Synthesis Of Nanostructured Transition Metal Chalcogenides As Anode Materials For Lithium-ion Batteries

In recent years,lithium-ion batteries?LIBs?have become one of the most widely used energy storage device due to their advantages in energy density,life span and operation voltage etc...However,the traditional graphite anode materials could not afford the increasing demand due to the low over discharge capability and rate performance.This problem becomes much sharper after the advent of electronic vehicles.Therefore,it is urgent to development a kind of new anode materials with higher capacity and safer characteristics.Among various kinds of anode materials,transition metal chalcogenides have received much attention due to their high theoretical capacities,nature abundance and environment friendly.But transition metal chalcogenides suffer from low initial coulombic efficiency,short cycle life,poor cycle stability,which seriously limit their practical application.In this paper,we synthesized nano-size materials with different structures,introduction of oxygen vacancies,hybrid with buffering matrix and conductive materials to facilitate the diffusion of ions,enhance conductivity and prolong the cycling life.The relevant contexts and results as follow:1. Synthesis of porous Mn Co₂O₄ nanorods as anode materials for LIBs.Using oxalic acid as the precipitation reagent to synthesize the precursor(Mn_0.33Co_0.67C₂O₄·2H₂O),which will then transform to porous Mn Co₂O₄nanorods during the following calcination process at different temperature.The as-prepared porous Mn Co₂O₄ nanorods?MCO?exhibit excellent capacity retention of 1620 m Ah g^-1 after 700 cycles at the current density of 0.4 A g^-1.The as-prepared Mn Co₂O₄ nanorods also deliver fascinating rate performance,even being cycled at 30 A g^-1,the reversible capacity is still about 533 m Ah g^-1.2.Synthesis of?-Fe₂O_3-?nanoparticles as anode materials for LIBs.In this synthetic route,the precursor was synthesized by a sol-gel method,and then calcined in air via carbon-thermic method to yield?-Fe₂O₃nanoparticles with oxygen vacancies.The partial reduction of Fe?III?during the carbon-thermic process leads to the formation of oxygen vacancies in the final product.The introduction of oxygen vacancies enhanced the electrochemical performance,especially in reversible capacity,rate performance and cyclability.The as-prepared Fe₂O_3-?still maintained a reversible capacity of 1252 m Ah g^-1 at 2 C after 400 cycles.Even being cycled at 40 C,the as-prepared electrode material can still deliver a discharge capacity of 188 m Ah g^-1.3.Synthesis of?-Fe₂O_3-?nanostructured material as anode materials for LIBs.Due to the oxygen vacancies could enhance the electrochemical performance,we further investigated the influence of oxygen vacancies for structure stability.?-Fe₂O_3-?nanostructured material was successfully synthesized by hydrothermal method.In this hydrothermal synthesis process,sodium citrate was used as reducing agent assisted with appropriate amount acrylamide to control the morphology.Under the circumstance of hydrothermal,Fe?III?would be partial reduced,which will lead to the formation of?-Fe₂O_3-?nanostructured material.The as prepared?-Fe₂O_3-?shows high specific capacity and good cycle stability in long term cycling as anode materials for LIBs.After 800 cycles,the discharge capacity of the as prepared?-Fe₂O_3-?is as high as 1192.4 m Ah g^-1 at 400 m A g^-1.4.Synthesis of Co₉S₈/N-C hollow nanospheres as anode materials for LIBs.ZIF-67 hollow spheres were synthesized via a room temperature solution precipitation route,followed with in-suit pyrolysis and sulfurization process to obtain Co₉S₈/N-C hollow nanospheres.Co₉S₈nanoparticles homogenously dispersed in the N doped carbon nanosphere to form the hybrid hollow nanostructure.The obtained Co₉S₈/N-C hollow nanospheres exhibit a reversible capacity of⁷84 m Ah g^-1 at 1 C after400 cycles when applied as anode material for LIBs,which roots from its unique hollow hybrid structures.