Electrolyte, electrochemical apparatus and electronic device

Abstract

Disclosed in the present application are an electrolyte, an electrochemical apparatus and an electronic device. The electrolyte contains a carbonic ester compound and a substance T, wherein the substance T comprises a sulfur-containing compound; the carbonic ester compound comprises at least two of ethyl propionate, propylene carbonate, diethyl carbonate or propyl propionate, and at least contains ethyl propionate; and based on the total mass of the electrolyte, the mass percentage content of the carbonic ester compound is A, and the mass percentage content of the sulfur-containing compound is B, both of which satisfy: 6.5≤A / B≤45. The electrolyte of the present application can alleviate the expansion of a lithium-ion battery during charging and discharging, which is beneficial for improving the overcharge safety performance of the lithium-ion battery at a high temperature.

Description

Electrolytes, electrochemical devices, and electronic devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on March 6, 2024, with application number 2024102515294 and invention name “Electrolyte, Electrochemical Device and Electronic Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of electrochemical energy storage, and in particular to an electrolyte, an electrochemical device, and an electronic device. Background Art

[0004] As demand for electrochemical devices continues to grow, they are increasingly sought after for applications in portable electronic devices, e-bikes, electric vehicles, and energy storage systems, with ever-increasing demands for higher operating voltages and energy densities. During the charging process, lithium-ion batteries are prone to overcharging, which can lead to serious side effects and safety concerns due to gas production. With the advancement of technology and the diversification of our daily lives, the demand for the thermal and safety performance of lithium-ion batteries is also increasing. Summary of the Invention

[0005] In view of this, the present application provides an electrolyte, an electrochemical device, and an electronic device. Configuring the electrolyte in the electrochemical device and the electronic device can significantly improve the thermal performance and safety performance of the lithium-ion battery.

[0006] In a first aspect, the present application provides an electrolyte comprising a carbonate compound and a substance T, wherein substance T comprises a sulfur-containing compound, and the carbonate compound comprises at least two of ethyl propionate (EP), propylene carbonate (PC), diethyl carbonate (DEC), or propyl propionate (PP). Based on the total mass of the electrolyte, the mass percentage of the carbonate compound is A, and the mass percentage of the sulfur-containing compound is B, satisfying the following relationship: 6.5≤A / B≤45. The carbonate compound and the sulfur-containing compound decompose on the positive electrode material to form a stable and uniform CEI film, which inhibits the generation of side reactions during the charge and discharge reactions of the lithium-ion battery, thereby reducing gas generation, improving the battery expansion rate, and enhancing the overcharge safety performance of the electrochemical device at high temperatures.

[0007] In some embodiments, the electrolyte satisfies the following relationship: 16.5 ≤ A / B ≤ 45. This can inhibit oxidative decomposition of the electrolyte during the charge and discharge reactions, further reducing side reactions and gas generation during the charge and discharge processes, thereby improving the battery expansion rate and enhancing the overcharge safety performance of the electrochemical device at high temperatures.

[0008] In some embodiments, the electrolyte satisfies the following conditions: 2% ≤ B ≤ 10%. Electrolytes meeting these conditions can further suppress side reactions during charge and discharge, thereby reducing gas generation, improving battery expansion, and enhancing the overcharge safety of electrochemical devices at high temperatures. Preferably, 2% ≤ B ≤ 5%.

[0009] In some embodiments, the sulfur-containing compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, or 1,4-butene sultone. Carbonate compounds combined with these sulfur-containing compounds exhibit enhanced film-forming properties, decomposing to form a more stable and uniform CEI film. This suppresses side reactions during charge and discharge, reduces gas generation, improves battery expansion, and enhances the safety of electrochemical devices during overcharge at high temperatures.

[0010] In some embodiments, the sulfur-containing compound includes 1,3-propane sultone, and substance T further includes lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of lithium difluorophosphate is C, satisfying: 2≤A / C≤100. The present application can effectively improve the pass rate of the hot box test of the electrochemical device under high temperature (>130°C) conditions by regulating the ratio of 1,3-propane sultone and lithium difluorophosphate within the above range, and the substance formed by lithium difluorophosphate and 1,3-propane sultone can effectively reduce the generation of gas in the electrochemical device during the heating process, thereby improving the high temperature storage performance of the electrochemical device. Preferably, 16≤A / C≤80.

[0011] In some embodiments, substance T further comprises a compound of formula I;

[0012] In Formula I, R is selected from a C1-C5 alkylene group. The compound of Formula I can effectively improve the pass rate of hot box testing of electrochemical devices under high temperature (>130°C) conditions, improve the CEI film formed at the positive electrode interface between carbonate compounds and 1,3-propane sultone, and effectively reduce gas generation in the electrochemical device during heating. The cyano group of the compound of Formula I can attach to the CEI film formed at the positive electrode interface, further capturing gas molecules formed during the reaction, thereby improving the high-temperature storage performance of the electrochemical device.

[0013] In some embodiments, the mass percentage D of the compound of Formula I is 3 wt % to 10 wt % based on the total mass of the electrolyte. When the content of the compound of Formula I is within this range, the gas production of the electrochemical device during the temperature increase process is more effectively reduced, thereby further improving the high-temperature storage performance of the electrochemical device.

[0014] In some embodiments, the electrolyte further contains a nitrile compound, the nitrile compound being selected from at least one of succinonitrile, glutaronitrile, adiponitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, 1,3,6-hexanetricarboxylic acid nitrile, or ethylene glycol (bis)propionitrile ether. The mass percentage of the nitrile compound is 1 wt % to 7 wt % based on the total mass of the electrolyte. Preferably, the mass percentage of the nitrile compound is 2 wt % to 4.5 wt %. Nitrile compounds meeting this range have a certain high voltage window and can be preferentially oxidized over other components. This can effectively improve the pass rate of the hot box test of the electrochemical device under high temperature (>130° C.) conditions, while reducing the generation of gas in the electrochemical device during the heating process, thereby improving the high temperature storage performance of the electrochemical device.

[0015] In a second aspect, the present application provides an electrochemical device, which includes a positive electrode plate and an electrolyte. The positive electrode plate includes a positive electrode collector and a positive electrode material layer arranged on at least one side surface of the positive electrode collector. The electrolyte is the electrolyte of any one of the above-mentioned first aspects.

[0016] In some embodiments, the positive electrode material layer contains a positive electrode material, and at least a portion of the surface of the positive electrode material particles is provided with a discontinuous coating layer containing aluminum. The lattice fringe interlayer spacing of the positive electrode material measured under a field emission transmission electron microscope is 0.230nm to 0.360nm. A discontinuous coating layer is defined as a coating layer on the positive electrode material substrate that is non-continuous, that is, some point areas may contain trace amounts of the coating material or a smaller amount of the coating material than other areas. Positive electrode materials that meet this discontinuous coating layer and lattice fringe interlayer spacing range can improve the structural instability of the positive electrode material during the charge and discharge process, reduce the migration of transition metals in the positive electrode material into the electrolyte, and especially inhibit the structural changes of the positive electrode material under high temperature conditions, thereby improving the high-temperature cycle performance of the electrochemical device. Positive electrode materials that meet the appropriate range of lattice fringe interlayer spacing can enable electron transport to have a suitable transmission path and speed, thereby improving the charge and discharge performance of the assembled electrochemical device. Preferably, the distribution of the coating layer on the substrate can be an island-like or discrete distribution. Through the above design, suitable channels can be better reserved for the transmission of electrons on the surface of the material, thereby further improving the charge and discharge performance of the assembled electrochemical device.

[0017] In some embodiments, the positive electrode material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, or lithium nickel cobalt manganese oxide. In this case, the high-temperature cycle performance of the lithium-ion battery is improved more effectively.

[0018] In some embodiments, a covering material layer is provided on the positive electrode material particles, and the covering material layer and the aluminum-containing discontinuous coating layer are at least partially overlapped.

[0019] In some embodiments, a covering material layer is provided on the positive electrode material particles, and the covering material layer and the aluminum-containing discontinuous coating layer are alternately and flatly arranged on the surface of the positive electrode material particles.

[0020] In some embodiments, the covering material layer contains lithium phosphate and / or lithium niobate. When the surface of the positive electrode material is covered with a covering material layer containing lithium phosphate and / or lithium niobate, the lithium phosphate or lithium niobate will have a certain force with the surface of the positive electrode material, forming a stable covering layer. The covering layer material can improve the structural stability of the internal positive electrode material, reduce the effect of the electrolyte on the positive electrode material, and reduce the precipitation of transition metals during the reaction, thereby improving the charge and discharge performance of the assembled electrochemical device under high and low temperature conditions. When combined with the coating layer material, the long cycle capability of the assembled electrochemical device under high and low temperature conditions can be further improved through synergistic effect with the coating layer material.

[0021] In some embodiments, the mass ratio of lithium phosphate to lithium niobate is 1:(1-3). In this case, the internal structural stability of the positive electrode material can be better improved, the effect of the electrolyte on the positive electrode material can be reduced, and the precipitation of transition metals during the reaction can be reduced, thereby improving the charge and discharge performance of the assembled electrochemical device under high and low temperature conditions.

[0022] In a third aspect, the present application provides an electronic device, which includes the electrochemical device according to any one of the second aspects above.

[0023] The beneficial effects of the technical solutions provided by some embodiments of the present application include at least:

[0024] In the electrolyte provided by the present application, during the charge and discharge process of the electrochemical device, the carbonate compound and the sulfur-containing compound decompose on the positive electrode material to form a stable and uniform CEI film, which inhibits the oxidative decomposition of the electrolyte during the charge and discharge reaction, reduces the generation of side reactions and the amount of gas generated during the charge and discharge process, thereby improving the expansion rate of the battery and enhancing the overcharge safety performance of the electrochemical device at high temperatures. At the same time, combining the electrolyte with the positive electrode material that meets the requirements of the present application and combining it with the covering material lithium phosphate / lithium niobate can further improve the structural stability of the positive electrode material during use, thereby improving the thermal safety pass rate of the electrochemical device at high temperatures, reducing the high-temperature storage thickness expansion rate of the electrochemical device, and improving both the high-temperature and low-temperature cycle performance of the electrochemical device. DETAILED DESCRIPTION

[0025] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0026] As used in this application, the terms "including," "containing," and "comprising" are used in their open, non-limiting sense.

[0027] In addition, amounts, ratios, and other numerical values ​​are sometimes presented herein in a range format. It should be understood that such a range format is used for convenience and brevity and should be interpreted flexibly to include not only the values ​​explicitly specified as limits of the range, but also all individual values ​​or sub-ranges encompassed within the range, as if each value and sub-range were explicitly specified.

[0028] In the detailed description and claims, a list of items connected by the terms "one or more of," "one or more of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0029] electrolyte

[0030] The electrolyte contains a carbonate compound and a substance T, where substance T includes a sulfur-containing compound. The carbonate compound includes at least two of ethyl propionate, propylene carbonate, diethyl carbonate, or propyl propionate. Based on the total mass of the electrolyte, the mass percentage of the carbonate compound is A, and the mass percentage of the sulfur-containing compound is B, satisfying the following: 6.5≤A / B≤45. Exemplarily, the A / B ratio is 6.5, 8.5, 10, 13, 15, 16.5, 17, 20, 23, 25, 27, 30, 33, 35, 40, 43, 45, or a range consisting of any two of the foregoing values.

[0031] In some embodiments, the mass percentage B of the sulfur-containing compound is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6.5%, 8%, 10% or a range consisting of any two of the above values.

[0032] In some embodiments, the sulfur-containing compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, or 1,4-butene sultone.

[0033] Specifically, in some examples, the sulfur-containing compound is selected from any one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, or 1,4-butene sultone. In other examples, the sulfur-containing compound is selected from any two or three of 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, or 1,4-butene sultone. In other examples, the sulfur-containing compound includes 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, and 1,4-butene sultone.

[0034] In some embodiments, the sulfur-containing compound includes 1,3-propane sultone, the substance T includes lithium difluorophosphate, and the mass percentage of lithium difluorophosphate based on the total mass of the electrolyte is C, satisfying the following: 2≤A / C≤100. Exemplarily, the A / C ratio is 2, 4, 6, 8, 10, 16, 18, 20, 25, 35, 50, 75, 80, 95, 100, or a range consisting of any two of the foregoing values.

[0035] In some embodiments, substance T further comprises a compound of formula I;

[0036] In Formula I, R is selected from a C1-C5 alkylene group, and the mass percentage D of the compound of Formula I is 3 wt% to 10 wt% based on the total mass of the electrolyte. Exemplarily, the mass percentage D of the compound of Formula I is 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 10 wt%, or a range consisting of any two of the foregoing values.

[0037] In some embodiments, the electrolyte further contains a nitrile compound, wherein the nitrile compound is selected from at least one of succinonitrile, glutaronitrile, adiponitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, 1,3,6-hexanetricarboxylic acid nitrile, or ethylene glycol (bis)propionitrile ether, and the weight percentage of the nitrile compound is 1 wt % to 7 wt % based on the total weight of the electrolyte. Exemplarily, the weight percentage of the nitrile compound is 1 wt %, 1.5 wt %, 2 wt %, 3.5 wt %, 4.5 wt %, 5 wt %, 6.5 wt %, 7 wt %, or a range consisting of any two of the foregoing values.

[0038] In some embodiments, the electrolyte further contains vinyl sulfate (DTD) and vinylene carbonate (VC), the sum of the mass of vinyl sulfate and vinylene carbonate is denoted as P, the sum of the mass of other substances in the electrolyte (excluding the remaining substances of DTD and VC) is denoted as P', and 8≤P' / P≤16. Exemplarily, the ratio of P' / P is 8, 9, 10, 12, 13, 15, 16, or a range consisting of any two of the above values.

[0039] In some embodiments, the electrolyte may further include an ionizable lithium salt, the ionizable lithium salt including at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiPO2F2, LiC(CF3SO2)3, or LiC4BO8. The concentration of the ionizable lithium salt in the electrolyte is not particularly limited, but is preferably 0.5 mol / L or more, more preferably 0.8 mol / L or more, and further preferably 1.0 mol / L or more. In addition, it is preferably 3 mol / L or less, more preferably 2 mol / L or less, and further preferably 1.7 mol / L or less. If the concentration of these ionizable lithium salts is too low, it may result in an insufficient number of mobile lithium ions in the electrolyte. On the other hand, if the concentration of these ionizable lithium salts is too high, it may result in an increase in the viscosity of the electrolyte, resulting in an increase in the impedance of the electrolyte, which may reduce the lithium ion migration rate and thus may reduce the performance of the electrochemical device.

[0040] In some embodiments, the electrolyte further comprises at least one of fluoroether, fluoroethylene carbonate, or ether nitrile.

[0041] In some embodiments, the electrolyte may further include a non-aqueous solvent comprising at least one of a fluorocarbonate compound, a carboxylate compound, an ether compound or other organic solvent. Specifically, examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate or a combination thereof. Examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, mevalonolactone, caprolactone, methyl formate or a combination thereof. Examples of ether compounds include dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof. Examples of other organic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, phosphate esters, or a combination thereof.

[0042] electrochemical devices

[0043] The electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0044] The electrolyte is the electrolyte mentioned above.

[0045] The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The positive electrode material layer contains positive electrode material, and a discontinuous aluminum coating layer is disposed on at least a portion of the surface of the positive electrode material particles. The lattice fringe interlayer spacing of the positive electrode material measured under a field emission transmission electron microscope is 0.230 nm to 0.360 nm. The lattice fringe interlayer spacing is defined as the distance between the upper layers of the lattice fringes of the material observed by HRTEM (field emission transmission electron microscopy). The positive electrode material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, or lithium nickel cobalt manganese oxide. Exemplarily, the lattice stripe interlayer spacing of the aluminum-containing discontinuous coating is 0.230nm, 0.232nm, 0.233nm, 0.235nm, 0.237nm, 0.239nm, 0.241nm, 0.243nm, 0.245nm, 0.250nm, 0.260nm, 0.270nm, 0.280nm, 0.290nm, 0.300nm, 0.310nm, 0.320nm, 0.330nm, 0.340nm, 0.350nm, 0.360nm or a range consisting of any two of the above values.

[0046] In some embodiments, a covering material layer is provided on the positive electrode material particles, and the covering material layer and the aluminum-containing discontinuous coating layer are at least partially overlapped; or, the covering material layer and the aluminum-containing discontinuous coating layer are staggered and laid flat on the surface of the positive electrode material particles, and the covering material layer contains lithium phosphate and / or lithium niobate, and the mass ratio of lithium phosphate to lithium niobate is 1:(1 to 3).

[0047] In some embodiments, the positive electrode current collector may be aluminum foil or other commonly used positive electrode current collectors in the art. The thickness of the positive electrode current collector may be 1 μm to 200 μm, and the positive electrode material layer may be coated only on a portion of the positive electrode current collector. The thickness of the positive electrode material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary, and other suitable thicknesses may be used.

[0048] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductor. The positive electrode binder may include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinyl pyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene. The positive electrode conductor may include at least one of conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes or carbon fibers.

[0049] The negative electrode sheet 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 may be disposed on one or both sides of the negative electrode current collector. The negative electrode current collector may be at least one of copper foil, nickel foil, or a carbon-based current collector. The thickness of the negative electrode current collector may be 1 μm to 200 μm. The negative electrode active material layer may be coated only on a portion of the negative electrode current collector. The thickness of the negative electrode active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary and other suitable thicknesses may be employed.

[0050] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The negative electrode active material includes at least one of natural graphite, artificial graphite, or a silicon-based material. The silicon-based material includes at least one of silicon, a silicon oxide, a silicon carbon compound, or a silicon alloy.

[0051] In some embodiments, the negative electrode active material layer may further include a negative electrode conductor and / or a negative electrode binder. The negative electrode conductor may include at least one of carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the negative electrode binder may include at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylate, polyacrylate, polyvinyl pyrrolidone, polyimide, polysiloxane, or styrene-butadiene rubber. It should be understood that the materials disclosed above are only exemplary, and the negative electrode active material layer may be made of any other suitable material. In some embodiments, the mass ratio of the negative electrode active material, the negative electrode conductor, and the negative electrode 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 only exemplary and is not intended to limit the present application.

[0052] The separator includes at least one of a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, a polyethylene terephthalate separator, a polyimide separator, or an aramid separator. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene are particularly effective in preventing short circuits and can improve battery safety through a shutdown effect. In some embodiments, the separator has a thickness ranging from approximately 3 μm to 480 μm.

[0053] In some embodiments, the surface of the isolation membrane may further include a porous layer, the porous layer being disposed on at least one surface of the isolation membrane, the porous layer comprising at least one of inorganic particles or a binder, the inorganic particles being selected from at least one of aluminum oxide (Al2O3), 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 isolation 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, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, 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. The separator can also include a high-melting-point crystalline polymer or a high-temperature-resistant amorphous polymer. The high-temperature-resistant resin includes at least one of polypropylene, poly-4-methylpentene, polytetrafluoroethylene, polyvinylidene fluoride, and a cycloolefin copolymer. The high-melting-point crystalline polymer includes at least one of polypropylene, poly-4-methylpentene, polytetrafluoroethylene, or polyvinylidene fluoride, and the high-temperature-resistant amorphous polymer includes a cycloolefin copolymer. Based on the mass of the polyolefin porous substrate, the mass percentage z of the high-temperature-resistant resin is 2% to 10%. For example, the mass percentage z of the high-temperature-resistant resin is 2%, 3%, 5%, 7%, 8%, 10%, or a range consisting of any two of these values. When the aforementioned high-temperature-resistant resin is added to the polyolefin porous substrate and the mass percentage of the high-temperature-resistant resin is controlled within the above range, the separator's melt temperature is increased, improving its strength and the high-temperature performance of the electrochemical device.

[0054] In some embodiments, the electrochemical device is a lithium-ion battery, but the present application is not limited thereto.

[0055] In some embodiments of the present application, taking lithium-ion batteries as an example, the positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, which is then encapsulated in a shell such as an aluminum-plastic film, and the electrolyte is injected, formed, and packaged to make a lithium-ion battery.

[0056] electronic devices

[0057] The electronic devices of the embodiments of the present application are not particularly limited and can be any electronic devices known in the prior art. In some embodiments, the electronic devices may include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0058] Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein a lithium-ion battery is used as an example.

[0059] Example 1-1

[0060] <Preparation of lithium-ion batteries>

[0061] Preparation of positive electrode

[0062] Lithium iron phosphate particles, acetylene black as a positive electrode conductor, and polyvinylidene fluoride (PVDF) as a positive electrode binder were mixed in a mass ratio of 85:7:8. N-methylpyrrolidone (NMP) was added as a solvent and stirred evenly to prepare a positive electrode slurry with a solid content of 75wt%. The positive electrode slurry was evenly coated on one surface of a 13μm thick positive electrode current collector aluminum foil and dried at 85°C to obtain a positive electrode sheet coated with a positive electrode mixture layer on one side. The above steps were repeated on the other side of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. The sheet was then cold pressed, cut, and slit, and then dried under vacuum at 85°C for 4 hours to obtain a positive electrode sheet with a size of 74mm×867mm.

[0063] Preparation of negative electrode sheet

[0064] A negative electrode active material (artificial graphite), a conductive agent (conductive carbon black), a binder (styrene-butadiene rubber), and a thickener (sodium carboxymethyl cellulose) were mixed in a weight ratio of 96.5:1.5:1:1. Deionized water was added and the mixture was stirred uniformly in a vacuum mixer to obtain a negative electrode slurry having a solid content of 75 wt%. The negative electrode slurry was evenly coated on one surface of a 13 μm negative electrode current collector copper foil and dried at 120°C to obtain a negative electrode sheet coated with a 90 μm thick negative electrode active material layer on one side. The above steps were repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. The sheet was then cold pressed, cut, and slit to obtain a negative electrode sheet measuring 76 mm x 851 mm.

[0065] Preparation of electrolyte

[0066] In a glove box filled with argon, first add 2% of 1,3-propanesulfone and 90% of carbonate compounds (the mass ratio of EP:PC:DEC:PP is 15:14:15:56) accounting for the total mass of the electrolyte, stir thoroughly, add lithium salt LiPF6, and mix well to obtain the electrolyte.

[0067] Preparation of isolation membrane

[0068] A 10 μm thick polyethylene (PE) microporous membrane was selected as the separator.

[0069] Preparation of lithium-ion batteries

[0070] The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator placed between the positive and negative electrode sheets to serve as an isolation. The electrode assembly is wound and the electrode tabs are welded. The electrode assembly is placed in an outer packaging aluminum-plastic film. After dehydration at 80°C, the above-mentioned electrolyte is injected. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, a lithium-ion battery is obtained.

[0071] <Lithium-ion battery performance test>

[0072] (1) Low temperature performance test

[0073] The lithium ion batteries of the embodiments and comparative examples were repeatedly charged and discharged by the following steps, and the discharge capacity retention rates of the lithium ion batteries were calculated.

[0074] In an environment of -20°C, the first charge and discharge were carried out. Constant current charging was performed at a charging current of 2C to a full charge voltage of 3.8V (the battery containing lithium cobalt oxide positive electrode material was charged to 4.2V, and the battery containing lithium nickel cobalt manganese oxide material was charged to 4.5V). Then, constant voltage charging was performed at the maximum voltage until the current was 0.02C. Then, constant current discharge was performed at a discharge current of 0.5C until the final voltage was 2.0V. The discharge capacity of the first cycle was recorded. The above steps were then repeated for 400 charge and discharge cycles, and the discharge capacity of the 400th cycle was recorded.

[0075] Cycle capacity retention rate=(discharge capacity at the 400th cycle / discharge capacity at the first cycle)×100%.

[0076] (2) 3.5C 5V 80℃ overcharge test

[0077] The battery was discharged at 0.5C to 2.0V at 25°C, then charged at a constant current of 3.5C to 4.5V, and then charged at a constant voltage for 3 hours. The surface temperature change of the battery cell was monitored (the passing standard was that the battery cell did not catch fire, burn, or explode).

[0078] (3) Hot box test

[0079] The lithium-ion batteries in each example and comparative example were charged at room temperature at a constant current rate of 0.5C to a full charge voltage of 3.8V. Charging was continued at a constant voltage of 3.8V to a cutoff current of 0.05C, bringing them to a fully charged state. The appearance was inspected to ensure that the lithium-ion batteries were in normal usable condition. The fully charged batteries were placed in an oven and heated at a rate of 5°C / min until reaching the designated hot box test temperature of 135°C. The temperature was maintained for one hour, during which the battery condition was observed.

[0080] Judgment standard: The battery does not catch fire or explode.

[0081] Hot box test pass rate = hot box test pass number / total number

[0082] (4) 45℃ charge and discharge performance test

[0083] The lithium ion batteries of the embodiments and comparative examples were repeatedly charged and discharged by the following steps, and the discharge capacity retention rates of the lithium ion batteries were calculated.

[0084] In an environment of 45°C, the first charge and discharge were carried out. Constant current charging was performed at a charging current of 2C to a full charge voltage of 3.8V (the battery containing lithium cobalt oxide positive electrode material was charged to 4.2V, and the battery containing lithium nickel cobalt manganese oxide material was charged to 4.5V). Then, constant voltage charging was performed at the maximum voltage until the current was 0.02C. Then, constant current discharge was performed at a discharge current of 0.5C until the final voltage was 2.0V. The discharge capacity of the first cycle was recorded. The above steps were then repeated for 500 charge and discharge cycles, and the discharge capacity of the 500th cycle was recorded.

[0085] Cycle capacity retention rate=(discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0086] (5) Gas generation test at 65°C

[0087] At 25°C, constant current charging was performed at 0.3C until the battery reached 3.8V (4.2V for lithium cobalt oxide positive electrode materials and 4.5V for nickel cobalt manganese oxide positive electrode materials). After that, constant voltage charging was performed at 3.8V (4.2V for lithium cobalt oxide positive electrode materials and 4.5V for nickel cobalt manganese oxide positive electrode materials) for 1 hour. The charged batteries were then stored in a thermostatic chamber at 60°C. After 200 hours, the batteries were removed from the thermostatic chamber and returned to room temperature. The amount of gas generated by each battery was measured to evaluate the storage characteristics of the batteries at 3.8V (4.2V for lithium cobalt oxide positive electrode materials and 4.5V for nickel cobalt manganese oxide positive electrode materials). The amount of gas generated was determined using the Archimedean method: the test battery was placed in a container filled with ultrapure water, and the volume of the single-layer laminated battery was determined by the weight change before and after the test battery was placed. As an apparatus for measuring volume from weight change, a densimeter MDS-300 manufactured by AlphaMirage Corp. was used.

[0088] (6) Battery expansion rate before and after cycling at 65°C

[0089] At 65°C, the lithium-ion battery is charged to 3.8V at a constant current of 1C (charged to 4.2V for lithium cobalt oxide positive electrode materials and 4.5V for lithium nickel cobalt manganese oxide positive electrode materials), then charged at a constant voltage to a current of 0.05C, and then discharged to 2.0V at a constant current of 1C. This is the first cycle. The lithium-ion battery is cycled 20 times under the above conditions. The battery thickness before and after the cycle is measured using a height gauge. The thickness expansion rate is calculated using the following formula:

[0090] Thickness expansion ratio = [(thickness after cycle - thickness before cycle) / thickness before cycle] × 100%.

[0091] (7) Measurement method of lattice fringe interlayer spacing

[0092] An exemplary testing method involves adding appropriate amounts of powder and ethanol to a small beaker and subjecting it to ultrasonic oscillation for 10 to 30 minutes. After 3 to 5 minutes, the resulting mixture of powder and ethanol is drawn up using a glass capillary tube. Two to three drops of this mixture are then dripped onto a microgrid. After 20 minutes, when the alcohol has evaporated, the sample is mounted on a sample stage for testing. Field-emission transmission electron microscopy (HRTEM) is used to obtain an image of the material's lattice fringe. The interlayer spacing of the lattice fringe is measured and compared with reference literature and other test results to obtain interlayer spacing information.

[0093] Example 1-2 to Example 1-12

[0094] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0095] Example 2-1', Example 2-1 to Example 2-20

[0096] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-4.

[0097] Preparation of the coating layer and covering layer of Example 3-1

[0098] An exemplary method for preparing the discontinuous coating and covering layer is provided as follows: the positive electrode material prepared according to Example 1-1 is added to an aluminum nitrate solution, maintaining a mass ratio of the positive electrode material to aluminum nitrate nonahydrate at 90:25. Under continuous stirring, ammonia water is slowly added dropwise to precipitate all aluminum ions in the solution as Al(OH)3, with the rate of ammonia water addition being 10 seconds per drop. The mixed precipitate is filtered, washed, and heated in a muffle furnace at 320°C for 4.5 hours to obtain an aluminum oxide-coated lithium iron phosphate positive electrode material. A mixed target of lithium phosphate and lithium niobate is co-sputtered in a mixed atmosphere of argon and nitrogen using a magnetron sputtering method to prepare a positive electrode material containing a mixed lithium phosphate and lithium niobate covering material, wherein the magnetron sputtering power is 550W.

[0099] The positive electrode material containing the coating layer and the coating layer prepared above, the positive electrode conductive agent acetylene black, and the positive electrode binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 85:7:8, N-methylpyrrolidone (NMP) was added as a solvent and stirred evenly to prepare a positive electrode slurry with a solid content of 75wt%. The positive electrode slurry was evenly coated on one surface of a 13μm thick positive electrode current collector aluminum foil and dried at 85°C to obtain a positive electrode sheet coated with a positive electrode mixture layer on one side. The above steps were repeated on the other side of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85°C for 4 hours to obtain a positive electrode sheet with a specification of 74mm×867mm.

[0100] Example 3-2 to Example 3-10

[0101] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 3-1.

[0102] Example 3-11

[0103] Except that the mass ratio of the positive electrode material to aluminum nitrate nonahydrate was maintained at 80:25, the rest was the same as that of Example 3-1.

[0104] Comparative Example 1-1 to Comparative Example 1-5

[0105] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0106] Table 1

[0107] Compared with Comparative Example 1-1, Examples 1-1 to 1-7 show that the combination of carbonate compounds and sulfur-containing compounds can inhibit gas production during the charge and discharge reaction of lithium-ion batteries. The expansion change rate of the lithium-ion batteries before and after cycling at 65°C is less than or equal to 4.16%, and the pass rate in the overcharge test at 80°C 3.5C 5V is also high, not less than 9 / 10 (i.e., at least 9 out of 10 samples passed the test). It can be seen that the combination of carbonate compounds and sulfur-containing compounds can improve the overcharge safety performance of electrochemical devices at high temperatures. Compared with Comparative Example 1-1, Examples 1-6 and 1-8 to 1-10 show that any one of the sulfur-containing compounds of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, and 1,4-butene sultone can achieve the technical effects of the present application. By comparing Examples 1-1 to 1-7, Examples 1-11 to 1-12, and Comparative Examples 1-2 to 1-5, it can be seen that the content of the sulfur-containing compound in the electrolyte is appropriate, which is more conducive to inhibiting the gas production behavior of the lithium-ion battery during the charging and discharging process. In particular, the content of the sulfur-containing compound in the present application can better improve the overcharge performance of the lithium-ion battery at high temperature.

[0108] Table 2

[0109] In conjunction with Table 2, compared with Example 2-1, Example 2-1′ and Example 1-4, it can be seen that further adding lithium difluorophosphate to the electrolyte of Example 1-4 can improve the hot box test pass rate of the lithium ion battery under high temperature (>130°C), and the substance formed by lithium difluorophosphate and 1,3-propane sultone can effectively reduce the generation of gas in the electrochemical device during the heating process, thereby improving the high temperature storage performance of the lithium ion battery, and the ratio of 1,3-propane sultone to lithium difluorophosphate is in a suitable range, which can better achieve the above technical effects. Compared with Example 2-12 to Example 2-20, it can be seen that further adding the compound of formula I to the electrolyte can improve the hot box test pass rate of the lithium ion battery at high temperature and improve the high temperature storage performance of lithium ions. It can effectively reduce the amount of gas generated under 65°C. Compared with Example 2-15 to Example 2-20, it can be seen that the content of the compound of formula I is appropriate and can better achieve the above effects.

[0110] Table 3

[0111] The above description is only a preferred embodiment of the present application and is not intended to limit the present application.

[0112] Any modifications, equivalent substitutions and improvements made within the provisions of the present invention shall be included in the scope of protection of this application.

Claims

1. An electrolyte, characterized in that: The electrolyte contains a carbonate compound and a substance T, wherein the substance T includes a sulfur-containing compound; The carbonate compound includes at least two of ethyl propionate, propylene carbonate, diethyl carbonate or propyl propionate and at least contains ethyl propionate; Based on the total mass of the electrolyte, the mass percentage of the carbonate compound is A, and the mass percentage of the sulfur-containing compound is B, satisfying: 6.5≤A / B≤45.

2. The electrolyte according to claim 1, characterized in that Meets: 16.5≤A / B≤45.

3. The electrolyte according to claim 1 or 2, characterized in that Meet: 2%≤B≤10%.

4. The electrolyte according to claim 3, characterized in that Meet: 2%≤B≤5%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The sulfur-containing compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone and 1,4-butene sultone.

6. The electrolyte according to any one of claims 1 to 4, characterized in that The substance T also includes lithium difluorophosphate; The sulfur-containing compound includes 1,3-propane sultone; Based on the total mass of the electrolyte, the mass percentage of lithium difluorophosphate is C, satisfying: 2≤A / C≤100.

7. The electrolyte according to claim 6, characterized in that Meet: 16≤A / C≤80.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The substance T also includes a compound of formula I; In Formula I, R is selected from a C1 to C5 alkylene group.

9. The electrolyte according to claim 8, characterized in that Based on the total mass of the electrolyte, the mass percentage D of the compound of formula I is 3 wt % to 10 wt %.

10. An electrochemical device, characterized in that The electrochemical device includes a positive electrode sheet and an electrolyte; The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one side surface of the positive electrode current collector; The electrolyte is the electrolyte according to any one of claims 1 to 9.

11. The electrochemical device according to claim 10, characterized in that The positive electrode material layer contains positive electrode material, and at least part of the surface of the positive electrode material particles is provided with an aluminum-containing discontinuous coating layer. The lattice fringe interlayer spacing of the positive electrode material measured under a field emission transmission electron microscope is 0.230nm to 0.360nm.

12. The electrochemical device according to claim 11, characterized in that The positive electrode material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, or lithium nickel cobalt manganese oxide.

13. The electrochemical device according to claim 11 or 12, characterized in that A covering material layer is provided on the positive electrode material particles; The covering material layer and the aluminum-containing discontinuous coating layer are at least partially overlapped; or, The covering material layer and the aluminum-containing discontinuous coating layer are alternately and flatly arranged on the surface of the positive electrode material particles; The covering material layer contains lithium phosphate and / or lithium niobate.

14. The electrochemical device according to claim 13, wherein The mass ratio of the lithium phosphate to the lithium niobate is 1:(1 to 3).

15. An electronic device, characterized in that: The electronic device comprises the electrochemical device according to any one of claims 10 to 14.