Investigation of the effect of degree of prelithiation on high-performing hybrid supercapacitors made with porous CaFe2O4 anodes

Abstract

Prelithiation typically has a substantial impact on the electrochemical performance of lithium-ion batteries and hybrid supercapacitors (HSC), though the optimum prelithiation point of most materials, let alone conversion-type anodes, remains unexplored. In this study, the first HSCs made with porous CaFe2O4 (pCFO) anodes prelithiated to different degrees are investigated. While prelithiation affects the morphologies and compositions of pCFO anodes in predictable ways, prelithiation has a more stochastic influence on HSC electrochemical performance. Deeper probing into the electrode-specific characteristics via three-electrode cycling indicates that the anodes in all devices quickly drop near 0 V vs. Li/Li+. This low-voltage plateauing is a marker of lithium plating, which is usually parasitic for electrochemical energy storage devices and could interfere with the beneficial effects of prelithiation. However, many of the pCFO-based HSCs perform competitively with other HSCs, both with respect to energy and power density (20–140 Wh kg−1 at 1000–10,000 W kg−1) and long-term cycling stability (> 70 % capacity retention after 5000 cycles at 2 A g−1), indicating that pCFO may be uniquely resistant to the influence of lithium plating and so is a promising candidate for next-generation HSCs.