Controllable Design Hierarchical Porous Carbons Prepared Through Template Method And Their Electrochemical Lithium/Potassium Charge Storage

With the rapid development of portable electronics and electric vehicles,traditional electrochemical energy storage devices cannot meet the commercial requirements,thus it is urgent to develop a new-type energy storage devices with high performance in energy density and power density as well as long-term cycle stability.Lithium-ion capacitors(LICs)and potassium ion capacitors(PICs)combining a battery anode and a capacitive cathode into one cell,exhibits the advantages of high energy density,high power density and long cycle life,which shows the great potential applications in areas such as electric cars,rail transportation and artificial intelligence.Due to their different ion storage mechanisms of two electrodes in LICs and PICs,the main issue of these hybrid cells is the kinetic mismatch between anode and cathode.To solve these issues,we designed high-performance porous carbon anode materials through structural optimization and heteratomic doping strategies.The details are as follows:1)To improve the electrochemical lithium storage performance of carbon anode materials,a strategy combining heteroatom doping and pore optimization was proposed.The nitrogen/phosphorus co-doped hierarchical porous carbon spheres(N/P-HMCN)were prepared by polymerization and high temperature carbonization using silica as hard template,aniline as carbon source and nitrogen doping source,and phytic acid as phosphorus doping source.N/PHMCN has a microporous/mesoporous hierarchical porous characteristic with an average pore size of 9 nm.N/P-HMCN sample is rich in N and P elements with the contents of 3.99 and 3.04 wt%,respectively.Electrochemical tests showed that the reversible specific capacity of N/PHMCN reaches 1108.6 mAh g-1 at the current density of 0.1 A g-1,and 276.5 mAh g-1 at the high current density of 8 A g-1.It is further found that N/P-HMCN anode has good cyclic stability,and the capacity retention rate can reach 85%after 1000 cycles at a current density of 5 A g-1.According to the density functional theory(DFT)calculation and analysis,heteroatoms doping including nitrogen and phosphorus is beneficial to improve the adsorption capacity of carbon materials to lithium,and then improves the electrochemical performance of anode materials.Furthermore,a new-type of LIC was assembled by using N/P-HMCN as anode and home-made porous carbon(PDPC)as cathode in an organic 1.0 M LiPF6 electrolyte.This LIC shows a high energy density up to 103 Wh kg-1 and high power density up to 44,630 W kg-1.In addition,this LIC shows a good cycling stability.Even after 10000 cycles at 2 A g-1,the specific capacity of this LIC decreases only by～12.5%.2)To solve the problem of poor rate performance and cyclic stability of potassium ion capacitors due to large size of potassium ion,a nitrogen/phosphorus co-doped two-dimensional layered hierarchical porous carbon(N/P-MC@RGO)anode material was proposed by using electrostatic self-assembly,template etching and heteroatom doping strategies.Apart from preserving the layered structure of the original GO template,N/P-MC@RGO has the honeycomb-like pore structure with an average pore size of 9.3 nm.XPS characterization confirmed that N/P-MC@RGO is rich in N and P heteroatoms with the contents of 4.17 and 3.34 wt%,respectively.Electrochemical tests showed that N/P-MC@RGO delivers a specific capacity of 387.6 mAh g-1 at a current density of 0.05 A g-1.Under a high current density of 2 A g-1,N/P-MC@RGO still delivers a specific capacity of 96.9 mAh g-1.In addition,a capacity retention rate of 66.6%after 3500 cycles at 0.5 A g-1 is achieved,suggesting the excellent cyclic performance of N/P-MC@RGO anode.The density functional theory was further used to demonstrate that nitrogen/phosphorus doping can improve the adsorption capacity of carbon materials to K,leading to an enhanced electrochemical performance of N/P-MC@RGO anode.A PIC fabricated by employing N/P-MC@RGO as anode,PDPC as cathode yields a high operating voltage up to 4.2 V,a maximum high energy density of 110.9 Wh kg-1 and a maximum power density of 18.3 kW kg-1 as well as long-term cycle stability exceeding 43,000 cycles.