A positive electrode material, an electrochemical device including the same, and an electric device

Abstract

This application provides a cathode material, an electrochemical device comprising the cathode material, and an electrical device thereof. The cathode material comprises lithium cobalt oxide having a P63mc crystal structure. The Raman spectrum of the cathode material shows a peak at 490 cm⁻¹. ‑1 ±5cm ‑1 The peak intensity of the characteristic peak within the range is I1, at 592 cm⁻¹. ‑1 ±5cm ‑1 The peak intensity of the characteristic peak within the range is I2, satisfying 1 < I2 / I1 < 5. The cathode material of this application can support the transition metal layer, thereby reducing the collapse of the transition metal layer, improving the structural stability of the cathode material in the high delithiation state, and thus improving the cycle performance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a cathode material, an electrochemical device comprising the cathode material, and an electrical device thereof. Background Technology

[0002] Lithium-ion batteries are characterized by high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in consumer electronics and other fields.

[0003] With the rapid development of electric vehicles and mobile electronic devices, people have increasingly higher requirements for the energy density, safety, and cycle performance of lithium-ion batteries, making it urgent to improve the cathode materials in lithium-ion batteries to enhance the cycle performance of existing lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a cathode material, an electrochemical device comprising the cathode material, and an electrical device thereon, so as to improve the cycle performance of the electrochemical device. The specific technical solution is as follows:

[0005] The first aspect of this application provides a cathode material comprising lithium cobalt oxide having a P63mc crystal structure, wherein the Raman spectrum of the cathode material shows a peak at 490 cm⁻¹. -1 ±5cm -1 The peak intensity of the characteristic peak within the range is I1, at 592 cm⁻¹. -1 ±5cm -1 The peak intensity of the characteristic peak within the range is I2, satisfying 1 < I2 / I1 < 5. The cathode material of this application can support the transition metal layer, thereby reducing the collapse of the transition metal layer, improving the structural stability of the cathode material in the high delithiation state, and thus improving the cycle stability of the electrochemical device.

[0006] In some embodiments of this application, 1.2 ≤ I2 / I1 ≤ 4.3. At this value, the cathode material exhibits better cycle stability, thereby improving the cycle performance of the electrochemical device.

[0007] In some embodiments of this application, the lithium cobalt oxide contains an alkaline earth metal element M, and the Li sites of the lithium cobalt oxide are doped with element M. In this case, the doping of element M into the Li sites can form a pillar effect, which can support the transition metal layer in the high delithiation state, reduce the collapse of the transition metal layer, and thus improve the structural stability of the cathode material in the high delithiation state.

[0008] In some embodiments of this application, the molar percentage of element M in lithium cobalt oxide is 0.5% to 5%, based on the molar amount of metal elements other than Li, Na, and M in the lithium cobalt oxide.

[0009] In some embodiments of this application, element M includes at least one of Ca or Mg. In this case, element M can remain relatively stable, effectively doping into Li sites to form a pillar effect, and the cathode material exhibits good cycle stability.

[0010] In some embodiments of this application, the lithium cobalt oxide further comprises Na and a metallic element Q; the Q element includes at least one selected from Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Lu, or Yb; based on the molar amount of metallic elements other than Li, Na, and M in the lithium cobalt oxide, the molar percentage content of Na in the lithium cobalt oxide is 0.5% to 5%, and the molar percentage content of Q in the lithium cobalt oxide is 2% to 10%.

[0011] In some embodiments of this application, the general formula of lithium cobalt oxide is Na. a Li b M y Co 1-z Q z O 2±n T n Wherein, 0 < a ≤ 0.05, 0.65 ≤ b ≤ 1.1, 0 < y ≤ 0.05, 0 ≤ z ≤ 0.1, 0 ≤ n ≤ 0.1, M is an alkaline earth metal element, Q includes at least one of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Lu or Yb, and T is a halogen element. In this configuration, the cathode material exhibits good cycle stability.

[0012] In some embodiments of this application, the Dv50 of the cathode material is from 5 μm to 25 μm. At this size, the cathode material exhibits good cycle performance.

[0013] A second aspect of this application provides an electrochemical device comprising a positive electrode sheet, the positive electrode sheet including a positive electrode active material layer, wherein the positive electrode active material layer comprises the positive electrode material in any of the foregoing embodiments. The positive electrode material provided by this application exhibits good cycle stability, thereby the electrochemical device provided by this application has good cycle performance.

[0014] In some embodiments of this application, the charging cut-off voltage of the electrochemical device is not lower than 4.50V. At this voltage, the electrochemical device has a higher reversible capacity and good cycle performance.

[0015] A third aspect of this application provides an electrical device that includes the electrochemical device in any of the foregoing embodiments. The electrochemical device provided by this application has good cycle performance, thereby providing a long service life.

[0016] The beneficial effects of this application are as follows: This application provides a cathode material, an electrochemical device comprising the cathode material, and an electrical device thereof, wherein the cathode material comprises lithium cobalt oxide having a P63mc crystal structure, and the Raman spectrum of the cathode material shows a peak at 490 cm⁻¹. -1 ±5cm -1 The peak intensity of the characteristic peak within the range is I1, at 592 cm⁻¹. -1 ±5cm -1 The peak intensity of the characteristic peak within the range is I2, satisfying 1 < I2 / I1 < 5. The cathode material of this application can support the transition metal layer in the high delithiation state, thereby reducing the collapse of the transition metal layer, improving the structural stability of the cathode material in the high delithiation state, and thus improving the cycle performance of the electrochemical device.

[0017] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0018] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0019] Figure 1 These are the Raman spectra of Examples 1 to 3 and Comparative Examples 1 to 2 of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application are within the scope of protection of this application.

[0021] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0022] The first aspect of this application provides a cathode material comprising lithium cobalt oxide having a P63mc crystal structure. The Raman spectrum of the cathode material shows a peak at 490 cm⁻¹. -1 ±5cm -1 The peak intensity of the characteristic peak within the range is I1, at 592 cm⁻¹. -1 ±5cm -1The peak intensity of the characteristic peak within the range is I2, satisfying 1 < I2 / I1 < 5. In one embodiment, 1.2 ≤ I2 / I1 ≤ 4.3. By adjusting the ratio of I2 to I1 within the above range, the cathode material in this application can support the transition metal layer in the high delithiation state, thereby reducing the collapse of the transition metal layer, improving the structural stability of the cathode material in the high delithiation state, and thus improving the cycle stability of the lithium-ion battery.

[0023] In this application, the "high delithiation state" refers to a state where the cathode material is in a high delithiation state when the charging cutoff voltage is ≥4.55V. Compared to the initial fully discharged state, the amount of lithium delithiation in the cathode material at this state is generally ≥0.7mol. For example, the initial fully discharged state material composition is Li 0.9 The cathode material composition changes to Li when the delithiation amount of CoO2 is 0.7 mol. 0.2 CoO2.

[0024] In some embodiments of this application, the lithium cobalt oxide contains an alkaline earth metal element M, and the Li sites of the lithium cobalt oxide are doped with element M. The doping of element M into the Li sites can form a pillar effect, which can support the transition metal layer in the high delithiation state, reduce the collapse of the transition metal layer, and improve the structural stability of the cathode material in the high delithiation state, thereby improving the cycle performance of the lithium-ion battery.

[0025] In some embodiments of this application, the molar percentage of element M in lithium cobalt oxide is 0.5% to 5%, based on the molar amount of metal elements other than Li, Na, and M in the lithium cobalt oxide.

[0026] In some embodiments of this application, element M includes at least one of Ca or Mg. In this case, element M can remain relatively stable, effectively doping into Li sites to form a pillar effect, and the lithium-ion battery exhibits better cycle stability.

[0027] In some embodiments of this application, the lithium cobalt oxide further comprises Na and a metal element Q; the Q element includes at least one selected from Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Lu, or Yb; based on the molar amount of the metal elements other than Li, Na, and M in the lithium cobalt oxide, the molar percentage of Na in the lithium cobalt oxide is 0.5% to 5%, and the molar percentage of Q in the lithium cobalt oxide is 2% to 10%, and the lithium-ion battery containing this cathode material exhibits good cycle performance.

[0028] In some embodiments of this application, the general formula of lithium cobalt oxide is Na. a Li b M y Co 1-z Q z O2±n T n , where 0 < a ≤ 0.05, 0.65 ≤ b ≤ 1.1, 0 < y ≤ 0.05, 0 ≤ z ≤ 0.1, 0 ≤ n ≤ 0.1, the M element is an alkaline earth metal element, the Q element includes at least one of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Lu or Yb, the T element is a halogen element, and the T element includes at least one of F, Cl, Br or I. By using the positive electrode material having the above general formula, the lithium ion battery exhibits good cycle stability.

[0029] In some embodiments of the present application, the Dv50 of the positive electrode material is 5 μm to 25 μm. By controlling the Dv50 of the positive electrode material within the above range, the lithium ion battery has good cycle performance.

[0030] In the present application, Dv50 refers to the particle size of 50% of the particles in the volume distribution of the positive electrode material.

[0031] The present application does not particularly limit the preparation method of the positive electrode material, as long as the object of the present application can be achieved. For example, the preparation method of the positive electrode material may include but is not limited to the following steps:

[0032] Step 1: Add soluble cobalt salt and metal salt containing doping element Q in proportion to a solvent to form a uniform mixed solution, then add a precipitant and a complexing agent, adjust the pH to 5 to 9 to form a homogeneous precipitate, and then perform processes such as sintering, crushing and screening on the precipitate to obtain a metal oxide material;

[0033] Step 2: Weigh and mix the metal oxide material, sodium-containing compound and compound containing doping element M in proportion, and keep it at a temperature of 750 °C to 1050 °C for 24 h to 72 h to obtain sodium cobalt oxide with a P63mc structure;

[0034] Step 3: Use the sodium cobalt oxide with a P63mc structure as a precursor material, mix it evenly with a lithium-containing compound, load it into a corundum crucible, and carry out a solid-phase reaction at a temperature of 220 °C to 280 °C for 2 to 8 h, and cool to obtain a mixture containing a lithium cobalt oxide positive electrode material;

[0035] Step 4: Crush the mixture material in Step 3, wash it with deionized water multiple times to remove soluble sodium salts and lithium salts in the mixture, and then perform steps such as suction filtration, drying and screening on the residual powder to obtain a lithium cobalt oxide positive electrode material.

[0036] In step 1, the soluble cobalt salt and the metal salt containing the doped element are at least one of chloride, acetate, sulfate, or nitrate. For example, the soluble cobalt salt includes cobalt chloride, cobalt acetate, cobalt nitrate, and cobalt sulfate; the metal salt containing the doped element includes nickel nitrate, manganese nitrate, and yttrium nitrate; the sodium-containing compound is at least one of Na₂O, Na₂O₂, Na₂CO₃, or NaOH, preferably Na₂O and Na₂CO₃; the compound containing the doped element M is preferably a chloride or carbonate of element M, for example, including calcium chloride, calcium carbonate, and magnesium carbonate; this application does not particularly limit the mixing ratio of the soluble cobalt salt and the metal salt containing the doped element Q, as long as the purpose of this application is achieved, they can be mixed according to the designed ratio. For example, the soluble cobalt salt and the metal salt containing the doped element Q are mixed at a ratio of 1:(0.02 to 0.11); this application does not particularly limit the precipitant and complexing agent, as long as the purpose of this application is achieved. For example, precipitants include ammonium carbonate and ammonium bicarbonate, and complexing agents include ammonia and sodium hydroxide. There are no particular limitations on the amount of precipitant and complexing agent added, as long as the purpose of this application is achieved. For example, based on the molar amount of Co, the amount of precipitant added is 1 to 2.5 times, and the amount of complexing agent added is 1 to 1.5 times. This application does not have particular limitations on the sintering temperature; for example, the sintering temperature can be from 450°C to 700°C. This application can use an air jet mill for crushing and a vibrating screen for particle size separation, thereby controlling the particle size of the metal oxide material.

[0037] In step 2, this application does not impose any particular restrictions on the mixing ratio of metal oxide materials, sodium-containing compounds and compounds containing doped element M, and they can be added according to the designed ratio.

[0038] In step 3, this application does not impose any particular restrictions on lithium-containing compounds, as long as they can achieve the purpose of this application. For example, lithium-containing compounds include, but are not limited to, lithium sulfate, lithium carbonate, lithium nitrate, lithium halides, lithium carboxylate, lithium squaric acid, lithium alkoxide, etc.

[0039] This application does not impose any particular limitations on the methods for controlling the peak intensities I1 and I2. For example, I2 typically increases with the increase of Co-O bending vibration intensity, and I1 typically increases with the increase of Co-O stretching vibration intensity. Based on this, the bending and stretching vibration intensities of the Co-O bond can be controlled by adjusting the sintering process and doping, thereby controlling the range of the I1 to I2 ratio.

[0040] A second aspect of this application provides an electrochemical device comprising a positive electrode sheet, the positive electrode sheet including a positive electrode active material layer, wherein the positive electrode active material layer comprises the positive electrode material in any of the foregoing embodiments. The positive electrode material provided by this application exhibits good cycle stability, thereby the electrochemical device provided by this application has good cycle performance.

[0041] In some embodiments of this application, the charging cut-off voltage of the electrochemical device is not lower than 4.50V. At this voltage, the electrochemical device has a higher reversible capacity and good cycle performance.

[0042] The electrochemical device of this application includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode comprises a positive current collector and a positive active material layer. 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, the positive current collector may comprise aluminum foil, aluminum alloy foil, or a composite current collector. In this application, there are no particular limitations on the thickness of the positive current collector and the positive active material layer, as long as they achieve the purpose of this application. For example, the thickness of the positive current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive active material layer is 30 μm to 120 μm. In this application, the positive active material layer may be disposed on one surface in the thickness direction of the positive current collector, or on two surfaces in the thickness direction of the positive current collector. Optionally, the positive active material layer may also include a conductive agent and a binder. This application does not impose any particular limitation on the type of binder in the positive electrode active material layer, as long as it can achieve the purpose of this application. For example, the binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. This application does not impose any particular limitation on the type of conductive agent in the positive electrode active material layer, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of conductive carbon black (SuperP), 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. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer; those skilled in the art can select these ratios according to actual needs, as long as the purpose of this application can be achieved.

[0043] This application does not impose any particular limitation on the negative electrode sheet, as long as it achieves the purpose of this application. For example, the negative electrode sheet includes a negative current collector and a negative active material layer. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. For example, the negative current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, or copper foam, etc. The negative active material layer of this application includes a negative active material. This application does not impose any particular limitation on the type of negative active material, as long as it achieves the purpose of this application. For example, the negative active material may include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO2, etc. x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 The material comprises at least one of Li-Al alloy or metallic lithium. In this application, there are no particular limitations on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application is achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 130 μm. Optionally, the negative electrode active material layer may further include at least one of a conductive agent, a stabilizer, and a binder. This application does not particularly limit the types of conductive agents, stabilizers, and binders in the negative electrode active material layer, as long as the purpose of this application is achieved. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, stabilizer, and binder in the negative electrode active material layer, as long as the purpose of this application is achieved.

[0044] The electrochemical device of this application also includes a diaphragm. This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. For example, it can be at least one of the following: polyethylene (PE), polypropylene (PP), polyolefin (PO) diaphragms primarily composed of polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide (PI) membranes, polyamide (PA) membranes, spandex, aramid membranes, woven membranes, nonwoven membranes (non-woven fabrics), microporous membranes, composite membranes, diaphragm paper, rolled membranes, or spun membranes, preferably PP. The diaphragm of this application can have a porous structure, and the pore size is not particularly limited, as long as it achieves the purpose of this application. For example, the pore size can be from 0.01 μm to 1 μm. In this application, the thickness of the diaphragm is not particularly limited, as long as it achieves the purpose of this application. For example, the thickness can be from 5 μm to 500 μm.

[0045] For example, the diaphragm 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, but is not limited to, 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, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials.

[0046] The inorganic layer may include, but is not limited to, inorganic particles and inorganic layer binders. This application does not impose any particular limitation on the inorganic particles, as long as they achieve the purpose of this application. For example, they may include, but are not limited to, 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. This application does not impose any particular limitation on the inorganic layer binder. For example, it may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material may include, but is not limited to, at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride and hexafluoropropylene.

[0047] In this application, the electrochemical device further includes an electrolyte, which comprises a lithium salt and a non-aqueous solvent. The lithium salt may include at least one selected from LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of this application is achieved. For example, the concentration of the lithium salt in the electrolyte may be from 0.9 mol / L to 1.5 mol / L. Exemplarily, the concentration of the lithium salt in the electrolyte may be 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.3 mol / L, 1.5 mol / L, or a range consisting of any two of the above values. This application does not impose any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0048] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the electrochemical device may include, but is not limited to, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery. In one embodiment, the electrode assembly structure includes a wound structure or a stacked structure.

[0049] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device. Furthermore, overcurrent protection elements, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device. This application has no limitations on the packaging bag; those skilled in the art can choose according to actual needs, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag may be used.

[0050] A third aspect of this application provides an electrical device that includes the electrochemical device in any of the foregoing embodiments. The electrochemical device provided by this application has good cycle performance, thereby providing a long service life.

[0051] This application does not specifically limit the electrical device, which can be any electrical device known in the prior art. For example, the electrical device may include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, over-ear 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, household large-capacity batteries, and lithium-ion capacitors.

[0052] Example

[0053] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0054] Test methods and equipment:

[0055] Raman test:

[0056] The cathode materials prepared in each embodiment and comparative example were tested using a spectrometer (Jobin Yvon LabRAM HR) with a light source of 532 nm and a test range of 200 cm⁻¹. -1 Up to 4000cm -1 .

[0057] Cathode material particle size testing:

[0058] The cathode materials prepared in each embodiment and comparative example were tested using a Malvern particle size analyzer (Master Sizer 2000). In the volume-based particle size distribution of the cathode active material, the particle size reaching 50% of the volumetric accumulation was defined as Dv50, starting from the smallest particle size.

[0059] XRD test:

[0060] X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE) was used to test the cathode material. The target material was Cu Kα, the test voltage was 40 kV, the test current was 35 mA, the scanning angle range was 10° to 90°, and the scanning rate was 0.02° / s. The strongest diffraction peak intensity was required to be greater than 10,000 (in counts). The acquired XRD patterns were refined using Fullprof software to determine the phase structure and dopant site occupancy.

[0061] Cathode material elemental composition test:

[0062] The Li and metal element content in the cathode material was determined using an inductively coupled plasma atomic absorption spectrometer (ICP, instrument model: PE Optima 7000DV). First, an appropriate amount of powder sample was weighed, and approximately 10 mL of aqua regia was added. The sample was heated at approximately 185°C for 30 to 50 minutes to ensure complete digestion before being tested.

[0063] Cyclic performance test:

[0064] After aging the button cells at 25°C for 24 hours, the resulting button cells were subjected to charge-discharge tests within a voltage range of 3V to 4.6V. The first two cycles were activated at a charge-discharge rate of 0.1C, and subsequent cycles were performed at a charge-discharge rate of 0.5C. The battery capacity retention rate was calculated based on the battery capacity in the third cycle, with 1C = 273mA / g.

[0065] Cycle capacity retention rate = Discharge capacity in the nth cycle / Discharge capacity in the 3rd cycle × 100%.

[0066] Example 1

[0067] <Preparation of cathode materials>

[0068] 13.35 kg of cobalt sulfate heptahydrate (CoSO4·7H2O) and 0.66 kg of nickel sulfate hexahydrate (NiSO4·6H2O) were weighed out and dissolved in deionized water with rapid stirring. Ammonium carbonate and ammonia were then added to adjust the pH to 8. After the reaction was complete, a homogeneous carbonate precipitate was formed. The precipitate was sintered at 650℃ for 12 h. After crushing and sieving, the metal oxide (Co) was obtained. 0.95 Ni 0.05 )3O4;

[0069] Sodium carbonate (Na2CO3), calcium carbonate (CaCO3) and the prepared metal oxide were mixed evenly according to the metal element molar ratio Na∶Ca∶(Co+Ni)=0.8∶0.01∶1 and then kept at 830℃ for 48h. After crushing and sieving, sodium cobalt oxide material with P63mmc crystal structure was obtained.

[0070] The prepared sodium cobalt oxide material, lithium nitrate (LiNO3) and lithium chloride (LiCl) were mixed evenly in a molar ratio of 1:4:1 and then placed into an alumina crucible. The mixture was first reacted at 235°C for 4 hours, and then reacted at 250°C for 4 hours. After cooling, a mixture containing lithium cobalt oxide cathode material was obtained.

[0071] The mixture containing lithium cobalt oxide cathode material was crushed and 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 filtered, dried, and sieved to obtain lithium cobalt oxide material with a Dv50 of 9.3 μm.

[0072] <Preparation of the positive electrode>

[0073] The lithium cobalt oxide obtained above was used as the positive electrode active material. Conductive carbon black (SP) was used as the conductive agent, and polyvinylidene fluoride (PVDF) was used as the binder. They were mixed at a mass ratio of 80:10:10, and N-methyl-2-pyrrolidone (NMP) was added as the solvent. The mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 60 wt%. A 12 μm aluminum foil was used as the positive electrode current collector. A 100 μm thick coating was coated on the current collector aluminum foil. The foil was first baked in a 90℃ forced-air drying oven for 4 h, and then baked in a 110℃ vacuum drying oven for 24 h. The fully dried electrode sheet was then subjected to cold pressing, punching, and weighing processes to obtain a circular positive electrode sheet with a diameter of 1.4 cm.

[0074] <Preparation of Negative Electrode Sheets>

[0075] Lithium metal sheets are used as counter electrodes.

[0076] <Preparation of Electrolyte>

[0077] In a dry argon-atmospheric glove box, fluoroethylene carbonate (FEC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:8 to obtain an organic solvent. Lithium salt LiPF6 was then added to the organic solvent, dissolved, and mixed thoroughly to obtain the electrolyte. The concentration of LiPF6 was 1 mol / L.

[0078] <Preparation of the diaphragm>

[0079] A porous PE film with a thickness of 7μm was used.

[0080] <Preparation of Lithium-ion Batteries>

[0081] Under a dry argon atmosphere, the above-mentioned positive electrode sheet is assembled with a separator, a negative electrode sheet and an electrolyte to form a coin cell.

[0082] Example 2

[0083] The only difference from Example 1 is in the following aspects of the preparation steps of the cathode material: the molar ratio of metal elements of Na2CO3, CaCO3 and the prepared metal oxide is Na∶Ca∶(Co+Ni)=0.8∶0.03∶1.

[0084] Example 3

[0085] The only difference from Example 1 is in the following aspects of the preparation steps of the cathode material: the molar ratio of metal elements of Na2CO3, CaCO3 and the obtained metal oxide is Na∶Ca∶(Co+Ni)=0.8∶0.05∶1.

[0086] Example 4

[0087] The only difference from Example 1 lies in the following aspects of the preparation steps of the cathode material:

[0088] 13.49 kg of cobalt sulfate heptahydrate (CoSO4·7H2O) and 0.34 kg of manganese sulfate monohydrate (MnSO4·H2O) were weighed out and dissolved in deionized water with rapid stirring. Ammonium carbonate was then added to adjust the pH to 8. After the reaction was complete, a homogeneous carbonate precipitate was formed. The precipitate was sintered at 650℃ for 12 h. After crushing and sieving, the metal oxide (Co) was obtained. 0.06 Mn 0.04 )3O4;

[0089] Sodium carbonate (Na2CO3), magnesium oxide (MgO) and the prepared metal oxide were mixed evenly according to the metal element molar ratio Na∶Mg∶(Co+Mn)=0.8∶0.01∶1 and then kept at 850℃ for 48h. After crushing and sieving, sodium cobalt manganese oxide material with P63mmc crystal structure was obtained.

[0090] The prepared sodium cobalt oxide material, lithium nitrate (LiNO3) and lithium hydroxide (LiOH) were mixed evenly in a molar ratio of 1:4:1 and then placed into an alumina crucible. The mixture was reacted at 250°C for 8 hours and then cooled to obtain a mixture containing lithium cobalt manganese oxide cathode material.

[0091] The prepared mixture was crushed and 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 filtered, dried and sieved to obtain lithium cobalt manganese oxide material with a Dv50 of 10.2 μm.

[0092] Example 5

[0093] The only difference from Example 4 is in the following aspects of the preparation steps of the cathode material: the molar ratio of metal elements of Na2CO3, MgO and the prepared metal oxide is Na∶Mg∶(Co+Mn)=0.8∶0.03∶1.

[0094] Example 6

[0095] The difference from Example 4 lies only in the following aspects of the preparation steps of the cathode material: the molar ratio of metal elements of Na2CO3, MgO and the prepared metal oxide is Na∶Mg∶(Co+Mn)=0.8∶0.05∶1.

[0096] Examples 7 to 11

[0097] The difference from Example 1 lies only in the following aspects of the preparation steps of the cathode material: the types of Q elements are adjusted as shown in Table 1 by replacing NiSO4·6H2O with Y(NO3)3, Nb(NO3)5, La(NO3)3, Fe(NO3)3, and Cu(NO3)2 respectively, and the amount of CaCO3 added is changed to adjust the content of Ca elements as shown in Table 1.

[0098] Examples 12 to 16

[0099] The difference from Example 4 lies only in the following aspects of the preparation steps of the cathode material: MnSO4·H2O was replaced with Cr(NO3)3, TiCl4, W(NO3)3, Lu(NO3)3, and Yb(NO3)2 respectively to adjust the type of Q element as shown in Table 1, and the amount of MgO added was changed to adjust the content of Mg element as shown in Table 1.

[0100] Example 17

[0101] The only difference from Example 4 is the following aspect of the preparation steps of the cathode material: 2 wt% NH4F is added during the sintering process of sodium carbonate (Na2CO3), magnesium oxide (MgO) and the prepared metal oxide.

[0102] Example 18

[0103] The only difference from Example 4 is the following aspect of the preparation steps of the cathode material: 5 wt% NH4F is added during the sintering process of sodium carbonate (Na2CO3), magnesium oxide (MgO) and the prepared metal oxide.

[0104] Comparative Example 1

[0105] The only difference from Example 1 is in the following aspects of the preparation steps of the cathode material: no CaCO3 is added, and the molar ratio of Na2CO3 to the metal element in the prepared metal oxide is Na∶(Co+Ni)=0.8∶1.

[0106] Comparative Example 2

[0107] The only difference from Example 1 is in the following aspects of the preparation steps of the cathode material: the molar ratio of metal elements of Na2CO3, CaCO3 and the prepared metal oxide is Na∶Ca∶(Co+Ni)=0.8∶0.07∶1.

[0108] Comparative Example 3

[0109] The only difference from Example 2 is the following aspect of the preparation steps of the cathode material: Ca is introduced in the form of Ca(NO3)2 during the precursor co-precipitation stage.

[0110] Comparative Example 4

[0111] The only difference from Example 5 is the following aspect of the preparation steps of the cathode material: Mg is introduced in the form of Mg(NO3)2 during the precursor co-precipitation stage.

[0112] The preparation and performance parameters of each embodiment and comparative example are shown in Table 1.

[0113]

[0114] Referring to Table 1, it can be seen from Examples 1 to 18 and Comparative Examples 1 to 4 that the capacity retention rate of the coin cell after 100 cycles is significantly improved, indicating that by controlling the relationship between the peak intensity of the cathode material as I1 and the peak intensity as I2 within the scope of this application, it is beneficial to improve the cycle performance of lithium-ion batteries.

[0115] Figure 1 The Raman spectra of the materials of Examples 1 to 3 and Comparative Examples 1 to 2 are shown. Figure 1 Two Raman characteristic peaks can be observed, located at 490±5 cm. -1 and 592±5cm -1 The former represents the bending vibration mode of O-Co-O, and the latter represents the stretching vibration mode of Co-O.

[0116] As can be seen from Examples 1 to 3 and Comparative Examples 1 to 2, the higher the relative content of element M, the larger the peak intensity ratio I2 / I1, and when I2 / I1 is within the range of this application, the coin cell exhibits excellent cycle performance. This indicates that by controlling the relationship between the peak intensity of the cathode material as I1 and the peak intensity as I2 within the range of this application, it is beneficial to improve the cycle performance of lithium-ion batteries. As can be seen from Examples 2 and 3, and Examples 5 and 4, under the same doping amount of element M, when element M is introduced in the co-precipitation precursor stage, the resulting material has a smaller I2 / I1 ratio, while when element M is introduced in the sodium cobalt oxide sintering stage, the resulting material has a larger I2 / I1 ratio. One possible explanation is that M is introduced in the precursor stage through co-precipitation, and M tends to be uniformly distributed in the bulk of the target material. However, when M is introduced in the sodium cobalt oxide sintering stage, it may be distributed in a gradient in the target material, with the doping concentration on the surface being higher than that on the bulk. Therefore, the I2 / I1 ratio is higher, and the actual improvement effect on the material's structural stability, especially the stability of the surface interface, is more significant.

[0117] From Examples 1 to 3 and Comparative Examples 1 to 2, it can also be seen that when the relative Ni content is 0.05 mol, as the Ca doping content at Li sites increases, the Raman characteristic peak intensity ratio I2 / I1 of the material shows an increasing trend, while the capacity retention rate after 100 battery cycles shows a trend of first increasing and then decreasing. When there is no Ca doping, the Raman characteristic peak intensity ratio I2 / I1 of the material provided in Comparative Example 1 is about 0.7, and the capacity retention rate of the material after 100 battery cycles is low, only 67%. With the increase of Ca doping, the Raman characteristic peak intensity ratio I2 / I1 of Examples 1 to 3 is between 1 and 5, and the battery cycle capacity retention rate is significantly improved, greatly increasing to 87% to 93%. When the Ca doping amount is further increased to 0.07, the Raman characteristic peak intensity ratio I2 / I1 of the material provided in Comparative Example 2 is 5.5, and the battery cycle capacity retention rate begins to decrease, only 62%. ICP testing was performed on the fully charged positive electrode sheets of Examples 1 to 3 after 100 cycles. The measured Ca content was the same as that of the initial powder state, indicating that Ca did not undergo insertion / extraction reactions during charge and discharge. It is speculated that the main reason for the improved Ca doping is that Ca forms a pillar effect at the Li sites, stabilizing the structure. However, due to Ca... 2+ and Li + Significant differences in radius mean that excessive doping will disrupt the overall crystal structure balance and worsen structural stability. A comparison of Examples 1-3 and Comparative Examples 1-2 shows that Ca... 2+ The preferred doping concentration should not exceed 5% (molar percentage).

[0118] Referring to Table 1, the type of metal element Q in lithium cobalt oxide usually also affects the performance of coin cells. As can be seen from Examples 7 to 16, by controlling the type of metal element Q within the scope of this application, it is beneficial to obtain lithium-ion batteries with high cycle performance.

[0119] Comparing Examples 17 and 18 with Example 4, it can be seen that the inclusion of halogen elements in lithium cobalt oxide can further improve the cycling stability of the material. Compared with Example 4, Examples 17 and 18 were doped with F and Cl, respectively, and the capacity retention of the resulting materials after 100 cycles increased from 86% in Example 4 to 94% and 89%, respectively.

[0120] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A positive electrode material, characterized by: The lithium cobalt oxide includes a P63mc crystal structure, The peak intensity of the characteristic peak in the Raman spectrum of the positive electrode material in the range of 490 cm -1 ± 5 cm -1 -1 is I1, and the peak intensity of the characteristic peak in the range of 592 cm -1 ± 5 cm -1 -1 is I2, and satisfies: 1.2 ≤ I2 / I1 ≤ 4.

3. The lithium cobalt oxide contains an alkaline earth metal element M; The M element includes at least one of Ca or Mg.

2. The positive electrode material of claim 1, wherein: At least one of the following is satisfied: (1) Li sites of the lithium cobalt oxide are doped with the M element; (2) a molar percentage content of the M element in the lithium cobalt oxide is 0.5% to 5% based on a molar amount of metal elements other than Li, Na, and M in the lithium cobalt oxide.

3. The positive electrode material of claim 2, wherein: The lithium cobalt oxide further contains a Na element and a metal element Q; The Q element includes at least one of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Lu, or Yb; A molar percentage content of the Na element in the lithium cobalt oxide is 0.5% to 5% and a molar percentage content of the Q element in the lithium cobalt oxide is 2% to 10% based on a molar amount of metal elements other than Li, Na, and M in the lithium cobalt oxide.

4. The positive electrode material of claim 1, wherein: The general formula of the lithium cobalt oxide is Na a Li b M y Co 1-z Q z O 2±n T n , 0 < a ≤ 0.05, 0.65 ≤ b ≤ 1.1, 0 < y ≤ 0.05, 0 ≤ z ≤ 0.1, 0 ≤ n ≤ 0.1, The M element is an alkaline earth metal element, the Q element includes at least one of Al, Zr, Ni, Mn, Y, Nb, La, Fe, Cu, Cr, Ti, W, Lu, or Yb, and the T element is a halogen element.

5. The cathode material of claim 1, wherein: A Dv50 of the positive electrode material is 5 μm to 25 μm.

6. An electrochemical device, characterized by: The positive electrode material includes a positive electrode active material layer, and the positive electrode active material layer includes the positive electrode material of any one of claims 1-5.

7. The electrochemical device of claim 6, wherein: A charge cut-off voltage of the electrochemical device is not less than 4.50 V.

8. An electric device including the electrochemical device of claim 6 or 7.

Images