An ultrahigh-energy-density lithium metal capacitor

Abstract Lithium-ion capacitors (LICs), shrewdly integrating a battery-type negative electrode and a capacitive-type carbon positive electrode, are expected to inherit simultaneously both the high specific energy of lithium-ion batteries (LIBs) and high specific power of electrochemical capacitors (ECs). However, state-of-the-art LICs are approaching their specific energy limits yet are still far away from that dictated by LIBs. Herein, we report an aprotic Li-metal capacitor (LMC) strategy to solve this problem through coupling a Li-metal negative electrode with a three-dimensional scaffold activated carbon (3D-SAC) positive electrode. The employment of metal Li negative electrode leads to an ultrahigh specific capacitance up to 280 F gpositive electrode−1 within high potential range from 1.5 to 4.3 V vs Li/Li+, giving a remarkable specific energy of 633 Wh kgpositive electrode−1. Combing with theoretical simulation and advanced characterizations, it is revealed that such a high capacitance is the contribution resulting from multiple electrical double-layer mechanisms on carbon positive electrode that involves the desorption of PF6− anions, the exchange between adsorbed PF6− anions and solvated cation clusters, and the adsorption of solvated cation clusters. The unique desolvation behavior and the electrochemical adsorption of desolvated Li+-related cations boost the specific capacitance and specific energy at low current rates. This is completely different from the reported LICs. This findings provide a new strategy for developing high-energy-and-power capacitors and batteries.