Positive electrode material, electrochemical device, and electronic device

Abstract

This application discloses a cathode material, an electrochemical device, and an electronic device. The cathode material has a sheet-like structure and its general chemical formula is Li. x Na y Ni a Mn c O2, 0.7≤x≤1.1, 0.003≤y≤0.2, 0.3≤a≤0.9, 0.001≤c≤0.7, 0.8≤x+y≤1.1, the thickness of the positive electrode material is 0.2μm to 3μm, and the aspect ratio of the positive electrode material is 2 to 10. The positive electrode material provided in this application enables the electrochemical device to have good kinetic performance and cycle stability.

Description

Technical Field

[0001] This application relates to the field of electrochemistry, and more particularly to a cathode material, an electrochemical device, and an electronic device. Background Technology

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and aerospace. However, higher demands are being placed on the energy density, cycle life, and safety performance of lithium-ion batteries. Traditional polycrystalline ternary materials are prone to secondary particle breakage during cycling, exacerbating side reactions in the electrolyte and limiting improvements in battery performance. Summary of the Invention

[0003] The inventors of this application have discovered that single-crystal materials can not only enhance the mechanical strength of materials and reduce interfacial side reactions, but also improve the structural stability and cycle stability of materials.

[0004] This patent successfully prepared a sheet-like single-crystal cathode material through optimized preparation methods and composition. The sheet-like single-crystal cathode material comprehensively improves electrochemical performance. For example, the reduced surface area decreases the probability of side reactions and improves the diffusion path of lithium ions in the cathode material, enhancing kinetic performance. Furthermore, this morphology effectively suppresses particle pulverization, inhibits electrolyte side reactions, and improves cycle life. Against this technological backdrop, the innovative process and manufacturing method for sheet-like single-crystal ternary materials will provide crucial support for the development of next-generation lithium battery technology.

[0005] In view of this, this application provides a cathode material, an electrochemical device, and an electronic device.

[0006] The first aspect of this application provides a cathode material, which has a sheet-like structure and has the general chemical formula Li. x Na y Ni a Mn c O2, 0.7≤x≤1.1, 0.003≤y≤0.2, 0.3≤a≤0.9, 0.001≤c≤0.7, 0.8≤x+y≤1.1, the thickness of the positive electrode material is 0.2μm to 3μm, and the aspect ratio of the positive electrode material is 2 to 10.

[0007] The cathode material of this application has a sheet-like structure, which, compared to the spherical structure in the prior art, reduces the volume deformation of the electrochemical device during charging and discharging, and reduces the generation of stress and cracks in the bulk phase during cycling, thereby improving the cycle life and safety performance of the electrochemical device. This application further reduces the volume deformation of the electrochemical device by controlling the thickness range of the cathode material, further reducing stress and cracks in the bulk phase during cycling and improving cycle life. This application also provides a shorter transport path for lithium ions by controlling the aspect ratio, increasing the migration speed of lithium ions in the cathode material, thereby improving the charge / discharge rate of the electrochemical device.

[0008] Based on the first aspect, in some possible implementations, 0.8≤x≤1.01, 0.01≤y≤0.08, 0.3≤a≤0.9, 0.1≤c≤0.7, 0.82≤x+y≤1.02, the thickness of the positive electrode material is 0.4μm to 2.3μm, and the aspect ratio of the positive electrode material is 3.9 to 7.5.

[0009] Based on the first aspect, in some possible implementations, the thickness of the positive electrode material is 1 μm to 3 μm; the aspect ratio of the positive electrode material is 3.5 to 8.

[0010] This application further improves the cycle life, charge / discharge rate, and safety performance of the electrochemical device by further controlling the thickness and aspect ratio of the oxide cathode material to meet the above range.

[0011] Based on the first aspect, in some possible implementations, the thickness of the positive electrode material is 1.4 μm to 2 μm; the aspect ratio of the positive electrode material is 4.5 to 5.5.

[0012] This application further improves the cycle life, charge / discharge rate, and safety performance of the electrochemical device by further controlling the thickness and aspect ratio of the oxide cathode material to meet the above range.

[0013] Based on the first aspect, in some possible implementations, the cathode material includes element Q, which includes F, and also includes at least one of B, Si and P.

[0014] In this application, by adding element Q, the electronic structure of element Q differs from that of transition metal elements Ni and Mn. Therefore, the interactions between element Q and oxygen, as well as between oxygen and Ni and Mn, are improved, reducing phase transitions during cycling and further enhancing the cycling performance of the electrochemical device. Furthermore, the addition of element Q replaces lithium sites and / or transition metal sites, improving the structural stability of the material and increasing the lithium-ion diffusion coefficient, thereby enhancing the kinetic performance and cycling stability of the electrochemical device.

[0015] Based on the first aspect, in some possible implementations, the average thickness of the cathode material is 1 μm to 2.5 μm.

[0016] When the average thickness of the cathode material in this application meets the above-mentioned range, the volume deformation of the electrochemical device is smaller, further reducing the stress and crack generation in the bulk phase during cycling and improving cycle life.

[0017] Based on the first aspect, in some possible implementations, the specific surface area of ​​the cathode material is 0.5 m². 2 / g to 5m 2 / g.

[0018] This application controls the specific surface area of ​​the cathode material to meet the above-mentioned range, thereby reducing the contact area between the cathode material and the electrolyte, reducing the side reactions of the electrolyte on the surface of the cathode material during the charging and discharging process of the electrochemical device, improving gas production, and further improving the cycle life of the electrochemical device.

[0019] The second aspect of this application provides a method for preparing a cathode material, comprising: reacting a transition metal oxide and / or a transition metal hydroxide with a sodium salt to obtain a sodium-containing intermediate, wherein the reaction temperature is 950°C to 1050°C and the reaction time is 12h to 48h; adding the intermediate to an organic solvent or molten salt containing lithium and heating it at a temperature of 240°C to 600°C for 2h to 24h; and after stirring, washing, centrifuging, and drying, obtaining the cathode material.

[0020] In the above preparation method, by controlling the temperature and time of the reaction between transition metal oxides and / or transition metal hydroxides and sodium salts, the atomic ratio of each transition metal element (Ni, Mn) and element Q in the cathode material can be controlled, so that the electrochemical device has good cycle life, charge-discharge rate and safety performance.

[0021] A third aspect of this application provides an electrochemical device, including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the aforementioned positive electrode material, thereby enabling the electrochemical device to have good cycle life, charge / discharge rate, and safety performance.

[0022] Based on the third aspect, in some possible implementations, the negative electrode sheet includes a negative electrode active material, which includes silicon-based negative electrode materials and / or graphite, so that the electrochemical device has good cycle life, charge-discharge rate and safety performance.

[0023] Based on the third aspect, in some possible implementations, the electrolyte includes adiponitrile and fluoroethylene carbonate, which enables the electrochemical device to have good cycle life, charge / discharge rate and safety performance.

[0024] The fourth aspect of this application provides an electronic device including the aforementioned electrochemical device, which has good cycle life, charge / discharge rate and safety performance, thereby improving the service life and safety of the electronic device. Attached Figure Description

[0025] Figure 1 This is a SEM image of the surface of the cathode material in Example 3. Detailed Implementation

[0026] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. The reagents and materials described in the following embodiments are all commercially available.

[0027] cathode materials

[0028] One embodiment of this application provides a cathode material, which has a sheet-like structure and the general chemical formula of the cathode material is Li. x Na y Ni a Mn c For O2, the thickness of the positive electrode material is 0.7≤x≤1.1, 0.003≤y≤0.2, 0.3≤a≤0.9, 0.001≤c≤0.7, and 0.8≤x+y≤1.1. The thickness of the positive electrode material is 0.2μm to 3μm, for example, the thickness can be any value within the range of 0.2μm, 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm, 1.9μm, 2.1μm, 2.3μm, 2.5μm, 2.7μm, 2.9μm, 3μm or any of the above values; the aspect ratio of the positive electrode material is 2 to 10, for example, the aspect ratio can be 2, 2.5, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10.

[0029] The cathode material of this application has a sheet-like structure, which, compared to the spherical structure in the prior art, reduces the volume deformation of the electrochemical device during charging and discharging, and reduces the generation of stress and cracks in the bulk phase during cycling, thereby improving the cycle life and safety performance of the electrochemical device. This application further reduces the volume deformation of the electrochemical device by controlling the thickness range of the cathode material, further reducing stress and cracks in the bulk phase during cycling and improving cycle life. This application also provides a shorter transport path for lithium ions by controlling the aspect ratio, increasing the migration speed of lithium ions in the cathode material, thereby improving the charge / discharge rate of the electrochemical device.

[0030] This application further improves the cycle life, charge / discharge rate, and safety performance of the electrochemical device by further adjusting 0.8≤x≤1.01, 0.01≤y≤0.08, 0.3≤a≤0.9, 0.1≤c≤0.7, and 0.82≤x+y≤1.02, with the thickness of the cathode material ranging from 0.4μm to 2.3μm and the aspect ratio of the cathode material ranging from 3.9 to 7.5.

[0031] This application further improves the cycle life, charge / discharge rate, and safety performance of the electrochemical device by further adjusting the thickness of the oxide cathode material to 1 μm to 3 μm and the aspect ratio of the cathode material to 3.5 to 8.

[0032] This application further improves the cycle life, charge / discharge rate, and safety performance of the electrochemical device by further controlling the thickness of the oxide cathode material to 1.4 μm to 2 μm and the aspect ratio of the cathode material to 4.5 to 5.5.

[0033] In some embodiments, the cathode material includes element Q, which includes F, and also includes at least one of B, Si, and P.

[0034] In this application, by adding element Q, the electronic structure of element Q differs from that of transition metal elements Ni and Mn. Therefore, the interactions between element Q and oxygen, as well as between oxygen and Ni and Mn, are improved, reducing phase transitions during cycling and further enhancing the cycle performance of the electrochemical device. Furthermore, the addition of element Q replaces lithium sites and / or transition metal sites, improving the structural stability of the cathode material and increasing the lithium-ion diffusion coefficient, thereby enhancing the kinetic performance and cycle stability of the electrochemical device.

[0035] In some embodiments, the average thickness of the positive electrode material is from 1 μm to 2.5 μm. For example, the average thickness can be any value within the range of 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, or any of the above values.

[0036] When the average thickness of the cathode material in this application meets the above-mentioned range, the volume deformation of the electrochemical device is smaller, further reducing the stress and crack generation in the bulk phase during cycling and improving cycle life.

[0037] In some embodiments, the specific surface area of ​​the cathode material is 0.5 m². 2 / g to 5 m 2 / g, for example, the specific surface area can be 0.5 m². 2 / g, 0.7 m2 / g, 0.9m 2 / g, 1.2 m 2 / g, 1.5 m 2 / g, 1.8 m 2 / g、2 m 2 / g、2.3 m 2 / g, 2.6 m 2 / g、2.9 m 2 / g、3 m 2 / g、3.2 m 2 / g, 3.5 m 2 / g, 3.7 m 2 / g、4 m 2 / g、4.2 m 2 / g, 4.5 m 2 / g, 4.7 m 2 / g、5m 2 Any value within the range of / g or any of the values ​​above.

[0038] This application controls the specific surface area of ​​the cathode material to meet the above-mentioned range, thereby reducing the contact area between the cathode material and the electrolyte, reducing the side reactions of the electrolyte on the surface of the cathode material during the charging and discharging process of the electrochemical device, improving gas production, and further improving the cycle life of the electrochemical device.

[0039] This application also provides a method for preparing a cathode material, comprising: reacting a transition metal oxide and / or a transition metal hydroxide with a sodium salt to obtain a sodium-containing intermediate, wherein the reaction temperature is 950°C to 1050°C and the reaction time is 12h to 48h; adding the intermediate to an organic solvent or molten salt containing lithium and heating, stirring, washing, centrifuging, and drying to prepare the cathode material, wherein the heating temperature is 240°C to 600°C and the heating time is 2h to 24h.

[0040] The aforementioned sodium salts include at least one of sodium carbonate, sodium oxalate, sodium acetate, sodium nitrite, sodium nitrate, sodium hydroxide, and sodium citrate.

[0041] The above intermediates can be added to an organic solvent or molten salt containing lithium and heated by at least one of resistance wire heating, microwave heating, and plasma sintering.

[0042] In the above preparation method, transition metal oxides and transition metal hydroxides provide the source of transition metal elements (Ni, Mn) and element Q in the cathode material. By controlling the temperature and time of the reaction between the transition metal oxides and / or transition metal hydroxides and sodium salts, the atomic proportions of each transition metal element (Ni, Mn) and element Q in the cathode material can be controlled, resulting in electrochemical devices with good cycle life, charge / discharge rate, and safety performance.

[0043] Positive electrode sheet

[0044] The positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, including but not limited to current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive active material layer contains the positive electrode material of this application, enabling the electrochemical device to have good cycle life, charge / discharge rate, and safety performance.

[0045] The positive electrode active material layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0046] The positive electrode active material layer may also include a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0047] Negative electrode sheet

[0048] The negative electrode sheet of this application includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer includes a negative electrode active material, and optionally a conductive agent, a binder, and a thickener.

[0049] The negative electrode active material of this application includes silicon-based negative electrode materials and / or graphite, with silicon-based negative electrode materials specifically including silicon-carbon composite materials. The positive electrode material of this application, combined with silicon-based negative electrode materials or graphite, enables the electrochemical device to possess excellent cycle life, charge / discharge rate, and safety performance.

[0050] The specific type of conductive agent is not limited and can be selected according to needs. For example, conductive agents include, but are not limited to, at least one of conductive graphite, superconducting carbon, acetylene black, conductive carbon black (Super P), Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0051] The specific type of adhesive is not limited and can be selected according to requirements. As an example, adhesives include, but are not limited to, at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose.

[0052] The specific type of thickener is not limited and can be selected according to needs. As an example, thickeners include, but are not limited to, sodium carboxymethyl cellulose (CMC).

[0053] However, this application is not limited to the above-mentioned materials. The negative electrode sheet of this application may also use other known materials that can be used as negative electrode active materials, conductive agents, binders and thickeners.

[0054] Separating membrane

[0055] The material and shape of the separator used in the electrochemical device of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0056] For example, the separator 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, and 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.

[0057] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes 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, and 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 alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0058] electrolyte

[0059] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0060] In some embodiments, the additives include adiponitrile and fluoroethylene carbonate. The additives selected in this application are adiponitrile and fluoroethylene carbonate, which enable the electrochemical device to have good cycle life, charge / discharge rate and safety performance.

[0061] In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0062] In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate.

[0063] Electrochemical device

[0064] The electrochemical device of this application also includes a housing (such as a packaging bag) for containing the aforementioned positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of electrochemistry. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be a housing known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used. This application does not impose any particular limitation on the type of chemical device; it can include any device in which an electrochemical reaction occurs. The electrochemical device containing the aforementioned positive electrode material has good cycle life, charge / discharge rate, and safety performance.

[0065] Electronic devices

[0066] The aforementioned electrochemical devices are applied to electronic devices to power loads within them. Furthermore, these electrochemical devices possess excellent cycle life, charge / discharge rate, and safety performance, thus improving the lifespan and safety of electronic devices. These electronic devices may include, but are not limited to, laptops, pen-based 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, and lithium-ion capacitors, etc.

[0067] Example 1

[0068] <Preparation of cathode materials>

[0069] 1. In a 5L continuous reactor, a 2M metal salt solution was prepared by mixing nickel sulfate and manganese sulfate in an aqueous solution at a molar ratio of Ni:Mn = 50:50, and connected to the reactor. 3L of deionized water was added to the reactor, and nitrogen gas was introduced at a rate of 2L / min to remove dissolved oxygen. Then, a certain amount of 3M NaOH solution was introduced into the reactor, while the mixture was stirred uniformly at 1200 rpm at 60°C and the pH was adjusted to 12.0. Next, the 2M metal salt solution, the 3M NaOH solution, and a 10% NH4OH aqueous solution were gradually added at specific rates, and the mixture was allowed to react completely for 24 hours to obtain Ni. 0.5 Mn 0.5 (OH)2 precursor.

[0070] 2. The obtained Ni 0.5 Mn 0.5The (OH)2 precursor and sodium carbonate were thoroughly mixed in a (Ni+Mn):Na molar ratio of 1:1.05. The mixture was heated to 1000℃ at a heating rate of 5℃ / min and reacted for 24h. The temperature was then reduced to 70℃ at a cooling rate of 25℃ / min. Finally, the mixture was crushed and sieved to obtain a sodium-containing intermediate.

[0071] 3. The sodium-containing intermediate is mixed with lithium salt (a mixture of lithium hydroxide and lithium nitrate in a molar ratio of 1:1) at a mass ratio of 1:10, heated to 600°C at a heating rate of 10°C / min for 24 hours, and then cooled to room temperature in a mixture of Ar and air (volume ratio of 1:1) at a cooling rate of 50°C / min. The mixture is then thoroughly soaked and stirred in deionized water, and the cathode material is obtained by filtration, vacuum drying, crushing, and sieving.

[0072] 4. The above-mentioned cathode material is thoroughly mixed with NaF powder, and heated to 650°C in an Ar and air mixture (volume ratio of 1:1) at a heating rate of 10°C / min for 12 hours. The mixture is then cooled to room temperature at a cooling rate of 10°C / min, crushed, and sieved to obtain the cathode material of this application.

[0073] <Preparation of the positive electrode>

[0074] Polyvinylidene fluoride (PVDF) binder, conductive carbon black (Super P) conductive agent, and positive electrode material were mixed uniformly at a weight ratio of 1.5:1.5:97. N-methylpyrrolidone (NMP) was added as a solvent to obtain a positive electrode slurry with a viscosity of 3000 mPas to 6000 mPas. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil for positive electrode current collectors and dried at 120°C for 1 hour to obtain a positive electrode sheet with a single-sided coating of a 60 μm thick positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material layers. The sheet was dried under vacuum at 120°C for 1 hour, and then cold-pressed, cut, and had tabs welded to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0075] <Preparation of Negative Electrode Sheets>

[0076] Graphite (anode active material), sodium carboxymethyl cellulose (thickener), and styrene-butadiene rubber (binder) were mixed in a weight ratio of 96:2:2. Deionized water was added, and the mixture was stirred until homogeneous to obtain a cathode slurry with a solid content of 75 wt%. The cathode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector and dried at 100°C to obtain a cathode sheet with a single-sided cathode material coating of 80 μm thickness. The above steps were repeated on the other surface of the copper foil to obtain a cathode sheet with a double-sided cathode material coating. The cathode sheet was dried under vacuum at 100°C for 1 hour, and then cold-pressed, cut, and slit to obtain a cathode sheet with a size of 78 mm × 875 mm.

[0077] <Preparation of Electrolyte>

[0078] In an argon-atmosphere glove box with a water content of <10 ppm, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a 1:1:1 mass ratio. Thoroughly dried lithium salt LiPF6 was then dissolved in the above non-aqueous solvent, and 2% 1,3-propanesulfonate lactone was added to prepare the electrolyte used in the examples. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 13%. <Preparation of the Separating Membrane>

[0079] A 7μm thick polypropylene / polyethylene composite film was used as the separator.

[0080] <Preparation of Lithium-ion Pouch Batteries>

[0081] The positive electrode, separator, and negative electrode prepared above are stacked, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. Following vacuum sealing, settling, formation (with an upper limit voltage of 4.35V, a formation temperature of 85℃, and a settling time of 2 hours), degassing, and edge trimming, a lithium-ion soft-pack battery is obtained.

[0082] Examples 2 to 10

[0083] The difference between Examples 2 to 10 and Example 1 is that the ratio of precursor Ni and Mn, reaction temperature, reaction time, heating temperature and heating time are different in <Preparation of cathode material>. The other conditions / preparation methods are the same as in Example 1. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0084] Example 11

[0085] The difference between Example 11 and Example 1 is that in the <Preparation of Electrolyte>, 1% fluorocarbonate and 0.5% adiponitrile are added. The other conditions / preparation methods are the same as in Example 1. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0086] Example 12

[0087] The difference between Example 12 and Example 1 is that in step 4 of the <Preparation of Cathode Material>, in addition to adding NaF, boric acid also needs to be added. The other conditions / preparation methods are the same as in Example 1. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1 and Table 2.

[0088] Comparative Example 1

[0089] The difference between Comparative Example 1 and Example 1 is that in step 1 of the <Preparation of Cathode Material>, the molar ratio of Ni to Mn is adjusted to 20:80; in step 4 of the <Preparation of Cathode Material>, NaF is not added, and the other conditions / preparation methods are the same as in Example 1. The specific preparation parameters mentioned above can be adjusted accordingly according to Tables 1 and 2.

[0090] Test methods

[0091] (1) Test methods for the length, width and thickness of cathode materials

[0092] The morphology of the cathode material particles was observed and micrographs were taken using a scanning electron microscope (Thermo Scientific FEI-Apreo S SEM, accelerating voltage: 0.2KV to 30KV). Thirty plate-like particles were randomly selected from the images. Using the measuring tools provided with the scanning electron microscope, the average length of the longest plane of each plate was measured as the length, the average width perpendicular to that maximum length as the width, and the average thickness perpendicular to the plate plane as the thickness. The aspect ratio is the ratio of length to width.

[0093] (2) Cell specific capacity test

[0094] The lithium-ion pouch battery was charged at 25°C with a constant current of 0.04C to 4.35V, then charged at 4.35V with a constant voltage to 0.02C; allowed to stand for 5 minutes, and then discharged at a constant current of 0.04C to 2.8V, and allowed to stand for 5 minutes. The specific capacity of the cell is obtained by dividing the discharge capacity by the total mass of the positive electrode active material.

[0095] (3) Thickness expansion rate test at 85℃

[0096] A lithium-ion pouch battery was charged at 25°C with a constant current of 0.5C to 4.35V, and then charged at 4.35V with a constant voltage to 0.05C. The thickness of the lithium-ion pouch battery at this point was measured and recorded as H0 using a micrometer. The lithium-ion pouch battery was then stored in an 85°C oven for 24 hours. After removal, the thickness of the lithium-ion pouch battery was measured and recorded using a micrometer, denoted as H1. The thickness expansion rate (%) of the lithium-ion pouch battery after storage at 85°C for 24 hours is calculated as (H1 - H0) / H0 × 100%.

[0097] (4) 45℃ Cyclic Capacity Retention Rate Test

[0098] The lithium-ion pouch battery was placed in a 45℃ constant temperature chamber and left to stand for 30 minutes to reach a constant temperature. The battery was then charged at a constant current of 1.5C to 4.35V at 45℃, followed by constant voltage charging to 0.02C at 4.35V. After standing for 5 minutes, it was discharged at a constant current of 4C to 2.8V, and then left to stand for 5 minutes. This discharge capacity was recorded as the first cycle discharge capacity. This charge-discharge cycle was repeated 500 times, and the discharge capacity of the battery in the 500th cycle was recorded as the 500th cycle discharge capacity. The capacity retention rate (%) of the lithium-ion pouch battery after 500 cycles at 45℃ = (500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0099] (5) 2C / 0.1C test method

[0100] The lithium-ion pouch battery was charged at 25°C with a constant current of 0.7C to 4.35V, then charged at 4.35V with a constant voltage to 0.025C; allowed to rest for 5 minutes, and then discharged at a constant current of 0.1C to 2.8V, and allowed to rest for 5 minutes. The capacity of the 2C constant current discharge was divided by the capacity of the 0.1C constant current discharge; the ratio is the rate factor 2C / 0.1C.

[0101] (6) Specific surface area test method

[0102] According to the national standard "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method" (GB / T 19587-2017), the specific surface area of ​​the cathode material was tested by nitrogen adsorption using a specific surface area analyzer (model TristarⅡ3020).

[0103] (7) Element content test

[0104] The cathode material was dissolved in aqua regia solution (for example, 0.4 g of cathode material was dissolved in 10 ml of aqua regia solution (the aqua regia solution was a 1:1 volume ratio of aqua regia to deionized water, and the aqua regia solution was a 3:1 volume ratio of concentrated hydrochloric acid to concentrated nitric acid), and the volume was adjusted to 100 mL. Then, the mass percentage of elements such as Li, Na, Ni and manganese in the solution was tested using an ICP analyzer.

[0105] Figure 1 This is a SEM image of the surface of the cathode material in Example 3. From... Figure 1 As can be seen from the above, the cathode material of this application has a sheet-like single crystal morphology, which is beneficial to shortening the lithium ion transport path and thus improving the kinetic performance of the electrochemical device.

[0106] The parameters of Examples 1 to 12 and Comparative Example 1 are recorded in Tables 1 and 2.

[0107] Table 1

[0108]

[0109] Table 2

[0110]

[0111] Note: " / " in Table 2 indicates that the corresponding substance or parameter does not exist.

[0112] As can be seen from Tables 1 and 2, compared with Example 1, Examples 2 to 10, by adjusting the reaction temperature, reaction time, heating temperature, and heating time in the <Preparation of Cathode Material>, all affect the cycle, rate capability, and safety performance of the electrochemical device.

[0113] Compared with Example 1, Example 11 further improved the high-temperature (45°C and above) cycle performance, charge-discharge rate and safety performance of the electrochemical device by adding 5% fluorocarbonate and 0.5% adiponitrile to the <preparation of electrolyte>.

[0114] Compared with Example 1, Example 12 further improved the high-temperature (45°C and above) cycle performance and safety performance of the electrochemical device by adding boric acid in step 4 of the <Preparation of Cathode Material>.

[0115] In Comparative Example 1, the molar ratio of Ni to Mn was adjusted to 20:80 in step 1 of the <Preparation of Cathode Material>, and NaF was not added in step 4. It can be seen that compared with Comparative Example 1, Example 1 significantly improved the high-temperature (45°C and above) cycle performance and safety performance of the electrochemical device.

[0116] Furthermore, by controlling the thickness of the cathode material to be within the range of 0.2 μm to 3 μm and the aspect ratio of the cathode material to be within the range of 2 to 10, this application enables the electrochemical device to have good cycle life, charge / discharge rate and safety performance.

[0117] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, The cathode material has a sheet-like structure, and its general chemical formula is Li. x Na y Ni a Mn c O2, 0.7≤x≤1.1, 0.003≤y≤0.2, 0.3≤a≤0.9, 0.001≤c≤0.7, 0.8≤x+y≤1.1, the thickness of the positive electrode material is 0.2μm to 3μm, and the aspect ratio of the positive electrode material is 2 to 10.

2. The cathode material according to claim 1, characterized in that, 0.8≤x≤1.01, 0.01≤y≤0.08, 0.3≤a≤0.9, 0.1≤c≤0.7, 0.82≤x+y≤1.02, the thickness of the positive electrode material is 0.4μm to 2.3μm, and the aspect ratio of the positive electrode material is 3.9 to 7.

5.

3. The cathode material according to claim 1, characterized in that, The thickness of the positive electrode material is 1 μm to 3 μm; the aspect ratio of the positive electrode material is 3.5 to 8.

4. The cathode material according to claim 1, characterized in that, The thickness of the positive electrode material is 1.4 μm to 2 μm; the aspect ratio of the positive electrode material is 4.5 to 5.

5.

5. The cathode material according to any one of claims 1 to 4, characterized in that, The cathode material includes element Q, which includes F, and also includes at least one of B, Si and P.

6. The cathode material according to any one of claims 1 to 4, characterized in that, The average thickness of the cathode material is 1 μm to 2.5 μm.

7. The cathode material according to any one of claims 1 to 4, characterized in that, The specific surface area of ​​the cathode material is 0.5 m². 2 / g to 5 m 2 / g.

8. An electrochemical device, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes the positive electrode material as described in any one of claims 1 to 7.

9. The electrochemical device according to claim 8, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes silicon-based negative electrode material and / or graphite.

10. The electrochemical device according to claim 8, characterized in that, The electrolyte comprises adiponitrile and fluoroethylene carbonate.

11. An electronic device, characterized in that, Includes the electrochemical device as described in any one of claims 8 to 10.

Images