MLi₂Ti₆O₁₄ (M = 2Na, Sr, Ba, Pb) Titanate Anodes for Hybrid Lithium-Ion Capacitors

(Hybrid) lithium-ion capacitors (LICs) form high-power durable energy storage devices combining battery anode and capacitor cathode. Here, we demonstrate combustion synthesized carbon coated nanometric MLi₂Ti₆O₁₄ (M = 2Na, Sr, Ba, and Pb; MLTO) titanate anodes with flat voltage profiles (1.2-1.4 V) for the first time as intercalation anodes in asymmetric lithium-ion capacitors vs activated carbon (AC). The MLTO-LICs delivered an energy density and power density in the range of 10-45 Wh kg^-1 and 0.5-1200 W kg^-1. Further, we show that the appearance of a voltage step in MLTO-LICs is critical for understanding performance variations and explain this behavior using structural insights (rod packing) related to Li-storage sites within MLTO and their evolution during cycling. Additionally, we identify different Li-storage site types, migration pathways, and associated barriers, establishing how intrinsic material effects govern early-cycle performance, while extrinsic factors become dominant during the later cycles. Overall, this work presents MLTO titanates as a new potential class of faradaic anodes for LICs.