embodiments of the present application, the positive electrode active material layer can also optionally comprise a conductive agent. As an example, the conductive agent can comprise at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0040] In some embodiments of the present application, the positive electrode active material layer can also optionally comprise a binder. As an example, the binder can comprise at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0041] In some embodiments of the present application, the positive electrode sheet can be prepared by dispersing the above-mentioned components (e.g., positive electrode active material, conductive agent, binder) for preparing the positive electrode sheet in an organic solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the same to drying, cold pressing, and the like to obtain the positive electrode sheet.

[0042] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material.

[0043] In some embodiments of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0044] In some embodiments of the present application, the negative electrode active material can be a negative electrode active material known in the art. As an example, the negative electrode active material can include at least one of graphite, soft carbon, hard carbon, silicon-based material, tin-based material, etc. The silicon-based material can include at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can include at least one of elemental tin, tin oxide compound, and tin alloy.

[0045] In some embodiments of the present application, the negative electrode active material layer can further optionally include a binder. The binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0046] In some embodiments of the present application, the negative electrode active material layer can further optionally include a conductive agent. The conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0047] In some embodiments of the present application, the negative electrode active material layer can further optionally include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0048] In some embodiments of the present application, the negative electrode sheet can be prepared by dispersing the above-mentioned components (e.g., negative electrode active material, conductive agent, binder, and any other components) for preparing the negative electrode sheet in an organic solvent (e.g., deionized water) to form a negative electrode slurry, coating the negative electrode slurry on a negative electrode current collector, and then drying, cold-pressing, or the like to obtain the negative electrode sheet.

[0049] The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used. In some embodiments of the present application, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0050] The lithium ion battery of the present application can include a battery monomer form, a battery module form, and a battery pack form. In some embodiments, the battery monomer can be assembled into a battery module, and the number of battery monomers contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module. In some embodiments, the battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0051] The third aspect of the present application provides a power utilization system. According to the embodiments of the present application, the power utilization system includes: a power utilization device, and an energy storage device, the energy storage device supplies power for the power utilization device, and the energy storage device includes the electrolyte of the above embodiments or the lithium ion battery of the above embodiments. Therefore, the energy storage device of the power utilization system has excellent high-temperature cycle performance, service life, and safety performance. It should be noted that the features and advantages described above for the battery also apply to the power utilization device, which will not be described here.

[0052] The above-mentioned energy storage device can be used as a power source for a power utilization device, or as an energy storage unit for a power utilization device. The above-mentioned power utilization device can include, but is not limited to, portable electronic devices such as mobile phones, tablet computers, notebook computers, desktop computers, smart bracelets, smart watches, e-readers, game consoles, etc. It can also include, but is not limited to, vehicles such as cars, trucks, cars, trucks, bullet trains, high-speed rails, electric automatic vehicles, etc. In addition, it can also be various household appliances, such as refrigerators, electric lamps, air conditioners, etc.

[0053] In addition, the energy storage device of the present application can include at least one of a power generation side power storage device for a power system, a power distribution side power storage device (e.g., an electrochemical energy storage device) for a power system, and a user side power storage device for a power system.

[0054] The embodiments of the present application are described in detail below, it should be noted that the embodiments described below are exemplary, only for explaining the present application, and can not be understood as limiting the present application. In addition, if not specifically stated, all reagents used in the following examples are commercially available or can be synthesized according to the methods described herein or known to those skilled in the art, and the reaction conditions not listed are also readily available to those skilled in the art.

[0055] Example 1

[0056] 1) Preparation of positive electrode sheet

[0057] The positive electrode active material lithium iron phosphate, conductive carbon black (SP), and the binder polyvinylidene fluoride (PVDF) were dispersed in the organic solvent N-methyl pyrrolidone (NMP) and mixed uniformly to obtain a positive electrode slurry, wherein the mass ratio of lithium iron phosphate, conductive carbon black, and PVDF was 97:0.7:2.3, and the solid content of the positive electrode slurry was 50wt%. The positive electrode slurry was coated on the positive electrode current collector aluminum foil, and the coating weight per unit area (1540.25mm 2 ) of the positive electrode slurry was 330mg. After drying, cold pressing, slitting, and cutting, the positive electrode sheet was obtained.

[0058] 2) Preparation of negative electrode sheet

[0059] The negative electrode active material artificial graphite, conductive carbon SP, thickening agent CMC, and binder SBR were dispersed in deionized water according to the mass ratio of 96.5:0.5:1:2 and mixed uniformly to obtain a negative electrode slurry, and the solid content of the negative electrode slurry was 50wt%. The negative electrode slurry was coated on the negative electrode current collector copper foil, and the coating weight per unit area (1540.25mm 2 ) of the negative electrode slurry was 144mg. After drying, cold pressing, slitting, and cutting, the negative electrode sheet was obtained.

[0060] 3) Preparation of electrolyte

[0061] In an argon atmosphere glove box with a water content of ≤1ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed according to the mass ratio of 2:1:2, and then dry lithium hexafluorophosphate was dissolved in the organic solvent, and the mass fraction of lithium hexafluorophosphate in the electrolyte was 13%. After stirring the lithium hexafluorophosphate to completely dissolve, the first additive as shown in formula I-3 and the second additive as shown in formula II-1 were added and mixed uniformly to obtain the electrolyte, wherein the mass fraction of the first additive as shown in formula I-3 in the electrolyte was 1%, and the mass fraction of the second additive as shown in formula II-1 in the electrolyte was 1%.

[0062] 4) Isolation film

[0063] The polyethylene film with a thickness of 16 microns is selected as the separator.

[0064] 5) Assembly of the battery

[0065] The prepared positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, so that the separator is in the middle of the positive and negative electrodes to separate the positive and negative electrode sheets. After winding, a bare cell is formed. After welding the tab, the bare cell is assembled into an outer package. After injecting the prepared electrolyte, the cell is packaged, rested, formed, shaped, capacity tested, etc. Finally, the lithium ion battery is prepared.

[0066] Example 2

[0067] The preparation method of this example is basically the same as that of example 1, and the only difference is that the additive in the electrolyte is:

[0068] The first additive shown as formula I-3 is replaced by the first additive shown as formula I-1.

[0069] Example 3

[0070] The preparation method of this example is basically the same as that of example 1, and the only difference is that the additive in the electrolyte is: the first additive shown as formula I-3 is replaced by the first additive shown as formula I-2.

[0071] Example 4

[0072] The preparation method of this example is basically the same as that of example 1, and the only difference is that the additive in the electrolyte is: the second additive shown as formula II-1 is replaced by the second additive shown as formula II-2.

[0073] Example 5

[0074] The preparation method of this example is basically the same as that of example 1, and the only difference is that the additive in the electrolyte is: the second additive shown as formula II-1 is replaced by the second additive shown as formula II-3.

[0075] Example 6

[0076] The preparation method of this example is basically the same as that of example 1, and the only difference is that the additive in the electrolyte is: the mass percentage of the first additive in the electrolyte is 0.2%.

[0077] Example 7

[0078] The preparation method of this example is basically the same as that of example 1, and the only difference is that the additive in the electrolyte is: the mass percentage of the first additive in the electrolyte is 1.5%.

[0079] Example 8

[0080] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte: the mass percentage of the first additive in the electrolyte is 2.5%.

[0081] Example 9

[0082] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte: the mass percentage of the first additive in the electrolyte is 3.5%.

[0083] Example 10

[0084] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte: the mass percentage of the first additive in the electrolyte is 5%.

[0085] Example 11

[0086] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte: the mass percentage of the second additive in the electrolyte is 0.2%.

[0087] Example 12

[0088] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte: the mass percentage of the second additive in the electrolyte is 1.5%.

[0089] Example 13

[0090] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte: the mass percentage of the second additive in the electrolyte is 2.5%.

[0091] Example 14

[0092] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte:

[0093] the mass percentage of the second additive in the electrolyte is 3.5%.

[0094] Example 15

[0095] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte:

[0096] the mass percentage of the second additive in the electrolyte is 5%.

[0097] Example 16

[0098] The preparation method of this example is basically the same as that of Example 1, with the only difference being the additive in the electrolyte:

[0099] The first additive accounts for 0.1% by mass in the electrolyte, and the second additive accounts for 0.1% by mass in the electrolyte.

[0100] Example 17

[0101] The preparation method of this example is basically the same as that of Example 1, except that the additives in the electrolyte are different:

[0102] The first additive accounts for 7% by mass in the electrolyte, and the second additive accounts for 7% by mass in the electrolyte.

[0103] Example 18

[0104] The preparation method of this example is basically the same as that of Example 1, except that the additives in the electrolyte are different:

[0105] Fluoroethylene carbonate (FEC) is also included, and the mass fraction of fluoroethylene carbonate (FEC) in the electrolyte is 0.2%.

[0106] Example 19

[0107] The preparation method of this example is basically the same as that of Example 18, except that the additives in the electrolyte are different:

[0108] Fluoroethylene carbonate (FEC) is also included, and the mass fraction of fluoroethylene carbonate (FEC) in the electrolyte is 1%.

[0109] Example 20

[0110] The preparation method of this example is basically the same as that of Example 18, except that the additives in the electrolyte are different:

[0111] Fluoroethylene carbonate (FEC) is also included, and the mass fraction of fluoroethylene carbonate (FEC) in the electrolyte is 2.5%.

[0112] Example 21

[0113] The preparation method of this example is basically the same as that of Example 1, except that the additives in the electrolyte are different:

[0114] 2-Fluoro-pyridine (2FP) is also included, and the mass fraction of 2-Fluoro-pyridine (2FP) in the electrolyte is 1%.

[0115] Example 22

[0116] The preparation method of this example is basically the same as that of Example 1, except that the additives in the electrolyte are different:

[0117] 2-fluoro-5-aminopyridine (5A-2FP) was also included, and the mass fraction of 2-fluoro-5-aminopyridine (5A-2FP) in the electrolyte was 1%.

[0118] Comparative Example 1

[0119] The preparation method of the present comparative example was basically the same as that of Example 1, except that the electrolyte did not contain the first additive as shown in Formula I-3 and the second additive as shown in Formula II-1.

[0120] Comparative Example 2

[0121] The preparation method of the present comparative example was basically the same as that of Example 1, except that the electrolyte did not contain the first additive as shown in Formula I-3 and the second additive as shown in Formula II-1.

[0122] The preparation method of the present comparative example was basically the same as that of Example 1, except that the electrolyte did not contain the first additive as shown in Formula I-3 and the second additive as shown in Formula II-1.

[0123] Comparative Example 3

[0124] The preparation method of the present comparative example was basically the same as that of Example 1, except that the electrolyte did not contain the first additive as shown in Formula I-3 and the second additive as shown in Formula II-1.

[0125] The preparation method of the present comparative example was basically the same as that of Example 1, except that the electrolyte did not contain the first additive as shown in Formula I-3 and the second additive as shown in Formula II-1.

[0126] The parameters of Examples 1-22 and Comparative Examples 1-3 are shown in Table 1.

[0127] Table 1

[0128] The 25℃ 500 cycle 1C capacity retention rate, 45℃ 500 cycle 1C capacity retention rate and 60℃ storage for 60 days volume expansion rate of the lithium ion batteries obtained from Examples 1-22 and Comparative Examples 1-3 were tested respectively, and the results are shown in Table 2.

[0129] The test method of 25℃ 500 cycle 1C capacity retention rate is as follows:

[0130] The lithium ion battery was subjected to charge-discharge cycle test on a charge-discharge instrument, the test temperature was 25℃, the cycle rate was 1C (i.e. the charge rate and discharge rate were both 1C), the charge voltage was 2.5V to 3.65V, and the capacity retention rate after cycle was calculated. The capacity retention rate after 25℃ cycle was calculated by the formula: capacity retention rate after 500th cycle = (discharge capacity after 500th cycle / discharge capacity of the first cycle) * 100%.

[0131] The test method of 45℃ 500 cycle 1C capacity retention rate is as follows:

[0132] The lithium ion battery is subjected to charge-discharge cycle test on a charge-discharge instrument, the test temperature is 45°C, the cycle rate is 1C (i.e. the charge rate and the discharge rate are both 1C), the charging voltage is 2.5V to 3.65V, and the capacity retention rate after cycling is calculated. The capacity retention rate calculation formula for 45°C cycling is: the capacity retention rate after the 500th cycle = (the discharge capacity after the 500th cycle / the discharge capacity of the first cycle) * 100%.

[0133] The test method for the volume expansion rate of 60°C storage for 60 days is as follows:

[0134] The temperature of the constant temperature box is adjusted to 25°C, and the cell is rested for 10 min, 0.33C constant current charging to 3.65V, and then 3.65V constant voltage charging to 0.05C cut-off, resting for 30 min, and testing the initial full charge state volume V0 of the cell; the temperature of the constant temperature box is adjusted to 60°C, and the cell is rested for 30 min, 0.33C constant current charging to 3.65V, and then rested for 1h, and the cell is cycled twice for power compensation, stored for 60 days, and the cell is cooled, and the full charge state volume V1 of the cell at this time is tested; then the volume expansion rate of the cell at 60°C storage for 60 days = (V1 / V0-1) * 100%.

[0135] Table 2

[0136] As can be seen from Table 2, compared with Comparative Examples 1-3, the 25°C 500 cycle 1C capacity retention rate and the 45°C 500 cycle 1C capacity retention rate of Examples 1-22 are obviously improved, and the 60°C storage for 60 days volume expansion rate of Examples 1-22 is obviously reduced, which shows that when the first additive and the second additive are simultaneously added to the electrolyte, the high-temperature protection effect on the cell is excellent, which is because the polysulfide compound (i.e. the second additive) has a higher reduction potential and static potential than the cyclic sulfate compound (i.e. the first additive), and the polysulfide can increase the interface lithium ion concentration, thereby promoting the degradation of the cyclic sulfate, and finally making the inorganic components in the SEI interface layer mainly lithium sulfide and lithium sulfonate more. At high temperature, the addition of polysulfide can make up for the rate-limiting process of the cyclic lithium sulfate on the interface, and at the same time, due to the strong dipole effect of lithium ions on the sulfonic acid group in the first additive, the ring-opening of the first additive can be promoted, and a more robust SEI layer can be induced, thereby ensuring the stable performance of the high temperature.

[0137] It can also be seen from Table 2 that compared with Example 16, the 500 cycle 1C capacity retention and the 45℃ 500 cycle 1C capacity retention of Examples 1, 6-15 are further improved, and the 60℃ storage for 60 days volume expansion rate of Examples 1, 6-15 is further reduced. Compared with Example 17, the 500 cycle 1C capacity retention and the 45℃ 500 cycle 1C capacity retention of Examples 1, 6-15 are further improved, and the 60℃ storage for 60 days volume expansion rate of Examples 1, 6-15 is further reduced. It can be seen that when the mass percentage of the first additive in the electrolyte is in the range of 0.2% to 5%, and the mass percentage of the second additive in the electrolyte is in the range of 0.2% to 5%, the high-temperature cycle performance and high-temperature storage performance of the lithium ion battery are relatively excellent.

[0138] Compared with Example 1, the 25℃ 500 cycle 1C capacity retention and the 45℃ 500 cycle 1C capacity retention of Examples 18-22 are further improved, and the 60℃ storage for 60 days volume expansion rate of Examples 18-22 is further reduced. It can be seen that by simultaneously adding the third additive in the electrolyte, the high-temperature cycle performance and high-temperature storage performance of the lithium ion battery can be further improved.

[0139] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0140] 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 limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. An electrolyte, wherein, comprising an electrolyte salt, an organic solvent, and additives, the additives comprising a first additive comprising at least one of the compounds of Formula I and a second additive comprising at least one of the compounds of Formula II; wherein R1, R2, R3 and R4 are each independently selected from at least one of hydrogen, fluorine, vinyl, methyl, R5 and R6 are each independently selected from at least one of methyl, ethyl, propyl, vinyl, propenyl, (triethoxysilyl)propyl, and n is an integer from 3 to 6.

2. The electrolyte of claim 1, wherein, R5 and R6 are the same.

3. The electrolyte of claim 1 or 2, wherein, n is 3 or 4.

4. The electrolyte according to any one of claims 1 to 3, wherein, The first additive includes at least one of the following compounds:

5. The electrolyte according to any one of claims 1 to 4, wherein, The second additive includes at least one of the following compounds:

6. The electrolyte according to any one of claims 1 to 5, wherein, The mass percentage of the first additive in the electrolyte is a, satisfying 0.2%≤a≤5%; And / or, the mass percentage of the second additive in the electrolyte is b, satisfying 0.2%≤b≤5%.

7. The electrolyte of claim 6, wherein, The ratio of a to b is 1:(0.5-1.5).

8. The electrolyte according to any one of claims 1 to 7, wherein, The additive comprises a third additive, the third additive comprising at least one of fluoro-vinylene carbonate, 2-fluoro-pyridine and 2-fluoro-5-amino pyridine.

9. The electrolyte of claim 8, wherein, The mass percentage of the third additive in the electrolyte is c, satisfying 0.2%≤c≤3%.

10. The electrolyte according to any one of claims 1 to 9, wherein, The mass percentage of the electrolyte salt in the electrolyte is 5%-20%; And / or, the electrolyte salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate and lithium bis(trifluoromethanesulfonyl)imide; And / or, the organic solvent comprises a cyclic carbonate and a chain carbonate.

11. A battery, wherein, The electrolyte of any one of claims 1-10.

12. An electric power utilization system wherein, The electrolyte of any one of claims 1-10. The electrolyte of any one of claims 1-10. The electrolyte of any one of claims 1-10. The electrolyte of any one of claims 1-10.

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