Boosting Chem-insertion and Phys-adsorption in S/N co-doped Porous Carbon Nanospheres for High-performance Symmetric Li-ion Capacitors

Li-ion capacitor (LIC) is spotted as a promising energy device that combines the advantages of lithium-ion battery (LIB) and supercapacitor (SC). However, it is challenging for LIC to achieve high energy densities at high power densities due to the mismatch of kinetic properties between LIB-type anode and SC-type cathode. Herein, we construct a symmetric LIC (SLIC) with superb high power and energy densities by boosting the electrochemical insertion and capacitive adsorption in carbon-based electrodes. Density functional theory calculations combine with the experimental results prove that the excellent electrochemical performances are attributed to our well-prepared carbon that owns high content of heteroatom dopants (S and N), large surface area with porosity and enlarged interlayer space. Those properties endow the carbon with high electrical conductivity, abundant active sites, reduced Li+ diffusion barrier, as well as rapid ions-transport and large ions-storage in both anode and cathode. As a result, the assembled SLIC can deliver a high energy density of 222.9 Wh kg-1 at 275 W kg-1, and even at an ultrahigh power density of 93.8 kW kg-1 with discharging time of 0.32 s, the SLIC can still maintain an energy density of 8.3 Wh kg-1 as well as ultralong cycle life (0.0026 % energy decay per cycle over 10000 cycles at 5 kW kg-1).