The Study Of Transition Metal Oxides Used In Lithium Ion Batteries

In order to meet the world's growing demand for energy,scientists around the world are working on the research and development of new energy storage equipment.Because of its excellent energy and power density and environment-friendly,lithium ion battery is one of the most widely studied energy storage devices,especially in the field of mobile applications.In recent years,the electrode material is the key to advance the performance of lithium ion batteries,which is being widely accepted.Therefore,it is necessary to study the positive and negative materials more centrally to improve the performance of the battery.Transition metal oxides are hot topics in recent years,because they have high theoretical capacity,high electronic conductivity,abundant polyvalent states.Since the capacity of transition metal oxide is easy to decline and slow in dynamics,this paper introduces two schemes to enhance its performance as anode material for lithium-ion battery,by simply modifying and optimizing transition metal oxide.1.MoO2/Mo2C imbedded carbon fibers(MoO2/Mo2C ICFs)have been successfully synthesized via an electrospinning and a reduction/carbonization at high temperature.In particular,it is observed that the MoO2/Mo2C ICFs derived from phosphomolybdic acid have more highly porous structures than those derived from ammonium molybdate,about 20-30 nm and 5 nm,respectively.The electrochemical investigations illustrated that the MoO2/Mo2C ICFs could deliver an initial discharging capacity of 1422.0 mA h g'1 and an original coulombic efficiency of 63.3%,and the subsequent reversible capacity could reach as high as 1103.6 mA h g-1 even after 70 cycles at a current density of 0.1 A g-1,while,the MoO2/Mo2C ICF prepared from ammonium molybdate only provided an initial coulomb efficiency of 45.7%and a capacity retention of 78.6%.This work provides an idea for the preparation of other porous carbon composites.2.A facile one-step hydrothermal approach is proposed to deposit Co8W12O42(OH)4(H2O)8 micron crystals or CoWO4 particles on a commercial copper foam(respectively denoted as COW-POM and COW-Salt)via adjusting temperature which can be used as binder-free electrodes for LIBs directly.Combining the extraordinary redox stability and excellent lattice deformability of POMs with the 3D dispersed volume accommodation of substrate,the as prepared CoW-POM was endowed with an extraordinary and better electrochemical performances(capacity,rate capability and cycle life)than that of CoW-Salt.In detail,the CoW-POM can deliver a reversible capacity of 737.8 mA h g'1 at the current density of 0.1 A g-1 and provide a capacity retention of 90.1%even after 100 cycles,while COW-Salt can only provide the discharge capacity of 559.7 mA h g-1 and the capacity maintenance rate of 28.1%.This work will inevitably promote the extensive and intensive research on POMs based materials for energy storage and conversion.