Design And Controllable Preparation Of Two-Dimensional-Based Electrode Materials Towards High-Rate Energy Storage

With the growing demand for portable electronic devices,improving the charge-discharge rate of energy storage devices has attracted much attention.Meanwhile,developing the next-generation electrochemical energy storage devices(EESDs)with high rate performance is becoming an important direction to promote energy storage technology.Supercapacitors and lithium-sulfur batteries are typical next-generation EESDs.Owing to superior power density and long cycle life,supercapacitors play a key role in some practical applications,such as smart electric grids,regenerative braking systems in hybrid electric vehicles.Lithium-sulfur batteries have become one of the most promising candidates for next-generation energy storage system due to their high theoretical energy density and low-cost.However,the development of supercapacitors with high energy density leads to the sacrifice of rate performance and power density.And lithium-sulfur batteries suffer from a poor rate performance because of the slow electrode reaction kinetics,the intrinsic electronically insulation of sulfur and shuttle effect of polysulfide.Thus,improving rate performance of supercapacitors and lithium-sulfur batteries are of great significance to the development of next-generation EESDs.Design of high-performance electrode materials is important for the improvement of energy storage devices.In this dissertation,aiming at accelerating ion transport and electrochemical reaction,we fabricate porous electrode materials with biomass-derived carbon and Ti₃C₂T_x for the high-rate EESDs.Firstly,the energy density and rate performance of electrical double layer capacitors are improved by the rational design of porous carbon structure.We prepared a sheet-like porous carbon with thin-layer walls by the carbonization and activation of walnut shells with hard texture using excessive activated agent.The sheet-like porous carbon has an ultrahigh specific surface area of up to 3577 m² g^-1 and a large pore volume of 2.19 cm³ g^-1.And its advanced characteristics of high electrical conductivity and hierarchical porous structure result in the excellent electrochemical performance at high rates.The sheet-like porous carbon-based supercapacitors achieve high energy density of up to 120 Wh kg^-1 or power density of 100 k W kg^-1,respectively.Secondly,the rate performance of pseudocapacitors is improved by the Ti₃C₂T_xassemblies with high accessible surface area.Start with two-dimensional Ti₃C₂T_xnanosheets,we presented a solution-based assembly of Ti₃C₂T_x,which can prevent the restacking of Ti₃C₂T_x flakes.And with different drying processes,Ti₃C₂T_x hydrogels can be further transformed into MXene monoliths with entirely different microstructures.The sliced Ti₃C₂T_x hydrogels were directly used as the supercapacitor electrodes.An outstanding capacitive performance at high rates is achieved because of the abundant activated sites,high ion-accessible surface area,rapid ion transport channel and conductive network of the three-dimensional(3D)Ti₃C₂T_x assemblies.Finally,the 3D Ti₃C₂T_x-based composites are used in a lithium-sulfur battery,which accelerate the electrons,ions transport and the electrochemical reaction,as well as enhance the sulfur utilization at high rates.We prepare the Ti₃C₂T_x/graphene composites and Ti₃C₂T_x/TiN composites with 3D architecture via solution-based assembly and an in-situ nitridation process,which contribute to rapid electrons,ions transport and catalytic conversion of polysulfides.Therefore,an excellent rate performance has been achieved in a lithium-sulfur battery.