Preparation And Electrochemical Performances Of MCo₂O₄?M=Ni,Zn? Materials

The binary cobalt-based materials have attracted progressively more attentions in becoming the next generation of lithium-ion battery anodes,owing to their high theoretical specific capacity and excellent safety performance.Whereas,the low ionic/electrical conductivities and volume expansion of cobalt-based material always leads to their capacity degradation and poor rate performance,which limits its practical applications.In this paper,ZnCo₂O₄ and NiCo₂O₄ have been selected as the study object.It is expected to develop a high performance lithium ion battery anode material through the structural design and optimization of preparation process.The main results are described as follows:?1?ZnCo₂O₄ nano-fibers were synthesized by electrospinning technique combined with a calcination treatment at first.We regulated the calcination temperatures and rates to prepare a series of different ZnCo₂O₄ products.It was found that when calcined at 550°C with a ramping rate of 2°C min^-1,the material presented a preferable fiber structure,and much better electrochemical performance.The sample had an initial specific capacity of 972.9 mAh g^-1 at100 mA g^-1,and maintained the capacity of 431.2 mAh g^-1 after 200 cycles with a capacity retention of 44.3%.In order to further improve the cyclic stability of ZnCo₂O₄ nanofibers,ZnCo₂O₄@TiO₂ composite nanofibers with different proportion titanium dioxide were prepared by solvent-evaporation method combined with an annealing treatment.The results showed that ZnCo₂O₄@TiO₂ composites with 10%TiO₂ amount exhibited an enhanced cyclic performance compared with single ZnCo₂O₄ electrode,and retained a charge capacity of 607.5 mAh g^-1 with the capacity retention of 70.3%for 200 cycles.?2?ZnCo₂O₄ nanoparticles were fabricated by the co-precipitation of metal ions using Zn-Co-ZIF as precursor,respectively,the effects of different solvents on microstructures and electrochemical properties of ZnCo₂O₄ products had been investigated in detail.The results showed that the ZnCo₂O₄-M treated by methanol delivered a high specific capacity of 1097.3mAh g^-1 at 100 mA g^-1.As the current density increased to 1600 mA g^-1,the specific capacity could still be maintained at 581.5 mAh g^-1,which indicated excellent capability at high current.On this basis,we firstly reported a hierarchical ZnCo₂O₄@NiO nanosheet arrays/nickel foam.When served as binder-free electrodes for Li-ion batteries,it yielded high initil charge capacity of 1595.8 mAh g^-1 at 100 mA g^-1 with the coulombic efficiency of75.4%.?3?NiCo₂O₄ samples were synthesized by a hydrothermal strategy combined with a post-annealing treatment using the Ni-Co-BTC MOFs as precursor,to explore the effect of diverse Ni/Co ratios and hydrothermal temperatures on the structure,morphology and study the Li-storage properties.The results showed that when the Ni/Co ratios was 1:4,hydrothermal temperature is 130°C,the sample had a core-shell structure with higher crystallinity and delivered a high reversible capacity of 1408.3 mAh g^-11 at 100 mA g^-1 and414.3 mAh g^-11 for 200 cycles.