Electrochemical device and electronic device including the same

Abstract

The application discloses an electrochemical device and an electronic device comprising the same. In the electrochemical device, the positive active material comprises a lithium transition metal composite oxide with a P63mc crystal structure, and an electrolyte comprises an additive A; the additive A comprises at least one of a compound of formula I or a compound of formula II, so that the electrochemical device has significantly improved cycle performance at high voltage.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries are widely used in portable electronic products, electric vehicles, aerospace and other fields due to their high energy density, good cycle performance, safety, environmental protection, and no memory effect. In order to meet the needs of social development, it is urgent to seek lithium ion batteries with high energy density and high power density, which requires the positive active material used to have higher specific capacity and higher voltage platform. In order to obtain higher specific capacity, the positive active material is developing towards high voltage. The current positive active material, such as lithium cobaltate with R-3m crystal structure, which has been commercially used on a large scale, will cause a series of irreversible damage to the crystal structure as the voltage increases, resulting in the release of lattice oxygen, and the cycle performance of the battery is greatly reduced. At the same time, as the voltage increases, the oxidation of the electrolyte on the surface of the positive active material is enhanced, which further reduces the cycle performance of the battery. + A large amount of lithium is released, the crystal structure is damaged, the lattice oxygen is released, and the cycle performance of the battery is greatly reduced. At the same time, as the voltage increases, the oxidation of the electrolyte on the surface of the positive active material is enhanced, which further reduces the cycle performance of the battery. SUMMARY

[0003] Based on the defects of the prior art, the purpose of the present application is to provide an electrochemical device and an electronic device comprising the same, so as to improve the cycle stability of the electrochemical device at high voltage.

[0004] In a first aspect, the present application provides an electrochemical device, comprising a positive electrode, a negative electrode and an electrolyte, the positive electrode comprising a positive active material, the positive active material comprising a lithium transition metal composite oxide with a P63mc crystal structure, and the electrolyte comprising an additive A; the additive A comprising at least one of a compound of formula I or a compound of formula II,

[0005]

[0006] wherein one or two of Q, R, X and Z are N atoms, and the rest are C(R 16 ); R 16 each independently selected from H, halogen, substituted or unsubstituted C 1～5 alkyl or substituted or unsubstituted C 1～5 alkoxy; R 11 and R 13 each independently selected from -CO- or -SO2-; R 12 each independently selected from -N(R2)- or -O-; R2each independently selected from H, substituted or unsubstituted C 1～5 alkyl or substituted or unsubstituted C 1～5Alkoxyalkyl; R 14 Each is independently selected from substituted or unsubstituted C 1～5 Alkylene, substituted or unsubstituted C 1～5 alkeneoxy, substituted or unsubstituted C 2～5 alkenyl, or substituted or unsubstituted C 2～5 Ethyne group; R 15 Each is independently selected from -O- or -CH(R3)-, and each R3 is independently selected from H, F, substituted or unsubstituted C. 1～5 Alkyl or substituted or unsubstituted C 1～5 Alkyl group; when substituted, each substituent is independently selected from a halogen; Y - Each was independently selected from PF6 - FSI - or TFSI - ,

[0007]

[0008] In some embodiments, the mass percentage a of additive A is 0.01% to 5% based on the mass of the electrolyte. In some embodiments, a is 0.1% to 3%.

[0009] In some embodiments, additive A comprises at least one of the following compounds:

[0010]

[0011]

[0012] In some embodiments, the electrolyte further includes a sulfur-containing oxygen double bond compound, wherein the mass percentage b of the sulfur-containing oxygen double bond compound is 0.01% to 8% based on the mass of the electrolyte. In some embodiments, b is 0.1% to 6%.

[0013] In some embodiments, additive A comprises the compound of formula II, and the mass percentage of the compound of formula II is c, based on the mass of the electrolyte, satisfying: 0.1 ≤ b / c ≤ 80. In some embodiments, 5 ≤ b / c ≤ 30.

[0014] In some embodiments, the sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonate lactone (PS), 2,4-butanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate (DTD), propenyl-1,3-sulfonate lactone, methylene disulfonate (MMDS), 1,3-propane disulfonic anhydride, 4-methyl vinyl sulfate (methyl DTD), or pentaerythritol bicyclic sulfate.

[0015] In some embodiments, the electrolyte further comprises additive B, which includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the mass percentage d of additive B is 0.01% to 5% based on the mass of the electrolyte. In some embodiments, d is 0.1% to 3%.

[0016] In some embodiments, when the electrochemical device is fully charged, the XRD pattern of the positive electrode active material has a characteristic peak in the range of 17.5° to 20.5°, and the half-peak width of the characteristic peak is 0.05° to 0.1°.

[0017] In some embodiments, when the electrochemical device is fully charged, the DSC spectrum of the positive electrode active material shows an exothermic peak in the range of 300°C to 400°C.

[0018] In some embodiments, the lithium transition metal composite oxide having a P63mc crystal structure comprises Co and optionally M, wherein the M element comprises at least one selected from Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr, or Al; and in the lithium transition metal composite oxide having a P63mc crystal structure, the sum of the molar amounts of Co and M is n. Co+M The molar amount of element M is n M The n M With the n Co+M The ratio y satisfies 0 ≤ y ≤ 0.15.

[0019] In some embodiments, the lithium transition metal composite oxide having a P63mc crystal structure further comprises Na, wherein the molar amount of Na in the lithium transition metal composite oxide having a P63mc crystal structure is n. Na The n Na With the n Co+M The ratio z satisfies 0 <z≤0.03。

[0020] In some embodiments, the lithium transition metal composite oxide having a P63mc crystal structure includes Li x Na z Co 1-y M y O 2±n , where 0.6≤x≤1.01, 0≤y≤0.15, 0≤z≤0.03, and 0≤n≤0.1.

[0021] Secondly, this application provides an electronic device including the aforementioned electrochemical device.

[0022] Compared with the prior art, the beneficial effects of this application are as follows: Lithium transition metal composite oxides with a P63mc crystal structure have high crystal structure stability under high voltage, which can reduce the risk of particle breakage and oxygen release phase transition, and can improve the cycle performance of electrochemical devices under high voltage to a certain extent. However, due to its strong surface oxidizability, it aggravates the decomposition of electrolyte and the deposition of by-products on the surface of positive electrode active material, which is not conducive to further improvement of cycle performance under high voltage. By adding additive A to the electrolyte, a dense passivation layer can be formed on the surface of positive electrode active material in advance, reducing the reactivity of the positive electrode interface. At the same time, the electron-deficient N element contained therein can complex with the transition metal on the surface of positive electrode active material. On the one hand, it can inhibit the dissolution of transition metal and improve the structural stability of positive electrode active material under high voltage. On the other hand, it can strengthen the bonding between the passivation layer and the surface of positive electrode active material under high voltage, thereby improving the stability of the positive electrode interface under high voltage and improving the long cycle performance of electrochemical devices under high voltage. Furthermore, the addition of sulfur-containing oxygen double bond compounds and / or additive B to the electrolyte can synergistically improve the long-cycle performance of the electrochemical device under high voltage. Detailed Implementation

[0023] To better illustrate the purpose, technical solution, and advantages of this application, the following detailed description of the application will be provided in conjunction with specific embodiments. The purpose of this description is to facilitate a thorough understanding of the content of this application by those skilled in the art, rather than to limit the scope of this application.

[0024] I. Electrochemical Device

[0025] According to a first aspect of this application, an electrochemical device is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprising a lithium transition metal composite oxide having a P63mc crystal structure, and the electrolyte comprises an additive A; the additive A comprises at least one compound of formula I or formula II.

[0026]

[0027] One or two of Q, R, X, and Z are N atoms, and the rest are C(R) atoms. 16 ); R 16 Each is independently selected from H, halogen, substituted or unsubstituted C. 1～5 Alkyl or substituted or unsubstituted C 1～5 Alkoxy; R 11 and R 13 Each is independently selected from -CO- or -SO2-; R 12 Each is independently selected from -N(R2)- or -O-; R2 is independently selected from H, substituted or unsubstituted C. 1～5Alkyl or substituted or unsubstituted C 1～5 Alkoxyalkyl; R 14 Each is independently selected from substituted or unsubstituted C 1～5 Alkylene, substituted or unsubstituted C 1～5 alkeneoxy, substituted or unsubstituted C 2～5 alkenyl, or substituted or unsubstituted C 2～5 Ethyne group; R 15 Each is independently selected from -O- or -CH(R3)-, and each R3 is independently selected from H, halogen, substituted or unsubstituted C. 1～5 Alkyl or substituted or unsubstituted C 1～5 Alkyl group; when substituted, each substituent is independently selected from a halogen; Y - Each was independently selected from PF6 - FSI - or TFSI - ,

[0028]

[0029] The aforementioned electrochemical device uses a lithium transition metal composite oxide with a P63mc crystal structure as its positive electrode active material. This material exhibits high crystal structure stability under high voltage, reducing the risk of particle breakage and crystal structure damage. This improves the cycling performance of the electrochemical device under high voltage to some extent. However, its strong surface oxidizability exacerbates electrolyte decomposition and byproduct deposition on the positive electrode active material surface, hindering further improvement in cycling performance under high voltage. Adding additive A to the electrolyte allows for the pre-oxidation of the positive electrode active material surface to form a dense passivation layer, reducing the reactivity of the positive electrode interface. Simultaneously, the electron-deficient nitrogen element it contains can complex with the transition metal on the positive electrode active material surface. This inhibits the dissolution of the transition metal, improving the structural stability of the positive electrode active material under high voltage. Furthermore, it strengthens the bonding between the passivation layer and the positive electrode active material surface under high voltage, thereby improving the stability of the positive electrode interface under high voltage and enhancing the long-cycle performance of the electrochemical device under high voltage.

[0030] In some embodiments, among Q, R, X, and Z, only Q, only R, only X, or only Z are N elements. In some embodiments, Q and R, Q and X, Q and Z, R and X, R and Z, or X and Z are N elements.

[0031] In some embodiments, C 1～5 The alkylene group can be methylene, ethylene, n-propylene, isopropylene, n-butylene, sec-butylene, tert-butylene, n-pentylene, etc. In some embodiments, C 1～5 The alkene oxide is a methoxy group, an ethoxy group, a propoxy group, a butoxy group, or a pentylene oxide, etc. In some embodiments, C2～5 The alkenyl group can be vinylene, n-propenylene, isopropenylene, n-butenylene, sec-butenylene, n-pentenylene, isopentenylene, etc. In some embodiments, C 2～5 The ynylene group is ethynylene, propynylene, butynylene, or pentylyyl, etc., in some embodiments. 1～5 The alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, isopentyl, etc. In some embodiments, C 1～5 Alkoxy groups can be methoxy, ethoxy, propoxy, butoxy, or pentoxy, etc.

[0032] In some embodiments, the halogen is F, Cl, Br, or I, etc.

[0033] In some embodiments, the mass percentage a of additive A is 0.01% to 5% based on the mass of the electrolyte. In some embodiments, a is a range of 0.01%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, or any combination of these values. In some embodiments, a is 0.1% to 3%.

[0034] In some embodiments, additive A comprises at least one of the following compounds:

[0035]

[0036]

[0037] In some embodiments, the electrolyte further includes a sulfur-oxygen double bond compound, wherein the mass percentage b of the sulfur-oxygen double bond compound is 0.01% to 8% based on the mass of the electrolyte. By further adding the sulfur-oxygen double bond compound to the electrolyte, it can participate in the film formation of additive A on the surface of the positive electrode active material. The abundant polar sulfur-oxygen double bonds therein can further enhance the bonding between the passivation layer and the surface of the positive electrode active material, improving the high-voltage stability of the passivation layer, thereby further improving the stability of the positive electrode interface under high voltage and enhancing the cycle performance of the electrochemical device under high voltage. In some embodiments, b is a range of 0.01%, 0.05%, 0.1%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, or any combination thereof. In some embodiments, b is 0.1% to 6%.

[0038] In some embodiments, additive A comprises the compound of formula II described above, and the mass percentage of the compound of formula II is c, based on the mass of the electrolyte, satisfying: 0.1 ≤ b / c ≤ 80. The compound of formula II, since it also contains sulfur-oxygen double bonds, can further enhance the bonding between additive A and the sulfur-oxygen double-bond-containing compound during film formation, improving the high-voltage stability of the passivation layer, thereby further improving the stability of the positive electrode interface under high voltage and enhancing the cycle performance of the electrochemical device under high voltage. In some embodiments, b / c is a range of 0.1, 0.5, 1, 3, 5, 10, 20, 30, 40, 50, 60, 80, or any combination of these values. In some embodiments, 5 ≤ b / c ≤ 30.

[0039] In some embodiments, the sulfur-containing double bond compound comprises at least one of 1,3-propanesulfonate lactone (PS), 2,4-butanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate (DTD), propenyl-1,3-sulfonate lactone, methylene disulfonate (MMDS), 1,3-propane disulfonic anhydride, 4-methyl vinyl sulfate (methyl DTD), or pentaerythritol bicyclic sulfate.

[0040] In some embodiments, the electrolyte further comprises additive B, which includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the mass percentage d of additive B is 0.01% to 5% based on the mass of the electrolyte. Additive B can synergistically form a passivation film on the surface of the positive electrode active material with additive A, reducing the impedance of the passivation film. Simultaneously, the sulfonyl groups it contains can improve the high-voltage stability of the passivation film, thereby further improving the cycle performance of the electrochemical device under high voltage. In some embodiments, d is a range of 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any combination of these values. In some embodiments, d is 0.1% to 3%.

[0041] In some embodiments, the positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer comprising a positive active material.

[0042] In some embodiments, when the electrochemical device is in a fully discharged state, the XRD pattern of the above-mentioned positive electrode active material has a characteristic peak in the range of 17.5° to 19°, and the full width at half maximum (FWHM) of this characteristic peak is 0.05° to 0.1°. The characteristic peak in the range of 17.5° to 19° corresponds to the (002) crystal plane of a lithium transition metal composite oxide with a P63mc crystal structure. The XRD pattern can be obtained by the following testing methods: directly measuring the surface of the positive electrode active layer using an XRD testing device (such as a Bruker D8 ADVANCE), or dissolving the positive electrode active layer in an organic solvent (such as N-methylpyrrolidone), filtering, drying the resulting solid to obtain powder, and then detecting the powder using an XRD testing device.

[0043] In some embodiments, when the electrochemical device is in a fully discharged state, the DSC spectrum of the above-mentioned positive electrode active material exhibits an exothermic peak in the range of 300°C to 400°C. The DSC spectrum is obtained by the following testing method: the positive electrode active material (obtained by disassembling the electrochemical device after full discharge, taking the middle portion of the positive electrode sheet, and cleaning it three times with dimethyl carbonate) is placed in a DSC testing apparatus (TOPEM TMDSC) and heated to 460°C at a heating rate of 5°C / min to obtain a temperature-heat flow curve.

[0044] In some embodiments, the lithium transition metal composite oxide having a P63mc crystal structure comprises Co and optionally M, wherein the M element comprises at least one selected from Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr, or Al; and in the lithium transition metal composite oxide having a P63mc crystal structure, the sum of the molar amounts of Co and M is n. Co+M The molar amount of element M is n M The n M With the n Co+M The ratio y satisfies 0 ≤ y ≤ 0.15.

[0045] In some embodiments, the lithium transition metal composite oxide having a P63mc crystal structure further comprises Na, wherein the molar amount of Na in the lithium transition metal composite oxide having a P63mc crystal structure is n. Na The n Na With the n Co+M The ratio z satisfies 0 <z≤0.03。

[0046] Lithium transition metal composite oxides with a P63mc crystal structure can accommodate volume changes and embed more Li due to the presence of lithium vacancies in their crystal structure. During the synthesis of lithium transition metal composite oxides with a P63mc crystal structure, a very small amount of Na is introduced. Na occupies some Li sites and acts as a pillar to support the crystal structure, which can improve the structural stability of the material. Moreover, it has a lower lithium-ion migration energy compared to O3 phase lithium cobalt oxide. In addition, further introducing element M into lithium transition metal composite oxides with a P63mc crystal structure can further improve its structural stability to a certain extent.

[0047] In some embodiments, the lithium transition metal composite oxide having a P63mc crystal structure includes Li x Na z Co 1-y M y O 2±n , where 0.6≤x≤1.01, 0≤y≤0.15, 0≤z≤0.03, and 0≤n≤0.1.

[0048] In some embodiments, x is a range of 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.01, or any combination of these values.

[0049] In some embodiments, y is 0, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.13, 0.14, 0.15, or a range of any two of these values.

[0050] In some embodiments, z is a range of 0, 0.002, 0.003, 0.004, 0.005, 0.006, 0.008, 0.01, 0.015, 0.02, 0.025, 0.03, or any combination of these values.

[0051] The content of each element in lithium transition metal composite oxide with P63mc crystal structure can be tested by the following method: after the electrochemical device is fully loaded, it is disassembled, the positive active material in the positive active layer is taken out, dissolved and then tested by ICP (inductively coupled plasma atomic emission spectrometry).

[0052] In some embodiments, the positive electrode active layer further includes an adhesive. In some embodiments, the adhesive includes, but is not limited to, at least one of: polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylic acid, polyacrylate, or polyacrylate.

[0053] In some embodiments, the positive electrode active layer further includes a conductive agent. In some embodiments, the conductive agent includes, but is not limited to, at least one of: carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, metal powder, metal fiber, or conductive agent polymer.

[0054] In some embodiments, the positive current collector includes, but is not limited to: aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, or a polymer substrate coated with a conductive metal.

[0055] In some embodiments, the electrolyte further includes an organic solvent and a lithium salt. The organic solvent may be any organic solvent known in the art that can be used as a solvent for an electrolyte. In some embodiments, the organic solvent includes, but is not limited to, at least one of: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propyl propionate (PP), or ethyl propionate (EP). In some embodiments, the lithium salt includes, but is not limited to, at least one of: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium di(oxalatoborate) LiBF2(C2O4) (LiDFOB). In some embodiments, the concentration of the lithium salt in the electrolyte is: 0.5-3 mol / L, 0.5-2 mol / L, or 0.8-1.5 mol / L.

[0056] The negative electrode that can be used in the above-described electrochemical device includes any technology disclosed in the prior art. In some embodiments, the negative electrode comprises a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector.

[0057] In some embodiments, the negative electrode active layer comprises a negative electrode active material. In some embodiments, the negative electrode active material comprises, but is not limited to, at least one of carbon materials, silicon-based materials, or lithium metal. In some embodiments, the carbon material comprises at least one of natural graphite, artificial graphite, hard carbon, soft carbon, or coke. In some embodiments, the silicon-based material comprises at least one of silicon, silicon-oxygen composites, silicon-carbon composites, or silicon alloys.

[0058] In some embodiments, the negative electrode active layer further includes an adhesive. In some embodiments, the adhesive includes, but is not limited to, at least one of: polyvinyl alcohol, carboxymethyl cellulose salt, hydroxypropyl cellulose salt, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber.

[0059] In some embodiments, the negative electrode active layer further includes a conductive agent. In some embodiments, the conductive agent includes, but is not limited to, at least one of: carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, metal powder, metal fiber, or conductive agent polymer.

[0060] In some embodiments, the negative current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal.

[0061] In some embodiments, the electrochemical device further includes a separating membrane. For example, the separating membrane may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0062] A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be at least one of an adhesive layer or a heat-resistant layer.

[0063] The heat-resistant layer comprises inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene.

[0064] The adhesive layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or a copolymer of polyvinylidene fluoride and hexafluoropropylene.

[0065] II. Electronic Devices

[0066] According to a second aspect of this application, this application provides an electronic device that can be any electronic device that uses the electrochemical device according to this application.

[0067] In some embodiments, the electronic device includes, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0068] The present application will be described in more detail below using lithium-ion batteries as an example and in conjunction with specific embodiments.

[0069] The performance testing methods for the lithium-ion batteries obtained in each embodiment and comparative example are as follows:

[0070] (1) Cyclic performance test

[0071] At an ambient temperature of 25℃, a lithium-ion battery was charged at a constant current of 1C (battery capacity of 2000mAh) to a voltage of 4.6V, and then charged at a constant voltage of 4.6V to a current of 0.05C. The charging capacity at this point is recorded as the first charge capacity of the lithium-ion battery. After resting for 5 minutes, it was discharged at a constant current of 0.5C to a voltage of 3.0V, and then rested for 5 minutes. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as the first discharge capacity of the lithium-ion battery. The lithium-ion battery was subjected to 500 charge-discharge cycles using the above method, and the discharge capacity of the 500th cycle was measured. The capacity retention rate (%) after 500 cycles at 25℃ = (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.

[0072] (2) X-ray diffraction test

[0073] After fully charging the lithium-ion battery, disassemble it, remove the positive electrode sheet, and use a Bruker D8 ADVANCE to test it, obtaining the XRD diffraction pattern of the positive electrode active material.

[0074] (3) DSC test

[0075] After fully charging the lithium-ion battery, disassemble it and take the middle part of the positive electrode (the middle part along the length and width of the positive electrode). Clean it three times with dimethyl carbonate and then use it for differential scanning calorimetry (DSC) testing. The test temperature range is 25℃-460℃, the heating rate is 5℃ / min, and the position of the exothermic peak between 300℃-400℃ is observed.

[0076] Examples 1-23

[0077] Preparation of electrolyte

[0078] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed uniformly at a mass ratio of EC:PC:DEC = 2:2:6 to obtain a mixed solvent. Fully dried lithium salt LiPF6 was then dissolved in the aforementioned mixed solvent, and appropriate additives were added and mixed uniformly to obtain the electrolyte. The additives in these electrolytes are shown in Table 1. The content of each component is a mass percentage calculated based on the mass of the electrolyte, where the mass percentage of LiPF6 is 12.5%.

[0079] Preparation of positive electrode sheet

[0080] Li, the positive electrode active material x Na z Co 1-y M y O2, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1.4:1.6, and then N-methylpyrrolidone (NMP) is added and stirred thoroughly to form a uniform positive electrode slurry. The solid content of the positive electrode slurry is 72wt%. The positive electrode slurry is uniformly coated onto the positive electrode current collector aluminum foil. The coated aluminum foil is dried, then cold-pressed, cut, and slit, and finally dried under vacuum to obtain the positive electrode sheet.

[0081] Among them, the positive electrode active material Li x Na z Co 1-y M y The preparation method of O2 includes the following steps: (1) Cobalt tetroxide and sodium carbonate powder are mixed in a molar ratio of Na to Co of 0.75:1; the uniformly mixed powder is sintered in an oxygen atmosphere at 800°C for 46 hours to obtain Na with P63mc structure. 0.75 CoO2; (2) Na 0.75 CoO2 and lithium nitrate were mixed uniformly at a Na to Li molar ratio of 0.5:5 and reacted at 300°C in air for 6 hours. The reactants were washed repeatedly with deionized water until the molten salt was removed, and the powder was dried to obtain Li with a P63mc structure. 0.85 Na 0.01 CoO2.

[0082] Preparation of negative electrode sheet

[0083] Artificial graphite (anode active material), conductive carbon black (Super P), sodium carboxymethyl cellulose (CMC) thickener, and styrene-butadiene rubber (SBR) binder were mixed in a mass ratio of 96.4:1.5:0.5:1.6. Deionized water was added and the mixture was stirred until homogeneous to obtain a cathode slurry with a solid content of 54 wt%. The cathode slurry was coated onto a copper foil current collector, then dried, cold-pressed, cut, welded with tabs, and dried again to obtain the cathode electrode sheet.

[0084] Preparation of the separating membrane

[0085] A 5μm thick polyethylene (PE) porous membrane was selected. One side was coated with polyvinylidene fluoride (PVDF) slurry, and the other side was coated with Al2O3 slurry and polyvinylidene fluoride (PVDF) slurry in sequence. After drying, the final isolation membrane was obtained.

[0086] Preparation of lithium-ion batteries

[0087] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. Then, they are wound to obtain a bare cell. After welding the tabs, the bare cell is placed in an outer packaging aluminum-plastic film. The prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained.

[0088] Comparative Examples 1-2

[0089] The difference between Comparative Example 1 and Example 1 is that additive A was not added to the electrolyte. The difference between Comparative Example 2 and Example 4 is that the positive electrode active material is LiCoO2 with an R-3m structure.

[0090] Examples 24-27

[0091] The difference between Examples 24-27 and Example 4 lies in the type of positive electrode active material. Specifically, the positive electrode active material Li... x Na z Co 1-y M y The preparation method of O2 includes the following steps: (1) Cobalt chloride and sulfate of element M are added to deionized water at a molar ratio of Co to M of 1-y:y, sodium carbonate as precipitant and ammonia as complexing agent are added to adjust the pH value to 7, so as to precipitate; then the precipitate is sintered at 600℃ for 7h and ground to obtain (Co 1-y M y (2) 3O4 powder. 1-y M y3O4 powder and sodium carbonate powder were mixed in a Na to Co molar ratio of 0.63:1-y; the uniformly mixed powder was sintered in an oxygen atmosphere at 800℃ for 46 hours to obtain Na 0.63 Co 1-y M y O2. (3) Na 0.63 Co 1-y M y O2 and lithium nitrate were mixed uniformly at a Na to Li molar ratio of 0.6:5 ​​and reacted at 300°C in air for 6 hours. The reactants were washed repeatedly with deionized water until the molten salt was removed, and the powder was dried to obtain Li with a P63mc structure. x Na z Co 1-y M y O2.

[0092] Examples 28-51

[0093] The difference between Examples 28-31 and Example 3 is that a sulfur-containing oxygen double bond compound is further added to the electrolyte. The difference between Examples 32-51 and Example 17 is that a sulfur-containing oxygen double bond compound and / or additive B are further added to the electrolyte. See Table 3 for details.

[0094] Table 1

[0095]

[0096]

[0097] As shown in Table 1, compared with Comparative Examples 1 and 2, the lithium-ion batteries in Examples 1-23, which used lithium transition metal composite oxides with a P63mc crystal structure as the positive electrode active material and added additive A to the electrolyte, exhibited significantly improved long-cycle performance at high voltages. This is because lithium transition metal composite oxides with a P63mc crystal structure have high crystal structure stability at high voltages, reducing the risk of particle breakage and oxygen release phase transition, and thus improving the cycle performance of lithium-ion batteries at high voltages to some extent. However, due to their strong surface oxidizability, they exacerbated electrolyte decomposition and the presence of byproducts at the positive electrode active material. The deposition of reactive material on the surface is not conducive to further improvement of cycle performance under high voltage. However, by adding the above-mentioned additive A to the electrolyte, a dense passivation layer can be formed on the surface of the positive electrode active material in advance through oxidation, reducing the reactivity of the positive electrode interface. At the same time, the electron-deficient nitrogen element contained therein can complex with the transition metal on the surface of the positive electrode active material. On the one hand, it can inhibit the dissolution of the transition metal and improve the structural stability of the positive electrode active material under high voltage. On the other hand, it can strengthen the bonding between the passivation layer and the surface of the positive electrode active material under high voltage, thereby improving the stability of the positive electrode interface under high voltage and enhancing the long cycle performance of lithium-ion batteries under high voltage.

[0098] A comparison of Examples 3-4 and Examples 11-21 shows that the presence of Compound II in the electrolyte further improves the long-cycle performance of lithium-ion batteries at high voltages compared to Compound I. This is because Compound II contains sulfur-oxygen double bonds, which enhance the high-voltage stability of the passivation layer, thereby further improving the long-cycle performance of lithium-ion batteries at high voltages.

[0099] Table 2

[0100]

[0101]

[0102] As shown in Table 2, under full charge, the characteristic peak of the (002) crystal plane of the lithium transition metal composite oxide with P63mc structure is located in the range of 17.5° to 20.5°, and the full width at half maximum (FWHM) of the characteristic peak is in the range of 0.05° to 0.1°. By further doping it with M element, the position of the exothermic peak in its DSC spectrum can be improved, indicating that the stability of its crystal structure is further improved, thereby further enhancing the long cycle performance of lithium-ion batteries under high voltage.

[0103] Table 3

[0104]

[0105]

[0106] As shown in Table 3, compared to Examples 3 and 17 without the addition of sulfur-oxygen double bond compounds, Examples 28-44, which further added sulfur-oxygen double bond compounds, showed further improvement in the long-cycle performance of lithium-ion batteries at high voltage. A comparison of Examples 28-31 and Examples 34-37, 40-44 shows that, compared to the combination of Formula I compound and sulfur-oxygen double bond compound, the combination of Formula II compound and sulfur-oxygen double bond compound further improves the long-cycle performance of lithium-ion batteries at high voltage. This may be because Formula II compound, also containing sulfur-oxygen double bonds, can further enhance the bonding between additive A and the sulfur-oxygen double bond compound during film formation, improving the high-voltage stability of the passivation layer, thereby further improving the stability of the positive electrode interface at high voltage. Furthermore, a comparison of Examples 32-39 shows that when the b / c ratio is in the range of 5-30, the lithium-ion battery exhibits better cycle performance at high voltage.

[0107] Compared to Example 17 without additive B, Examples 45-50 with additive B showed further improvement in the long-cycle performance of lithium-ion batteries at high voltages. This is because additive B can synergistically form a passivation film on the surface of the positive electrode active material with additive A, reducing the impedance of the passivation film. At the same time, the sulfonyl groups it contains can improve the high-voltage stability of the passivation film, thereby further enhancing the cycle performance of lithium-ion batteries at high voltages.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode includes a positive electrode active material, the positive electrode active material includes a lithium transition metal composite oxide having a P63mc crystal structure, the lithium transition metal composite oxide having a P63mc crystal structure contains Co element, Na element and an optional M element, wherein the M element includes at least one of Ni, Mn, Ti, Zn, Y, La, Zr, Mg, Fe, Cu, Nb, Cr or Al; in the lithium transition metal composite oxide having a P63mc crystal structure, the sum of the molar amounts of the Co element and the M element is n Co+M , the molar amount of the M element is n M , the molar amount of the Na element is n Na , the n Na and the n Co+M The ratio z satisfies 0 < z ≤ 0.03; the electrolyte includes additive A; the additive A includes at least one of a compound of formula I or a compound of formula II One or two of Q, R, X, and Z are N atoms, and the rest are C(R) atoms. 16 ); R 16 Each is independently selected from H, halogen, substituted or unsubstituted C. 1～5 Alkyl or substituted or unsubstituted C 1～5 Alkoxy; R in compounds of formula I and formula II 11 and R 13 Each is independently selected from -CO- or -SO2-; R in compounds of formula I and formula II 12 Each is independently selected from -N(R2)- or -O-; R2 is independently selected from H, substituted or unsubstituted C. 1～5 Alkyl or substituted or unsubstituted C 1～5 Alkoxyalkyl; R 14 Selected from substituted or unsubstituted C 1～5 Alkylene, substituted or unsubstituted C 1～5 alkeneoxy, substituted or unsubstituted C 2～5 alkenyl or substituted or unsubstituted C 2～5 Ethyne group; R 15 Selected from -O- or -CH(R3)-, where R3 is independently selected from H, halogen, substituted or unsubstituted C. 1～5 Alkyl or substituted or unsubstituted C 1～5 Alkoxy; During substitution, each substituent is independently selected from halogens; Y - Selected from PF6 - FSI - or TFSI - , 2. The electrochemical device as described in claim 1, characterized in that, Based on the mass of the electrolyte, the mass percentage a of additive A is 0.01% to 5%.

3. The electrochemical device as described in claim 1, characterized in that, Additive A includes at least one of the following compounds:

4. The electrochemical device as described in claim 1, characterized in that, The electrolyte also includes a sulfur-containing oxygen double bond compound, and the mass percentage b of the sulfur-containing oxygen double bond compound is 0.01% to 8% based on the mass of the electrolyte.

5. The electrochemical device as described in claim 4, characterized in that, The electrochemical device satisfies at least one of the following conditions: (1) Based on the mass of the electrolyte, the mass percentage b of the sulfur-containing oxygen double bond compound is 0.1% to 6%; (2) The additive A includes the compound of formula II, and the mass percentage of the compound of formula II is c based on the mass of the electrolyte, satisfying: 0.1≤b / c≤80; (3) The sulfur-containing oxygen double bond compound includes at least one of 1,3-propanesulfonate lactone, 2,4-butanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, propenyl-1,3-sulfonate lactone, methylene disulfonate, 1,3-propane disulfonic anhydride, 4-methyl vinyl sulfate or pentaerythritol bicyclic sulfate.

6. The electrochemical device as claimed in claim 1, characterized in that, It also contains additive B, which includes at least one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethylsulfonyl)imide; the mass percentage d of additive B is 0.01% to 5% based on the mass of the electrolyte.

7. The electrochemical device as described in claim 6, characterized in that, Based on the mass of the electrolyte, the mass percentage d of additive B is 0.1% to 3%.

8. The electrochemical device as claimed in claim 1, characterized in that, The electrochemical device satisfies at least one of the following conditions: (1) When the electrochemical device is fully charged, the XRD pattern of the positive electrode active material has a characteristic peak in the range of 17.5° to 20.5°, and the half width of the characteristic peak is 0.05° to 0.1°. (2) When the electrochemical device is fully charged, the DSC spectrum of the positive electrode active material has an exothermic peak in the range of 300°C to 400°C.

9. The electrochemical device as claimed in claim 1, characterized in that, At least one of the following conditions must be met: (1) The n M With the n Co+M The ratio y satisfies 0 ≤ y ≤ 0.15; (2) The lithium transition metal composite oxide with a P63mc crystal structure includes Li x Na z Co 1-y M y O 2±n , where 0.6≤x≤1.01, 0≤y≤0.15, 0≤z≤0.03, and 0≤n≤0.

1.

10. An electronic device, characterized in that, Includes the electrochemical device as described in any one of claims 1 to 9.

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