Electrolyte and electrochemical device

Abstract

The application provides an electrolyte and an electrochemical device, the electrolyte comprises a phosphine compound shown in formula I-A, and the cycle performance and high-temperature storage performance of a lithium ion battery can be improved, and the cycle impedance increase is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, and in particular, to an electrolyte and an electrochemical device. BACKGROUND

[0002] With the wide application of electrochemical devices (e.g., lithium ion batteries) in various electronic products, users have put forward higher and higher requirements for the performance of electrochemical devices, especially the cycle performance and high-temperature storage performance. Therefore, further improvement is urgently needed to meet people's increasing use requirements. SUMMARY

[0003] In view of the problems in the background art, the purpose of the present application is to provide an electrolyte that effectively improves the high-temperature storage performance of an electrochemical device, slows down the increase of cycle impedance, and reduces the voltage drop during high-temperature storage.

[0004] To achieve the above-mentioned purpose, the present application provides an electrolyte comprising a compound of formula I-A:

[0005]

[0006] wherein n is an integer selected from 1-2; R 11 , R 12 , R 13 , R 14 are independently selected from substituted or unsubstituted C1-C 10 alkyl, substituted or unsubstituted C3-C 10 cycloalkyl, substituted or unsubstituted C2-C 10 alkenyl, substituted or unsubstituted C2-C 10 alkynyl, substituted or unsubstituted C6-C 10 aryl, and when substituted, the substituents include halogen; R 15 are independently selected from substituted or unsubstituted C1-C 10 alkylene, substituted or unsubstituted C3-C 10 cycloalkylene, substituted or unsubstituted C2-C 10 alkenylene, substituted or unsubstituted C2-C 10 alkynylene, substituted or unsubstituted C6-C 10 arylene, and the substituents include halogen.

[0007] In some embodiments, the compound of formula I-A includes at least one of the following compounds:

[0008]

[0009] According to some embodiments of the present application, the mass percentage content of the compound of formula I-A can be any value in the range of 0.01%-0.1%, 0.1%-0.2%, 0.2%-0.3%, 0.3%-0.4%, 0.4%-0.5%, 0.5%-0.6%, 0.6%-0.7%, 0.7%-0.8%, 0.8%-0.9%, 0.9%-1%, 1%-2%, 2%-3%. In some embodiments, the mass percentage content of the compound of formula I-A is 0.01%-3% based on the mass of the electrolyte.

[0010] In some embodiments, the electrolyte further comprises a polycarbonitrile compound, wherein the mass percentage content of the polycarbonitrile compound is 0.01%-5% based on the mass of the electrolyte.

[0011] The polycarbonitrile compound comprises at least one of the following compounds:

[0012]

[0013] In some embodiments, the ratio W of the mass percentage content of the compound of formula I-A to the mass percentage content of the polycarbonitrile compound is I 0.01≤W I ≤50. In some embodiments, 0.01≤W I ≤1.

[0014] In some embodiments, the electrolyte further comprises a sulfur-oxygen double bond containing compound, wherein the mass percentage content of the sulfur-oxygen double bond containing compound is 0.08%-10% based on the mass of the electrolyte; the sulfur-oxygen double bond containing compound comprises at least one of a compound of formula II-A and a compound of formula II-B:

[0015]

[0016] wherein Q and Z are each independently selected from at least one of , represents a bonding site to an adjacent atom; R 21 , R 22 are each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C 10 alkenyl, wherein the substituents are halogen or C6-C 10 aryl. R 23 and R 24 are each independently selected from substituted or unsubstituted C1-C5 alkylene, substituted or unsubstituted C2-C 10 alkenylene, wherein the substituents are halogen or C6-C 10 aryl.

[0017] In some embodiments, the sulfur-oxygen double bond containing compound includes at least one of 1,3-propane sulfite, 1,4-butane sulfite, methane disulfite, 1,3-propane disulfonic anhydride, ethylene sulfate, 4-methyl ethylene sulfate, 2,4-butane sulfite, 2-methyl-1,3-propane sulfite, 1,3-butane sulfite, propylene-1,3-sulfite, or propylene sulfate.

[0018] In some embodiments, the ratio of the mass percentage content of the compound of Formula I-A to the mass percentage content of the compound of Formula II W II is 0.01≤W II ≤5.

[0019] In some embodiments, the electrolyte further includes a compound of Formula III:

[0020]

[0021] wherein R 31 is selected from substituted C1-C6 alkylene, substituted or unsubstituted C2-C6 alkenylene; when substituted, the substituents include at least one of halogen or C2-C6 alkenyl.

[0022] The mass percentage content of the compound of Formula III is 0.01% to 15% based on the mass of the electrolyte.

[0023] In some embodiments, the compound of Formula III includes at least one of the following compounds:

[0024]

[0025] In some embodiments, the electrolyte further includes a boron-containing lithium salt, wherein the mass percentage content of the boron-containing lithium salt is 0.01% to 1% based on the mass of the electrolyte.

[0026] In some embodiments, the boron-containing lithium salt includes at least one of lithium tetrafluoroborate, lithium bis-oxalate borate, or lithium difluoro-oxalato borate.

[0027] In some embodiments, the ratio of the mass percentage content of the boron-containing lithium salt to the mass percentage content of the compound of Formula I-A is 0.1-50. In some embodiments, the ratio is 0.1-1.

[0028] The present application also discloses an electrochemical device including the aforementioned electrolyte.

[0029] The present application at least includes the following beneficial effects: the present application introduces a phosphine compound represented by formula I-A into the electrolyte, formula I-A can be oxidized to form a film on the positive electrode, in addition, the phosphorus in formula I-A can absorb the oxygen released by the positive electrode, these two properties together stabilize the positive electrode interface and inhibit the continuous decomposition of the electrolyte. DETAILED DESCRIPTION

[0030] It will be understood that the disclosed embodiments are merely examples of the present application, which can be implemented in various forms, therefore, the specific details disclosed herein should not be interpreted as limiting, but merely as a basis for the claims and as a basis for teaching a person of ordinary skill in the art to implement the present application in various ways.

[0031] In the description of the present application, unless otherwise explicitly specified and limited, the terms "formula I", "formula II", etc. are only for illustrative purposes, and cannot be understood as indicating or implying relative importance and mutual existence.

[0032] At present, the main method to improve the energy density of the electrochemical device includes increasing the charging voltage of the electrochemical device, but when the charging voltage of the electrochemical device is increased, the higher charging voltage will accelerate the oxidative decomposition of the high-valence state transition metal in the positive electrode active material to the electrolyte, the high-valence state transition metal will obtain electron compensation from the oxygen atom, resulting in oxygen release, further accelerating the decomposition of the electrolyte, resulting in increased gas production of the electrochemical device, affecting the high-temperature storage performance of the electrochemical device, therefore, it is necessary to stabilize the high-valence state transition metal in the positive electrode active material, improve the high-temperature storage performance of the electrochemical device, slow down the increase of the cycle impedance and reduce the voltage drop during the high-temperature storage process.

[0033] <electrolyte>

[0034] In some embodiments, the electrolyte comprises a compound of formula I-A:

[0035]

[0036] wherein n is an integer selected from 1-2; R 11 , R 12 , R 13 , R 14 are independently selected from substituted or unsubstituted C1-C 10 alkyl, substituted or unsubstituted C3-C 10 cycloalkyl, substituted or unsubstituted C2-C 10 alkenyl, substituted or unsubstituted C2-C 10 alkynyl, substituted or unsubstituted C6-C 10 aryl, when substituted, the substituents include halogen; R 15 are independently selected from substituted or unsubstituted C1-C10 Alkylene, substituted or unsubstituted C3-C 10 Cycloalkylene, substituted or unsubstituted C2-C 10 alkenyl groups, substituted or unsubstituted C2-C 10 alkyne group, substituted or unsubstituted C6-C 10 The aryl group, with substituents including halogens.

[0037] In the electrolyte, the compound represented by formula IA can be oxidized to form a film at the positive electrode. Furthermore, the phosphorus in formula IA can absorb oxygen released from the positive electrode, and both work together to stabilize the positive electrode interface. By introducing the compound of formula IA into the electrolyte, the positive electrode interface can be protected, thus inhibiting the continuous decomposition of the electrolyte.

[0038] In some embodiments, the compound of formula IA includes at least one of the following compounds:

[0039]

[0040]

[0041] In some embodiments, the mass percentage of compound IA is 0.01%-3% based on the mass of the electrolyte. If the mass percentage of compound IA is too low, its effect on improving the high-temperature storage and cycling performance of the electrochemical device and reducing the growth of cycling impedance is relatively limited; if the mass percentage of compound IA is too high, its effect on improving the high-temperature storage and cycling performance of the electrochemical device no longer increases significantly, and further increasing its content may lead to excessively high electrolyte viscosity. In some embodiments, the mass percentage of compound IA can be 0.01%, 0.1%, 0.5%, 1%, 2%, or 3% based on the mass of the electrolyte.

[0042] In some embodiments, the electrolyte further includes a polynitrile compound, wherein the mass percentage of the polynitrile compound is 0.01% to 5% based on the mass of the electrolyte. The polynitrile compound can synergize with the compound of formula IA in the electrolyte, providing stronger protection for the positive electrode interface, further inhibiting electrolyte decomposition, and thus further improving the cycle performance of the electrochemical device.

[0043] If the mass percentage of the polycarbonitrile compound is too low, it cannot effectively protect the positive electrode interface, and the effect of improving the performance of the electrochemical device is not significant. If the mass percentage of the polycarbonitrile compound is too high, for example, greater than 5%, the effect of the polycarbonitrile compound on improving the performance of the electrochemical device is no longer significantly improved, which can lead to an increase in the viscosity of the electrolyte, affecting the kinetics, and affecting the cycle impedance growth and high-temperature storage performance of the electrochemical device. In some embodiments, the mass percentage of the polycarbonitrile compound can be 0.01%, 0.5%, 1%, 2% based on the mass of the electrolyte.

[0044] In some embodiments, the polycarbonitrile compound comprises at least one of the following compounds:

[0045]

[0046] In some embodiments, the ratio W of the mass percentage of the compound of formula I-A to the mass percentage of the polycarbonitrile compound is I 0.01≤W I ≤1.

[0047] In some embodiments, the electrolyte further comprises a compound containing a sulfur-oxygen double bond, wherein the mass percentage of the compound containing a sulfur-oxygen double bond is 0.08% to 10% based on the mass of the electrolyte. The compound containing a sulfur-oxygen double bond has strong antioxidant ability and can improve the stability of the positive electrode interface. On the other hand, the compound containing a sulfur-oxygen double bond can be reduced on the surface of the negative electrode to form a protective film, inhibit the decomposition of the electrolyte, and further enhance the stability of the interface. Therefore, the combined use of the compound containing a sulfur-oxygen double bond can further improve the high-temperature storage performance and cycle performance of the electrochemical device.

[0048] If the mass percentage of the compound containing a sulfur-oxygen double bond is too low, its effect on alleviating the reaction of the electrolyte at the positive and negative electrodes is relatively limited. If the mass percentage of the compound containing a sulfur-oxygen double bond is too high, for example, greater than 10%, the effect of the compound containing a sulfur-oxygen double bond on enhancing the stability of the positive electrode interface and the negative electrode interface is no longer significantly improved, and it can lead to an excessively large viscosity of the electrolyte, affecting the kinetics, and affecting the low-temperature discharge performance of the electrochemical device. In some embodiments, the mass percentage of the compound containing a sulfur-oxygen double bond can be 0.1%, 0.5%, 1%, 3%, 5%, 7% based on the mass of the electrolyte.

[0049] The compound containing a sulfur-oxygen double bond comprises at least one of the following compounds:

[0050]

[0051] wherein Q and Z are each independently selected from at least one of represents a binding site with an adjacent atom; R 21 , R 22 each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C6 alkenyl, wherein the substituents are halogen or C6-C10 aryl. R 10 each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C6 alkenyl, wherein the substituents are halogen or C6-C10 aryl. R 10 each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C6 alkenyl, wherein the substituents are halogen or C6-C10 aryl. R 23 and R 24 each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C6 alkenyl, wherein the substituents are halogen or C6-C10 aryl. R 10 each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C6 alkenyl, wherein the substituents are halogen or C6-C10 aryl. R 10 each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C6 alkenyl, wherein the substituents are halogen or C6-C10 aryl. R

[0052] In some embodiments, the sulfur-oxygen double bond containing compound includes at least one of 1,3-propane sulfite, 1,4-butane sulfite, methane disulfite, 1,3-propane disulfonic anhydride, ethylene sulfate, 4-methyl ethylene sulfate, 2,4-butane sulfite, 2-methyl-1,3-propane sulfite, 1,3-butane sulfite, propylene-1,3-sulfite, or propylene sulfate.

[0053] In some embodiments, the ratio of the mass percentage of the compound of formula I-A to the mass percentage of the compound of formula II W II is 0.01≤W II ≤5. In some embodiments, the ratio of the mass of the compound of formula I-A to the mass of the sulfur-oxygen double bond containing compound based on the mass of the electrolyte can be: 0.062, 0.1, 0.167, 0.333, 0.5, 1, 5.

[0054] In some embodiments, the electrolyte further includes a compound of formula III:

[0055]

[0056] wherein R 31 is selected from substituted or unsubstituted C1-C6 alkylene, substituted or unsubstituted C2-C6 alkenylene; when substituted, the substituents are selected from halogen, C1-C6 alkyl, C2-C6 alkenyl. The compound of formula III can assist in enhancing the film formation stability of the negative electrode solid electrolyte interface (SEI) film. The use of the compound of formula III can increase the flexibility of the SEI film, further enhance the protection of the active material, reduce the interface contact probability between the active material and the electrolyte, and reduce the side reactions between the electrolyte and the active material, thereby reducing the impedance generated by the accumulation of by-products during the cycle.

[0057] In some embodiments, the mass percentage of the compound of Formula III is 0.01% to 15% based on the mass of the electrolyte. If the mass percentage of the compound of Formula III is too low, it does not sufficiently protect the interface, and the performance of the electrochemical device is limited in improvement; if the mass percentage of the compound of Formula III is too high, for example, greater than 15%, the enhancement of the stability of the SEI by the cyclic carbonate compound is no longer significantly improved. In some embodiments, the mass percentage of the compound of Formula III is 0.01%, 0.1%, 1%, 5%, 10%, 15% based on the mass of the electrolyte.

[0058] In some embodiments, the compound of Formula III includes at least one of the following compounds:

[0059]

[0060] In some embodiments, the electrolyte further includes a lithium salt containing boron, wherein the mass percentage of the lithium salt containing boron is 0.01% to 1% based on the mass of the electrolyte. The lithium salt containing boron can form a film at the cathode interface, protect the cathode interface, and produce a synergistic effect with the compound of Formula I-A, which can further improve the cycle performance of the electrochemical device.

[0061] In some embodiments, the lithium salt containing boron includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, or lithium difluoro(oxalato)borate.

[0062] In some embodiments, the ratio of the mass percentage of the lithium salt containing boron to the mass percentage of the compound of Formula I-A is 0.1-50. In some embodiments, the ratio is 0.1-1. If the mass percentage of the lithium salt containing boron is too low, it is not sufficient to protect the cathode interface, and its effect on cycle improvement is relatively limited; if the mass percentage of the lithium salt containing boron is too high, for example, greater than 1%, the effect of the lithium salt containing boron on cycle improvement is no longer significantly improved. In some embodiments, the mass percentage of the lithium salt containing boron is 0.01%, 0.1%, 0.5%, 1% based on the mass of the electrolyte.

[0063] In some embodiments, the electrolyte can further include other non-aqueous organic solvents and electrolyte salts. The non-aqueous organic solvents can include at least one of carbonates, carboxylates, ethers, or other aprotic solvents. Examples of carbonate solvents include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinyl carbonate, propylene carbonate, butylene carbonate, di(2,2,2-trifluoroethyl) carbonate, and the like. Examples of carboxylate solvents include methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone, 2,2-difluoroethyl acetate, valerolactone, butyrolactone, ethyl 2-fluoroacetate, ethyl 2,2-difluoroacetate, ethyl trifluoroacetate, ethyl 2,2,3,3,3-pentafluoropropionate, methyl 2,2,3,3,4,4,4,4-heptafluorobutyrate, methyl 4,4,4-trifluoro-3-(trifluoromethyl)butyrate, ethyl 2,2,3,3,4,4,5,5,5,5-nonafluoropentanoate, methyl 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononanoate, ethyl 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononanoate, and the like. Examples of ether solvents include dimethyl glycol ether, diethyl glycol ether, tetraethyl glycol ether, dibutyl ether, tetrahydrofuran, 2-methyl tetrahydrofuran, bis(2,2,2-trifluoroethyl) ether, and the like.

[0064] In some embodiments, the electrolyte salt of the present application includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the electrolyte salt includes at least one of lithium hexafluorophosphate LiPF6, lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (abbreviated as LiFSI), or lithium hexafluorocerate (LiCsF6), lithium perchlorate LiClO4, lithium triflate LiCF3SO3.

[0065] In some embodiments, the mass percentage of the electrolyte salt is 10%-15% based on the mass of the electrolyte. If the concentration of the electrolyte salt is too low, the ionic conductivity of the electrolyte is low, which affects the rate and cycle performance of the electrochemical device; if the concentration of the electrolyte salt is too high, the viscosity of the electrolyte is too large, which affects the rate performance of the electrochemical device. Alternatively, the mass percentage of the electrolyte salt is 12%-15%.

[0066] <Anode sheet>

[0067] In some embodiments, the negative electrode can include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer can be disposed on one side or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector can employ at least one of a copper foil, an aluminum foil, a nickel foil, or a carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector can be 1 µm to 200 µm. In some embodiments, the negative electrode active material layer can be coated only on a partial area of the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer can be 10 µm to 500 µm. It should be understood that these are merely exemplary, and other suitable thicknesses can be employed.

[0068] In some embodiments, the negative electrode active material layer includes a negative electrode active material. In some embodiments, the negative electrode active material in the negative electrode active material layer includes at least one of lithium metal, natural graphite, artificial graphite, or a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, a silicon oxide compound, a silicon carbon compound, or a silicon alloy.

[0069] In some embodiments, the negative electrode active material layer can further include a conductive agent and / or a binder. The conductive agent in the negative electrode active material layer can include at least one of carbon black, acetylene black, ketjen black, flake graphite, graphene, carbon nanotube, carbon fiber, or carbon nanowire. In some embodiments, the binder in the negative electrode active material layer can include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylate ester, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, butadiene-styrene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. It should be understood that the above-disclosed materials are merely exemplary, and any other suitable materials can be employed for the negative electrode active material layer. In some embodiments, the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode active material layer can be (80-99):(0.5-10):(0.5-10), it should be understood that this is merely exemplary, and is not intended to limit the present application.

[0070] <Positive Electrode Sheet>

[0071] In some embodiments, the positive electrode can include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer can be located on one side or both sides of the positive electrode current collector. In some embodiments, the positive electrode current collector can employ an aluminum foil, of course, other positive electrode current collectors commonly used in the art can also be employed. In some embodiments, the thickness of the positive electrode current collector can be 1 µm to 200 µm. In some embodiments, the positive electrode active material layer can be coated only on a partial area of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer can be 10 µm to 500 µm. It should be understood that these are merely exemplary, and other suitable thicknesses can be employed.

[0072] In some embodiments, the cathode active material layer includes a cathode active material. In some embodiments, the cathode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCo 1-y MyO2, LiNi 1-y MyO2, LiMn 2-y MyO4, LiNi x Co y Mn z M 1-x-y- z O2, wherein M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, or Ti, and 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1. In some embodiments, the cathode active material can include at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese phosphate, lithium nickel cobalt aluminum phosphate, or lithium nickel manganese phosphate, which can be doped and / or coated.

[0073] In some embodiments, the cathode active material layer further includes a binder and a conductive agent. In some embodiments, the binder in the cathode active material layer can include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, a polyamide, a polyacrylonitrile, a polyacrylate, a polyacrylic acid, a polyacrylate salt, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, a polyvinyl ether, a polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. In some embodiments, the conductive agent in the cathode active material layer can include at least one of conductive carbon black, acetylene black, ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the mass ratio of the cathode active material, the conductive agent, and the binder in the cathode active material layer can be (70-98):(1-15):(1-15). It should be understood that the above is merely an example, and the cathode active material layer can employ any other suitable materials, thickness, and mass ratio.

[0074] <separator>

[0075] In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a good effect on preventing short circuits, and can improve the stability of the battery through the shutdown effect. In some embodiments, the thickness of the separator is in the range of about 3 μm to 500 μm.

[0076] In some embodiments, the surface of the separator film can further include a porous layer disposed on at least one surface of the separator film, the porous layer including at least one of inorganic particles or a binder, the inorganic particles selected from at least one of aluminum oxide (AI2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator film have a diameter in a range of about 0.01 pm to 1 pm. The binder of the porous layer is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer of the surface of the separator film can improve the heat resistance, oxidation resistance, and electrolyte infiltration properties of the separator film, and enhance the adhesion between the separator film and the electrode sheet.

[0077] <case>

[0078] The case is used to package the electrode assembly. In some embodiments, the case can be a hard shell case or a flexible case. The material of the hard shell is, for example, metal. The flexible case is, for example, a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0079] (electrochemical device)

[0080] The electrochemical device of the present application is not particularly limited and can include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device can include, but is not limited to, a lithium ion battery.

[0081] In some embodiments, the electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator film, an electrolyte, and a case.

[0082] The electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly. In some embodiments, the electrochemical device is a lithium ion battery, but the present application is not limited thereto.

[0083] In some embodiments of the present application, taking a lithium ion battery as an example, the positive electrode, the separator film, and the negative electrode are wound or stacked in order to form an electrode assembly, which is then packaged in, for example, an aluminum plastic film case, injected with an electrolyte, formed, and packaged to form a lithium ion battery. Then, the prepared lithium ion battery is subjected to performance testing.

[0084] Those skilled in the art will appreciate that the above-described method for preparing an electrochemical device (e.g., a lithium ion battery) is merely an example. Other methods commonly used in the art can be employed without departing from the disclosure.

[0085] (electronic device)

[0086] Embodiments of the present application also provide an electronic device comprising the above-described electrochemical device. The electronic device of embodiments of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, a power tool, a flashlight, a camera, a home-use large storage battery, and a lithium ion capacitor, etc.

[0087] The present application will be further described below with reference to lithium ion batteries as an example of the electrochemical device and in conjunction with specific embodiments. It should be understood that these embodiments are merely illustrative of the present application and are not intended to limit the scope of the present application.

[0088] (1) Preparation of the positive electrode

[0089] The positive electrode active material lithium cobaltate LiCoO2, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride (PVDF) were dissolved in N-methyl pyrrolidone (NMP) solution in a weight ratio of 97.9:0.9:1.2 to form a positive electrode slurry. An aluminum foil of 13 μm was used as the positive electrode current collector, and the positive electrode slurry was coated on the positive electrode current collector. After drying, cold pressing, and cutting, the positive electrode was obtained. The tap density of the positive electrode was 4.15 g / cm3. 3 .

[0090] (2) Preparation of the negative electrode

[0091] The negative electrode active material artificial graphite, the binder styrene butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC) were dissolved in deionized water in a weight ratio of 97.4:1.4:1.2 to form a negative electrode slurry. A copper foil of 10 μm thickness was used as the negative electrode current collector, and the negative electrode slurry was coated on the negative electrode current collector. After drying, cold pressing, and cutting, the negative electrode was obtained. The tap density of the negative electrode was 1.8 g / cm3. 3 .

[0092] (3) Preparation of the separator

[0093] The separator film substrate is 5 μm thick polyethylene (PE), on one side of the separator film substrate is coated with a 2 μm thick layer of aluminum oxide ceramic, and finally on both sides of the separator film coated with a single layer of ceramic is coated with 2.5 mg / 1540.25 mm 2 of the binder polyvinylidene fluoride (PVDF), and dried. The porosity of the separator film is 39%.

[0094] (4) Preparation of electrolyte

[0095] Ethylene carbonate (abbreviated as EC), propylene carbonate (abbreviated as PC), diethyl carbonate (abbreviated as DEC), ethyl propionate (abbreviated as EP), and propyl propionate (abbreviated as PP) are mixed in a mass ratio of 1:1:1:1:1 in an environment with a water content of less than 10 ppm, and then LiPF6 is dissolved in the above non-aqueous solvent to form an electrolyte, wherein the mass percentage of LiPF6 in the electrolyte is 12.5% based on the mass of the electrolyte. A certain amount of additive is added to the above electrolyte to obtain the electrolyte in each example. The difference between each example is that the type and / or content of the additive used in the electrolyte are different. The specific types of additives and their mass percentages in the electrolyte are shown in Tables 1 to 3 below. The mass percentage of the additive is calculated based on the mass of the electrolyte. The correspondence of the abbreviations of some additives is as follows: succinonitrile (SN), adiponitrile (ADN), 1,3,6-hexanetricarbonitrile (HTCN), 1,2,3-tris(2-cyanoethoxy)propane (TCEP), 1,2,3,4,5-pentakis(2-cyanoethoxy)pentane (PCEP).

[0096] (5) Preparation of lithium ion battery

[0097] The positive electrode, the separator film, and the negative electrode are sequentially stacked in order, with the separator film between the positive electrode and the negative electrode to serve as a separator, and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer packaging aluminum plastic film, and after removing the water at 80°C, the above electrolyte is injected and packaged, and after formation, degassing, and edge cutting processes, a lithium ion battery is obtained. The test method of each parameter of the present application is described below.

[0098] Next, the performance of the lithium ion battery is tested:

[0099] (1) 25°C cycle performance and cycle impedance test:

[0100] The lithium-ion battery was charged at 0.7C to 4.5V at 25℃, and then charged at a constant voltage to 0.05C at 4.5V. It was then discharged at 0.7C to 3.0V, and this cycle of 0.7C charging and 1C discharging was repeated for 800 cycles. The discharge capacity of the third cycle was used as the baseline, and the capacity retention rate was used as the indicator to evaluate the cycle performance of the lithium-ion battery. The impedance was measured after the third cycle and after the 300th cycle at 1000Hz.

[0101] Cycle capacity retention = Discharge capacity at 800th cycle / Discharge capacity at 3rd cycle × 100%.

[0102] Cyclic impedance growth rate = impedance after the 300th cycle / impedance after the 3rd cycle × 100%.

[0103] (2) High-temperature storage performance test:

[0104] The lithium-ion battery was charged at 25℃ with a constant current of 0.5C to 4.5V, and then charged with a constant voltage to a current of 0.05C. The thickness of the lithium-ion battery was measured and recorded as d0. The battery was then placed in an 80℃ oven for 4 hours, and the thickness was monitored and recorded as d. The thickness expansion rate (%) of the lithium-ion battery after 4 hours of high-temperature storage is calculated as (d-d0) / d0×100%. The test was stopped when the thickness expansion rate exceeded 50%.

[0105] The types and contents of additives used in the examples and comparative examples are shown in Tables 1-5. The contents of each additive are calculated as a percentage of mass based on the total mass of the electrolyte.

[0106] The specific test results are as follows:

[0107] Table 1. Parameters of Examples 1-11 and Comparative Examples 1-2

[0108]

[0109] As can be seen from Examples 1-11 and Comparative Examples 1-2 in Table 1, the inclusion of the compound of Formula I-A can improve the cycle performance and high-temperature storage performance of the lithium ion battery and reduce the cycle impedance growth, and the degree of improvement is greater as the mass percentage of the compound of Formula I-A increases, and finally tends to be balanced. Trivalent P is easily oxidized and can absorb active oxygen released from the positive electrode on the surface of the positive electrode to reduce the oxidative decomposition of the electrolyte by the active oxygen. The compound of Formula I-A has multiple P-containing functional groups, and multiple reaction sites can participate in oxidation to form an interface film. The interface film formed by oxidation is more stable than the single P-containing functional group of trimethylphosphine, has a stronger interface protection effect, and has a better effect of inhibiting the continuous consumption of the electrolyte. When the content of the compound of Formula I-A is within the scope of the present application, the cycle performance and high-temperature storage performance of the electrochemical device and the cycle impedance growth reduction performance are more optimal.

[0110] Parameters of Examples 2 and 12-20 in Table 2

[0111]

[0112] As can be seen from Examples 2 and 12-20 in Table 2, the combination of the compound of Formula I-A and the polycarbonyl compound can further improve the cycle performance and high-temperature storage performance of the electrochemical device. The polycarbonyl compound can stabilize the high-valence transition metal in the positive electrode active material, and has a synergistic effect with the compound of Formula I-A to stabilize the positive electrode interface and inhibit the consumption of the electrolyte and gas production. When the value of WI is within the scope of the present application, the cycle performance and safety performance are more optimal, and when the value of WI is too large or too small, the cycle performance and high-temperature storage performance will be affected.

[0113] Parameters of Examples 2 and 21-29 in Table 3

[0114]

[0115]

[0116] As can be seen from Examples 2 and 21 and 28 in Table 3, the combination of the compound of Formula I-A and the compound containing a sulfur-oxygen double bond can further improve the high-temperature storage performance and cycle performance of the lithium ion battery. When the value of W II is within the scope of the present application, the cycle performance and safety performance are more optimal, and when the value of W II is too large or too small, the cycle performance and high-temperature storage performance will be affected.

[0117] Parameters of Examples 2 and 29-40 in Table 4

[0118]

[0119]

[0120] It can be seen by comparing Example 2 and Examples 29-40 that the combination of the compound of formula I-A and the lithium salt containing boron can further improve the cycle performance, the combination of the compound of formula I-A and the lithium salt containing phosphorus can further improve the high-temperature storage performance and cycle performance of the lithium ion battery, and the combination of multiple additives can better obtain a lithium ion battery with excellent performance.

[0121] Table 5 Parameters of Example 3 and Examples 41-47

[0122]

[0123] It can be seen by comparing Example 2 and Examples 41-47 that the combination of the compound of formula I and the compound of formula III can significantly improve the cycle performance of the lithium ion battery.

[0124] The above disclosed features are not intended to limit the scope of the present disclosure, and equivalent changes made to the content described in the claims of the present disclosure should be included in the scope of the claims of the present disclosure.

Claims

1. An electrolyte comprising a compound of formula I-A; said compound I-A comprising at least one of I-16 and I-20: ； The electrolyte also includes a compound of formula III: in, R 31 It is selected from substituted or unsubstituted C1-C6 alkylene groups and substituted or unsubstituted C2-C6 alkenyl groups; when substituted, the substituent is selected from halogens, C1-C6 alkyl groups, and C2-C6 alkenyl groups. Based on the mass of the electrolyte, the mass percentage of the compound of formula I-A is 0.01%-3%; Based on the mass of the electrolyte, the mass percentage of the compound of formula III is from 0.01% to 15%.

2. The electrolyte according to claim 1, wherein, The compound of formula I-A further includes at least one of the following compounds: 。 3. The electrolyte according to claim 1, wherein, Based on the mass of the electrolyte, the mass percentage of the compound of formula I-A is 0.08%-3%.

4. The electrolyte according to claim 1, wherein the electrolyte further comprises a polynitrile compound, wherein, Based on the mass of the electrolyte, the mass percentage of the polynitrile compound is from 0.01% to 5%. The polynitrile compound includes at least one of the following compounds: 。 5. The electrolyte according to claim 1, wherein, The ratio W of the mass percentage of compound I-A to the mass percentage of polynitrile compound. Ⅰ For 0.01≤W Ⅰ ≤1.

6. The electrolyte according to claim 1, wherein, The electrolyte also includes a sulfur-containing oxygen double bond compound, wherein the mass percentage of the sulfur-containing oxygen double bond compound is 0.08% to 10% based on the mass of the electrolyte. The sulfur-containing oxygen double bond compound includes at least one of the compounds of formula II-A and formula II-B: Q and Z are each independently selected from At least one of them, Indicates the binding site with adjacent atoms; R 21 R 22 Each is independently selected from substituted or unsubstituted C1-C5 alkyl groups, substituted or unsubstituted C2-C5 alkyl groups. 10 The alkenyl group, wherein the substituent is halogen or C6-C 10 aryl, R 23 and R 24 Each is independently selected from substituted or unsubstituted C1-C5 alkylene groups, substituted or unsubstituted C2-C5 alkylene groups. 10 The alkenyl group, wherein the substituent is halogen or C6-C 10 Aryl groups.

7. The electrolyte according to claim 6, wherein, The sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methylene disulfonate, 1,3-propanedisulfonic anhydride, vinyl sulfate, 4-methyl vinyl sulfate, 2,4-butanesulfonate lactone, 2-methyl-1,3-propanesulfonate lactone, 1,3-butanesulfonate lactone, propenyl-1,3-sulfonate lactone, or propenyl sulfate.

8. The electrolyte according to claim 1, wherein, The ratio W of the mass percentage of compound I-A to the mass percentage of compound II. Ⅱ For 0.01≤W Ⅱ ≤5.

9. The electrolyte according to claim 1, wherein the compound of formula III comprises at least one of the following compounds: 。 10. The electrolyte according to claim 1, wherein the electrolyte further comprises a boron-containing lithium salt, wherein, Based on the mass of the electrolyte, the mass percentage of the boron-containing lithium salt is from 0.01% to 1%.

11. The electrolyte according to claim 10, wherein the boron-containing lithium salt comprises at least one of lithium tetrafluoroborate, lithium dioxalate borate, or lithium difluorooxalate borate.

12. The electrolyte according to claim 10, wherein the mass percentage of the boron-containing lithium salt is 0.1-1 to the mass percentage of the compound of formula I-A.

13. An electrochemical device comprising an electrolyte according to any one of claims 1 to 12.

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