Energy density maximization of Li-ion capacitor using highly porous activated carbon cathode and micrometer-sized Si anode

A very-high-energy-density Li-ion capacitor (LIC) was developed using commercially available activated carbon (AC) having a high surface area of 3041 m 2 g(-1) and conventional 2 mu m-sized Si as the cathode and anode material, respectively, at an AC:Si mass ratio of 6.37. The LIC delivered a maximum energy density of 400 Wh kg(-1) at a power density of 32 W kg(-1) and exhibited excellent rate stability (200 Wh kg(-1) at 6 kW kg(-1)) over the cell voltage range of 1.0-4.3 V; these values were based on the total mass of the active materials in the cathode (AC) and anode (Si). However, its low cycling stability induced a 79.9% decrease in its energy density (278 to 56 Wh kg(-1)) following 10 0 0 cycles at similar to 650 W kg(-1). The potential variations of the cathode and anode were investigated during charge/discharge cycling. Postmortem electrode analyses indicated that the anode permitted the delamination of Si particles and the formation of a thick passive solid electrolyte interphase layer (60 nm) mainly constituted of LiF. Reducing the cell voltage range to 2.0-4.0 V and the mass ratio to 3.30 reduced the energy density to 183 Wh kg(-1) but improved the sustainability (176 to 156 Wh kg(-1), 88.6% retention) and maintained the power density (> 10 kW kg(-1) at 100 Wh kg(-1)) following 2000 cycles at similar to 1 kW kg(-1). (C) 2021 Elsevier Ltd. All rights reserved.