Preparation Of Graphene By Physical Method And Its Application In Anode Materials Of Lithium-ion Batteries

Graphene,a new two-dimensional material with many excellent physical properties,such as extremely high specific surface area and electron mobility,has high potential in the application of electrochemical energy storage materials.However,most-used graphene preparation processes are costly but low-yield,even causing structural destruction to the carbon matrix of graphene like the preparation of graphite oxide.All the defects will affect the conductivity of graphene,which hindering its application in electronic fields.As for the anode material of lithium-ion batteries?LIBs?,graphene should have a good lattice structure,meanwhile,the amount of graphene production should meet the demand.Moreover,balancing the producing cost and performance is most critical in graphene-based LIBs.We use natural graphite as raw material and prepare graphene powder by physical stripping?supercritical CO₂ exfoliation?to prepare high-performance anode materials for LIBs.The results show that the layer number of graphene has been reduced with the repetition of exfoliating process and few defects have been introduced into the structure.To obtain the optimal particle size of graphene,we have investigate the size distribution on the performance of LIBs.The electrochemical performance showed that the capacitance of anode has increased with the increase of exfoliation operation process.After 10 times'exfoliation,the capacitance reached about 459 m Ah/g at the current density of 50 m A/g,which is higher than commercial graphite?400 m Ah/g?.The electrochemical performance based on different size distribution showed that the capacitance has increased with the decrease of particle size in some degree.When the particle size is between 400 and 800 meshes,the performance reach the best.At the current density of 50 m A/g,the capacitance is above 500 m Ah/g,which exceeds the commercial graphite about 25%;while at the current density of 1000 m A/g,the capacitance of graphene is 2 folds of the commercial graphite.To further improve the electrochemical properties of the anode materials,we prepare graphene/cobalt oxide?GNS/Co O?nanocomposites,then test its electrochemical properties for different Co O loading ratio and compare with commercial graphite.The results show that with the increase of Co O loading ratios,the capacity of the LIB is continuously increasing.However,when the loading ratio is increased from 11%up to15%,this effect has become weak.Considering the actual application,the anode material should have most capacity at 0-1 V.When the loading ratio is 11%,the total capacity of GNS/Co O exceeds 600 m Ah/g,and its capacity in the 0-1 V also reaches 526 m Ah/g,so11%is considered to be the optimal ratio.At the same time,when the material circulating100 cycles at the current density of 150 m A/g,its capacity has no decrease,showing excellent cycling stability.