Facile Synthesis of Porous Hollow Cobalt‐Doped λ‐MnO 2 Nano Architectures as a High‐performance Anode Material for Li‐ion Batteries and Li‐ion Hybrid Supercapacitors

The cost-effectiveness and easy availability of MnO2 have attracted researchers′ attention as an anode electrode for LIBs over other transition metal oxides. However, MnO2 usage has been limited to its low reaction reversibility and poor conversion kinetics. Besides, Li-ion hybrid supercapacitors (LiHSCs) are in urgent demand which offers higher power densities than LIBs without compromising energy density. Among different polymorphs of MnO2, λ-MnO2, due to its 3D spinel structure, can be applied in many applications. Usually, λ-MnO2 can be obtained by extracting lithium from LiMn2O4 using complex electrochemical or acid leaching methods. This study presents a modified Li2O2 assisted method to obtain cobalt-doped 3D architectures of λ-MnO2 porous hollow nanostructures. The resultant MnxCo1-xOy hollow structures with 5 % cobalt addition are used as anode for LIBs exhibited excellent charge reversibility and cycle stability over thousands of reaction cycles. This result is known to be one of the finest among MnO2 anodes reported to date. Also, a LiHSC device is fabricated with MnxCo1-xOy hollow structures as anode and the device exhibits an excellent comprehensive electrochemical performance in terms of high operating voltage (4.2 V), with a specific cell capacity of 33 mAh g−1 at a high current density of 5 A g−1 and achieved the maximum power density of 12261 W kg−1 (with energy density at 81.7 Wh kg−1) with long cycle life.