Electrolyte, lithium ion battery and electronic equipment

Abstract

The invention discloses an electrolyte, a lithium ion battery and electronic equipment. The electrolyte comprises a compound as shown in a formula I and fluoro-carbonic ester; in the formula I, R1 and R2 are respectively and independently substituent groups with the carbon atom number of 1 to 6, the unsaturation degree of 0 to 4 and the heteroatom number of 0 to 3. The lithium ion battery adopting the electrolyte has excellent low-temperature dynamic performance and high-temperature cycle performance.

Description

Technical Field

[0001] The present invention provides an electrolyte, a lithium-ion battery, and an electronic device. Background Art

[0002] With the continuous growth in the demand for electric vehicles and portable devices, the development of lithium-ion batteries has also advanced by leaps and bounds. In commercial lithium-ion batteries, the cathode material has become a key factor determining the energy density and cost of lithium-ion batteries. Among numerous candidate cathode materials, the high-nickel cathode material LiNi x M 1-x O2 (M = Mn, Co, Al, etc.) has the potential to achieve high energy density and is the most maturely developed, with an energy density ranging from 650 Wh kg -1 to over 850 Wh kg -1 , and at the same time, the cycle life is also quite considerable, reaching 1500 - 3000 cycles.

[0003] However, the high-nickel cathode has a phenomenon of structural collapse, which may stem from two types of side reactions: one is the decomposition reaction of lithium-related compounds remaining on the surface (such as LiOH, LiHCO3, and Li2CO3) and the side reaction with the acidic environment of the system; the other is the oxidation reaction between the electrolyte and the high-nickel cathode in the high delithiated state. This will cause damage to the material structure, mechanical failures of the battery casing, and even battery explosion. Therefore, there are certain potential safety hazards.

[0004] The existing means to solve the transition metal spillage of the high-nickel cathode are mainly: 1) coating the material; 2) adjusting the solvent ratio in the electrolyte. Coating the material is mainly achieved by atomic layer deposition to coat an oxide protective film on the material or electrode level. However, such a method will affect the energy density of the system and has a negative effect on the kinetics of the material. On the other hand, adjusting the solvent ratio in the electrolyte and reducing the use of ethylene carbonate (EC) can reduce the oxidation side reaction of EC on the cathode side, thereby reducing gas generation at high temperatures, but the reduction of EC also has a relatively serious impact on kinetics. Summary of the Invention

[0005] In order to solve the above technical problems existing in the prior art, the present invention provides an electrolyte, a lithium-ion battery, and an electronic device. The electrolyte of the present invention contains a specific additive, and the lithium-ion battery using the electrolyte has both excellent low-temperature kinetic performance and high-temperature cycle performance.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect of the present invention, there is provided an electrolyte, which includes a compound represented by Formula I and a fluorinated carbonate;

[0008]

[0009] Formula I

[0010] Wherein, R1 and R2 are each independently a substituent having 1-6 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms.

[0011] The second aspect of the present invention provides a lithium-ion battery, and the lithium-ion battery includes the electrolyte as described above.

[0012] The third aspect of the present invention provides an electronic device, and the electronic device includes the lithium-ion battery as described above.

[0013] The positive and progressive effects of the present invention are as follows:

[0014] By adding a specific cyanophosphate compound as an additive to the electrolyte and cooperating with fluorinated carbonate, through the complexation of metal ions and nucleophilic substitution reaction, a copolymerized SEI film containing LiF and phosphate-carbonate can be formed on the electrode surface during the operation of the lithium-ion battery, while improving the low-temperature kinetic performance and high-temperature cycling performance of the lithium-ion battery. Detailed Embodiments

[0015] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions in the following examples are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0016] In the electrolyte described in the first aspect of the present invention, the electrolyte includes the compound shown in Formula I and fluorinated carbonate;

[0017]

[0018] Formula I

[0019] Wherein, R1 and R2 are each independently a substituent having 1-6 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms.

[0020] In the present invention, the compound represented by Formula I is a cyanophosphonate compound. This structure contains a cyano group, and its mechanism of complexing metal ions mainly involves coordination chemistry and structural characteristics. The N atom has a lone pair of electrons and can act as a Lewis base to coordinate with metal ions; while the P atom has an empty 3d orbital, which may participate in π-back bonding or auxiliary coordination and also has the effect of complexing transition metals. The cyanophosphonate compound represented by Formula I is used in combination with a fluorinated carbonate. The phosphorus atom in the fluorinated carbonate (due to the strong electron-withdrawing effect of the cyano group, the P=O bond is polarized and the phosphorus is positively charged) may become the nucleophilic attack site of the fluorine atom in the fluorinated carbonate. The C-F bond in the fluorinated carbonate undergoes substitution under the action of a nucleophile (such as an ethoxy group or a cyano group) to generate a fluorinated phosphate derivative and release LiF. The nucleophilic group (such as an ethoxy group or a cyano group) in the cyanophosphonate compound attacks the carbonyl carbon of the fluorinated carbonate, causing the cyclic carbonate to open and form a SEI film of a phosphate-carbonate covalent compound containing LiF.

[0021] In some embodiments, each of R1 and R2 is independently one or more of an alkyl group, an alkenyl group, an alkynyl group, a carbonyl group, an ester group, an alkyl group substituted with an amino group, and a heterocyclic group having 1-6 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms. It should be noted that the description "having 1-6 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms" herein limits "alkyl group, alkenyl group, alkynyl group, carbonyl group, ester group, alkyl group substituted with an amino group, and heterocyclic group", rather than only limiting "alkyl group".

[0022] In some preferred embodiments, the compound represented by Formula I is selected from one or more of Compounds 1-4;

[0023] Compound 1 and Compound 2 ,

[0024] Compound 3 and Compound 4 .

[0025] In some embodiments, the content of the compound represented by Formula I is 0.05 wt.% - 3 wt.%, preferably 0.1 wt.% - 1 wt.%, such as 0.3 wt.% or 3.5 wt.%. wt.% is the mass percentage of the compound represented by Formula I in the electrolyte.

[0026] In some embodiments, the fluorinated carbonate is fluoroethylene carbonate (FEC).

[0027] In some embodiments, the content of the fluorinated carbonate is 0.5 wt.% - 8 wt.%, preferably 0.5 wt.% - 5 wt.%. wt.% is the mass percentage of the fluorinated carbonate in the electrolyte.

[0028] In some embodiments, the total content of the compound represented by Formula I and the fluorinated carbonate is 0.6 wt.% - 10 wt.%, such as 0.8 wt.%, 5.05 wt.%, 5.3 wt.%, 6 wt.%, 8 wt.%, 8.3 wt.% or 8.5 wt.%. wt.% is the mass percentage of the sum of the mass of the compound represented by Formula I and the fluorinated carbonate in the electrolyte.

[0029] In some preferred embodiments, the content of the compound represented by Formula I is 0.05 wt.% - 3 wt.%, and the content of the fluorinated carbonate is 0.5 wt.% - 8 wt.%.

[0030] In some specific embodiments, the compound represented by Formula I is Compound 1, and the fluorinated carbonate is vinyl fluorocarbonate.

[0031] In some specific embodiments, the compound represented by Formula I is Compound 1, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 1 is 0.3 wt.%, and the content of vinyl fluorocarbonate is 5 wt.%.

[0032] In some specific embodiments, the compound represented by Formula I is Compound 1, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 1 is 0.3 wt.%, and the content of vinyl fluorocarbonate is 0.5 wt.%.

[0033] In some specific embodiments, the compound represented by Formula I is Compound 1, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 1 is 1 wt.%, and the content of vinyl fluorocarbonate is 5 wt.%.

[0034] In some specific embodiments, the compound represented by Formula I is Compound 1, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 1 is 3 wt.%, and the content of vinyl fluorocarbonate is 5 wt.%.

[0035] In some specific embodiments, the compound represented by Formula I is Compound 1, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 1 is 0.05 wt.%, and the content of vinyl fluorocarbonate is 5 wt.%.

[0036] In some specific embodiments, the compound represented by Formula I is Compound 1, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 1 is 3.5 wt.%, and the content of vinyl fluorocarbonate is 5 wt.%.

[0037] In some specific embodiments, the compound represented by Formula I is Compound 1, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 1 is 0.3 wt.%, and the content of vinyl fluorocarbonate is 8 wt.%.

[0038] In some specific embodiments, the compound represented by Formula I is Compound 2, and the fluorinated carbonate is vinyl fluorocarbonate.

[0039] In some specific embodiments, the compound represented by Formula I is Compound 2, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 2 is 0.3 wt.%, and the content of vinyl fluorocarbonate is 5 wt.%.

[0040] In some specific embodiments, the compound represented by Formula I is Compound 3, and the fluorinated carbonate is vinyl fluorocarbonate.

[0041] In some specific embodiments, the compound represented by Formula I is Compound 3, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 3 is 0.3 wt.%, and the content of vinyl fluorocarbonate is 5 wt.%.

[0042] In some specific embodiments, the compound represented by Formula I is Compound 4, and the fluorinated carbonate is vinyl fluorocarbonate.

[0043] In some specific embodiments, the compound represented by Formula I is Compound 4, the fluorinated carbonate is vinyl fluorocarbonate, the content of Compound 4 is 0.3 wt.%, and the content of vinyl fluorocarbonate is 5 wt.%.

[0044] In some embodiments, the solvent in the electrolyte is selected from one or more of diethyl carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate, trifluoroethyl methyl carbonate, difluoroethyl acetate, ethers, and nitriles.

[0045] Among them, the ethers are preferably ethylene glycol dimethyl ether and / or diethylene glycol diethyl ether.

[0046] Among them, the nitriles are preferably one or more of acetonitrile, propionitrile, butyronitrile, and valeronitrile.

[0047] In some preferred embodiments of the invention, the solvent in the electrolyte includes diethyl carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Among them, the volume ratio of diethyl carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) is preferably 3:5:2.

[0048] In some embodiments, the content of the solvent in the electrolyte is 70 wt.% - 80 wt.%, where wt.% is the mass percentage of the solvent in the electrolyte.

[0049] In some embodiments, the lithium salt in the electrolyte is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium acetate, lithium methanesulfonate, and lithium trifluoromethanesulfonate.

[0050] In some embodiments, the lithium salt includes lithium hexafluorophosphate.

[0051] In some embodiments, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Wherein, the mass ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is 14:(1 - 3), such as 14:1, 14:2, or 13:2.

[0052] In some embodiments, the content of the lithium salt in the electrolyte is 12 wt.% - 16 wt.%, such as 12.5 wt.%, where wt.% is the mass percentage of the lithium salt in the electrolyte.

[0053] In some embodiments, the electrolyte further includes one or more of vinylene sulfate (DTD), allyl-1,3-sultone (PST), tetravinylsilane (TVSI), and tris(trimethylsilyl) phosphate (TMSP).

[0054] In some embodiments, the electrolyte further includes tris(trimethylsilyl) phosphate, and the content of the tris(trimethylsilyl) phosphate is preferably 0.1 wt.% - 1.0 wt.%, such as 0.5 wt.%.

[0055] In some specific embodiments, the electrolyte includes 0.3 wt.% of Compound 1, 5 wt.% of fluoroethylene carbonate, and 0.5 wt.% of tris(trimethylsilyl) phosphate.

[0056] In some embodiments, the electrolyte further includes allyl-1,3-sultone, and the content of the allyl-1,3-sultone is preferably 0.1 wt.% - 1.0 wt.%, such as 0.5 wt.%.

[0057] In some specific embodiments, the electrolyte includes 0.3 wt.% of Compound 1, 5 wt.% of fluoroethylene carbonate, and 0.5 wt.% of allyl-1,3-sultone.

[0058] In some embodiments, the electrolyte further includes tetravinylsilane, and the content of the tetravinylsilane is preferably 0.1 wt.% - 1.0 wt.%, such as 0.5 wt.%.

[0059] In some specific embodiments, the electrolyte includes 0.3 wt.% of Compound 1, 5 wt.% of vinylene carbonate fluoride, and 0.5 wt.% of tetravinylsilane.

[0060] In the lithium-ion battery described in the second aspect of the present invention, the lithium-ion battery includes the electrolyte as described above.

[0061] In the present invention, the lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte as described above.

[0062] Positive electrode sheet

[0063] In the present invention, the positive electrode sheet may include a positive electrode current collector and a positive electrode material layer, and the positive electrode material layer is disposed on at least one surface of the positive electrode current collector; the positive electrode material layer includes a positive electrode material.

[0064] In some embodiments, the positive electrode material is a nickel-containing positive electrode material.

[0065] In some embodiments, the chemical formula of the nickel-containing positive electrode material is LiNi x M 1-x O2, where M is selected from one or more of Mn, Co, and Al, and x is 0.4 - 0.95.

[0066] In some specific embodiments, the nickel-containing positive electrode material is LiNi 0.9 Mn 0.05 Co 0.05 O2.

[0067] In some embodiments, the positive electrode material layer further includes a conductive agent. For the conductive agent, it is a reagent for ensuring good charge and discharge performance of the electrode. It can be arbitrarily selected from graphite materials such as natural graphite and artificial graphite, carbon black materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, etc., conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride powder, aluminum powder, nickel powder, etc., conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides or polyphenylene derivatives such as titanium dioxide, for example, conductive carbon black.

[0068] In some embodiments, the positive electrode material layer further includes a binder. The binder can be a component that helps the combination between the positive electrode material and the conductive agent and helps the combination between the positive electrode material and the positive electrode current collector. It can generally be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, such as PVDF.

[0069] In some embodiments, the positive electrode material layer includes a positive electrode material, polyvinylidene fluoride, and conductive carbon black.

[0070] In some specific embodiments, the mass ratio of the positive electrode material, polyvinylidene fluoride, and conductive carbon black is 8:1:1.

[0071] In the present invention, the positive electrode current collector can be a conventional positive electrode current collector in the art. For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without limitation. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can usually be used, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. To enhance adhesion, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, or porous body, etc.

[0072] In some alternative embodiments, the positive electrode current collector is aluminum foil.

[0073] In some alternative embodiments, the thickness of the positive electrode current collector can be 8 - 16 μm, for example, 10 μm.

[0074] In the present invention, the positive electrode sheet can be prepared by a conventional method in the art.

[0075] In some alternative embodiments, the preparation method of the positive electrode sheet includes the following steps:

[0076] After mixing the positive electrode material, the binder, and the conductive agent according to a certain mass ratio, a solvent is added and mixed evenly to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on at least one surface of the positive electrode current collector; and then through processes such as drying, rolling, and slitting, a positive electrode sheet is prepared.

[0077] Negative electrode sheet

[0078] In the present invention, the negative electrode sheet can include a negative electrode current collector and a negative electrode material layer. The negative electrode material layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode material.

[0079] In the present invention, the negative electrode material in the negative electrode material layer can be a negative electrode material conventionally used in the art, such as a graphite-based negative electrode material, a silicon oxide-based negative electrode material, or a silicon carbon-based negative electrode material.

[0080] In some embodiments, the negative electrode material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon monoxide, and silicon carbon materials.

[0081] In some embodiments, the negative electrode material layer further includes a conductive agent.

[0082] Among them, the conductive agent is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, specifically, the following can be used: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as conductive carbon black (Super P, abbreviated as SP), carbon nanotubes (CNT), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal carbon black, or carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0083] In some specific embodiments, the conductive agent in the negative electrode material layer is acetylene black.

[0084] In some embodiments, the negative electrode material layer further includes a binder.

[0085] Among them, the type of the binder is not particularly limited and can be arbitrarily selected from polyvinylidene fluoride, polyvinyl fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfide, styrene-butadiene rubber (SBR), fluororubber, and various copolymers, for example, SBR.

[0086] In some embodiments, the negative electrode material layer further includes a thickening agent.

[0087] Among them, the addition of the thickening agent can increase the system viscosity of each component in the negative electrode slurry and can be a thickening agent conventionally used in the art for preparing negative electrode sheets, for example, sodium carboxymethyl cellulose (CMC).

[0088] In the present invention, the negative electrode current collector may be a conventional negative electrode current collector in the art. The negative electrode current collector serves as a substrate supporting the negative electrode material layer, and is generally a metal foil having a thickness of 3-500 μm. There is no particular restriction on the material, as long as it has high electrical conductivity and does not produce chemical reactions in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative electrode current collector generally has a smooth surface, but fine lines may also be formed on its surface to increase the adhesion between the negative electrode material layer and the current collector. In addition to foil, the negative electrode current collector may also be in the form of a film, mesh, porous, foam or non-woven fabric, or any one or more combinations thereof. Generally, the negative electrode current collector is copper foil.

[0089] In some embodiments, the preparation method of the negative electrode sheet includes the following steps: thoroughly stirring and mixing the components of the negative electrode material layer in a solvent to obtain a negative electrode slurry, coating it on at least one surface of the negative electrode current collector, drying, cold pressing, and cutting.

[0090] diaphragm

[0091] In some optional embodiments, the separator may be a polypropylene film or a polyethylene film.

[0092] In the present invention, the preparation method of the lithium-ion battery can be a conventional preparation method in the field, which can be a process of winding a positive electrode sheet, a separator, and a negative electrode sheet in this order to obtain a battery cell, then packaging the battery cell in a packaging shell and injecting the electrolyte; or a process of stacking a positive electrode sheet, a separator, and a positive electrode sheet in this order to obtain a battery cell, then packaging the battery cell in a packaging shell and injecting the electrolyte; and then undergoing processes such as standing, hot and cold pressing, formation, clamping, and capacity separation to obtain a lithium-ion battery.

[0093] In the electronic device described in the third aspect of the present invention, the electronic device includes the lithium-ion battery.

[0094] Illustratively, the electronic devices described in the present invention may be, but are not limited to, mobile devices (such as mobile phones, tablet computers, laptop computers, video recorders, portable printers / copiers, 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, ships and satellites, energy storage systems and backup power supplies, etc.

[0095] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0096] The reagents and raw materials used in the following examples and comparative examples are all commercially available.

[0097] Example 1

[0098] (1) Preparation of electrolyte

[0099] In a glove box with a nitrogen content of 99.999%, an actual oxygen content of 0.1 ppm, and a moisture content of 0.1 ppm, compound 1 was mixed uniformly with fluoroethylene carbonate (FEC) and a solvent (EC:DMC:EMC = 3:5:2, volume ratio), and then lithium hexafluorophosphate after sufficient drying was added to prepare an electrolyte; wherein, based on the total mass of the electrolyte being 100 wt.%, the content of compound 1 was 0.3 wt.%, the content of FEC was 5 wt.%, and the content of lithium hexafluorophosphate was 12.5 wt.%.

[0100] (2) Preparation of the positive electrode sheet

[0101] Weigh the positive electrode material LiNi 0.9 Mn 0.05 Co 0.05 O2, conductive agent acetylene black, and binder polyvinylidene fluoride in a mass ratio of 95:3:2. After fully stirring and mixing uniformly in N-methylpyrrolidone solvent, it was coated on aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0102] (3) Preparation of the negative electrode sheet

[0103] Weigh artificial graphite, natural graphite, silicon-carbon material, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 43:43:10:2:1:1. After fully stirring and mixing uniformly in a deionized water solvent system, it was coated on copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0104] (4) Preparation of the separator

[0105] Using polyethylene with a thickness of 9 μm as the base film, and coating a nano-aluminum oxide coating with a thickness of 3 μm on the base film to obtain the separator.

[0106] (5) Assembly of the lithium-ion battery

[0107] Stack the positive electrode sheet, separator, and negative electrode sheet prepared in the previous steps in sequence to obtain a bare cell, with the separator in the middle between the positive electrode sheet and the negative electrode sheet to play an isolation role, obtaining a bare cell. Then the bare cell was placed into an aluminum-plastic film, and after baking and removing water at 80 o °C, the electrolyte prepared in step (1) was injected and sealed. After that, through processes such as standing, hot and cold pressing, formation, clamping, and grading, a lithium-ion battery was obtained.

[0108] Examples 2 - 12 and Comparative Examples 1 - 4

[0109] Examples 2-10 and Comparative Examples 1-3 were the same as Example 1 in all steps and conditions except that the contents of the compound shown in Formula I and fluoroethylene carbonate in the electrolyte were different from those in Example 1. The contents of the compound shown in Formula I and fluoroethylene carbonate in the electrolytes of Examples 1-10 and Comparative Examples 1-3 are shown in Table 1.

[0110] In Examples 11-13, the electrolyte further included tris(trimethylsilyl) phosphate, allyl-1,3-sultone or tetraethenylsilane, and the remaining steps and conditions were the same as those in Example 1. In Comparative Example 4, except that vinylene carbonate (VC) was used to replace fluoroethylene carbonate in the electrolyte, the remaining steps and conditions were the same as those in Example 1. The components in Examples 11-13 and Comparative Example 4 are shown in Table 2.

[0111] Table 1

[0112]

[0113] Note: " / " indicates that the component is not included.

[0114] Table 2

[0115]

[0116] Note: " / " indicates that the component is not included.

[0117] Effect Examples

[0118] 1. Impedance DCR at -20°C

[0119] Adjust the temperature of the thermostat to -20°C, let it stand for 2 h, charge at a constant current of 0.33C to 4.25V, then charge at a constant voltage of 4.25V until cutoff at 0.05C, let it stand for 30 min, then discharge at a constant current of 0.33C to 2.5V; perform 2 charge-discharge cycles at 0.33C, record the last discharge capacity as C0; after standing for 30 min, discharge at 0.33C to 50%C0, adjust the SOC of the battery cell to 50%, let it stand for 30 min, record the terminal voltage V1 at the end of standing, discharge at a constant current of C0 for 30 s, record the terminal voltage V2 and current I, and calculate DCR = (V1 - V2) / I. The test results are shown in Table 3.

[0120] Table 3

[0121]

[0122] 2. Capacity retention rate during high-temperature cycling at 45°C

[0123] Adjust the temperature of the environmental chamber to 45°C, and let it stand for 1 h. Charge the lithium-ion battery at a constant current of 0.5C until 4.4V, then charge it at a constant voltage of 4.4V until the current is less than 0.05C. After leaving it standing for 10 min, discharge it at a constant current of 1.0C until 2.8 V. After leaving it standing for 10 min, record the discharge capacity of the lithium-ion battery at this time, which is the discharge capacity of the first cycle; perform multiple cycles on the battery according to the above conditions, and calculate the capacity retention rate of the battery after 800 cycles.

[0124] Calculate the cycle capacity retention rate according to the following formula:

[0125] Capacity retention rate (%) = (Discharge capacity corresponding to 800 cycles / Discharge capacity of the first cycle) × 100%.

[0126] The test results are shown in Table 3.

[0127] As can be seen from Table 3, the lithium-ion battery prepared with the electrolyte of the present invention has excellent low-temperature kinetic performance and high-temperature cycle performance. The DCR at -20°C is lower than 550Ω, more preferably lower than 500Ω, and the capacity retention rate after 800 cycles at 45°C is above 81%, more preferably up to 85% or more. The electrolyte in Comparative Example 1 does not add a cyanophosphoric acid ester compound nor a fluorinated carbonate; Comparative Example 2 only adds a cyanophosphoric acid ester compound, and Comparative Example 3 only adds a fluorinated carbonate; although Comparative Example 4 adds a cyanophosphoric acid ester compound, it uses an equivalent amount of vinylene carbonate to replace the fluorinated carbonate; the low-temperature kinetic performance and high-temperature cycle performance of Comparative Examples 1-4 cannot simultaneously achieve the effects of the present invention.

[0128] In the above specific embodiments, the purpose, technical solution, and beneficial effects of the present invention are further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes a compound represented by Formula I and a fluorinated carbonate; ， Formula I wherein R1 and R2 are each independently a substituent having 1-6 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms.

2. The electrolyte according to claim 1, characterized in that, R1 and R2 are each independently one or more of an alkyl group, an alkenyl group, an alkynyl group, a carbonyl group, an ester group, an amino-substituted alkyl group, and a heterocyclic group having 1-6 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms.

3. The electrolyte according to claim 1, characterized in that, The compound represented by Formula I is selected from one or more of Compounds 1-4; Compound 1 , Compound 2 , Compound 3 , Compound 4 .

4. The electrolyte according to claim 1, characterized in that, The content of the compound represented by Formula I is 0.05 wt.% - 3 wt.%, and wt.% is the mass percentage of the compound represented by Formula I in the electrolyte.

5. The electrolyte according to claim 1, characterized in that, The fluorinated carbonate is vinylene carbonate; and / or, the content of the fluorinated carbonate is 0.5 wt.% - 8 wt.%, and wt.% is the mass percentage of the fluorinated carbonate in the electrolyte.

6. The electrolyte according to claim 1, wherein The solvent in the electrolyte is selected from one or more of diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, trifluoroethyl methyl carbonate, difluoroethyl acetate, ethers, and nitriles; and / or, the content of the solvent in the electrolyte is 70 wt.% - 80 wt.%, and wt.% is the mass percentage of the solvent in the electrolyte.

7. The electrolyte according to claim 1, wherein The lithium salt in the electrolyte is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, and lithium trifluoromethanesulfonate; and / or, the content of the lithium salt in the electrolyte is 12 wt.% - 16 wt.%, and wt.% is the mass percentage of the lithium salt in the electrolyte.

8. The electrolyte according to claim 1, characterized in that, The electrolyte further includes one or more of ethylene sulfate, allyl-1,3-sultone, tetravinylsilane, and tris(trimethylsilyl) phosphate.

9. A lithium-ion battery, characterized in that, The lithium ion battery includes the electrolyte according to any one of claims 1-8.

10. An electronic device, characterized in that, The electronic device includes the lithium ion battery according to claim 9.

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