Ternary high-nickel positive electrode material with hollow structure, preparation method of ternary high-nickel positive electrode material and lithium ion battery

Abstract

The invention discloses a ternary high-nickel positive electrode material with a hollow structure, a preparation method of the ternary high-nickel positive electrode material and a lithium ion battery, and belongs to the technical field of lithium ion batteries. The preparation method comprises the following steps: mixing polymer microspheres with an organic titanium source in a first liquid phase, and hydrolyzing to prepare surface modified TiO2 polymer microspheres; placing the surface-modified TiO2 polymer microspheres in a second liquid phase, adding an aqueous solution of nickel salt, cobalt salt and manganese salt, and preparing a core-shell structure precursor through a coprecipitation method; and mixing the core-shell structure precursor with a lithium source, and sintering in stages in an oxygen-containing atmosphere to obtain the lithium-ion battery positive electrode material. The preparation method disclosed by the invention is simple in process, the template is easy to remove, the obtained ternary high-nickel positive electrode material with the hollow structure has low powder impedance, and a battery assembled by adopting the ternary high-nickel positive electrode material has excellent rate capability and cycling stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a hollow ternary high-nickel cathode material and its preparation method, and a lithium-ion battery. Background Technology

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

[0003] With the rapid development of new energy vehicles and energy storage technologies, higher demands are being placed on the energy density, cycle stability, and cost control of lithium-ion batteries. As a core component of lithium-ion batteries, the cathode material directly determines the overall performance and manufacturing cost of the battery. Ternary cathode materials (LiNi) are a key component. x Co y Mn z O2 (NCM) has become the mainstream cathode material for lithium-ion batteries due to its high energy density and relatively low cost. Among them, high-nickel ternary cathode materials (usually referring to NCM systems with high nickel content) have become an important research direction for improving the performance of ternary materials in recent years because they can further increase the number of lithium-ion insertion / extraction active sites, thereby significantly improving the specific capacity and battery energy density. However, while high-nickel materials bring the advantage of high energy density, they also face more prominent challenges: on the one hand, high nickel content easily leads to a decrease in the stability of oxygen ions in the material lattice, making it easier for lattice oxygen to be released and structural collapse to occur during charge and discharge, exacerbating the volume expansion effect, and making the material particles more prone to cracking or even breakage during cycling; on the other hand, high-nickel materials usually have a high content of residual alkali substances on the surface, which are prone to interfacial side reactions with the electrolyte, generating reaction products with high impedance, resulting in a decrease in battery cycle performance and rate performance. At the same time, the synthesis process of high-nickel materials is more sensitive to process conditions such as atmosphere and temperature, and is prone to cation mixing, which further affects the structural stability and electrochemical performance of the material.

[0004] To address the aforementioned issues with high-nickel materials, cathode materials with unique morphologies have become a research hotspot in recent years. For example, core-shell structured cathode materials provide high capacity through the core layer, while the shell layer suppresses interfacial side reactions and phase transitions to reduce cycle decay. However, the fabrication process for such core-shell structured materials is typically complex and requires stringent sintering conditions, limiting their large-scale application.

[0005] Hollow-structured materials are considered an effective way to improve structural stability because their internal cavities can effectively buffer volume changes. However, existing methods for preparing hollow structures still have many shortcomings: hard template methods require the use of strong acids or bases to remove the template, which can easily damage the material structure; soft template methods have difficulty ensuring the uniformity of product size; in addition, the poor compatibility between organic templates and inorganic precursors leads to uneven nucleation and growth, and the gases generated by template decomposition during high-temperature treatment may impact the inner surface of the material, reducing mechanical strength and making the material prone to cracking during cycling. Therefore, developing a simple, morphology-controllable, and high-strength preparation method for high-nickel ternary cathode materials is an urgent problem to be solved. Summary of the Invention

[0006] In view of this, the present invention provides a hollow ternary high-nickel cathode material and its preparation method, and a lithium-ion battery. The present invention uses TiO2-modified polymer microspheres as templates to prepare hollow ternary high-nickel cathode materials, which has the advantages of simple process and easy template removal, and the obtained material has high strength and excellent electrochemical performance.

[0007] In a first aspect, the present invention provides a method for preparing a hollow ternary high-nickel cathode material, comprising the following steps: Polymer microspheres were mixed with organic titanium source in the first liquid phase and hydrolyzed to prepare surface-modified TiO2 polymer microspheres; The TiO2-modified polymer microspheres were placed in a second liquid phase, and aqueous solutions of nickel salt, cobalt salt, and manganese salt were added to prepare a core-shell structure precursor by co-precipitation. The core-shell precursor is mixed with a lithium source and then sintered in stages under an oxygen-containing atmosphere to obtain a hollow ternary high-nickel cathode material; its structural formula is LiNi. x Co y Mn 1-x-y O2, 0.8≤x≤0.98, 0 <y<0.2。

[0008] Preferably, the polymer microspheres are selected from one or more of polystyrene microspheres, polymethyl methacrylate microspheres, and cross-linked polystyrene microspheres; the polymer microspheres are monodisperse and have an average particle size of 1~3μm.

[0009] Preferably, the organic titanium source is selected from one or more of isopropyl titanate, tetrabutyl titanate, or titanium acetylacetonate; the mass ratio of the polymer microspheres to the organic titanium source is 1:(0.8~1.2).

[0010] Preferably, the solvent of the first liquid phase is an aqueous ethanol solution; the hydrolysis temperature is 40~60℃, and the hydrolysis time is 1~5h.

[0011] Preferably, the solvent of the second liquid phase is water, and the pH is adjusted to 10-13 by alkaline solution; the nickel salt is selected from nickel nitrate, nickel sulfate, nickel chloride or nickel acetate; the cobalt salt is selected from cobalt nitrate, cobalt sulfate, cobalt chloride or cobalt acetate; and the manganese salt is selected from manganese nitrate, manganese sulfate, manganese chloride or manganese acetate.

[0012] Preferably, the particle size D50 of the core-shell structure precursor is 4~8μm.

[0013] Preferably, in the step of mixing the core-shell structure precursor with the lithium source, the ratio of the molar amount of Li to the total molar amount of Ni, Co and Mn is controlled to be (1~1.1):1; the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate and lithium acetate.

[0014] Preferably, the oxygen volume fraction in the oxygen-containing atmosphere is above 95%; the segmented sintering specifically involves: first heating to 300~500℃ and holding for sintering for 3~6 hours, then heating to 700~900℃ and holding for sintering for 8~20 hours.

[0015] Secondly, the present invention provides a hollow ternary high-nickel cathode material prepared by the above-mentioned preparation method.

[0016] Thirdly, the present invention provides a lithium-ion battery comprising the aforementioned hollow ternary high-nickel cathode material.

[0017] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The preparation method of hollow ternary high-nickel cathode material provided by the present invention is simple and the template is easy to remove. By using polymer microspheres modified with TiO2 on the surface as sacrificial templates, the polymer microspheres can decompose to generate CO2 and H2O in the low-temperature sintering stage through co-precipitation and segmented sintering. No additional etching steps are required, which simplifies the process and reduces the damage to the substrate material caused by strong acid / alkali etching. It can efficiently prepare ternary high-nickel cathode materials with uniform hollow structure, high mechanical strength and excellent electrochemical performance, further ensuring the structural integrity and performance stability of the material.

[0018] (2) The present invention utilizes the TiO2 layer generated by the hydrolysis of organic titanium source to modify the polymer microspheres with hydrophilicity, which greatly improves the wettability of the hydrophobic polymer surface with inorganic salt solution, ensuring that the ternary precursor can uniformly and densely nucleate and grow heterogeneously on its surface, avoiding self-generated homogeneous nucleation, and ensuring the morphological uniformity of the core-shell structure precursor from the source, laying the foundation for the integrity of the subsequent hollow structure.

[0019] (3) During the template removal process, the TiO2 layer on the surface of the polymer microspheres diffuses and accumulates in the inner surface layer at high temperature, forming a good protective layer. This effectively avoids the problem of the hollow structure cracking or collapsing due to the huge internal pressure generated by the template decomposition at high temperature, ensuring the material's good structural integrity and mechanical strength, and solving the defect of traditional hollow materials being prone to cracking during cycling due to insufficient mechanical strength.

[0020] (4) The hollow structure cathode material prepared by the present invention can shorten the lithium ion transport path, improve the rate performance and reduce the impedance on the one hand; on the other hand, it can effectively alleviate the volume expansion during cycling. The assembled battery retains a capacity of >93% after 50 cycles under 1C charge and discharge conditions, which significantly improves the cycle stability. Attached Figure Description

[0021] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0022] Figure 1 This is a cross-sectional SEM image of the hollow ternary high-nickel cathode material of Embodiment 1 of the present invention; Figure 2 These are the first charge-discharge curves of the batteries assembled in Embodiment 1 and Comparative Example 1 of the present invention; Figure 3 These are the discharge capacity change curves of the batteries assembled in Embodiment 1 and Comparative Example 1 of the present invention after 50 cycles at a 1C charge-discharge rate. Detailed Implementation

[0023] 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.

[0024] This invention provides a method for preparing a hollow ternary high-nickel cathode material, comprising the following steps: Polymer microspheres were mixed with organic titanium source in the first liquid phase and hydrolyzed to prepare surface-modified TiO2 polymer microspheres; The TiO2-modified polymer microspheres were placed in a second liquid phase, and aqueous solutions of nickel salt, cobalt salt, and manganese salt were added to prepare a core-shell structure precursor by co-precipitation. The core-shell precursor is mixed with a lithium source and then sintered in stages under an oxygen-containing atmosphere to obtain a hollow ternary high-nickel cathode material; its structural formula is LiNi.x Co y Mn 1-x-y O2, where 0.8 ≤ x ≤ 0.98 and 0 < y < 0.2.

[0025] In the above technical solution of the present invention, first, a TiO2 modification layer is formed on the surface of the polymer microspheres through the hydrolysis reaction of an organic titanium source. This process utilizes the controllable hydrolysis characteristics of the titanium source in the liquid phase, enabling the TiO2 precursor to nucleate and grow into a continuous coating on the surface of the microspheres. This not only improves the interfacial wettability between the hydrophobic polymer microspheres and the subsequent inorganic salt solution but also provides stable heterogeneous nucleation sites for the deposition of the ternary precursor.

[0026] Subsequently, during the coprecipitation process, the metal ions undergo a coprecipitation reaction under alkaline conditions. At this time, the TiO2 layer of the polymer microspheres with surface-modified TiO2 can induce the deposition of metal hydroxide (Ni x Co y Mn 1-x-y (OH)2) precursors on the surface of the microspheres uniformly and densely, forming a core-shell structure with the polymer microspheres with surface-modified TiO2 as the core and the precursor as the shell. This process effectively avoids the spontaneous homogeneous nucleation of metal ions in the solution and ensures the thickness uniformity and structural integrity of the precursor shell layer.

[0027] Finally, after the core-shell structure precursor is mixed with the lithium source and subjected to segmented sintering, in an oxygen-containing atmosphere, at the low-temperature stage, the polymer microspheres are thermally decomposed into volatile products (such as CO2, H2O) and completely removed, leaving a hollow cavity composed of the precursor shell layer; at the high-temperature stage, the active lithium ions generated by the decomposition of the lithium source react with the precursor through a solid-phase reaction to form a LiNi x Co y Mn 1-x-y O2 lattice. At the same time, the TiO2 modification layer diffuses and enriches towards the inner surface of the hollow structure at high temperature, forming a stable protective layer. This process not only constructs a hollow structure by removing the template, shortening the lithium-ion transmission path and buffering the volume expansion, but also enhances the structural mechanical strength through the TiO2 inner surface protective layer, ultimately achieving a synergistic improvement in the high energy density, cycle stability, and rate performance of the material.

[0028] In an optional embodiment of the present invention, the range of x is more preferably 0.85 ≤ x ≤ 0.92, and the range of y is more preferably 0 < y < 0.15. The larger the value of x, the higher the Ni content, which can further increase the number of reversible redox couples and thus significantly improve the specific capacity and battery energy density of the material; however, the Ni content should not be too high, otherwise, the cycle stability will be significantly reduced.

[0029] In an optional embodiment of the present invention, the polymer microspheres are selected from one or more of polystyrene microspheres, polymethyl methacrylate microspheres, and cross-linked polystyrene microspheres. Cross-linked polystyrene microspheres are polymer microspheres with a regular spherical structure formed by chemically cross-linking polystyrene (PS) with cross-linking agents such as divinylbenzene (DVB). The molecular structure of the above-mentioned polymer microspheres is stable; they do not hydrolyze, degrade, or swell under the hydrolysis process of the organic titanium source and under alkaline co-precipitation conditions. Furthermore, they can be completely decomposed into volatile products (such as CO2 and H2O) during high-temperature sintering, leaving no residual impurities, thus meeting the core requirement of easy template removal. The present invention does not impose special restrictions on the source of the above-mentioned polymer microspheres; they can be prepared in-house or obtained through commercial channels.

[0030] In an optional embodiment of the present invention, the polymer microspheres are monodisperse. Monodisperse microspheres ensure uniform particle size of the core-shell structure precursor, avoiding inconsistent hollow structure sizes due to template particle size differences, which would affect the consistency of material properties. The average particle size of the polymer microspheres is 1~3μm. If the particle size is too small, the hollow cavity will be too small, resulting in limited shortening of the lithium-ion transport path and insignificant impedance reduction; if the particle size is too large, the cavity will be too large, leading to insufficient mechanical strength and easy breakage during cycling.

[0031] In an optional embodiment of the present invention, the organic titanium source is selected from one or more of isopropyl titanate, tetrabutyl titanate, or titanium acetylacetonate. Isopropyl titanate or tetrabutyl titanate can be gradually hydrolyzed in solution to generate a Ti(OH)4 precursor, which is directionally adsorbed onto the surface of polymer microspheres and condenses into a TiO2 layer; titanium acetylacetonate is a chelating titanium source, which achieves more uniform nucleation and growth by slowly releasing titanium ions, avoiding localized excessive hydrolysis that leads to TiO2 particle agglomeration. More preferably, the organic titanium source is isopropyl titanate or tetrabutyl titanate.

[0032] In an optional embodiment of the present invention, the mass ratio of the polymer microspheres to the organic titanium source is 1:(0.8~1.2). Insufficient organic titanium source results in a too-thin modified layer, insufficient improvement in hydrophilicity, and uneven precursor deposition; excessive organic titanium source results in an too-thick modified layer, which may block some cavities during subsequent high-temperature diffusion, affecting the formation of the hollow structure. In this invention, the polymer microspheres are added in the form of a polymer microsphere emulsion, wherein the mass fraction of the polymer microspheres in the emulsion is 5~20wt%. The present invention does not impose special limitations on the preparation method of the polymer microsphere emulsion; commonly used methods for preparing polymer microsphere emulsions are acceptable.

[0033] In an optional embodiment of the present invention, the solvent of the first liquid phase is an aqueous ethanol solution; ethanol can reduce solvent polarity, improve the wettability of hydrophobic polymer microspheres, and prevent microsphere aggregation; water provides OH- for the hydrolysis of the titanium source. -This promotes the formation of TiO2 precursors, and the two work synergistically to maintain the balance between microsphere dispersion and titanium source hydrolysis. In the ethanol-water solution, the volume fraction of ethanol is preferably 80-99%, more preferably 90-98%. In this invention, the hydrolysis temperature is 40-60℃, more preferably 45-55℃, and the hydrolysis time is 1-5 hours. This ensures that the organic titanium source is fully hydrolyzed and forms a continuous and uniform TiO2 layer on the microsphere surface. In the first liquid phase of this invention, a dispersant, such as polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG), can also be added to promote the dispersion of polymer microspheres.

[0034] In an optional embodiment of the present invention, the solvent of the second liquid phase is water, and the pH is adjusted to 10-13 by an alkaline solution. The alkaline solution is an aqueous solution of sodium hydroxide and / or an aqueous solution of ammonia. The nickel salt is selected from nickel nitrate, nickel sulfate, nickel chloride, or nickel acetate; the cobalt salt is selected from cobalt nitrate, cobalt sulfate, cobalt chloride, or cobalt acetate; the manganese salt is selected from manganese nitrate, manganese sulfate, manganese chloride, or manganese acetate, and those skilled in the art can select according to actual needs.

[0035] This invention does not impose special limitations on the specific process of preparing core-shell structured precursors by co-precipitation. In optional embodiments of this invention, an aqueous solution of sodium hydroxide is used as the precipitant, with a concentration of 5-12 mol / L; an aqueous solution of ammonia is used as the complexing agent, with a concentration of 5-8 mol / L; and in the aqueous solutions of nickel, cobalt, and manganese salts, Ni... 2+ Co 2+ and Mn 2 + The total concentration was 1.5–2.5 mol / L; aqueous solutions of nickel, cobalt, and manganese salts, precipitant, and complexing agent were injected separately to maintain the pH of the reaction system at 10–13. The temperature during the coprecipitation reaction was 45–60 °C, and the stirring speed was 400–1000 rpm. Core-shell structured precursors to the target particle size were prepared by coprecipitation.

[0036] In an optional embodiment of the present invention, the particle size D50 of the core-shell structure precursor is 4~8 μm. A particle size D50 that is too small will result in a thin shell, leading to insufficient mechanical strength of the hollow structure after sintering, making it prone to breakage during cycling; a particle size that is too large will result in a thick shell, leading to a small proportion of the hollow cavity, limited effect on shortening the lithium-ion transport path, and insignificant impedance reduction. A suitable particle size ensures that the hollow cavity can effectively buffer volume expansion, shorten the ion transport path, and maintain sufficient mechanical strength, which is key to balancing material capacity, rate performance, and cycling stability. Particle size D50 refers to the particle size value corresponding to a cumulative particle size distribution percentage of 50%.

[0037] In an optional embodiment of the present invention, in the step of mixing the core-shell structure precursor with the lithium source, the molar ratio of Li to the total molar ratio of Ni, Co and Mn is controlled to be (1~1.1):1, more preferably (1.02~1.08):1; a slight excess of lithium source can compensate for the loss caused by lithium volatilization during high-temperature sintering; the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate, more preferably lithium hydroxide and / or lithium carbonate, and lithium hydroxide is preferably its hydrate.

[0038] In an optional embodiment of the present invention, the oxygen volume fraction in the oxygen-containing atmosphere is 95% or more, more preferably 99% or more. The segmented sintering specifically involves: first, heating to 300-500℃ and holding for sintering for 3-6 hours; the low-temperature stage is used for polymer microsphere decomposition, slowly releasing gas to prevent the cavity from cracking; then heating to 700-900℃ and holding for sintering for 8-20 hours, more preferably 8-15 hours; the high-temperature stage promotes the reaction of lithium ions with the precursor solid phase to generate complete LiNi. x Co y Mn 1-x-y The O2 lattice allows the TiO2-modified layer to diffuse and enrich into the hollow inner surface, forming a protective layer and enhancing structural stability. This invention does not impose special limitations on the heating rate during sintering, but it is preferably 2~10℃ / min.

[0039] The present invention also provides a hollow ternary high-nickel cathode material prepared by the above preparation method.

[0040] The present invention also provides a lithium-ion battery comprising the above-mentioned hollow ternary high-nickel cathode material.

[0041] The hollow structure cathode material prepared by this invention can shorten the lithium-ion transport path, improve rate performance and reduce impedance. On the other hand, it can effectively alleviate volume expansion during cycling. The assembled battery retains a capacity of >93% after 50 cycles under 1C charge and discharge conditions, which significantly improves cycle stability.

[0042] This invention does not impose any special limitations on the structure and preparation method of the above-mentioned lithium-ion battery; commonly used structures and preparation methods in the field can be used.

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0044] Example 1 This embodiment provides a hollow ternary high-nickel cathode material and its preparation method.

[0045] (1) Preparation of TiO2@PS composite microspheres: Monodisperse micron-sized (average particle size of 2 μm) polystyrene (PS) microsphere emulsion (PS microsphere mass fraction of 10 wt%) was dispersed in ethanol, and the volume ratio of PS microsphere emulsion to ethanol was controlled at 1:10; a uniform dispersion was formed; isopropyl titanate (TTIP) was added, and the mass ratio of PS microspheres to TTIP was controlled at 1:1; the mixture was continuously stirred and hydrolyzed at 50℃ and 1000 rpm for 2 h to obtain TiO2@PS composite microsphere solution (containing about 30 wt% TiO2@PS composite microspheres).

[0046] (2) Preparation of core-shell structure precursors (coprecipitation method): Solution A: Prepare a mixed aqueous solution of nickel nitrate, cobalt nitrate, and manganese nitrate according to the molar ratio of Ni, Co, and Mn of 0.9:0.05:0.05, and control the Ni content. 2+ Co 2+ Mn 2+ The total concentration was 2.1 mol / L.

[0047] Solution B: A 10 mol / L sodium hydroxide solution; it serves as a precipitant.

[0048] Solution C: An aqueous solution of ammonia with an ammonia concentration of 6 mol / L; it is a complexing agent.

[0049] Preparation of the base solution: Place the TiO2@PS composite microsphere solution from step (1) in the reactor, add pure water, and control the ratio of TiO2@PS composite microsphere solution to pure water to be 10g: 200mL; then add ammonia water to make the ammonia concentration 0.5mol / L; then adjust the pH of the system to 12.5 with 10mol / L sodium hydroxide solution.

[0050] The stirring speed in the reactor was controlled at 850 rpm, and the temperature was controlled at 50℃. Solutions A, B, and C were added to the reactor via a peristaltic pump to undergo a co-precipitation reaction. The injection rate of solution A was controlled at 15 mL / min, and the injection rate of solution C was controlled at 3 mL / min. The pH of the reaction system was stabilized at 10~12.5 by controlling solutions B and C. After the particle size D50 grew to 5±0.5 μm, the injection was stopped, and the product was centrifuged, washed with pure water, and dried at 110℃ to obtain the core-shell structure precursor.

[0051] (3) Preparation of hollow ternary high-nickel cathode material: The prepared core-shell precursor and LiOH·H2O were mixed in a high-speed mixer, and the molar ratio of Li / (Ni+Co+Mn) was controlled at 1.05. The mixture was then placed in a crucible and sintered in a pure oxygen atmosphere (oxygen volume fraction ≥99%). The temperature was first increased to 450℃ at 2℃ / min and held for 4 h, and then increased to 800℃ at 5℃ / min and held for 12 h. The mixture was then cooled to room temperature in the furnace, pulverized, and sieved to obtain a hollow ternary high-nickel cathode material with the structural formula LiNi. 0.9 Co 0.05 Mn 0.05 O2.

[0052] The cross-sectional SEM (scanning electron microscope) image of the hollow ternary high-nickel cathode material prepared in this embodiment is shown below. Figure 1 As shown, the prepared material has a hollow structure and a relatively uniform particle size of about 5 μm. This is mainly due to the hydrophilic modification of the PS microspheres by the TiO2 layer formed by the hydrolysis of titanate, which improves the wettability of the microsphere surface to inorganic salt solutions, thereby ensuring that the ternary precursor can uniformly and densely nucleate and grow heterogeneously on its surface, avoiding homogeneous nucleation.

[0053] Example 2 The difference between this embodiment and Embodiment 1 is that the average particle size of the PS microspheres in this embodiment is 3 μm.

[0054] Example 3 The difference between this embodiment and Example 1 is that this embodiment uses monodisperse micron-sized (average particle size of 1 μm) polymethyl methacrylate microsphere emulsion instead of PS microsphere emulsion.

[0055] Comparative Example 1 The difference between this comparative example and Example 1 is that PS microspheres are used instead of TiO2@PS composite microspheres in this comparative example. The steps of this comparative example are as follows: (1) Preparation of core-shell structure precursors (coprecipitation method): Solution A: Prepare a mixed aqueous solution of nickel nitrate, cobalt nitrate, and manganese nitrate according to the molar ratio of Ni, Co, and Mn of 0.9:0.05:0.05, and control the Ni content. 2+ Co 2+ Mn 2+ The total concentration was 2.1 mol / L.

[0056] Solution B: A 10 mol / L sodium hydroxide solution; it serves as a precipitant.

[0057] Solution C: An aqueous solution of ammonia with an ammonia concentration of 6 mol / L; it is a complexing agent.

[0058] Preparation of the base solution: Place the monodisperse micron-sized (average particle size of 2μm) PS microsphere emulsion (PS microsphere mass fraction of 10wt%) in the reactor, add pure water, and control the volume ratio of PS microsphere emulsion to pure water to be 10g : 200mL; then add ammonia water to make the ammonia concentration 0.5mol / L; then adjust the pH of the system to 12.5 with 10mol / L sodium hydroxide solution.

[0059] The stirring speed in the reactor was controlled at 850 rpm, and the temperature was controlled at 50℃. Solutions A, B, and C were added to the reactor via a peristaltic pump to undergo a co-precipitation reaction. The injection rate of solution A was controlled at 15 mL / min, and the injection rate of solution C was controlled at 3 mL / min. The pH of the reaction system was stabilized at 10~12.5 by controlling solutions B and C. After the particle size D50 grew to 5±0.5 μm, the injection was stopped, and the product was centrifuged, washed with pure water, and dried at 110℃ to obtain the core-shell structure precursor.

[0060] (2) Preparation of hollow ternary high-nickel cathode material: The prepared core-shell precursor and LiOH·H2O were mixed in a high-speed mixer, and the molar ratio of Li / (Ni+Co+Mn) was controlled at 1.05. The mixture was then placed in a crucible and sintered in a pure oxygen atmosphere (oxygen volume fraction ≥99%). The temperature was first increased to 450℃ at 2℃ / min and held for 4 h, and then increased to 800℃ at 5℃ / min and held for 12 h. The mixture was then cooled to room temperature in the furnace, pulverized, and sieved to obtain a hollow ternary high-nickel cathode material with the structural formula LiNi. 0.9 Co 0.05 Mn 0.05 O2.

[0061] Comparative Example 2 The difference between this comparative example and Example 1 is that TiO2@PS composite microspheres are not added in this comparative example. Solutions A, B, and C are the same as in Example 1, and the specific steps are as follows: Pure water was added to the reactor, followed by ammonia solution to achieve an ammonia concentration of 0.5 mol / L. The pH of the system was then adjusted to 12.5 using a 10 mol / L sodium hydroxide solution. The stirring speed in the reactor was controlled at 850 rpm, and the temperature was controlled at 50℃. Solutions A, B, and C were added to the reactor via a peristaltic pump to induce a co-precipitation reaction. The injection rate of solution A was controlled at 15 mL / min, and the injection rate of solution C was controlled at 3 mL / min. The pH of the reaction system was stabilized between 10 and 12.5 using solutions B and C. Once the particle size D50 reached 5 ± 0.5 μm, the injection was stopped. The sample was then centrifuged, washed with pure water, and dried at 110℃ using a forced-air drying process to obtain the precursor.

[0062] The prepared precursor and LiOH·H2O were mixed using a high-speed mixer, and the molar ratio of Li / (Ni+Co+Mn) was controlled at 1.05. The mixture was then placed in a crucible and sintered in a pure oxygen atmosphere (oxygen volume fraction ≥99%). The temperature was first increased to 450℃ at 2℃ / min and held for 4 h, and then increased to 800℃ at 5℃ / min and held for 12 h. The mixture was then cooled to room temperature in the furnace, pulverized, and sieved to obtain a ternary high-nickel cathode material with the structural formula LiNi. 0.9 Co 0.05 Mn 0.05 O2.

[0063] Comparative Example 3 The difference between this comparative example and Example 1 is that the average particle size of the PS microspheres is 0.5 μm.

[0064] Comparative Example 4 The difference between this comparative example and Example 1 is that the average particle size of the PS microspheres is 4 μm.

[0065] Test case 1. Powder impedance measurement: The ternary high-nickel cathode materials of Examples 1-3 and Comparative Examples 1-4 were formed by powder pressing, and the volume impedance was measured by an impedance meter and the volume resistivity was calculated. The results are shown in Table 1.

[0066] Table 1. Powder impedance of ternary high-nickel cathode materials in Examples 1-3 and Comparative Examples 1-3

[0067] As shown in Table 1, the hollow-structured ternary high-nickel cathode material prepared using TiO2@PS composite microspheres as a template exhibits the lowest powder impedance, decreasing by approximately 50% compared to the non-hollow-structured ternary high-nickel cathode material (Comparative Example 2). PS microspheres can also reduce powder impedance to some extent when used as a template, but the reduction is not significant. A comparison between Comparative Example 3 and Example 1 shows that when the hollow cavity is too small, the impedance increases. This is because a small hollow cavity results in a longer lithium-ion transport path.

[0068] 2. Button battery performance testing: The ternary high-nickel cathode materials of Examples 1-3 and Comparative Examples 1-4, polyvinylidene fluoride (PVDF), and conductive carbon black were mixed in a mass ratio of 8:1:1 and dissolved in N-methylpyrrolidone to prepare a cathode slurry. The slurry was made free of particles. The slurry was then uniformly coated onto aluminum foil using a coating machine to form an electrode sheet. The coated electrode sheet was placed in a vacuum drying oven at 120°C and vacuum dried for 12 hours. The electrode sheet was then removed and rolled on a roller press for later use. The electrode sheet was cut into 12mm diameter circular pieces using a cutting machine, placed in a vacuum drying oven at 60°C and dried for 12 hours to obtain the cathode electrode sheet, which was then weighed using an electronic balance. Finally, the positive electrode, lithium sheet, spring sheet, gasket, positive electrode shell, negative electrode shell, separator, and electrolyte were assembled into a CR2025 coin cell in an argon-filled glove box. The electrolyte was a 1M NaPF6 solution dissolved in a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) (by volume, EC:DMC = 1:1). The lithium metal sheet served as the counter electrode. The charge / discharge voltage range was 2.8–4.4 V, the initial charge / discharge rate was 0.1C, and the nominal specific capacity was 200 mAh / g at 1C. Cycling performance testing was conducted at a charge / discharge rate of 50 cycles at 1C. Rate performance testing was performed at discharge rates of 0.5C, 1C, and 2C. The results are shown in Table 2.

[0069] Table 2 Electrochemical performance data of batteries assembled from ternary high-nickel cathode materials in the examples and comparative examples.

[0070] Figure 2 The first charge-discharge curves of the batteries assembled in Example 1 and Comparative Example 1 are shown. Figure 3 The discharge capacity change curves of the batteries assembled in Example 1 and Comparative Example 1 after 50 cycles at a 1C charge-discharge rate.

[0071] From Table 1 and Figure 2 , Figure 3As can be seen, the embodiments exhibit higher discharge specific capacity and initial charge-discharge efficiency, as well as higher discharge specific capacity at different rates and good cycle stability. At 1C, the capacity retention rate after 50 cycles is >93%, which is a significant improvement compared to the battery assembled with the non-hollow ternary high-nickel cathode material (Comparative Example 2). If only PS microspheres are used as templates, the performance improvement of the battery assembled with the hollow ternary high-nickel cathode material is not significant, and the capacity retention rate after 50 cycles at 1C is far lower than that of the embodiments. This shows that TiO2 modification can significantly improve the cycle stability of the ternary high-nickel cathode material. This is partly due to the TiO2 layer generated by the hydrolysis of isopropyl titanate, which hydrophilically modifies the PS template, greatly improving the wettability of the hydrophobic PS surface with the inorganic salt solution. This ensures that the ternary precursor can uniformly and densely nucleate and grow heterogeneously on its surface, avoiding self-generated homogeneous nucleation and ensuring high particle uniformity. On the other hand, this special hollow structure effectively shortens the lithium-ion transport path, reduces impedance, and improves rate performance. Simultaneously, the TiO2-modified layer enriches on the inner surface, forming a robust and stable protective layer. This prevents the hollow structure from cracking or collapsing due to the enormous internal pressure generated by PS decomposition at high temperatures, ensuring good structural integrity and mechanical strength. It also alleviates volume expansion caused by anisotropic stress concentration during cycling, improving cycle stability. If the hollow cavity is too large, it reduces the material's mechanical strength and cycle stability; if the hollow cavity is too small, it lengthens the lithium-ion transport path, increasing impedance and degrading rate performance.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow ternary high-nickel cathode material, characterized in that, Includes the following steps: Polymer microspheres were mixed with organic titanium source in the first liquid phase and hydrolyzed to prepare surface-modified TiO2 polymer microspheres; The TiO2-modified polymer microspheres were placed in a second liquid phase, and aqueous solutions of nickel salt, cobalt salt, and manganese salt were added to prepare a core-shell structure precursor by co-precipitation. The core-shell precursor is mixed with a lithium source and then sintered in stages under an oxygen-containing atmosphere to obtain a hollow ternary high-nickel cathode material; its structural formula is LiNi. x Co y Mn 1-x-y O2, 0.8≤x≤0.98, 0 <y<0.2。 2. The preparation method according to claim 1, characterized in that, The polymer microspheres are selected from one or more of polystyrene microspheres, polymethyl methacrylate microspheres, and cross-linked polystyrene microspheres; the polymer microspheres are monodisperse and have an average particle size of 1~3μm.

3. The preparation method according to claim 1, characterized in that, The organic titanium source is selected from one or more of isopropyl titanate, tetrabutyl titanate, or titanium acetylacetonate; the mass ratio of the polymer microspheres to the organic titanium source is 1:(0.8~1.2).

4. The preparation method according to claim 1, characterized in that, The solvent for the first liquid phase is an aqueous ethanol solution; the hydrolysis temperature is 40~60℃, and the hydrolysis time is 1~5h.

5. The preparation method according to claim 1, characterized in that, The solvent of the second liquid phase is water, and the pH is adjusted to 10-13 by alkaline solution; the nickel salt is selected from nickel nitrate, nickel sulfate, nickel chloride or nickel acetate; the cobalt salt is selected from cobalt nitrate, cobalt sulfate, cobalt chloride or cobalt acetate; the manganese salt is selected from manganese nitrate, manganese sulfate, manganese chloride or manganese acetate.

6. The preparation method according to claim 1, characterized in that, The particle size D50 of the core-shell structure precursor is 4~8μm.

7. The preparation method according to claim 1, characterized in that, In the step of mixing the core-shell structure precursor with the lithium source, the ratio of the molar amount of Li to the total molar amount of Ni, Co and Mn is controlled to be (1~1.1):1; the lithium source is selected from one or more of lithium hydroxide, lithium carbonate, lithium nitrate and lithium acetate.

8. The preparation method according to claim 1, characterized in that, In the oxygen-containing atmosphere, the volume fraction of oxygen is above 95%; the segmented sintering specifically involves: first heating to 300~500℃ and holding for sintering for 3~6 hours, then heating to 700~900℃ and holding for sintering for 8~20 hours.

9. A hollow ternary high-nickel cathode material prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, Including the hollow ternary high-nickel cathode material as described in claim 9.

Images