Abstract
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.
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