Li-metal free “in aqua” lithiation and re-lithiation of protected graphite anode for 4-V class aqueous lithium-ion capacitor

Abstract

Lithium-ion capacitors, typically composed of a capacitive cathode and a pre-lithiated graphite anode in non-aqueous electrolyte, are promising power sources for energy harvesting applications with higher energy densities than standard electrochemical double layer capacitors. Superior energy density can be achieved by using pseudocapacitive cathodes in an aqueous electrolyte coupled with a water-stable protected anode. Lithiation of the graphite anode is one of the performance-governing processes influencing the working voltage, energy density, and cyclability of such power sources. Here, we report an effective, time-efficient, and safe lithiation procedure without the need of lithium metal or lithium-containing compounds as electrodes. The “in aqua” electrochemical lithiation of graphite is performed by using an over-sized activated carbon cathode and the salt dissolved in the aqueous electrolyte as the source of lithium ions. Subsequently, the protected anode (LixC6 + Li) is used as the counter electrode in an aqueous hybrid supercapacitor showing ∼70 % of capacity retention after 10,000 cycles. Nonetheless, the cycle life and capacity retention of the protected anode was further extended via an “in aqua” re-lithiation process allowing a 95 % retention of the initial capacity after 10,000 galvanostatic charge/discharge cycles.