Application Of Crumpled Graphene In Energy Storage Materials

Graphene,a two-dimensional planar structural material composed of sp²hybridized carbon atoms,has attracted widespread attention due to its unique physical and chemical properties,since its first discovery in 2004.The structure of monoatomic layer gives graphene extremely high specific surface area,outstanding electrical conductivity and excellent mechanical properties.However,the thermodynamic instability of two-dimensional graphene crystal easily leads to crumpling of graphene,while the van de Waals force results in easily aggregating of graphene sheets.In this paper,three-dimensional crumpled graphene was constructed to solve the problem of aggregation of graphene sheets,and was applied in lithium-sulfur batteries and sodium anode.The pore structure of crumpled graphene plays a role in physically limiting sulfur,and the chemsorption of oxygen-containing functional groups on incompletely reduced graphene to polysufides improves the cycle stability of lithium-sulfur battery.In addition,crumpled graphene improves the stability of the sodium deposition-dissolution process when acts as substrate of sodium deposition-dissolution.The main results and conclusions are summarized as below:?1?In chapter three,graphene oxide?GO?was used as raw material to prepare crumpled graphene?crGO?by spray drying method.We obtained thermally reduced crumpled graphene?cG-800?through annealing crGO at 800 ^oC to improve the reduction degree of crGO.Compared with crGO,the specific surface area,pore volume and electrical conductivity of cG-800 had been greatly improved.Then,crumpled graphene-sulfur composite?crGO/S?and thermally reduced crumpled graphene-sulfur composite?cG-800/S?were prepared by hot melt impregnation method.By comparing the electrochemical properties of crGO/S and cG-800/S as cathode materials for lithium-sulfur batteries,we found that the specific capacity and rate capability of cG-800/S were superior to that of crGO/S.?2?In chapter four,we took Na₂S₂O₃ as a sulfur source to prepare crumpled graphene-sulfur composite?S@crGO?using a one-step spray drying method.This method simplified the preparation procedure of composite materials,and realized the uniform coating of sulfur by graphene.The chemisorption of oxygen-containing functional groups on the surface of incompletely reduced graphene to polysulfides can inhibit the shuttle effect of lithium-sulfur batteries.Then,S@crGO was employed as cathode material for lithium-sulfur battery.It was found that the capacity remained 54.4%after 500 cycles at 0.5 C,while the decay rate was only 0.091%per cycle.?3?In chapter five,crGO was further reduced by hydrated hydrazine vapor to reduce crGO and the resulting material was marked as hydrated hydrazine reduced crumpled graphene?cG?.cG was applied as the substrate for sodium deposition-dissolution.It was found that the sodium deposition-dissolution performance on cG substrate can stably cycle 1000 h even when the deposition capacity was 3 mAh cm^-2,which was superior to that on Cu substrate.We assembled full cells using carbon-coated sodium vanadium phosphate?C@NVP?as cathode,cG and Cu pre-deposited with 0.25mAh cm^-2 sodium as anode respectively.The results showed that the cycle performance and rate capability of cG-C@NVP full battery were better than that of Cu-C@NVP full cells.