Positive electrode material, electrochemical device, and electronic device

Abstract

Provided in the present application are a positive electrode material, an electrochemical device and an electronic device. The positive electrode material comprises lithium cobalt oxide and a coating layer formed on the lithium cobalt oxide, wherein the coating layer comprises a sodium superionic conductor and a boron-containing compound; the lithium cobalt oxide has a crystal structure belonging to the space group P63mc; and the lithium cobalt oxide further contains an element M1, M1 comprising at least one of Ni or Mn. The positive electrode material provided by the present application can reduce direct contact between the lithium cobalt oxide and an electrolyte while maintaining a relatively high ionic conductivity, and therefore the cycle performance of the positive electrode material under high voltages is improved.

Description

Cathode materials, electrochemical devices and electronic devices Technical Field

[0001] This application relates to the field of electrochemical energy storage, and in particular to a cathode material, an electrochemical device using the cathode material, and an electronic device using the electrochemical device. Background Technology

[0002] Currently, commercially available lithium cobalt oxide exhibits an extremely unstable crystal structure at voltages above 4.6V, accompanied by severe capacity decay. This prevents it from reaching its theoretical capacity at high voltages and hinders stable cycle performance, thus limiting the commercial application of lithium cobalt oxide. Summary of the Invention

[0003] This application provides a cathode material that can improve cycle performance.

[0004] In addition, this application also provides an electrochemical device using a positive electrode material and an electronic device using the electrochemical device.

[0005] The first aspect of this application provides a cathode material, including lithium cobalt oxide and a coating layer formed on the lithium cobalt oxide. The coating layer includes a sodium superionic conductor and a boron-containing compound. The lithium cobalt oxide has a P63mc crystal structure and also contains an element M1, which includes at least one of Ni or Mn.

[0006] In this application, the sodium superionic conductor solid electrolyte increases the interfacial ionic conductivity, facilitating ion transport between lithium cobalt oxide and the electrolyte, reducing interfacial impedance, and minimizing side reactions between the lithium cobalt oxide surface and the electrolyte, thereby improving the cycle performance of the electrochemical device. Furthermore, the sodium superionic conductor and boron-containing compound co-coating the surface of the lithium cobalt oxide further suppress direct contact between the lithium cobalt oxide and the electrolyte, reducing interfacial side reactions and further improving the cycle performance of the electrochemical device. Simultaneously, the combination of the sodium superionic conductor and the boron-containing compound allows the cathode material to maintain high ionic conductivity while reducing direct contact between the lithium cobalt oxide and the electrolyte, thus achieving a balance between high conductivity and structural stability, improving the cycle performance of the cathode material under high voltage. Additionally, doping the lithium cobalt oxide with M1 element improves the stability of the cathode material and enhances the initial discharge specific capacity and cycle performance of the electrochemical device.

[0007] Based on the first aspect, in some possible implementations, the sodium superionic conductor is Li. 1+x Al x Ti 2-x (PO4)3 or Li 1+y Al y Ge2-y (PO4)3, where 0 ≤ x ≤ 0.5 and 0 ≤ y ≤ 1. The above sodium superionic conductor has high ionic conductivity and chemical stability. Coating the lithium cobalt oxide with the sodium superionic conductor can increase the ionic conductivity of the lithium cobalt oxide and the electrolyte, thereby reducing the interfacial side reactions between the lithium cobalt oxide and the electrolyte and improving the cycling performance of the electrochemical device.

[0008] Based on the first aspect, in some possible embodiments, 0 < m1 / m2 ≤ 15%, where m1 is the amount of substance of M1 and m2 is the sum of the amount of substance of M1 and the amount of substance of Co element. This is beneficial for the cathode material to have better first charge-discharge specific capacity and cycling performance.

[0009] Based on the first aspect, in some possible embodiments, the cathode material further contains an M2 element, and the M2 element includes at least one of Mg, Ca, La, Y, Ti, and Zr. The mass fraction of the M2 element in the lithium cobalt oxide is n, where 0 < n ≤ 1%. The M2 element can slow down the rapid change of the layer spacing during the insertion and extraction of active ions, thereby stabilizing the layered lithium cobalt oxide. At the same time, the M2 element can also reduce the oxygen activity of the cathode material, thereby improving the stability of the cathode material and further enhancing the safety and cycle life of the electrochemical device.

[0010] Based on the first aspect, in some possible embodiments, the boron-containing compound includes at least one of boron-containing oxides or borates. The boron-containing oxides include at least one of B2O3, BO, HBO3, and H3BO3, and the borates include at least one of Na2B4O7, NH4H2BO3, CaB2O4, and Mg(B(OH)4)2. The above boron-containing oxides can uniformly coat the surface of the lithium cobalt oxide, block the direct contact between the electrolyte and the lithium cobalt oxide, reduce side reactions, and thus improve the cycling performance of the electrochemical device.

[0011] Based on the first aspect, in some possible embodiments, based on the mass of the cathode material, the mass ratio of the sodium superionic conductor is ω1, where 0 < ω1 ≤ 1%. This is beneficial for increasing the ionic conductivity of the cathode material while the cathode material has good specific capacity and low impedance, thereby improving the cycling performance and rate performance of the electrochemical device.

[0012] Based on the first aspect, in some possible embodiments, the mass ratio of boron element in the boron-containing compound is ω2, where 0 < ω2 ≤ 0.5%. This is beneficial for minimizing the impact on the interfacial impedance after coating with the boron-containing compound on the premise of reducing the direct contact between the lithium cobalt oxide and the electrolyte.

[0013] Based on the first aspect, in some possible implementations, 0 < ω1 + ω2 ≤ 1.5%. This is beneficial for increasing the ionic conductivity of the cathode material and improving the energy density of the electrochemical device; it can also reduce interfacial impedance by reducing side reactions of lithium cobalt oxide and electrolyte, thereby improving the cycle performance of the cathode material.

[0014] Based on the first aspect, in some possible implementations, the lithium cobalt oxide is a single crystal particle, and the lithium cobalt oxide has cracks. The presence of cracks can reduce and release the stress generated by the lattice expansion and contraction process during charging and discharging, thereby suppressing the rapid propagation of lattice defects and thus helping to improve the structural stability of the cathode material.

[0015] Based on the first aspect, in some possible implementations, the median particle size D of the sodium superionic conductor 50 The particle size is 50nm to 100nm. This size is beneficial for improving the uniformity of sodium superionic conductor coating on lithium cobalt oxide. Furthermore, at this particle size, it is also beneficial for increasing the contact area between the sodium superionic conductor and the lithium cobalt oxide, reducing the risk of the sodium superionic conductor detaching from the lithium cobalt oxide, thereby improving the stability of the sodium superionic conductor formed on the surface of the lithium cobalt oxide and enhancing the stability of the cathode material.

[0016] A second aspect of this application provides an electrochemical device including a positive electrode and a negative electrode. The positive electrode includes a current collector and a positive electrode material layer disposed on the current collector. The positive electrode material layer includes a positive electrode material. The lithium cobalt oxide in the positive electrode material is coated with a sodium superionic conductor and a boron-containing compound, which can reduce interfacial impedance, reduce side reactions between the lithium cobalt oxide and the electrolyte, and improve the cycle performance of the positive electrode material under high voltage, thereby improving the cycle life and charge / discharge rate of the electrochemical device.

[0017] A third aspect of this application provides an electronic device, including an electrochemical device. The electrochemical device supplies power to the electronic device and includes a positive electrode material. The surface of the lithium cobalt oxide in the positive electrode material is coated with a sodium superionic conductor and a boron-containing compound, which can improve the cycle life of the electrochemical device, thereby improving the lifespan and charge / discharge rate of the electronic device. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0019] Figure 1 is an X-ray diffraction pattern of the lithium cobalt oxide prepared in Example 1.

[0020] Figure 2 is a scanning electron microscope image of the lithium cobalt oxide prepared in Example 1.

[0021] Figure 3 shows the surface EDS spectrum of the lithium cobalt oxide prepared in Example 1.

[0022] Figure 4 is a scanning electron microscope image of the cross section of the lithium cobalt oxide prepared in Example 1.

[0023] Figure 5 is a scanning electron microscope image of the lithium cobalt oxide prepared in Comparative Example 2. Detailed Implementation

[0024] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0025] One embodiment of this application provides an electrochemical device, which includes a housing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the housing.

[0026] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, the electrochemical device can be a flexible packaged electrochemical device. In other embodiments, the electrochemical device can also be a steel-cased electrochemical device, an aluminum-cased electrochemical device, etc.

[0027] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The electrode assembly can be a stacked structure, formed by layering the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding the stacked positive electrode, separator, and negative electrode.

[0028] Positive electrode sheet

[0029] The positive electrode sheet includes a positive current collector and a positive electrode material layer. The positive electrode material layer includes a positive electrode material, a binder, and a conductive agent.

[0030] According to some embodiments of this application, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil or nickel foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.

[0031] This application provides a cathode material comprising lithium cobalt oxide and a coating layer formed on the lithium cobalt oxide. The coating layer comprises a sodium superionic conductor and a boron-containing compound. The lithium cobalt oxide has a P63mc crystal structure. The lithium cobalt oxide also contains an element M1, wherein M1 includes at least one of Ni or Mn.

[0032] In this application, a sodium superionic conductor and a boron-containing compound are formed on the surface of lithium cobalt oxide. The solid electrolyte of the sodium superionic conductor can increase the ionic conductivity of the interface, which is beneficial for ion transport between lithium cobalt oxide and electrolyte, and also helps to reduce interfacial impedance. Simultaneously, it can reduce side reactions between the lithium cobalt oxide surface and the electrolyte, thereby improving the cycle performance of the electrochemical device. Furthermore, the joint coating of the lithium cobalt oxide surface with the sodium superionic conductor and boron-containing compound further suppresses direct contact between lithium cobalt oxide and electrolyte, thereby reducing interfacial side reactions between lithium cobalt oxide and electrolyte, further improving the cycle performance of the electrochemical device. At the same time, the combination of the sodium superionic conductor and boron-containing compound not only reduces interfacial impedance but also reduces side reactions between lithium cobalt oxide and electrolyte, improving the cycle performance of the cathode material under high voltage. Doping lithium cobalt oxide with M1 element can improve the stability of the cathode material and increase the initial discharge specific capacity and cycle performance of the electrochemical device.

[0033] In this application, sodium superionic conductors (NaSICONs) possess high ionic conductivity and chemical stability. Formed on the surface of lithium cobalt oxide, they can increase ion transport between the cathode material and the electrolyte. However, because sodium superionic conductors do not easily completely coat the surface of lithium cobalt oxide, and considering the low melting point of boron-containing compounds, they readily and uniformly adhere to the surface of lithium cobalt oxide, reducing exposed defect sites and decreasing the specific surface area of ​​the cathode material, thereby reducing interfacial side reactions. The combination of sodium superionic conductors and boron-containing compounds allows the cathode material to maintain high ionic conductivity while also reducing direct contact between lithium cobalt oxide and the electrolyte. This results in a cathode material that balances high conductivity and structural stability, thereby improving the cycle performance of the cathode material.

[0034] In some embodiments, the sodium superionic conductor is Li 1+x Al x Ti 2-x (PO4)3 (abbreviated as LATP) or Li 1+y Al y Ge 2-y (PO4)3 (abbreviated as LAGP), where 0≤x≤0.5, 0≤y≤1. Sodium superionic conductors possess high ionic conductivity, low toxicity, and high chemical stability. Coating the surface of lithium cobalt oxide with sodium superionic conductors can significantly increase the ionic conductivity of lithium cobalt oxide and the electrolyte, thereby reducing interfacial side reactions and improving the cycle performance of electrochemical devices. For example, sodium superionic conductors can be used to coat Li... 1.4 Al 0.4 Ti 1.6 (PO4)3 and Li 1.5 Al 0.5 Ge 1.5At least one of (PO4)3.

[0035] In some embodiments, 0 < m1 / m2 ≤ 15%, where m1 is the amount of substance of M1 and m2 is the sum of the amount of substance of M1 and the amount of substance of Co element. When the doping amount of M1 in lithium cobalt oxide is within the above range, it is beneficial for the cathode material to have better initial charge-discharge specific capacity and cycling performance. If the value of m1 / m2 is relatively large, such as a relatively high content of Mn element, Mn is doped in lithium cobalt oxide in the form of Mn 4+ and is electrochemically inert during charge and discharge, which will reduce the discharge specific capacity of the cathode material; if the content of Ni element is relatively large, it increases the probability of Ni element mixing and reduces the structural stability of the cathode material, thus affecting the cycling performance of the cathode material. In some embodiments, the ratio of m1 / m2 can be 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15% or any value within the range composed of any two of the above values.

[0036] In some embodiments, the cathode material further contains M2 element, and M2 element includes at least one of Mg, Ca, La, Y, Ti or Zr. The mass ratio of M2 element in lithium cobalt oxide is n, and 0 < n ≤ 1%. Adding M2 element to the cathode material can slow down the rapid change of the layer spacing during the insertion and extraction of active ions, thereby stabilizing the layered lithium cobalt oxide. At the same time, the doped M2 element can also reduce the oxygen activity of the cathode material, thereby improving the stability of the cathode material and further enhancing the safety and cycling life of the electrochemical device. If there is too much M2 element doped in lithium cobalt oxide, it will generate resistance to the insertion and extraction of active ions and affect the insertion and extraction and transmission of active ions. In some embodiments, n can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any value within the range composed of any two of the above values.

[0037] In some embodiments, the boron-containing compound includes at least one of boron-containing oxides or borates. The boron-containing oxides include at least one of B2O3, BO, HBO3, H3BO3, and the borates include at least one of Na2B4O7, NH4H2BO3, CaB2O4, Mg(B(OH)4)2. The above boron-containing oxides can uniformly coat the surface of lithium cobalt oxide, block the direct contact between the electrolyte and lithium cobalt oxide, reduce side reactions, and thus improve the cycling performance of the electrochemical device.

[0038] In some embodiments, the mass ratio of sodium superionic conductors is ω1, where 0 < ω1 ≤ 1%, based on the mass of the cathode material. Within this range, sodium superionic conductors in lithium cobalt oxide can increase the ionic conductivity of the cathode material while maintaining good specific capacity and low impedance, thereby improving the cycle performance and rate performance of the electrochemical device. If the mass ratio of sodium superionic conductors in the cathode material is large, i.e., a large number of sodium superionic conductors are formed on the surface of lithium cobalt oxide, it will not only reduce the specific capacity of the cathode material, but also increase the impedance of the cathode material since sodium superionic conductors are not electrochemical, affecting the cycle performance and rate performance of the cathode material. In some embodiments, ω1 can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any value within the range of any two of the above values.

[0039] In some embodiments, based on the mass of the cathode material, the mass ratio of boron in the boron-containing compound is ω2, where 0 < ω2 ≤ 0.5%. The boron-containing compound has poor conductivity and its effect on improving the electrical performance of the cathode material is not significant. Within the above-mentioned range, the mass ratio of boron in the boron-containing compound aims to minimize the impact on interfacial impedance after coating with the boron-containing compound, while reducing direct contact between lithium cobalt oxide and the electrolyte. If the mass ratio of boron in the boron-containing compound is large, it will increase the mass of the boron-containing compound, significantly increasing the interfacial impedance between the cathode material and the electrolyte, thereby worsening the impedance of the electrochemical device. In some embodiments, ω2 can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any value within the range of any two of the above values.

[0040] In some embodiments, 0 < ω1 + ω2 ≤ 1.5%. In the cathode material, sodium superionic conductors and boron-containing compounds within the above range are beneficial for increasing the ionic conductivity of the cathode material and improving the energy density of the electrochemical device; they can also reduce interfacial impedance by reducing side reactions between lithium cobalt oxide and the electrolyte, thereby improving the cycle performance of the cathode material. If ω1 + ω2 is large, the content of at least one of sodium superionic conductors and boron-containing compounds will be high, which will reduce the specific capacity of the cathode material and increase the interfacial impedance, thus affecting the cycle performance of the electrochemical device. In some embodiments, ω1 + ω2 can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any value within the range of any two of the above values.

[0041] In some embodiments, the lithium cobalt oxide is a single crystal particle with cracks, as shown in Figure 4. The lithium cobalt oxide has a layered structure with internal cracks. Some cracks are located inside the grain, while others extend from the grain to the grain surface. The direction of the cracks is parallel to the transition metal layer (Co layer). The presence of these cracks can reduce and release the stress generated by the lattice expansion and contraction process during charging and discharging, thereby suppressing the rapid propagation of lattice defects. This helps to improve the structural stability of the cathode material and improve electrochemical performance.

[0042] In some embodiments, the median particle size D of the sodium superionic conductor 50 The particle size is 50 nm to 100 nm. Sodium superionic conductors within this nanometer range are advantageous in improving the uniformity of lithium cobalt oxide coating. Furthermore, this particle size also helps increase the contact area between the sodium superionic conductor and the lithium cobalt oxide, reducing detachment and thus improving the stability of the sodium superionic conductor formed on the lithium cobalt oxide surface, thereby enhancing the stability of the cathode material. In some embodiments, the median particle size D of the sodium superionic conductor... 50 It can be 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or any value within the range of any two of the above values.

[0043] This application also provides a method for preparing a cathode material, including the following steps:

[0044] (1) Refine the NaSICON solid electrolyte.

[0045] Ball milling of NaSICON solid electrolyte refines its particle size, making it easier for NaSICON solid electrolyte to coat lithium cobalt oxide.

[0046] (2) The refined NaSICON solid electrolyte and lithium cobalt oxide are mixed and dispersed in a solvent to obtain a suspension.

[0047] The solid-liquid mass ratio of the suspension is 1:0.5 to 1:5, which helps to improve the uniformity of NaSICON solid electrolyte coating on lithium cobalt oxide.

[0048] (3) The suspension is dried so that the NaSICON solid electrolyte is coated on the surface of the lithium cobalt oxide to obtain an intermediate; the intermediate and the boron-containing compound are mixed evenly and then annealed.

[0049] Methods for drying suspensions include either spray drying or rotary evaporation drying.

[0050] The annealing temperature is 180–250℃, preferably 190–220℃. The annealing time is 6–24 hours, preferably 8–12 hours.

[0051] Boron-containing compounds include at least one of boron oxides or borates. Boron oxides include at least one of B₂O₃, BO, HBO₃, and H₃BO₃, while borates include at least one of Na₂B₄O₇, NH₄H₂BO₃, CaB₂O₄, and Mg(B(OH)₄)₂. When boric acid is used as the coating material, its low melting point (approximately 171°C) allows it to melt and form a liquid during preparation, uniformly adhering to the surface of the lithium cobalt oxide. Simultaneously, during the coating process, boric acid can remove residual lithium from the surface of the lithium cobalt oxide, thereby optimizing the capacity and cycle life of the electrochemical device and improving the stability of the coated lithium cobalt oxide.

[0052] (4) The annealed material is sieved and dispersed to obtain the positive electrode material.

[0053] The adhesive in the positive electrode material layer is used to bond the positive electrode material particles, thereby facilitating the formation of the film layer, and also improving the bonding force between the positive electrode material layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, adhesive polymers, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, polyolefin adhesives include at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0054] In some embodiments, the conductive agent includes carbon-based materials, metal-based materials, conductive polymers, or mixtures thereof. Examples of carbon-based materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fibers; examples of metal-based materials include metal powders or fibers of copper, nickel, aluminum, silver, etc.; and examples of conductive polymers include polyphenylene derivatives.

[0055] Negative electrode sheet

[0056] This application does not impose any particular limitation on the negative electrode sheet, as long as it can achieve the purpose of this application. For example, the negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector.

[0057] In this application, the negative electrode material layer can be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0058] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (such as carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.).

[0059] In this application, there are no particular limitations on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 12 μm, and the thickness of the negative electrode material layer is 30 μm to 130 μm. In this application, there are no particular limitations on the thickness of the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode sheet is 50 μm to 280 μm.

[0060] The negative electrode material layer of this application includes a negative electrode material, which may include, but is not limited to, graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiOx (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and spinel-structured lithium titanate lithiation TiO2-Li4Ti5O. 12 At least one of Li-Al alloy and metallic lithium.

[0061] The negative electrode material layer in this application may further include a negative electrode binder and a negative electrode conductive agent, or the negative electrode material layer may further include a negative electrode binder, a negative electrode conductive agent, and a thickener. This application does not particularly limit the types of negative electrode binders and negative electrode conductive agents, as long as they achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of the aforementioned positive electrode binders, and the negative electrode conductive agent may include, but is not limited to, at least one of the aforementioned positive electrode conductive agents. This application does not particularly limit the types of thickeners, as long as they achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose.

[0062] In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0063] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0064] Separating membrane

[0065] The material and shape of the separator used in the electrochemical device of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0066] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0067] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic materials. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.

[0068] The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0069] electrolyte

[0070] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0071] The organic solvent in the electrolyte of this application may be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the prior art. The additives in the electrolyte according to this application may be any additives known in the prior art that can be used as electrolyte additives. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or ethyl propionate.

[0072] In some embodiments, the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxapentane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one selected from fluoroethylene carbonate and adiponitrile.

[0073] According to some embodiments of this application, the electrochemical device of this application includes, but is not limited to, a lithium-ion electrochemical device. In some embodiments, the electrochemical device includes a lithium-ion electrochemical device.

[0074] This application also applies the electrochemical device to electronic devices, whereby the electrochemical device supplies power to the load in the electronic device. The electrochemical device in the aforementioned electronic device includes a positive electrode material, on which a sodium superionic conductor and a boron-containing compound are formed on the surface of the lithium cobalt oxide. This helps to reduce the interfacial impedance of the positive electrode material and decrease side reactions between the lithium cobalt oxide and the electrolyte, thereby improving the cycle performance and charging efficiency of the electrochemical device, and consequently increasing the lifespan and charging efficiency of the electronic device.

[0075] The electronic devices or apparatus described in this application are not particularly limited. In some embodiments, the electronic devices described in this application include, but are not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0076] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0077] Example 1

[0078] (1) Preparation of NaSICON type solid electrolyte

[0079] Li was prepared by solid-state reaction method. 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) and Li 1.5 Al 0.5 Ge 1.5 (PO4)3(LAGP)NaSICON solid electrolyte powder. The preparation process is as follows:

[0080] Preparation of Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP): According to Li 1.4 Al 0.4 Ti 1.6 The stoichiometric proportions of raw materials Li₂C₂O₄, Al(NO₃)₂·9H₂O, TiO₂, and NH₄H₂PO₄ were weighed out for (PO₄)₃. The weighed raw materials were placed in a ball mill jar and ball-milled to ensure thorough and homogeneous mixing. The mixed raw materials were then placed in a high-temperature furnace and held at 400°C for 2 hours to induce thermal decomposition, which promotes the chemical reaction. The sample was then heated to 800°C and held for 10 hours to further promote the reaction and crystal formation. After cooling, LATP solid electrolyte powder was obtained.

[0081] Preparation of Li 1.5 Al 0.5 Ge 1.5 (PO4)3(LAGP): Preparation of Li 1.5 Al 0.5Ge 1.5 Methods and preparation of (PO4)3(LAGP) Li 1.4 Al 0.4 Ti 1.6 The steps are the same as those for (PO4)3(LATP), except that TiO2 is replaced with GeO2.

[0082] (2) Preparation of lithium cobalt oxide

[0083] Cobalt sulfate, nickel sulfate, and manganese sulfate were weighed in a molar ratio of 90:5:5 and dissolved in deionized water by rapid stirring. After thorough mixing, ammonium carbonate was added to adjust the pH of the solution to 8-9, ensuring a complete reaction and producing a uniform carbonate precipitate. The precipitate was sintered at 650℃ for 12 hours, followed by crushing and sieving to obtain a metal oxide precursor. Sodium carbonate was mixed with the metal oxide precursor in a molar ratio of 0.45:1 and held at 850℃ for 48 hours. After cooling, it was crushed and sieved to obtain a sodium cobalt oxide precursor. The sodium cobalt oxide precursor, lithium nitrate, and lithium hydroxide were mixed in a molar ratio of 1:2:3 and reacted at 250℃ for 6 hours. After cooling, a mixture containing lithium cobalt oxide was obtained. The mixture was then crushed and washed repeatedly with deionized water to remove soluble sodium and lithium salts. After washing with deionized water until the conductivity of the supernatant is less than 200 uS / cm, the residual solid is centrifuged, dried and graded to finally obtain layered lithium cobalt oxide.

[0084] The elemental composition was determined using inductively coupled plasma mass spectrometry (ICP), and the chemical formula of the resulting layered lithium cobalt oxide was Li. 0.9 Na 0.003 Co 0.9 Ni 0.05 Mn 0.05 O2. Figure 1 shows the XRD pattern of the obtained layered lithium cobalt oxide. By comparing it with the standard PDF card, it can be seen that the material is a pure phase material with a P63mc (No. 186) crystal structure.

[0085] (3) Preparation of cathode materials

[0086] LATP powder was ball-milled in a ball mill jar to refine the powder, resulting in a median particle size of 50–100 nm, such as 73 nm, to improve the uniformity of LATP coating. The refined LATP material was then mixed with the prepared lithium cobalt oxide, with LATP accounting for 0.3% of the cathode material by mass. Deionized water was added at a solid-liquid mass ratio of 1:1, and the mixture was stirred until homogeneous, resulting in a suspension. The mass ratio of the suspension was 1:2. The suspension was then spray-dried to remove moisture, ensuring that LATP was uniformly distributed on the surface of the layered lithium cobalt oxide material.

[0087] The lithium cobalt oxide obtained through spray drying was weighed and mixed with boric acid (boron source) in a specific mass ratio, wherein the boron element accounted for 0.3% of the cathode material by mass. The uniformly mixed material was placed in a box furnace and annealed at 200°C. During annealing, the boric acid melted and uniformly coated the material surface. After cooling, the annealed product was sieved through a 200-mesh sieve to obtain the cathode material.

[0088] The cathode material prepared in Example 1 was tested by scanning electron microscopy (SEM). As shown in Figure 2, the LATP-coated particles on the surface of the cathode material are clearly visible. Figure 3 shows the surface EDS test results of the cathode material in Example 1. The line scan along the direction of the dashed arrow shows that LATP is mainly coated on the material surface in the form of dots, while boron is uniformly coated on the entire material surface.

[0089] Furthermore, the material was cut by plasma beam and the morphology of the grain cross section was observed by SEM. The test results are shown in Figure 4. Cracks exist in the lithium cobalt oxide single crystal particles in Figure 4 (elliptical dashed lines in Figure 4). Some cracks are located inside the grains, and some cracks extend from inside the grains to the grain surface. The direction of the cracks is parallel to the transition metal layer (Co layer). The presence of these cracks can reduce and release the stress generated by the lattice expansion and contraction process during charging and discharging, thereby inhibiting the rapid propagation of lattice defects. This is beneficial to improving the structural stability of the cathode material and improving the electrochemical performance of the electrochemical device.

[0090] Preparation of lithium-ion batteries:

[0091] The battery cell has a design size of 5 mm × 32 mm × 77 mm and a design capacity of 2 Ah.

[0092] Preparation of the positive electrode sheet: The positive electrode material prepared in Example 1, conductive carbon (SP), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.6:1.1:1.3 and thoroughly stirred in an N-methylpyrrolidone solvent system to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto a positive electrode current collector aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0093] Preparation of the negative electrode sheet: Commercial graphite, conductive carbon (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:1:1.5:1.5. An appropriate amount of water was added to adjust the viscosity of the slurry to 4000-6000 Pa·s, thus preparing the negative electrode slurry. The prepared negative electrode slurry was coated onto a copper foil used as a negative electrode current collector, dried, and cold-pressed to obtain the negative electrode sheet.

[0094] The positive and negative electrode sheets have a unit area capacity of approximately 2.6 mAh cm⁻¹. -2 and 2.7mAh cm -2 The corresponding negative / positive capacity ratio (N / P) is approximately 1.045. The positive and negative electrode sheets are separated using a 7µm polyethylene (PE) separator via a winding process. Ethylene carbonate / propylene carbonate / diethylene carbonate / propyl propionate (EC / PC / DEC / PP) in a volume ratio of 1:1:1:1 is mixed, and 1M LiPF6 is added to the solvent and mixed thoroughly. Then, 5wt.% fluoroolefin carbonate (FEC) and 2wt.% 1,3,6-hexamethylenetrionitrile (HTCN) are added as electrolyte additives, resulting in an electrolyte retention coefficient of 1.6 g / Ah. After aging, formation, and capacity testing, a lithium-ion battery is manufactured.

[0095] Example 2

[0096] The difference between Example 2 and Example 1 is that LATP is replaced with an equal amount of LAGP, while the rest of the preparation process is exactly the same as in Example 1.

[0097] Examples 3 to 8

[0098] The difference from Example 1 is that in the preparation step of layered lithium cobalt oxide, sodium carbonate and precursor are mixed evenly at a molar ratio of 0.45:1, and 0.2% Ca is incorporated in the form of Ca(OH)2. The boron coating amount in LATP and boron-containing compounds is adjusted according to Table 1. The rest of the preparation process is exactly the same as in Example 1.

[0099] Examples 9 to 14

[0100] The difference from Example 1 is that the Ni and Mn doping concentrations in the coprecipitation precursor material were adjusted, and 0.3% La was incorporated in the form of nano-La2O3 during the sintering process at 850℃. The boron coating amount in LAGP and boron-containing compounds was also adjusted. The specific material composition is shown in Table 1.

[0101] Examples 15 to 24

[0102] The difference from Example 1 is that the Ni and Mn doping concentrations in the co-precipitated precursor material were adjusted, and doping elements other than Ni and Mn were introduced during the sintering process at 850°C. Mg, Y, Ti and Zr elements were introduced in the form of nano MgO, nano Y2O3, nano TiO2 and nano ZrO2, respectively. The coating amounts of LATP and boric acid were also adjusted. The specific material composition is shown in Table 1.

[0103] Comparative Example 1

[0104] The difference from Example 1 is that, in the process of preparing lithium cobalt oxide, the metal oxide precursor was not doped with metal elements other than Co, such as Ni and Mn, and the lithium cobalt oxide was not coated. The specific material composition is shown in Table 1.

[0105] Comparative Example 2

[0106] The difference from Example 1 is that in the process of preparing lithium cobalt oxide, the metal oxide precursor is doped with Ni and Mn elements, but without any coating treatment. The specific material composition is shown in Table 1.

[0107] Scanning electron microscopy (SEM) tests were performed on the cathode material of Comparative Example 2. As shown in Figure 5, the surface of the lithium cobalt oxide material was relatively smooth, while the surface of Example 1 (Figure 2) had obvious coated particles attached, indicating that LATP had been coated on the lithium cobalt oxide.

[0108] Comparative Examples 3 to 5

[0109] The difference from Example 1 is that the precursor is doped with Ni and Mn elements, and the surface of the lithium cobalt oxide is coated with only one of NaSICON solid electrolyte or boron-containing compound. The specific material composition is shown in Table 1.

[0110] Performance testing

[0111] The XRD testing method includes: using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE) to test the cathode material, wherein the target material is Cu Kα, the test voltage is 40KV, the test current is 35mA, the scanning angle range is 10° to 90°, and the scanning rate is 0.02° / s.

[0112] The inductively coupled plasma mass spectrometry (ICP) testing method includes: using an inductively coupled plasma spectrometer (ICP, instrument model: PE Optima 7000DV) to test the content of elements such as Li and transition metals in the cathode material. First, weigh an appropriate amount of powder sample, add about 10 mL of aqua regia, and heat in a plate heater at about 185℃ for 30 to 50 minutes to ensure complete digestion of the sample, and then perform the test on the instrument.

[0113] The SEM testing method includes: taking material powder, observing it using a ZEISS SEM (Sigma-02-33), and performing elemental composition testing by EDS linear scanning.

[0114] To observe internal defects within grains, a slicing machine is used to slice the positive electrode sheet, obtaining a cross-section perpendicular to the surface of the positive current collector. A scanning electron microscope is then used to capture the cross-sectional backscattered image. Cracks within the grain can be observed on the cross-section; in the cross-sectional image, closed areas of a different color from the surrounding area are the cracks.

[0115] The performance of the lithium secondary batteries prepared in Examples 1-24 and Comparative Examples 1-5 was evaluated using the following methods, and the specific test results are listed in Table 1.

[0116] The test steps for initial charge / discharge efficiency include:

[0117] At room temperature (25°C), the lithium-ion battery was charged to 4.4V at 1.3C, and then further charged to 4.55V at 0.7C. The voltage was then maintained at a constant 4.55V until the current dropped to 0.05C. It was then discharged to 3.0V at 0.5C. This process was repeated twice, and the specific capacity of the cathode material was calculated based on the discharge capacity from the second discharge.

[0118] The battery cycle performance testing steps include:

[0119] At room temperature (25°C), the lithium-ion battery was charged to 4.4V at 2C, and then further charged to 4.55V at 1.3C. The voltage was then maintained at a constant 4.55V until the current dropped to 0.05C. It was then discharged to 3.0V at 1C. This charge-discharge cycle was repeated 300 times. The discharge capacity of the battery after 300 cycles was recorded, where C represents the current rate, 1C = 2A. The capacity retention rate of the battery was calculated using the following formula: Capacity retention rate = (Discharge capacity of the 300th cycle / Discharge capacity of the third cycle) * 100%.

[0120] Table 1

[0121] As can be seen from Table 1 above, compared with the uncoated lithium cobalt oxide in Comparative Example 1, the cycle performance of the lithium-ion batteries assembled with cathode materials coated with sodium superionic conductors and boron compounds in Examples 1 to 24 is improved. This indicates that the surface of the lithium cobalt oxide is coated with sodium superionic conductors and boron compounds, which is beneficial to improving the cycle performance of the cathode material.

[0122] Compared to Comparative Example 1, Comparative Example 2 contains lithium cobalt oxide doped with Ni and Mn elements. Comparative Example 2 shows improvements in both initial discharge specific capacity and 300-cycle retention rate, indicating that Ni and Mn elements affect the initial discharge specific capacity and cycle performance of the cathode material.

[0123] Compared to Comparative Examples 3 to 5, which only used either the sodium superionic conductor or the boron-containing compound to coat lithium cobalt oxide, Examples 1 and 2 used both the sodium superionic conductor and the boron-containing compound to coat lithium cobalt oxide. Table 1 shows that individual coating and co-coating have little impact on the initial discharge specific capacity of the cathode material, but the difference in cycle stability is very significant. The individually coated sample retained only about 60% of its capacity after 300 cycles, while the co-coated sample significantly improved to over 75%. This indicates that only when NaSICON solid electrolytes (LATP and LAGP) and the boron-containing compound (H3BO3) are co-coated can the cycle stability of the material be significantly improved.

[0124] NaSICON solid electrolyte material possesses relatively stable physicochemical properties and high conductivity, making it an excellent material for coating lithium cobalt oxide. However, due to the difficulty in forming a uniform coating layer on the surface of lithium cobalt oxide, complete coating is not easily achieved, leading to the presence of localized exposed defect sites on the lithium cobalt oxide, which affects the coating effect. When using boron-containing compounds such as H3BO3 for coating, H3BO3 has a low melting point (approximately 171℃). When the coating temperature exceeds its melting point, H3BO3 melts into a liquid state and uniformly adheres to the material surface, thereby reducing the number of exposed defect sites on the material surface, lowering the specific surface area of ​​the material, and thus reducing the direct contact between the cathode material and the electrolyte, avoiding the occurrence of interfacial side reactions. Furthermore, statistical analysis in this application shows that the specific surface area of ​​lithium cobalt oxide materials coated with H3BO3 is reduced by an average of 0.2–0.4 μm compared to uncoated materials. 2 / g. The coating layer includes both NaSICON and boron-containing compounds. NaSICON has high conductivity, which can improve the problem of increased interfacial impedance of the cathode material due to the poor conductivity of H3BO3. H3BO3 easily forms a uniform coating on the surface of lithium cobalt oxide, which can improve the problem of NaSICON not easily forming a uniform coating on the surface of lithium cobalt oxide. This gives the cathode material the advantages of high conductivity and stability, thereby improving the cycle stability of the cathode material.

[0125] In particular, when 0 < ω1 ≤ 1%, 0 < ω2 ≤ 0.5%, or 0 < ω1 + ω2 ≤ 1.5%, it is beneficial for ion transport, suppresses the increase in the impedance of the cathode material, and thus improves the cycle stability of the cathode material.

[0126] In Examples 9 to 14, the doping amounts of Ni and Mn also affect the first discharge specific capacity and cycling performance of the cathode material. The doping amount of Ni has a relatively small negative impact on the first discharge specific capacity of the cathode material, but the doping of Mn reduces the specific capacity of the material. In the cathode material, Mn is doped into the lattice in the form of Mn 4+ and cannot change during the charge-discharge process, showing electrochemical inertness. As the total doping amount of Ni and Mn increases, the cycling capacity retention rate of the cathode material first increases and then decreases. When the total doping amount of Ni and Mn is below 15%, the cathode material still has good first discharge specific capacity and cycling stability.

[0127] In Examples 15 to 18, on the basis of doping Ni and Mn in lithium cobalt oxide, M2 element is also doped. When 0 < n ≤ 1%, the comprehensive electrical performance improvement effect of lithium cobalt oxide is better.

[0128] In Examples 19 to 24, on the basis of doping Ni and Mn in lithium cobalt oxide, different M2 elements or multiple metal elements are co-doped, and the corresponding cathode materials all have good cycling capacity retention rates.

[0129] The above-disclosed are only the preferred embodiments of the present application. Of course, the present application cannot be limited thereby. Therefore, equivalent changes made in accordance with the present application still fall within the scope covered by the present application.

Claims

1. A cathode material, wherein, It includes lithium cobalt oxide and a coating layer formed on the lithium cobalt oxide. The coating layer includes a sodium superionic conductor and a boron-containing compound. The lithium cobalt oxide has a P63mc crystal structure, and the lithium cobalt oxide further contains an element M1, and M1 includes at least one of Ni or Mn.

2. The cathode material as described in claim 1, wherein, The sodium superionic conductor is Li 1+x Al x Ti 2-x (PO4)3 or Li 1+y Al y Ge 2-y (PO4)3, where 0≤x≤0.5, 0≤y≤1.

3. The cathode material as described in claim 1 or 2, wherein, 0 < m1 / m2 ≤ 15%, where m1 is the amount of substance of M1 and m2 is the sum of the amount of substance of M1 and the amount of substance of Co element.

4. The cathode material according to any one of claims 1 to 3, wherein, The positive electrode material further contains an element M2, and the element M2 includes at least one of Mg, Ca, La, Y, Ti, and Zr. The mass proportion of the element M2 in the lithium cobalt oxide is n, and 0 < n ≤ 1%.

5. The cathode material according to any one of claims 1 to 4, wherein, The boron-containing compound includes at least one of boron-containing oxides or borates. The boron-containing oxides include at least one of B2O3, BO, HBO3, and H3BO3. The borates include at least one of Na2B4O7, NH4H2BO3, CaB2O4, and Mg(B(OH)4)2.

6. The cathode material according to any one of claims 1 to 5, wherein, Based on the mass of the positive electrode material, the mass ratio of the sodium superionic conductor is ω1, and the mass ratio of boron element in the boron-containing compound is ω2. The positive electrode material satisfies at least one of the following conditions: (1) 0 < ω1 ≤ 1%; (2) 0 < ω2 ≤ 0.5%; (3) 0 < ω1 + ω2 ≤ 1.5%.

7. The cathode material according to any one of claims 1 to 6, wherein, The lithium cobalt oxide is single crystal particles, and the lithium cobalt oxide has cracks.

8. The cathode material according to any one of claims 1 to 7, wherein, The median particle size D of the sodium superionic conductor 50 The range is from 50nm to 100nm.

9. An electrochemical device comprising a positive electrode and a negative electrode, wherein, The positive electrode sheet includes a current collector and a positive electrode material layer provided on the current collector. The positive electrode material layer includes the positive electrode material according to any one of claims 1 to 8.

10. An electronic device, wherein, An electrochemical device including the one according to claim 9.

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