Electrochemical devices and electronic devices

Abstract

Embodiments of the present application provide an electrochemical device and an electronic device. The electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material, wherein the mass of the negative electrode active material is ag. The separator is arranged between the positive electrode sheet and the negative electrode sheet. The electrolyte includes ethylene carbonate, and the mass content of ethylene carbonate is b% based on the mass of the electrolyte, and b / a is 1.6 to 6.4. By controlling the ratio of the mass percentage of ethylene carbonate in the electrolyte to the mass of the negative electrode active material, the cycle performance of the electrochemical device, the thickness expansion rate of high temperature storage, the capacity retention rate after storage and the safety performance can be improved.

Description

[0001] This application is a divisional application of the invention patent with the application number 202111011717.2 and the invention name "Electrochemical Device and Electronic Device", which was filed on August 31, 2021. Technical Field

[0002] This application relates to the field of electrochemical energy storage, and particularly to electrochemical devices and electronic devices. Background Art

[0003] Currently, electrochemical devices (e.g., lithium-ion batteries) are widely used in fields such as electric vehicles, consumer electronics, and energy storage devices. Due to advantages such as high energy density and no memory effect, lithium-ion batteries have gradually become the mainstream batteries in the above fields. In addition, there are also some fields with relatively harsh usage environments or working conditions. How to improve the high-temperature storage, cycling performance, charging performance, and safety performance of lithium-ion batteries while maintaining their high energy density has become an urgent problem in the industry. Summary of the Invention

[0004] Embodiments of this application provide an electrochemical device, which includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The negative electrode plate includes a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material, where the mass of the negative electrode active material is a g. The separator is disposed between the positive electrode plate and the negative electrode plate. The electrolyte includes ethylene carbonate, and based on the mass of the electrolyte, the mass content of ethylene carbonate is b%, and b / a is 1.6 to 6.4.

[0005] In some embodiments of this application, b is 1 to 25.

[0006] In some embodiments of this application, the electrolyte further includes at least one of vinylene carbonate or fluoroethylene carbonate. Based on the mass of the electrolyte, the mass content of vinylene carbonate is m%, and the mass content of fluoroethylene carbonate is n%, m + n = c, and 0.01 ≤ c < 2.

[0007] In some embodiments of this application, the electrolyte further includes at least one of vinylene carbonate or fluoroethylene carbonate. Based on the mass of the electrolyte, the mass content of vinylene carbonate is m%, and the mass content of fluoroethylene carbonate is n%. In some embodiments, 0 ≤ m < 2; in some embodiments, 0 ≤ n < 2.

[0008] In some embodiments of this application, c / a is 0.001 to 0.36.

[0009] In some embodiments of this application, based on the mass of the electrolyte, in some embodiments, m < n.

[0010] In some embodiments of the present application, the electrolyte further includes a compound containing a sulfur-oxygen double bond. The compound containing a sulfur-oxygen double bond includes at least one of 1,3-propane sultone (PS), 1,4-butane sultone (BS), vinylene sulfate (DTD), methylene methane disulfonate (MMDS), 1,3-propane disulfonic anhydride (PA), 2-methylbutane sultone, or propenyl-1,3-sulfonic lactone (PES).

[0011] In some embodiments of the present application, based on the mass of the electrolyte, the mass content of the compound containing a sulfur-oxygen double bond is d%, and the positive electrode sheet includes a positive electrode active material layer. The positive electrode active material layer includes a positive electrode active material, and the mass of the positive electrode active material is e g. The value of d / e is from 0.1 to 0.6.

[0012] In some embodiments of the present application, the positive electrode active material contains cobalt element.

[0013] In some embodiments of the present application, the electrolyte further includes a lithium salt. The lithium salt includes at least one of lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium bis(fluorosulfonyl)imide salt (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF 4 ), lithium tetraborate (B 4 Li 2 O 7 ), lithium borate (Li 3 BO 3 ), or lithium trifluoromethanesulfonate (CF 3 LiO 3 S). Based on the mass of the electrolyte, the mass content of the lithium salt is from 0.01% to 3%.

[0014] In some embodiments of the present application, the electrolyte further includes a polynitrile compound. The polynitrile compound includes at least one of succinonitrile (SN), adiponitrile (ADN), 1,2-bis(cyanoethoxy)ethane (DENE), 1,4-dicyano-2-butene, 1,3,6-hexanetricarbonitrile (HTCN), or 1,2,3-tris(2-cyanoethoxy)propane. Based on the mass of the electrolyte, the mass content of the polynitrile compound is from 0.01% to 6%.

[0015] Some embodiments of the present application provide an electronic device including the above-mentioned electrochemical device.

[0016] In the embodiments of the present application, by controlling the ratio of the mass percentage of ethylene carbonate in the electrolyte to the mass of the negative electrode active material, the cycle performance, the thickness expansion rate during high-temperature storage, the capacity retention rate after storage, and the safety performance of the electrochemical device can be improved. Detailed implementation mode

[0017] The following embodiments can enable those skilled in the art to understand the present application more comprehensively, but do not limit the present application in any way.

[0018] To maintain good high-temperature performance of an electrochemical device, it is necessary to use a solvent or additive with better stability in the electrolyte to form a protective effect at the electrode interface to inhibit the side reaction between the electrolyte and the active material. However, the interaction modes between different solvents and additives and the active material are different. The content relationship between the solvent or additive and the electrode active material is one of the important parameters affecting the above-mentioned effect. When the electrolyte components cannot form a good protective interface on the surface of the electrode, it will affect the charge-discharge performance and storage performance of the electrochemical device to varying degrees, thus affecting the normal operation of the electrochemical device and bringing potential safety hazards such as lithium deposition during charging. The embodiments of the present application can improve the comprehensive performance of the electrochemical device while maintaining the high energy density of the electrochemical device by properly matching the electrolyte solvent and additive with the positive electrode active material and the negative electrode active material, so that the electrochemical device has good performance in terms of high-temperature storage performance, cycle performance, charging performance and safety performance.

[0019] The embodiments of the present application provide an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. Among them, the separator is disposed between the positive electrode sheet and the negative electrode sheet. In some embodiments, the negative electrode sheet may include a negative electrode active material layer, and the negative electrode active material layer includes a negative electrode active material, where the mass of the negative electrode active material is a g. In some embodiments, the negative electrode active material may include at least one of graphite, hard carbon, silicon, silicon monoxide or silicone.

[0020] In some embodiments, the electrolyte may include ethylene carbonate (EC). In some embodiments, based on the mass of the electrolyte, the mass content of ethylene carbonate is b%, and b / a is from 1.6 to 6.4. In some embodiments, as the ratio b / a increases, the comprehensive performance of the electrochemical device, such as the cycling performance, the high-temperature storage performance at different states of charge (SOC), the capacity retention rate after storage, and the safety performance, is significantly improved. This may be because when b / a is within a certain range, EC has a good protective effect on the negative electrode interface and a good passivation effect on the lithium deposition interface of the negative electrode. When b / a is too small, EC cannot protect the negative electrode interface, thus having an adverse effect on the cycling performance of the electrochemical device under normal and high-temperature conditions. Moreover, due to the poor passivation effect on the lithium deposition interface of the negative electrode, the storage and safety performance of the electrochemical device at low states of charge are affected; while when b / a > 6.4, the cycling performance of the electrochemical device cannot be further improved, and the storage performance and safety performance at high states of charge are affected. This may be because when b / a is too large, the interfacial kinetics between the electrolyte and the negative electrode deteriorates, resulting in lithium deposition during charging and causing a violent reaction during storage at high temperature, leading to thermal failure of the electrochemical device. In some embodiments, b / a may be from 2 to 6, from 2.5 to 5.5, from 3 to 5, or from 3.5 to 4.5, etc.

[0021] In some embodiments, the negative electrode sheet may further include a negative electrode current collector, and the negative electrode current collector may be at least one of a copper foil, a nickel foil, or a carbon-based current collector. In some embodiments, the negative electrode active material layer may be located on one or both sides of the negative electrode current collector. In some embodiments, the negative electrode active material layer may further include a conductive agent and a binder. In some embodiments, the conductive agent in the negative electrode active material layer may include at least one of conductive carbon black, Ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the binder in the negative electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode active material layer may be (78 - 98.5):(0.1 - 10):(0.1 - 10). It should be understood that the above are only examples, and any other suitable materials and mass ratios may be used.

[0022] In some embodiments, b is 1 to 25, that is, based on the mass of the electrolyte, the mass content of ethylene carbonate (EC) is 1% to 25%. When the mass content of EC is too small, the protection of EC on the negative electrode interface and the passivation effect on the negative electrode lithium deposition interface are relatively limited; when the mass content of EC is too large, the electrolyte undergoes side reactions during the cycle of the electrochemical device, resulting in the consumption of the electrolyte and the expansion of the electrochemical device. In some embodiments, b can be 5 to 20, 8 to 18, 10 to 15 or 13, etc.

[0023] In some embodiments, a is less than or equal to 15, that is, the mass of the negative electrode active material is less than or equal to 15g. Since EC and the negative electrode active material can only play a synergistic role when b / a is in the range of 1.6 to 6.4, resulting in better interface performance, when the mass of the negative electrode active material is too large, excessive EC concentration will cause side reactions in the electrolyte during the cycle. In some embodiments, a can be 1 to 15, 2 to 14, 3 to 12, or 4 to 10, etc.

[0024] In some embodiments, the electrolyte may further include at least one of vinylene carbonate (VC) or fluoroethylene carbonate (FEC). In some embodiments, based on the mass of the electrolyte, the mass content of vinylene carbonate is m%, where 0≤m<2, and based on the mass of the electrolyte, the mass content of fluoroethylene carbonate is n%, where 0≤n<2, m+n=c, and 0.01≤c<2. Based on the interface formed by EC and the negative electrode active material, VC and / or FEC can well repair the electrode interface solid electrolyte membrane that is damaged during the cycle and storage process, thereby inhibiting the side reaction of the electrolyte at the electrode interface and inhibiting the lithium deposition at the negative electrode interface. However, when the content of VC and FEC is too high, the negative electrode interface impedance is too large, and there is too much residue after formation, which is easy to oxidize and produce gas at the positive electrode interface, thereby affecting the charging performance after storage, and also bringing storage gas production and safety hazards. In some embodiments, c can be 0.05 to 1.8, 0.1 to 1.5, 0.2 to 1.3, 0.3 to 1 or 0.5 to 0.8, etc.

[0025] In some embodiments, c / a is 0.001 to 0.36. When c / a is 0.001 to 0.36, but the ratio c / a is too large, the relative content of VC and / or FEC is too high, which affects the negative electrode interface performance, and further affects the charging performance after storage, and also brings storage gas production and safety hazards. In some embodiments, c / a can be 0.05 to 0.3, 0.1 to 0.25 or 0.15 to 0.2, etc.

[0026] In some embodiments, on the basis described above, when m < n, an interfacial composite protective film with a lower impedance is formed on the electrode surface during formation and cycling of the electrolyte, which can improve the cycling performance of the electrochemical device to a certain extent, and the storage characteristics of the electrochemical device under high-temperature conditions are also significantly improved.

[0027] In some embodiments, the electrolyte may further include a compound containing a sulfur-oxygen double bond, for example, a sulfonate ester. In some embodiments, the compound containing a sulfur-oxygen double bond may include at least one of 1,3-propane sultone, 1,4-butane sultone, ethylene sulfate, methylene methanedisulfonate, 1,3-propane disulfonic anhydride, 2-methylbutane sultone, or allyl-1,3-sulfonic lactone.

[0028] In some embodiments, based on the mass of the electrolyte, the mass content of the compound containing a sulfur-oxygen double bond is d%. In some embodiments, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the mass of the positive electrode active material is e g, and d / e is from 0.1 to 0.6. On the basis that EC and the negative electrode active material satisfy b / a of 1.6 to 6.4, when the ratio d / e is too small, the effect of the compound containing a sulfur-oxygen double bond on stabilizing the CEI film and SEI film is relatively limited, and the improvement of various performance of the lithium-ion battery is not obvious; when the ratio d / e is too large, it has an obvious impact on the storage and safety performance of the electrochemical device at low SOC. In some embodiments, d / e can be 0.2 to 0.5 or 0.3 to 0.4, etc.

[0029] In some embodiments, the positive electrode active material contains cobalt element. In some embodiments, the positive electrode active material may include at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganate, lithium nickel manganate, or lithium iron phosphate. In some embodiments, Dv50 and Dv90 of the positive electrode active material satisfy: 0.4 μm ≤ D V 50 ≤ 20 μm, 2 μm ≤ D V90 ≤ 40 μm; wherein, Dv50 and Dv90 respectively refer to the particle sizes corresponding to the cumulative 50% and 90% from left to right in the volume distribution. In some embodiments, the positive electrode active material includes element A, and element A includes at least one of Mg, Ti, Cr, B, Fe, Zr, Y, Na, or S. Based on the mass of the positive electrode active material, the mass content of element A is less than 0.5%. In some embodiments, the positive electrode sheet may further include a positive electrode current collector, and the positive electrode current collector may be made of Al foil. Of course, other current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 200 μm. In some embodiments, the positive electrode active material layer may be located on one or both sides of the positive electrode current collector. In some embodiments, the positive electrode active material layer may include a conductive agent and a binder. In some embodiments, the conductive agent in the positive electrode active material layer may include at least one of conductive carbon black, Ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the binder in the positive electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer may be (78-99):(0.1-10):(0.1-10). In some embodiments, the thickness of the positive electrode active material layer may all be 10 μm to 200 μm. It should be understood that the above are only examples, and the positive electrode active material layer may be made of any other suitable materials, thicknesses, and mass ratios.

[0030] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium tetraborate, lithium borate, or lithium trifluoromethanesulfonate. Adding a lithium salt to the electrolyte can significantly improve the cycling performance, high-temperature storage performance, and safety performance of the electrochemical device. This is because the lithium salt forms low-impedance SEI and CEI films on the surfaces of the positive and negative electrodes, improves the charging performance, and reduces side reactions caused by lithium deposition. At the same time, the stable protective film can effectively reduce the side reactions between the electrolyte and the positive and negative electrodes during storage and cycling, while reducing the consumption of active lithium and improving the capacity retention rate.

[0031] In some embodiments, based on the mass of the electrolyte, the mass content of the lithium salt is 0.01% to 3%. If the mass content of the lithium salt is too small, its effect on improving the charging performance is relatively limited; while if the mass content of the lithium salt is too large, the viscosity of the electrolyte will be too high, affecting the kinetic performance of the electrochemical device. In some embodiments, based on the mass of the electrolyte, the mass content of the lithium salt can be 0.05% to 2.5%, 0.1% to 2%, 0.5% to 1.8%, or 1% to 1.5%, etc.

[0032] In some embodiments, the electrolyte may further include a polynitrile compound, and the polynitrile compound includes at least one of succinonitrile, adiponitrile, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,3,6-hexanetricarbonitrile, or 1,2,3-tris(2-cyanoethoxy)propane. Adding a polynitrile compound to the electrolyte can significantly improve the high-temperature storage performance and safety performance of the electrochemical device. This is because the polynitrile compound can complex well with the cathode active material, reducing the oxidation activity of the cathode active material, reducing side reactions, and at the same time inhibiting the deposition of the cathode transition metal on the anode after dissolution, which can damage the SEI film, thereby reducing gas generation and improving the capacity retention rate. In addition, when EC is used in combination with the polynitrile compound, EC can inhibit the decomposition of the polynitrile compound at the anode interface, reduce the growth of the anode impedance, so that more polynitrile compounds can effectively act on the cathode; while the passivation of the cathode by the polynitrile compound can reduce the oxidation of EC at the cathode interface, so that more EC can be used for the protection of the anode interface, thus maximizing the advantages of the two substances and achieving the best electrical performance.

[0033] In some embodiments, based on the mass of the electrolyte, the mass content of the polynitrile compound is 0.01% to 6%. When the mass content of the polynitrile compound is too small, the improvement effect of the polynitrile compound is relatively limited; while when the mass content of the polynitrile compound is too large, the improvement effect of the polynitrile compound will not increase further, and it is not conducive to the improvement of the energy density of the electrochemical device. In some embodiments, based on the mass of the electrolyte, the mass content of the polynitrile compound can be 0.05% to 5%, 0.1% to 4%, 0.5% to 3%, or 1% to 2%, etc.

[0034] In some embodiments, the electrolyte may further include a P-O bond-containing compound, and the P-O bond-containing compound includes at least one of tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) phosphite (TTSPi), triallyl phosphate, tripropargyl phosphate, triallyl phosphite, or tripropargyl phosphite.

[0035] In some embodiments, the electrolyte may further include a non-aqueous solvent. The non-aqueous solvent can be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.

[0036] The carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0037] Examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene ethylene carbonate (VEC), or combinations thereof. Examples of the fluorinated carbonate compound 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, trifluoromethyl ethylene carbonate, or combinations thereof.

[0038] Examples of the carboxylic acid ester compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or combinations thereof.

[0039] Examples of the ether compound are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0040] Examples of other organic solvents are 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, and phosphate esters, or combinations thereof.

[0041] In some embodiments, the separator may include at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a good effect on preventing short circuits and can improve the stability of the battery through the shut-off effect. In some embodiments, the thickness of the separator is in the range of about 5 μm to 500 μm.

[0042] In some embodiments, the surface of the separator may further include a porous layer, the porous layer is disposed on at least one surface of the substrate of the separator, and the porous layer includes inorganic particles and a binder, and the inorganic particles are selected from alumina (Al2 O 3 ) silica (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium dioxide (HfO 2 ), tin oxide (SnO 2 ), cerium dioxide (CeO 2 ), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate, or at least one of them. 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 vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the separator membrane can improve the heat resistance, antioxidant performance, and electrolyte infiltration performance of the separator membrane, and enhance the adhesion between the separator membrane and the electrode sheet.

[0043] In some embodiments of the present application, the electrode assembly of the electrochemical device is a wound electrode assembly, a stacked electrode assembly, or a folded electrode assembly. In some embodiments, the positive electrode sheet and / or the negative electrode sheet of the electrochemical device can be a multi-layer structure formed by winding or stacking, or a single-layer structure formed by stacking a single positive electrode sheet, a separator membrane, and a single negative electrode sheet. In some embodiments, the electrochemical device includes a lithium-ion battery, but the present application is not limited thereto.

[0044] In some embodiments of the present application, taking a lithium-ion battery as an example, the positive electrode sheet, the separator membrane, and the negative electrode sheet are wound or stacked in sequence into an electrode component, and then are encapsulated in, for example, an aluminum-plastic film, injected with an electrolyte, formed, and encapsulated to make a lithium-ion battery. Then, the performance of the prepared lithium-ion battery is tested.

[0045] Those skilled in the art will understand that the preparation method of the above-described electrochemical device (for example, a lithium-ion battery) is only an example. Other methods commonly used in the art can be adopted without departing from the content disclosed in the present application.

[0046] Embodiments of the present application also provide an electronic device including the above-mentioned electrochemical device. The electronic device of the embodiments of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0047] Some specific embodiments and comparative examples are listed below to better illustrate the present application, in which a lithium-ion battery is taken as an example.

[0048] Example 1-1

[0049] Preparation of the positive electrode sheet: Using 10 μm aluminum foil as the positive electrode current collector, dissolve the positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O 2 , conductive agent conductive carbon black, and binder polyvinylidene fluoride in a mass ratio of 97:1.4:1.6 in an N-methylpyrrolidone (NMP) solution to form a positive electrode slurry. Coat the positive electrode slurry on both sides of the positive electrode current collector, with a coating thickness of 80 μm on one side to obtain a positive electrode active material layer. Then, after drying at 85 °C, cold pressing, and cutting, the positive electrode sheet is obtained.

[0050] Preparation of the negative electrode sheet: Dissolve artificial graphite, conductive agent conductive carbon black, sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in deionized water in a mass ratio of 96.4:1.5:0.5:1.6 to form a negative electrode slurry, where the solid content of the negative electrode slurry is 54 wt%. Using 8 μm copper foil as the negative electrode current collector, coat the negative electrode slurry on both sides of the negative electrode current collector, with a coating thickness of 50 μm on one side to obtain a negative electrode active material layer. After drying at 85 °C and cutting, the negative electrode sheet is obtained.

[0051] Preparation of the separator: The separator uses 7 μm thick polyethylene (PE).

[0052] Preparation of the electrolyte: In an environment with a water content of less than 10 ppm, LiPF 6Add a non-aqueous organic solvent (ethylene carbonate (EC): propylene carbonate (PC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 10:30:30:30, mass ratio), and the concentration of LiPF 6 is 1 mol / L. Mix evenly to obtain a basic electrolyte. The types and amounts of some other additives are shown in the following table, and the content of each substance is the mass percentage calculated based on the mass of the electrolyte.

[0053] Preparation of lithium-ion battery: Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play a role in isolation, and wind to obtain an electrode assembly. Place the electrode assembly in an outer packaging aluminum-plastic film, remove moisture at 80 °C, inject the above electrolyte and encapsulate it, and obtain a lithium-ion battery through processes such as formation, degassing, and edge trimming.

[0054] The remaining examples and comparative examples are based on Example 1-1 for parameter changes. Among them, the mass of the negative active material and the mass of the positive active material are adjusted by the length of the wound electrode sheet. Among them, in the examples and comparative examples provided in this application, the mass of the negative active material / the mass of the positive active material = 0.55, and the electrolyte mass retention / the positive active mass = 0.7. In addition, the content of EC in the electrolyte and the content of additives may be different from those in Example 1. The remaining part of the electrolyte except for EC and additives consists of the same mass of PC, EMC, and DEC. For the specific content of EC and additives, please refer to the following table and related descriptions.

[0055] The following describes the test methods for each parameter of this application.

[0056] (1) Cycle performance test of lithium-ion battery

[0057] Place the lithium-ion battery in a 25 °C constant temperature oven and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature. Charge the lithium-ion battery at a constant current of 1C until the voltage reaches 4.2V, then charge it at a constant voltage of 4.2V until the current reaches 0.05C, and then discharge it at a constant current of 1C until the voltage reaches 2.8V. This is one charge-discharge cycle. Taking the capacity of the first discharge as 100%, repeat the charge-discharge cycle until the discharge capacity decays to 80%, then stop the test and record the number of cycles as an index to evaluate the cycle performance of the lithium-ion battery.

[0058] At the same time, test the cycle performance of the lithium-ion battery at 45 °C. The test method is the same as the above 25 °C cycle performance test except for the different temperature.

[0059] (2) High-temperature storage performance test of lithium-ion battery (60 °C, store for 1680 h)

[0060] A: 100% SOC storage

[0061] Place the lithium-ion battery in an incubator at 25 °C and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature. Charge it at a constant current of 1C to 4.2V, then charge it at a constant voltage until the current is 0.05C, and then discharge it at a constant current of 1C to 2.8V. Record the discharge capacity as the initial capacity of the lithium-ion battery. Then charge it at a constant current of 0.5C to 4.2V, charge it at a constant voltage until the current is 0.05C, and use a micrometer to test and record the thickness of the lithium-ion battery. Transfer the tested lithium-ion battery to an incubator at 60 °C for storage for 1680h. During this period, take out the lithium-ion battery every 168h, test the thickness (Thickness, abbreviated as THK), open circuit voltage (Open circuit voltage, abbreviated as OCV), and impedance (Impedance, abbreviated as IMP) of the lithium-ion battery, and transfer the lithium-ion battery to an incubator at 25 °C and let it stand for 60 minutes. Discharge it at a constant current of 0.5C to 2.8V and record the discharge capacity as the residual capacity of the lithium-ion battery. Charge it at a constant current of 0.5C to 4.2V, charge it at a constant voltage until the current is 0.05C, and then discharge it at a constant current of 0.5C to 2.8V and record the discharge capacity as the recoverable discharge capacity of the lithium-ion battery. Calculate the storage thickness expansion rate of the lithium-ion battery and use it as an index to evaluate the gas generation amount of the lithium-ion battery during high-temperature storage; calculate the residual capacity retention rate and recoverable capacity retention rate of the lithium-ion battery after storage. At the same time, record the number of lithium-ion batteries that smoke and burn during the storage of 10 stored lithium-ion batteries.

[0062] Thickness expansion rate = (thickness after storage - initial thickness) / initial thickness × 100%

[0063] Recoverable capacity retention rate = recoverable discharge capacity after storage / initial discharge capacity × 100%

[0064] B: 50% SOC storage

[0065] Place the lithium-ion battery in an incubator at 25 °C and let it stand for 30 minutes to bring the lithium-ion battery to a constant temperature. Charge it at a constant current of 1C to 4.2V, then charge it at a constant voltage until the current reaches 0.05C, and then discharge it at a constant current of 1C to 2.8V. Record the discharge capacity as the initial capacity of the lithium-ion battery. Then charge it at a constant current of 0.5C to 3.65V, charge it at a constant voltage until the current reaches 0.05C (50% SOC), and use a micrometer to measure and record the thickness of the lithium-ion battery. Transfer the tested lithium-ion battery to an incubator at 60 °C for storage for 1680 h. During this period, take out the lithium-ion battery every 168 h to measure the thickness (Thickness, abbreviated as THK), open circuit voltage (Open circuit voltage, abbreviated as OCV), and impedance (Impedance, abbreviated as IMP) of the lithium-ion battery, and transfer the lithium-ion battery to an incubator at 25 °C and let it stand for 60 minutes. Discharge it at a constant current of 0.5C to 2.8V and record the discharge capacity as the residual capacity of the lithium-ion battery. Charge it at a constant current of 0.5C to 4.2V, charge it at a constant voltage until the current reaches 0.05C, and then discharge it at a constant current of 0.5C to 2.8V. Record the discharge capacity as the recoverable discharge capacity of the lithium-ion battery. Calculate the storage thickness expansion rate of the lithium-ion battery and use it as an index to evaluate the gas generation of the lithium-ion battery during high-temperature storage; calculate the residual capacity retention rate and recoverable capacity retention rate of the lithium-ion battery after storage. At the same time, record the number of lithium-ion batteries that smoke and burn during the storage of 10 stored lithium-ion batteries.

[0066] Thickness expansion rate = (thickness after storage - initial thickness) / initial thickness × 100%

[0067] C: 0% SOC storage

[0068] Place the lithium-ion battery in an incubator at 25°C and let it stand for 30 minutes to reach a constant temperature. Charge the lithium-ion battery at a constant current of 1C to 4.2V, then charge it at a constant voltage until the current reaches 0.05C, and then discharge it at a constant current of 1C to 2.8V. Record the discharge capacity as the initial capacity of the lithium-ion battery. Use a micrometer to measure and record the thickness of the lithium-ion battery. Transfer the tested lithium-ion battery to an incubator at 60°C for storage for 1680h. During this period, take out the lithium-ion battery every 168h to measure the thickness (Thickness, abbreviated as THK), open circuit voltage (Open circuit voltage, abbreviated as OCV), and impedance (Impedance, abbreviated as IMP) of the lithium-ion battery, and transfer the lithium-ion battery to an incubator at 25°C and let it stand for 60 minutes. Charge it at a constant current of 0.5C to 4.2V, then charge it at a constant voltage until the current reaches 0.05C, and then discharge it at a constant current of 0.5C to 2.8V. Record the discharge capacity as the recoverable discharge capacity of the lithium-ion battery. Calculate the storage thickness expansion rate of the lithium-ion battery and use it as an index to evaluate the gas generation amount of the lithium-ion battery during high-temperature storage; calculate the recoverable capacity retention rate of the lithium-ion battery after storage. At the same time, record the number of lithium-ion batteries that smoke and burn during the storage of 10 stored lithium-ion batteries.

[0069] Thickness expansion rate = (thickness during storage - initial thickness) / initial thickness × 100%

[0070] Recoverable capacity retention rate = recoverable discharge capacity during storage / initial discharge capacity × 100%

[0071] (3) Overcharge test of lithium-ion battery

[0072] Discharge the lithium-ion battery at 0.5C to 2.8V at 25°C, then charge it at a constant current of 2C to 5.4V, and then charge it at a constant voltage for 3 hours. Monitor the surface temperature change of the lithium-ion battery (the passing standard is: the battery does not catch fire, burn, or explode). Test 10 lithium-ion batteries for each example and record the passing rate.

[0073] (4) Thermal box test

[0074] Charge the lithium-ion battery at a constant current of 0.5C to 4.2V at 25°C, then charge it at a constant voltage of 4.2V until the current is less than or equal to 0.05C. After fully charging the lithium-ion battery, place it in a high and low temperature box and heat it to 150°C at a rate of 5°C / minute. Keep it at a constant temperature of 150°C for 1 hour and monitor the lithium-ion battery. The passing standard is: the battery does not catch fire or explode. Test 10 batteries for each example and record the passing rate.

[0075] Table 1 and Table 2 show the various parameters and evaluation results of Examples 1-1 to 1-12 and Comparative Examples 1 to 4.

[0076] Table 1

[0077]

[0078]

[0079] Table 2

[0080]

[0081] By comparing Examples 1-1 to 1-12 and Comparative Examples 1 to 4, it can be seen that within a certain range, as the ratio b / a increases, the cycle performance of the lithium-ion battery, the high-temperature storage performance at different SOCs, the capacity retention rate after storage, and the safety performance are significantly improved. This may be due to the protection of the EC on the negative electrode interface and the good passivation effect on the lithium deposition interface of the negative electrode. However, when b / a is too small, EC cannot protect the negative electrode interface, so it has an adverse effect on the cycle performance of the electrochemical device under normal and high-temperature conditions. Moreover, due to the poor passivation effect on the lithium deposition interface of the negative electrode, the storage and safety performance of the electrochemical device at low state of charge are affected; when b / a > 6.4, the cycle performance cannot be further improved, and the storage performance and safety performance at high state of charge are affected. This may be because when b / a is too large, the interfacial kinetics between the electrolyte and the negative electrode are affected, resulting in lithium deposition during charging, and intense reactions occur during storage at high temperature, leading to thermal failure of the lithium-ion battery.

[0082] Table 3 and Table 4 show the various parameters and evaluation results of Examples 1-2, 2-1 to 2-11 and Comparative Examples 5 to 6. Among them, in the following examples and comparative examples, the mass of the negative electrode active material is 5.5 g.

[0083] Table 3

[0084]

[0085] Table 4

[0086]

[0087]

[0088] It can be seen from Comparative Examples 5 to 6, Examples 1-2 and the comparison with Examples 2-1 to 2-11 that adding a specific content of the solvents EC and the carbonates VC or FEC to the electrolyte can significantly improve the cycling performance, high-temperature storage performance, capacity retention rate after storage and safety performance of lithium-ion batteries compared with the case of not adding the additive VC and the additive FEC or adding only one of them. This is mainly due to the fact that VC and FEC can well repair the SEI damaged at the negative electrode interface during storage, inhibit side reactions and lithium deposition at the negative electrode. Among them, when the content of VC is lower than that of FEC, the high-temperature storage performance and the capacity retention rate during storage are better. This may be because, at this concentration, the electrolyte forms a composite interfacial protective film with lower impedance on the electrode surface, reducing the consumption of active lithium after storage. In addition, when the contents of VC and FEC are too high, the impedance of the negative electrode interface is too large, and there is too much residue after formation, which is easy to generate gas by oxidation at the positive electrode interface, thus affecting the charging performance after storage and also bringing potential safety hazards of gas generation during storage.

[0089] Tables 5 and 6 show the various parameters and evaluation results of Example 2-6, Examples 3-1 to 3-12 and Comparative Examples 5 and 7. Among them, in each of the following examples and comparative examples, the dosages of the positive and negative active materials are the same as those in Example 2-6.

[0090] Table 5

[0091]

[0092]

[0093] Table 6

[0094]

[0095] It can be seen from the comparison of Example 2-6, Examples 3-1 to 3-12 and Comparative Examples 5 and 7 that adding a specific content of the solvent EC, the carbonate and the compound containing a sulfur-oxygen double bond to the electrolyte can significantly improve the cycling, storage and safety performance of lithium-ion batteries in different states compared with the case of adding only EC and one of the carbonate and the compound containing a sulfur-oxygen double bond. Comparing Example 3-1 with Example 2-6, it can be seen that in this system, when the ratio of the compound containing a sulfur-oxygen double bond to the mass of the positive active material is low, the improvement of the various performances of the lithium-ion battery is not obvious; comparing Example 3-9 with Examples 3-1 to 3-7 and Examples 3-10 to 3-12, it can be seen that when the ratio of the compound containing a sulfur-oxygen double bond to the mass of the positive active material is too high, it has an obvious impact on the storage and safety performance of the battery at high SOC.

[0096] Tables 7 and 8 show the respective parameters and evaluation results of Examples 2-6, 4-1 to 4-13, and Comparative Example 5. Among them, in each of the following examples and comparative examples, the amounts of the positive and negative active materials are the same as those in Example 2-6.

[0097] Table 7

[0098]

[0099] Table 8

[0100]

[0101]

[0102] From the comparison of Examples 2-6, 4-1 to 4-13, and Comparative Example 5, it can be seen that adding a specific content of the solvent EC and lithium salt to the electrolyte can significantly improve the cycling performance, high-temperature storage performance, and safety performance of the lithium-ion battery compared with the case where no lithium salt is added. This is mainly due to the formation of low-impedance SEI films and CEI films on the surfaces of the positive and negative electrodes by the lithium salt, which improves the charging performance and reduces side reactions caused by lithium deposition. At the same time, the stable protective films can effectively reduce side reactions between the electrolyte and the positive and negative electrodes during storage and cycling, while reducing the consumption of active lithium and improving the capacity retention rate.

[0103] Tables 9 and 10 show the respective parameters and evaluation results of Examples 2-6, 5-1 to 5-13, and Comparative Examples 5 and 8. Among them, in each of the following examples and comparative examples, the contents of the positive and negative active materials are the same as those in Example 2-6.

[0104] Table 9

[0105]

[0106] Table 10

[0107]

[0108] From the comparison of Examples 2-6, 5-1 to 5-13 and Comparative Examples 5 and 8, it can be seen that adding a specific content of solvent EC and polynitrile compound to the electrolyte can significantly improve the high-temperature storage performance and safety performance of lithium-ion batteries compared with the case of not adding EC and polynitrile compound or adding only one of them. This is mainly due to the fact that the polynitrile compound can well complex with the cathode active material, reduce the oxidation activity of the cathode material, reduce side reactions, and at the same time inhibit the damage of the SEI film caused by the deposition of the dissolved cathode transition metal on the anode, thereby reducing gas generation and improving the capacity retention rate. In addition, the combined advantage of EC and the polynitrile compound is that EC can inhibit the decomposition of the polynitrile compound at the anode interface, reduce the growth of the anode impedance, and enable more polynitrile compounds to act effectively on the cathode; while the passivation of the cathode by the polynitrile compound can reduce the oxidation of EC at the cathode interface, enabling more EC to be used for the protection of the anode interface, thus maximizing the advantages of the two substances and achieving the best electrical performance.

[0109] The above description is only the preferred embodiments of the present application and the explanation of the applied technical principles. Those skilled in the art should understand that the scope of disclosure involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features. For example, the technical solutions formed by mutually replacing the above features with the technical features having similar functions disclosed in the present application.

Claims

1. An electrochemical device comprising: Positive electrode; A negative electrode sheet, the negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, wherein the mass of the negative electrode active material is ag; A separator, disposed between the positive electrode sheet and the negative electrode sheet; An electrolyte, wherein the electrolyte comprises ethylene carbonate, and based on the mass of the electrolyte, the mass content of the ethylene carbonate is b%, and b / a is 1.6 to 6.4; The electrolyte further comprises at least one of lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium tetraborate, lithium borate or lithium trifluoromethanesulfonate; Based on the mass of the electrolyte, the mass content of at least one of lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium tetraborate, lithium borate or lithium trifluoromethanesulfonate is 0.01% to 3%.

2. The electrochemical device according to claim 1, wherein: b / a is 2 to 6.

3. The electrochemical device according to claim 1, wherein b is 5 to 20 or b / a is 2.5 to 5.

5.

4. The electrochemical device according to claim 1, wherein Based on the mass of the electrolyte, the mass content of at least one of lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium tetraborate, lithium borate or lithium trifluoromethanesulfonate is 0.5% to 3%.

5. The electrochemical device according to claim 1, wherein Based on the mass of the electrolyte, the mass content of at least one of the lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium tetraborate, lithium borate or lithium trifluoromethanesulfonate is 1% to 3%.

6. The electrochemical device according to claim 1, wherein The electrolyte also includes at least one of vinylene carbonate or fluoroethylene carbonate. Based on the mass of the electrolyte, the mass content of vinylene carbonate is m%, the mass content of fluoroethylene carbonate is n%, m+n=c, and 0.01≤c<2.

7. The electrochemical device according to claim 6, wherein: Based on the mass of the electrolyte, the mass content of vinylene carbonate is m%, the mass content of fluoroethylene carbonate is n%, and the electrochemical device satisfies at least one of the following relationships: i) 0≤m<2; ii) 0≤n<2; iii) m<n; iv) c / a is from 0.001 to 0.

36.

8. The electrochemical device according to claim 1, wherein The electrolyte further includes a compound containing a sulfur-oxygen double bond, and the compound containing a sulfur-oxygen double bond includes at least one of 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, methylene disulfonate, 1,3-propane disulfonic anhydride, 2-methylbutane sultone or propenyl-1,3-sultone.

9. The electrochemical device according to claim 8, wherein: Based on the mass of the electrolyte, the mass content of the compound containing sulfur-oxygen double bonds is d%, and the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the mass of the positive electrode active material is eg, and d / e is 0.1 to 0.

6.

10. The electrochemical device according to claim 9, wherein: The positive electrode active material contains cobalt element.

11. The electrochemical device according to claim 1, wherein The electrolyte also includes a polynitrile compound, which includes at least one of succinonitrile, adiponitrile, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,3,6-hexanetrinitrile or 1,2,3-tris(2-cyanoxy)propane, and the mass content of the polynitrile compound is 0.01% to 6% based on the mass of the electrolyte.

12. The electrochemical device according to claim 11, wherein The mass content of the polynitrile compound is 1% to 6%.

13. The electrochemical device according to claim 12, wherein: The mass content of the polynitrile compound is 2% to 6%.

14. An electronic device comprising the electrochemical device according to any one of claims 1 to 13.

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