Improved water-stable protected anodes with low resistance for aqueous energy storage devices

Abstract

Multi-component anodes, fabricated by assembling lithium metal or pre-lithiated graphite negative electrode, a lithium-ion conducting solid electrolyte with water stability and a polymer or gel electrolyte in between the negative electrode and solid electrolyte, are promising as water-stable protected anodes for next-generation batteries and hybrid capacitors. By applying the protected anode to hybrid capacitors, operating voltage of 4 V can be achieved in aqueous electrolytes. However, the protected anode suffers from large resistance due to its multi-component structure, leading to insufficient power density and energy conversion efficiency. Here we analyze various protected anodes by using electrochemical impedance spectroscopy (EIS) to evaluate the bottleneck components in order to reduce the overall resistance. Protected anodes with different polymers or gel membranes, lithium salts and ionic liquid additives, negative electrode materials, binders, and solid electrolytes, were fabricated and the impedance components were analyzed. The resistance of the protected anode was successfully reduced by selecting proper materials.