Encapsulation of Fe3O4 between Copper Nanorod and Thin TiO2 Film by ALD for Lithium-Ion Capacitors.

Lithium-ion capacitors (LICs) are considered to be promising power sources due to their combination of high-rate capacitors and high-capacity batteries. However, development of a high-performance LIC is still restricted by the sluggish intercalation reaction and unsatisfied specific capacities in battery-type bulk anodes. To overcome these issues, herein, we utilize two-step atomic layer deposition (ALD) to realize a uniform coating of FeO x and TiO2 on CuO nanorods, which results in the formation of ternary CuO@FeO x@TiO2 composite. After further treatment in H2/Ar atmosphere, the as-derived Fe3O4 is encapsulated between conductive Cu nanorod and hollow TiO2 shell (denoted as Cu@Fe3O4@TiO2). Owing to the rational design, the binder-free Cu@Fe3O4@TiO2 electrode exhibits an ultrahigh Li-ion storage capacity (1585 mA h g-1 at 0.2 A g-1), superior rate capability, and excellent cycle performance (no decay after 1000 cycles), which could efficiently boost the energy-storage capability of LICs. By employing an anode of Cu@Fe3O4@TiO2 and a cathode of activated carbon, the as-constructed full LIC device provides high energy//powder densities (154.8 Wh kg-1 at 200 W kg-1; 66.2 Wh kg-1 at 30 kW kg-1). These superior results demonstrate that ALD-enabled architectures hold great promise for synthesizing high-capacity anodes for LICs.