The Application Of Metal-Organic Frame Materials And Its Derived Phosphate In Lithium-Ion Batteries

Metal-organic frameworks?MOFs?are a class of porous crystalline materials constructed by metal ion and organic building blocks.Benefiting from their advantages such as structural versatility,abundant electroactive constituents,and large ion diffusion tunnels,MOFs have intensively been applied in the field of anodes of batteries and supercapacitors in recent years.But in terms of battery,the actual performance of the lithium-ion battery fails to meet people's requirements and expectations.Therefore,the development of high performance lithium battery materials has emerged as a hot topic of scientific research.In this dissertation,two kinds of MOF materials were introduced into lithium ion batteries and their superior electrochemical properties were verified.This thesis mainly contents the following two parts:In the first part,we have demonstrated the synthesis of Co₂?DOBDC?MOF via an improved hydrothermal method.The as-prepared material possesses a rod-like prism morphology and benign crystallinity.When tested as anode materials in Li-ion coin cells,this Co₂?DOBDC?electrode maintains a reversible capacity of 878.5 mAh g^-1 at 100 mA g^-1 after 100 cycles and 526.1 mAh g^-1 at 500 mA g^-1 after 200 cycles.Moreover,a reversible capacity of 408.2 mAh g^-1 at 2 A g^-1 can be retained for Co₂?DOBDC?while maintaining an remarkable rate capability among MOFs-based anode materials.The ex-situ soft X-ray absorption spectroscopy?sXAS?and electron paramagnetic resonance spectroscopy?EPR?studies imply that localized high-spin?S=3/2?Co²⁺in pristine Co₂?DOBDC?would gradually converted to delocalized high-spin Co²⁺after discharging.It was also found that the highly reversibly capacity of Co₂?DOBDC?is mainly ascribed to surface-dominated pseudocapacitance process,which benefits fast Li⁺ion diffusion during electrochemical cycling.In the second part,we synthesized a laminated structure LVP@M-101 carbon coating materials through solid-state reduction method by using vanadium metal-organic framework?MIL-101?V??as both vanadium and carbon sources.Compared with the LVP that synthesized by V₂O₅,the LVP@M-101 carbon composite displays a remarkable improved electrochemical stability with a high reversible capacity of 113.1 and 105.8 mA h g^-1 at the rate of 0.5C and 1C after1000 cycles.Moreover,we first attempted to explain the lithiation/delithiation process of LVP@M-101 electrode by ex-situ X-band EPR and it was offering a new method to study the mechanism of cathode materials of batteries.