Bifunctional Li6CoO4 serving as prelithiation reagent and pseudocapacitive electrode for lithium ion capacitors

Lithium ion capacitors (LICs) have been widely used as energy storage devices due to their high energy density and high power density. For LICs, pre-lithiation of negative electrode is necessary. In this work, we employ a bifunctional Li6CoO4 (LCO) as cathodic pre-lithiation reagent to improve the electrochemical performance of LICs. The synthesized LCO exhibited high first charge specific capacity of 721 mAh g−1 and extremely low initial coulombic efficiency of 3.19%, providing sufficient Li+ for the pre-lithiation of negative electrode in the first charge. Simultaneously, Li6–xCoOy is generated from LCO during the first charge process, which exhibits pseudocapacitive property and contributes to capacity in form of surface capacitance during subsequent cycles, increasing the capacity of capacitive positive electrode. With the appropriate amounts of addition to the positive side in LICs, this bifunctional prelithiation reagent LCO shows significantly improved the electrochemical performance with the energy density of 78.5 Wh kg−1 after 300 cycles between 2.0 and 4.2 V at 250 mA g−1.