Modeling and Simulation of a Lithium Manganese Oxide/Activated Carbon Asymmetric Supercapacitor

Asymmetric supercapacitors are expected to represent the future of energy storage devices because of their good performance concerning both energy density and power density. This paper first presents a mathematical model of an asymmetric supercapacitor, which consists of a LiMn2O4 electrode and an activated carbon (AC) electrode. Including electrical and concentration fields, the dynamic model is used to investigate the effect of the thickness of the AC electrode on supercapacitor performance in COMSOL Multiphysics. Surprisingly, a distinctive effect of relaxation is found in the supercapacitor for the first time by simulating the production, consumption, and transport of Li ions. Relaxation is shown to play a key role in capacity recovery and lifetime extension. The relative error of energy densities and power densities in the Ragone plots is less than 10% compared with experimental results when the current density is below 200 A/m(2). The present model is conclusively verified to be effective and successfully provides a methodology to optimize the cell size in various applications.