Research On Reduction Method Of Graphene Oxide And Its Application In Negative Electrode Of Lithium Metal Battery

High energy-density lithium metal battery is one of the main development directions of lithium battery in the future,and the growth and volume expansion effect of negative side dendrites of lithium metal battery are the main bottlenecks restricting its development.The design of graphene based three-dimensional structure host material is expected to solve the above issues of lithium metal anode.Based on this,this thesis systematically studied the effects of different graphite raw materials and different reduction methods on the morphology,structure and physicochemical properties of graphene,and then controllably constructed a three-dimensional self-supporting porous graphene host material compounded with metal organic framework ZIF-8.Next,electrochemical mechanism of regulating lithium-ion deposition behavior and alleviating volume expansion effect were further analyzed its.Furthermore,the design on three-dimensional conductive network and lithophilic free-standing structure,is proved to be beneficial for optimizing the growth of dendrite lithium,thus enabling high-performance lithium metal battery.Firstly,microcrystalline graphite and flake graphite-based graphene oxide(graphene)were prepared by Hummers’method,and then the effects of hydrazine hydrate reduction method and thermal reduction method on the quality of graphene were systemetrically explored.The two graphite raw materials could be both oxidized with the similar oxidation degree by the improved Hummers’method.Notably,the quality of graphene prepared by thermal stripping reduction method was better than that prepared by hydrazine hydrate reduction method,closer to the lattice spacing of graphite structure,higher carbon oxygen atom ratio,fewer oxygen-containing functional groups and better thermal stability.In addition,the oxygen-containing functional groups of flake graphene oxide were easier to remove than that of microcrystalline graphite oxide graphene,and graphene with higher reduction degree was obtained.Then,to solve the problems of negative side dendrite growth,volume expansion effect and dead lithium generation in lithium metal batteries.A three-dimensional free-standing lithophilic host(ZIF-8@RGO)was constructed by using metal organic framework material(ZIF-8)and graphene material.The addition of ZIF-8 enabled the composite electrode possessing larger specific surface area and pore volume,which could significantly improve the lithium capacity in the process of lithium plating and alleviate its volume expansion effect.In addition,the Zn element introduced by ZIF-8 presented highly lithophilic,which can induce the uniform deposition of lithium on the three-dimensional structure of graphene and reduce the growth of lithium dendrites.Moreover,the assembled Li||Li symmetrical battery with ZIF-8@RGO electrode presented the polarization voltage of the is only 10m V after 600cycle at 1m A/cm~2 and 1 m Ah/cm~2.Spectifically,the assembled Li||ZIF-8@RGO asymmetrucals exhibited the average coulomb efficiency of 98.5%after 350 cycles at Current density of 0.5 m A/cm~2 and capacity density of 0.5 m Ah/cm~2.In addition,the assembled lithium iron phosphate full battery showed a much more excellent rate performance and cycle life.At 0.5C,it still shows a specific discharge capacity of 135 m Ah/g,with capacity retention rate of 96.5%after 200 cycles.In this work,through the construction of free-standing three-dimensional conductive lithophilic ZIF-8@RGO host,the potential safety hazard caused by the growth of lithium dendrite is effectively solved,and the application prospect of three-dimensional host material in lithium metal battery is confirmed.