High-spin-state transition metal defect type metal oxide composite electrocatalyst, preparation method and application in alkali metal-sulfur battery

Abstract

The invention discloses a high-spin-state transition metal defect type metal oxide composite electrocatalyst, a preparation method of the high-spin-state transition metal defect type metal oxide composite electrocatalyst and application of the high-spin-state transition metal defect type metal oxide composite electrocatalyst in an alkali metal-sulfur battery, and belongs to the technical field of electrochemical energy storage. And a high spin transition metal atom anchored to a defect region or adjacent region of the metal oxide support having the engineered defect; high-spin-state transition metal atoms are induced or stabilized in a high-spin state by forming an unsaturated coordination environment, modifying a carrier electronic structure or introducing a specific coordination group. The defect site of the carrier stably anchors the transition metal atoms in the high spin state, and the high spin state of the transition metal is induced or stabilized through strong carrier-metal interaction. And unpaired electrons in a high-spin-state transition metal atom d orbit and polysulfide form orbital hybridization to enhance chemical adsorption. High-spin-state electrons are easy to transfer, electron transmission is accelerated, a polysulfide conversion path energy barrier is reduced, and rapid and reversible conversion of sulfur species is promoted.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to high-spin-state transition metal defect type metal oxide composite electrocatalysts, their preparation methods, and their application in alkali metal-sulfur batteries. Background Technology

[0002] As the global energy transition towards clean and low-carbon energy progresses, the large-scale application of renewable energy sources such as solar and wind power is placing higher demands on the performance of energy storage technologies. While traditional lithium-ion batteries are widely used in consumer electronics and electric vehicles, the theoretical energy density of their cathode materials is generally low, making it difficult to meet the needs of scenarios such as long-range electric vehicles and large-scale grid energy storage. Lithium-sulfur batteries, however, boast a theoretical energy density of 2600 Wh / kg. -1 With its ultra-high theoretical energy density, lithium-sulfur batteries are considered the most promising next-generation high-energy-density energy storage technology for commercialization. From a practical application perspective, lithium-sulfur batteries can not only effectively improve the range of electric vehicles but also reduce the unit capacity cost of large-scale energy storage systems, supporting the efficient utilization of renewable energy and playing a significant role in driving the energy revolution.

[0003] However, the commercialization of lithium-sulfur batteries still faces three key technical challenges: sulfur and the discharge end product lithium sulfide have extremely low conductivity, hindering charge transfer and affecting the battery's rate performance; the large volume change between sulfur and lithium sulfide during charging and discharging can easily lead to electrode structure damage, active material shedding, and reduced cycle stability; and the intermediate product lithium polysulfide is readily soluble in the electrolyte and migrates back and forth between the positive and negative electrodes, forming a shuttle effect that causes loss of active material and generates insulating products on the lithium anode surface, reducing coulombic efficiency and cycle life. To solve these problems, researchers have tried various methods, among which adding an electrocatalyst is the core means to suppress the shuttle effect. Through strong interaction with lithium polysulfide, it enhances adsorption and accelerates redox reactions. Currently, there are four common types of electrocatalysts: transition metals and their compounds, which rely on coordination adsorption at metal sites for catalysis, but the active sites are prone to aggregation; metal-organic frameworks, which have large specific surface areas and tunable pores, can confine lithium polysulfides and provide catalytic sites, but have poor conductivity and insufficient stability; covalent organic frameworks, which have regular structures and good conductivity, and can enhance adsorption through modification, but have few catalytic active sites; and single-atom catalysts, which can maximize atom utilization, but are complex to prepare, costly, and prone to site migration. In addition, strategies such as introducing defects or adjusting the coordination environment to increase unsaturated active centers have also been effective in improving battery stability.

[0004] Despite some progress in electrocatalyst research, several issues still hinder the commercialization of lithium-sulfur batteries. First, most catalysts can only focus on improving one aspect of adsorption or accelerating reaction kinetics. For example, transition metal compounds have strong adsorption but slow reactions, while covalent organic frameworks have good conductivity but weak adsorption, making it impossible to achieve both simultaneously. Second, strategies that simply increase unsaturated active sites have limited effectiveness; either the adsorption is too strong, hindering subsequent reactions, or these active sites are easily eroded or reconstructed by the electrolyte during cycling, leading to decreased catalytic activity. Furthermore, the interaction between the catalyst active component and the support is mostly simple, lacking strong interactions, making active sites prone to detachment. Moreover, the conductivity of the support and the catalytic performance of the catalyst are often mismatched, affecting charge transport efficiency. Additionally, high-performance materials such as single-atom catalysts and complex metal-organic framework derivatives have complex preparation processes, are difficult to mass-produce, and are costly. These problems mean that current lithium-sulfur batteries do not yet meet the standards for practical application in terms of energy density, cycle life, rate performance, and cost. There is a need to develop novel, efficient, stable, and low-cost electrocatalysts that can achieve synergistic effects through multiple mechanisms. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a high-spin-state transition metal defect-type metal oxide composite electrocatalyst, its preparation method, and its application in alkali metal-sulfur batteries. This addresses the technical problem of how to precisely control the spin state of the transition metal and anchor it on an engineered defect metal oxide support to synergistically enhance the adsorption capacity and conversion kinetics of polysulfides.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a high-spin-state transition metal defect type metal oxide composite electrocatalyst, comprising: a metal oxide support with engineered defects, and high-spin-state transition metal atoms anchored in the defect region or adjacent region of the metal oxide support with engineered defects. High-spin transition metal atoms can be induced or stabilized in a high-spin state by forming an unsaturated coordination environment, modifying the electronic structure of the support, or introducing specific coordination groups.

[0007] Preferably, the metal oxide support with engineered defects is at least one of titanium oxide, zinc oxide, cerium oxide, zirconium oxide, aluminum oxide, and silicon oxide.

[0008] Preferably, the engineered defects of the metal oxide support with engineered defects are oxygen vacancies, cation vacancies, interstitial defects, grain boundary defects, or surface unsaturated sites.

[0009] Preferably, the high-spin transition metal atom is at least one of cobalt, iron, nickel, manganese, and chromium.

[0010] This invention also discloses a method for preparing the above-mentioned high-spin-state transition metal defect type metal oxide composite electrocatalyst, comprising the following steps: First, a metal oxide support with engineered defects is prepared; then, the metal oxide support with engineered defects is mixed with a transition metal precursor to anchor the transition metal atoms in the defect region or adjacent region of the metal oxide support with engineered defects; the metal oxide support with engineered defects and anchored transition metal atoms is heat-treated to induce or stabilize the high spin state of the transition metal atoms, thus obtaining a high spin state transition metal defect type metal oxide composite electrocatalyst.

[0011] Preferably, the metal oxide support with engineered defects is prepared by hydrothermal method, solvothermal method, coprecipitation method or molten salt method; transition metal atoms are anchored to the defect region or adjacent region of the metal oxide support with engineered defects by atomic layer deposition, chemical vapor deposition, impregnation-reduction method or electrodeposition method.

[0012] Preferably, the heat treatment temperature is 300-700℃; the heat treatment time is 1-8h.

[0013] This invention also discloses the application of the above-mentioned high-spin-state transition metal defect type metal oxide composite electrocatalyst in the preparation of alkali metal-sulfur batteries.

[0014] Preferably, alkali metal-sulfur batteries include lithium-sulfur batteries, sodium-sulfur batteries, or potassium-sulfur batteries.

[0015] Preferably, a high-spin-state transition metal defect type metal oxide composite electrocatalyst is used to modify the separator, as a positive electrode additive, or coated on the current collector to construct an alkali metal-sulfur battery.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a high-spin transition metal defect-type metal-oxide composite electrocatalyst. The metal sites exposed by oxygen vacancies on the metal oxide support surface form coordination bonds with transition metal atoms, restricting atomic migration and stabilizing their high-spin state. In the electrochemical reaction, the unpaired d electrons of the high-spin transition metal overlap with the sulfur atoms of polysulfides, forming a strong chemisorption effect. Simultaneously, high-spin electrons readily transfer to polysulfides, lowering the activation energy barrier for sulfur species transformation and accelerating the conversion of liquid polysulfides to solid lithium sulfide. The synergistic effect of support defects and metal atoms effectively inhibits polysulfide diffusion while simultaneously increasing the redox reaction rate. By precisely controlling the coordination environment of the transition metal through support defects, it maintains a high-spin state, exhibiting both strong adsorption and high catalytic activity. Compared to simply increasing the specific surface area or defect concentration of the support, this approach achieves essential optimization of active sites through electronic structure regulation. This solves the problem of the difficulty in synergistically enhancing polysulfide adsorption and catalytic conversion. Support defects stabilize the high-spin state of the transition metal, allowing it to continuously provide unpaired electrons, strengthening the anchoring effect on polysulfides. Meanwhile, the high-spin electron transfer capability accelerates the sulfur species conversion kinetics, reducing the accumulation and migration of intermediate products. This composite structure remains stable during cycling, significantly improving the battery's capacity retention and rate performance. Utilizing metal oxides with abundant engineered defects as a support, the defect sites not only stably anchor high-spin transition metal atoms but also further induce or stabilize the high-spin state of the transition metal through strong support-metal interactions (SMSI). High-spin transition metal atoms possess a unique electronic structure, with a large number of unpaired electrons in their d orbitals. These unpaired electrons can form strong orbital hybridization with polysulfide species (especially the p orbitals of S atoms), thereby significantly enhancing the chemisorption of polysulfides. Simultaneously, the easy transferability of high-spin electrons accelerates electron transport in electrochemical reactions, lowers the energy barrier of polysulfide conversion pathways, and thus promotes the rapid and reversible conversion of sulfur species.

[0017] Furthermore, metal oxide supports play a crucial role in catalyst systems through their unique crystal structures and defect-forming capabilities. For example, oxygen vacancy defects in titanium oxide supports can serve as anchoring sites for transition metal atoms, achieving stable metal atom loading through the formation of Ti-OM bonds; zinc vacancy defects in zinc oxide supports can alter the local electron cloud distribution, promoting spin state modulation of transition metal d-orbital electrons; and cerium oxide supports can achieve stable loading through Ce... 3+ / Ce 4+Oxygen vacancies generated by redox pairs can enhance electron transfer between the support and transition metals; the high surface energy defect sites of zirconia supports can inhibit the migration and aggregation of transition metal atoms; the mesoporous structure of alumina supports can increase the exposed area of ​​active sites; and the surface silanol groups of silica supports can coordinate with transition metal precursors, achieving atomic-level dispersion. These support materials, through defect engineering, synergistically solve the problems of insufficient defect density and weak anchoring ability in traditional catalyst supports.

[0018] Furthermore, oxygen vacancies trap free electrons, forming localized charge accumulation regions that preferentially attract transition metal atoms to these defect sites via electrostatic interactions. Simultaneously, the stress field generated by lattice distortion around the vacancies alters the coordination environment of the transition metal. Cation vacancies form covalent bonds with the transition metal through exposed coordinating unsaturated sites; the matching of vacancy size with the radius of the metal atom determines anchoring stability. Interstitial defects introduce additional atoms to occupy lattice interstices, causing changes in the surrounding metal-oxygen bond length, thereby modulating the carrier Fermi level position to optimize electron transfer paths. Grain boundary defects construct continuous lattice distortion channels, lowering the electron migration barrier; simultaneously, dangling bonds at the interface can serve as secondary anchoring points for the transition metal. Surface unsaturated sites coordinate with the transition metal through unsaturated chemical bonds; the electron cloud rearrangement caused by the decrease in coordination number can induce the transition metal to maintain a high-spin state.

[0019] Furthermore, when cobalt, iron, nickel, manganese, and chromium are high-spin transition metal atoms, the number of unpaired electrons increases with increasing spin state. After anchoring at defect sites on the metal oxide support, these metal atoms interact strongly with sulfur atoms in polysulfides through dp orbital hybridization, inhibiting the dissolution and migration of polysulfides. For example, the d orbital electrons of high-spin cobalt hybridize with the p orbital electrons of polysulfides to form covalent bonds, enhancing adsorption strength; high-spin iron accelerates the redox reaction of polysulfides through electron transfer. Combinations of different metals can further optimize the electronic structure; for example, the cobalt-iron bimetallic system can synergistically improve adsorption and catalytic efficiency.

[0020] This invention discloses a method for preparing high-spin transition metal defect-type metal oxide composite electrocatalysts, employing a rational design strategy of "defect construction-atomic anchoring-spin modulation," which offers significant technical advantages. First, by controllably introducing high-density engineered defects into the metal oxide, abundant and highly stable anchoring sites are provided for subsequent transition metal atoms, fundamentally solving the problem of active site agglomeration and deactivation in traditional supported catalysts. Second, various mature chemical methods are used to precisely "lock" transition metal atoms onto these defect sites, achieving atomic-level dispersion of active centers and greatly improving atom utilization. Finally, and most importantly, by precisely controlling the heat treatment conditions, the strong support-metal interaction (SMSI) and the unique coordination environment of the defect region are utilized to effectively induce and stabilize the "high-spin state" of the transition metal atoms. This stepwise, controllable preparation method ensures that the final catalyst possesses both high-density atomic-level active sites and a unique electronic structure, which is the fundamental guarantee for its efficient adsorption and catalytic conversion of polysulfides.

[0021] Furthermore, hydrothermal, solvothermal, precipitation, or template methods are classic and efficient techniques for preparing nanostructured metal oxide supports. These methods are chosen because they allow for the controlled preparation of support materials with high specific surface area, porous structures, and abundant intrinsic defects (such as surface unsaturated sites) under relatively mild conditions. For example, hydrothermal / solvothermal methods easily control the crystal phase and morphology of the products (e.g., nanosheets, nanorods), while template methods can construct well-organized hierarchical channels. These structural features provide an ideal physical platform for the subsequent introduction of engineered defects and the efficient and uniform anchoring of transition metal atoms. A high specific surface area, porous support not only maximizes the exposure of active sites but also provides convenient channels for electrolyte wetting and rapid transport of sulfur species, thereby synergistically improving the overall electrochemical performance of the catalyst.

[0022] Furthermore, the heat treatment temperature (300-700℃) and time (1-8h) are the core process windows for realizing and stabilizing the high-spin state of transition metals. Their purpose and benefits are reflected in the following two aspects: First, achieving the induction and stabilization of the high-spin state. Within this temperature range, the system can obtain sufficient energy to promote the formation of stable chemical bonds (such as Ti-O-Co bonds) between transition metal atoms and support defect sites (such as oxygen vacancies). Simultaneously, the local lattice distortion and unsaturated coordination environment caused by defects alter the crystal field, prompting a rearrangement of the d-orbital electrons of the transition metal atoms, transitioning from a low-spin state to a more energy-favorable high-spin state. Second, maintaining the integrity and high activity of the support structure. This upper temperature limit (700℃) has been carefully selected to ensure the formation of the high-spin state while avoiding severe sintering of the support material, collapse of the pore structure, or massive annihilation of defects, thus completely preserving the catalyst's high specific surface area and high density of active sites. Similarly, a processing time of 1-8 hours represents the optimal balance between ensuring sufficient spin-state transition and preventing material performance degradation. Therefore, this optimized combination of heat treatment parameters is essential for obtaining composite electrocatalysts that possess both high activity and high stability.

[0023] This invention discloses the application of high-spin transition metal defect-type metal oxide composite electrocatalysts in the preparation of alkali metal-sulfur batteries. In a lithium-sulfur battery system, oxygen-vacancy titanium oxide support material anchored by high-spin cobalt atoms is uniformly coated on the membrane surface to form a functionalized interlayer. The high-spin cobalt atoms in this composite electrocatalyst form strong hybridization with the p orbitals of polysulfides through unpaired d electrons, continuously adsorbing liquid-phase polysulfides and accelerating their solid-liquid conversion during charge and discharge. When polysulfides diffuse into the modified membrane region, the oxygen vacancy defects on the support surface synergistically work with the high-spin cobalt to promote the nucleation and growth of Li₂S₂ / Li₂S by lowering the sulfur chain breaking energy barrier. In sodium-sulfur battery applications, defect-type cerium oxide modified with high-spin sites of iron-nickel bimetallic oxide is used as a cathode additive. The anchoring sites provided by its grain boundary defects stabilize the coordination environment of transition metal atoms, and the bimetallic synergistic effect increases the number of electron transfer channels, thereby improving the kinetic rate of polysulfide redox reactions. By synergistically designing high-spin transition metals and defect supports, a continuous electron transport network is established while maintaining chemisorption strength, enabling a closed-loop adsorption-catalytic conversion process of polysulfides. Compared to conventional methods that simply increase the density of active sites, the unique orbital hybridization capability of high-spin electrons can overcome the mutual constraints between adsorption strength and reaction kinetics, maintaining stable catalytic activity during cycling. This effectively solves the capacity decay problem caused by polysulfide diffusion in alkali metal-sulfur batteries, significantly improving the utilization rate of sulfur cathode materials. The strong orbital hybridization of high-spin transition metals firmly anchors polysulfides in the catalytic active site region, while the optimized electronic structure lowers the activation energy barrier for sulfur species conversion. The strong interaction between support defects and metal atoms ensures the structural stability of catalytic sites during long-term cycling, thereby extending the battery's cycle life. This technical solution achieves dual suppression of the polysulfide shuttle effect while maintaining high battery energy density, providing an effective solution for the practical application of high-energy-density alkali metal-sulfur batteries.

[0024] Furthermore, this composite electrocatalyst plays a dual role in lithium-sulfur, sodium-sulfur, or potassium-sulfur batteries by anchoring high-spin-state transition metal atoms on a defect support. For the lithium-sulfur system, the unpaired d electrons of the cobalt-based catalyst preferentially form strong chemisorption with sulfur atoms of lithium polysulfides; in the sodium-sulfur system, the high-spin-state electrons of the iron-based catalyst more readily overlap with the larger sodium polysulfides; and for the potassium-sulfur system, the manganese-based catalyst adjusts its spin state density to match the charge distribution characteristics of potassium ions. The stable anchoring sites provided by defect engineering can adapt to the volume expansion during the conversion of different alkali metal sulfides, and grain boundary defects and oxygen vacancies synergistically maintain the structural stability of the catalytic active sites.

[0025] Furthermore, when the electrocatalyst is applied to membrane modification, the porous membrane coating can both physically restrict the diffusion of polysulfides and form strong chemisorption through the hybridization of unpaired d electrons of high-spin transition metals with the p orbitals of polysulfides. As a cathode additive, the catalyst particles are uniformly dispersed in the sulfur-carbon composite cathode, and the exposed high-spin metal sites on their surface can directly catalyze the solid-liquid conversion reaction of liquid polysulfides, reducing the polarization overpotential. The catalyst layer coated on the current collector surface constructs a continuous electron transport network, improving reaction kinetics by reducing interfacial charge transfer impedance. These three application methods can be implemented individually or in combination to form a multi-stage synergistic catalytic system, specifically addressing the problems of polysulfide shuttle effect and sluggish sulfur species conversion kinetics. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0028] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0029] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0030] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0031] In this invention, unless otherwise specified, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply a shortened representation of these numerical combinations.

[0032] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0033] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0034] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0035] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0036] The present invention provides a high-spin-state transition metal defect type metal oxide composite electrocatalyst, comprising: a metal oxide support with engineered defects; and at least one high-spin-state transition metal atom, wherein the transition metal atom is anchored to a defect region of the metal oxide support or a region adjacent to it.

[0037] The metal oxide support with engineered defects is selected from at least one of titanium oxide (TiO2), zinc oxide (ZnO), cerium oxide (CeO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), silicon oxide (SiO2), or composite oxides thereof. Composite oxides include mixed metal oxides having a single stable crystalline phase, composed of two or more of the aforementioned metal oxides, such as oxides forming solid solutions, spinel structures, or perovskite structures.

[0038] Engineered defects include, but are not limited to, oxygen vacancies, cation vacancies, interstitial defects, grain boundary defects, or surface unsaturated sites.

[0039] The high-spin transition metal atoms are selected from cobalt (Co), iron (Fe), nickel (Ni), manganese (Mn), chromium (Cr), or combinations thereof.

[0040] The high-spin transition metal atoms are bimetallic or multimetallic combinations composed of at least two high-spin transition metals. Different transition metal atoms in the multimetallic combination can work synergistically to optimize electrocatalytic performance.

[0041] High-spin transition metal atoms can be induced or stabilized in a high-spin state by forming an unsaturated coordination environment, modifying the electronic structure of the support, or introducing specific coordination groups.

[0042] Electrocatalyst preparation methods include, but are not limited to, hydrothermal methods, solvothermal methods, atomic layer deposition (ALD), chemical vapor deposition (CVD), coprecipitation methods, molten salt methods, or electrodeposition methods. These methods can precisely control the type and number of defects, as well as the anchoring environment of high-spin transition metal atoms.

[0043] Among these methods, the main approaches for preparing metal oxide supports with engineered defects are hydrothermal, solvothermal, coprecipitation, or molten salt methods. These methods are adept at synthesizing metal oxides with specific nanostructures (such as nanosheets and nanorods) and high specific surface areas in solution or high-temperature environments. By controlling reaction parameters (such as pH, temperature, and precursor concentration), intrinsic defects can be effectively constructed or ideal support platforms can be provided for the subsequent introduction of engineered defects (such as introducing oxygen vacancies through annealing).

[0044] Methods for anchoring transition metal atoms to defect sites on a support mainly employ atomic layer deposition (ALD), chemical vapor deposition (CVD), impregnation-reduction, or electrodeposition to precisely control the loading and dispersion of active metal species.

[0045] To achieve an integrated method for carrier preparation and atomic anchoring, a co-precipitation method or a one-pot hydrothermal / solvothermal method is used to simultaneously add the carrier precursor and the transition metal precursor to the reaction system. This integrated strategy allows for the in-situ "embedding" or anchoring of transition metal atoms to their defect sites during the crystallization and growth of the metal oxide carrier, achieving efficient and uniform atomic-level dispersion.

[0046] Electrocatalysts are used to modify membranes, as cathode additives, or coated onto current collectors to construct high-performance alkali metal-sulfur batteries.

[0047] Alkali metal-sulfur batteries include, but are not limited to, lithium-sulfur batteries, sodium-sulfur batteries, or potassium-sulfur batteries.

[0048] Universal applications of high-spin transition metals: not limited to cobalt, but extended to a wider range of transition metals with tunable spin states (such as Fe, Ni, Mn, Cr), enabling the design of various high-spin electrocatalysts.

[0049] Multi-metal synergistic effect: Introducing at least two high-spin transition metal atoms (such as high-spin cobalt and high-spin iron) to form bimetallic or multi-metal high-spin sites, and utilizing the synergistic effect of d orbital electrons of different metals to further optimize adsorption strength and catalytic activity, thereby achieving better catalytic performance.

[0050] Engineered defect supports: Metal oxide supports with precise control over the type and number of defects (such as oxygen vacancies TiO2, cation vacancies ZnO, grain boundary defects CeO2, etc.) are used. These defects not only serve as anchoring points for transition metals, but also further stabilize and optimize the high-spin states of the loaded transition metals by changing the local electronic structure of the support.

[0051] The mechanism of induction and stabilization of high spin states: Through precise material design and preparation processes, such as controlling the coordination environment of metal oxides, performing non-metallic doping (such as N doping), or controlling the morphology of nanostructures, the high spin states of transition metals can be actively induced and stabilized for a long time, ensuring their continued effectiveness in long-term cycling.

[0052] Broad application prospects: Not limited to lithium-sulfur batteries, this electrocatalyst concept can be extended to other alkali metal-sulfur battery systems (such as sodium-sulfur batteries and potassium-sulfur batteries), as well as other electrochemical systems that require efficient electrocatalytic conversion.

[0053] Through the above innovative design, the electrocatalyst prepared by this invention can significantly suppress polysulfide shuttle and accelerate sulfur species conversion kinetics, thereby greatly improving the capacity, cycle stability and rate performance of alkali metal-sulfur batteries, and is expected to achieve higher energy density in practical applications.

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The components of the embodiments of the present invention shown herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0055] Example 1 Preparation of high-spin cobalt-anchored TiO2 nanosheets with high oxygen vacancies and their application in lithium-sulfur batteries Preparation of TiO2 nanosheets with high oxygen vacancies: Tetrabutyl titanate was dissolved in anhydrous ethanol and stirred until homogeneous.

[0056] A mixture of deionized water and concentrated nitric acid was slowly added dropwise, and the mixture was hydrothermally reacted at 180°C for 24 hours to form a TiO2 precursor.

[0057] The TiO2 precursor was washed and dried, and then annealed at 600℃ for 2 hours in a reducing atmosphere (Ar / H2 mixture). By precisely controlling the annealing temperature and time, a high concentration of oxygen vacancies was introduced to form TiO2 nanosheets with abundant unsaturated edge sites and high oxygen vacancy.

[0058] High-spin cobalt anchoring: The prepared high-oxygen vacancy TiO2 nanosheets were dispersed in a cobalt salt (cobalt acetate) solution.

[0059] By adjusting the pH and reaction temperature and introducing a small amount of reducing agent, selective adsorption and in-situ reduction of cobalt ions at oxygen vacancies and unsaturated edge sites on TiO2 nanosheets are promoted.

[0060] Subsequently, the cobalt atoms were subjected to low-temperature heat treatment at 400℃ for 2 hours under an inert atmosphere to ensure that they were firmly anchored in the TiO2 defect region and that their high-spin state was induced or stabilized through the carrier-metal interaction.

[0061] Applications of electrocatalysts in lithium-sulfur batteries: The prepared HSCo / TiO 2-x The composite material is uniformly coated on the surface of a polypropylene (PP) diaphragm to form a modified diaphragm.

[0062] The lithium-sulfur battery uses a sulfur / carbon composite cathode (75% sulfur content), a lithium metal anode, and a conventional ether electrolyte (LiTFSI / DOL / DME).

[0063] Example 2 Preparation of high-spin iron-anchored defect-type zinc oxide nanorods and their application in lithium-sulfur batteries Preparation of defective zinc oxide nanorods: Zinc oxide (ZnO) nanorods are synthesized by solvothermal or hydrothermal methods, and appropriate post-treatments (such as annealing or surface etching) are introduced to generate zinc vacancies, oxygen vacancies or interstitial defects.

[0064] For example, ZnO nanorods can be reduced at high temperatures to generate oxygen vacancies.

[0065] High-spin iron anchoring: Defective ZnO nanorods are mixed with iron salt (such as ferric nitrate) precursors and treated under a mild reducing atmosphere by co-precipitation or impregnation calcination to anchor iron atoms at the defect sites of the ZnO nanorods.

[0066] Controlling the heat treatment temperature and atmosphere to ensure that iron atoms form high-spin states (e.g., Fe). 2+ or Fe 3+ (Under specific coordination conditions).

[0067] application: HSFe / ZnO composite material can be used as a catalytic additive for the cathode material of lithium-sulfur batteries, or coated onto the separator.

[0068] Its electrocatalytic performance for polysulfide conversion was tested, and compared with HSCo / TiO₂. 2-x A comparison was made. It is expected that HSFe / ZnO will also significantly improve battery performance.

[0069] Example 3 Preparation of high-spin cobalt-iron bimetallic nanoparticles anchored to defective CeO2 nanoparticles and their application in lithium-sulfur batteries Preparation of defective CeO2 nanoparticles: CeO2 nanoparticles were synthesized by hydrothermal or precipitation methods.

[0070] By introducing Ce 3+ Alternatively, calcination under a reducing atmosphere can introduce oxygen vacancy defects. CeO2 nanoparticles are placed in a tube furnace and heated to 550°C at a rate of 5°C / min under a mixed H2 / Ar atmosphere (H2 volume fraction of 5%), and then kept at this temperature for 2 hours to introduce a high concentration of oxygen vacancy defects.

[0071] High-spin state cobalt-iron bimetallic anchoring: Defective CeO2 nanoparticles were co-impregnated with a mixed solution of cobalt and iron salts (such as cobalt acetate and ferric nitrate).

[0072] Subsequently, heat treatment is performed in an inert atmosphere, which anchors cobalt and iron atoms simultaneously to oxygen vacancies or other defect sites in CeO2, forming a high-spin bimetallic cooperative center.

[0073] application: HSCoFe / CeO2 composite material is used as a separator coating or cathode additive for lithium-sulfur batteries.

[0074] It is expected that this bimetallic high-spin catalyst will exhibit a synergistic catalytic effect superior to that of a single metal catalyst, further improving the polysulfide conversion rate and battery performance.

[0075] Example 4 Stabilization of high-spin nickel on N-doped TiO2 support and its application in lithium-sulfur batteries Preparation of N-doped defective TiO2 supports: N-doped TiO2 nanomaterials were prepared by co-calcining a titanium source with a nitrogen-containing precursor (such as urea or melamine) at high temperature. N doping can induce additional defects (such as nitrogen vacancies or Ti-N bonds) and modulate the electronic structure of TiO2, further stabilizing the high-spin state of the loaded metal.

[0076] Control the calcination temperature and nitrogen source ratio to optimize the N doping amount and defect type.

[0077] High-spin nickel anchoring: The N-doped defective TiO2 support is mixed with a nickel salt (such as nickel chloride) solution.

[0078] By using hydrothermal methods or calcination after impregnation, nickel atoms are anchored at the defect sites of N-doped TiO2 and near the N atoms, utilizing the coordination environment of the N atoms to stabilize the high-spin state of nickel.

[0079] application: The HSNi / N-TiO2 composite material was used as the cathode or separator in lithium-sulfur batteries to evaluate its electrocatalytic activity and battery performance. The synergistic effect of N doping is expected to further enhance the catalytic stability of high-spin nickel.

[0080] Example 5 Atomic layer deposition (ALD) for the preparation of high-spin chromium-anchored hierarchical porous Al2O3 structures and their application in sodium-sulfur batteries Preparation of hierarchical porous Al2O3 structures: Porous Al2O3 supports with hierarchical structures of micropores, mesopores, and macropores were prepared using template method or aerogel method to provide abundant surface area and diffusion channels.

[0081] Specific defects are introduced through annealing.

[0082] High-spin chromium anchoring (ALD technology): Hierarchical porous Al2O3 support was placed in an atomic layer deposition (ALD) reactor.

[0083] Using ALD technology, the deposition amount of chromium atoms and their anchoring at Al2O3 defect sites are precisely controlled by alternately introducing chromium precursors (such as Cr(CO)6) and oxidants / reducants (such as H2O / H2). The single-atom-layer deposition characteristics of ALD ensure that chromium atoms are highly dispersed and form unsaturated coordination, thereby stabilizing their high-spin state.

[0084] The loading and spin state of chromium atoms were optimized by controlling the number of cycles and the reaction temperature of ALD.

[0085] Applications in sodium-sulfur batteries: HSCR / Al2O3 composite material was used as the separator coating for sodium-sulfur batteries.

[0086] Sodium-sulfur batteries are assembled using sodium metal anodes, sulfur / carbon cathodes, and ether or ester electrolytes.

[0087] Charge-discharge cycle and rate performance tests were conducted to verify its electrocatalytic effect on polysulfide conversion in sodium-sulfur batteries. It is expected to significantly improve the performance of sodium-sulfur batteries.

[0088] Example 6 Preparation of high-spin manganese anchored on defective zirconia / silica composite supports and its application in potassium-sulfur batteries Preparation of defective ZrO2-SiO2 composite supports A co-precipitation-molten salt combined method was employed, in which zirconium oxychloride, sodium silicate, and potassium chloride were mixed, and the pH was adjusted to 9 to generate a mixed hydroxide precipitate. After drying, the precipitate was melted at 800℃ for 2 hours, and then cooled to leach out the potassium chloride template. Subsequently, under a mixed reducing atmosphere of H2 / Ar, a two-stage heat treatment was performed: first, annealing at 700℃ for 1 hour to introduce high-density oxygen and zirconium vacancies, followed by plasma etching to replenish unsaturated sites and interstitial defects on the surface, resulting in a defect-type ZrO2-SiO2 composite support that combines the characteristics of both uncovered supports.

[0089] High-spin manganese anchoring The composite support was dispersed in a manganese nitrate solution, and sodium borohydride was added using an impregnation-reduction method to promote the selective adsorption of manganese ions at defect sites. Subsequently, it underwent a staged treatment under an inert atmosphere: first, Mn was stabilized by heat treatment at 300℃ for 8 hours. 2+ The high-spin state was then heated to 500℃ and held for 4 hours to enhance the carrier-metal interaction, thus obtaining the HSMn / ZrO2-SiO2 composite material.

[0090] application The HSMn / ZrO2-SiO2 composite material was applied in two ways: firstly, it was coated onto the surface of the current collector as the positive electrode active component; secondly, it was used to modify a polypropylene separator to form a modified separator. Potassium-sulfur batteries were assembled using a sulfur / carbon composite positive electrode (70% sulfur content), a potassium metal negative electrode, and an ether-based electrolyte (KFSI / DOL / DME). The catalytic performance and the effect of inhibiting polysulfide shuttle were simultaneously verified through these two application methods.

[0091] Example 7 Preparation of high-spin manganese-iron bimetals anchored to N-doped defect-type silicon oxide and their application in sodium-sulfur batteries Preparation of N-doped defective SiO2 support A precursor was generated by mixing tetraethyl orthosilicate and melamine using a solvothermal method and reacting at 180°C for 12 hours. The precursor was then calcined at 600°C for 3 hours under an inert atmosphere. Nitrogen vacancy defects were introduced by N doping while retaining unsaturated sites on the surface, resulting in a functionalized derivative of silicon oxide.

[0092] High-spin manganese-iron bimetallic anchoring A combined chemical vapor deposition-atomic layer deposition (CVD-ALL) method was employed. First, the support was co-impregnated with a mixed solution of manganese nitrate and ferric chloride. Then, Fe(CO)₅ and Mn(CO)₅ precursors were introduced, followed by heat treatment at 400℃ for 5 hours. Next, Mn(EtCp)₂ precursor and H₂O oxidant were alternately introduced, and deposition was performed for 15 cycles. The dispersion of manganese and iron atoms was precisely controlled to form high-spin Mn atoms. 3+ / Fe 3+ Bimetallic synergistic sites were used to prepare HSMnFe / N-SiO2 composite materials.

[0093] application The composite material was used as the membrane coating for sodium-sulfur batteries. Sodium metal anode, sulfur / carbon cathode and ester electrolyte were used. The coating thickness was optimized to 5 μm to balance ion conduction and catalytic activity. The focus was on verifying the promoting effect of bimetallic synergy on the conversion of sodium polysulfides.

[0094] Example 8 Preparation of high-spin chromium-nickel bimetallic anchors on defective cerium oxide-zirconia composite supports and their application in lithium-sulfur batteries Preparation of defective CeO2-ZrO2 composite supports The sol-gel method was used to mix cerium nitrate, zirconium oxychloride, and citric acid, and after drying, the mixture was heat-treated at 650℃ for 2 hours to introduce oxygen vacancies and cation vacancies (Ce). 3+ / Zr 4+ By combining vacancies and grain boundary defects, a zirconium oxide-containing composite support was obtained.

[0095] High-spin state chromium-nickel bimetallic anchoring Atomic layer deposition (ALD) was used to alternately introduce Cr(CO)6 and Ni(acac)2 precursors, followed by heat treatment at 450℃ for 3 hours. This process co-anchored Cr and Ni atoms in the defect region, forming high-spin Cr atoms. 3+ / Ni 2+ Synergistic sites were used to prepare HSCrNi / CeO2-ZrO2 composite materials.

[0096] application The composite material was used as an additive in the positive electrode of lithium-sulfur batteries. It was prepared by mixing the composite material with a sulfur / carbon composite material at a mass ratio of 3:7, and achieving a high sulfur loading (8 mg / cm³). 2 The test was conducted under the specified conditions to verify its effect on improving battery cycle stability.

[0097] Industrial applicability The high-spin-state transition metal defect-type metal-oxide composite electrocatalyst provided by this invention significantly enhances the adsorption capacity and conversion kinetics of polysulfides in alkali metal-sulfur batteries through the synergistic engineering design of the transition metal spin state and support defects. Its technical advantages are: High performance: It can achieve high area capacity, long cycle life and excellent rate performance, especially under harsh conditions such as high sulfur loading and lean electrolyte, showing great potential for practical application.

[0098] Universality and scalability: The core concept of this invention (the combination of high-spin transition metals and engineered defect carriers) is universal and can be applied to a variety of transition metals and metal oxide carriers, and extended to different alkali metal-sulfur battery systems (such as lithium-sulfur, sodium-sulfur, and potassium-sulfur), and even other electrochemical conversion reactions.

[0099] The preparation process is controllable: The proposed preparation methods (such as hydrothermal method, ALD, etc.) have good controllability and can achieve precise control of catalyst structure, composition and spin state, laying the foundation for large-scale production.

[0100] Therefore, this invention has broad industrial application prospects in fields such as electric vehicles, portable electronic devices, and large-scale energy storage, and is expected to accelerate the commercialization process of alkali metal-sulfur battery technology.

[0101] In summary, the high-spin transition metal defect-type metal oxide composite electrocatalyst, its preparation method, and its application in alkali metal-sulfur batteries disclosed in this invention are highly efficient composite electrocatalysts for alkali metal-sulfur batteries (such as lithium-sulfur batteries and sodium-sulfur batteries), aiming to solve the problems of polysulfide shuttle effect and slow sulfur species conversion kinetics. This electrocatalyst consists of high-spin transition metal atoms and a metal oxide support with engineered defects. By precisely controlling the type (such as oxygen vacancies, cation vacancies, interstitial defects, etc.) and quantity of defects in the metal oxide support, this invention can provide abundant, unsaturated, and highly stable anchoring sites for the high-spin transition metal atoms. Simultaneously, by designing and controlling the electronic structure of the transition metal, it ensures that it maintains a high spin state during electrochemical cycling, thereby providing a large number of unpaired d electrons and significantly enhancing the interaction between the transition metal and polysulfides (such as LiPS). x The strong metal-sulfur orbital hybridization and electron transfer capabilities between the cobalt and alkali metals are crucial for the effective adsorption and confinement of polysulfides. This effect simultaneously lowers the Gibbs free energy barrier for sulfur species transformation, accelerates polysulfide reduction / oxidation kinetics, suppresses the shuttle effect, and enhances the cycle stability and rate performance of the battery. This invention is not limited to the application of a single high-spin cobalt atom on titanium oxide, but innovatively extends to a wider range of transition metals (such as iron, nickel, manganese, chromium, etc.), their multi-metal combinations (such as bimetallic and multi-metal high-spin sites), and various metal oxide supports with engineered defects. The electrocatalyst prepared by this invention enables high-energy-density, long-cycle-life alkali metal-sulfur batteries, possessing enormous industrial application potential.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-spin-state transition metal defect type metal oxide composite electrocatalyst, characterized in that, include: A metal oxide support with engineered defects, and high-spin transition metal atoms anchored to the defect region or adjacent region of the metal oxide support with engineered defects. The high-spin transition metal atoms are induced or stabilized in the high-spin state by forming an unsaturated coordination environment, modifying the electronic structure of the support, or introducing specific coordination groups.

2. The high-spin-state transition metal defect type metal oxide composite electrocatalyst according to claim 1, characterized in that, The metal oxide support with engineered defects is at least one of titanium oxide, zinc oxide, cerium oxide, zirconium oxide, aluminum oxide, and silicon oxide.

3. The high-spin-state transition metal defect type metal oxide composite electrocatalyst according to claim 1, characterized in that, The engineered defects of the metal oxide support with engineered defects are oxygen vacancies, cation vacancies, interstitial defects, grain boundary defects, or surface unsaturated sites.

4. The high-spin-state transition metal defect type metal oxide composite electrocatalyst according to claim 1, characterized in that, The high-spin transition metal atom is at least one of cobalt, iron, nickel, manganese, and chromium.

5. The method for preparing the high-spin-state transition metal defect type metal oxide composite electrocatalyst according to any one of claims 1 to 4, characterized in that, Includes the following steps: First, a metal oxide support with engineered defects is prepared; then, the metal oxide support with engineered defects is mixed with a transition metal precursor to anchor the transition metal atoms in the defect region or adjacent region of the metal oxide support with engineered defects; the metal oxide support with engineered defects and anchored transition metal atoms is heat-treated to induce or stabilize the high-spin state of the transition metal atoms, thereby obtaining a high-spin state transition metal defect type metal oxide composite electrocatalyst.

6. The method for preparing the high-spin-state transition metal defect type metal oxide composite electrocatalyst according to claim 5, characterized in that, Metal oxide supports with engineered defects are prepared using hydrothermal, solvothermal, coprecipitation, or molten salt methods. Transition metal atoms are then anchored to the defective regions or adjacent regions of the engineered metal oxide supports using atomic layer deposition, chemical vapor deposition, impregnation-reduction, or electrodeposition.

7. The method for preparing the high-spin-state transition metal defect type metal oxide composite electrocatalyst according to claim 5, characterized in that, The heat treatment temperature is 300-700℃; the heat treatment time is 1-8h.

8. The application of the high-spin-state transition metal defect type metal oxide composite electrocatalyst according to any one of claims 1 to 4 in the preparation of alkali metal-sulfur batteries.

9. The application of the high-spin-state transition metal defect type metal oxide composite electrocatalyst according to claim 8 in the preparation of alkali metal-sulfur batteries, characterized in that, The alkali metal-sulfur battery includes lithium-sulfur batteries, sodium-sulfur batteries, or potassium-sulfur batteries.

10. The application of the high-spin-state transition metal defect type metal oxide composite electrocatalyst according to claim 8 in the preparation of alkali metal-sulfur batteries, characterized in that, The high-spin-state transition metal defect type metal oxide composite electrocatalyst is used to modify the separator, as a positive electrode additive, or coated on the current collector to construct an alkali metal-sulfur battery.