Electrolyte and electrochemical device comprising the same

Abstract

The application discloses an electrolyte and an electrochemical device, the electrolyte comprising a compound shown in formula I; wherein n is an integer selected from 1 to 3, A 11 , A 12 are each independently selected from and at least one of R 1 , R 11 , R 12 are each independently selected from a covalent single bond, a substituted or unsubstituted C1-C5 alkylene, when substituted, the substituent comprises halogen or C1-C3 alkyl, and represents a binding site with an adjacent atom. By introducing the compound shown in formula I into the electrolyte, the application can inhibit the continuous decomposition of the electrolyte, thereby delaying the cycle impedance growth of the electrochemical device, and improving the room temperature cycle performance and high temperature storage performance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to an electrolyte and an electrochemical device comprising the electrolyte. Background Technology

[0002] With the widespread application of electrochemical devices (such as lithium-ion batteries) in various electronic products, users have put forward increasingly higher requirements for the performance of electrochemical devices, especially high-energy-density lithium-ion batteries. At present, the main method to improve the energy density of lithium-ion batteries is to increase the charging voltage. However, a higher charging voltage will accelerate the oxidative decomposition of the electrolyte by the high-valence transition metals of the positive electrode active material in the lithium-ion battery. The high-valence transition metals will obtain electron compensation from oxygen atoms, resulting in oxygen release, which in turn accelerates the decomposition of the electrolyte, leading to increased gas production in the lithium-ion battery and affecting the room temperature cycle performance and high temperature storage performance of the lithium-ion battery. Summary of the Invention

[0003] In view of this, this application provides an electrolyte and an electrochemical device containing the electrolyte. The electrolyte has good oxidation resistance, can stabilize the interface between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, can suppress gas generation in the electrolyte, delay the growth of the cycle impedance of the electrochemical device, and thus improve the room temperature cycle performance and high temperature storage performance of the electrochemical device.

[0004] In a first aspect, this application provides an electrolyte comprising a compound of formula I;

[0005]

[0006] Where n is an integer selected from 1 to 3, A 11 A 12 Each independently selected And it contains at least one and R 1 R 11 R 12 Each is independently selected from covalently single-bonded, substituted or unsubstituted C1-C5 alkylene groups; when substituted, the substituents include halogens or C1-C3 alkyl groups. Indicates the binding site with adjacent atoms.

[0007] In some implementations, n is selected from integers 1 to 2, and R 1 R 11 R 12 Each is independently selected from a covalent single bond or a C1-C3 alkylene group.

[0008] This application introduces the compound shown in Formula I into the electrolyte. The compound shown in Formula I is beneficial for forming an interfacial protective layer between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte. This can inhibit the continuous decomposition of the electrolyte, thereby delaying the growth of the cycle impedance of the electrochemical device and improving the room temperature cycle performance and high temperature storage performance of the electrochemical device.

[0009] In some embodiments, the compound represented by Formula I is selected from at least one of the following compounds:

[0010]

[0011] Meeting the above conditions can better improve the room temperature cycling performance and high temperature storage performance of electrochemical devices.

[0012] In some embodiments, the mass percentage of the compound represented by Formula I is from 0.08 wt% to 3 wt%, based on the mass of the electrolyte. When the mass percentage of the compound represented by Formula I in the electrolyte is too low (e.g., less than 0.08 wt%), its effect on improving the cycle performance and high-temperature storage performance of the electrochemical device is relatively limited. Conversely, when the mass percentage of the compound represented by Formula I is too high (e.g., above 3 wt%), its effect on improving the cycle performance of the electrochemical device no longer increases significantly, and further increasing its content may lead to excessively high electrolyte viscosity, which is detrimental to improving cycle performance. Preferably, the mass percentage of the compound represented by Formula I is from 1 wt% to 2 wt%.

[0013] In some embodiments, the electrolyte further includes the compound shown in Formula II;

[0014]

[0015] Where n is selected from integers from 0 to 4, A 2 Selected from R 21 R 22 R 23 R 24 Each is independently selected from a covalent single bond, a C1-C5 alkylene group, a C2-C4 alkenyl group, or... Any one of them; where R 25 Selected from hydrogen, cyano, C1-C3 alkyl, or cyano-substituted C1-C3 alkyl, R 26 R 27Each compound is independently selected from covalent single bonds or C1-C3 alkylene groups. This application further adds the compound shown in Formula II to the electrolyte containing the compound shown in Formula I. The compound having the structure shown in Formula II is beneficial for stabilizing high-valence transition metals in the positive electrode active material. Through the synergistic effect between the compound shown in Formula I and the compound shown in Formula II, a stronger protective effect can be provided on the interface, further inhibiting electrolyte decomposition and better improving the room-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0016] In some embodiments, the compound represented by Formula II is selected from at least one of the following compounds:

[0017] Meeting the above conditions can better improve the room temperature cycling performance and high temperature storage performance of electrochemical devices.

[0018] In some embodiments, the compound represented by Formula II is selected from at least two of the compounds described above.

[0019] In some embodiments, based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is denoted as W1, and the mass percentage of the compound represented by Formula II is denoted as W2, W... a = W1 / W2, satisfying: 0.01≤W a ≤5. Preferably, it satisfies: 0.05≤W a ≤2. Meeting the above conditions can better enable the compounds shown in Formula I and Formula II to work together, further improving the room temperature cycling performance and high temperature storage performance of the electrochemical device.

[0020] In some embodiments, the mass percentage of the compound shown in Formula II is between 0.1 wt% and 5 wt%, based on the mass of the electrolyte. If the mass percentage of the compound shown in Formula II is too low (e.g., below 0.1 wt%), it will not provide adequate protection for the positive electrode interface, and the effect of improving the performance of the electrochemical device will not be significant. If the mass percentage of the compound shown in Formula II is too high (e.g., above 5 wt%), the performance-enhancing effect of the compound shown in Formula II will no longer be significant, leading to increased electrolyte viscosity and affecting the kinetic performance of the electrochemical device. Therefore, when the mass percentages of the compounds shown in Formula I and Formula II are within the above-mentioned range, it is more conducive to their synergistic effect, further improving the room-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0021] In some embodiments, the electrolyte also includes the compound shown in Formula III;

[0022]

[0023] Where m is selected from 0 or 1, A32 A 33 Each independently selected At least one of them; R 33 R 34 Each is independently selected from substituted or unsubstituted C1-C5 alkylene groups and substituted or unsubstituted C2-C5 alkenyl groups, wherein, when substituted, the substituents include halogens.

[0024] In some embodiments, the compound represented by Formula III is selected from at least one of the following compounds:

[0025] Meeting the above conditions can better improve the cycle performance of electrochemical devices.

[0026] In this application, a compound of Formula III is further added to the electrolyte. The compound of Formula III is a compound containing a sulfur-oxygen double bond, which has strong antioxidant capacity. An appropriate amount of the compound of Formula III is beneficial to cooperate with other compounds in the electrolyte. On the one hand, it can further improve the stability of the positive electrode interface. On the other hand, it can be reduced on the negative electrode surface to form a protective film. When combined with other compounds, it can further inhibit the decomposition of the electrolyte and further improve the cycle performance of the electrochemical device.

[0027] In some embodiments, based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is denoted as W1, and the mass percentage of the compound represented by Formula III is denoted as W3, W... b = W1 / W3, satisfying: 0.1≤W b ≤12.5. Preferably, it satisfies: 0.2≤W b ≤1. Meeting the above conditions can better improve the cycle performance of electrochemical devices.

[0028] In some embodiments, the mass percentage of the compound represented by Formula III is from 0.08 wt% to 5 wt%, depending on the mass of the electrolyte. If the mass percentage of the compound represented by Formula III is too low (e.g., below 0.08 wt%), its effect on mitigating the electrolyte reaction at the positive and negative electrodes is relatively limited. If the mass percentage of the compound represented by Formula III is too high (e.g., above 5 wt%), its effect on enhancing the stability of the positive and negative electrode interfaces is no longer significantly improved, and it may lead to excessive electrolyte viscosity, affecting the kinetic performance of the electrochemical device.

[0029] In some embodiments, the electrolyte also includes a compound as shown in Formula IV;

[0030]

[0031] Among them, R41 It is selected from substituted C1-C6 alkylene groups, substituted or unsubstituted C2-C6 alkenyl groups, where the substituent is selected from F or C2-C6 alkenyl groups.

[0032] This application further adds the compound shown in Formula IV to the electrolyte. The compound shown in Formula IV can help enhance the film-forming stability of the solid-state interfacial membrane (SEI) of the negative electrode. Using the compound shown in Formula IV can increase the flexibility of the SEI membrane, further enhance the protection of the active material, reduce the probability of interfacial contact between the active material and the electrolyte, reduce the side reactions between the electrolyte and the active material, and thus reduce the impedance caused by the accumulation of by-products during cycling.

[0033] In some embodiments, the compound represented by Formula IV is selected from at least one of the following compounds:

[0034]

[0035] Meeting the above conditions can better improve the cycle performance of electrochemical devices.

[0036] In some embodiments, the mass percentage of the compound represented by Formula IV is from 0.1 wt% to 15 wt%, based on the mass of the electrolyte. If the mass percentage of the compound represented by Formula IV is too low (e.g., below 0.1 wt%), it will not adequately protect the interface and will have limited effect on improving the performance of the electrochemical device. If the mass percentage of the compound represented by Formula IV is too high (e.g., above 15 wt%), the enhancement effect on SEI stability will no longer be significant, and it may even affect the kinetic performance of the electrochemical device. Preferably, the mass percentage of the compound represented by Formula IV is from 1 wt% to 10 wt%.

[0037] In some embodiments, the electrolyte further includes a boron-containing lithium salt selected from at least one of lithium tetrafluoroborate (LiBF4), lithium dioxalate borate (LiBOB), or lithium difluorooxalate borate, with a mass percentage content of 0.01 wt% to 1 wt% based on the mass of the electrolyte. The boron-containing lithium salt can form a film at the positive electrode interface, protecting the interface and synergistically interacting with the compound shown in Formula I, further improving the cycle performance of the electrochemical device. If the mass percentage content of the boron-containing lithium salt is too low (e.g., below 0.01 wt%), it is insufficient to protect the positive electrode interface, and its effect on cycle improvement is relatively limited. If the mass percentage content of the boron-containing lithium salt is too high (e.g., above 1 wt%), the effect of the boron-containing lithium salt on cycle improvement no longer significantly increases.

[0038] Secondly, this application provides an electrochemical device, which includes the electrolyte described above. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0040] electrolyte

[0041] The first aspect of this application provides an electrolyte comprising a compound of formula I;

[0042]

[0043] Where n is an integer selected from 1 to 3, A 11 A 12 Each independently selected And it contains at least one and R 1 R 11 R 12 Each is independently selected from covalently single-bonded, substituted or unsubstituted C1-C5 alkylene groups; when substituted, the substituents include halogens or C1-C3 alkyl groups. Indicates the binding site with adjacent atoms.

[0044] In some embodiments, the compound represented by Formula I is selected from at least one of the following compounds:

[0045]

[0046]

[0047] In some embodiments, the mass percentage of the compound represented by Formula I is from 0.08 wt% to 3 wt%, based on the mass of the electrolyte. Exemplarily, the mass percentage of the compound represented by Formula I is 0.08 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, or a range consisting of any two of the above values.

[0048] In some embodiments, the electrolyte further includes the compound shown in Formula II;

[0049]

[0050] Where n is selected from integers from 0 to 4, A 2 Selected from R 21 R 22 R 23 R24 Each is independently selected from a covalent single bond, a C1-C5 alkylene group, a C2-C4 alkenyl group, or... Any one of them; where R 25 Selected from hydrogen, cyano, C1-C3 alkyl, or cyano-substituted C1-C3 alkyl, R 26 R 27 Each is independently selected from a covalent single bond or a C1-C3 alkylene group.

[0051] In some embodiments, the compound represented by Formula II is selected from at least one of the following compounds:

[0052]

[0053]

[0054] In some embodiments, the mass percentage of the compound represented by Formula I is denoted as W1, and the mass percentage of the compound represented by Formula II is denoted as W2, W... a = W1 / W2, satisfying: 0.01≤W a ≤5. For example, W a The range is 0.01, 0.03, 0.05, 0.1, 0.5, 0.8, 1, 1.5, 2, 3, 4, 5 or any two of the above values.

[0055] In some embodiments, the mass percentage of the compound represented by Formula II is from 0.1 wt% to 5 wt%, based on the mass of the electrolyte. Exemplarily, the mass percentage of the compound represented by Formula II is 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or a range consisting of any two of the above values.

[0056] In some embodiments, the electrolyte further includes the compound shown in Formula III;

[0057]

[0058] Where m is selected from 0 or 1, A 32 A 33 Each independently selected At least one of them; R 33 R 34 Each is independently selected from substituted or unsubstituted C1-C5 alkylene groups and substituted or unsubstituted C2-C5 alkenyl groups, wherein, when substituted, the substituents include halogens.

[0059] In some embodiments, the compound represented by Formula III is selected from at least one of the following compounds:

[0060]

[0061] In some embodiments, the mass percentage of the compound represented by Formula I is denoted as W1, and the mass percentage of the compound represented by Formula III is denoted as W3, W b = W1 / W3, satisfying: 0.1≤W b ≤12.5. For example, W b The range is 0.1, 0.2, 0.5, 0.8, 1, 3, 5, 8, 10, 12, 12.5 or any two of the above values.

[0062] In some embodiments, the mass percentage of the compound represented by Formula III is from 0.08 wt% to 5 wt%, based on the mass of the electrolyte. Exemplarily, the mass percentage of the compound represented by Formula III is 0.08 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or a range consisting of any two of the above values.

[0063] In some embodiments, the electrolyte further includes a compound as shown in Formula IV;

[0064]

[0065] Among them, R 41 It is selected from substituted C1-C6 alkylene groups, substituted or unsubstituted C2-C6 alkenyl groups, where the substituent is selected from F or C2-C6 alkenyl groups.

[0066] In some embodiments, the compound represented by Formula IV is selected from at least one of the following compounds:

[0067]

[0068] In some embodiments, the mass percentage of the compound represented by Formula IV is from 0.1 wt% to 15 wt%, based on the mass of the electrolyte. Exemplarily, the mass percentage of the compound represented by Formula IV is 0.1 wt%, 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 13 wt%, 15 wt%, or a range consisting of any two of the above values.

[0069] In some embodiments, the electrolyte further includes a boron-containing lithium salt selected from at least one of lithium tetrafluoroborate, lithium dioxalate borate, or lithium difluorooxalate borate, wherein the mass percentage of the boron-containing lithium salt is from 0.01 wt% to 1 wt% based on the mass of the electrolyte. Exemplarily, the mass percentage of the boron-containing lithium salt is 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, or a range consisting of any two of the above values.

[0070] In some embodiments, the electrolyte may also include other non-aqueous organic solvents and electrolyte salts; the other non-aqueous organic solvents may include at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or other aprotic solvents.

[0071] Examples of carbonate solvents include at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, or butene carbonate.

[0072] Examples of carboxylic acid ester solvents include at least one of 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, valproic acid lactone, and butyrolactone.

[0073] Examples of ether solvents include at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and bis(2,2,2-trifluoroethyl) ether.

[0074] The electrolyte salt includes at least one of organic lithium salts or inorganic lithium salts. In some embodiments, the electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiN(CF3SO2)2, abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), abbreviated as LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4), and lithium trifluoromethanesulfonate (LiCF3SO3).

[0075] In some embodiments, the mass percentage of the electrolyte salt is 10% to 15% based on the mass of the electrolyte. If the electrolyte salt concentration is too low, the ionic conductivity of the electrolyte will be low, affecting the rate capability and cycle performance of the electrochemical device; if the electrolyte salt concentration is too high, the viscosity of the electrolyte will be too high, affecting the rate capability of the electrochemical device. Preferably, the mass percentage of the electrolyte salt is 12% to 15%.

[0076] Electrochemical device

[0077] The second aspect of this application provides an electrochemical device, which includes a housing and an electrode assembly. The housing is used to encapsulate the electrode assembly, which includes a positive electrode, a negative electrode, a separator, and the electrolyte described in the first aspect.

[0078] Positive electrode sheet

[0079] The positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer can be located on one or both sides of the positive current collector.

[0080] In some embodiments, the positive current collector may be aluminum foil, or other positive current collectors commonly used in the art, such as aluminum alloy foil or composite current collectors (e.g., composite current collectors with a metal layer disposed on the surface of a polymer layer).

[0081] In some embodiments, the thickness of the positive current collector can be from 1 μm to 200 μm. This application does not impose any particular limitation on the thickness of the positive current collector, as long as it achieves the purpose of this application.

[0082] In some embodiments, the positive electrode active material layer may be coated only on a portion of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer may be from 10 μm to 500 μm. This application does not impose any particular limitation on the thickness of the positive electrode active material layer, as long as it achieves the purpose of this application.

[0083] In some embodiments, the positive electrode active material layer includes a positive electrode active material, such as LiCoO2, LiNiO2, LiMn2O4, or 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.

[0084] In some embodiments, the positive electrode active material may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium nickel manganese oxide, and the above positive electrode active material may be subjected to doping and / or coating treatment.

[0085] In some embodiments, the positive electrode active material layer further includes a binder and a conductive agent; the binder may include at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene; the conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, sheet graphite, graphene, carbon nanotubes, or carbon fibers.

[0086] In some embodiments, the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer can be 70–98:1–15:1–15. It is understood that this application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0087] Negative electrode sheet

[0088] The negative electrode may 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 being disposed on one or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may be at least one of copper foil, aluminum foil, nickel foil, or carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be from 1 μm to 200 μm. In some embodiments, the negative electrode active material layer may be coated only on a portion of the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer may be from 10 μm to 500 μm. It should be understood that these are merely exemplary, and other suitable thicknesses may be used.

[0089] 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 silicon-based materials. In some embodiments, the silicon-based material includes at least one of silicon, silicon oxides, silicon carbide compounds, or silicon alloys.

[0090] In some embodiments, the negative electrode active material layer may further include a conductive agent and / or a binder. The conductive agent in the negative electrode active material layer may include at least one of carbon black, acetylene black, Ketjen black, sheet graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. In some embodiments, the binder in the negative electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. It should be understood that the materials disclosed above are merely exemplary, and the negative electrode active material layer may use any other suitable material. In some embodiments, the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode active material layer may be 80–99:0.5–10:0.5–10. It should be understood that this is merely exemplary and not intended to limit the scope of this application.

[0091] Separating membrane

[0092] The separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene, in particular, are effective in preventing short circuits and can improve battery stability through a turn-off effect. In some embodiments, the thickness of the separator ranges from about 3 μm to 500 μm.

[0093] In some embodiments, the surface of the separator membrane may further include a porous layer disposed on at least one surface of the separator membrane. The porous layer comprises at least one of inorganic particles or a binder. The inorganic particles are selected from at least one of alumina (Al₂O₃), silicon (SiO₂), magnesium (MgO), titanium (TiO₂), hafnium (HfO₂), tin (SnO₂), cerium (CeO₂), nickel (NiO), zinc (ZnO), calcium (CaO), zirconium (ZrO₂), yttrium (Y₂O₃), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator membrane have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the separator can improve the separator's heat resistance, oxidation resistance, and electrolyte wetting properties, and enhance the adhesion between the separator and the electrode.

[0094] case

[0095] The shell can be a rigid shell or a flexible shell. For example, the rigid shell is made of a metal, and the flexible shell is made of a metal plastic film, such as an aluminum plastic film or a steel plastic film.

[0096] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, a lithium-ion battery. The electrode assembly in 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 this application is not limited thereto. In some embodiments of this application, taking a lithium-ion battery as an example, the positive electrode, separator, and negative electrode are wound or stacked in sequence to form an electrode assembly, which is then encapsulated in a housing such as an aluminum-plastic film, an electrolyte is injected, and the battery is formed and encapsulated to produce a lithium-ion battery. Then, the prepared lithium-ion battery is subjected to performance testing. Those skilled in the art will understand that the electrochemical device described above, for example, the method for preparing a lithium-ion battery, is merely an example. Other methods commonly used in the art can be used without departing from the disclosure of this application.

[0097] The present application is further illustrated below using a lithium-ion battery as an example of an electrochemical device and in conjunction with specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. The following examples and comparative examples are provided to illustrate the implementation of the present application in more detail. Unless otherwise stated, all parts, contents, percentages, and ratios listed are based on weight.

[0098] Preparation of positive electrode sheet

[0099] Lithium cobalt oxide (LiCoO2), conductive carbon black, and polyvinylidene fluoride (PVDF) were dissolved in N-methylpyrrolidone (NMP) solution at a weight ratio of 97.9:0.9:1.2 to form a positive electrode slurry. A 13μm aluminum foil was used as the positive electrode current collector. The positive electrode slurry was coated onto the current collector, and after drying, cold pressing, and cutting, the positive electrode was obtained. The compacted density of the positive electrode was 4.15 g / cm³. 3 .

[0100] Preparation of negative electrode sheet

[0101] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener were dissolved in deionized water at a weight ratio of 97.4:1.4:1.2 to form a negative electrode slurry. A 10μm thick copper foil was used as the negative electrode current collector. The negative electrode slurry was coated onto the current collector, and after drying, cold pressing, and cutting, the negative electrode was obtained. The compacted density of the negative electrode was 1.8 g / cm³. 3 .

[0102] Preparation of the separating membrane

[0103] The separator substrate is 5μm thick polyethylene (PE). A 2μm thick alumina ceramic layer is coated on one side of the separator substrate. Finally, a 2.5mg / 1540.25mm thick alumina ceramic layer is coated on each of the two sides of the separator with the single ceramic layer. 2 The binder, polyvinylidene fluoride (PVDF), was dried. The porosity of the separator membrane was 39%.

[0104] Preparation of electrolyte

[0105] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) were mixed uniformly in a mass ratio of 1:1:1:1:1. The electrolyte salt LiPF6 was then dissolved in the above non-aqueous solvent and mixed uniformly to form an electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 12.5%. A certain amount of the compound shown in Formula I was then added to the above electrolyte to obtain the various examples shown in Table 1. The difference between Examples 1 to 10 in Table 1 lies in the specific types and / or contents of the compound shown in Formula I used in the electrolyte, as detailed in Table 1. The content of the compound shown in Formula I is a mass percentage calculated based on the mass of the electrolyte.

[0106] The difference between Examples 11 to 19 and Example 3 is that Examples 11 to 19 further added the compound shown in Formula II to the electrolyte of Example 3. The specific parameters are shown in Table 2.

[0107] The difference between Examples 20 to 41 and Example 3 is that Examples 20 to 41 further added the compound shown in Formula III, the compound shown in Formula IV, and boron-based lithium salt to the electrolyte of Example 3. The specific parameters are shown in Table 3.

[0108] The difference between Examples 42 and 43 and Example 3 is that Examples 42 and 43 further add the compounds shown in Formula II, Formula III, Formula IV and boron lithium salts to the electrolyte of Example 3. The specific parameters are shown in Table 4.

[0109] Preparation of lithium-ion batteries

[0110] The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to form the electrode assembly. The electrode assembly is placed in an outer aluminum-plastic film package, and after removing moisture at 80°C, the electrolyte is injected and the assembly is sealed. Following formation, degassing, and edge trimming processes, a lithium-ion battery is obtained.

[0111] Performance testing:

[0112] (1) Cyclic performance test at 25℃:

[0113] At 25°C, the lithium-ion battery was charged to 4.5V at 0.7C, and then charged at a constant voltage to 0.05C at 4.5V. It was then discharged to 3.0V at 0.7C, and this cycle of 0.7C charging and 1C discharging was repeated for 800 cycles. The discharge capacity at 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.

[0114] Cycle capacity retention = Discharge capacity at 800th cycle / Discharge capacity at 3rd cycle × 100%.

[0115] (2) High-temperature storage performance test:

[0116] The lithium-ion battery was charged to 4.5V at a constant current of 0.5C at 25℃, and then charged to 0.05C at a constant voltage. The thickness of the lithium-ion battery was measured and recorded as d0. The battery was placed in an 85℃ oven for 4 hours, and the thickness was monitored and recorded as d.

[0117] The thickness expansion rate (%) of a lithium-ion battery after 4 hours of high-temperature storage is calculated as (d-d0) / d0×100%. If the thickness expansion rate exceeds 50%, the test is stopped.

[0118] Table 1. Parameters of Examples 1-10 and Comparative Example 1

[0119]

[0120] Comparing Examples 1-10 with Comparative Example 1, it can be seen that adding the compound shown in Formula I to the electrolyte can improve the room temperature cycle performance and high temperature storage performance of lithium-ion batteries. The degree of improvement increases with increasing mass percentage, eventually reaching a balance. This is because the compound shown in Formula I can form a stable interfacial protective layer between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, inhibiting the continuous decomposition of the electrolyte and thus suppressing gas production. In particular, when the content of the compound shown in Formula I is within the aforementioned range, the cycle performance and high temperature storage performance of the electrochemical device are even better. Specifically, the electrolyte in Comparative Example 1, which does not contain the compound shown in Formula I, cannot achieve 800 cycles at room temperature, and its thickness expansion rate at high temperature is greater than 50%. Examples 1 to 8 further added an appropriate amount of the compound shown in Formula I to the electrolyte of Comparative Example 1, achieving a capacity retention rate of over approximately 62% after 800 cycles at room temperature, and a thickness expansion rate of less than approximately 50% at high temperature. In particular, Example 5 further added an appropriate amount of Formula I-5 to the electrolyte of Comparative Example 1, achieving a capacity retention rate of 72.5% after 800 cycles at room temperature, and a thickness expansion rate as low as 29.6% at high temperature. Examples 6-10 are parallel examples of Example 3, differing only in the types of compounds of Formula I added to the electrolyte. Examples 6-10 can achieve similar effects to Example 3.

[0121] Table 2 Parameters of Examples 3 and 11-19

[0122]

[0123] Comparing Examples 11-19 with Example 3, it can be seen that the combined use of the compound shown in Formula I and the compound shown in Formula II can further improve the cycle performance and high-temperature storage performance of the electrochemical device. This is because the compound shown in Formula II can stabilize the high-valence transition metal in the positive electrode active material, and it can work synergistically with the compound shown in Formula I to jointly stabilize the positive electrode interface and suppress electrolyte consumption and gas generation. When W a When the value of W is within the range of this application, the loop performance is better. a Both excessively high and low values ​​can affect the cycle performance and high-temperature storage performance of lithium-ion batteries. In particular, Example 16, based on the electrolyte of Example 3, further adds appropriate amounts of the two compounds shown in Formula II. Through the synergistic effect of the compounds shown in Formula I and Formula II, a capacity retention rate of up to 82.7% can be achieved after 800 cycles at room temperature, and its thickness expansion rate at high temperatures is as low as 12.2%. Examples 19 and 13 are parallel examples, differing only in the types of compounds shown in Formula I. Example 19 achieves similar technical effects to Example 13.

[0124] Table 3 Parameters of Examples 3 and 20-41

[0125]

[0126] Comparing Examples 20-41 with Example 3, it can be seen that adding compounds of formula III, formula IV, and / or boron-based lithium salts to the electrolyte of Example 3 can further improve the cycle performance of the electrochemical device. When W b When W is within the range of this application, the loop performance is better. b Both excessively high and low values ​​will affect cycle performance. In particular, the electrolyte of Example 39 is based on the electrolyte of Example 3, with the addition of compound III, compound IV, and boron-based lithium salt. Example 39 exhibits a capacity retention rate of up to 87.1% after 800 cycles at room temperature. Examples 40-41 are parallel examples of Example 39, differing only in the specific substances of compound III, compound IV, and boron-based lithium salt. Examples 40-41 achieve similar technical effects to Example 39.

[0127] Table 4 Parameters of Examples 3 and 42-43

[0128]

[0129] Examples 42 and 43 are based on the electrolyte of Example 3, with the addition of appropriate amounts of compounds shown in Formula II, Formula III, Formula IV, and boron-based lithium salts. According to Table 4, the capacity retention rate of Examples 42 and 43 after 800 cycles at room temperature can reach more than 88%. It can be seen that the compounds shown in Formula I, Formula II, Formula III, Formula IV, and boron-based lithium salts have a synergistic effect within the scope of this application, which can further improve the cycle performance of lithium-ion batteries.

[0130] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises the compound shown in Formula I; Where n is an integer selected from 1 to 3, A 11 A 12 Each independently selected And contains at least one and R 1 R 11 R 12 Each is independently selected from covalently single-bonded, substituted or unsubstituted C1-C5 alkylene groups; when substituted, the substituents include halogens or C1-C3 alkyl groups. Indicates the binding site with adjacent atoms.

2. The electrolyte according to claim 1, characterized in that, The compound represented by Formula I is selected from at least one of the following compounds:

3. The electrolyte according to claim 1, characterized in that, Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is from 0.08 wt% to 3 wt%.

4. The electrolyte according to claim 1, characterized in that, The electrolyte also includes the compound shown in Formula II; Where n is selected from integers from 0 to 4, A 2 Selected from R 21 R 22 R 23 R 24 Each is independently selected from a covalent single bond, a C1-C5 alkylene group, a C2-C4 alkenyl group, or... any one of them; Among them, R 25 Selected from hydrogen, cyano, C1-C3 alkyl, or cyano-substituted C1-C3 alkyl, R 26 R 27 Each is independently selected from a covalent single bond or a C1-C3 alkylene group.

5. The electrolyte according to claim 4, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The compound represented by Formula II is selected from at least one of the following compounds: (2) Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is denoted as W1, and the mass percentage of the compound represented by Formula II is denoted as W2, W... a = W1 / W2, satisfying: 0.01≤W a ≤5; (3) Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula II is from 0.1 wt% to 5 wt%.

6. The electrolyte according to claim 1, characterized in that, The electrolyte also includes the compound shown in Formula III; Where m is selected from 0 or 1, A 32 A 33 Each independently selected At least one of them; R 33 R 34 Each is independently selected from substituted or unsubstituted C1-C5 alkylene groups and substituted or unsubstituted C2-C5 alkenyl groups, wherein, when substituted, the substituents include halogens.

7. The electrolyte according to claim 6, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The compound represented by Formula III is selected from at least one of the following compounds: (2) Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula I is denoted as W1, and the mass percentage of the compound represented by Formula III is denoted as W3, W... b = W1 / W3, satisfying: 0.1≤W b ≤12.5; (3) Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula III is from 0.08 wt% to 5 wt%.

8. The electrolyte according to claim 1, characterized in that, The electrolyte also includes a compound as shown in Formula IV; Among them, R 41 It is selected from substituted C1-C6 alkylene groups, substituted or unsubstituted C2-C6 alkenyl groups, where the substituent is selected from F or C2-C6 alkenyl groups.

9. The electrolyte according to claim 8, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The compound represented by Formula IV is selected from at least one of the following compounds: (2) Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula IV is from 0.1 wt% to 15 wt%; (3) Based on the mass of the electrolyte, the mass percentage of the compound represented by Formula IV is from 1 wt% to 10 wt%.

10. The electrolyte according to claim 1, characterized in that, The electrolyte also includes boron-containing lithium salt; The boron-containing lithium salt is selected from at least one of lithium tetrafluoroborate, lithium dioxaborate or lithium difluorooxaborate. Based on the mass of the electrolyte, the boron-containing lithium salt has a mass percentage content of 0.01 wt% to 1 wt%.

11. An electrochemical device, characterized in that, The electrochemical device includes the electrolyte according to any one of claims 1 to 10.

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