Study On Construction And Electrochemical Properties Of New Carbon Matrix Composites

It is necessary to develop and promote advanced and effective energy storage technologies in order to reduce the dependence on traditional energy structures and promote the economic development of China.Supercapacitor is considered as the most promising energy storage device due to its long cycle life,fast charging and discharging rate,high coulombic efficiency and wide operating temperature,etc.High activity and high stability of electrode materials determine the development and breakthrough of supercapacitors.At present,the design of high-performance electrode material is usually based on the increase of specific surface and active sites and improving the structural stability by designing the composition and structure of the electrode material,and effectively constructing the functional interface.In view of this,carbon-based electrode materials with high heteroatom doping,controllable morphology and stable structure were prepared in this paper.Through morphology and structure characterization,DFT calculation and electrochemical analysis,the electrochemical properties and energy storage mechanism of the electrode materials and the corresponding supercapacitors were deeply studied.The main contents are as follows:(1)Nitrogen/oxygen co-doped porous carbons(NOPCs)with predominant micropores were prepared via carbonization and activation of a solvent-free synthesized polymer as monomers.Kinetics studies and density functional theory(DFT)simulations reveal that N/O heteroatoms credibly introduces pseudocapacitance and greatly improves the chemisorption of K+,leading to an outstanding electrochemical performance.The obtained NOPCs exhibit interconnected microporous structure,large specific surface area(3297 m2 g-1),narrow pore size distribution(ca.<1 nm),suitable heteroatoms content(N:4.13%,O:13.06%)and high carbon yield of 48 wt%.Benefitting from these features,the optimal NOPC-800 delivers a remarkable specific capacitance of 410 F g-1 at 1 A g-1 and retains 270 F g-1 at 50 A g-1.The solid-state microsupercapacitors fabricated from the NOPCs presents areal capacitance up to 29.7 mF cm-2 and energy density up to 0.97 μWh cm-2.(2)The three-dimensional heterogeneous structure of graphene/Ni-Co-S composite electrode material(Ni-Co-S/G)was synthesized based on an ultrathin exfoliated graphene with highly electrochemically active nickel-cobalt sulfide(Ni-Co-S)loaded on its interface by a twostep hydrothermal method.The graphene is used as a conductive matrix to provide fast transfer channels for lateral charge transfer,and Ni-Co-S provides abundant active sites for reversible redox reactions.The formed three-dimensional heterogeneous structure fully exposes the active sites and ensures the efficient ion and electron transport.Thus,the constructed Ni-Co-S/G electrode exhibits remarkable specific capacitance of 1579.7 F g-1 at 1 A g-1 and outstanding rate performance of 1240 F g-1 at 20 A g-1.In symmetrical-electrode system,it delivers superior energy outputs of 75.3 Wh kg-1 at 1125 W kg-1.Furthermore,the material shows outstanding cycling stability with capacitance retention rate of 88.4%after 5000 cycles at 10 A g-1 It leads to new ideas for construction of high-performance three-dimensional heterogeneous structures for the practical application of supercapacitors.