Positive electrode material, electrochemical device, and electronic device

Abstract

A positive electrode material, an electrochemical device, and an electronic device. The positive electrode material comprises lithium cobalt oxide particles, wherein the lithium cobalt oxide particles have a P63mc structure and a Cmca structure, and the lithium cobalt oxide particles comprise a niobium element and an oxygen element.

Description

Cathode materials, electrochemical devices and electronic devices 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 (LIBs), as a highly efficient energy storage technology, are widely used in portable electronic devices, electric vehicles, and energy storage systems. Lithium cobalt oxide (LiCoO2) has become the primary cathode material for commercially available lithium-ion batteries due to its high energy density and good cycle performance. However, LiCoO2 exhibits poor structural stability at high voltages, which can easily lead to capacity decay and safety issues. Summary of the Invention

[0003] In view of this, this application provides a cathode material, an electrochemical device, and an electronic device.

[0004] The first aspect of this application provides a cathode material comprising lithium cobalt oxide particles having a P63mc structure and a Cmca structure, and the lithium cobalt oxide particles comprising niobium and oxygen.

[0005] This application involves adding niobium to lithium cobalt oxide particles. 5+ It has high electronegativity and can form a strong bond (Nb-O) with O. This strong bond can significantly reduce the mobility of oxygen atoms at the interface. This strong bond makes it more difficult for surface oxygen to leave the interface, increases the formation energy of surface oxygen vacancies, and helps to improve the stability of lithium cobalt oxide particle structure, so that the electrochemical device has good room temperature cycling performance.

[0006] Furthermore, niobium has high electronegativity and different electronic configurations, which can interact with the 2p orbitals of oxygen. This interaction can lead to the redistribution and reduction of the 2p orbital energy levels of oxygen, thereby reducing the activity of surface oxygen. This helps to stabilize the position of oxygen atoms in the delithiation state, prevent them from escaping from the interface, and reduce interfacial side reactions. As a result, the stability of the lithium cobalt oxide particle structure is improved, enabling the electrochemical device to have good room temperature cycling performance while also having low electrochemical impedance and interfacial impedance.

[0007] This application presents lithium cobalt oxide particles with P63mc and Cmca structures. These particles have a high lithium content and a stable crystal structure, reducing the probability of phase transitions or lattice distortions. This reduces the migration resistance of lithium ions in the crystal lattice, resulting in electrochemical devices with good room-temperature cycling performance as well as low electrochemical impedance and interfacial impedance. The P63mc and Cmca structures represent different delithiation states of lithium cobalt oxide. When the battery's state of charge (SOC) is greater than 70%, it is the P63mc phase; when 50% < SOC < 70%, it is the Cmca phase.

[0008] Based on the first aspect, in some possible implementations, the molar content of niobium is 0.2% to 3%, based on the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%.

[0009] By controlling the molar content of niobium in lithium cobalt oxide particles to meet the above-mentioned range, this application helps to shorten the migration path of lithium ions in the cathode material, improves the lithium ion transport rate, and enables the electrochemical device to have good kinetic performance. In addition, it can further control the internal resistance of the electrochemical device within a suitable range, thereby improving the room temperature cycling performance of the electrochemical device.

[0010] Based on the first aspect, in some possible implementations, the molar content of niobium is 0.6% to 1%, based on the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%.

[0011] This application further improves the room temperature cycling performance of the electrochemical device while reducing the electrochemical impedance and interfacial impedance by further controlling the molar content of niobium in the lithium cobalt oxide particles to meet the above range.

[0012] Based on the first aspect, in some possible embodiments, the lithium cobalt oxide particles further include yttrium, and the molar content of yttrium is 0.03% to 1.5% based on the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%.

[0013] This application achieves this by adding yttrium to lithium cobalt oxide particles and controlling its molar content to meet the above-mentioned range, thus increasing the yttrium ion (Y) content. 3+ The introduction of ) can enhance the stability of the LiCoO2 lattice and reduce structural distortion under high voltage. In addition, the stable lattice structure helps to suppress oxygen migration and release, further improving the room temperature cycling performance of the electrochemical device while reducing electrochemical impedance and interfacial impedance.

[0014] Based on the first aspect, in some possible embodiments, the lithium cobalt oxide particles further include yttrium, and the molar content of yttrium is 0.03% to 0.2% based on the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%.

[0015] This application further improves the room temperature cycling performance of the electrochemical device while reducing the electrochemical impedance and interfacial impedance by further controlling the molar content of yttrium in the lithium cobalt oxide particles to meet the above range.

[0016] A second aspect of this application provides an electrochemical device including a positive electrode plate comprising the aforementioned positive electrode material, such that the electrochemical device has good room temperature cycling performance while also having low electrochemical impedance and interfacial impedance.

[0017] Based on the second aspect, in some possible implementations, the electrolyte includes fluoroethylene carbonate.

[0018] This application introduces fluoroethylene carbonate into the electrolyte. Due to its high dielectric constant, fluoroethylene carbonate facilitates the dissolution of lithium salts and increases the ionic conductivity of the electrolyte. Furthermore, it exhibits good chemical stability, improving the room-temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance. Fluoroethylene carbonate participates in the interfacial film-forming reaction between the positive and negative electrodes, promoting the formation of low-impedance interfacial components that are stable during cycling, thereby further improving the capacity decay problem during the cycling process of the electrochemical device.

[0019] Based on the second aspect, in some possible implementations, the organic solvent accounts for 20% to 70% of the total mass of the electrolyte.

[0020] This application improves the room-temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance by controlling the mass ratio of organic solvent in the electrolyte to meet the above-mentioned range.

[0021] Based on the second aspect, in some possible implementations, the electrolyte also includes oxonium.

[0022] This application adds oxonitrile to the electrolyte. Due to its relatively small molecular structure, oxonitrile can penetrate into the electrode interface, which helps to form a good SEI film. This further improves the room temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance.

[0023] Based on the second aspect, in some possible implementations, the electrolyte also includes lithium difluorophosphate.

[0024] This application improves the room-temperature cycling performance of the electrochemical device by adding lithium difluorophosphate to the electrolyte, while also reducing its electrochemical impedance and interfacial impedance.

[0025] A third aspect of this application provides an electronic device including the aforementioned electrochemical device. The electrochemical device has good room temperature cycling performance as well as low electrochemical impedance and interfacial impedance, which is beneficial to improving the service life of the electronic device. Attached Figure Description

[0026] Figure 1 is the XRD pattern of the lithium cobalt oxide in Example 1.

[0027] Figure 2 shows the XRD pattern of lithium cobalt oxide in Comparative Example 2.

[0028] Figure 3 is an EDS image of the lithium cobalt oxide surface coated with LiNbO3 in Example 1.

[0029] Figure 4 is a magnified view of a portion of Figure 3.

[0030] Figure 5 is an EDS line scan of niobium in the LiNbO3-coated lithium cobalt oxide in Example 1. Detailed Implementation

[0031] 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.

[0032] cathode materials

[0033] One embodiment of this application provides a cathode material comprising lithium cobalt oxide particles having a P63mc structure and a Cmca structure, and the lithium cobalt oxide particles comprising niobium and oxygen.

[0034] This application involves adding niobium to lithium cobalt oxide particles. 5+ It has high electronegativity and can form a strong bond (Nb-O) with O. This strong bond can significantly reduce the mobility of oxygen atoms at the interface. This strong bond makes it more difficult for surface oxygen to leave the interface, increases the formation energy of surface oxygen vacancies, and helps to improve the stability of lithium cobalt oxide particle structure, so that the electrochemical device has good room temperature cycling performance.

[0035] Furthermore, niobium has high electronegativity and different electronic configurations, which can interact with the 2p orbitals of oxygen. This interaction can lead to the redistribution and reduction of the 2p orbital energy levels of oxygen, thereby reducing the activity of surface oxygen. This helps to stabilize the position of oxygen atoms in the delithiation state, prevent them from escaping from the interface, and reduce interfacial side reactions. As a result, the stability of the lithium cobalt oxide particle structure is improved, enabling the electrochemical device to have good room temperature cycling performance while also having low electrochemical impedance and interfacial impedance.

[0036] This application presents lithium cobalt oxide particles with P63mc and Cmca structures. These particles have a high lithium content and a stable crystal structure, reducing the probability of phase transitions or lattice distortions. This reduces the migration resistance of lithium ions in the crystal lattice, resulting in electrochemical devices with good room-temperature cycling performance as well as low electrochemical impedance and interfacial impedance. The P63mc and Cmca structures represent different delithiation states of lithium cobalt oxide. When the battery's state of charge (SOC) is greater than 70%, it is the P63mc phase; when 50% < SOC < 70%, it is the Cmca phase.

[0037] In some embodiments, the molar content of niobium is 0.2% to 3%, based on the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%. For example, the molar content of niobium can be any value within the range of 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.9%, 1%, 1.2%, 1.4%, 1.6%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or any value above.

[0038] By controlling the molar content of niobium in lithium cobalt oxide particles to meet the above-mentioned range, this application helps to shorten the migration path of lithium ions in the cathode material, improves the lithium ion transport rate, and enables the electrochemical device to have good kinetic performance. In addition, it can further control the internal resistance of the electrochemical device within a suitable range, thereby improving the room temperature cycling performance of the electrochemical device.

[0039] In some embodiments, the molar content of niobium is 0.6% to 1%, based on the molar content of metal elements other than lithium in the lithium cobalt oxide particles being 100%.

[0040] This application further improves the room temperature cycling performance of the electrochemical device while reducing the electrochemical impedance and interfacial impedance by further controlling the molar content of niobium in the lithium cobalt oxide particles to meet the above range.

[0041] In some embodiments, the lithium cobalt oxide particles further include yttrium, with the molar content of yttrium ranging from 0.03% to 1.5% based on the molar content of all metal elements other than lithium in the lithium cobalt oxide particles being 100%. For example, the molar content of yttrium can be any value within the range of 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.09%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any of the above values.

[0042] This application achieves this by adding yttrium to lithium cobalt oxide particles and controlling its molar content to meet the above-mentioned range, thus increasing the yttrium ion (Y) content. 3+ The introduction of ) can enhance the stability of the LiCoO2 lattice, reduce structural distortion under high voltage, and the stable lattice structure helps to suppress oxygen migration and release, further improving the room temperature cycling performance of the electrochemical device while reducing electrochemical impedance and interfacial impedance.

[0043] In some embodiments, the lithium cobalt oxide particles also include yttrium, with the molar content of yttrium being 0.03% to 0.2% based on the molar content of all metal elements other than lithium in the lithium cobalt oxide particles being 100%.

[0044] This application further improves the room temperature cycling performance of the electrochemical device while reducing the electrochemical impedance and interfacial impedance by further controlling the molar content of yttrium in the lithium cobalt oxide particles to meet the above range.

[0045] Positive electrode sheet

[0046] The positive electrode includes a positive current collector and a positive electrode material layer disposed on the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application; for example, it may include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). The positive electrode material layer contains the positive electrode material of this application.

[0047] The positive electrode material layer also includes a conductive agent and a binder. This application does not particularly limit the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the binder may include, but is not limited to, one or more of the following: polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. The conductive agent may include, but is not limited to, at least one of the following: conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0048] Negative electrode sheet

[0049] The negative electrode sheet of this application includes a negative electrode current collector and a negative electrode 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.

[0050] The specific type of anode material is not limited and can be selected according to requirements. For example, anode materials include, but are not limited to, natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, lithium-tin alloys, Sn, SnO, SnO2, and spinel-structured Li4Ti5O. 12 At least one of lithium-aluminum alloys.

[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] In this application, the electrochemical device also includes a separator membrane to separate the positive and negative electrode plates, prevent short circuits within the electrochemical device, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0056] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, 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 used. Optionally, a surface treatment layer is provided 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 mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited and may include 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 not particularly limited and may be at least one of the binders described above. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0057] electrolyte

[0058] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0059] In some embodiments, the organic solvent accounts for 20% to 70% of the total mass of the electrolyte. By controlling the mass percentage of organic solvent in the electrolyte to meet the above range, this application further improves the room-temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance.

[0060] In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), 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).

[0061] In some embodiments, the lithium salt of this application is lithium difluorophosphate (LiPO2F2). By adding lithium difluorophosphate to the electrolyte, this application further improves the room temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance.

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

[0063] In some embodiments, the additive is fluoroethylene carbonate.

[0064] This application introduces fluoroethylene carbonate into the electrolyte. Due to its high dielectric constant, fluoroethylene carbonate facilitates the dissolution of lithium salts and increases the ionic conductivity of the electrolyte. Furthermore, it exhibits good chemical stability, improving the room-temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance. In addition, fluoroethylene carbonate participates in the interfacial film-forming reaction between the positive and negative electrodes, promoting the formation of low-impedance interfacial components that are stable during cycling, thereby further mitigating the capacity decay problem during the cycling process of the electrochemical device.

[0065] In some embodiments, the additive is oxadionitrile.

[0066] This application adds oxonitrile to the electrolyte. Due to its relatively small molecular structure, oxonitrile can penetrate into the electrode interface, which helps to form a good SEI film. This further improves the room temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance.

[0067] Electrochemical device

[0068] 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 exhibits good room-temperature cycling performance while also possessing low electrochemical impedance and interfacial impedance.

[0069] Electronic devices

[0070] The aforementioned electrochemical device is applied to electronic devices to power loads within them. Furthermore, this electrochemical device exhibits excellent room-temperature cycling performance along with low electrochemical and interfacial impedance, which helps extend the lifespan of the electronic device. 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.

[0071] Example 1

[0072] <Preparation of cathode materials>

[0073] 1. Preparation of sodium-containing cobalt oxides

[0074] Sodium carbonate (Na₂CO₃), cobalt tetroxide (Co₃O₄), and yttrium oxide (Y₂O₃) were weighed according to a molar ratio of 1:1:0.01. The raw materials were then mixed thoroughly and kept at 800℃ for 36 hours. Post-processing was then performed to obtain the corresponding sodium-cobalt oxide material. The obtained sodium-cobalt oxide had a P₆₃ / mmc, Cmca structure.

[0075] 2. Preparation of lithium cobalt oxide

[0076] The above-mentioned sodium cobalt oxide material, lithium nitrate and lithium chloride were mixed evenly in a molar ratio of 1:2:3, placed in an alumina crucible, and reacted in a solid phase at 250°C for 6 hours. After cooling, a mixture of lithium cobalt oxides was obtained.

[0077] The above-mentioned mixture was crushed and then washed repeatedly with deionized water to remove soluble sodium and lithium salts until the conductivity of the supernatant was less than 200 μS / cm. The remaining powder was then subjected to filtration, drying, and sieving to obtain the target lithium-containing cobalt oxide material. The obtained lithium-cobalt oxide has a P63mc, Cmca structure.

[0078] 3. LiNbO3-coated lithium cobalt oxide

[0079] First, an organic niobium source and a lithium source were prepared as a lithium-ion conductor precursor solution for later use. The lithium cobalt oxide cathode material was dispersed in a water or ethanol solution. While rapidly stirring, the lithium-ion conductor precursor solution was added using a peristaltic pump. After homogeneous mixing, the mixture was heated while continuously stirred. After the ethanol evaporated, LiNbO3 gel uniformly covered the surface of the lithium cobalt oxide. Finally, heat treatment at 200℃ for 2 hours yielded LiNbO3-coated lithium cobalt oxide.

[0080] <Preparation of the positive electrode>

[0081] 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 current collector 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 the positive electrode material layer. 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.

[0082] <Preparation of Negative Electrode Sheets>

[0083] A negative electrode material (graphite), a thickener (sodium carboxymethyl cellulose, CMC-Na), and a binder (styrene-butadiene rubber, SBR) were mixed in a weight ratio of 96:2:2. Deionized water was added, and the mixture was stirred until homogeneous to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector and dried at 120 °C to obtain a single-sided negative electrode sheet with a coating thickness of 80 μm. The above steps were repeated on the other surface of the copper foil to obtain a double-sided negative electrode sheet. After drying under vacuum at 120 °C for 1 hour, the sheet was cold-pressed, cut, and slit to obtain a negative electrode sheet with dimensions of 78 mm × 875 mm.

[0084] <Preparation of Electrolyte>

[0085] In an argon-atmospheric glove box with a water content of <10 ppm, organic solvents—propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC)—were mixed in a 1:1:1 mass ratio. Thoroughly dried lithium salt LiPF6 was then dissolved in the organic solvents, 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%, and the mass percentage of the organic solvent was 18%.

[0086] <Preparation of the separating membrane>

[0087] A porous polyethylene (PE) film with a thickness of 7 μm was used as the separator.

[0088] <Preparation of Lithium-ion Pouch Batteries>

[0089] 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.

[0090] Examples 2 to 7

[0091] The difference between Examples 2 to 7 and Example 1 is that the molar content of niobium in the lithium cobalt oxide particles is different. 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.

[0092] Examples 8 to 10

[0093] The difference between Examples 8 to 10 and Example 5 is that yttrium was added to the lithium cobalt oxide particles and its mass ratio was adjusted. The other conditions / preparation methods are the same as in Example 5. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1.

[0094] Example 11

[0095] The difference between Example 11 and Example 5 is that fluoroethylene carbonate is added in the <Preparation of Electrolyte>, while the other conditions / preparation methods are the same as in Example 5. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1.

[0096] Implemented for 12 to 14 years

[0097] The difference between Examples 12 to 14 and Example 5 is that the mass content of the organic solvent in the <Preparation of Electrolyte> is adjusted. The other conditions / preparation methods are the same as in Example 5. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1.

[0098] Example 15

[0099] The difference between Example 15 and Example 5 is that oxonium is added in the <Preparation of Electrolyte>, while the other conditions / preparation methods are the same as in Example 5. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1.

[0100] Example 16

[0101] The difference between Example 16 and Example 5 is that the lithium salt LiPF6 in <Preparation of Electrolyte> is replaced with LiPO2F2, while the other conditions / preparation methods are the same as in Example 5. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1.

[0102] Comparative Example 1

[0103] The difference between Comparative Example 1 and Example 5 is that the lithium cobalt oxide particles do not contain niobium. The other conditions / preparation methods are the same as those in Example 5. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1.

[0104] Comparative Example 2

[0105] The difference between Comparative Example 2 and Example 5 is that sodium carbonate (Na2CO3), cobalt tetroxide (Co3O4), and yttrium oxide (Y2O3) were weighed according to a molar ratio of 0.4:1:0.01. The other conditions / preparation methods are the same as in Example 5. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1.

[0106] Comparative Example 3

[0107] The difference between Comparative Example 3 and Example 5 is that the lithium cobalt oxide particles do not contain niobium and do not have P63mc and Cmca structures. The other conditions / preparation methods are the same as those in Example 5. The specific preparation parameters mentioned above can be adjusted accordingly according to Table 1.

[0108] Test methods

[0109] (1) Elemental composition (molar content) test of lithium cobalt oxide particles

[0110] The elemental composition of the cathode material was tested, and the contents of elements such as Li and transition metals were measured using an Optima 7000DV inductively coupled plasma optical emission spectrometer (ICP) from Pepperl Inc. (PE).

[0111] (2) Elemental analysis of the surface of lithium cobalt oxide particles

[0112] Cross-sectional SEM images of the samples were obtained using a FEI Scios 2 HiVac focused ion beam scanning electron microscope (FIB-SEM).

[0113] (2) Testing of P63mc and Cmca structures

[0114] The cathode material was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), with Cu Kα as the target material; the voltage and current were 40 kV / 35 mA, the scanning angle range was 10° to 70°, and the scanning rate was 5° / min.

[0115] (3) 25℃ Cyclic Capacity Retention Rate Test

[0116] After aging the coin cell at a constant temperature (25℃) for 24 hours, it was then subjected to a voltage range of 3V to x (where x can be 4.6V, 4.7V, or 4.8V, vs. Li / Li). + The voltage range was repeatedly tested for 20 charge-discharge cycles at a current density of 0.3 mA / cm². 2 .

[0117] Among them, the capacity of the second discharge is used as the reference benchmark for the cyclic capacity decay, that is, the capacity retention rate of the nth discharge = the capacity of the nth discharge / the capacity of the second discharge × 100%.

[0118] The discharge voltage is the battery voltage corresponding to 50% capacity discharge.

[0119] (4) Electrochemical impedance (Rct) and interfacial impedance (Rf) tests after 50 cls of cycling.

[0120] The button cell battery was activated by charging and discharging at a current of 0.1C within a voltage range of 3V to 4.6V for 3 weeks. After that, the battery was fully charged to 4.6V at a current of 0.1C and left to stand for 1 hour. Then, the battery was connected to a high-power multi-channel electrochemical workstation and AC impedance was tested at room temperature of 23±2℃. The test frequency range was 0.01Hz to 100000Hz, the amplitude was 5mV, and 30 points were sampled per cycle. The test data were then fitted using ZView software.

[0121] Figure 1 shows the XRD pattern of the lithium cobalt oxide particles from Example 1. As can be seen from Figure 1, the lithium cobalt oxide particles from Example 1 contain P63mc and Cmca structures.

[0122] Figure 2 shows the XRD pattern of the lithium cobalt oxide particles in Comparative Example 2. As can be seen from Figure 2, the main peak of the lithium cobalt oxide sample in Comparative Example 2 is located at 17.9°, which is a lower angle compared to the main peak of the lithium cobalt oxide in Example 1. The main peak corresponds to the (002) peak of the lithium cobalt oxide. A smaller 2θ value in the XRD indicates a lower Li content. A crystal structure with low Li content belongs to a highly delithiated state, which leads to changes in the lattice structure of the lithium cobalt oxide, potentially causing phase transitions or lattice distortions. These structural changes increase the migration resistance of lithium ions in the lattice, thereby increasing the electrochemical impedance.

[0123] Figure 3 is an EDS image of the lithium cobalt oxide particles from Example 1. Figure 3 clearly shows a lamellar coating layer on the surface of the lithium cobalt oxide particles. Figure 4 is a magnified view of a portion of Figure 3. An EDS line scan of the area shown in Figure 4 is shown in Figure 5, confirming that the lamellar coating layer on the surface of the lithium cobalt oxide particles contains Nb.

[0124] The test data of Examples 1 to 16 and Comparative Examples 1 to 3 are recorded in Table 1.

[0125] Table 1 Note: " / " in Table 1 indicates that the corresponding substance or parameter does not exist.

[0126] As can be seen from Table 1, compared with Examples 1 and 2, Examples 3 to 7, by changing the molar content of niobium in the lithium cobalt oxide particles, and ensuring that the molar content meets the range of this application (0.2% to 3%), enable the electrochemical device to have good room temperature cycling performance while also having low electrochemical impedance and interfacial impedance.

[0127] Compared to Example 5, Examples 9 and 10 further improve the room temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance by adding yttrium to the lithium cobalt oxide particles and controlling its molar content to meet the range of this application (0.03% to 1.5%).

[0128] Compared to Example 5, Example 11 improved the room temperature cycling performance of the electrochemical device by adding fluoroethylene carbonate in the <Preparation of Electrolyte>, Example 15 added oxonitrile in the <Preparation of Electrolyte>, and Example 16 replaced lithium salt LiPF6 with LiPO2F2, while also reducing its electrochemical impedance and interfacial impedance.

[0129] Compared to Example 5, Examples 12 to 14 further improved the room temperature cycling performance of the electrochemical device while reducing its electrochemical impedance and interfacial impedance by adjusting the mass content of the organic solvent in the <preparation of electrolyte> to meet the scope of this application (20% to 70%).

[0130] As can be seen from the comparison of Example 5 and Comparative Examples 1 to 3, when the lithium cobalt oxide particles include niobium and the phase composition (including both P63mc and Cmca structures), the electrochemical device has good room temperature cycling performance while also having low electrochemical impedance and interfacial impedance.

[0131] 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, It includes lithium cobalt oxide particles, which have P63mc and Cmca structures, and the lithium cobalt oxide particles include niobium and oxygen.

2. The cathode material according to claim 1, characterized in that, Based on the molar content of the metal elements other than lithium in the lithium cobalt oxide particles being 100%, the molar content of niobium is 0.2% to 3%.

3. The positive electrode material according to claim 1, characterized in that, Based on the molar content of the metal elements other than lithium in the lithium cobalt oxide particles being 100%, the molar content of niobium is 0.6% to 1%.

4. The cathode material according to any one of claims 1 to 3, characterized in that, The lithium cobalt oxide particles also include yttrium, and the molar content of yttrium is 0.03% to 1.5% based on the molar content of all metal elements other than lithium in the lithium cobalt oxide particles being 100%.

5. The cathode material according to any one of claims 1 to 3, characterized in that, The lithium cobalt oxide particles also include yttrium, and the molar content of yttrium is 0.03% to 0.2% based on the molar content of all metal elements other than lithium in the lithium cobalt oxide particles being 100%.

6. An electrochemical device, characterized in that, It includes a positive electrode sheet, which includes the positive electrode material as described in any one of claims 1 to 5.

7. The electrochemical device according to claim 6 further includes an electrolyte, characterized in that, The electrolyte includes an organic solvent, and the organic solvent accounts for 20% to 70% of the total mass of the electrolyte.

8. The electrochemical device according to claim 7, characterized in that, The electrolyte also includes oxonitrile and / or fluoroethylene carbonate.

9. The electrochemical device according to any one of claims 6 to 8, characterized in that, The electrolyte also includes lithium difluorophosphate.

10. An electronic device, characterized in that, Includes the electrochemical device as described in any one of claims 6 to 9.

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