Synthesis And Lithium Storage Properties Of Metal Oxide And Metal Phosphide Nanomaterials

Due to the low theoretical specific capacity(372 mAh g^-1)of the graphite anode in lithium-ion batteries,it cannot meet the increasing demand of people.Oxides and phosphates of metals have very high theoretical specific capacity,which makes them ideal materials to replace graphite.For example,the theoretical specific capacity of ZnO,Co₃O₄,Sn₄P₃and Zn₃P₂are 972 mAh g^-1,890 mAh g^-1,1255 mAh g^-1and 935mAh g^-1,respectively,which are more than twice that of graphite.Based on the above several kinds of materials for research object,this paper based on the carbon composite strategy,combined with nano structure design idea,design and synthesis of the hard and soft carbon carbon shell network assembly 3D framework ZnO@Dual carbon,CNTs connect Co-Co₃O₄/secondary CNTs/amorphous carbon and Zn₃P₂/Sn/Sn_xP_y@TiO₂@carbon hollow cube three kinds of composite material,their structure and lithium storage performance are studied,the main contents are as follows:（1）The ZnO nanoparticles with an average particle size of 30.6 nm were assembled by chemical polymerization and PVP boiling method and carbonized to obtain a three-dimensional framework of hard carbon shell and soft carbon net assembly ZnO@Dual carbon.The ZnO nanoparticles were fully dispersed in the carbon framework,with abundant micropores and large specific surface area(153.7 m²g^-1).ZnO@Dual Carbon has excellent performance in reversible specific capacity,cycle stability and rate performance.At a current density of 500 mAh g^-1for 350 cycles,the specific discharge capacity still reaches 701 mAh g^-1.Even when the current reaches2.0 A g^-1,the specific discharge capacity remains stable at 469.6 mAh g^-1.Excellent lithium battery performance is due to the hard and soft carbon shell assembly structure,hard carbon derived from phenolic resin dispersed the ZnO nanoparticles,and improved its stability and conductivity,formed by polyvinylpyrrolidone soft carbon further disperse of hard carbon assemble ZnO,which was the main reason for the formation of the frame structure,not only convenient for electrolyte seepage,and further improve the conductivity and structure stability.（2）CNTs connect Co-Co₃O₄/secondary CNTs/amorphous carbon were obtained by precipitation,carbonization and oxidation.MWCNTs connected the amorphous carbon derived from ZIF-67 in series.Co-Co₃O₄nanoparticles with shell core structure were embedded in the amorphous carbon,and a large number of secondary CNTs grew on the surface of amorphous carbon,forming a unique conductive tentacle.The material not only has high discharge specific capacity,but also has good cycle stability.At the current density of 500 m A g^-1,the discharge specific capacity can still reach 714mAh g^-1for 100 cycles,and the capacity retention rate is about 92.4%.Its excellent lithium storage performance is closely related to its carbon composite nanostructure.Co-Co₃O₄nanoparticles were partially coated by amorphous carbon,which enhanced their electrical conductivity and structural stability,while the metallic Co particles in the center of Co-Co₃O₄nanoparticles again enhanced their electrical conductivity.MWCNTs provide structural support for the whole material,avoid the agglomeration between materials,and also act as a rapid electron migration channel to improve the electrical conductivity of the material.The secondary carbon tubes formed in the outermost layer of amorphous carbon form conductive tentacles,which provide additional channels for electron transfer between the materials and further enhance the electrical conductivity.（3）The Zn₃P₂/Sn/Sn_xP_yhollow cubes were synthesized by co-precipitation method and self-etching method combined with gas phosphating.The Zn₃P₂/Sn/Sn_xP_yhollow cubes were further coated with TiO₂and Carbon to obtain the Zn₃P₂/Sn/Sn_xP_y@TiO₂@Carbon.The electrochemical test results show that the Zn₃P₂/Sn/Sn_xP_y@TiO₂@Carbon hollow cube has high specific capacity and cycle stability.The discharge specific capacity is 644.5 mAh g^-1at the current density of 1 A g^-1for 150 cycles,the capacity retention rate is as high as 88.8%,and the rate performance is excellent.When the current density reaches 4 A g^-1,the average discharge specific capacity is still as high as 441.1 mAh g^-1.Zn₃P₂/Sn/Sn_xP_y@TiO₂@Carbon performance of lithium ion battery is because the hollow cube has larger specific surface area,and to provide additional space,ease in the process of circulation of large volume change,improve the stability of the structure,at the same time,the coating of TiO₂layer can effectively increase the structural strength,improve the cycle life,coated Carbon layer can greatly enhance the conductivity of the material.