Defects Regulation Of MO_x(M=Co,Ni)by Modification In Gas Phase And The Electrochemical Lithium Storage Performance

With the rapid development of various portable mobile electronic devices,new energy vehicles and large-scale energy storage technology,higher requirements have been proposed to lithium ion batteries.At present,the theoretical capacity of commercial graphite is only 372 mAh g-1,which can not meet the further demand of improving lithium ion battery performance.Transition metal oxides are expected to be the next generation materials of lithium ion battery due to their high natural abundance,simple synthesis,low cost,high theoretical capacity and high electrochemical stability.However,the large volume change,low conductivity and ion diffusion ability limit the practical application.To solve the above disadvantages,gas phase reduction modification of Co3O4 and NiO was carried out to study the effect of defect structure on lithium ion storage performance.The detail contents are as follows:Firstly,the cubic Co3O4 nanoparticles were prepared by hydrothermal method and the oxygen vacancies were changed by Ar anneal treatment,while avoiding the formation of other phases.Electrochemical analysis shows that the Co3O4-250 electrode with the best oxygen vacancy content has the best electrochemical performance that the capacity is 904.2 mAh g-1 at a current density of 0.1 A g-1.The oxygen vacancies are beneficial to improve the performance of lithium storage at Co3O4 electrode.And there is a positive correlation between pure oxygen vacancy content and reversible capacity.Based on the Ar treatment,the cubic Co3O4 particles were also modified by H2/Ar atmosphere and investigated.The results show that the interface of CoO/Co3O4 appears after modification and the capacity of modified samples changes significantly.The reversible capacity of the 15-Co3O4 electrode is maintained at 883.4 mAh g-1 after 150 cycles at 0.5 A g-1 current density compared to the reversible capacity of AP-Co3O4 at 625.6 mAh g-1,which proves the feasibility of this method.Secondly,porous Co3O4 nanosheets were successfully obtained by hydrothermal method and calcination treatment,which were modified by H2/Ar atmosphere.The modification producted Co3O4/CoO interface structure and oxygen vacancies in which the morphology did not change.The optimized sample Co3O4-30 exhibits excellent electrochemical performance with a reversible capacity of 891.5 mAh g-1 after 200 cycles at 0.5 A g-1,which even maintains reversible capacity of 250.0 mAh g-1 at a high current density of 5.0 A g-1.Finally,NiO porous nanosheets were successfully prepared by hydrothermal and calcination treatment,which were modified by H2/Ar gas phase treatment.The H2/Ar gas phase treatment successfully regulated the oxygen vacancy content of NiO porous nanosheets,and the oxygen vacancy concent increseed with the increasement of reduction time.The electrochemical performance of NiO-30 sample is the best which maintains at 678.8 mAh g-1 for 30 cycles at a current density of 0.1 A g-1 The above analysis further confirms the effect of oxygen vacancies on the performance of lithium ion negative materials.