Emerging composite electrode architectures based on transition metal oxides for high-performance Li-ion capacitors

Lithium-ion capacitors (LICs) have emerged as next-generation electrochemical energy storage systems by effectively bridging the long-standing performance gap between lithium-ion batteries and supercapacitors (SCs), offering a rare combination of high energy density, high power density, and ultralong cycle life. Despite their tremendous potential for electric vehicles, grid stabilization, and high-power electronics, the widespread deployment of LICs remains fundamentally constrained by the limited kinetics, structural instability, and interfacial incompatibility of electrode materials. In this context, transition metal oxides (TMOs) have attracted considerable interest as LIC electrode materials due to their exceptionally high theoretical pseudocapacitance, Earth-abundance, low cost, and environmental compatibility. However, a critical misconception persists in the field that high pseudocapacitance alone guarantees superior LIC performance, whereas in reality, the decisive factors lie in the rational integration of composition, nanostructure, electronic conductivity, and electrode-electrolyte interface design. This review provides a comprehensive and critical analysis of TMO-based composite electrodes for LICs, systematically correlating synthesis strategies, structural engineering, heterointerface construction, and defect chemistry with charge-storage mechanisms and device-level performance. Beyond experimental progress, we integrate emerging theoretical, multiscale modeling, and data-driven approaches to establish predictive structure-property-performance relationships. By unifying materials chemistry, electrochemical kinetics, and interface science, this work identifies key bottlenecks in current TMO-based LIC technologies, clarifies prevalent oversimplifications in performance interpretation, and formulates validated design principles for achieving simultaneously high energy, high power, and long-term durability. Ultimately, this review offers a forward-looking framework to guide the scalable development of sustainable, high-performance TMO-based LICs for future energy storage technologies.