Synthesis And Lithium Storage Performance Of Transition Metal Oxide Electrode Materials

Lithium ion batteries?LIBs?technology is regarded as the key technology to solve the problem of energy storage for large-scale grid and the electrical vehicles.However,its safety,energy density,power density and cycle performance need to be improved urgently.Electrode materials are critical to the performance of LIBs.Up until now,typical anode materials in LIBs have mainly centralized upon graphite,but its low theoretical specific capacity and charge/discharge voltage plateau,resulting in low energy density and potential safety hazards of batteries.Therefore,it is an urgent task to develop high-performance anode materials.Lithium ion batteries?LIBs?technology is the main developing trend of energy storage technology in the field of large-scale grid energy storage and the electrical vehicles,etc.For now,the urgent problem for lithium ion battery technology is to improve its safety,energy density,power density and cycle performance.Most of these problems are related to the cathode and anode materials of LIBs.However,the cathode materials generally have specific energy density so it is difficult to have further room for improvement.Therefore,researchers focus on anode materials of LIBs.It is hope that to obtain higher energy density,power density and longer life lithium ion batteries through a reasonable adjustment.Up until now,typical anode materials in LIBs have mainly centralized upon graphite,but its low theoretical capacity and the low charge/discharge voltage plateau seriously hinder the development of LIBs.Therefore,it is urgent to develop new anode materials with high energy and high power density to improve the electrochemical performance of LIBs.Transition metal oxides?TMOs?have attracted much attention as anode materials for lithium ion batteries due to their high theoretical capacity,high charging/discharging voltage,good safety and abundant reserves.However,the poor conductivity and large volume expansion during charging/discharging lead to rapid capacity decay and poor cyclic stability,which restrict their application.In order to solve these problems,morphology controling,element doping,structural designing and compositing with carbon were conducted to improve their electrochemical properties.Cobalt-based and iron-based oxides are used as representative transition metal oxides.The specific research contents and results are as follows:?1?Co₃O₄ nanosheets is synthesised with metal organic framework?MOF?as the precursor,and its electrochemical properties are greatly improved by compositing with carbon materials.The two-dimensional nanosheets assembled by Co₃O₄ nanoparticles shorten the diffusion path of lithium ions.The carbon-coated layer avoid the direct interaction between Co₃O₄ and electrolyte,and form a stable solid electrolyte interphase?SEI?layer.Furthermore,the rGO alleviates the stress of volume change during the charging/discharging process of Co₃O₄.Thus,the degradation of the electrodes can be relieved and the cycling stability can be improved.When it is used as the anode of LIBs,it exhibits excellent cycle stability and rate performance:the specific capacity of lithium-ion batteries remains 555.6 mAh g^-1 after 1000 cycles at 1A g^-1 and 278 mAh g^-1 at high current density of 10A g^-1.?2?Boron and nitrogen co-doped reduced graphene oxide?rGO?coated ZnFe₂O₄ composites are prepared by ionic liquid?ILs?assisted method.The doping of boron and nitrogen not only improves the conductivity of electrode materials,but also increases the lithium ion storage active sites of the electrode,and the volume change of ZnFe₂O₄ during the cycling process is alleviated by the coating of rGO.Thanks to this element doping and rGO coating,the composite exhibits good electrochemical properties:The capacity remains 668.1 mAh g^-1 after 100 cycles at current density of 1 A g^-1,even at current density of 5.0 A g^-1,the capacity retention reaches 82.5%after1200 cycles at current density of 5.0 A g^-1.?3?Zero-dimensional?0D??Fe,Co?₃O₄ particles/one-dimensional?1D?Co₃O₄ nanorods/two-dimensional?2D?rGO nanosheets hybrid composites are fabricated by simple and efficient one-step hydrothermal method.The optimal lithium storage performance is obtained by adjusting the mass ratio of rGO:at current density of 1 A g^-1,the composite discharge capacity remained at1351.1 mAh^-1 after 500 cycles,the capacity retention rate ia as high as 80.97%.The structure combines the synergistic effect of low-dimensional nanomaterials:rGO not only alleviates the volume change of?Fe,Co?₃O₄ and Co₃O₄ during charging and discharging,but also provides a continuous three-dimensional conductive network for electrode materials.Moreover?Fe,Co?₃O₄sub-microparticles and Co₃O₄ nanorods inhibit the stacking of rGO sheets,improve its conductivity,and enhance the transport of lithium ions and electrons.In addition,the porous structures in multi-dimensional composites facilitate the diffusion of electrolytes and the transport of electron and ion.