Graphene Oxide Modulates The Morphology Of Biomass Carbon And Its Application In Lithium Batteries

In terms of energy storage field,as a kind of secondary clean energy,lithium batteries are increasingly applied into the fields of wearable devices,mobile phones and automobiles.However,current commercialized lithium-ion batteries cannot meet the requirement of high capacity.Therefore,the development of electrode materials with high performance and low cost has become a problem demanding prompt solution.Biomass carbon-based materials have been widely used in lithium batteries and received excellent electrochemical properties.during recent years due to its advantages of low cost,abundant source,renewability,etc.However,the biomass carbon-based materials’lithium storage performance is still under certain limitation due to their complex structure and composition.In view of the above problems,this paper has taken the regulation of structure and morphology of biomass carbon-based material by graphene oxide（GO）as its theme,and conducted researches in three aspects as follows.（1）Starch was selected as the carbon precursor.With the assistance of graphene oxide（GO）,hard carbon materials with different ratios of GO to starch were prepared through simple hydrothermal carbonization process.Different proportions of GO and starch materials were characterized by SEM,BET,Raman and electrochemical tests.It was discovered that the addition of GO changes the biomass carbon-based material from original carbon globe structure into lamellar structure.When the ratio of GO to starch was1:30,the specific surface area was 247 m²/g.The material was used as the carbon anode material to assemble a button battery.The battery can still preserve a discharge capacity of245 mAh/g and a coulombic efficiency of above 98%after a long circulation of 500 cycles at current density of 1 A/g.It can still preserve a discharge capacity of 325 mAh/g and a coulombic efficiency of above 98%after a long circulation of 100 cycles at current density of 0.1 A/g.（2）A nano-porous skeleton material embedded with nano-particles of Fe₃O₄ was synthesized in situ by hydrothermal method with glucose and ferric chloride（FeCl₃）as raw materials and via the assistance of GO.Serving as a carbon matrix,the nano-porous skeleton can effectively regulate the volume expansion of Fe₃O₄ nano-particles,and facilitate the entry of lithium ions into liquid electrolyte.Compared to the control samples without glucose and without GO.The anode electrode composite has a high specific surface area of 122.7 m²/g.The composite was used to assemble a button battery.According to the subsequent test,the battery preserves a specific capacity of 830.8 mAh/g after a circulation of 200 cycles at current density of 1 A/g,which is 88.7%of its original value.It still preserves a specific capacity of 650 mAh/g at a high current density of 4 A/g.The anode composite material demonstrates high specific capacity,excellent multiplying power and cycling performance.（3）Compared with lithium-ion batteries,lithium-sulfur batteries have a higher theoretical capacity and energy density.Therefore,based on the first experiment,Fe（OH）₃nano-particles were generated in situ by simple oil bath heating from FeCl₃ solution upon materials from GO/starch hydrothermal carbonization process.The nano-particles were then sulphurized to produce the lithium-sulfur cathode composite material.Fe（OH）₃ has a great number of hydrophilic groups and can adsorb polysulfides in both physical and chemical manners.The material made of GO and starch upon hydrothermal carbonization process has a higher specific surface area and can load more active substance S.The battery assembled by lithium-sulfur cathode composite material demonstrates excellent electrochemical performance.Its initial capacity could be 1124 mAh/g at 0.2C and remain over 800 mAh/g after 100 cycles of circulation;its initial capacity could be 900 mAh/g at 0.5C and remain over 600 mAh/g after 300 cycles of circulation.