Study On The Electrochemical Properties Of Transition Metal Selenide And Oxide Anode Materials In Potassium /sodium Ion Batteries

With the increasing demand for electrochemical energy storage,the development of scientific energy storage devices has become one of the most common challenges in the future scientific and social development.At present,lithium ion batteries（LIBs）,as a pioneer,have been successfully commercialized.Lithium battery（LIBs）is the mainstream energy storage device nowadays,but its development is limited due to its high manufacturing cost and lithium shortage.The natural reserves of potassium and sodium in the earth’s crust are abundant and the production cost is low,which can provide guarantee for the supply of long-term consumption in modern society.Anode material is the key factor affecting the performance of battery.Therefore,the design and synthesis of high reversible specific capacity and high stability of anode materials has become a research focus,among which the transition metal selenides and metal oxides are very good anode materials.In the second chapter,sodium tartrate was selected as the precursor to prepare rod-like zinc tartrate precursor.Using rod-like precursor as template,glucose as binder and carbon source,Zn Se/C composite material（LN-Zn Se/C）with layered network structure was obtained after freeze drying and selenization.The carbon layer generated by the addition of glucose in the preparation process acts as a binder to connect the Zn Se nanorods into a stable interconnected conductive network,and effectively inhibits the volume change of Zn Se nanorods in the process of potassium implanting and depotassium.The layered network structure also provides more transport channels and active sites for electron ion transport.As the anode material of PIBs,the material has good rate performance and excellent cycling performance.It is a very promising anode material.Inspired by the two-dimensional structure of flake Zn Se/C material,in the third chapter,we used sodium citrate as the precursor to prepare flake Zn Se/C materials by hydrothermal method,freeze drying and one-step calcination.On the one hand,the two-dimensional sheet structure of the material improves the utilization rate of the active material and provides a shorter ion diffusion path,on the other hand,it also provides more active sites for electrochemical reactions.Due to the carbonization of glucose and precursor,Zn Se/C material can effectively alleviate the volume expansion problem during the cycle and improve the electronic conductivity.Monometal selenides have excellent electrochemical performance,and bimetal selenides have been reported more and more,and have achieved better performance than monometal selenides.Inspired by this,in the fourth chapter,sodium citrate was used as the precursor,and after hydrothermal,freeze drying and conventional selenization processes,the electrochemical properties of Zn Se/Ni Se-C composites in PIBs were investigated.Specifically,the reversible capacity remains 434.8 m A h·g^-1after 200 cycles at 0.2 A·g^-1 current density.This excellent potassium storage performance can be attributed to its unique hollow spheroidal structure and heterostructure leading to electron redistribution and lattice distortion.They effectively inhibit the volume expansion in the charging and discharging process,maintain the integrity of the structure,increase the transmission channel and active site,so that the electrochemical performance is good.In addition,the carbon layer resulting from the carbonization of the precursor and glucose not only improves the conductivity of the material itself,but also prevents the powder and aggregation of the material.The synergistic advantages of hollow structure,spherical morphology and carbon material further improve the structure stability.Among many anode materials,metal oxide is also one of the main forces.Therefore,in the fifth chapter,we only use simple hydrothermal method to prepare octahedral Cr-doped Sr Mo O₄ material（Cr-Sr Mo O₄）and study its sodium storage performance in SIBs.The material has good cyclic stability and good sodium storage performance.