Electrolyte, battery, battery pack and electric equipment

Abstract

The invention provides an electrolyte, a battery, a battery pack and electric equipment. The electrolyte comprises a first additive and a second additive, the first additive comprises a compound shown as a formula I: # imgabs 0 #, and the second additive comprises a compound shown as a formula II: # imgabs 1 #. According to the electrolyte provided by the invention, the specific first additive and second additive are combined, so that the high-temperature cycle performance of the battery is effectively improved; and the high-temperature cycle performance of the battery can be effectively improved.

Description

Technical Field

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

[0002] In recent years, with the continuous development of renewable energy such as tidal energy and solar energy, energy storage systems, as a key technology affecting their development, have attracted more and more attention. Lithium-ion batteries, as green and environmentally friendly energy storage devices, have been widely used in energy storage fields such as the electronics market and new energy vehicles due to their outstanding advantages such as high energy density, long cycle life, safety and pollution-free, greatly improving human production and living standards.

[0003] Lithium iron phosphate (LIFP) has attracted widespread attention due to its outstanding advantages, including abundant resources, low price, high safety, long cycle life, and wide distribution. It is considered one of the most important cathode materials for lithium-ion batteries. However, LFP suffers from drawbacks, such as the tendency for metal to dissolve at high temperatures, which severely limits its capacity and capacity retention in extreme environments. As battery performance requirements in extreme environments continue to increase, the high-temperature performance of existing LFP batteries has become a major bottleneck restricting their further application. Summary of the Invention

[0004] The present invention provides an electrolyte, which can solve the problem of insufficient cycle life of batteries at high temperatures to a certain extent.

[0005] The present invention also provides a battery. Since the battery includes the above electrolyte, the battery has good high-temperature cycle stability.

[0006] The present invention also provides a battery pack. Since the battery pack includes the battery, the battery pack has the advantage of long cycle life.

[0007] The present invention also provides an electric device. Since the electric device includes the battery pack, the electric device has good safety and a long service life.

[0008] In a first aspect, the present invention provides an electrolyte comprising a first additive and a second additive, wherein the first additive comprises a compound having a structure as shown in Formula I:

[0009]

[0010] wherein R1 is -NH-, 1≤x≤5, 0≤y≤5, and R2-R4 are each independently H, halogen, cyano, sulfonyl, fluorosulfonyl, hydroxyl, sulfonic acid, amino, amide, C1-C10 alkyl, C1-C10 alkenyl, C3-C9 cycloalkyl, saturated or unsaturated C1-C10 alkoxy, C6-C20 aryl, C6-C20 heteroaryl, or C3-C20 heterocyclyl;

[0011] The second additive comprises a compound having a structure as shown in Formula II:

[0012]

[0013] Wherein, 1≤n≤6, R5-R7 are each independently H, halogen, cyano, sulfonyl, fluorosulfonyl, hydroxyl, sulfonic acid, amino, amide, saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, C6-C20 aryl group, C6-C20 heteroaryl group, C3-C20 heterocyclic group.

[0014] Optionally, in the compound represented by Formula I, at least one of the saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, and C6-C20 aryl group contains a heteroatom and / or a cyano group, and the heteroatom includes at least one of F, N, S, Si, B, and P;

[0015] In the compound shown in Formula II, at least one of the saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, and C6-C20 aromatic group contains heteroatoms and / or cyano groups, and the heteroatoms include at least one of F, N, S, Si, B, and P.

[0016] Optionally, the number average molecular weight of the compound represented by Formula II is less than or equal to 5000.

[0017] Optionally, the first additive comprises at least one compound having a structure such as Formula I-1 to I-3:

[0018]

[0019] Optionally, the second additive comprises at least one compound having a structure as shown in Formula II-1 to II-5:

[0020]

[0021]

[0022] Optionally, in the electrolyte, the addition amount of the first additive is 0.1-10 wt%, and the addition amount of the second additive is 0.1-10 wt%.

[0023] Optionally, in the electrolyte, the total amount of the first additive and the second additive is 0.1-15 wt %;

[0024] And / or, the mass ratio of the first additive to the second additive is 1:1-2.

[0025] Optionally, the electrolyte further includes a solvent; the solvent includes ethyl acetate.

[0026] Optionally, in the solvent, the mass proportion of ethyl acetate is 10-50%.

[0027] In a second aspect, the present invention provides a battery comprising a positive electrode sheet, a negative electrode sheet, and the electrolyte described in the first aspect.

[0028] In a third aspect, the present invention provides a battery pack comprising the battery described in the second aspect.

[0029] In a fourth aspect, the present invention provides an electrical device comprising the battery described in the second aspect or the battery pack described in the third aspect.

[0030] The electrolyte provided by the present invention can effectively improve the high-temperature cycle performance of the battery by combining a specific first additive and a second additive. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0032] In a first aspect, the present invention provides an electrolyte comprising a first additive and a second additive, wherein the first additive comprises a compound having a structure as shown in Formula I:

[0033]

[0034] wherein R1 is -NH-, 1≤x≤5, 0≤y≤5, and R2-R4 are each independently H, halogen, cyano, sulfonyl, fluorosulfonyl, hydroxyl, sulfonic acid, amino, amide, C1-C10 alkyl, C1-C10 alkenyl, C3-C9 cycloalkyl, saturated or unsaturated C1-C10 alkoxy, C6-C20 aryl, C6-C20 heteroaryl, or C3-C20 heterocyclyl;

[0035] The second additive comprises a compound having a structure as shown in Formula II:

[0036]

[0037] Wherein, 1≤n≤6, R5-R7 are each independently H, halogen, cyano, sulfonyl, fluorosulfonyl, hydroxyl, sulfonic acid, amino, amide, saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, C6-C20 aryl group, C6-C20 heteroaryl group, C3-C20 heterocyclic group.

[0038] In the present invention, the high-temperature cycle performance of the battery can be effectively improved by introducing the first additive and the second additive into the electrolyte. The main reasons include: on the one hand, the present invention uses the compound represented by Formula I as an electrolyte additive, which can promote the formation of an organic interface film on the surface of the positive and negative electrodes, thereby improving the high-temperature performance of the battery, and because the thiophene five-membered ring group of the compound represented by Formula I can undergo electropolymerization under high pressure, a network-structured electrolyte interface (CEI) film can be formed, thereby enhancing the interfacial stability of the CEI film, inhibiting the precipitation and migration of metal ions, and further improving the high-temperature / high-pressure performance of the battery. In addition, the present invention also provides a side chain group of R1-R4 in the compound represented by Formula I, which can further improve the film-forming performance of the negative electrode. On the other hand, the present invention introduces a second additive into the electrolyte. First, the intermediate part of the second additive can undergo electropolymerization, and cooperate with the first additive to interactively polymerize under high pressure to form a three-dimensional flexible network structure rich in groups such as C=O and S=O, thereby improving ion conduction and reducing interfacial impedance. Secondly, since the compound shown in Formula I easily leads to an increase in the acidity of the electrolyte, the compound shown in Formula II introduced in the present invention includes a Si-O six-membered ring, which is easy to open during the reaction and can effectively remove acidic substances in the electrolyte, prevent the active material from being corroded by acid, and reduce the dissolution of transition metals, thereby improving the high-temperature cycle performance of the battery; finally, the side-chain fluorinated benzene ring structure of the compound shown in Formula II can improve the solubility of the oligomer in the electrolyte, thereby further improving the high-temperature performance of the battery cell.

[0039] In one embodiment, in the compound represented by Formula I, at least one of the saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, and C6-C20 aryl group contains a heteroatom and / or a cyano group, wherein the heteroatom includes at least one of F, N, S, Si, B, and P;

[0040] In the compound shown in Formula II, at least one of the saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, and C6-C20 aromatic group contains heteroatoms and / or cyano groups, and the heteroatoms include at least one of F, N, S, Si, B, and P.

[0041] In the embodiment described above, by further introducing a heteroatom or a cyano group into the structure of the compound represented by Formula I or Formula II, the stability of the electrode SEI film can be further increased, making it less likely to be destroyed and reorganized during the cycle, effectively inhibiting the reduction and decomposition of the electrolyte on the negative electrode surface, and at the same time reducing the impedance of the SEI film, thereby improving the chemical kinetics of the negative electrode interface.

[0042] In one embodiment, the number average molecular weight of the compound represented by Formula II is less than or equal to 5,000.

[0043] Among them, the compound with the above-mentioned molecular weight can have good solubility in the solvent, thereby ensuring the performance of the battery cell.

[0044] In one embodiment, the first additive comprises at least one compound having a structure as shown in Formula I-1 to I-3:

[0045]

[0046] In one embodiment, the second additive comprises at least one compound having a structure as shown in Formula II-1 to II-3:

[0047]

[0048] It should be noted that the first additive and the second additive of the present invention can be obtained through existing methods such as purchasing commercial products, synthesizing using conventional methods, or custom-making synthesis.

[0049] By way of example and not limitation, in some embodiments, the preparation process of the compound represented by Formula I-1 comprises:

[0050] The compound represented by Formula 1 (CAS No.: 27757-86-4) and the compound represented by Formula 2 (CAS No.: 79-10-7) are mixed and subjected to an esterification reaction (exemplary esterification reaction conditions include: adding 3-5 wt% concentrated sulfuric acid, 0.1-2 wt% of catalyst Cu, and heating to 90°C-110°C for reaction) to obtain the compound represented by Formula I-1. The process is as follows:

[0051]

[0052] When preparing the compound shown in I-3, the compound of formula 1 is first subjected to a fluorination reaction to obtain an F-substituted intermediate, and then the reaction is carried out with reference to the preparation process of the compound shown in formula 1-1; when preparing the compound shown in formula 1-2, the compound of formula 2 is replaced with the compound shown in formula 4, and the compound shown in formula 4 can be prepared by dehydrating the compound shown in formula 3 (CAS number: 591-81-1) in concentrated sulfuric acid (3%-5%) and 0.2-0.5wt% TiO2 as a catalyst at 160-180°C to form an olefin.

[0053]

[0054] By way of example and not limitation, in some embodiments, the compound of Formula II, taking Formula II-1 as an example, is prepared by: 1) preparing the main central molecule:

[0055] Cyclopentadiene is subjected to chlorination reaction and hydrolysis reaction in sequence to obtain the compound shown in Formula 5. The process is as follows:

[0056]

[0057] The compound represented by Formula 5 is subjected to a catalytic oxidation reaction (exemplary reaction conditions include: using a Mo-V composite oxide as a catalyst and a reaction temperature of 250-300° C.) to obtain a compound represented by Formula 6. The compound represented by Formula 6 is subjected to a sulfonation reaction (exemplary reaction conditions include: 3-5% concentrated sulfuric acid and a reaction temperature of 70-90° C.) to obtain a compound represented by Formula 7. The process is as follows:

[0058]

[0059] 2) End-group esterification with functional monomers:

[0060] Hexamethylcyclotrisiloxane (CAS No.: 541-05-9) is subjected to chlorination reaction and hydrolysis reaction in sequence to obtain the compound shown in Formula 8. The process is as follows:

[0061]

[0062] The compound represented by Formula 8 and the compound represented by Formula 7 are subjected to an esterification reaction (exemplary reaction conditions include: adding 3-5 wt% concentrated sulfuric acid, 0.1-2 wt% of catalyst Cu, and heating to 90°C-110°C for esterification) to obtain the compound represented by Formula II-1. The process is as follows:

[0063]

[0064] The preparation process of the compounds represented by formula II-3, formula II-4 and formula II-5 can refer to the preparation process of the compound represented by formula II-1; the preparation process of the compound represented by formula II-2 is based on the compound represented by formula II-1, and nitration and reduction reactions are performed. The process is as follows:

[0065]

[0066] In addition, in Formula II, the value of n can be controlled by adjusting the addition ratio of the compound shown in Formula 7.

[0067] In a specific embodiment, in the electrolyte, the amount of the first additive added is 0.1-10 wt %, and the amount of the second additive added is 0.1-10 wt %.

[0068] Among them, the first additive and the second additive within the above addition amount range can more significantly improve the cycle performance of the battery under high temperature conditions while ensuring solubility.

[0069] Exemplarily, the amount of the first additive and the amount of the second additive added are each independently 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 1.5wt%, 2.0wt%, 3.wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%, 5.5wt%, 6.0wt%, 6.5wt%, 7.0wt%, 7.5wt%, 8.0wt%, 8.5wt%, 9.0wt%, 9.5wt%, 10.0wt%, etc., any one of the values ​​or a range consisting of any two of them.

[0070] In one embodiment, the total amount of the first additive and the second additive in the electrolyte is 0.1-15 wt %;

[0071] And / or, the mass ratio of the first additive to the second additive is 1:1-2.

[0072] The embodiment described above can further ensure that the acidic substances in the electrolyte can be effectively removed by limiting the total addition amount of the first additive and the second additive, and / or the mass ratio of the first additive to the second additive, while increasing the degree to which the two additives participate in film formation at the positive and negative electrodes, thereby further improving the high-temperature stability of the battery.

[0073] Exemplarily, the total amount of the first additive and the second additive added is 0.1wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%, 5.5wt%, 6.0wt%, 6.5wt%, 7.0wt%, 7.5wt%, 8.0wt%, 8.5wt%, 9.0wt%, 9.5wt%, 10.0wt%, 10.5wt%, 11.0wt%, 12.0wt%, 13.0wt%, 14.0wt%, 15.0wt%, or any of the following values, or a range consisting of any two of them.

[0074] The first additive and the second additive provided in the embodiment of the present invention are applicable to the above-mentioned various organic solvent systems, and can provide more feasible implementation plans, thereby facilitating the promotion and application of the additives provided in the embodiment of the present invention.

[0075] In a specific embodiment, the electrolyte further includes a solvent, wherein carbonate solvents have good electrochemical properties, but such solvents have poor high-temperature performance. The electrolyte of the present invention can improve the high-temperature performance of carbonate solvents to a limited extent by introducing specific first additives and second additives. Since the electrolyte system can be well matched with different types of solvents; therefore, the solvent includes but is not limited to: at least one of carbonate solvents, carboxylate solvents, and ether solvents.

[0076] For example, the carbonate solvents include propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), etc. The carboxylate solvents include ethyl formate, ethyl acetate (EA), propyl acetate, methyl propionate, ethyl propionate (EP), n-propyl propionate (PP), isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate, n-pentyl valerate, butyrolactone, etc. The ether solvents include 1,3-oxycyclopentane (DOL), ethylene glycol dimethyl ether (DME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), etc.

[0077] In one embodiment, the carboxylate solvent accounts for 10% to 50% of the total mass of the solvent;

[0078] And / or, the sum of the carbonate solvent and the ether solvent accounts for 50%-90% of the total mass of the solvent.

[0079] When the organic solvent is within the above range, the lithium salt can be fully dissolved in the electrolyte, which helps to prepare an electrolyte with high conductivity and strong stability, thereby stabilizing the electrochemical performance of the battery.

[0080] In one embodiment, the solvent includes ethyl acetate (EA). This embodiment utilizes EA to improve kinetics and conductivity, thereby improving the low-temperature performance of the battery cell by utilizing its lower viscosity and good wettability with the positive and negative electrodes.

[0081] In order to further improve the low-temperature performance of the battery core, the mass proportion of the ethyl acetate in the solvent is 10-50%.

[0082] The electrolyte further includes a lithium salt; the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, trifluorosulfonyl lithium, lithium difluoro(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, tris(trifluoromethylsulfonyl)methyl lithium, lithium dioxalatoborate, lithium bismalonateborate, lithium oxalophosphate, and lithium tris(difluoromalonate)phosphate;

[0083] In a specific embodiment, the amount of the lithium salt added to the electrolyte is 0.8 mol / L to 1.8 mol / L.

[0084] Among them, when the lithium salt is within the above range, the lithium salt can be dissolved in the organic solvent to form an electrolyte with high stability and good lithium conductivity. At the same time, the viscosity of the electrolyte can be made appropriate, so that lithium ions can migrate rapidly in the electrolyte, thereby making the battery exhibit excellent rate and cycle performance.

[0085] In a specific embodiment, a third additive is further included, and the third additive includes at least one of vinylene carbonate or its derivatives, cyclic carbonate, and halogen-substituted cyclic carbonate. The third additive has good affinity to the electrode surface and can form a stable SEI film on the electrode surface, thereby protecting the electrode structure from solvent molecules, HF, F in the electrolyte. - and other impurities, which helps to further improve the high-temperature cycle performance of the battery.

[0086] The amount of the third additive is not particularly limited in the present invention. Generally speaking, the amount of the third additive does not exceed 10 wt % of the electrolyte.

[0087] In one embodiment, the third additive includes one or more of vinylene carbonate, vinyl ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, and bisfluoroethylene carbonate. In a more preferred embodiment, the third additive is vinylene carbonate. The introduction of vinylene carbonate can reduce the initial capacity loss of lithium-ion batteries and significantly improve the stability of the SEI film under high temperature conditions.

[0088] In a second aspect, the present invention provides a battery comprising the electrolyte, positive electrode sheet and negative electrode sheet described in the first aspect.

[0089] It should be noted that the above-mentioned batteries may include but are not limited to single cells, battery modules, battery packs, etc., that is, the actual application form of the battery provided by the present invention may be but is not limited to the listed products, and may also be other application forms. When the battery is a single cell, it includes at least one of a cylindrical battery, a square battery, etc.

[0090] Generally speaking, the positive electrode sheet includes a positive current collector and a positive active slurry layer located on the positive current collector, wherein the positive active slurry layer includes a positive active material, a positive binder, and a positive conductive agent. The negative electrode sheet includes a negative current collector and a negative active slurry layer located on the negative current collector, wherein the negative active slurry layer includes a negative active material, a negative binder, and a negative conductive agent. The specific types of the positive active material, positive binder, positive conductive agent, negative active material, negative binder, and negative conductive agent are not subject to specific restrictions and can be selected according to needs.

[0091] The electrolyte system of the present invention is well compatible with various common positive and negative electrode materials. For example, the positive electrode materials include, but are not limited to, polyanionic compounds, transition metal oxides, and Prussian blue compounds. Negative electrode materials include, but are not limited to, carbon-based materials (soft carbon, hard carbon, carbon fiber, natural graphite, artificial graphite, silicon-carbon composites, silicon carbide), alloy materials, and metal oxide materials.

[0092] Furthermore, the above-mentioned positive electrode active materials include but are not limited to: LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-b M b O2、LiCo 1-b M b O2、LiFe 1-b M b PO4, Li2Mn 1-b O4、LiNi x Co y Mn zAt least one of O2, etc., M is selected from one or more of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0≤a<0.2, 0≤b<1, x+y+z=1.

[0093] The above-mentioned negative electrode active materials include but are not limited to: graphite and / or silicon, such as natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy, etc.

[0094] The positive electrode binder and the negative electrode binder are independently selected from at least one of styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0095] As for the particle size distribution of the above-mentioned positive electrode active material and the negative electrode active material, the present invention does not make any specific limitation. For example, the D50 of the above-mentioned positive electrode active material or the negative electrode active material may be 5-16 μm, specifically including but not limited to: 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.; D99 may be 14-30 μm, specifically including but not limited to: 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, etc.; D10 may be 2-10 μm, specifically including but not limited to: 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, etc.

[0096] The thickness and surface density of the positive and negative electrodes are not specifically limited in the present invention. However, in order to balance the battery capacity, cycle life and energy density, in one embodiment, the thickness of the positive or negative electrode is 40-120 μm, including but not limited to 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, etc.; the surface density of the positive or negative electrode is 3-10 mg / cm 2 , specifically including but not limited to: 3.5mg / cm 2 , 4mg / cm 2 , 4.5mg / cm 2 , 5mg / cm 2 , 5.5mg / cm 2 , 6mg / cm 2、6.5mg / cm 2 , 7mg / cm 2 , 7.5mg / cm 2 , 8mg / cm 2 , 8.5mg / cm 2 , 9mg / cm 2 , 9.5mg / cm 2 wait.

[0097] Illustratively, the battery further includes a separator, such as polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, etc.

[0098] In a third aspect, the present invention provides a battery pack comprising the battery described in the second aspect.

[0099] In a fourth aspect, the present invention provides an electrical device comprising the battery described in the second aspect or the battery pack described in the third aspect.

[0100] It should be noted that the above-mentioned electronic devices can be any conventional devices that require electricity, for example, including but not limited to computers, electric cars, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0101] The present invention will be further described below with reference to specific embodiments:

[0102] Example 1

[0103] This example provides an electrolyte, which, calculated based on the total mass of the electrolyte, comprises 0.5 wt% of the compound represented by formula I-1, 0.5 wt% of the compound represented by formula II-1, 13.0 wt% of lithium hexafluorophosphate (LiPF6), 1.0 wt% of vinyl sulfate (DTD), 3.0 wt% of vinylene carbonate (VC) and 1.0 wt% of fluoroethylene carbonate (FEC) as a third additive, and ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl acetate (EA) as a non-aqueous organic solvent system, wherein, by mass, EC:DMC:EA=30:30:40.

[0104] Example 2-20

[0105] The method is basically the same as Example 1, with the only difference being that the amount of the first additive and / or the type and amount of the second additive are changed. For details, see Table 1.

[0106] Comparative Example 1

[0107] The process is basically the same as Example 1, except that the compound represented by Formula Ι-1 and the compound represented by Formula II-1 are not added.

[0108] Comparative Example 2

[0109] The reaction mixture is basically the same as Comparative Example 1, except that EC:DMC:EMC=30:50:20 is used as the solvent.

[0110] Comparative Example 3

[0111] The process is basically the same as Example 1, except that the compound represented by formula 1-1 is not added.

[0112] Comparative Example 4

[0113] The process is basically the same as Example 1, except that the compound represented by formula II-1 is not added.

[0114] Test example

[0115] Batteries were prepared using the electrolytes of the above examples and comparative examples, respectively, including the following steps:

[0116] Preparation of positive electrode sheet: LFP powder, conductive agent carbon nanotubes (CNT) and binder polyvinylidene fluoride (PVDF) are weighed respectively in a mass ratio of 97.6:0.8:1.6; then they are evenly dispersed in N-methylpyrrolidone (NMP) to ensure that the slurry is evenly dispersed and free of particles; then the positive electrode slurry is evenly coated on the carbon-coated current collector aluminum foil, and the positive electrode sheet is vacuum dried at 95°C; next, it is cold pressed, followed by trimming, cutting and striping; then it is baked under vacuum conditions at 95°C for 36 hours, and the aluminum tabs are welded to make the positive electrode sheet.

[0117] Preparation of negative electrode sheet: Graphite, conductive agent carbon black (Super-P), thickener CMC, and binder SBR are weighed respectively in a mass ratio of 96.6:1.0:1.2:1.2; then evenly dispersed in deionized water to ensure that the slurry is evenly dispersed and free of particles; then the negative electrode slurry is evenly coated on the current collector copper foil, and the negative electrode sheet is vacuum dried at 95°C; then cold pressed, followed by trimming, cutting, and striping; then dried under vacuum conditions at 110°C for 24 hours, and the copper tabs are welded to make the negative electrode sheet.

[0118] Preparation of LFP battery: Use polyethylene (PE) porous polymer film as separator; stack the prepared positive electrode sheet, separator, and negative electrode sheet in order into three layers (the separator is between the positive and negative electrodes), and then wind them in the same direction to obtain a bare cell. Wrap the bare cell with a steel shell that exactly matches the size of the bare cell, and then bake the open cell at 90°C for 48 hours to remove moisture. The non-aqueous electrolyte prepared above (qualified electrolyte: moisture ≤ 20ppm, acidity ≤ 50ppm) is injected into the dried bare cell, packaged, allowed to stand, formed (0.02C constant current charging to 3.3V, then 0.1C constant current charging to 3.5V), shaped, and tested for capacity to complete the preparation of cylindrical LFP batteries.

[0119] Performance testing:

[0120] The following tests were performed on the cylindrical LFP battery prepared in the experimental example. The test results are shown in Table 1:

[0121] 1. Low-temperature discharge performance: At a constant temperature of 23±2°C, charge the freshly divided battery to 3.65V at 0.2C constant current and constant voltage, with a cutoff of 0.025C; then discharge to 2.5V at 0.2C constant current; repeat this cycle twice, and record the second discharge capacity as the initial capacity at room temperature. Continue charging at this room temperature at 0.2C constant current and constant voltage to 3.96V, with a cutoff of 0.025C; then place the battery in a -20°C thermostat for 4 hours, and discharge to 2.5V at 0.2C constant current. Test the battery's capacity retention (discharge capacity at -20°C / initial capacity at room temperature × 100%).

[0122] 2. Room Temperature Cycling Performance: Freshly divided batteries were charged at a constant temperature of 23±2°C at a constant current and voltage of 0.5C to 3.65V, with a cutoff of 0.025C. They were then discharged at a constant current of 0.5C to 2.5V. This constituted one cycle. Repeat this cycle 4500 times, and record the battery's capacity retention.

[0123] 3. High-temperature cycling performance: Place the freshly divided batteries in a 45°C thermostat for 2 hours. Charge them at a constant current and constant voltage of 0.5C to 3.65V, then cut off at 0.025C. Then discharge them at a constant current of 0.5C to 2.5V. This constitutes one cycle. Repeat this cycle 2500 times and record the battery's capacity retention.

[0124] Table 1:

[0125]

[0126] In the table: “ / ” means that this component is not present in the electrolyte.

[0127] From the data in Table 1, it can be seen that, by comparing the comparative example with the example, the electrolyte of the example has a certain degree of improvement in the high-temperature performance of the battery cell due to the addition of the first additive and the second additive;

[0128] Furthermore, compared with Comparative Example 1 and Comparative Example 2, the solvent system is significantly adjusted and EA is added as the main solvent, which greatly reduces the viscosity of the electrolyte (especially the viscosity reduction is more obvious at low temperatures), which is beneficial to improving the low-temperature discharge of the battery cell, but there is a significant deterioration in both normal temperature cycling and high temperature cycling; in Comparative Example 3 and Comparative Example 4, since only the first additive or the second additive is added to the electrolyte, the high and low temperature performance of the battery cell is not improved; the embodiment can significantly improve the high and low temperature performance of the battery cell by adding the first additive and the second additive at the same time.

[0129] Furthermore, it can be seen from Examples 16-18 that the ratio of the first additive to the second additive is 1:1-2, which has a more obvious improvement on the high and low temperature performance of the battery cell; it can be seen from Examples 18-20 that in the polymer of Formula II, when n≤5, the high and low temperature performance of the battery cell is more obviously improved.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that The method comprises a first additive and a second additive, wherein the first additive comprises a compound having a structure as shown in Formula I: wherein R1 is -NH-, 1≤x≤5, 0≤y≤5, and R2-R4 are each independently H, halogen, cyano, sulfonyl, fluorosulfonyl, hydroxyl, sulfonic acid, amino, amide, C1-C10 alkyl, C1-C10 alkenyl, C3-C9 cycloalkyl, saturated or unsaturated C1-C10 alkoxy, C6-C20 aryl, C6-C20 heteroaryl, or C3-C20 heterocyclyl; The second additive comprises a compound having a structure as shown in Formula II: Wherein, 1≤n≤6, R5-R7 are each independently H, halogen, cyano, sulfonyl, fluorosulfonyl, hydroxyl, sulfonic acid, amino, amide, saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, C6-C20 aryl group, C6-C20 heteroaryl group, C3-C20 heterocyclic group.

2. The electrolyte according to claim 1, characterized in that In the compound represented by Formula I, at least one of the saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, and C6-C20 aryl group contains a heteroatom and / or a cyano group, and the heteroatom includes at least one of F, N, S, Si, B, and P; In the compound shown in Formula II, at least one of the saturated or unsaturated C1-C10 aliphatic group, C3-C9 cycloalkyl group, saturated or unsaturated C1-C10 alkoxy group, and C6-C20 aromatic group contains heteroatoms and / or cyano groups, and the heteroatoms include at least one of F, N, S, Si, B, and P.

3. The electrolyte according to claim 1 or 2, characterized in that The number average molecular weight of the compound represented by formula II is less than or equal to 5,000.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The first additive comprises at least one compound having a structure such as those in Formulas 1-1 to 1-3:

5. The electrolyte according to any one of claims 1 to 4, characterized in that The second additive comprises at least one compound having a structure as shown in Formula II-1 to II-5:

6. The electrolyte according to any one of claims 1 to 5, characterized in that In the electrolyte, the addition amount of the first additive is 0.1-10 wt %, and the addition amount of the second additive is 0.1-10 wt %.

7. The electrolyte according to claim 6, characterized in that In the electrolyte, the total addition amount of the first additive and the second additive is 0.1-15 wt %; And / or, the mass ratio of the first additive to the second additive is 1:1-2.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The electrolyte further includes a solvent; the solvent includes ethyl acetate.

9. The electrolyte according to claim 8, characterized in that In the solvent, the mass proportion of the ethyl acetate is 10-50%.

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

11. A battery pack, characterized in that: A battery comprising the battery of claim 10.

12. An electrical device, characterized in that: The method comprises the battery according to claim 10 or the battery pack according to claim 11.

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