Preparation method for regulating and controlling particle entropy distribution of lithium cobalt oxide positive electrode material and high-voltage lithium ion battery

Abstract

The invention discloses a preparation method of a lithium cobalt oxide positive electrode material for particle entropy distribution regulation and control and a high-voltage lithium ion battery, belongs to the technical field of electrochemical energy storage, and relates to a method for directly converting chemical energy into electric energy. The preparation method comprises the following steps: coating the surface of a single crystal LiCoO2 particle with a hydroxide shell layer containing Co, Mg, Al, Ti, La and Ce through a coprecipitation method to form a core-shell heterostructure precursor; then, through a high-temperature solid-phase reaction, Mg < 2 + >, La < 3 + > and Ce < 3 + > in a precursor shell layer are induced to synergistically segregate and be enriched on the surfaces of the particles, and meanwhile Al < 3 + > and Ti < 4 + > are diffused into the particles, so that a unique gradient structure with the surface enriched with Mg, La and Ce is constructed in situ in the single crystal. The prepared positive electrode material has excellent thermal safety (the thermal runaway initial temperature gt and 250 DEG C), excellent cycling stability and high first efficiency under the high voltage of 4.6 V.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, and relates to a method for directly converting chemical energy into electrical energy. Specifically, it relates to a preparation method for controlling the entropy distribution of lithium cobalt oxide cathode material particles and a high-voltage lithium-ion battery. Background Technology

[0002] The information disclosed in this background section is intended only to enhance some understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art.

[0003] The improvement of energy density in lithium-ion batteries is highly dependent on breakthroughs in the operating voltage of cathode materials. Lithium cobalt oxide (LiCoO2), as one of the most commercially successful cathode materials, relies on high voltage (≥4.6 V) to realize its theoretical capacity and meet the long-lasting battery life requirements of high-end electronic devices. However, under high voltage, LiCoO2 faces multiple challenges, including lattice oxygen loss, harmful phase transitions, and severe interfacial side reactions, leading to a sharp deterioration in its cycle life and thermal safety, constituting a core bottleneck for its high-voltage applications.

[0004] To overcome the aforementioned challenges, modification strategies in this field have continued to evolve along two main directions: "complex composition" and "refined structure," and have now formed a technical path that progresses from shallow to deep, but both face inherent bottlenecks: 1. Bulk uniform doping Represented by the applicant's prior patent (CN 111663182 B), this technology successfully achieved uniform bulk doping of elements such as Mg and Al through cation precursor design, preparing large-size single-crystal LiCoO2, effectively suppressing bulk phase transitions under high voltage and improving the structural integrity of the material. However, practice has shown that while this "average" reinforcement strategy stabilizes the material's "skeleton," it is difficult to specifically strengthen the most vulnerable "skin" (i.e., surface and interface) under high voltage, thus creating a bottleneck in improving battery thermal safety and long-term cycle stability.

[0005] 2. Multi-component high-entropy doping In search of breakthroughs, research has shifted towards introducing more elements, attempting to leverage the "high entropy effect" to enhance overall stability. For example: (1) High-entropy bulk doping over a wide temperature range: For example, in "Enhancing the wide-temperature range performance of LiCoO2 through high-entropy doping", multiple elements such as La, Ce, Y, Mg, Al, and Ti are used for bulk uniform doping. Although this strategy stabilizes the overall structure and improves the performance over a wide temperature range through high configurational entropy, its "egalitarian" doping mode still fails to specifically and efficiently solve the key failure mode of surface lattice oxygen loss.

[0006] (2) Conventional solid-state method of high-entropy coating / doping: such as the existing technology reflected in the patent "A high-entropy doped lithium cobalt oxide cathode material and its preparation method and application", which is mostly based on simple mechanical mixing and high-temperature sintering. This method not only makes it difficult to avoid polycrystalline structure, but also easily forms an electrochemically inert coating layer with weak bonding force with the bulk matrix and hinders lithium-ion conduction, and cannot construct an integrated reinforced structure.

[0007] 3. Gradient / Core-Shell Structure Design Recognizing the need for differentiated enhancement between surface and bulk phases, research began to actively explore the design of non-uniform element distributions: (1) Chemical competitive adsorption gradient: For example, the paper "Chemical competitive doping strategy for high-voltage LiCoO2: Synergistic improvement of lithium-ion battery performance by surface high-entropy region and bulk oxygen anchoring" proposed multi-element competitive doping of Ti, Mo, W and Mg, observed the gradient distribution of Mg and formed the concept of surface high-entropy region. This marks an important exploration from "uniform" to "gradient" design. However, this method relies heavily on the uncontrollable chemical competition and adsorption kinetics in the co-precipitation stage, resulting in random gradient and poor process reproducibility. More importantly, its product is still polycrystalline secondary particles, and the large number of grain boundaries inside are prone to become crack sources and side reaction channels in high-pressure cycling.

[0008] (2) Diffusion-controlled core-shell doping: The applicant's team (as reported in "Cation heterodoping alleviates lattice distortion in high-voltage single-crystal LiCoO2") first clearly demonstrated the use of the intrinsic diffusion coefficient difference of different dopant ions in the solid phase (such as Ti) to regulate core-shell doping. 4+ Slow diffusion, Mg 2+ Al 3+ (Fast diffusion) Surface-enriched Ti was successfully prepared via a two-step solid-state method. 4+ Internal enrichment of Mg 2+ / Al 3+ This work is a landmark achievement, demonstrating the feasibility of achieving gradient doping within a single crystal based on classical physical diffusion theory, and advancing the technology from "polycrystalline" and "uncontrollable gradient" to "single crystal" and "controllable gradient".

[0009] However, the applicant's in-depth analysis shows that the current state-of-the-art technology, represented by "diffusion-controlled core-shell doping," is completely confined to the traditional theoretical framework of "relying on a single, known intrinsic physical property of the ion (diffusion coefficient)." This leads to two fundamental limitations: first, the technical approach is limited to a few ion combinations with significantly different diffusion rates (such as Ti and Mg / Al), resulting in a narrow design space; second, existing technologies have neither revealed nor provided any implementation path or theoretical expectation for the "chemical synergistic interactions" (such as charge compensation, lattice strain synergy, etc.) that may exist between different types of ions (especially rare earth ions and transition metal ions with special electronic structures) that transcend simple physical diffusion, and whether these interactions can be actively excited and used to construct more stable and functional surface composite structures.

[0010] Therefore, after existing technologies have reached the level of "utilizing known diffusion differences", the field faces a higher-order and untapped challenge: whether it is possible to break through the limitations of traditional theories, discover a new material physicochemical phenomenon, and develop a completely new preparation paradigm based on this, thereby potentially obtaining a next-generation high-pressure stable single-crystal lithium cobalt oxide material with superior comprehensive performance (especially thermal safety) compared to the current "diffusion regulation" strategy. Summary of the Invention

[0011] Based on an in-depth analysis of the evolution path of existing technologies and their common bottlenecks, this invention aims to solve a higher-order technical problem that has not been revealed and solved by existing technologies: how to break through the traditional doping design paradigm that relies on the physical properties of a single ion (such as the diffusion coefficient), and by discovering and utilizing new and unpredictable physicochemical synergistic effects between different ions, to directionally construct a novel surface structure with composite composition and function inside single-crystal LiCoO2, so as to simultaneously achieve ultra-high thermal safety and ultra-long cycle stability that cannot be achieved by existing technologies.

[0012] To address the aforementioned problems, this invention, through a carefully designed multi-element combination and core-shell precursor structure, unexpectedly promotes the synthesis of Mg during high-temperature heat treatment. 2+ La 3+ and Ce 3+ Synergistic segregation and enrichment on the particle surface, while Al 3+ and Ti 4+ The ions diffuse inward, thereby constructing a surface-enriched Mg-La-Ce composite gradient structure in situ within the single crystal, a feat not previously achieved by existing technologies. The formation mechanism of this unique structure likely involves complex interionic interactions, and its final distribution cannot be simply predicted by the intrinsic diffusion coefficients of each ion.

[0013] The technical solution adopted in this invention has the following three aspects: In a first aspect, the present invention provides a method for preparing lithium cobalt oxide cathode material with controlled particle entropy distribution, wherein the general molecular formula of the lithium cobalt oxide cathode material is Li[Co]. 1-x₋y-z-l-m Mg x Al y Ti z La l Ce m O2, where 0 < x ≤ 0.03, 0 < y ≤ 0.03, 0 < z ≤ 0.02, 0 < l ≤ 0.01, 0 < m ≤ 0.01, and x + y + z + l + m ≤ 0.05, the method includes the following steps: (1) Preparation of core-shell heterostructure precursor: Disperse single-crystal LiCoO2 particles and react them with Co-containing... 2+ Mg 2+ Al 3+ Ti 4+ La 3+ and Ce 3+ The solution mixture of ions, in the presence of a complexing agent, forms a hydroxide shell [Co] on the surface of single-crystal LiCoO2 particles through a co-precipitation reaction. 1-v Mg a Al b Ti c La d Ce e ](OH)2, yielding a core-shell heterostructure precursor, denoted as LiCoO2@[Co 1-v Mg a Al b Ti c La d Ce e ](OH)2, where a, b, c, d, and e represent the mole fractions of Mg, Al, Ti, La, and Ce, respectively, and satisfy: 0 (2) Constructing a surface composite gradient through heat treatment: Adding a lithium source to the precursor obtained in step (1), mixing, and then carrying out a high-temperature solid-phase reaction at 900-1100 °C in an oxygen-containing atmosphere; the high-temperature solid-phase reaction causes the Mg in the precursor shell layer to be reduced. 2+ La 3+ and Ce 3+ Synergistic segregation and enrichment in the particle surface region, while Al 3+ and Ti 4+ ​Diffusion into the interior of the particles creates a gradient structure on the surface enriched with Mg, La, and Ce.

[0014] In this invention, the general molecular formula of the lithium cobalt oxide cathode material is x + y + z + l + m ≤ 0.05. Experimental verification shows that this doping amount can effectively control the entropy distribution of LiCoO2 particles, forming a surface Mg... 2+ / La 3+ / Ce 3+ The enriched high-entropy layer can maintain thermodynamic stability under high voltage, suppress surface lattice loss, mitigate interfacial side reactions, and improve the stability of high-voltage LiCoO2 and the safety of lithium-ion batteries.

[0015] Preferably, in step (1), the core-shell heterostructure precursor can be prepared by various methods. This invention preferably employs a hydroxide coprecipitation route. This route, by precisely controlling the precipitation process in the liquid phase, enables highly uniform mixing and coating of dopant elements at the atomic scale under mild conditions. The resulting precursor has high purity and controllable composition, and is particularly beneficial for inducing uniform and controllable ion interdiffusion in subsequent high-temperature steps, thereby forming an ideal gradient structure. Furthermore, this route has low raw material costs, mild process conditions, and is easy to scale up, making it particularly suitable for large-scale industrial production.

[0016] Preferably, in step (1), Co is included. 2+ Mg 2+ Al 3+ Ti 4+ La 3+ and Ce 3+ A solution of ions, wherein the solute is a nitrate or a sulfate.

[0017] Preferably, in step (1), the complexing agent is ammonia, the pH value of the coprecipitation reaction is controlled at 10.5-11.5, and the reaction temperature is 30-70 ℃.

[0018] Preferably, in step (1), LiCoO2@[Co 1-v Mg a Al b Ti c La d Ce e In the (OH)2 core-shell heterostructure precursor, the hydroxide shell [Co] 1-v Mg a Al b Ti c La d Ce eThe proportion of (OH)2 in the total molar number of the core-shell heterostructure precursor is 5% to 20%. Experimental verification shows that it can provide sufficient Mg / La / Ce to form a high-entropy surface layer, while Mg / Al / Ti can fully diffuse to form a stable bulk phase, achieving optimal synergy. Due to the relatively low doping concentration inside the particles and the relatively high doping concentration on the particle surface, a LiCoO2 material with a gradually increasing entropy value from the inside to the surface of the particles is formed.

[0019] More preferably, [Co 1-v Mg a Al b Ti c La d Ce e The molar ratio of (OH)2 is 0.1 to 0.15.

[0020] Preferably, in step (2), the lithium source is one or both of lithium hydroxide and lithium carbonate. Lithium source addition amount: After adding the lithium source, the molar ratio of lithium ions to all cations except lithium ions in the mixture, Li / TM = 1.0-1.05.

[0021] More preferably, the lithium source is lithium carbonate.

[0022] Preferably, in step (2), the high-temperature solid-phase reaction time is 1-24 h; the high-temperature sintering atmosphere is air or oxygen atmosphere; More preferably, the high-temperature solid-state reaction conditions are 950-1000 °C for 4-8 h; and the high-temperature sintering atmosphere is air.

[0023] The gradient formation mechanism of this invention is not a simple single path of "heavy ions moving slowly and light ions moving quickly," but a more sophisticated two-step synergistic process: Step 1: Synergistic surface segregation at high temperature (for Mg) 2+ with La 3+ / Ce 3+ ) In the initial stage of the high-temperature solid-phase reaction, magnesium ions (Mg) in the shell... 2+ ) and lanthanum / cerium ions (La 3+ / Ce 3+ It exhibits a strong tendency for synergistic surface segregation. This is due to: synergistic effect of charge compensation and lattice strain; and the large radius La... 3+ / Ce 3+ Ingress into the surface lattice results in significant localized lattice strain. Mg, with its smaller radius but lower charge, exhibits this characteristic. 2+ Simultaneous segregation to adjacent sites can synergistically regulate local charge balance and release lattice stress, making this combination thermodynamically more likely to exist stably on the surface. Formation of a high-entropy composite layer on the surface: Mg 2+Rather than being a fast-diffusing light ion, it is one of the active builders of the surface high-entropy stable layer, together with La and Ce, forming a thermodynamically more stable surface composite high-entropy layer rich in various strong bonds (Mg-O, La-O, Ce-O).

[0024] Step 2: Differential diffusion within the bulk phase (for Al) 3+ With Ti 4+ ) Meanwhile, aluminum ions (Al) in the shell 3+ ) and titanium ions (Ti 4+ They follow the classic bulk diffusion behavior. Due to their high diffusion coefficient, they migrate from the surface to the depth of the particle interior, achieving relatively uniform bulk doping. Their main function is to stabilize the crystal framework of the bulk phase (through strong Al-O / Ti-O bonds).

[0025] In a second aspect, the present invention provides a LiCoO2 cathode material prepared by the method described in the first aspect, wherein the entropy value of the particles gradually increases from the interior to the surface, and the cathode material is a primary single crystal particle; and, by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) line scanning characterization, the atomic concentrations of Mg, La and Ce are distributed in a gradient that increases continuously from the particle core to the surface, and are enriched in the outermost surface region.

[0026] Preferably, the average particle size range of the primary single crystal particles (D) 50 The thickness is 5-30 μm; More preferably, 10 μm ≤D 50 ≤20 μm.

[0027] Thirdly, the present invention provides a high-voltage lithium-ion battery with LiCoO2, whose entropy value gradually increases from the interior to the surface of the particles as described in the second aspect, as the positive electrode. This high-voltage lithium-ion battery is used to directly convert chemical energy into electrical energy.

[0028] Preferably, the charging cutoff voltage of the battery is not less than 4.5 V.

[0029] Compared with the related technologies known to the inventors, one of the technical solutions of the present invention has the following beneficial effects: (1) Structural innovation and synergistic performance: A "Mg-La-Ce composite co-enriched surface layer" was obtained, which is impossible to obtain by any existing technical approach (including the latest two-step diffusion method). This structure is composed of multiple strong chemical bonds (Mg-O, La-O, Ce-O), and its ability to anchor surface oxygen, interfacial stability, and thermodynamic stability are theoretically far superior to those of a single slow-diffusion ion (such as Ti). 4+ A surface layer consisting of a random mixture or a combination of other materials.

[0030] (2) Innovative principle, revealing a new mechanism: For the first time, a new paradigm of "heterogeneously induced synergistic segregation and diffusion segregation" was proposed. This is completely different from and cannot be based on "Ti 4+ / Mg 2+ This method transcends the traditional doping design that relies on a single physical property (such as the diffusion coefficient) and induces Mg in the specific chemical environment of this invention, as predicted or explained by existing theories of "diffusion coefficient difference". 2+ with La 3+ / Ce 3+ Unexpected phenomenon of co-segregation to the surface, while Al 3+ / Ti 4+ They then diffuse into the bulk phase. This active design and control of ion behavior enables directional and programmed arrangement of element distribution, resulting in good process repeatability.

[0031] (3) Significantly improved overall performance: Thanks to the unique structure described above, this material exhibits the following characteristics at a high voltage of 4.6 V: ① Excellent thermal safety (delithiation thermal runaway initiation temperature > 250 ℃); ② Excellent cycle stability (attenuation rate under test conditions is much lower than that of similar technologies); ③ Good kinetic performance (high first-cycle coulombic efficiency and reversible capacity). Its overall performance, especially the synergistic improvement in thermal safety and cycle life, is directly due to the strengthening and stabilizing effect of the "Mg-La-Ce" composite surface layer, which surpasses existing technologies.

[0032] (4) Good process inheritance and great industrialization potential: The preparation method is based on mature aqueous coprecipitation and solid-state sintering process, which is easy to control, the raw materials are readily available, the process is simple, and it is suitable for large-scale industrial production, providing a practical new path for the industrialization of high-performance high-voltage single crystal lithium cobalt oxide. Attached Figure Description

[0033] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0034] Figure 1 Example 1 prepared 90% LiCoO2@10% [Co 0.85 Mg 0.05 Al 0.05 Ti 0.03 La 0.01 Ce 0.01 SEM image of the (OH)2 heterostructure precursor; Figure 2 [Co] prepared in Comparative Example 1 0.985 Mg 0.005 Al 0.005 Ti 0.003 La0.001 Ce 0.001 SEM image of the homogeneous doped precursor of (OH)2; Figure 3 Comparative Example 2: 90% LiCoO2@10% [Co] 0.92 Al 0.05 Ti 0.03 SEM image of the (OH)2 heterostructure precursor; Figure 4 XRD pattern of LiCoO2 material prepared in Example 2 with progressively increasing entropy from the interior to the surface of the particles; Figure 5 XRD pattern of uniformly doped LiCoO2 material prepared in Comparative Example 4; Figure 6 SEM image of LiCoO2 material prepared in Example 2, showing a gradual increase in entropy from the interior to the surface of the particles; Figure 7 SAED diagram of LiCoO2 material prepared in Example 2 with gradually increasing entropy from the inside to the surface of the particles; Figure 8 SEM image of the uniformly doped LiCoO2 material prepared in Comparative Example 4; Figure 9 TEM-EDS images of LiCoO2 material prepared in Example 2, showing the gradual increase in entropy from the inside to the surface of the particles; A is a TEM image of the LiCoO2 material prepared in Example 2, B shows the concentration distribution of Co, C shows the concentration distribution of Mg, D shows the concentration distribution of Al, E shows the concentration distribution of Ti, F shows the concentration distribution of La, G shows the concentration distribution of Ce, and H shows the concentration distribution of all dopants (Mg, Al, Ti, La, Ce) from the inside to the surface of the particles.

[0035] Figure 10 TEM-EDS images of LiCoO2 material with uniform particle entropy distribution prepared in Comparative Example 5; A is the TEM image of LiCoO2 material prepared in Comparative Example 5, B shows the concentration distribution of Co, C shows the concentration distribution of Ti, and D shows the concentration distribution of Al.

[0036] Figure 11 DSC images of the LiCoO2 cathode materials prepared in Example 2 and Comparative Example 6 at a cutoff voltage of 4.6 V; Figure 12 Cycling curves of the LiCoO2 cathode materials prepared in Example 2 and Comparative Example 6 at a high voltage of 4.6 V and a cycle time of 0.2 C; Figure 13 The first-cycle charge-discharge curves of the LiCoO2 cathode materials prepared in Example 2 and Comparative Example 6 at a high voltage of 4.6 V and a charge-discharge rate of 0.2 C.

[0037] Figure 14 Cycling curves of the LiCoO2 cathode materials prepared in Example 2 and Comparative Example 7 at a high voltage of 4.6 V and a cycle time of 0.2 C.

[0038] Figure 15 DSC diagrams of the LiCoO2 cathode materials prepared in Example 2 and Comparative Example 7 at a cutoff voltage of 4.6 V. Detailed Implementation

[0039] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, 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.

[0040] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0041] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0042] Example 1: Preparation of 90% LiCoO2@10% [Co 0.85 Mg 0.05 Al 0.05 Ti 0.03 La 0.01 Ce 0.01 (OH)2 heterostructure precursor Weigh out 2.389 kg of CoSO4·7H2O, 0.155 kg of Mg(NO3)2·9H2O, 0.188 kg of Al(NO3)3·9H2O, 0.059 kg of TiOSO4·2H2O, 0.043 kg of La(NO3)3·6H2O, and 0.043 kg of Ce(NO3)3·6H2O to prepare 5 L of salt solution, wherein the molar ratio of Co-Mg-Al-Ti-La-Ce is 0.85 / 0.05 / 0.05 / 0.03 / 0.01 / 0.01. Add 8.809 kg of single-crystal LiCoO2 to the reactor, and simultaneously add the above salt solution dropwise to a continuously stirred reactor. Maintain the pH value in the reactor at approximately 11.4 using a mixed solution of 5M NaOH and 1.0M ammonia, and keep the temperature at 50°C. At ℃, the rotation speed was controlled at around 500 rpm until the above salt solution was completely consumed. The precipitate was then centrifuged, washed, and dried to obtain the magnesium-aluminum co-doped target precursor 90%LiCoO2@10%[Co]. 0.85 Mg 0.05 Al 0.05 Ti 0.03 La 0.01 Ce 0.01 [OH]2, its SEM image is as follows Figure 1 As shown, a uniform coating layer is observed on the surface of the single crystal, confirming that LiCoO2@[Co 0.85 Mg 0.05 Al 0.05 Ti 0.03 La 0.01 Ce 0.01 Successful synthesis of (OH)2 heterostructure precursor.

[0043] Comparative Example 1: Preparation of homogeneous doped precursor [Co] 0.985 Mg 0.005 Al 0.005 Ti 0.003 La 0.001 Ce 0.001 ](OH)2 Weigh out 2.768 kg CoSO4·7H2O, 0.0155 kg Mg(NO3)2·9H2O, 0.0188 kg Al(NO3)3·9H2O, 0.0059 kg TiOSO4·2H2O, 0.0043 kg La(NO3)3·6H2O, and 0.0043 kg Ce(NO3)3·6H2O to prepare 5 L of salt solution, wherein the molar ratio of Co-Mg-Al-Ti-La-Ce is 0.985 / 0.005 / 0.005 / 0.003 / 0.001 / 0.001. Add the above salt solution dropwise to a continuously stirred reactor, while simultaneously using 5 M... A mixed solution of NaOH and 1.0M ammonia was used to maintain the pH of the reactor at approximately 11.4, and the rotation speed was controlled at approximately 500 rpm until the salt solution was completely consumed. The precipitate was then centrifuged, washed, and dried to obtain the magnesium-aluminum co-doped target precursor [Co]. 0.985 Mg 0.005 Al 0.005 Ti 0.003 La 0.001 Ce 0.001 ](OH)2, its SEM is as follows Figure 2 As shown.

[0044] Comparative Example 2: Preparation of 90% LiCoO2@10% [Co 0.92 Al 0.05 Ti 0.03 (OH)2 heterostructure precursor Weigh 2.89 kg CoSO4·7H2O, 0.188 kg Al(NO3)3·9H2O, and 0.059 kg TiOSO4·2H2O to prepare 5 L of salt solution, with a Co-Al-Ti molar ratio of 0.92 / 0.05 / 0.03. Add 8.809 kg of single-crystal LiCoO2 to the reactor, while simultaneously adding the above salt solution dropwise to a continuously stirred reactor. Maintain the pH value in the reactor at approximately 11.4 using a mixed solution of 5M NaOH and 1.0M ammonia, and keep the stirring speed at approximately 500 rpm until the salt solution is completely consumed. Centrifuge, wash, and dry the precipitate to obtain the magnesium-aluminum co-doped target precursor 90% LiCoO2@10% [Co 0.92 Al 0.05 Ti 0.03 [OH]2, its SEM image is as follows Figure 3 As shown, a uniform coating layer is observed on the surface of the single crystal, confirming that LiCoO2@[Co 0.92 Al 0.05 Ti 0.03 Successful synthesis of (OH)2 heterostructure precursor.

[0045] Comparative Example 3: Preparation of 98.5% LiCoO2@1.5% [Mg 0.33 Al 0.33 Ti 0.20 La 0.07 Ce 0.07 (OH)2 heterostructure precursor Weigh out 1.023 kg of Mg(NO3)2·9H2O, 1.238 kg of Al(NO3)3·9H2O, 0.392 kg of TiOSO4·2H2O, 0.303 kg of La(NO3)3·6H2O, and 0.304 kg of Ce(NO3)3·6H2O to prepare 5 L of salt solution, wherein the molar ratio of Mg-Al-Ti-La-Ce is 0.33 / 0.33 / 0.20 / 0.07 / 0.07. Add 64.27 kg of single-crystal LiCoO2 to the reactor, and simultaneously add the above salt solution dropwise to a continuously stirred reactor, while simultaneously using 5 M... A mixed solution of NaOH and 1.0M ammonia was used to maintain the pH of the reactor at approximately 11.4, and the rotation speed was controlled at approximately 500 rpm until the salt solution was completely consumed. The precipitate was then centrifuged, washed, and dried to obtain the magnesium-aluminum co-doped target precursor 98.5% LiCoO2@1.5% [Mg 0.33 Al 0.33 Ti 0.20 La 0.07 Ce 0.07 (OH)2 heterostructure precursor.

[0046] Example 2: Preparation of LiCoO2 with gradually increasing entropy from the interior to the surface of the particles Weigh 97.37 g of the 90% LiCoO2@10% [Co] prepared in Example 1 above. 0.85 Mg 0.05 Al 0.05 Ti 0.03 La 0.01 Ce 0. 01 A heterostructure precursor of (OH)₂ was added with 3.69 g of battery-grade lithium carbonate, mixed thoroughly, and sintered in a muffle furnace at 950 °C in air for 6 h. The high-temperature solid-state reaction resulted in a LiCoO₂ material with a gradually increasing entropy value from the interior to the surface of the particles. Its XRD pattern is shown in the figure. Figure 4 As shown, its SEM is as follows Figure 6 As shown, SAED Figure 7 As shown, TEM-EDS Figure 9 As shown.

[0047] Comparative Example 4: Preparation of uniformly doped LiCoO2 Weigh 92.9 g of the precursor [Co] prepared in Comparative Example 1. 0.985 Mg0.005 Al 0.005 Ti 0.003 La 0.001 Ce 0.001 ](OH)2 was uniformly mixed with 36.95 g of battery-grade Li2CO3 (Li / TM = 1.0) and sintered in a muffle furnace at 950 °C in air atmosphere for 6 h to obtain uniformly doped LiCoO2. Its SEM is shown in Figure 1. Figure 8 As shown.

[0048] Comparative Example 5: Preparation of LiCoO2 with uniformly distributed particle entropy. Weigh 97.37 g of the above Comparative Example 2 to prepare 90% LiCoO2@10% [Co 0.92 Al 0.05 Ti 0.03 A heterostructure precursor of (OH)₂ was added with 3.69 g of battery-grade lithium carbonate, mixed thoroughly, and sintered in a muffle furnace at 950 °C in air for 6 h. Due to the rapid diffusion of light ions, uniform doping was achieved in the particles, and finally, a high-temperature solid-state reaction was performed to form LiCoO₂ material, the XRD of which is shown in the figure. Figure 5 As shown, its TEM-EDS is as follows Figure 10 As shown.

[0049] Comparative Example 6: Preparation of high-entropy oxide-coated LiCoO2 Weigh 97.37 g of the above Comparative Example 3 to prepare 98.5% LiCoO2@1.5% [Mg 0.33 Al 0.33 Ti 0.20 La 0.07 Ce 0.07 A heterostructure precursor of ](OH)₂ was sintered in a muffle furnace at 500 °C in air for 6 h. Due to the high-entropy component nucleation effect, cation diffusion was suppressed, resulting in the preparation of 98.5% LiCoO₂@1.5% [Mg 0.33 Al 0.33 Ti 0.20 La 0.07 Ce 0.07 O n Because the high-entropy oxide on the surface is an electrochemically inert coating layer, it hinders lithium-ion insertion / extraction during charging and discharging, reducing the first-cycle efficiency and reversible specific capacity of the LiCoO2 cathode material, such as... Figure 13 As shown.

[0050] Comparative Example 7: Preparation of core-shell-like LiCoO2 Weigh out 80.27 g Co3O4, 0.98 g Al2O3, 0.98 g MgO, and 40.64 g Li2CO3 (Li / Co=1.1) in stoichiometric ratio, mix thoroughly, pre-calcine at 760 °C for 2 h and sinter at 1000 °C for 12 h to prepare 1 wt. Mg / Al co-doped LiCoO2. Further mix 0.98 g TiO2 into this particle and sinter at 900 °C for 10 h. Due to the high temperature of Ti... 4+ Diffusion at the LiCoO2 / TiO2 grain boundaries was hindered, ultimately resulting in a core-shell-like LiCoO2 structure with the following properties: Figure 14 As shown, at a 0.2C rate, the first-cycle reversible capacity and cycling stability of the core-shell-like LiCoO2 were worse than those of Example 2.

[0051] from Figure 1 As can be seen in Example 1, 90% LiCoO2@10% [Co 0.85 Mg 0.05 Al 0.05 Ti 0.03 La 0.01 Ce 0.01 ](OH)2 consists of micron-sized particles encapsulated by small surface particles.

[0052] from Figure 2 As can be seen in Comparative Example 1, the homogeneous doped precursor [Co] 0.985 Mg 0.005 Al 0.005 Ti 0.003 La 0.001 Ce 0.001 ](OH)2 is a micron-sized secondary particle formed by the assembly of nano-sized small particles.

[0053] from Figure 3 As can be seen in Comparative Example 2, 90% LiCoO2@10% [Co] 0.92 Al 0.05 Ti 0.03 ](OH)2 consists of micron-sized particles encapsulated by small surface particles.

[0054] from Figure 4 and Figure 5 As can be seen, the entropy values ​​from the inside to the surface of the particles prepared in Example 2 and Comparative Example 5 gradually increase. Both the LiCoO2 and the uniformly doped LiCoO2 are pure phase layered structures.

[0055] Figure 6 Example 2 yielded a single crystal of LiCoO2 with large particles, exhibiting a gradual increase in entropy from the interior to the surface of the particles, with a particle size ≤ D of 5 μm. 50 ≤ 30 μm. Figure 7 Example 2 yielded SAED of LiCoO2 with gradually increasing entropy from the inside to the surface of the particle, confirming it as a single crystal.

[0056] Figure 8 Comparative Example 4 shows that uniformly doped LiCoO2 is polycrystalline.

[0057] Figure 9 Example 2 shows that Mg / La / Ce is enriched on the particle surface, while the light ions Al / Ti are uniformly doped, confirming that the entropy value from the inside to the surface of the prepared LiCoO2 particles gradually increases.

[0058] Figure 10 Comparative Example 5 shows that the light ion Al / Ti was uniformly doped, confirming that the entropy value inside the prepared LiCoO2 particles is uniformly distributed, indicating that Mg / La / Ce is the key to forming a high-entropy layer.

[0059] Thermal safety analysis: To comprehensively evaluate the thermal stability of the material of this invention under high voltage, differential scanning calorimetry (DSC) tests were performed on the fully delithiated (4.6 V) samples of Example 2 and two key comparative examples (Comparative Example 6: high-entropy oxide coating; Comparative Example 7: diffusion-controlled core-shell structure). The results are as follows: Figure 11 and Figure 15 As shown.

[0060] like Figure 11 As shown, DSC testing reveals that the entropy value gradually increases from the interior to the surface of the delithiated particles. LiCoO2 exhibits a higher thermal runaway temperature and less exothermic lithium content, indicating that the formation of a high-entropy surface doped layer mitigates lattice oxygen loss and side reactions. Specifically, Comparative Example 6 (high-entropy oxide-coated LiCoO2) experiences a violent exothermic reaction at approximately 247 °C, indicating that its physical coating layer has limited inhibitory effect on thermal runaway. In contrast, the exothermic peak onset temperature of the material in Example 2 is significantly delayed to approximately 254 °C, and the peak intensity is significantly reduced. This demonstrates that the integrated surface gradient high-entropy structure constructed in this invention is significantly superior to simple heterogeneous physical coatings in suppressing oxygen loss and interfacial exothermic side reactions.

[0061] like Figure 15 As shown, Comparative Example 7 (based on Ti) 4+ / Mg 2+ / Al 3+ The thermal runaway initiation temperature of the core-shell structured LiCoO2 prepared by diffusion coefficient difference was approximately 249 °C, which is better than that of Comparative Example 6, but still lower than that of Example 2 (254 °C). Simultaneously, the sharpness of its exothermic peak was also higher than that of Example 2. This comparison is crucial, demonstrating the novel "co-segregation" mechanism proposed in this invention (utilizing Mg...). 2+ with La3+ / Ce 3+ The thermal stability achieved by the synergistic effect of actively constructing the surface layer surpasses the limits that can be reached by the traditional physical path based on the "difference in single ion diffusion coefficient" in existing technologies.

[0062] Comprehensive analysis Figure 11 and Figure 15 It is evident that the lithium cobalt oxide material prepared by this invention through a novel paradigm of "heterogeneous precursor-induced synergistic segregation and diffusion segregation" achieves the highest thermal safety performance (thermal runaway initiation temperature > 250℃) currently available in the field. Its superior thermal stability directly stems from the thermodynamically more stable "Mg-La-Ce composite high-entropy layer" formed on the surface. This structure cannot be obtained through existing strategies such as "uniform doping," "physical coating," or "diffusion-controlled gradient," demonstrating a dual breakthrough in both principle and performance.

[0063] Electrochemical performance analysis: To rigorously evaluate the intrinsic stability of the material under high voltage, all electrochemical tests were performed at a low rate of 0.2C / 0.2C (charge / discharge). This condition significantly extends the stress time of the material in the high delithiation state (high voltage), and the test of the material's structural stability and ability to suppress interfacial side reactions is far greater than that of higher rate tests, thus more realistically reflecting the material's degradation behavior during long-term use. Performance comparison of Example 2 with relevant comparative examples: Figure 12 , Figure 13 and Figure 14 As shown.

[0064] First week charge / discharge performance as Figure 13 As shown. At the outset of this rigorous testing, the material in Example 2 exhibited excellent initial performance: a first-week coulombic efficiency of approximately 96% and a reversible specific capacity of approximately 217 mAh / g. In contrast, Comparative Example 6 (high-entropy oxide coating) showed only approximately 87% efficiency and a capacity of 196 mAh / g. This directly demonstrates that the integrated gradient structure of this invention is significantly superior to heterogeneous physical coatings that introduce interfacial impedance in ensuring efficient lithium-ion transport.

[0065] Long-cycle stability such as Figure 12 and Figure 14 As shown.

[0066] Figure 12 Example 2 was compared with Comparative Example 5 (LiCoO2 with uniform particle entropy distribution). After 50 cycles at a stringent 0.2C rate, Example 2 exhibited a capacity retention of 95.4%, while Comparative Example 5, which only underwent bulk uniform doping, retained only 89.6%. This clearly demonstrates that the active design of the surface entropy gradient is far more effective than "egalitarian" bulk doping in resisting long-term high-pressure stress and delaying capacity decay.

[0067] Figure 14 Example 2 was compared with Comparative Example 7 (diffusion-regulated core-shell structure LiCoO2). Under the same stringent conditions, the capacity retention of Example 2 (95.4%) was still significantly better than that of Comparative Example 7 (91.6%). This comparison is particularly crucial, as it demonstrates that the surface structure constructed by the novel "synergistic segregation" mechanism proposed in this invention exhibits superior stability and protective effect against sustained high-voltage damage compared to gradient structures designed based on traditional ion diffusion theory.

[0068] Comprehensive electrochemical performance analysis shows that, under a uniform and stringent 0.2C testing scale, the material of this invention comprehensively outperforms all key electrochemical indicators, including first-cycle efficiency, reversible capacity, and long-cycle stability. This irrefutably confirms its unique "core-shell precursor + synergistic segregation" preparation paradigm, successfully constructing a novel gradient structure that combines excellent kinetic performance with superior intrinsic thermodynamic stability. This structure effectively addresses the most prevalent failure modes under high voltage, providing a reliable material solution for developing next-generation high-safety, long-life high-voltage lithium cobalt oxide batteries.

[0069] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing lithium cobalt oxide cathode material with controlled entropy distribution of particles, characterized in that, The lithium cobalt oxide cathode material has a general formula of Li[Co 1-x₋y-z-l-m Mg x Al y Ti z La l Ce m ]O2, wherein 0 < x ≤ 0.03, 0 < y ≤ 0.03, 0 < z ≤ 0.02, 0 < l ≤ 0.01, 0 < m ≤ 0.01, and x + y + z + l + m ≤ 0.05, and the method comprises the following steps: (1) Preparation of the core-shell heterostructure precursor: single-crystal LiCoO2 particles are dispersed and mixed with a solution containing Co 2+ , Mg 2+ , Al 3+ , Ti 4+ , La 3+ and Ce 3+ ions. In the presence of a complexing agent, a hydroxide shell layer [Co 1-v Mg a Al b Ti c La d Ce e ](OH)2 is coated on the surface of the single-crystal LiCoO2 particles by a co-precipitation reaction to obtain a core-shell heterostructure precursor, denoted as LiCoO2@[Co 1-v Mg a Al b Ti c La d Ce e ](OH)2, wherein a, b, c, d and e represent the molar fractions of Mg, Al, Ti, La and Ce, respectively, and satisfy: 0 < a ≤ 0.05, 0 < b ≤ 0.05, 0 < c ≤ 0.03, 0 < d ≤ 0.01, 0 < e ≤ 0.01, v = a + b + c + d + e, and 0.05 ≤ v ≤ 0.

15. (2) Constructing a surface composite gradient through heat treatment: Adding a lithium source to the precursor obtained in step (1), mixing, and then carrying out a high-temperature solid-phase reaction at 900-1100 °C in an oxygen-containing atmosphere; the high-temperature solid-phase reaction causes the Mg in the precursor shell layer to be reduced. 2+ La 3+ and Ce 3+ Synergistic segregation and enrichment in the particle surface region, while Al 3+ and Ti 4+ Diffusion into the interior of the particles creates a gradient structure on the surface enriched with Mg, La, and Ce.

2. The preparation method for controlling the entropy distribution of lithium cobalt oxide cathode material particles as described in claim 1, characterized in that, In step (1), Co is present 2+ Mg 2+ Al 3+ Ti 4+ La 3+ and Ce 3+ A solution of ions, wherein the solute is a nitrate or a sulfate.

3. The preparation method for controlling the entropy distribution of lithium cobalt oxide cathode material particles as described in claim 1, characterized in that, In step (1), the complexing agent is ammonia, the pH value of the coprecipitation reaction is controlled at 10.5-11.5, and the reaction temperature is 30-70℃.

4. The preparation method for controlling the entropy distribution of lithium cobalt oxide cathode material particles as described in claim 1, characterized in that, In step (1), LiCoO2@[Co 1-v Mg a Al b Ti c La d Ce e In the (OH)2 core-shell heterostructure precursor, the hydroxide shell [Co] 1- v Mg a Al b Ti c La d Ce e The proportion of (OH)2 in the total molar number of the core-shell heterostructure precursor is 5% to 20%.

5. The preparation method for controlling the entropy distribution of lithium cobalt oxide cathode material particles as described in claim 1, characterized in that, In step (2), the lithium source is one or both of lithium hydroxide and lithium carbonate.

6. The preparation method for controlling the entropy distribution of lithium cobalt oxide cathode material particles as described in claim 1, characterized in that, In step (2), after replenishing the lithium source, the molar ratio of lithium ions to all cations except lithium ions in the mixture, Li / TM, is 1.0-1.

05.

7. The preparation method for controlling the entropy distribution of lithium cobalt oxide cathode material particles as described in claim 1, characterized in that, In step (2), the high-temperature solid-phase reaction time is 1-24 h; the high-temperature sintering atmosphere is air or oxygen atmosphere.

8. The preparation method for controlling the entropy distribution of lithium cobalt oxide cathode material particles as described in claim 1, characterized in that, In step (2), the high-temperature solid-phase reaction conditions are 950-1000 °C for 4-8 h; the high-temperature sintering atmosphere is air.

9. A LiCoO2 cathode material prepared by any one of claims 1 to 8, wherein the entropy value gradually increases from the interior to the surface of the particle.

10. A high-voltage lithium-ion battery using the material of claim 9 as the positive electrode.

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