Preparation Of Ni-MOF Based-derivatives For Lithium Ion Batteries

Lithium-ion batteries?LIBs?have been widely used in consumer electronics such as mobile phones,computers,hybrid electric vehicles because of their long cycling life,high energy capacity and environmental friendliness.However,the current commercial graphite displays a limited theoretical capacity of 372 mAh g^-1,which hinders the practical application for LIBs.Thus,exploring novel anode materials with high capacity,good cycling performance and low cost is vital for the development of LIBs.Recently,a class of electrode materials derived from metal organic framework?MOFs?with porous structures has been successfully applied in the field of energy storage.In this thesis,we fabricated the anode materials for LIBs by postprocessing porous Ni-MOF precursor,including introduction of the carbonaceous materials?phosphorization and sulfuration.The major contents are as follows:1.The CNTs surface was functionalized with negative charge by acid treatment,and NiO/CNTs were successfully fabricated by the pyrolysis of nickel metal-organic framework precursors with functionalized CNTs.The results show that NiO/CNTs exhibit higher reversible capacity and better cycling stability than NiO.The NiO/CNTs-10 displays a high reversible capacity of 812 mAh g^-11 at a current density of 100 mA g^-1 after 100 cycles.Even at 2 A g^-1,a capacity of 502 mAh g^-1 is still kept after 300 cycles.2.The yolk-shell Ni₂P/C nanostructure was synthesized by carbonization and further phosphorization of Ni-MOF and used as anodes for LIBs.Benefitting from the unique yolk-shell structure?large specific surface area and void space between yolk and shell?and carbon layer which can provide more active sites for Li⁺and buffer the volume changes during cycling,the as-prepared yolk-shell Ni₂P/C exhibits excellent lithium storage performance,including high specific capacity(420.7 mAh g^-1 at 100mA g^-1 after 100 cycles),outstanding long-term cycling stability(228.3 mAh g^-1 at 2A g^-1 after 1000 cycles and 89.4%capacity retention)and excellent rate performance(80.06%,67.06%and 58.11%,capacity retention at 0.25,0.5 and 1 A g^-1).3.The porous NiS/C electrode materials were synthesized via two-step treatment process.When evaluated as anode materials for LIBs,NiS/C shows a high initial discharge capacity of 1165.3 mAh g^-11 at 100 mA g^-1 and still maintains a reversible capacity of 878.6 mAh g^-1 after 100 cycles,and high coulomb efficiency?initial>60%?.The excellent electrochemical performance should be attributed to the large specific surface area and porous structure,which can enhance the electrode/electrolyte contact area.