Li 2 Se as a Cathode Prelithiation Additive for Lithium-Ion Batteries.

In conventional lithium-ion batteries (LIBs), active lithium (Li) ions, which function as charge carriers and could only be supplied by the Li-containing cathodes, are also consumed during the formation of the solid electrolyte interphase. Such irreversible Li loss reduces the energy density of LIBs and is highly desired to be compensated by prelithiation additives. Herein, lithium selenide (Li 2 Se), which could be irreversibly converted into selenide (Se) at 2.5-3.8 V and thus supplies additional Li, is proposed as a cathode prelithiation additive for LIBs. Compared with previously reported prelithiation reagents ( e.g. , Li 6 CoO 4 , Li 2 O, and Li 2 S), the delithiation of Li 2 Se not only delivers a high specific capacity but also avoids gas release and incompatibility with carbonate electrolytes. The electrochemical characterizations show that with the addition of 6 wt % Li 2 Se to the LiFePO 4 (LFP) cathodes, a 9% increase in the initial specific capacity in half Li||LFP cells and a 19.8% increase in the energy density (based on the total mass of the two electrodes' materials) could be achieved without sacrificing the other battery performance. This work demonstrates the possibility to use Li 2 Se as a high-efficiency prelithiation additive for LIBs and provides a solution to the high-energy LIBs.