Positive electrode material and preparation method thereof, electrochemical device and electronic equipment

Abstract

The invention provides a positive electrode material and a preparation method thereof, an electrochemical device and electronic equipment, and particularly relates to the technical field of battery materials. The positive electrode material comprises an inner core and a coating layer, the inner core comprises a nickel-based layered transition metal oxide, and the molar ratio of the nickel element in the nickel-based layered transition metal oxide is greater than or equal to 60% based on the total amount of metal elements except lithium; the coating layer is coated on the surface of the inner core, the coating layer is an ion-electron mixed conductor layer, the material of the coating layer comprises Li7La3Zr2-x-yCoxMyO12, x is more than or equal to 0.3 and less than or equal to 0.5, y is more than or equal to 0 and less than or equal to 0.2, and M comprises one or more of Al, Nb, Ta, Mo and In. The surface of the nickel-based layered transition metal oxide is coated with the ion-electron mixed conductor layer, so that the speed of ions and electrons penetrating through the particle surface can be effectively improved, polarization is reduced, and the cycle performance and rate capability of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a cathode material and its preparation method, an electrochemical device, and an electronic device. Background Technology

[0002] With the widespread application of lithium-ion batteries in portable electronic devices, new energy vehicles, and large-scale energy storage systems, the market demand for battery energy density continues to rise. Nickel-based transition metal oxides (with a nickel molar percentage ≥ 60%) have become the core material for achieving high energy density in lithium-ion batteries due to their extremely high theoretical specific capacity. Compared to traditional ternary materials (with a nickel molar percentage below 60%), they can significantly extend the driving range of new energy vehicles or increase the energy storage capacity of energy storage batteries, making them the mainstream research and development direction for high-energy-density lithium-ion battery cathode materials.

[0003] However, the inherent interfacial instability of nickel-based transition metal oxides (with a nickel molar percentage ≥60%) severely limits their large-scale commercial application. Surface coating is one of the conventional methods to improve interfacial instability, but existing coating technologies have many problems: mainstream coating materials such as inert metal oxides and phosphates, although having certain chemical stability, are typical ionic and electronic insulators. After coating, they will hinder lithium-ion migration and increase electronic contact resistance, leading to increased battery interfacial impedance, decreased rate performance and capacity loss, forming a contradiction between improved stability and deteriorated kinetics; at the same time, existing coating layers have a single function and cannot synergistically solve the multiple complex interfacial problems faced by high-nickel materials, such as chemical corrosion, mechanical failure and electrochemical degradation. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention provides a cathode material and its preparation method, an electrochemical device and an electronic device to improve the technical problem of interface instability of nickel-based layered transition metal oxides.

[0005] To achieve the above and other related objectives, the present invention provides a cathode material comprising: a core and a coating layer; the core comprising a nickel-based layered transition metal oxide, wherein, based on the total amount of metal elements other than lithium, the molar percentage of nickel in the nickel-based layered transition metal oxide is greater than or equal to 60%; the coating layer covers the surface of the core, and the coating layer is an ion-electron hybrid conductor layer, the material of the coating layer comprising Li7La3Zr. 2-x-y Co x M y O 12 Where 0.3≤x≤0.5, 0≤y≤0.2, and M includes one or more of Al, Nb, Ta, Mo, and In.

[0006] In one embodiment of the present invention, the mass percentage of the coating layer to the mass of the core is a, then 0 < a ≤ 8%.

[0007] In one embodiment of the present invention, when the molar percentage of nickel in the nickel-based transition metal oxide is 60% to 80%, the mass percentage of the coating layer to the mass percentage of the core satisfies: 0 < a ≤ 5%.

[0008] In one embodiment of the present invention, when the molar percentage of nickel in the nickel-based transition metal oxide is greater than 80%, the mass percentage of the coating layer to the mass percentage of the core satisfies: 5% < a ≤ 8%.

[0009] This invention also provides a method for preparing a cathode material, characterized by comprising the following steps: Preparation of coating solution: According to the stoichiometry of the coating layer material, measure the lanthanum source, zirconium source, cobalt source and dopant source and dissolve them in the solvent to obtain the coating solution; Dispersion substrate: The precursor powder of nickel-based transition metal oxide is dispersed in deionized water to obtain a precursor slurry; Co-precipitation coating: The precursor slurry and the coating solution are mixed, and a precipitant and a complexing agent are added at the same time, so that the coating layer precursor is nucleated on the surface of the nickel-based morphological transition metal oxide precursor. After aging, washing and drying, the coated precursor is obtained. Sintering: The coated precursor is thoroughly mixed with the lithium source and then sintered to obtain the cathode material.

[0010] In one embodiment of the present invention, in the coprecipitation coating step, the temperature of the reaction system is controlled at 20~30℃, the pH value is 10~12, and the stirring rate is 450~2000rpm; and / or, the aging time is not less than 6 hours.

[0011] In one embodiment of the present invention, the precipitant includes one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0012] In one embodiment of the present invention, the complexing agent includes ammonia water, and the ratio of the molar amount of ammonia to the molar amount of total metal ions in the reaction system with respect to co-precipitation coating is 0.60 to 0.75.

[0013] In one embodiment of the present invention, the lithium source includes one or more of lithium carbonate and lithium hydroxide.

[0014] In one embodiment of the present invention, the lanthanum source includes one or more of lanthanum nitrate and hydrated lanthanum nitrate.

[0015] In one embodiment of the present invention, the zirconium source includes one or more of zirconium nitrate and hydrated zirconium nitrate.

[0016] In one embodiment of the present invention, the cobalt source includes one or more of cobalt nitrate and hydrated cobalt nitrate.

[0017] In one embodiment of the present invention, the doping source includes one or more of aluminum source, niobium source, tantalum source, molybdenum source, and indium source; wherein, the aluminum source includes one or more of aluminum nitrate and hydrated aluminum nitrate, the niobium source includes one or more of niobium pentachloride and niobium nitrate, the tantalum source includes one or more of tantalum chloride and tantalum nitrate, the molybdenum source includes one or more of ammonium molybdate and molybdenum nitrate, and the indium source includes one or more of indium nitrate and hydrated indium nitrate.

[0018] The present invention also provides an electrochemical device, the electrochemical device comprising the above-described positive electrode material, or comprising a positive electrode material prepared by the above-described preparation method.

[0019] The present invention also provides an electronic device comprising the above-described electrochemical device.

[0020] The beneficial effects of this invention are as follows: This invention constructs an ion-electron hybrid conductor coating layer on the surface of a nickel-based transition metal oxide material, the main material of which is Li7La3Zr. 2-x-y Co x M y O 12 Compared to conventional coating materials (such as single ionic conductors or insulating coating materials), it possesses superior ionic and electronic conductivity. This characteristic accelerates the transport rate of ions and electrons on the surface of the cathode particles, effectively reducing interfacial polarization during charging and discharging. It can meet the rapid charge transfer requirements under high-rate conditions (such as fast charging scenarios) while reducing capacity decay caused by polarization accumulation during long-term cycling, significantly improving the rate performance and cycle life of the battery.

[0021] Furthermore, ion-electron hybrid conductor materials can form a uniform, continuous coating layer on the surface of nickel-based transition metal oxide materials, and can actively fill the natural trenches between primary cathode particles. On the one hand, this coating layer can act as a physical barrier, significantly reducing the direct contact between the nickel-based transition metal oxide cathode and the electrolyte, suppressing interfacial side reactions such as lattice oxygen evolution and transition metal dissolution under high voltage from the source, thereby reducing active lithium consumption and interfacial impedance growth. On the other hand, the trench-filling structure can enhance the bonding force between cathode particles, improve the mechanical stability of the material, avoid interfacial failure caused by particle breakage during cycling, and further ensure the reliability of the battery during long-term service. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0023] In the attached diagram: Figure 1 A scanning electron microscope (SEM) image of the core material in a cathode material provided in an embodiment of the present invention; Figure 2 This is a SEM image of a cathode material provided in an embodiment of the present invention; Figure 3 This is a SEM image of a cathode material provided in an embodiment of the present invention; Figure 4 These are EDS surface scan images of the cathode material provided in Embodiment 2 of the present invention, wherein... Figure 4 (a) in the diagram is the distribution of all elements. Figure 4 (b) in the diagram shows the distribution of Ni elements. Figure 4 (c) in the diagram represents the distribution of Zr elements; Figure 4 (d) in the diagram represents the distribution of Co. Figure 4 (e) in the diagram represents the distribution of the Mn element; Figure 4 (f) in the diagram represents the distribution of La elements.

[0024] Figure 5 This is a flowchart illustrating a method for preparing a cathode material according to an embodiment of the present invention. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0026] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0027] 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0028] The terms or phrases used in this article have the following meanings: In this article, the terms "multiple," "various," and "multiple times" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0029] In this document, terms such as “preferred,” “ideal,” “further,” “even more,” and “particularly” are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0030] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0031] While nickel-based transition metal oxides (based on the total amount of metal elements other than lithium, with a molar percentage of nickel greater than or equal to 60%) possess high theoretical specific capacity, they still suffer from some unavoidable defects in practical applications, among which interface problems are particularly prominent. The interface problems of high-nickel materials are complex, involving chemical, mechanical, and electrochemical processes: Firstly, there is the problem of chemical corrosion, where residual alkaline substances such as LiOH and Li₂CO₃ on the material surface easily react with the electrolyte, leading to capacity decay and gas generation; secondly, there is the problem of mechanical failure, where Ni… 3+ / Ni 4+ The repeated changes in the ionic radius cause repeated volume expansion and contraction of the crystal lattice, leading to microcracks at the grain boundaries and disrupting the integrity of the electrode structure. Thirdly, there is the problem of electrochemical degradation. Under high-voltage conditions, the material is prone to irreversible phase transformation from a layered structure to a spinel or rock salt phase. Simultaneously, surface oxygen atoms escape, forming oxygen vacancies, significantly reducing the Li... + Migration rate.

[0032] Surface coating is a common method to improve the interface problems of high-nickel materials. However, most of the current mainstream coating materials are inert metal oxides (such as Al2O3 and TiO2). While these materials have certain advantages in chemical stability, they are typical ionic and electronic insulators, which severely hinder the migration of lithium ions at the electrode / electrolyte interface and increase electronic contact resistance. This leads to a significant increase in the interfacial impedance of the battery, resulting in a decrease in rate performance and capacity loss. Although coating improves stability, it sacrifices the battery's crucial kinetic performance. Moreover, existing coating layers have a single function, only solving one type of interface problem and failing to synergistically address the multiple interface problems of high-nickel materials.

[0033] Based on this, the present invention provides a cathode material, a method for preparing the cathode material, an electrochemical device comprising the cathode material, and an electronic device comprising the electrochemical device. By constructing an ion-electron hybrid conductor coating layer on the surface of a nickel-based metamorphic transition metal oxide material, the rate at which ions and electrons pass through the particle surface can be increased, polarization can be reduced, thereby improving the cycle performance and rate performance of the battery.

[0034] The cathode material of the present invention includes a core and a coating layer, wherein the core is the active component in the cathode material, the core includes a nickel-based layered transition metal oxide, and the molar percentage of nickel in the nickel-based layered transition metal oxide is greater than or equal to 60% based on the total amount of metal elements other than lithium.

[0035] In some embodiments, the chemical formula of the nickel-based transition metal oxide is LiNi. b Co c Mn z A a O2, where 0.6 ≤ b < 1, 0 ≤ c < 0.4, 0 < z ≤ 0.4, 0 ≤ a ≤ 0.1, b + c + z + a = 1, and A represents a doping element selected from one or more of Al, Zr, Cr, Zn, Bi, La, Ti, and Mg. Those skilled in the art should understand that the core can be an undoped nickel-based layered transition metal oxide (i.e., a = 0). For example, b can be 0.6, 0.8, 0.9, or 0.95, etc.; the values ​​of c and z are not specifically limited, as long as b + c + z = 1 is satisfied. For example, c can be 0, 0.1, 0.2, 0.3, or 0.35, etc.; z can be 0.05, 0.1, 0.2, 0.3, or 0.4, etc. In some optional embodiments, the core can be a ternary material, such as LiNi. 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9Co 0.05 Mn 0.05 O2, etc.; the core can also be a binary material, such as LiNi. 0.8 Mn 0.2 O2, LiNi 0.7 Mn 0.3 O2, etc. The core can also be a doped nickel-based layered transition metal oxide (i.e., a > 0). The doping element can be Al, or Al and Zr, or a combination of three or more elements such as Ti, Mg, and Y. The total molar amount of the doping elements, a, does not exceed 0.1; for example, a can be 0.01, 0.05, 0.1, etc. In some optional embodiments, the core is LiNi. 0.8 Co 0.1 Mn 0.05 Al 0.05 O2 or LiNi 0.9 Co 0.05 Mn 0.04 Al 0.01 O2, etc.

[0036] The cladding layer coats the surface of the core. This cladding layer is an ion-electron hybrid conductor layer, meaning that the main material of the cladding layer is an ion-electron hybrid conductor with the general chemical formula Li7La3Zr. 2-x-y Co x M y O 12 Where 0.3≤x≤0.5, 0≤y≤0.2, and M includes one or more of Al, Nb, Ta, Mo, and In. For example, x can be 0.3, 0.4, or 0.5, etc., M represents the dopant element, which can be Al, Nb, or a combination of Ta and Mo, etc., and y represents the total amount of dopant element M. For example, y can be 0, 0.1, or 0.2, etc. The above material is based on Li7La3Zr2O. 12 (LLZO) is used as the matrix, and Co and M elements are doped into its lattice to form the matrix.

[0037] LLZO possesses excellent lithium-ion conductivity, chemical stability, and mechanical strength and structural robustness, but its electronic conductivity is relatively low. Doping LLZO with Co can achieve the desired Zr content. 4+ Site substitution, due to the lower Co valence state compared to Zr. 4+ To maintain lattice electrical neutrality, the system generates free electrons (e electrons). - ) and will part of Co 2+ Oxidized to Co 3+ Formation of Co 3+ / Co 2+Redox couples compensate for charge, thus providing a sufficient source of charge carriers for electron transport. Simultaneously, as a transition metal, Co's valence d-orbital electrons exhibit strong delocalization. After doping, the d-orbitals of Co form "dp conjugation" with the 2p orbitals of O in LLZO, breaking the electronic insulation property of the wide bandgap of pure LLZO. This allows electrons to migrate rapidly between adjacent Co ions via "small polaron hopping," forming continuous electron transport channels. Furthermore, Co doping introduces a small number of oxygen vacancies or lattice distortions due to the difference in ion radii between Co and Zr. These defects can act as electron "transfer stations," lowering the migration energy barrier and simultaneously weakening Li... + The binding effect with the crystal lattice prevents Li from + Migration interferes with electron pathways, further optimizing the electron transport environment. Therefore, Co doping transforms LLZO into an ion-electron hybrid conductor material with both ion and electron transport capabilities. Furthermore, M doping can further enhance the ionic conductivity of LLZO materials. The coating layer of this invention can form a dense physical barrier on the surface of nickel-based transition metal oxides, suppressing the side reactions between residual alkali on the surface of high-nickel materials and the electrolyte, while simultaneously providing a suitable environment for Li... + It provides a continuous transport path for electrons, increases the rate at which ions and electrons pass through the particle surface, reduces polarization, and thus improves the cycle life and rate performance of the battery.

[0038] Please see Figures 1 to 3 ,in, Figure 1 This is a scanning electron microscope (SEM) image of the core material (before coating) in a cathode material according to an embodiment of the present invention. Figure 2 This is a SEM image of a cathode material (i.e., a coating layer formed on the surface of the core) provided in an embodiment of the present invention. Figure 3 This is a high-magnification SEM image of the cathode material provided in an embodiment of the present invention. Before coating ( Figure 1 SEM images of the core material show that the core particles have regular morphology, uniform size distribution, smooth and clean surface, and clear outline. They exist mostly as independent particles or slightly aggregated, with no obvious foreign matter attached. SEM images after coating (Figure 2) show that fine coating phases adhere to the surface of the core particles and the interparticle spaces, resulting in a rougher overall morphology, reduced regularity, and partial coverage of the original particle outlines, presenting a composite structure of coating layer and core particles. Further observation at high magnification (…) Figure 3The small-particle coating material forms a continuous and uniform coating layer on the core surface, while also filling the gaps and grooves between the core particles. Multiple randomly selected fields of view were observed using SEM, and the particle size (calculated as the equivalent diameter based on the projected area) of at least 10 coating material particles in each field of view was statistically analyzed. The arithmetic mean of all statistically analyzed particles was taken as the average particle size of the coating material, which was approximately 50 nm.

[0039] The aforementioned coating material can form a uniform and continuous coating layer on the surface of nickel-based transition metal oxide materials, and can actively fill the natural gaps and grooves between primary particles of nickel-based transition metal oxides, achieving tight adhesion at the interface. The uniformity of the coating layer was verified by elemental distribution characterization using an energy dispersive spectroscopy (EDS) instrument. The test results are shown in Figure 4: As can be seen from the EDS elemental distribution map, the characteristic elements (Ni, Mn) of the core nickel-based transition metal oxide are uniformly distributed throughout the particle area, while the distribution range of the characteristic elements (Zr, La) of the coating layer completely overlaps with that of the core characteristic elements, and there is no obvious enrichment or deficiency on the particle surface, confirming that the coating layer of the present invention has uniformly and completely covered the surface of the core material. This coating layer can act as a physical barrier, significantly reducing the direct contact between nickel-based layered transition metal oxides and the electrolyte. It suppresses interfacial side reactions such as lattice oxygen evolution and transition metal dissolution under high voltage from the source, reducing active lithium consumption and interfacial impedance growth. On the other hand, the structure that fills the trenches can enhance the bonding force between cathode particles, improve the mechanical stability of the material, avoid interfacial failure caused by particle breakage during cycling, and further ensure the reliability of the battery in long-term service.

[0040] In some embodiments, the mass percentage of the coating layer to the core mass is 'a', where 0 < a ≤ 8%. For example, a can be 1%, 3%, 5%, or 8%. If the coating layer is too thin, a complete and uniform coating layer cannot be formed on the surface of the core particles, making it difficult to adequately isolate the active material from the electrolyte. This results in numerous interfacial side reactions and limited cycle life optimization. Furthermore, an incomplete coating layer cannot effectively buffer the stress generated by lattice stretching during cycling, and the risk of particle cracking remains high. If the coating layer is too thick, excessive coating material (non-active material) will dilute the proportion of the core (active material), directly leading to a decrease in the theoretical capacity of the cathode material. The applicant's research found that increasing the nickel content in nickel-based transition metal oxides significantly exacerbates their interfacial reactivity (increased surface residual alkali, accelerated dissolution of transition metal ions), structural instability (increased volume expansion rate, increased grain boundary microcracks and lithium-nickel mixing), and electrochemical degradation risk (accelerated phase transition and oxygen deficiency). At the same time, it increases particle surface roughness and porosity, and makes secondary agglomeration more obvious. Therefore, the higher the nickel content in nickel-based transition metal oxides, the higher the coating amount needs to be to match its enhanced instability, and prevent low coating amount from only forming discontinuous local protection, which is difficult to cover dense active sites, resist mechanical stress, or eliminate protection blind spots.

[0041] In some embodiments, the core is a nickel-based transition metal oxide with a nickel molar ratio of 60-80%. In this case, the mass percentage 'a' of the coating layer to the core satisfies 0 < a ≤ 5%, for example, a can be 1%, 2%, 3%, 4%, or 5%, etc. For example, the core is LiNi. 0.6 Co 0.1 Mn 0.3 O2, where a can be 1%; or the kernel is LiNi. 0.7 Co 0.1 Mn 0.2 O2, where a can be 3%; or the kernel is LiNi. 0.8 Co 0.1 Mn 0.1 O2, a can be 5%, etc.

[0042] In some embodiments, the core is a nickel-based transition metal oxide with a nickel molar percentage of 80% or more. In this case, the mass percentage 'a' of the coating layer to the core satisfies 5% < a ≤ 8%, for example, it can be 5.5%, 6%, 7%, or 8%, etc. For example, the core is LiNi. 0.9 Co 0.05 Mn 0.05 O2, where a can be 6%; or the kernel is LiNi. 0.92 Co 0.03 Mn 0.05 O2, where a can be 7%; or the kernel is LiNi. 0.95 Co 0.02 Mn 0.03 O2, a can be 8%, etc.

[0043] This invention adjusts the coating amount based on the nickel content in the core: for cores with relatively low nickel content, a low coating amount is used to minimize the impact on the specific capacity of the cathode material while suppressing basic corrosion and slight volume expansion; for cores with relatively high nickel content, an appropriate high coating amount is used to construct a dense and complete protective layer to block severe chemical corrosion and alleviate significant grain boundary stress and phase transition risks; it also avoids the problems of insufficient coating leading to protection failure or excessive coating causing ion transport obstruction and increased costs. Ultimately, while improving the cycle life, rate performance, and safety performance of the material, it also takes into account the cost controllability and process feasibility of industrial production, maximizing the performance potential of materials with different nickel contents.

[0044] The present invention also provides a method for preparing the above-mentioned cathode material. The preparation method adopts a co-precipitation method for preliminary coating, followed by a one-time sintering. Compared with the traditional solid-phase coating method, it can obtain a uniform, dense coating layer that is firmly bonded to the core. Moreover, the preparation method does not require the pre-preparation of coating material powder, reducing process steps and energy consumption.

[0045] Please see Figure 5 The preparation method of the above-mentioned cathode material includes the following steps: S1. According to the stoichiometry of the coating material, measure the lanthanum source, zirconium source, cobalt source and dopant source and dissolve them in a solvent to obtain the coating solution; S2. Disperse the nickel-based transition metal oxide precursor powder in deionized water to obtain a precursor slurry. S3. Mix the precursor slurry and coating solution, and add precipitant and complexing agent at the same time, so that the coating layer precursor is nucleated on the surface of the nickel-based transition metal oxide precursor. After aging, washing and drying, the coated precursor is obtained. S4. After thoroughly mixing the coating precursor with the lithium source, sintering is performed to obtain the cathode material.

[0046] Specifically, step S1 involves preparing the coating solution, and the coating layer material is Li7La3Zr. 2-x-y Co x M y O 12 Where 0.3≤x≤0.5, 0≤y≤0.2, and M includes one or more of Al, Nb, Ta, Mo, and In. When preparing the coating solution, based on the stoichiometry of the coating material, first measure the lanthanum source, zirconium source, cobalt source, and M dopant source (if the coating material is not doped with element M, i.e., y is 0, then it is not necessary to measure the M dopant source). The lanthanum source is selected from one or more of lanthanum nitrate (La(NO3)3) and hydrated lanthanum nitrate. For example, hydrated lanthanum nitrate can be La(NO3)3. 6H2O; the zirconium source includes one or more of zirconium nitrate (Zr(NO3)4) and hydrated zirconium nitrate, such as Zr(NO3)4. 5H2O, etc.; cobalt sources include one or more of cobalt nitrate (Co(NO3)3) and hydrated cobalt nitrate, such as Co(NO3)3. 6H2O, etc. The M doping source includes one or more of aluminum, niobium, tantalum, molybdenum, and indium sources, which are specifically determined by the doping elements in the coating material. For example, if the doping element is Al, the M doping source is an aluminum source, including one or more of aluminum nitrate (Al(NO3)3) and hydrated aluminum nitrate (Al(NO3)3·9H2O, etc.); if the doping element is Nb, the M doping source is a niobium source, including one or more of niobium pentachloride (NbCl5) and niobium nitrate (Nb(NO3)5); if the doping element is Ta, the M doping source is a tantalum source, including one or more of tantalum chloride (TaCl5) and tantalum nitrate (Ta(NO3)5); if the doping element is Mo, the M doping source is a molybdenum source, including one or more of ammonium molybdate (NH4)2MoO4 and molybdenum nitrate (Mo(NO3)3); if the doping element is In, the M doping source is an indium source, including indium nitrate (In(NO3)6) and hydrated indium nitrate (In(NO3)3·5H2O, etc.). Then, the weighed raw materials are placed in a solvent and stirred thoroughly until no precipitate remains, thus obtaining the coating solution. There are no restrictions on the type of solvent used here, as long as the above raw materials are completely dissolved. For example, the lanthanum source is La(NO3)3, the zirconium source is Zr(NO3)4, the cobalt source is Co(NO3)3, and the M doping source is Nb(NO3)5. Ethanol can be selected as the solvent to dissolve each raw material. There are no special restrictions on the specific ratio between the solvent and each raw material, as long as all raw materials are completely dissolved.

[0047] The chemical formula of the nickel-based transition metal oxide precursor in step S2 is Ni. b Co c Mn z A a (OH)₂, wherein 0.6≤b≤1, 0≤c≤0.4, 0≤z≤0.4, 0≤a≤0.1, b+c+z+a=1, and A is selected from one or more of Al, Y, Zr, Cr, Zn, Bi, La, Ti, and Mg. The stoichiometric ratios of the elements in the precursor are consistent with the chemical formula of the nickel-based transition metal oxide to be prepared. This precursor can be purchased commercially or prepared using conventional methods in the art.

[0048] An example of the precursor preparation process is as follows: First, a solution containing a transition metal element is prepared according to the chemical formula of the nickel-based transition metal oxide. This transition metal element includes Ni and Mn, or Ni, Co, and Mn. For example, a sulfate, nitrate, acetate, or chloride containing a transition metal element can be dissolved in deionized water to obtain a solution containing the transition metal element. Furthermore, a sulfate solution containing a transition metal element is preferred due to its low cost, good solubility, and low impurity content. If the nickel-based transition metal oxide to be prepared contains a dopant element, a dopant source, such as an Al source, Y source, or Zr source, needs to be added to the solution containing the transition metal element. The type of dopant source must correspond to the dopant element, and then the solution is stirred until completely dissolved.

[0049] Then, the pH and temperature of the solution are adjusted to allow the transition metals to co-precipitate and obtain the precursor. The pH and temperature can be selected based on the type of salt solution. For example, when using a sulfate solution, the pH of the mixture is 9.5–11, such as 9.5, 10, or 11, etc. If the pH is too low, Ni / Co / Mn precipitation will be incomplete; if the pH is too high, the precipitation rate will be too fast, leading to uneven particle morphology or agglomeration. The temperature is controlled at 40–60°C, such as 40°C, 50°C, or 60°C, etc. At this temperature, the reaction rate is moderate, which is conducive to the formation of spherical precursors with good crystallinity and uniform particle size.

[0050] Next, the nickel-based transition metal oxide precursor is added to a pre-dispersion vessel, and an appropriate amount of deionized water (or other solvent) is added and stirred to form a homogeneous and stable precursor slurry. In this step, the ratio of deionized water to precursor is controlled so that the solid content of the precursor slurry is 20% to 40% to ensure complete dispersion of the precursor particles and avoid agglomeration, laying the foundation for subsequent uniform coating. For example, the solid content of the precursor slurry can be 20%, 30%, or 40%, etc.

[0051] It should be noted that steps S1 and S2 are not sequential; S1 can be executed first, followed by S2; or S2 can be executed first, followed by S1; or S1 and S2 can be executed simultaneously. The amount of coating material used in step S1 and the amount of layered oxide precursor used in step S2 are calculated based on the mass percentage of the coating layer to the core in the cathode material to be prepared.

[0052] Step S3, co-precipitation coating, involves continuously and stably pumping the coating solution obtained in step S1, the precursor slurry obtained in step S2, along with the precipitant and complexing agent, into one or more co-precipitation reactors connected in series using a precision metering system. By controlling the reaction temperature, pH value, and stirring rate, the coating layer precursor undergoes heterogeneous nucleation and growth on the surface of the nickel-based transition metal oxide precursor. Simultaneously, the pH is monitored in real-time using an online pH meter, and the precipitant feed rate is automatically adjusted via a feedback system to stabilize the pH value within a set range. The precision metering system, co-precipitation reactor, and feedback system used in this step are all conventional reaction devices in the field and will not be described in detail here.

[0053] In some embodiments, during the coprecipitation coating process, the temperature of the reaction system is 20~30°C, for example 20°C, 25°C or 30°C; the pH value of the reaction system is 10~12, for example 10, 11 or 12, etc.; the stirring rate is 450~2000 rpm, for example 450 rpm, 900 rpm, 1300 rpm, 1700 rpm or 2000 rpm, etc.

[0054] In some embodiments, the precipitant includes one or more of sodium hydroxide (NaOH), potassium hydroxide (KOH), and lithium hydroxide (LiOH). These precipitants can be used alone or in combination, for example, NaOH as the precipitant, or a combination of NaOH and KOH, etc. The amount of precipitant added is adjusted according to the pH value of the reaction system.

[0055] In one embodiment, the complexing agent includes ammonia (NH3·H2O), and the amount of ammonia added is such that the ratio of the molar amount of ammonia to the molar amount of total metal ions in the reaction system is 0.60 to 0.75. For example, it can be 0.6, 0.65, 0.70, or 0.75, etc.

[0056] After the co-precipitation reaction is completed, the slurry flowing out of the reactor enters the aging tank and is left to stand for a long time to allow the crystallization of the coating layer to be more complete and the reaction to be more thorough. The aging time is at least 6 hours, and further, the aging time is controlled between 6 and 10 hours, for example, 6 hours, 8 hours or 10 hours, etc. Insufficient aging time will result in incomplete reaction, and excessive aging time will affect production efficiency.

[0057] The aged slurry is subjected to solid-liquid separation using a diaphragm filter press or centrifuge to obtain a filter cake. The filter cake is then subjected to multiple countercurrent washings with hot deionized water on the filter press to thoroughly remove residual sodium. + NO3 - NH4 + Impurity ions, etc.

[0058] The washed wet filter cake is then dried to obtain the core-shell structured precursor powder. The drying method is not limited here. For example, the washed wet filter cake is fed into a disc dryer, spray dryer, or belt dryer for drying to obtain a dried, coated core-shell structured precursor powder.

[0059] Step S4, the sintering step, involves thoroughly mixing the core-shell precursor powder obtained in step S3 with a lithium source. High-efficiency mixers, such as V-type mixers or three-dimensional motion mixers, can be used for mixing. The uniformly mixed material is then placed in a sintering container for high-temperature calcination. This causes the core precursor to undergo a lithiation reaction, crystallizing into a nickel-based transition metal oxide. The outer shell coating precursor reacts with lithium to crystallize into the target ion-electron hybrid conductor coating layer. The lithium source is selected from lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH). The amount of lithium added, based on the lithium element content, has a molar ratio of lithium element to the total required lithium element for both the core and coating precursors of 1.02 to 1.05. For example, this ratio can be 1.02, 1.03, 1.05, etc. A slight excess of lithium element prevents lithium deficiency due to evaporation during sintering while avoiding resource waste due to excessive lithium content.

[0060] In some optional embodiments, the sintering temperature in the sintering step is 700℃~750℃, such as 700℃, 730℃, or 750℃, etc.; the sintering time is 8~12h, such as 8h, 10h, or 12h, etc. By controlling the sintering temperature and sintering time, lithium can be uniformly doped into the crystal lattice to form a stable layered structure, while reducing the formation of impurity phases inside the matrix.

[0061] Afterwards, the sintered block material is gently pulverized by an air jet mill to restore it to the ideal particle size distribution. Large particles, foreign magnetic objects, and other foreign matter are removed by a vibrating screen and an iron remover, thus obtaining a cathode material with a uniform coating layer of nickel-based morphological transition metal oxide.

[0062] This invention employs a co-precipitation coating method. After coating, the coating layer is formed simultaneously with the formation of a nickel-based transition metal oxide by a single sintering process. Compared with traditional solid-phase coating methods, the preparation method of this invention can form a uniform and continuous coating layer on the surface of the nickel-based transition metal oxide material. It can also actively fill the natural gaps and grooves between the primary particles of the nickel-based transition metal oxide, achieving a tight interface. This results in a uniform, dense coating layer that is firmly bonded to the core. Furthermore, this preparation method does not require the pre-preparation of coating material powder, reducing process steps and energy consumption.

[0063] The present invention also provides an electrochemical device comprising the above-described positive electrode material or a positive electrode material prepared by the above-described preparation method.

[0064] In one embodiment, the electrochemical device includes a lithium-ion battery, which can be a liquid lithium-ion battery (with a non-aqueous electrolyte) or a solid lithium-ion battery (with a solid electrolyte), and there is no limitation herein.

[0065] The following is a detailed description of the structure of a liquid lithium-ion battery, taking it as an example: A lithium-ion battery includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator.

[0066] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive current collector is, for example, aluminum foil or carbon-coated aluminum foil, and has two surfaces disposed opposite to each other along its thickness direction. The positive active material layer can be disposed on one surface of the positive current collector or on both surfaces. The positive active material layer includes a positive active material, a positive conductive agent, and a positive binder, wherein the positive active material is the positive material described above in this invention. The positive binder includes any one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, polyamide, polyacrylonitrile, polyacrylate, polyethylene ether, polymethyl methacrylate, ethylene-propylene-diene terpolymer, polyhexafluoropropylene, etc. Exemplarily, the positive binder can be polyvinylidene fluoride or polytetrafluoroethylene, etc. The positive electrode conductive agent includes, but is not limited to, one or more of conductive carbon black (SP), acetylene black, carbon nanotubes, carbon fibers, and graphene. For example, the conductive agent is conductive carbon black; or a combination of carbon fibers and conductive carbon black; or a combination of carbon nanotubes and graphene, etc. The ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder can be set according to conventional settings in the art.

[0067] The preparation process of the positive electrode sheet is as follows: First, the positive active material, positive conductive agent and positive binder are mixed and stirred evenly in a solvent such as N-methylpyrrolidone (NMP) according to the set ratio to form a positive slurry. Then, the positive slurry is coated on the positive current collector. After drying, rolling, cutting and other processes, the positive electrode sheet is obtained.

[0068] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative current collector is selected, for example, from copper foil or carbon-coated copper foil, and has two surfaces disposed opposite to each other along its thickness direction. The negative active material layer can be disposed on one surface or both surfaces of the negative current collector. The negative active material layer includes a negative active material, a negative conductive agent, a negative binder, and a thickener. The specific types of the negative active material, negative conductive agent, negative binder, and thickener are not specifically limited here; materials known in the art for use in lithium-ion batteries can be used, and those skilled in the art can select them according to actual needs.

[0069] For example, the negative electrode active material includes, but is not limited to, artificial graphite, natural graphite, silicon carbide materials, etc. The negative electrode conductive agent is selected from one or more of acetylene black, conductive carbon black (Super P), carbon fiber (VGCF), carbon nanotubes (CNT), Ketjen black, and graphene; for example, it can be acetylene black, conductive carbon black, or a combination of carbon fiber and carbon nanotubes, etc. The negative electrode binder is selected from any one of vinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and styrene-butadiene rubber, or a combination of several in any proportion; for example, it can be vinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, or styrene-butadiene rubber, etc. The thickener is selected from sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0070] The preparation process of the negative electrode sheet is as follows: First, the negative electrode active material, negative electrode conductive agent, negative electrode binder and thickener are mixed and stirred evenly in a solvent such as deionized water according to the set ratio to form a negative electrode slurry. Then, the negative electrode slurry is coated on the negative electrode current collector. After drying, rolling, cutting and other processes, the negative electrode sheet is obtained.

[0071] A separator is placed between the positive and negative electrodes to separate them, preventing short circuits inside the battery. It also allows lithium ions to move between the positive and negative electrodes, facilitating the charging and discharging process. The separator can be made of porous materials such as polyethylene (PE), polypropylene (PP), glass fiber, or composite membranes.

[0072] Non-aqueous electrolytes play a role in conducting lithium ions during battery charging and discharging. Non-aqueous electrolytes include organic solvents and lithium salts. The lithium salt can be selected from one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). Further, lithium hexafluorophosphate or a combination of lithium hexafluorophosphate and other lithium salts with superior overall performance is selected, such as a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The organic solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0073] In some optional embodiments, the non-aqueous electrolyte also includes functional additives such as fluoroethylene carbonate (FEC), propylene-1,3-sulfonyl lactone (PST), tetravinylsilane (TVSI), vinylene carbonate (VC), vinyl sulfate (DTD), etc., which can be added according to the actual production needs.

[0074] Battery assembly: The prepared positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The bare cells are obtained by winding or stacking. The bare cells are then installed into the battery casing and thoroughly baked until the water content is below 450 ppm. After liquid injection, formation, sealing, and inspection, a lithium-ion battery is obtained.

[0075] In other embodiments, the lithium-ion battery is a solid-state lithium-ion battery. The electrolyte of the solid-state lithium-ion battery is solid. Common solid electrolytes include oxide solid electrolytes, halide solid electrolytes, sulfide solid electrolytes, etc., which will not be elaborated here. Those skilled in the art can choose according to actual production needs.

[0076] It should be noted that the structures not described in detail in the above lithium-ion batteries can all be set up with reference to existing technologies, and will not be elaborated here.

[0077] The present invention also provides an electronic device comprising the above-mentioned lithium-ion battery, which can be used in the form of a single cell, a battery module, or a battery pack to power the electronic device.

[0078] In some embodiments, electronic devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.

[0079] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0080] Example 1 This embodiment provides a cathode material comprising a core and a coating layer, wherein the core has the chemical formula LiNi. 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM811) is coated with Li7La3Zr. 1.7 Co 0.3 O 12 The mass of the coating layer is 2% of the core mass; the particle size of the coating layer material is approximately 50 nm.

[0081] The preparation method of the above-mentioned cathode material is as follows: Step 1: According to the stoichiometric ratio of the coating material, accurately prepare the coating material solution by dissolving appropriate amounts of La(NO3)3, Zr(NO3)4, and Co(NO3)3 in ethanol and stirring until no precipitate remains. Step 2: The precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 powder is added to a dispersion vessel, and deionized water is added and mixed by stirring to form a uniform and stable precursor slurry (solid content controlled at 30%). Step 3: The precursor slurry, coating solution, precipitant NaOH, and complexing agent NH3·H2O are continuously and stably pumped into the co-precipitation reactor through a metering system. The temperature of the reaction system is controlled at 25℃, the pH value at 10.5, and the stirring speed at 450 rpm. This allows the precursor material of the coating layer to undergo heterogeneous nucleation and growth on the surface of the nickel-based transition metal oxide precursor particles. At the same time, the pH value is monitored in real time by an online pH meter, and the feed rate of the precipitant is automatically adjusted through a feedback system to stabilize the pH value within the set range (10.5±0.5). Step 4: The slurry flowing from the reactor enters the aging tank and ages for 6 hours to ensure more complete crystallization of the coating layer and a more thorough reaction. After aging, the slurry undergoes solid-liquid separation using a diaphragm filter press to obtain a filter cake. The filter cake is then repeatedly washed countercurrently with deionized water on the filter press to thoroughly remove residual sodium. + NO3 - NH4 + Impurity ions; then the washed wet filter cake is conveyed to a disc dryer for drying to obtain a dry, fully coated "core-shell structure precursor" powder; Step 5: The dried precursor powder and lithium source Li2CO3 (the molar ratio of the total amount of Li required for the core and coating precursors to the Li element in the lithium source is 1:1.03) are thoroughly and uniformly mixed using a V-type mixer. The uniformly mixed material is then placed into a sintering container and calcined at 750°C for 12 hours. This allows the core precursor to undergo a lithiation reaction and crystallize into a layered oxide, while the outer coating precursor reacts and crystallizes into Li7La3Zr. 1.7 Co 0.3 O 12 The ion-electron mixed conductor phase is then formed. The sintered block material is then pulverized by an air jet mill, and large particles, foreign magnetic impurities, and other foreign matter are removed by a vibrating screen and an iron remover to obtain the positive electrode material.

[0082] Example 2 The difference between this embodiment and Embodiment 1 is that the mass of the coating layer is 3% of the core mass.

[0083] Example 3 The difference between this embodiment and Embodiment 1 is that the mass of the coating layer is 4% of the core mass.

[0084] Example 4 The difference between this embodiment and Embodiment 1 is that the mass of the coating layer is 1% of the core mass.

[0085] Example 5 The difference between this embodiment and Embodiment 1 is that the mass of the coating layer is 5% of the core mass.

[0086] Example 6 The difference between this embodiment and Embodiment 2 is that the chemical formula of the core is LiNi. 0.8 Co 0.1 Mn 0.05 Zr 0.05 O2.

[0087] Example 7 The difference between this embodiment and Embodiment 1 is that the chemical formula of the core is LiNi. 0.6 Co0.1 Mn 0.3 O2.

[0088] Example 8 The difference between this embodiment and Embodiment 2 is that the chemical formula of the core is LiNi. 0.82 Co 0.1 Mn 0.08 O2, the mass of the coating layer is 5.3% of the core mass.

[0089] Example 9 The difference between this embodiment and Embodiment 2 is that the chemical formula of the core is LiNi. 0.85 Co 0.1 Mn 0.05 O2, the mass of the coating layer is 6% of the core mass.

[0090] Example 10 The difference between this embodiment and Embodiment 2 is that the chemical formula of the core is LiNi. 0.9 Co 0.05 Mn 0.05 O2, the mass of the coating layer is 7% of the core mass; step five in the preparation method is to calcine at 700℃ for 12 hours.

[0091] Example 11 The difference between this embodiment and Embodiment 2 is that the chemical formula of the core is LiNi. 0.95 Co 0.02 Mn 0.03 O2, the mass of the coating layer is 8% of the mass of the core; step five in the preparation method is to calcine at 700℃ for 12 hours.

[0092] Example 12 The difference between this embodiment and Embodiment 2 is that the coating material is Li7La3Zr. 1.6 Co 0.4 O 12 .

[0093] Example 13 The difference between this embodiment and Embodiment 2 is that the coating material is Li7La3Zr. 1.5 Co 0.5 O 12 .

[0094] Example 14 The difference between this embodiment and Embodiment 2 is that the coating material is Li7La3Zr. 1.6 Co 0.3 Nb 0.1 O 12 .

[0095] Example 15 The difference between this embodiment and Embodiment 2 is that the coating material is Li7La3Zr. 1.6 Co 0.3 Al 0.1 O 12 .

[0096] Example 16 The difference between this embodiment and Embodiment 2 is that the coating material is Li7La3Zr. 1.6 Co 0.3 Ta 0.1 O 12 .

[0097] Example 17 The difference between this embodiment and Embodiment 2 is that the coating material is Li7La3Zr. 1.3 Co 0.5 Nb 0.2 O 12 .

[0098] Comparative Example 1 The difference between this comparative example and Example 1 is that no covering layer is provided.

[0099] Comparative Example 2 The difference between this comparative example and Example 2 is that the coating material is LLZO with a particle size of approximately 55 nm.

[0100] Comparative Example 3 The difference between this comparative example and Example 2 is that the coating material is Li7La3Zr. 1.3 Co 0.7 O 12 .

[0101] Comparative Example 4 The difference between this comparative example and Example 2 is that the coating material is Li7La3Zr. 1.9 Co 0.1 O 12 .

[0102] Comparative Example 5 The difference between this comparative example and Example 2 is that the coating material is Li7La3Zr. 1.6 Co 0.3 Mg 0.1 O 12 .

[0103] Comparative Example 6 The difference between this comparative example and Example 2 is that: The core NCM811 and the coating material Li7La3Zr1.7 Co 0.3 O 12 Physical mixing is used, and the coating material particles are 150nm.

[0104] This process requires the prior preparation of the coating material Li7La3Zr. 1.7 Co 0.3 O 12 The preparation process is as follows: (1) Powder synthesis: Weigh the corresponding raw materials according to the stoichiometric ratio (Li source Li in excess by 20% to compensate for the loss of Li volatilization during subsequent high-temperature sintering), and ball mill to mix them evenly; (2) High-temperature calcination: The ball-milled powder is calcined at 900℃ for 12 hours to allow the raw materials to undergo a preliminary reaction, forming a garnet phase and decomposing carbonates and hydroxides; (3) Fine particles are obtained by ball milling the hard solid after calcination; (4) Secondary sintering: The fine powder after ball milling is calcined again at 1000℃ for 5 hours to eliminate crystal defects and amorphous phases that may be introduced by long-term ball milling; (5) Ball milling and sieving to obtain Li7La3Zr with suitable particle size. 1.7 Co 0.3 O 12 Coating material; (6) Mixing, Li7La3Zr 1.7 Co 0.3 O 12 The coating material is mixed with NCM811 by ball milling for 10 hours.

[0105] To verify the performance of the cathode material of the present invention, the applicant assembled the cathode materials of each embodiment and comparative example into a battery. The specific composition of the battery is as follows: (1) Preparation of positive electrode sheet The positive electrode materials of the above embodiments and comparative examples were respectively mixed with the binder polyvinylidene fluoride (PVDF) and the conductive agent carbon black (Super P) at a mass ratio of 8:1:1. First, PVDF and solvent NMP were mixed, and then Super P was added and stirred at high speed to obtain a conductive slurry. Then, the positive electrode material was added according to the proportion to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated on aluminum foil and dried in a forced-air drying oven at 100°C for 120 minutes. Finally, the dried electrode sheet was rolled, cut, and made into a positive electrode sheet, and then placed in a vacuum drying oven and dried at 105°C for 240 minutes.

[0106] (2) Negative electrode: lithium metal sheet.

[0107] (3) Separator: 12μm thick PP membrane.

[0108] (4) Electrolyte preparation In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed evenly to obtain an electrolyte; wherein, the lithium salt concentration is 1mol / L.

[0109] (5) Battery assembly Inside the glove box, the lithium metal sheet is assembled with the aforementioned positive electrode, separator, and electrolyte to form a CR2032 button half-cell (with a designed capacity of 2.3mAh).

[0110] Then, the following tests were performed on the batteries of each embodiment and comparative example: (1) Cyclic test: At 25℃, the battery was first activated for 3 cycles at a rate of 0.1C within a voltage range of 2.5~4.25V. Then, the battery was charged at a constant current of 1C to 4.25V, and then charged at a constant voltage of 4.25V until the current was less than 0.05C. After resting for 10 minutes, the battery was discharged at a constant current of 1C to 2.5V. The discharge capacity of the battery at this time was tested, which is the discharge capacity of the first cycle. The battery was cycled multiple times under the above conditions until it reached 80% SOH. The number of cycles at this time was recorded, and the capacity retention rate of the battery after 200 cycles was calculated. Initial discharge capacity = discharge capacity in the first cycle / mass of positive electrode active material in the positive electrode sheet; Capacity retention rate (%) = (Discharge capacity after 200 cycles / Discharge capacity in the first cycle) × 100%.

[0111] (2) Rate performance test: First, charge and discharge the battery at a rate of 1C in the range of 2.5V~4.25V for 10 cycles, record the discharge capacity of each cycle, and then calculate the average capacity of 10 cycles as C0. Then, cycle at 2C, 3C, 5C and 6C for 10 cycles each, and then return to 1C for 10 cycles, record the discharge capacity of each cycle, calculate the average capacity after recovery as C1, and the recovery rate is C1 / C0×100%.

[0112] Table 1: Parameters and test results of Examples 1-17 and Comparative Examples 1-6

[0113] As can be seen from Table 1: Examples 1-5 and Comparative Example 1, under the premise of keeping other conditions the same, adjusted the mass ratio (coating amount) of the coating layer to the core material. The test results show that the introduction of the coating layer can effectively improve the cycle stability and rate performance of the nickel-based metamorphic transition metal oxide material. However, it should be noted that the presence of the coating layer dilutes the mass proportion of the core active material; when the coating amount is too high, it will directly cause a decrease in the initial specific capacity of the cathode material. Furthermore, Example 6, using a doped and modified core material, also showed significant improvements in cycle performance and rate performance.

[0114] Examples 2, 7-11, under the premise of keeping other conditions the same, the nickel content of the core material was adjusted and the coating amount of the coating layer was matched simultaneously. As the nickel content in the core material increases, the interfacial side reaction activity of the nickel-based transition metal oxide is significantly enhanced, and the crystal structure stability decreases simultaneously; therefore, the coating amount of the coating layer needs to be increased simultaneously to adapt to its increased instability, and to avoid the fact that a low coating amount can only form local discontinuous protection, which cannot fully cover the dense active sites on the core surface, resist the lattice stress during the charging and discharging process, or eliminate the protection blind zone on the particle surface; through the precise matching of coating amount and nickel content, the overall electrochemical performance of the battery, such as cycle stability and rate performance, is ultimately ensured to remain at an excellent level.

[0115] Examples 2, 12-13, and Comparative Examples 2-4, under the premise of keeping other conditions the same, adjusted the molar ratio of Co in the coating layer. The test results showed that when the molar ratio of Co was between 0.3 and 0.5, the coating layer could form a structurally stable protective system with synergistic ion-electron transport, exhibiting excellent coating effect and correspondingly better overall electrochemical performance of the battery. When the molar ratio of Co was too low (e.g., Comparative Example 4) or even undoped (e.g., Comparative Example 2), due to the electronic insulation of the LLZO matrix itself, an effective electron transport pathway could not be constructed, leading to a significant decrease in the electrochemical performance of the battery. Conversely, when the molar ratio of Co was too high, excessive Co atoms would occupy Zr in the LLZO lattice. 4+ The sites disrupt the crystal structure integrity of garnet-type LLZO, thereby hindering the Li... + The reduced efficiency of electron transport ultimately deteriorates the overall performance of the battery.

[0116] Examples 14-17 and Comparative Example 5, while maintaining other consistent conditions, focused on controlling the doping elements of the coating layer material. In Examples 14-17, the coating layer used LLZO as the matrix and employed synergistic doping with Co and M (Nb, Al, Ta) elements. Comparative Example 5 used co-doping with Co and Mg elements as a comparison. The test results showed that M elements (Nb, Al, Ta) could effectively enter the garnet-type lattice of LLZO, forming a synergistic doping effect with Co, significantly optimizing the ion transport channels of the coating layer, further improving its ionic conductivity, and thus improving the overall electrochemical performance of the battery, such as cycle stability and rate performance. However, when the doping element M was Mg, due to Mg... 2+ Unable to replace lattice sites in the LLZO crystal structure, it ultimately exists as an impurity phase in the coating layer, thus disrupting the integrity of the LLZO lattice and hindering the development of Li. + The efficient transfer of electrons leads to a significant decrease in battery performance.

[0117] The preparation method of Comparative Example 6 is different from that of Example 2. Comparative Example 6 uses a conventional physical mixing method to achieve the composite of the coating layer and the core material. The test results show that the conventional physical mixing method cannot form a uniform, dense and continuous coating layer on the surface of the core material. Moreover, the particle size of the resulting coating material is relatively large, making it difficult to fill the gaps and grooves between the core active material particles. This results in a protective blind zone in the coating layer and weak bonding force with the core interface, ultimately leading to an unsatisfactory protective effect of the coating layer.

[0118] The cathode material provided by this invention involves constructing an ion-electron hybrid conductor coating layer on the surface of a nickel-based layered transition metal oxide material. The main material of this coating layer is Li7La3Zr. 2-x-y Co x M y O 12 Compared to conventional coating materials (such as single ionic conductors or insulating coating materials), this invention possesses superior ionic and electronic conductivity. This characteristic accelerates the transport rate of ions and electrons on the surface of the cathode particles, effectively reducing interfacial polarization during charging and discharging. It meets the rapid charge transfer requirements under high-rate conditions (such as fast charging scenarios) while reducing capacity decay caused by polarization accumulation during long-term cycling, significantly improving the battery's rate performance and cycle life. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0119] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A positive electrode material, characterized in that, include: The core comprises a nickel-based transition metal oxide, wherein, based on the total amount of metal elements other than lithium, the molar percentage of nickel in the nickel-based transition metal oxide is greater than or equal to 60%. A cladding layer is formed on the surface of the core. This cladding layer is an ion-electron hybrid conductor layer, and the material of the cladding layer includes Li7La3Zr. 2-x-y Co x M y O 12 Where 0.3≤x≤0.5, 0≤y≤0.2, and M includes one or more of Al, Nb, Ta, Mo, and In.

2. The cathode material according to claim 1, characterized in that, If the mass percentage of the coating layer to the mass of the core is a, then 0 < a ≤ 8%.

3. The cathode material according to claim 2, characterized in that, When the molar percentage of nickel in the nickel-based transition metal oxide is 60% to 80%, the mass percentage 'a' of the coating layer to the core satisfies: 0 < a ≤ 5%.

4. The cathode material according to claim 2, characterized in that, When the molar percentage of nickel in the nickel-based transition metal oxide is greater than 80%, the mass percentage 'a' of the coating layer to the core satisfies: 5% < a ≤ 8%.

5. A method for preparing the positive electrode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Preparation of coating solution: According to the stoichiometry of the coating layer material, measure the lanthanum source, zirconium source, cobalt source and dopant source and dissolve them in the solvent to obtain the coating solution; Dispersion substrate: The precursor powder of nickel-based transition metal oxide is dispersed in deionized water to obtain a precursor slurry; Co-precipitation coating: The precursor slurry and the coating solution are mixed, and a precipitant and a complexing agent are added at the same time, so that the coating layer precursor is nucleated on the surface of the nickel-based morphological transition metal oxide precursor. After aging, washing and drying, the coated precursor is obtained. Sintering: The coated precursor is thoroughly mixed with the lithium source and then sintered to obtain the cathode material.

6. The method for preparing the cathode material according to claim 5, characterized in that, In the coprecipitation coating step, the temperature of the reaction system is controlled at 20~30℃, the pH value is 10~12, and the stirring rate is 450~2000rpm; and / or, the aging time is not less than 6 hours.

7. The method for preparing the cathode material according to claim 5, characterized in that, Includes any one of the following: The precipitant includes one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide; The complexing agent includes ammonia water, and the ratio of the molar amount of ammonia to the molar amount of total metal ions in the reaction system is 0.60~0.

75.

8. The method for preparing the cathode material according to claim 5, characterized in that, Includes any one of the following: The lithium source includes one or more of lithium carbonate and lithium hydroxide; The lanthanum source includes one or more of lanthanum nitrate and hydrated lanthanum nitrate; The zirconium source includes one or more of zirconium nitrate and hydrated zirconium nitrate. The cobalt source includes one or more of cobalt nitrate and hydrated cobalt nitrate. The doping source includes one or more of aluminum, niobium, tantalum, molybdenum, and indium; wherein the aluminum source includes one or more of aluminum nitrate and hydrated aluminum nitrate, the niobium source includes one or more of niobium pentachloride and niobium nitrate, the tantalum source includes one or more of tantalum chloride and tantalum nitrate, the molybdenum source includes one or more of ammonium molybdate and molybdenum nitrate, and the indium source includes one or more of indium nitrate and hydrated indium nitrate.

9. An electrochemical device, characterized in that, It includes the cathode material according to any one of claims 1 to 4, or the cathode material prepared by any one of claims 5 to 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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