Tuned Synthesis Of Transition Metal Sulfur/Selenium Compound Nanostructures And Studies Of Their Electrochemical Sodium Ion Storage Performance

The scarcity of lithium resources and the rapid growth of the market demand have exposed the potential challenges of lithium-ion-based energy storage.People are eager to get more economical and resource-free batteries than lithium-ion batteries.The abundance of sodium in nature is about 420 times that of lithium,and the development cost is much lower than that of lithium.The structural composition and working mechanism of sodium ion battery(SIB)and lithium ion battery(LIB)are very similar,but the radius of Na⁺is larger than that of Li⁺,which means that the successfully commercialized lithium-ion battery electrode materials cannot be directly used in sodium-ion batteries.Therefore,the exploration of suitable anode materials for sodium storage has become a key concern.Metal sulfide has become a potential electrode material with high performance due to their versatility in synthesis process,utilization potential,and high sodium-forming ability.However,the defects of transition metal sulfide,such as poor conductivity,large volume expansion in the redox process,easy solubility in electrolyte,poor redox reversibility and small diffusion coefficient of Na+,have become the fundamental problems that limit the practical application of transition metal sulfide.Mixed metal sulfides(MMSs)containing different metal sulfides exhibit richer redox reactions and higher electron conductivity than single metal sulfides,indicating potential advantages for sodium storage.1)Using a rational metal-organic framework(MOF)template method,a complete nanostructure of octahedral nanocube(CoS₂-CuS@NC)composited by nitrogen-doped carbon and CoS₂-CuS derived from Cu-doped CoZn-ZIF is designed and synthesized,in order to obtain high-efficiency sodium ion storage materials with excellent performance.It is found that the ZIF-derived preparation method enables the material to form unique geometric morphology,and the derived carbon skeleton provides good support and buffer for the material,which becomes the basis for improving the performance of sodium ion storage.The high temperature carbonization process removes the reduced zinc,which indirectly improves the stability of the material.The high-temperature vulcanization process realizes the N,S co-doping of the carbon framework,which enables it to have higher charge transport efficiency and more active sites for sodium storage.The mixed metal sulfide system of CuS and CoS₂ forms a favorable multiphase synergistic effect.Due to the advantages of the above structure,the as-synthesized CoS₂-CuS@NC exhibits high specific capacity(maintaining a specific capacity of 374 m Ah g^-1 for 50 cycles at 200 m A g^-1),high cycling stability(the capacity retention rate of 50 cycles was 83.6%)and high rate(specific capacity of279 m Ah g^-1 at 5 A g^-1)for sodium-ion storage performance.In addition,the CoS₂-CuS@NC material exhibits excellent performance for lithium storage and electrocatalytic water decomposition of oxygen in alkaline conditions.It shows that the CoS₂-CuS@NC material has great application prospects in the field of electrochemical energy conversion and storage.2)Rod-like stacked ZnMoO₄ microrod precursors are synthesized by a simple hydrothermal method,and porous Zn-Mo-S@MoO₂ composites are synthesized by high-temperature gas-phase vulcanization.The unique porous morphological structure cause by the high-temperature vulcanization process enhances its sodium storage ability,and the composite of the mixed metal sulfide system composed of ZnS and MoS₂ with MoO₂ forms a favorable synergistic effect and enhances its cycling stability.Zn-Mo-S@MoO₂ displays higher capacity(374 m Ah g^-1 after 100 cycles at a current density of 100 m Ah g^-1),good rate performance(at a current density of 2 A g^-1 shows a specific capacity of 262 m Ah g^-1),and good pseudocapacitive performance(70.8%pseudocapacitive contribution at a scan rate of 1 m V s^-1).Both CoS₂-CuS@NC nanomaterials and Zn-Mo-S@MoO₂ composites synthe-sized in this experiment show excellent sodium storage performance,which provides a reference for the synthesis of anode materials for sodium ion batteries,and has a great application prospect in the field of electrochemical energy conversion and storage.