Boosting High-Voltage Dynamics Towards High-Energy-Density Lithium-Ion Capacitors

Lithium-ion capacitors (LICs) are becoming important electrochemical energy storage systems due to their great potential to bridge the gap between supercapacitors and lithium-ion batteries. However, capacity lopsidedness and low output voltage greatly hinder the realization of high-energy-density LICs. Herein, a strategy of balancing capacity towards fastest dynamics is proposed to enable high-voltage LICs. Through electrochemical prelithiation of Nb₂C to be 1.1 V with 165 mAh g⁻¹, Nb₂C // LiFePO₄ LICs show a broadened potential window from 3.0 to 4.2 V and an according high energy density of 420 Wh kg⁻¹. Moreover, the underlying mechanism between prelithiation and high voltage is disclosed by electrochemical dynamic analysis. Prelithiation declines the Nb₂C anode potential that facilitates electron transmission in the interlayer of two-dimensional Nb₂C MXene. This effect induces small drive force for Li⁺ ions deposition and hence weakens the repulsive force from adsorbed ions on the electrode surface. Benefiting from even more Li⁺ ions deposition, a higher voltage is eventually delivered. In addition, prelithiation significantly increases Coulomb efficiency of the 1st cycle from 74% to 90%, which is crucial to commercial application of LICs.