Study On Fe,Co,V-Based Metal Oxides And Their Composites With Carbon As Anode Materials For Energy Storage Batteries

The effective use of renewable energy is the key to achieve the green transition in the energy fields and the goal of carbon neutrality in China.Electrochemical energy storage devices with low cost and high performance are the key technologies to support the development of renewable energy.Although lithium-ion batteries have occupied a dominant position in the consumer electronics market,their specific capacity,safety,and cost still need to be improved for the requirements of the potential large-scale energy storage market.The choice of anode material for energy storage battery directly determines its battery performance.This thesis mainly focuses on the design of anode material with low cost,high performance and high safety and the screening of electrolyte.Transition metal oxides have the advantage of high specific capacity compared with current commercial anode materials.At the same time,the working potential can effectively avoid the lithium metal precipitation and lithium metal dendrite formation,and thus effectively improve the safety performance of the battery.However,the disadvantages of poor cycling stability and low rate performance of transition metal oxides limit their application.The purpose of this thesis is to gradually reduce the manufacturing cost of batteries and improve the safety of batteries.Therefore,three kinds of transition metal compounds with gradually reduced cost are selected as anode materials to explore their electrochemical performance.Aiming at the energy storage system of lithium ion battery,a low-cost and high-performance C-hemp with three-dimensional pore array structure supported Co₃O₄ nanosheet and all-vanadium lithium ion battery LiVO₃ anode material are designed and developed.However,the increasing price of lithium salt year by year leads to the increase of overall battery cost and the use of organic electrolyte will bring great safety risks.Therefore,in order to further reduce the manufacturing cost of energy storage battery and increase its safety,a safe,reliable and low-cost aqueous magnesium iron dual-ion electrolyte system and its matched high-performance Fe₂O₃/GH anode material were designed and developed.By means of electrode structure design,new material research and battery system development,the electric conductivity of the anode material of energy storage battery is improved and the volume expansion effect of the material in the charging and discharging process is alleviated,so as to improve its electrochemical performance.The specific research results of this thesis are as follows:1.The Co₃O₄ nanomaterial was successfully grown on the biomass hemp carbon current collector,and a Co₃O₄electrode（Co₃O₄@C hemp）with a three-dimensional free-standing structure was obtained.It is found that hemp carbon has a unique three-dimensional pore structure,which can enhance the contact area between the Co₃O₄ electrode material and the electrolyte.At the same time,hemp carbon can be used as a conductive network to improve the conductivity of the whole electrode,thereby improving the electrochemistry of the Co₃O₄@C hemp electrode performance.When Co₃O₄ presents a composite microstructure of nanoneedles and nanosheets,Co₃O₄@C hemp exhibits the best cycle performance.When the current density is 2 m A cm^-2,the mass specific capacity of Co₃O₄@C-hemp reaches～481 m Ah g^-1,and the capacity hardly decreases after 50 charge and discharge cycles.2.The LiVO₃ nanoparticles were prepared by calcination and the lithium storage properties were explored.It is found that the crystallization and particle size of LiVO₃ material can be improved by adjusting the calcination temperature.The discharge specific capacity of the material can reach 326 m Ah g^-1 in the voltage window of 0.2 V～3 V.Higher operating voltage can effectively avoid the extraction of lithium metal,which futher improves the safety performance of the battery.At the same time,the capacity of material has barely decayed at a current density of 500 m A g^-1 after 500 cycles.Matching as-fabricated LiVO₃ with the cathode Li₃V₂（PO₄）₃ assembled into a low-cost LiVO₃-400‖Li₃V₂（PO₄）₃-base full battery.The battery system can obtain a specific capacity of～112 m Ah g^-1 after 100 cycles at a current density of50 m A g^-1,while the coulomb efficiency is maintained at 100%.In addition,at a current density of 500 m A g^-1,the specific capacity of the full battery remains at 65 m Ah g^-1 and is virtually non-decaying after 120 cycles.3.In view of the current increase in the price of lithium salt year by year resulting in the overall cost rise of battery and the use of organic electrolyte will bring great safety risks,we developed and designed a safe,reliable and low-cost aqueous magnesium iron dual-ion electrolyte system and its matched high-performance self-supporting Fe₂O₃/graphene（Fe₂O₃/GH）anode material.The material consists of Fe₂O₃ cube nanoparticles evenly dispersed on graphene.In addition,graphene in the material can alleviate the volume changes of Fe₂O₃in the electrochemical process,which can inhibit the structural damage of the electrode.Meanwhile,graphene as an electronic transmission channel can improve the conductivity,and improving the electrochemical properties of the material.At a current density of 100 m A g^-1,the discharge specific capacity of the Fe₂O₃/GH is 155 m Ah g^-1,and the capacity retention rate is 90%after 200 cycles with the coulomb efficiency of almost 100%.This also means that Mg-Fe bimetallic ions can have a reversible electrochemical storage performance in the Fe₂O₃/GH electrode.In addition,free-standing Fe₂O₃/GH electrodes do not require binders and conductive agents,which also help to increase the energy density of the battery.