MLi ₂ Ti ₆ O ₁₄ (M = 2Na, Sr, Ba, Pb) Titanate Anodes for Hybrid Lithium‐Ion Capacitors

Abstract

(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 MLi ₂ Ti ₆ O ₁₄ (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.